final preliminary feasibility study technical memorandum...

PREPARED FOR STOCKTON EAST WATER DISTRICT

Final Preliminary Feasibility Study Technical Memorandum for the

North Site Groundwater Banking ProjectF E B R UA R Y 2014

TABLE OF CONTENTS

1.0 INTRODUCTION ............................................................................................................... 1-1 1.1 SITE DESCRIPTION ...................................................................................................... 1-1 1.2 PILOT-SCALE RECHARGE TESTING ............................................................................. 1-3 1.3 ORGANIZATION OF THIS TECHNICAL MEMORANDUM ................................................. 1-4

2.0 SUMMARY OF PRELIMINARY ACTIVITIES ............................................................... 2-1 2.1 INITIAL SITE SCREENING ACTIVITIES .......................................................................... 2-1 2.2 PILOT-SCALE RECHARGE TESTING PREPARATORY ACTIVITIES .................................. 2-1 2.3 PHASE I ENVIRONMENTAL SITE ASSESSMENT ............................................................. 2-2 2.4 INITIAL STUDY AND NEGATIVE DECLARATION ........................................................... 2-2 2.5 PERMITS ...................................................................................................................... 2-3 2.6 UNDERGROUND SERVICE ALERT ................................................................................ 2-3 2.7 PILOT-SCALE RECHARGE TESTING WATER SOURCE ................................................... 2-3 2.8 SUMMARY OF FINDINGS OF PRELIMINARY ACTIVITIES ............................................... 2-3

3.0 SUMMARY OF PREVIOUS FIELD INVESTIGATIONS ................................................ 3-1 3.1 2006 AQUIFER TEST AT EVALUATION ......................................................................... 3-1 3.2 2006 PILOT –SCALE RECHARGE TESTS AT THE FORMER 35-ACRE SITE ...................... 3-1 3.3 2011 FIELD INVESTIGATIONS AT THE NORTH SITE ...................................................... 3-4

4.0 PRE-PILOT-SCALE RECHARGE TEST FIELD ACTIVITIES AND MONITORING ............................................................................................................................ 4-1

4.1 MONITORING WELL DRILLING, COMPLETION, AND DEVELOPMENT ........................... 4-1 4.1.1 Lithologic Data ................................................................................................... 4-5 4.1.2 Grain Size Analysis ............................................................................................ 4-7

4.2 WATER QUALITY SAMPLING ....................................................................................... 4-7 4.2.1 Monitoring Wells ............................................................................................... 4-8 4.2.2 Source Water .................................................................................................... 4-11

4.3 GROUNDWATER ELEVATION MONITORING ............................................................... 4-11

5.0 DESIGN, LOCATION, AND CONSTRUCTION OF PILOT-SCALE RECHARGE TEST ..................................................................................................................... 5-1

5.1 RECOMMENDED RECHARGE TECHNIQUES FOR PILOT-SCALE RECHARGE TESTING ..... 5-1 5.2 SELECTION OF PILOT-SCALE RECHARGE TEST LOCATIONS ........................................ 5-1 5.3 CONCEPTUAL PILOT-SCALE RECHARGE BASIN DESIGNS ............................................ 5-2 5.4 SPREADING BASIN CONSTRUCTION AND ACTIVITIES .................................................. 5-2

5.4.1 Spreading Basins ................................................................................................ 5-2 5.4.2 Water Source, Conveyance, and Measuring Devices ......................................... 5-3 5.4.3 Site Safety ........................................................................................................... 5-4

6.0 PILOT-SCALE RECHARGE TESTING RESULTS AND ANALYSIS ........................... 6-1 6.1 PILOT-SCALE RECHARGE TESTING DATA ................................................................... 6-1

6.1.1 Pilot-Scale Recharge Test Source Water Field Parameters ................................ 6-1 6.1.2 Spreading Basin Water Depths ........................................................................... 6-3 6.1.3 Groundwater Depth Data .................................................................................... 6-3 6.1.4 Groundwater Quality Data ................................................................................. 6-5 6.1.5 Microscopic Particulate Analysis ....................................................................... 6-5

Stockton East Water District i February 2014

Final Preliminary Feasibility Study Technical Memorandum North Site Groundwater Banking Project

6.1.6 Evaporation and Precipitation ............................................................................ 6-7 6.1.7 Site Conditions ................................................................................................... 6-7

6.2 GROUNDWATER ELEVATIONS ..................................................................................... 6-8 6.3 GROUNDWATER QUALITY ........................................................................................... 6-9 6.4 SPREADING BASIN RECHARGE PONDS ...................................................................... 6-12

6.4.1 Pond Depth ....................................................................................................... 6-12 6.4.2 Percolation Rates .............................................................................................. 6-13 6.4.3 Cumulative Percolation Volumes ..................................................................... 6-15 6.4.4 Decommissioning of Pilot-Scale Recharge Test Facilities .............................. 6-15

6.5 GROUNDWATER MOUNDING ..................................................................................... 6-15

7.0 CONCLUSIONS.................................................................................................................. 7-1 7.1 GROUNDWATER QUALITY ........................................................................................... 7-1 7.2 PERCOLATION RATES .................................................................................................. 7-2 7.3 GROUNDWATER LEVEL RESPONSE .............................................................................. 7-3 7.4 DRAWDOWN ............................................................................................................... 7-4

8.0 SUMMARY ......................................................................................................................... 8-1 8.1 GEOLOGY AND SOILS .................................................................................................. 8-1 8.2 LAND USE ................................................................................................................... 8-2 8.3 SOURCE WATER .......................................................................................................... 8-3 8.4 GROUNDWATER CONDITIONS ..................................................................................... 8-4 8.5 HABITAT ISSUES ......................................................................................................... 8-5

9.0 RECOMMENDATIONS ..................................................................................................... 9-1

10.0 REFERENCES .................................................................................................................. 10-1

February 2014 ii Stockton East Water District

Table of Contents

LIST OF FIGURES

Figure 1-1. Groundwater Recharge Program Site Area Map ...................................................... 1-2 Figure 3-1. Locations of Guelph Permeameter Testing, Monitoring Wells,

Production Wells, Pilot-Scale Recharge Testing, and Demonstration Testing in Vicinity of North Site ................................................................................. 3-3

Figure 4-1. Monitoring Well Completion Diagram ..................................................................... 4-2 Figure 4-2. Cross-Section from A-A’ Across the North Site....................................................... 4-3 Figure 5-1. Conceptual Drawing of Spreading Basin .................................................................. 5-3 Figure 5-2. Spreading Basins at North Site ................................................................................. 5-3 Figure 6-1. Groundwater Depth Monitoring ................................................................................ 6-4 Figure 6-2. Groundwater Quality Monitoring ............................................................................. 6-6 Figure 6-3. Microscopic Particulate Analysis Apparatus ............................................................ 6-7 Figure 6-4. Depth to Water vs. Time for Monitoring Wells ........................................................ 6-8 Figure 6-5. Depth to Water vs. Time for SEWD Wells ............................................................... 6-9 Figure 6-6. Depth of Water vs. Time for Test Pond Recharge Test .......................................... 6-13 Figure 6-7. Percolation vs. Time for Test Pond Recharge Test ................................................. 6-14 Figure 6-8. Cumulative Percolation Volume vs. Time for Test Pond Recharge

Test ............................................................................................................................ 6-15 Figure 7-1. Conceptual Locations of Seven New Extraction Wells and Existing

Extraction Wells on or Near the North Site ................................................................ 7-7

Stockton East Water District iii February 2014


LIST OF TABLES

Table 3-1. Results of Aquifer Test Evaluation ............................................................................ 3-1 Table 3-2. Results of Guelph Permeameter Testing, Pilot-Scale Recharge Testing,

and Demonstration Testing in Vicinity of North Site ................................................. 3-2 Table 4-1. Borehole Lithologic Data ........................................................................................... 4-6 Table 4-2. Grain Size Analysis of Samples Collected from Boreholes ....................................... 4-7 Table 4-3. Summary of Baseline Water Quality Constituents Detected ..................................... 4-9 Table 6-1. Source Water Field Parameters .................................................................................. 6-2 Table 6-2. Summary of Post-Test Water Quality Constituents Detected .................................. 6-10 Table 6-3. Summary of Post-Test Water Quality Constituents Detected at

Neighboring Wells .................................................................................................... 6-11 Table 6-4. Results of Microscopic Particulate Analysis Test .................................................... 6-12 Table 6-5. Hydraulic Properties Estimated from Pilot-Scale Recharge Testing ....................... 6-16 Table 7-1. Results from Theis Equation Calculation ................................................................... 7-8 Table 8-1. Geology and Soils ....................................................................................................... 8-1 Table 8-2. Land Use ..................................................................................................................... 8-2 Table 8-3. Source Water .............................................................................................................. 8-3 Table 8-4. Groundwater Conditions ............................................................................................ 8-4 Table 8-5. Habitat Issues .............................................................................................................. 8-5

February 2014 iv Stockton East Water District

Table of Contents

APPENDICES (enclosed on CD)

Appendix A – Data from Neighboring Wells

Appendix B –Pilot-Scale Field Recharge Plan

Appendix C – Phase I Environmental Site Assessment, North Site (Bozzano Site)

Appendix D – San Joaquin County Permit

Appendix E – Well Completion and Well Development Forms

Appendix F – Lithologic Logs

Appendix G – Photo Log of Split Spoon Samples

Appendix H – Grain Size Analysis

Appendix I – Laboratory Water Quality Reports

Appendix J – Conceptual Pilot-Scale Recharge Basin Designs

Appendix K – Microscopic Particulate Analysis Data Sheet

Stockton East Water District v February 2014


LIST OF ACRONYMS AND ABBREVIATIONS µg/L micrograms per liter µmhos/cm micro Siemens per centimeter ASTM American Society for Testing and Materials bgs below ground surface BMP best management practices Cal Water California Water Service Company CDPH California Department of Public Health CEQA California Environmental Quality Act CIMIS California Irrigation Management Information System City City of Stockton COC constituents of concern County San Joaquin County DHS California Department of Health Services DJWWTP Dr. Joe Waidhofer Water Treatment Plant EDR Environmental Data Resources EPA U.S. Environmental Protection Agency ESA Environmental Site Assessment ETo evapotranspiration ft/day feet per day ft/min feet per minute ft2/min feet squared per minute HAS hollow stem auger IS Initial Study MCL maximum contaminant levels mg/L milligrams per liter MPA microscopic particulate analysis MPN most probable number ND Negative Declaration NOD Notice of Determination PCB polychlorinated biphenyls PHG Public Health Goal Plan Water Bank Business Plan Program Manual Farmington Groundwater Recharge Program Manual REC recognized environmental conditions S’ approximated value using the Theis Solution for Recovery, is the ratio of

storativity during pumping to storativity during recovery SDC Stockton Diverting Canal SEWD Stockton East Water District SJCEHD San Joaquin County Environmental Health Department TDS Total Dissolved Solids TM technical memorandum USA Underground Service Alert USCS Unified Soil Classification System USGS U.S. Geological Survey VCP Voluntary Cleanup Program VOC volatile organic compounds

February 2014 vi Stockton East Water District

1.0 INTRODUCTION This Preliminary Feasibility Study technical memorandum (TM) summarizes results of the North Site pilot-scale recharge testing on farmland (known as the Bozzano property) located just north of the Stockton East Water District’s (SEWD) Dr. Joe Waidhofer Water Treatment Plant (DJWWTP) to determine its suitability as a groundwater recharge and extraction site.

The pilot-scale recharge testing is part of the North Site Groundwater Banking Feasibility Study (Study) that is being conducted by SEWD as part of the Water Bank Business Plan (Plan), developed in March of 2012. The Plan aimed to evaluate the feasibility of acquiring the Bozzano property and implementing a groundwater recharge facility on this site (North Site). If feasible, the recharge facility would store surface water from the Stanislaus and Calaveras rivers and then be extracted to serve as an additional water supply during dry years, when deliveries from surface water supplies are limited.

Pilot-scale recharge testing activities conducted at the North Site focused on two primary objectives: (1) collecting subsurface data to assess the nature, thickness, and permeability of the unsaturated or vadose zone in the area, and (2) collecting complete pilot-scale recharge testing data to estimate percolation rates and recharge performance.

1.1 SITE DESCRIPTION The North Site, shown in Figure 1-1, is located north of East Main Street, approximately two miles east of Highway 99 and the City of Stockton, in San Joaquin County, California. The North Site is bordered by the Stockton Diverting Canal (SDC) to the west, SEWD property to the south, and agricultural orchards to the north and east. The proposed recharge facility would consist of 265 acres, including the 230 acre Bozzano property and 35 acres of land already owned by SEWD.

Since 1989, the site has been used for agricultural purposes. Primary crops include corn, asparagus and tomatoes. The site is owned by Richard Bozzano and encompasses two assessors parcels (APN 101-040-22 and 101-050-02).

Stockton East Water District 1-1 February 2014


February 2014 1-2 Stockton East Water District

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1.0 Introduction

1.2 PILOT-SCALE RECHARGE TESTING The pilot-scale recharge testing conducted and described in this preliminary feasibility technical memorandum used the Farmington Groundwater Recharge Program, Program Manual (Program Manual) (USACE, 2004) as a guide for assessing the feasibility of the site for recharge operations. As described in the Program Manual, pilot-scale recharge testing is the second stage of a four-stage process to objectively evaluate a site for its groundwater recharge potential (USACE, 2004). Data collected and evaluated during each of the first three stages are used to support a decision about whether a site will advance to the fourth and final stage, be archived for evaluation at a future time, or be eliminated from further consideration for artificial groundwater recharge. If a site advances successfully through the first three stages, it is “fine-tuned” in the fourth stage for long-term, maximum artificial groundwater recharge performance.

The four stages are briefly described below, including information on the status of the North Site:

1. Initial Site Screening – The goal of Stage 1 is to make an initial, low-cost assessment of whether a site could be suitable for artificial groundwater recharge, and whether additional evaluations should be made. Noninvasive methods are used to acquire readily available data (e.g., site visits, literature search) for each site. If no significant conditions are identified that would likely impede or preclude artificial groundwater recharge, the site is advanced to Stage 2. Initial site screening was completed for the North Site and is described in Section 2.

2. Field Investigation – The goal of Stage 2 is to evaluate whether a site could be suitable for artificial groundwater recharge through the application of minimally invasive, site-specific field investigation activities (e.g., subsurface exploration and pilot-scale recharge testing). If results suggest that development of artificial groundwater recharge facilities may be possible, the site is advanced to Stage 3, with the consent of the landowner. Initial field investigations were conducted in 2011, as described in the Report of Managed Aquifer Recharge (SoundEarth Strategies, 2011a) and the Addendum to October 6, 2011 Report of Managed Aquifer Recharge (SoundEarth Strategies, 2011b). This TM summarizes results of Stage 2 activities at the North Site and provides a recommendation regarding whether the site should be advanced to the next stage of evaluation.

3. Demonstration-Scale Recharge Testing – The goal of Stage 3 is to determine if a site is suitable for long-term artificial groundwater recharge through designing and constructing full-scale recharge facilities and executing a performance test for 6 months to 3 years. Performance testing is designed to evaluate recharge effectiveness, aquifer response, and site maintenance requirements. If results indicate that long-term use of the site (up to 4 years) for artificial groundwater recharge is viable, the site will advance to Stage 4, with landowner consent.

4. Long-Term Operation and Maintenance – The goal of Stage 4 is to develop and implement best management practices (BMP) for maximizing groundwater recharge over the intended life of the site. BMPs will be based on general industry practices and site-specific information, including some of the performance and monitoring data collected during Stage 3.



Success of the recharge operations depends on the methodical application of this staged approach, which was designed to minimize costs by screening out likely unfavorable sites during Stages 1 and 2, which involve relatively inexpensive, non-invasive, or minimally invasive activities, before proceeding to more costly and time-consuming site work associated with Stages 3 and 4. Therefore, choosing to move a site forward from Stage 2 to Stage 3 represents an important economic decision. Should the Final Groundwater Banking Feasibility Study Report conclude that the site is feasible for recharge operations, it would be recommended that SEWD follow through with demonstration testing (Stage 3) prior to long-term implementation.

1.3 ORGANIZATION OF THIS TECHNICAL MEMORANDUM This TM is organized as follows:

1. Chapter 1, Introduction provides background information about groundwater recharge in eastern San Joaquin County, presents background on the North Site including a brief site description, discusses pilot-scale recharge testing, and describes the organization of the TM.

2. Chapter 2, Summary of Preliminary Activities presents a summary of the first phase of pilot-scale recharge testing at the North Site, including preliminary activities such as initial screening and preparatory activities for the site.

3. Chapter 3, Summary of Previous Field Investigations presents a summary of the previous field investigations completed on the North Site and neighboring properties.

4. Chapter 4, Pre-pilot–scale recharge test field activities and monitoring presents the results of monitoring well drilling, initial groundwater elevation monitoring, and initial groundwater quality testing conducted before initiation of pilot-scale recharge testing.

5. Chapter 5, Design, Location, and Construction of Pilot-Scale Recharge Test presents a summary of the design, location, and construction of the pilot-scale recharge tests after review and analysis of previous field investigations.

6. Chapter 6, Pilot-scale recharge testing results and analysis presents the results of pilot-scale recharge testing and analysis at the North Site.

7. Chapter 7, Conclusions - summarizes knowledge gained from the results of field investigations and technical analyses.

8. Chapter 8, Summary summarizes in a series of tables the pilot-scale recharge testing activities at the North Site in terms of ranking criteria outlined in the Farmington Groundwater Recharge Program Manual (USACE, 2004b).

9. Chapter 9, Recommendations presents recommendations regarding the suitability of the North Site for artificial groundwater recharge and what recharge techniques should be implemented.

10. Chapter 10, References contains sources used to prepare this TM.


2.0 SUMMARY OF PRELIMINARY ACTIVITIES The first phase of pilot-scale recharge testing at the North Site encompassed a series of preliminary activities including initial site screening, a Pilot-Scale Field Recharge Plan, a Phase I Environmental Site Assessment (ESA), a Draft Initial Study (IS) and Negative Declaration (ND) (SEWD, 2013), obtaining permits, completing underground service alert markings, and developing a health and safety plan. The Phase I ESA and document preparation was performed in April 2013. In addition, a Draft IS and ND was prepared in January 2013 by SEWD, although this particular document is not typically prepared as part of pilot-scale recharge testing. These assessments were a continuance of initial screening of the site, but conducted in more detail, to identify any obvious concerns before more costly site work began. Necessary permits and information on the presence of underground utilities were obtained before subsurface exploration or pilot-scale recharge testing commenced.

These preliminary site activities at the North Site are described in more detail in the following sections.

2.1 INITIAL SITE SCREENING ACTIVITIES Initial landowner coordination took place to assess landowner willingness to participate in the pilot-scale recharge testing to evaluate general site feasibility, and identify the presence of any significant conditions at or near the site that would likely impede or preclude artificial groundwater recharge.

Initial site screening also included review of existing studies conducted at the North Site and neighboring properties. Reports reviewed for this study were completed by SoundEarth Strategies (2011a, 2011b), previous recharge testing and aquifer testing from the neighboring SEWD Northwest Site (former 35-Acre site) (MWH, 2006a and 2006b), U.S. Geological Survey (USGS) testing of 74-01 and installation of STK7, a multi-completion monitoring well (see Appendix A), the Farmington Groundwater Recharge Program Manual (Program Manual) (USACE, 2004b), historical groundwater levels at neighboring wells, boring and well logs from existing borings and wells in the vicinity of the site.

These reports were reviewed to identify potential soil and water quality concerns, develop conceptual model of subsurface deposits and geologic features, determine the nature of surficial soils, develop an understanding of historical groundwater elevation data, potential water sources and conveyance structures, historical land use, accessibility, existing structures, and utilities and underground improvements.

2.2 PILOT-SCALE RECHARGE TESTING PREPARATORY ACTIVITIES Prior to pilot-scale recharge testing at the North Site, a Pilot-Scale Field Recharge Plan (Appendix B) was developed that documented the recommendations for pilot-scale recharge testing including testing locations, testing methods, and monitoring activities.



2.3 PHASE I ENVIRONMENTAL SITE ASSESSMENT A Phase I ESA, which is a limited environmental investigation, was conducted for the site in April 2013 in accordance with American Society for Testing and Materials (ASTM) standards (ASTM, 2000a, and ASTM, 2000b). The purpose of the ESA was to review past and current land uses and activities at the site to assess the possible presence of hazardous substances, including hazardous wastes that could prohibit implementing pilot-scale recharge testing activities. The Phase I ESA and associated appendices is available in Appendix C.

The ESA included a limited reconnaissance of the site and site vicinity; correspondence with agency contacts; and review of historical aerial photographs and historical topographic maps. The ESA also evaluated if any past or current land use activities could influence pilot-scale recharge testing activities. This was accomplished through review of a database of regulatory agency files by Environmental Data Resources (EDR) to find regulatory enforcement actions, permits, or investigations into hazardous materials or wastes associated with the site to identify any recognized environmental conditions (REC) (EDR, 2005).

The ASTM standard for a Phase I ESA (ASTM E-1527-00) (2000a) defines a REC as follows:

The presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, groundwater or surface water of the property. The term includes hazardous substances or petroleum products even under conditions in compliance with laws. The term is not intended to include de minimis conditions that generally do not present a material risk of harm to public health or the environment and that generally would not be the subject of an enforcement action if brought to the attention of appropriate governmental agencies.

As documented in the Phase I Environmental Site Assessment, North Site (Bozzano Site), report (Appendix C), no RECs were observed at the North Site that would preclude groundwater recharge testing activities. One Voluntary Cleanup Program (VCP) property, located within ½ mile of the North Site, was identified. However, this site is not likely to pose a REC for the recharge site because the site is at a lower elevation than the target property, the contamination was localized and impacted only surficial soils (no impact to groundwater), and the site is down gradient of the target property and is undergoing mitigation through a cleanup program. Recommendations of the ESA included gathering background groundwater quality data, monitoring groundwater levels at neighboring wells to evaluate the influence of recharge on adjacent properties, and further investigating the VCP property located within ½ mile of the North Site before implementing demonstration testing of the North Site.

2.4 INITIAL STUDY AND NEGATIVE DECLARATION A Draft Initial Study (IS) and Negative Declaration (ND) was prepared by SEWD as the California Environmental Quality Act (CEQA) Lead Agency (SEWD, 2013). A ND has been prepared concurrently with this IS to meet the requirements of CEQA. The purpose of the IS/ND are to disclose the environmental effects of groundwater recharge testing at the North Site. The


2.0 Summary of Preliminary Activities

IS/ND focus on environmental effects caused by the demonstration-level or full-scale recharge test and identifies best management practices (BMP) that would reduce environmental effects to a less-than-significant level. The Final ND and Notice of Determination (NOD) were certified in March 2013.

2.5 PERMITS After the site was approved for pilot-scale recharge testing activities, it was determined that three monitoring wells would be drilled for subsurface soil exploration and constructed. Drilling and well construction permits were obtained from the San Joaquin County Environmental Health Department (SJCEHD) before drilling activities commenced. SJCEHD was onsite to inspect the grouting procedures for the monitoring well. Inspections were performed to ensure that no open conduit to groundwater was present. Copies of the SJCEHD permits are included in Appendix D.

2.6 UNDERGROUND SERVICE ALERT Underground Service Alert (USA) was contacted before the monitoring wells were drilled. Areas containing USA markings and/or markings provided by SEWD staff were avoided during work activities.

2.7 PILOT-SCALE RECHARGE TESTING WATER SOURCE A 14,000 gallon tank was placed at the perimeter of the North Site and was plumbed into the Bozzano property main irrigation line for the purposes of pilot-scale recharge testing. The tank was fed with water from SEWD’s North pond which receives water from both New Melones and New Hogan via Peters and Bellota pipelines. Water from the North pond, fed by both New Melones and New Hogan water will be the long-term supply for full-scale implementation of the project.

2.8 SUMMARY OF FINDINGS OF PRELIMINARY ACTIVITIES Following are findings from preliminary activities at the North Site:

1. Based on the Phase I ESA, no evidence was found of prior industrial or other activities that would preclude pilot-scale testing recharge activities at the North Site (Appendix C).

2. No mitigation measures were identified in the ND as necessary for implementation of the recharge project.

3. Long-term source water for full-scale recharge testing is available from the North pond located just due south of the North Site.



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3.0 SUMMARY OF PREVIOUS FIELD INVESTIGATIONS The second phase of pilot-scale recharge testing at the North Site included characterizing subsurface conditions at the site. This was accomplished by reviewing previous studies conducted on the North site, as well as collecting soil lithologic data, groundwater elevation, and groundwater quality data. Data obtained from previous studies was used to guide pilot-scale recharge test design and location. These studies are described in more detail below.

3.1 2006 AQUIFER TEST AT EVALUATION The goal of the aquifer test evaluation conducted at the SEWD site in 2006 was to better define the aquifer properties. The results of the aquifer test showed that 2 of the 9 wells monitored during the test period exhibited definitive groundwater level responses to aquifer testing. The lack of responses from other wells, inferred the presence of a heterogeneous subsurface and the possible presence of a local confining unit. The results enabled the calculation of transmissivity, storativity, and horizontal hydraulic conductivity, as presented in Table 3-1.

Table 3-1. Results of Aquifer Test Evaluation

Aquifer Parameter Calculated Value Transmissivity 1.5 – 12 ft2/min Storativity 0.003 Hydraulic Conductivity (horizontal) 0.002 - 0.016 ft/min (3 - 23 ft/day) Key: ft/day = feet per day ft/min = feet per minute ft2/min = feet squared per minute

3.2 2006 PILOT –SCALE RECHARGE TESTS AT THE FORMER 35-ACRE SITE Two groundwater recharge pilot tests were conducted in 2006 on the former 35-Acre Site, which is located south of, and adjacent to, the North Site (Figure 1-1). These pilot tests evaluated two recharge techniques - flooded field and spreading basin. The flooded field technique consisted of applying water to a bermed field, while the spreading basin technique consisted of excavating the recharge area to a depth of 5 feet and applying water to the excavated area. The flooded field technique (although less expensive to construct) presented several drawbacks, including lower percolation rates (average equivalent to 0.36 feet per day [ft/day]) and seepage through the constructed berms which resulted in uncertainty regarding the actual percolation rate (USACE, 2006b). The flooded field technique yielded a higher recharge rate (average equivalent to 0.62 ft/day) with none of the nuisance seepage issues. The average recharge rates from these tests as well as long-term rates collected from the SEWD 60-Acre recharge facility and Guelph permeameter tests at the North Site are presented in Table 3-2. The approximate locations where these measurements were taken are presented in Figure 3-1.



Table 3-2. Results of Guelph Permeameter Testing, Pilot-Scale Recharge Testing, and

Demonstration Testing in Vicinity of North Site

Name Estimated

Percolation Rate

(ft/day) Guelph Permeameter Tests

BP02 0.01 BP03 0.05 BP10 0.23

BP081 0

BP012 NA Pilot-Scale & Demonstration Scale Recharge

Tests East Pond (60-Acre Site) 0.7

North Pond (60-Acre Site) 0.2 South Pond (60-Acre Site) 0.5 Flooded Field (former 35-Acre Site) 0.36 Spreading Basin (former 35-Acre Site) 0.62 Notes: 1 Location deferred and ultimately abandoned following release of large quantity of water into boreholes. 2 Testing begun on August 11, 2011, no drop in water level was observed for 1.25 hours, test terminated. Key: ft/day = feet per day


3.0 Summary of Previous Field Investigations


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3.3 2011 FIELD INVESTIGATIONS AT THE NORTH SITE Field investigations conducted in 2011 estimated percolation rates at 4 locations along the North Site boundary using a Guelph permeameter (SoundEarth Strategies, 2011a and 2011b). Results of these tests, which measure percolation rates on a small scale, were used to estimate the portions of the site with the highest and lowest potential percolation rates. The only Guelph permeameter test location that yielded an percolation rate in the acceptable range for long-term recharge operation (assumed to be at least 0.2 ft/day based on the Program Manual – USACE, 2004), was along the western site boundary (percolation rate equivalent to 0.23 ft/day).

In addition to estimating percolation rates at multiple sites, the field investigations conducted in 2011 included drilling four borings around the perimeter of the North Site. The boring information was then reviewed with other existing boring and well log information to develop a sediment texture model of the subsurface.


4.0 PRE-PILOT-SCALE RECHARGE TEST FIELD ACTIVITIES AND MONITORING

The following section describes field activities completed prior to initiating the pilot-scale recharge test at the East and West recharge basins. These activities included monitoring well drilling, completion, and development, water quality sampling from the monitoring wells and source water, and initial groundwater elevation monitoring.

4.1 MONITORING WELL DRILLING, COMPLETION, AND DEVELOPMENT To evaluate subsurface soil conditions at the North Site, boreholes were drilled in the locations of the three proposed monitoring wells between March 11 and March 13, 2013. One borehole was drilled just east of the western-most basin, one just west of the eastern-most basin, and one approximately halfway between the two basins, as shown in Figure 1-1. Borehole drilling services were provided by a subcontracted drilling company (Cascade Drilling, Inc.). Drilling was performed using the hollow stem auger (HSA) technique. Each well was drilled to approximately 73 feet below ground surface (bgs). During well drilling, soil samples were collected continuously using a split-spoon sampler. Lithologic logging was performed using the Unified Soil Classification System (USCS). The field lithologic logs and photos of split-spoon samples are provided in Appendices F and G.

Once lithologic logging was completed, monitoring wells were installed to collect groundwater quality and groundwater elevation data at the North Site. Monitoring well casings, well screens, filter pack sand, and well seals were installed by the driller immediately after drilling ended, as shown in Figure 4-1. Well screen intervals were selected based on observation of soil type, depth to first groundwater, and expected seasonal water table fluctuations. The monitoring wells were constructed with 2-inch diameter PVC screens and casings. The diagram in Figure 4-1 shows a typical well completion diagram for all three monitoring wells. Figure 4-2 presents a cross-section of the subsurface strata across the North Site.



Figure 4-1.

Monitoring Well Completion Diagram


4.0 Pre-Pilot-Scale Recharge Test Field Activities and Monitoring

Figure 4-2.

Cross-Section from A-A’ Across the North Site



Following completion of the monitoring wells, the wells were developed by purging at least three well casing volumes of water using the driller’s bailing and pumping techniques. This was performed to flush fine sediments from the filter pack surrounding the well screen. A copy of the completion well reports and well development information forms are provided in Appendix E.

4.1.1 Lithologic Data As mentioned, lithologic data was collected during drilling of the monitoring well boreholes. An on-site field geologist under the direct supervision of a California Registered Geologist described the samples during lithologic logging in accordance with the United Soil Classification System or USCS (ASTM, 2000c, and ASTM, 2000d). Appendix F contains lithologic logs filled out for the boreholes. Borehole lithology is described below.

Table 4-1 shows the borehole lithologic data logged at the site (see Appendix F for complete lithologic logs). Appendix G presents a photo log of split spoon samples collected during drilling. Lithologic data was collected with continuous cored sampling. Blow count data was also collected from the monitoring wells using a standard test method (ASTM, 1999). Blow counts are a method of penetration-testing soils with a split barrel sampling tool on the drill rig. The number of hits or blow counts created by a hammer of standard weight and height, dropped from a standard distance on the sampler at a specific depth, was recorded over a 0.5-foot depth.



Table 4-1. Borehole Lithologic Data

Monitoring Well ID

Sample Depth (feet

bgs) Blow

Counts Density/

Consistency USCS

MW-NS-01

0-3.5

stiff OH Organic Clayey Silt 3.5-10 9/9/9 stiff ML/MH Silt/Elastic Silt 10-11 8/9 very stiff ML Silt 11-12 8/8 very stiff ML/MH Silt/Elastic Silt

12-16.5 9/8/8 stiff ML Silt 16.5-22 9/7/7 stiff ML/MH Silt/Elastic Silt 22-24 8/9/8 stiff ML Silt 24-26 10/9/9 stiff ML/MH Silt/Elastic Silt

26-32.5 8/9/10 stiff ML Silt 32.5-33 9 stiff SM Silty Sand 33-35.5 11/9/9 stiff ML Silt 35.5-44 9/11/9 medium dense SM Silty Sand 44-56.5 10/10/10 very stiff ML/MH Silt/Elastic Silt 56.5-62 10/12/8 medium dense SM Silty Sand 62-73 6/6/9 loose SW Well-Graded Sand

MW-NS-02

0-2.5

medium stiff OH Organic Clayey Silt 2.5-4.5

soft to medium stiff ML Silt

4.5-55.5 6/7/7 stiff to very stiff ML Silt 55.5-58 9/8/8 very stiff ML/MH Silt/Elastic Silt 58-60 8/11/7 very stiff ML Silt

60-62.5 8/9/10 very stiff ML/MH Silt/Elastic Silt 62.5-63 9 very stiff ML Silt 63-71 9/8/9 very stiff ML/MH Silt/Elastic Silt 71-73 11/11/13 very stiff ML Silt

MW-NS-03

0-2.5

stiff OH Organic Clayey Silt 2.5-9 8/9/11 stiff to very stiff ML/OH Silt/Organic Clayey Silt 9-40 9/9/9 stiff to very stiff ML/MH Silt/Elastic Silt

40-41.5 9/9/6 stiff to very stiff ML Silt 41.5-42 7 stiff GM Silty Gravel 42-42.5 8 stiff to very stiff ML Silt 42.5-46 7/7/8 loose GM Silty Gravel 46-47 8/9 stiff ML Silt 47-48 9/10 medium dense GM Silty Gravel

48-53.5 10/9/10 very stiff ML/MH Silt/Elastic Silt 53.5-56.5 10/11/7 very stiff ML Silt 56.5-73 6/8/6 stiff to very stiff ML/MH Silt/Elastic Silt

Key: bgs = below ground surface USCS = Unified Soil Classification System

The counts required to penetrate soil correspond to a stiffness qualitative value, as specified in the USCS and shown for each borehole in Table 4-1. For increments greater than 1.5 feet (corresponding to 3 blow counts), only the first 3 blow counts are shown.



Based on analysis of the lithologic data collected during monitoring well drilling, the vast majority of soils encountered from ground surface to a depth of approximately 40 feet bgs consisted of silt, although some interbeds of sand and silty gravel are also present. The density of the silt was generally stiff to very stiff, while the sands and gravels were medium dense or loose (generally good for infiltration).

4.1.2 Grain Size Analysis Grain size analysis was performed on one soil sample from each of the three borehole locations in the screen interval below the groundwater surface. Soil samples were submitted to a subcontracted soils laboratory for grain size analysis. Table 4-2 summarizes the results of the grain size analysis; the complete grain size analysis report is provided in Appendix H.

Table 4-2. Grain Size Analysis of Samples Collected from Boreholes

Monitoring Well ID

Depth (feet bgs)

ASTM Soil Classification

Median Grain Size (mm)

Particle Size Distribution, wt. percent Silt & Clay Gravel

Sand Size Silt Clay Coarse Medium Fine

MW-NS-01 68-68.5 Lt. Brownish-

Gray Sand with Clay (SP-SC)

0.690 13.13 12.63 44.22 19.72 5.50 4.80 10.30

MW-NS-02 68-69 Lt. Brown Clay (CL) 0.005 0.00 0.00 0.91 11.17 38.65 49.27 87.92

MW-NS-03 55 Lt. Brown Silty Sand (SM) 0.079 0.00 0.00 5.15 45.57 37.71 11.58 49.29

Key: bgs = below ground surface ID = identification Lt = light mm = millimeters wt = weight

According to the grain size analysis data, the finest soils encountered were generally clay while the coarsest soils were medium sands in the screen interval zones sampled. Generally, the grain size analyses confirm the observations of the on-site geologist (Table 4-1).

4.2 WATER QUALITY SAMPLING Water quality samples were collected from groundwater in each of the monitoring wells and the source water feeding the East Recharge Basin (this source water also fed the West Recharge Basin). These samples were sent to a subcontracted certified analytical laboratory for analysis. The following sections describe results for each sample in further detail. Appendix I contains the complete analytical reports and a summary of water quality data for the samples, including maximum contaminant levels (MCL) for constituents based on California Department of Health Services (DHS) limits, unless otherwise specified.



4.2.1 Monitoring Wells The monitoring well samples were collected on March 25 and March 26, 2013, to establish the baseline water quality of the groundwater at the North Site. Baseline groundwater quality data was collected to ensure that groundwater recharge at this site would not cause the migration of any known constituents of concern (COC). Based on laboratory analysis (Appendix I), no volatile organic compounds (VOC), chlorinated herbicides, organochlorine pesticides, polychlorinated biphenyls (PCB) pesticides, or fecal coliform were reported above their respective detection limits in the baseline groundwater sample collected from the monitoring wells. Total Dissolved Solids (TDS) measurements for all three wells were also above the U.S. Environmental Protection Agency’s (EPA) Secondary Drinking Water Standard of 500 mg/L. In MW-NS-01 and MW-NS-03, nitrate levels exceeded the State and federal MCLs. Total coliform measurements from MW-NS-01 also exceeded the MCL. A summary of all detected constituents is provided in Table 4-3.

As discussed in Section 4.1, the monitoring well was screened in the first hydrogeologic zone encountered during drilling (42-72 feet bgs); therefore, reported groundwater quality represents shallow groundwater near the top of the saturated zone.



Stockton East Water District 4-9 February 2014 2013

Tabl

e 4-

3.

Sum

mar

y of

Bas

elin

e W

ater

Qua

lity

Con

stitu

ents

Det

ecte

d

Con

stitu

ent

Uni

ts

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

1 (3

/25/

13)

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

2 (3

/26/

13)

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

3 (3

/25/

13)

Sour

ce

Wat

er E

ast

Pond

(4

/3/1

3)

MC

L

Tota

l Alk

alin

ity

mg/

L 36

0 32

0 41

0 29

Bic

arbo

nate

as

CaC

O3

mg/

L 36

0 32

0 41

0 29

Car

bona

te a

s C

aCO

3 m

g/L

ND

N

D

ND

N

D

H

ydro

xide

as

CaC

O3

mg/

L N

D

ND

N

D

ND

Chl

orid

e m

g/L

24

30

40

1.3

2501

Spe

cific

Con

duct

ance

(EC

) µm

hos/

cm

890

810

1,00

0 77

Hex

aval

ent C

hrom

ium

µg

/L

6 4

4.2

ND

10

2

Tota

l Har

dnes

s as

CaC

O3

mg/

L 35

0 29

0 47

0 24

Nitr

ate

as N

m

g/L

13

10

14

ND

10

Nitr

ite a

s N

m

g/L

ND

N

D

ND

N

D

1

pH

pH u

nits

7.

25

7.39

7.

29

7.26

6.

5-8.

51

Sod

ium

Ads

orpt

ion

Rat

io

sqrt(

meq

/L)

1.8

2.3

1.5

0.24

Sul

fate

as

SO

4 m

g/L

44

45

57

2.1

2501

Tota

l Dis

solv

ed S

olid

s m

g/L

570

530

680

31

5001

Ars

enic

µg

/L

4.2

4.4

3.8

ND

10

Bor

on

µg/L

95

99

55

N

D

C

alci

um

µg/L

75

,000

62

,000

11

0,00

0 5,

800

C

oppe

r µg

/L

ND

N

D

ND

N

D

1300

Iron

µg/L

N

D

ND

N

D

130

3001

Mag

nesi

um

µg/L

39

,000

32

,000

51

,000

2,

300

M

anga

nese

µg

/L

ND

N

D

ND

N

D

501

Pot

assi

um

µg/L

79

00

5,90

0 71

00

ND

Sod

ium

µg

/L

75,0

00

90,0

00

75,0

00

2,80

0



Tabl

e 4-

3.

Sum

mar

y of

Bas

elin

e W

ater

Qua

lity

Con

stitu

ents

Det

ecte

d (c

ontd

.)

Con

stitu

ent

Uni

ts

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

1 (3

/25/

13)

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

2 (3

/26/

13)

Gro

undw

ater

Q

ualit

y M

onito

ring

Wel

l MW

-NS0

3 (3

/25/

13)

Sour

ce

Wat

er E

ast

Pond

(4

/3/1

3)

MC

L

Zinc

µg

/L

ND

N

D

ND

N

D

5,00

01

Tota

l Col

iform

s M

PN

/100

mL

350

2 <1

.8

>160

0 5

Feca

l Col

iform

s M

PN

/100

mL

<1.8

<1

.8

<1.8

11

5

Tota

l Trih

alom

etha

nes

(TH

M)

µg/L

N

D

0.59

N

D

0.62

80

N

otes

: 1 S

econ

dary

Sta

ndar

d 2 C

alifo

rnia

Dep

artm

ent o

f Pub

lic H

ealth

Max

imum

Con

tam

inan

t Lev

el

Bol

d te

xt in

dica

tes

exce

eden

ce o

f Fed

eral

MC

L K

ey:

µg/L

- m

icro

gram

s pe

r lite

r µm

hos/

cm -

mic

ro S

iem

ens

per c

entim

eter

M

CL

- max

imum

con

tam

inan

t lev

el

mg/

L - m

illig

ram

s pe

r lite

r M

PN

- m

ost p

roba

ble

num

ber

ND

- no

ne d

etec

ted


4.2.2 Source Water A baseline water quality sample was taken from the source water entering the East Pond to verify that the water would not contaminate the aquifer through recharge. Based on laboratory analysis (Appendix I), no VOCs, chlorinated herbicides, organochlorine pesticides and PCBs, pesticides, or nitrogen/phosphorus were reported above their respective detection limits in a sample collected on April 3, 2013, except where noted below. Total and Fecal coliform were reported at most probable number (MPN) concentrations of >1,600 and 11, respectively, which exceeded State and federal MCLs. The coliform values are not considered problematic because of the relatively thick unsaturated zone which will effectively remove these constituents from the source water before it reaches the saturated zone.

4.3 GROUNDWATER ELEVATION MONITORING Groundwater elevations were first monitored in the newly installed wells on April 2, 2013. At that time, groundwater levels were approximately 54 feet bgs in MW-NS-01, 60 feet bgs in MW-NS-02, and 59 feet bgs in MW-NS-03.


5.0 DESIGN, LOCATION, AND CONSTRUCTION OF PILOT-SCALE RECHARGE TEST

This section describes the design, location, and construction of the spreading basin recharge facilities at the SEWD North site, including preparatory and construction activities. SEWD staff constructed and installed all of the temporary equipment necessary for pilot-scale recharge testing.

Data collected from 2011 field investigations, pilot-scale recharge testing at the former 35-Acre site in 2006 (USACE, 2006b), and aquifer testing completed in 2006 (USACE, 2006a) were evaluated to establish the design and select locations for pilot-scale recharge testing at the site. Data collected from these studies included the following:

1. Borehole lithology, grain size analysis, blow count, and Guelph permeameter test data (SoundEarth Strategies, 2011a and 2011b)

2. Percolation rates, borehole lithology, grain size analysis, and blow counts (MWH, 2006b)

3. Aquifer properties including transmissivity, storativity, and hydraulic conductivity (MWH, 2006a)

5.1 RECOMMENDED RECHARGE TECHNIQUES FOR PILOT-SCALE RECHARGE TESTING The spreading basin recharge technique described in the Program Manual (USACE, 2004) was selected as the most appropriate method. This method involves excavating surface soil through low-permeability soils and/or shallow hardpan layers to depths of 2 to 5 feet. Borings from field investigations in 2011 (SoundEarth Strategies, 2011a) indicated the presence of a silty clay layer to a depth of 3 feet in the northeast corner of the perimeter (B0ALT1 boring), clayey silt to a depth of 10 feet (B03) in the southeast corner of the perimeter, clayey silt to a depth of 50 feet (B02) in the north central portion of the perimeter, clayey silt and organic clay to a depth of 33 feet (B01) in the northwest corner of the perimeter. In addition, previous pilot-scale recharge tests conducted at the former 35-Acre site indicated that the flooded field technique used at one of the test plots for this test was prone to seepage through sidewalls which made it difficult to estimate the actual percolation rate into the soil (USACE, 2006b). Based on a review of this data, it was recommended that two pilot-scale recharge spreading basins should be constructed at the site to observe the percolation rate of more permeable soils below the upper few feet of material.

5.2 SELECTION OF PILOT-SCALE RECHARGE TEST LOCATIONS Two recharge basins were constructed, one in the western portion of the North Site and one in the eastern portion of the site, as shown in Figure 1-1. These two areas were chosen for the recharge tests because they were considered to represent two potential end members (high and low) percolations rates, based on the existing data reviewed for the site. The goal of the pilot-scale recharge test was to select locations that would be considered representative of the entire site, thus evaluating the potential “high” and “low” percolation rate areas was concluded to provide the most representative information for the entire site.



5.3 CONCEPTUAL PILOT-SCALE RECHARGE BASIN DESIGNS A preliminary analysis of the potential for groundwater mounding under the two pilot-scale recharge basins was conducted before finalizing the conceptual pilot-scale recharge basin designs. The groundwater mounding analysis was completed using the Hantush equation (see Carleton, G. B., 2010) and a readily available tool produced by the USGS (USGS, 2012). Input data used for these calculations included recharge rate, specific yield, horizontal hydraulic conductivity, recharge basin length and width, duration of the infiltration period, and an initial thickness of the saturated zone (to the first confining or semi-confining unit). The sources for the data used to make initial groundwater mounding estimates were obtained from the following sources:

• Average recharge rates from the pilot-scale testing at the former 35-Acre site (USACE, 2006b)

• Specific yield values from California’s Groundwater: Bulletin 118 (DWR, 2003)

• Horizontal hydraulic conductivity from aquifer testing at the SEWD site (USACE, 2006a)

• Initial thickness of the saturated zone was estimated from a review of well logs and geophysical logs in the vicinity of the site (see Appendix A)

To maximize the potential for mounding that would be observed at monitoring wells, recharge basin length and width and the duration of infiltration period were varied. Based on the results of this analysis, a conceptual pilot-scale recharge basin size was recommended, as presented in the Pilot-Scale Field Recharge Plan (Appendix B).

An estimate of the volume of water required for testing was based on the Guelph permeameter tests (SoundEarth Strategies, 2011a and 2011b) and pilot-scale recharge tests at the former 35-Acre site (USACE, 2006b). Conceptual designs of both recharge tests are included in Appendix J.

5.4 SPREADING BASIN CONSTRUCTION AND ACTIVITIES This section discusses how the two test sites were constructed, and describes instrumentation that was installed, site measures observed, and conveyance used for delivering source water to the test plots.

5.4.1 Spreading Basins Recharging groundwater using spreading basins consists of applying water to an excavated basin created for this purpose; allowing for percolation of the water through the bottom and side walls of the excavation, as shown conceptually in Figure 5-1.

The locations of the spreading basins at the SEWD North site are illustrated in Figure 1-1. The locations for these spreading basins were finalized after discussion with the SEWD, as described in Section 4. Before initiating construction of the spreading basins, SEWD staff measured and staked out the locations of the pilot-scale recharge test basins according to the conceptual designs. Both spreading basins were approximately 100 feet by 100 feet and were excavated to a


5.0 Design, Location, and Construction of Pilot-Scale Recharge Test

depth of approximately 3 feet deep with an excavator and backhoe (see Figure 5-1). Heavy plastic sheeting was draped over the berms and on the vertical sidewalls of the spreading basins to protect from sloughing caused by wave erosion and to prevent excavated soils from blowing into the basins. During the entire test period, the plastic sheeting on the sidewalls remained intact.

Figure 5-1.

Conceptual Drawing of Spreading Basin

Note: Spreading Basin test plots at the North Site. A) Spreading Basin outlet, showing source water conveyance piping in foreground. B) Spreading Basin East Pond.

Figure 5-2. Spreading Basins at North Site

5.4.2 Water Source, Conveyance, and Measuring Devices Water was conveyed to both spreading basins for the purpose of pilot-scale recharge testing. The source water was obtained from SEWD’s north holding pond, and consisted of a mix of water from the Calaveras and Stanislaus rivers. This water is currently the surface water that is purchased by the lease of the Bozzano property. The source water was pumped into a large tank



daily which was attached to the irrigation main line on the Bozzano property. Existing irrigation pipelines on the site routed the water from the main line to the two different spreading basins at different turn-outs. SEWD coordinated with the lease holder to verify the feasibility of use of the pipelines for the duration of the recharge test.

5.4.2.1 Water Source Water used for pilot-scale recharge testing at both test plots was pumped from SEWD’s north holding ponds located at the SEWD site. Surface water originating from the Stanislaus River is stored in the holding ponds prior to being treated and delivered by SEWD.

5.4.2.2 Conveyance Pipelines Source water was conveyed from the holding pond to the recharge test plots through the Bozzano property main irrigation line and irrigation pipelines. A PVC “Tee” was installed along the pipeline to deliver water to the spreading basin. A ball valve was installed at each spreading basin to control the flow rate of source water into each plot during refilling. The discharge piping located within each test plot was a section of pipe installed upwards to prevent erosion and washout of the test plot bottom.

5.4.2.3 Measuring Devices Staff gauges were installed in each spreading basin to monitor pond depths during testing. The bottom, or zero reading, on each staff gauge was located at the base of the spreading basin. The pond depth in each spreading basin was typically measured and recorded on its respective staff gauge once per day (excluding weekends). A description of the methodology used to calculate percolation rates with the use of staff gauge data is provided in Section 6.2.

5.4.3 Site Safety The recharge basins were located within the Bozzano property, north of the SEWD facility grounds, but accessible through the SEWD facility. The SEWD grounds are enclosed by an 8-foot chain-link fence and are further protected by security and surveillance cameras. There was no opportunity for the public to access the spreading basins through the SEWD property. Public access to the spreading basins would be limited to access through private farm roads.


6.0 PILOT-SCALE RECHARGE TESTING RESULTS AND ANALYSIS

This chapter describes North Site pilot-scale recharge testing activities and results and decommissioning of pilot-scale testing facilities at the site.

As described above, the second phase of pilot-scale recharge testing at the North Site included characterizing subsurface conditions at the site. Previous field investigations at or near the site provided a basis for designing the recharge basins. However, data collected in conjunction with pilot-scale recharge testing were used to further characterize the site to identify its potential for groundwater recharge.

6.1 PILOT-SCALE RECHARGE TESTING DATA Various quantitative data were collected during pilot-scale recharge testing at the North Site. Source water field parameters (pH, electrical conductivity, turbidity, and temperature) and water depth within the recharge test plots were measured along with evaporation and precipitation data to determine final percolation rates. SEWD staff visited the site nearly every day to record test plot water depth, to refill the test plots to a depth between 1 and 3 feet, and to periodically measure the field parameters. Qualitative data for site conditions also were collected to determine whether algae and/or abundant suspended solids were evident. These data are described and analyzed in the following sections.

6.1.1 Pilot-Scale Recharge Test Source Water Field Parameters Physical characteristics (field parameters) of water used for pilot-scale recharge testing were measured to ensure that the source water did not negatively affect recharge performance. Source water at the North Site was pumped from SEWD’s North holding pond to the black storage tank distributing water to the North Site (Bozzano property) irrigation line. The source water was monitored during pilot-scale recharge testing according to the Pilot-Scale Field Recharge Plan (Appendix B) for the four field parameters listed in Table 6-1. Source water was sampled and analyzed on a weekly basis throughout the duration of the recharge test. Data in Table 6-1 show that source water used for pilot-scale recharge testing at the North Site had low turbidity and no other parameters that could potentially affect recharge testing results, like high total dissolved solids (TDS).




Tabl

e 6-

1.

Sour

ce W

ater

Fie

ld P

aram

eter

s

C

onst

ituen

t U

nits

04

/03/

13

04/1

0/13

04

/17/

13

04/2

4/13

05

/02/

13

05/0

7/13

05

/15/

13

05/1

6/13

East Pond

Turb

idity

N

TUs

2.59

2.

89

1.74

1.

70

4.05

3.

01

2.65

N

A

Con

duct

ivity

µS

/cm

80

.7

86.2

17

0 17

8 67

.0

55.0

40

9 N

A

Tem

pera

ture

°C

17

.5

16.3

15

.8

19.2

21

.2

21.0

21

.3

NA

TDS

ppm

N

A1

NA

1 N

A1

91.0

31

.0

27.0

16

6 N

A

pH

pH u

nits

8.

23

7.77

7.

00

7.26

7.

49

7.70

7.

48

NA

West Pond

Turb

idity

N

TUs

NA

2.

30

3.43

2.

91

3.74

3.

56

NA

1.

43

Con

duct

ivity

µS

/cm

N

A

95.8

21

4 34

3 99

.0

60.0

N

A

173

Tem

pera

ture

°C

N

A

16.3

15

.8

18.8

21

.0

20.2

N

A

20.6

TDS

ppm

N

A

NA

1 N

A1

170

39.0

30

.0

NA

87

.0

pH

pH u

nits

N

A

8.03

7.

21

7.19

7.

50

7.67

N

A

8.27

N

otes

: 1 Fi

eld

sens

or d

id n

ot h

ave

capa

bilit

y to

mea

sure

TD

S

Key

: °C

= d

egre

es C

elsi

us

µS/c

m =

mic

ro S

iem

ens

per c

entim

eter

N

A =

not

ava

ilabl

e N

TU =

nep

helo

met

ric tu

rbid

ity u

nits

pp

m =

par

ts p

er m

illio

n TD

S =

tota

l dis

solv

ed s

olid

s

6.0 Pilot-Scale Recharge Testing Results and Analysis

6.1.2 Spreading Basin Water Depths SEWD personnel measured and recorded the water depths in each test plot on a daily basis during the 6 week testing period. Water depth measurements were recorded from the staff gauges installed in each test plot, accurate to 0.01 feet.

6.1.3 Groundwater Depth Data Groundwater depth data was collected from the three monitoring wells (MW-NS-01, MW-NS-02, and MW-NS-03) throughout the duration of the recharge testing. Groundwater depths were also measured at 17 other wells, including three triple-nested monitoring wells (MW-1A through 1C, MW-2A through 2C, and MW-3A through 3C) that SEWD monitors monthly. In addition, groundwater depth data for four USGS wells in the area was obtained on the USGS Web page. The wells monitored during pilot-scale recharge testing are shown in Figure 6-1.




Fi

gure

6-1

. G

roun

dwat

er D

epth

Mon

itorin

g


6.1.4 Groundwater Quality Data Groundwater quality data was collected from the three monitoring wells near the end of the recharge test. This data was then compared to the baseline data collected at the start of the test to determine if recharging the aquifer using surface water would have any negative impacts on the groundwater quality in the area. Groundwater quality data was also collected from two wells, SEWD production well 74-01 and Bozzano shed, near the pilot-scale recharge tests that were screened at deeper depth intervals (see Appendix A for well logs). The locations of the wells from which groundwater quality samples were obtained are illustrated in Figure 6-2.

6.1.5 Microscopic Particulate Analysis In addition to groundwater quality testing at SEWD production well 74-01, a microscopic particulate analysis (MPA) was conducted to address the question of whether groundwater was under the influence of surface water during recharge testing. The SEWD Business Plan proposes using existing production wells, such as production well 74-01 for extraction as part of the implementation of the banking program. The MPA test was conducted to determine whether the pilot-scale recharge test and other existing SEWD recharge operations at the 60-acre site have influenced groundwater at the depth of the production well 74-01 well screen interval (210-515 feet bgs) such that the signature of surface water is detected in the groundwater quality.

The MPA test was conducted at the end of the pilot-scale recharge test period in accordance with testing protocol (see Appendix K). Water from production well 74-01 was routed from a sampling port off the pump and plumbed through tubing to the MPA apparatus, as illustrated in Figure 6-3. Approximately 1,000 gallons of water was plumbed through the MPA apparatus at a rate between 1 and 1.5 gallons per minute. The water was discharged to the ground surface near the pump house. The remaining water pumped from production well 74-01 during this test was fed through the existing SEWD facilities to an onsite reservoir.




Fi

gure

6-2

. G

roun

dwat

er Q

ualit

y M

onito

ring


Figure 6-3.

Microscopic Particulate Analysis Apparatus

6.1.6 Evaporation and Precipitation Evaporation and precipitation were monitored to obtain accurate volume measurements of recharged water. Evaporation and precipitation data were downloaded daily from the California Irrigation Management Information System (CIMIS) database and Web page. To obtain more representatives measurements, the data from two nearby stations, No. 70 near Manteca and No. 167 near Tracy, were averaged. Data from the nearest CIMIS station, No. 166 near the City of Lodi was not available during the testing period. The CIMIS station reports precipitation and reference evapotranspiration (ETo), which was converted for the pilot-scale recharge test to evaporation by multiplying by the correct monthly factor derived from data on the CIMIS Web page.

6.1.7 Site Conditions SEWD staff visited the site on a daily basis from April 2 to May 17, 2013, to monitor qualitative site conditions, including presence of vectors, algae, and suspended sediments.

6.1.7.1 Vector Control The recharge facilities were located approximately 1,400 feet and 1,650 feet from an SEWD north holding pond that contains water throughout much of the year. Therefore, the potential for recharge activities to increase the populations of mosquito and other water-borne vectors locally was not considered significant. As expected, SEWD staff did not observe any signs of vectors in or around the recharge test plots during routine site inspection activities.

6.1.7.2 Attractive Nuisances Due to the relatively remote location of the site, it is unlikely that testing activities and/or facilities were attractive nuisances. No complaints were received by adjacent landowners during testing. No evidence of trespassing or vandalism was observed during testing.



6.2 GROUNDWATER ELEVATIONS As mentioned, groundwater elevations were measured in the three monitoring wells and 17 other nearby wells on a weekly basis between April 2 and May 17, 2013. Groundwater elevation data was also downloaded weekly from the USGS Web site for 4 USGS wells. Figure 6-4 shows continuous measurements of the depth to water versus time collected with pressure transducers for monitoring wells MW-NS-01, MW-NS-02 and MW-NS-03. In MW-NS-01 and MW-NS-02, located next to the West Pond and East Pond, respectively, the groundwater elevations increased by approximately two feet over the course of the testing. The groundwater elevation in MW-NS-03, which was not located immediately next to either recharge pond, increased by approximately a half foot over the course of the test. Post-test, the groundwater elevations in all three monitoring wells exhibited a slightly deeper depth than at the initiation of the test. This could indicate that the monitoring wells were influenced by neighboring agricultural pumping during the early irrigation season, which overlapped with the early testing period.

Figure 6-4.

Depth to Water vs. Time for Monitoring Wells

Depth to water data for the additional wells and the three monitoring wells on the North Site is presented in Figure 6-5. Most of the wells, with the exception of two of the USGS wells, experienced a decrease in groundwater elevation of less than 10 feet during the course of the test, likely due to the influence of groundwater pumping during the irrigation season.

50

52

54

56

58

60

62

64

Dept

h to

Wat

er (f

eet)

MW-NS-01_Transducer

MW-NS-02 Transducer

MW-NS-03 Transducer



Figure 6-5.

Depth to Water vs. Time for SEWD Wells

6.3 GROUNDWATER QUALITY Groundwater quality samples were collected from monitoring wells MW-NS-01, MW-NS-02 and MW-NS-03 near the end of the test on May 15 and May 16, 2013. The results of this testing are presented in Table 6-2 below. In all three wells, the nitrate concentrations exceeded the State and Federal MCLs. In addition, TDS concentrations were above the U.S. EPA’s Secondary Drinking Water Standards. In MW-NS-01, the iron concentration also exceeded the Secondary Drinking Water Standard set by the U.S. EPA.

20

30

40

50

60

70

80

90

100

4/2/2013 4/16/2013 4/30/2013 5/14/2013 5/28/2013 6/11/2013

Dept

h to

Wat

er (f

eet)

Date

A4 (pump house)

MW 1A - west

MW 1B - center

MW 1C - east

T1 (pump house)

74-01 (pump station)

74-02 (pump station)

Bozzano

MW 2A - north

MW 2B - center

MW 2C - south

60 acre

PZ1

Cutter

MW 3A - north

MW 3B - center

MW 3C - south

USGS 375805121121101

USGS 375805121121102

USGS 375805121121103

USGS 375805121121104

MW-NS-01

MW-NS-02

MW-NS-03



Table 6-2. Summary of Post-Test Water Quality Constituents Detected

Constituent Units

Groundwater Quality

Monitoring Well MW-NS01

(5/16/13)

Groundwater Quality


(5/15/13)

Groundwater Quality


(5/16/13)

MCL

Total Alkalinity mg/L 340 980 440

Bicarbonate as CaCO3 mg/L 340 980 440

Carbonate as CaCO3 mg/L ND ND ND

Hydroxide as CaCO3 mg/L ND ND ND

Chloride mg/L 33 9.9 36 2501

Specific Conductance (EC) µmhos/cm 910 1100 1100

Hexavalent Chromium µg/L 6.8 5.8 4.9 102

Total Hardness as CaCO3 mg/L 350 400 440

Nitrate as N mg/L 13 18 15 10

Nitrite as N mg/L ND ND ND 1

pH pH units 7.21 7.33 7.14 6.5-8.51

Sodium Adsorption Ratio sqrt(meq/L) 1.5 1.9 1.7

Sulfate as SO4 mg/L 53 120 60 2501

Total Dissolved Solids mg/L 580 650 680 5001

Arsenic µg/L 5.2 3.6 3.7 10

Boron µg/L 54 110 ND

Calcium µg/L 8,0000 93,000 96,000

Copper µg/L 17 ND ND 1300

Iron µg/L 530 ND 280 3001

Magnesium µg/L 36,000 43,000 48,000

Manganese µg/L ND ND ND 501

Potassium µg/L 6,200 4,800 6,800

Sodium µg/L 65,000 86,000 82,000

Zinc µg/L ND ND ND 5,0001

Total Coliforms MPN/100mL 2 <1.8 <1.8 5

Fecal Coliforms MPN/100mL <1.8 <1.8 <1.8 5 Total Trihalomethanes (THM) µg/L ND ND ND 80

Notes: 1 Secondary Standard 2 California Department of Public Health Maximum Contaminant Level Bold text indicates exceedance of Federal MCL Key: µg/L = micrograms per liter MCL = maximum contaminant level mg/L = milligrams per liter MPN = most probable number ND = none detected



Groundwater samples were also collected at SEWD production well 74-01, on May 16, 2013, and at the Bozzano shed well May 17, 2013. The results of the water quality testing are shown in Table 6-3. All of the detected constituents in these two wells were present at concentrations below the State and federal MCLs.

Table 6-3. Summary of Post-Test Water Quality Constituents Detected at Neighboring Wells

Constituent Units Groundwater Quality

74-01 (5/16/13)

Groundwater Quality Bozzano

Well (5/17/13) MCL

Total Alkalinity mg/L 160 130

Bicarbonate as CaCO3 mg/L 160 130

Carbonate as CaCO3 mg/L ND ND

Hydroxide as CaCO3 mg/L ND ND

Chloride mg/L 8.7 5.2 2501

Specific Conductance (EC) µmhos/cm 360 300

Hexavalent Chromium µg/L ND ND 102

Total Hardness as CaCO3 mg/L 120 95

Nitrate as N mg/L 0.76 0.6 10

Nitrite as N mg/L ND ND 1

pH pH units 7.27 7.53 6.5-8.51

Sodium Adsorption Ratio sqrt(meq/L) 0.88 1.0

Sulfate as SO4 mg/L 20 14 2501

Total Dissolved Solids mg/L 250 200 5001

Arsenic µg/L 6 4.6 10

Boron µg/L ND ND

Calcium µg/L 26,000 19,000

Copper µg/L ND 24 1300

Iron µg/L ND ND 3001

Magnesium µg/L 13,000 12,000

Manganese µg/L ND ND 501

Potassium µg/L 6,800 7,400

Sodium µg/L 22,000 22,000

Zinc µg/L ND ND 5,0001

Total Coliforms MPN/100mL <1.8 <1.8 5

Fecal Coliforms MPN/100mL <1.8 <1.8 5

Total Trihalomethanes (THM) µg/L 2.2 0.98 80 Notes: 1 Secondary Standard 2 California Department of Public Health Maximum Contaminant Level

Key: µg/L = micrograms per liter MCL = maximum contaminant level mg/L = milligrams per liter MPN = most probable number ND = none detected



An MPA test was also conducted at production well 74-01 to determine whether the groundwater at the site was under the influence of surface water. The results of the MPA test, which are summarized in Table 6-4, indicate groundwater is not under the influence of surface water.

Table 6-4. Results of Microscopic Particulate Analysis Test

Bio-Indicator Result

Primary Giardia NS

Coccidia NS

Other Algae NS

Rotifers NS

Cryptosporidium NS

Diatoms NS

Insect/Larvae NS

Plant Debris NS

Secondary Amorphous Debris TNTC

Plant Pollen NS

Crustacea NS

Ciliates/Flagellates NS

Minerals TNTC

Nematodes NS

Amoeba NS

Other Organisms NS Key: NS = none seen TNTC = too numerous to count

6.4 SPREADING BASIN RECHARGE PONDS The bases of the North Site recharge basins both measured approximately 100 by 100 feet. Water depth in the basins varied between 0.85 and 2.81 feet during recharge testing. (Section 5 contains a conceptual illustration of a spreading basin and photos of the actual spreading basins constructed at the North Site.) The following section discusses pond depth, percolation rate, and cumulative percolation volume data collected during pilot-scale recharge testing of the test ponds.

6.4.1 Pond Depth Pond depth in the test ponds was monitored by SEWD personnel on a near-daily basis between April 2 and May 17, 2013. Water in the ponds was maintained at depths ranging from 0.85 feet to 2.81 feet for the duration of testing. The ponds were refilled continuously by SEWD staff by pumping source water into them. Figure 6-6 illustrates the depth of water versus time for the test ponds. Recharge basin depth data was not available for the East Basin on May 12, 2013.



Figure 6-6.

Depth of Water vs. Time for Test Pond Recharge Test

6.4.2 Percolation Rates Multiple variables were monitored to calculate percolation rates at the site, as listed below for the percolation rate equation. Water quantities necessary for pilot-scale recharge testing were estimated after reviewing previous studies and conducting an initial analysis. Evaporation and precipitation data were collected from the weather stations, as described above, and as mentioned, careful records of recharge basin water depths were collected during testing according to the Pilot-Scale Field Recharge Plan (Appendix B) to determine final percolation rates.

A water balance was used to derive the percolation rate during direct pilot-scale recharge testing, as shown below.

P = {(S1-S2) + P – E}/T

Where:

P = Percolation rate (feet per day)

S2 = Current depth of water in test site (feet)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

4/2 4/7 4/12 4/17 4/22 4/27 5/2 5/7 5/12 5/17

Wat

er D

epth

(fee

t)

Date

East Pond

West Pond



S1 = Previous depth of water in test site (feet)

P = Precipitation (feet)

E = Evaporation (feet)

T = Time (days)

Percolation rates were calculated using data collected from April 2 to May 17, 2013. For the West Pond, calculated percolation rates varied between 0.67 and 1.27 feet per day, with the average rate being approximately 0.93 feet per day. For the East Basin, percolation rates ranged between 0.32 and 0.59 feet per day, with an average rate of approximately 0.45 feet per day. Because water depth data was not available in the East Basin on May 12, the percolation rate for May 13 was averaged over a two-day period.

Clogging due to vegetation, biological, or chemical influences did not appear to affect the performance of the pilot-scale recharge test of the spreading basin at the North Site, but these factors should be considered during longer duration testing. Figure 6-7 shows percolation versus time for the test ponds.

Figure 6-7.

Percolation vs. Time for Test Pond Recharge Test

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

4/2 4/7 4/12 4/17 4/22 4/27 5/2 5/7 5/12 5/17

Perc

olat

ion

Rate

(fee

t/da

y)

Date

East Pond

West Pond

Precipitation (inches)

Average Percolation Rate = 0.93 feet per day

Average Percolation Rate = 0.45 feet per day



6.4.3 Cumulative Percolation Volumes Cumulative percolation volumes were calculated from data collected between April 2 and May 17, 2013. The volume of water that percolated during this period was 9.87 acre-feet for the West Basin and 4.76 acre-feet for the East Basin. Figure 6-8 shows the cumulative volume of water percolated over time in each test pond. The trend remains relatively stable throughout the duration of testing, suggesting that significant clogging effects did not occur during the test period.

Figure 6-8.

Cumulative Percolation Volume vs. Time for Test Pond Recharge Test

6.4.4 Decommissioning of Pilot-Scale Recharge Test Facilities At the time this document was prepared, SEWD staff had not yet decommissioned the recharge testing facilities.

6.5 GROUNDWATER MOUNDING As described above in Section 4, initial estimates of groundwater mounding underneath each of the two spreading basins were calculated using the Hantush equation, in the USGS’s Hantush Tool spreadsheet (USGS, 2012). Section 4 presents the sources from which estimates for the field parameters were obtained to make calculations for the North Site. After completion of the pilot-scale recharge tests, the tool was “calibrated” for the groundwater mounding observed at

0

2

4

6

8

10

12

4/2 4/7 4/12 4/17 4/22 4/27 5/2 5/7 5/12 5/17

Cum

ulat

ive

Perc

olat

ion

Volu

me

(acr

e-fe

et)

Date

East Pond

West Pond



the North Site during field testing. The average recharge rates were updated for the two sites based on field data, while the horizontal hydraulic conductivity and specific yield were varied to best fit the conditions observed (mounding exhibited at the monitoring wells next to the respective recharge basins and in the central well). From the testing it could not be distinguished from which test the central well was influenced, so the results from the calculations consider that it was caused entirely by one or the other recharge basins. These calculations provide a range of horizontal hydraulic conductivities and specific yield values for the subsurface. The parameters estimated by these calculations are presented in Table 6-5 for the two recharge basins.

Table 6-5. Hydraulic Properties Estimated from Pilot-Scale Recharge Testing

Recharge Rate Test Time Specific

Yield Horizontal

Conductivity (ft/day)

Test Size

0.93 46 0.15 18 100 by 100

0.45 46 0.09 10 100 by 100 Key: ft/day = feet per day


7.0 CONCLUSIONS The following section summarizes the key findings from the pilot-scale recharge testing and analysis.

7.1 GROUNDWATER QUALITY As described in Section 4 and 6, groundwater quality was collected at the three monitoring wells installed for the project, MW-NS-01, MW-NS-02, and MW-NS-03 both pre- and post-test. Following the pilot-scale recharge test, the groundwater quality demonstrated elevated concentrations of nitrate, iron, and TDS. In all three wells, the nitrate concentrations exceeded the State and Federal MCLs. In addition, TDS concentrations were above the U.S. EPA’s Secondary Drinking Water Standards. In MW-NS-01, the iron concentration also exceeded the Secondary Drinking Water Standard set by the U.S. EPA.

These results suggest that the source of the elevated constituents was intercepted between the ground surface and the water table in the vadose zone. The elevated concentrations may be a temporary phenomenon, which would be resolved after enough water was flushed through the soil column.

Deeper groundwater quality was tested at the Bozzano shed well, a well screened in a more intermediate zone (100-200 feet bgs) and production well 74-01, screened in a deeper zone of the Laguna Formation (210-515 feet bgs). All of the analyzed constituents in these two wells were present at concentrations below the State and Federal MCLs.

The source water to be used for recharge at the site was tested at the beginning of the test as described in Section 4. Total and Fecal coliform were reported at MPN concentrations of >1,600 and 11, respectively, which exceeded State and federal MCLs. The coliform values are not considered problematic because of the relatively thick unsaturated zone which will effectively remove these constituents from the source water before it reaches the saturated zone.

No issues related to the source water were identified that would be of concern for the banking program. Elevated nitrate and iron may be of potential concern for long-term operations. Elevated nitrate in the shallow groundwater is potentially associated with application of nitrate as part of agricultural practices in the region and may experience seasonal spikes in concentrations during the beginning of the irrigation season (as was the timing for the pilot-recharge test).

If groundwater for the banking project was extracted from wells screened at the same zones as the Bozzano shed well (100 – 200 feet bgs) or well 74-01 (215 – 510 feet bgs) it would not require blending to meet State and Federal drinking water quality standards. The groundwater quality of these wells did not exceed State or Federal MCLs. The SEWD plant would provide adequate treatment of extracted water from these wells. If groundwater were extracted from the shallow zone, as observed in monitoring wells MW-NS-01, MW-NS-02, and MW-NS-03, then this water would need to be blended with other groundwater from deeper zones before being blended with the raw water supply.

A simple mixing calculation was completed to conclude that groundwater from the shallow zone would require blending with deeper water before blending with the raw water supply if



constituents such as nitrate found in the shallow groundwater were persistent. The mixing equation is presented below.

Concentration = (C 1 V 1 +C 2 V 2) / (V 1 +V 2)

Where

C 1 = concentration of nitrate in groundwater, C 2 = concentration of nitrate in raw surface water supply. V1 = volume of groundwater

V2 = volume of raw surface water

The results of the calculations, using nitrate concentrations observed during the post-test groundwater quality testing at monitoring wells MW-NS-01, MW-NS-02, and MW-NS-03 show that nitrate concentrations would exceed the MCL if 80 percent of the raw water consisted of groundwater pumped from the screen interval consistent with those wells. In general, it is concluded that water quality concerns can be managed through treatment and blending, and do not present a significant limitation to the feasibility of a future banking project.

7.2 PERCOLATION RATES The soils underlying the North Site consist of silty clays, silts, silty sands, and clay. The upper 100 to 200 feet bgs is part of the Alluvium and Modesto/Riverbank Formation (DWR, 2003). As described in Section 7, the average percolation rates measured at the West Basin and East Basin were 0.93 ft/day and 0.45 ft/day, respectively. According to the ranking criteria presented in the Program Manual (USACE, 2004), the lower end of the range of estimated percolation rates (0.45 ft/day) would be considered moderately desirable in terms of the suitability of the geology and soil conditions. However, if it is assumed the actual percolation rate is somewhere in between the two average percolation rates from both basins (0.45 ft/day and 0.93 ft/day) then conditions may be considered more favorable. Although the Program Manual may indicate that percolation rates of 0.45 ft/day are moderately desirable, it should be noted that the conditions presented in the manual are more reflective of estimated percolation rates worldwide. Programs within the Central Valley of California have shown that infiltration rates less than 0.45 ft/day can result in successful groundwater recharge programs (e.g. Kern Water Bank with an estimated recharge rate of 0.3 ft/day). Therefore, for the purposes of this evaluation, the conditions at the North Site would indicate that the percolation rates are suitable for operating the site as a recharge facility.

Using the best available information, calculations were made with the Hantush equation, described above in Section 4, to calculate the potential mounding at the recharge basin assuming the hydraulic parameters estimated in Section 6 and an approximate full-scale recharge basin (4,000 feet by 2,900 feet). The Surface Water Availability Analysis completed in conjunction with this evaluation indicated that surplus surface water may be available for groundwater recharge in more than 50 percent of the future years with annual recharge amounts peaking around 44,000 acre-feet/year at the 2020 level of demand, assuming an average recharge rate of 0.6 feet per day. The length of time for recharge was calculated as the annual recharge of 44,000 acre-feet divided by the recharge basin area (4,000 feet by 2,900 feet), multiplied by the


7.0 Conclusions

average recharge rate (volume/area multiplied by recharge rate). Two rates were used, representing the two pilot basins’ average rates, resulting in two end-member time periods. The length of time calculated for the West and East Basins were 179 days and 369 days (more than a year to recharge 44,000 acre-feet if recharge rate was 0.45 feet per day). The results of the calculations made using the Hantush equation indicate that using hydraulic parameters estimated for the West Basin and East Basin (average recharge rates of 0.93 ft/day and 0.45 ft/day, respectively), the recharge basin would experience nearly 400 feet of mounding at the center of the basin. Based on these calculations, it appears that groundwater mounding will limit the amount of water that could be applied to the North Site in a given year. The results from this analysis indicate that continuous operation and flooding of the entire North Site is likely unreasonable, but that different operation scenarios may be more appropriate for operating the basin successfully. Calculations made using the Hantush equation indicated that the groundwater table would reach within 5 to 10 feet of the surface at the center of the basin after 9 days assuming the parameters for the West Basin and 11 days assuming the parameters for the East Basin. This would indicate that storage beneath the basin would have filled with water. In order to store additional water, the water directly beneath the site would need to migrate horizontally away from the site to create more available storage capacity. Therefore, different operational scenarios would be critical to maintain a sustainable long-term recharge rate. These calculations used the best available information, which we believe are reasonable at this stage, but will need to be borne out by demonstration-scale testing.

As described above, the estimated average recharge rate was 0.93 ft/day at the West Basin and 0.45 ft/day at the East Basin. The average recharge rate at the North Site and former 35-Acre site combined may decrease over time due to clogging, algae growth, or other causes. However, records from the SEWD 60-Acre site indicate that the average recharge rate has remained relatively constant since initiation of operation in 2002. Therefore, if comparable, the North Site may perform similarly.

7.3 GROUNDWATER LEVEL RESPONSE As described in Section 6 above, MW-NS-01 and MW-NS-02, located next to the West Pond and East Pond, respectively, the groundwater elevations increased by approximately two feet over the course of the pilot-recharge test. The groundwater elevation in MW-NS-03, which was not located immediately next to either recharge pond, increased by approximately a half foot over the course of the test. It is expected that the recharge water from North Site would primarily go to the shallow Alluvium and Modesto/Riverbank Formations which extend 100 to 200 feet bgs. The Laguna Formation underlies the Alluvium and Modesto/Riverbank Formations and extends from approximately 800-1,000 feet bgs (DWR, 2003). The Plio-Pleistocene Laguna Formation consists of discontinuous lenses of stream-laid sand and silt with lesser amounts of clay and gravel (DWR, 2003). Because of the high level of stratification of the aquifer (clay and silt lenses interbedded with more permeable sand and some gravel), the recharge water is expected to primarily move horizontally as opposed to vertically downward after it intercepts the water table. To maximize production, the proposed extraction wells would be similar to the existing agricultural wells, and would likely be screened from approximately 100 feet to 300 feet depth in the lower Alluvium and Modesto/Riverbank Formations and upper Laguna Formation.



The 2006 aquifer test evaluation, which involved pumping production well 74-02 (screened in the Laguna Formation between 200 and 500 feet bgs) concluded that it was not possible to evaluate the potential for recovering recharged groundwater through pumping at SEWD because of the limited time period of the aquifer test (USACE, 2006a). The report concluded that the subsurface under SEWD contains layers of interconnected sands that serve as conduits between wells and as a result, groundwater level responses in nearby wells will likely vary according to what sand layers each well and the pumping well are screened through (USACE, 2006a).

The information summarized above indicates that depending on the timing of storage and extraction, the majority of water extracted would be native groundwater from deeper zones (zones within screened interval), and not the groundwater recharged (assuming extraction well design similar to existing agricultural wells). The exact proportion of water that is from recharge or native sources will depend on the storage volume, storage time, and extraction timing.

It is not unexpected that the water extracted as part of the North Site Groundwater Banking Project would be native groundwater because it would not be recommended for economic and physical reasons to build shallow wells that would only extract water recharged by the project. An advantage of extracting native groundwater rather than shallow recharged water as part of the North Site Groundwater Banking Project is that little or no treatment may be required of deeper groundwater.

The profile of banked water beneath the North Site would consist of a mound that would develop under the site and have a lesser influence on groundwater levels with distance away from the center of the basin. General conclusions could be drawn from the preliminary calculations with the Hantush equation which indicate that the mound would be bell shaped with the peak at the center of the basin that declines at a shallow angle and then quickly drops off just beyond the extent of the basin.

7.4 DRAWDOWN The likely drawdown of recharged water for various drought scenarios would be dependent on a number of factors including, but not limited to, available surface water supply for irrigators who purchase water, potential changes in groundwater levels due to multiple year or single year dry periods and associated pump lift costs, pump efficiency, crop water demands, and distance of irrigation wells from the groundwater bank site. The potential drawdown of groundwater levels at the North Site due to pumping from the wells operated as part of the recharge program can be estimated by making some simplifying assumptions and using a simplified analytical approach. The analytical approach uses the Theis equation to evaluate concerns in a quantitative manner. The Theis equation assumes the well is within a confined system. This approach was selected because the results from aquifer test evaluation (USACE, 2006a) near the North Site indicate the presence of local semi-confined to confined system. The Theis equation is provided below.

Theis Equation

𝑠 =𝑄𝑊(𝑢)

4𝜋𝑇


7.0 Conclusions

𝑈 =𝑟2𝑆4𝑇𝑡

Where

s = drawdown (feet)

Q = discharge (pumping) rate of the well (gpm)

u = dimensionless time parameter

T = transmissivity of the aquifer (ft2/min)

r = distance from the pumping well to the point where drawdown is observed (feet)

S = storativity (unitless)

t = time since pumping began (minutes)

W(u) = the well function

The SEWD Business Plan indicates that the North Site Groundwater Banking Project would be operated on an 8 year cycle, which assumes 5 years of recharge at 26,500 acre-feet per year, and three years of extraction at 27,000 acre-feet per year. Calculations were completed to test the worst case scenario, in which SEWD would recharge 26,500 acre-feet and then immediately need to extract 27,000 acre-feet, yielding a net reduction in storage of 500 acre-feet per year. The following simplifying assumptions were made to calculate the potential drawdown at the North Site under the worst case scenario and estimate the area that would potentially be affected by a decline in groundwater levels from extraction operations at the site:

• Annual recharge (from SEWD Business Plan) = 26,500 acre-feet per year

• Annual extraction (from SEWD Business Plan) = 27,000 acre-feet per year

• Maximum extraction rate (from SEWD Business Plan, accounts for all 11 wells) = 36,600,000 gallons per day or 25,417 gallons per minute

• Confined aquifer (Theis equation applies)

• Hydraulic parameters from the SEWD aquifer test evaluation performed in 2006 (USACE, 2006a) (parameters presented in Table 3-1)

The analysis presented above with regards to the percolation rate evaluates the hydraulic limitations of the site to recharge potential peak annual recharge amount of 44,000 acre-feet. The evaluation of drawdown presented here considers an estimate of what would be recharged in a given year, as presented in the SEWD Business Plan (26,500 acre-feet per year). Although calculations presented in this section were for an unlikely worst case scenario, SEWD does not



anticipate that the North Site Groundwater Banking Project would be operated under this condition.

A series of calculations were made to estimate the maximum drawdown at the nearest irrigation well and the radial distance away from the site that would experience declines in groundwater levels. These calculations assume that pumping is occurring at the 11 wells presented in Figure 7-1, including 7 new wells conceptually shown in the figure as located around the North Site for extraction purposes. The location of the wells presented in Figure 7-1 could potentially be re-located to a more appropriate location, such as along the Peters Pipeline. However, the location of these wells will be further evaluated at a future planning phase of the North Site Groundwater Banking Project. Table 7-1 presents the results from calculating the Theis equation assuming that the annual pumped volume would be 500 acre-feet and that the discharge rates would vary between 754 gallons per minute (equivalent to a 150 day pumping period) to the maximum proposed rate of 25,417 gallons per minute (4.5 day pumping period). The potential drawdown observed at the nearest pumping well was estimated by assuming that the 11 extraction wells (spatial location conceptually shown in Figure 7-1) would extract all 500 acre-feet of water. An important assumption here is that the water table would rise due to the recharge of 26,500 acre-feet of water, and the net withdrawal effect of extracting 27,000 acre-feet of water would be equivalent to extraction of 500 acre-feet of groundwater. This assumes that the recharged water would not be kept in storage for a long dormant period which could allow the groundwater mound to dissipate.


7.0 Conclusions


Fi

gure

7-1

. C

once

ptua

l Loc

atio

ns o

f Sev

en N

ew E

xtra

ctio

n W

ells

and

Exi

stin

g Ex

trac

tion

Wel

ls o

n or

Nea

r the

Nor

th S

ite


Table 7-1 presents the results from these calculations.

Table 7-1. Results from Theis Equation Calculation

Pumping from SEWD

Site (gallons per

minute)

Change in Storage

(acre-feet)

Extraction, Change in Storage (gallons)

Days Pumping

Drawdown Less than 0.10 feet

(feet away from site)

Drawdown Less than 0.10 feet

(miles away from site)

Drawdown at the

Nearest Irrigation

Well1 25,417 500 162,925,500 4.5 16,003 3.0 68 11,000 500 162,925,500 10.3 22,199 4.2 30

754 500 162,925,500 150 56,682 11 2 Notes 1 Location of nearest irrigation well based on visual inspection of aerial imagery. For the purposes of the Theis calculations, areas with less than 0.10 feet of groundwater level decline were considered to have negligible impacts.

The results from these calculations show that the nearest irrigation well to the North Site could potentially experience up to 68 feet of drawdown under a short (4.5 days), more intense pumping period. The calculations show that if the pumping period extended 5 months (as shown in multiple years of the Surface Water Availability Analysis), then the nearest irrigation well to the North Site could potentially experience 2 feet of drawdown. Drawdown of 68 feet at the nearest irrigation well could potentially cause challenges for the well owner. Annual variations of 10 to 20 feet in groundwater levels is not unusual in the region during irrigation season, as observed from well hydrographs available through Department of Water Resources’ (DWR) CASGEM website. However, the measurements reported are likely not taken when the wells are pumping and may not reflect the pumping conditions at the wells.

The results of the calculations also indicate that as expected, for a confined system the longer the period of pumping (lower pumping rate needed to recover the same volume of water), the greater the radial distance away from the well the aquifer will be impacted. However, the greater the pumping rate (shorter duration) the less radial area that will be impacted.


8.0 SUMMARY This section summarizes pilot-scale recharge testing activities at the North site in terms of Stage 2 ranking criteria outlined in the Farmington Groundwater Recharge Manual (USACE, 2004).

8.1 GEOLOGY AND SOILS Two data types described below were used to evaluate the site geology and soils for the purpose of groundwater recharge: soil permeability and depth and thickness of the surface layer. Table 8-1 describes the data types and explains how soil samples were analyzed.

Table 8-1. Geology and Soils

Data Type Data Source/Data

Gathering Technique

Desirable Conditions? Explanation Yes No

Soil Permeability

• Guelph permeameter tests

X

Guelph permeameter tests were completed at three locations: BP-10, BP-02, and BP-02 (SoundEarth Strategies, 2011a and b). The highest initial percolation rate was observed in soil boring BP-10 of 0.23 ft/day. However, this would be considered moderately desirable in reference to the Program Manual (USACE, 2004). The other tests yielded results that would be considered least desirable using the same criteria (USACE, 2004).

• Pilot-scale recharge testing, – spreading basin

X

Data from two pilot-scale spreading basin recharge tests indicated that average percolation rates may vary between approximately 0.45 and 0.93 feet per day at the North Site. This range of values is not meant to suggest that the percolation rate will fluctuate over time (although that is possible); instead it represents the average calculated percolation rates observed at the two test sites based upon test data. The lower end of the range of estimated percolation rates (0.45 feet) would be considered moderately desirable, however assuming the actual percolation rate is somewhere in between 0.45 and 0.93 feet per day then conditions may be considered most favorable (USACE, 2004).

Depth and Thickness of Surface Surface Layer

• Lithologic logging X

Based on the soil borings, clays generally predominate from approximately 3 feet bgs to the ground surface. Below 3 feet bgs, silts and clayey silty soils are generally more prevalent. No significant hardpan and/or clay layer was observed to exist throughout the entire site.

• Grain size analysis X

Laboratory grain size analysis of soil samples in the screened zone indicated the presence of clay in MW-NS-02. However, no continuous clay layer appears to be observed across the site that would prohibit infiltration from the surface.

Key: bgs = below ground surface



8.2 LAND USE Two data types described in Table 8-2 were used to evaluate the SEWD North site land use for the purpose of groundwater recharge: possible contamination and adjacent land use concerns.

Table 8-2. Land Use


Gathering Technique


Possible Contamination

• Site inspections – visual observations

X No evidence of recognized environmental conditions (REC) was observed at the site.

• Verbal communication X The landowner has no knowledge of any existing

RECs.

• Environmental Site Assessment (ESA)

X No regulatory agency files related to hazardous waste were found for this site.

Adjacent Land Use Concerns

• Site inspections – visual observations

X No evidence of RECs was observed immediately adjacent to the site.

• Verbal communication X The landowner has no knowledge of any existing

RECs immediately adjacent to the site.

• ESA X

No regulatory agency files related to hazardous waste were found for properties immediately adjacent to the site. The Phase I ESA did identify a VCP site within 0.5 miles of the site that should be further investigated prior to demonstration testing.


8.0 Summary

8.3 SOURCE WATER The three data types described in Table 8-3 were used to evaluate SEWD North site source water for the purpose of groundwater recharge: surface water availability, quality, and proximity and capacity.

Table 8-3. Source Water

Data Type Data

Source/Data Gathering Technique


Surface Water Availability

• Observations X

It is understood that surface water in the north holding pond, from the Calaveras and Stanislaus rivers is available for groundwater recharge year round. A surface water availability analysis completed as Task 1 of the North Site Groundwater Banking Feasibility Study addresses this question.

Surface Water Quality

• Analytical laboratory analysis

X

Based on laboratory analysis, no VOCs, chlorinated herbicides, organochlorine pesticides and PCBs, pesticides, or nitrogen/phosphorus were reported above their respective detection limits in a sample collected on April 3, 2013, from the East Pond water source. Total and Fecal coliform was reported at most probable number (MPN) concentrations of greater than 1,600 and 11, respectively.

Surface Water Proximity and Capacity

• Observations X As described above, a surface water availability analysis completed as Task 1 of the North Site Groundwater Banking Feasibility Study addresses this question.

• Estimations X As described above, a surface water availability analysis completed as Task 1 of the North Site Groundwater Banking Feasibility Study addresses this question.

Key: µg/L = micrograms per liter DHS = California Department of Health Services mg/L = milligrams per liter MPN = most probable number SDC = Stockton Diverting Canal VOC= volatile organic compound



8.4 GROUNDWATER CONDITIONS Two data types described in Table 8-4 were used to evaluate groundwater conditions at the SEWD North site for the purpose of groundwater recharge: groundwater elevations and groundwater quality.

Table 8-4. Groundwater Conditions


Gathering Technique


Groundwater Elevations

• Monitoring well water level measurements

X

Groundwater elevation data were collected in March 2013 from the MW-NS-01, MW-NS-02, and MW-NS-03 wells installed as part of the project testing. At that time, depth to groundwater ranged from approximately 55-57 feet bgs. As this was prior to the start of the irrigation season, the data collected prior to initiation of the recharge test did not suggest that groundwater elevations were being influenced by pumping occurring nearby. Depth to groundwater data was collected during recharge testing at the three monitoring wells.

Groundwater Quality

• Monitoring well analytical laboratory analysis

X

Based on laboratory analysis, no volatile organic compounds (VOC), chlorinated herbicides, organochlorine pesticides, or polychlorinated biphenyls (PCB) pesticides were reported above their respective detection limits in the baseline groundwater samples collected from the MW-NS-01, MW-NS-02, or MW-NS-03 monitoring wells. Constituents that were detected and worth noting include: Nitrate as N exceeding the Federal MCL in all three monitoring wells post-test and total iron at concentration 5.3 mg/L in MW-NS-01 post-test. Nitrate was the only constituent found at concentrations exceeding Federal and State maximum contaminant levels (MCL).

Key: bgs = below ground surface


8.0 Summary

8.5 HABITAT ISSUES Three data types described in Table 8-5 were used to evaluate the existence of any habitat issues at the SEWD North site for the purpose of groundwater recharge: proximity to known habitat areas, development of unsolicited habitat, and existence of threatened and endangered species in source water.

Table 8-5. Habitat Issues


Gathering Technique


Proximity to Known Habitat Areas

• Site visits X Refer to SEWD, 2012 for more information regarding conclusions with regards to habitat issues.

• Negative Declaration X Refer to SEWD, 2012 for more information regarding

conclusions with regards to habitat issues.

Development of Unsolicited Habitat

• Site visits X Refer to SEWD, 2012 for more information regarding conclusions with regards to habitat issues.

Key: ND = none detected SEWD = Stockton East Water District


9.0 RECOMMENDATIONS This section contains recommendations regarding the next steps for consideration in the development of a groundwater bank at the North Site and existing SEWD facilities for recharge. Recommendations are based on evaluation of data collected during pilot-scale recharge testing and general considerations for groundwater banking programs across California.

• Further evaluation should be performed to estimate the approximate, long-term potential recharge rate of the 60-acre site, the 35-acre site (individually), and the cumulative project including the North Site, 60-acre site, and the 35-acre site in consideration of potential mounding effects that may limit recharge rates.

• Further evaluation should be performed to estimate the drawdown from existing SEWD extraction wells for a demonstration test given different extraction scenarios provided by SEWD (given locations of wells, pumping rates, and duration of pumping). Drawdown estimates should be made for the nearest adjacent production wells and sites with ongoing remediation activities including the Marley Cooling Towers site to the southeast and the VCP site identified in the Phase I ESA (approximately 0.5 miles east of the project area). Significant fluctuation in the groundwater elevation and/or gradient has the potential to affect remediation activities either in an adverse or positive manner.

• Complete demonstration testing at the 60-acre site, including documentation of data collected during the multi-year demonstration recharge testing of the facility by SEWD, and performing an extraction cycle at SEWD production wells 74-01 and 74-02 to test the potential drawdown to nearby wells under a banking scenario. Analysis of the data collected during the extraction cycle could then be used to verify analytical estimates of drawdown or improve on those estimates using field data.

• Conduct demonstration testing at the 35-acre site following recommendations presented in the Program Manual (USACE, 2004). The demonstration testing would further test the long-term recharge rates of the 35-acre site and would follow the suggested 6-month to 3 year length. Demonstration testing would include drilling one or two monitoring wells (depending on the availability/accessibility of the monitoring well MW-NW-1), water quality testing, and construction of the 35-acre facility to be consistent with the recommended final basin design.

• Collection of subsequent groundwater quality data from the shallow screened zone is recommended to evaluate whether nitrate concentrations persist above the State and Federal MCLs or if the data collected during recharge testing was a temporary phenomenon. This testing will help to improve recommendations for operational strategies under implementation of the groundwater bank.

• Development of a groundwater model would allow further quantification of the potential for recharge operations at the North Site to influence or be influenced by nearby contamination sites. Because of the limitations of generalized analytical equations, it is understood that the analytical modeling tools recommended for initial estimates of



mounding and drawdown listed above are reconnaissance-level only. The impacts of multiple pumping scenarios, estimations of vertical groundwater flow, regional groundwater flow conditions, and simultaneous operation of multiple recharge basins is best evaluated using finite element or finite difference (numerical) groundwater modeling. It is recommended to develop a semi-regional groundwater flow model that will provide higher confidence of the impact of a proposed full-scale project. The groundwater flow model would be developed after demonstration-scale testing described above is complete so that new information on subsurface conditions can be incorporated in the numerical model. A groundwater model could potentially be used to do some simplified particle tracking to resolve any concerns about these sites. The groundwater model would also be useful in planning scenarios for operation of the groundwater bank.


10.0 REFERENCES American Society for Testing and Materials (ASTM). 1999. Standard Test Method for

Penetration Test and Split-Barrel Sampling of Soils. ASTM D1586-99.

ASTM. 2000a. Standard Practice for Environmental Site Assessments: Phase 1 Environmental Site Assessment Process. ASTM E-1527-00.

ASTM. 2000b. Standard Practice for Environmental Site Assessments: Transaction Screen Process. ASTM E 1528-00.

ASTM. 2000c. Unified Soil Classification System. ASTM D 2487.

ASTM. 2000d. Unified Soil Classification System. ASTM D 2488.

California Department of Water Resources (DWR). 2003. California’s Groundwater, Bulletin 118 Update.

Carleton, G. B. 2010. Simulation of groundwater mounding beneath hypothetical stormwater infiltration basins: U.S. Geological Survey Scientific Investigations Report 2010-5102, 64 p.

Environmental Data Resources, Inc. (EDR). 2013. The EDR Radius Map with Geocheck, 6700 E. Cooperopolis Road. Inquiry Number 3518332.3. February 12.

SoundEarth Strategies. 2011a. Report of Managed Aquifer Recharge, Characterization and Site Assessment for the Bozzano Property (Also known as the North Site in the Farmington Groundwater Recharge Program), Stockton, CA. September.

SoundEarth Strategies. 2011b. Addendum to the Report of Managed Aquifer Recharge, Characterization and Site Assessment for the Bozzano Property, Stockton, CA. October.

Stockton East Water District (SEWD). 2013. Calaveras River Integrated Stormwater Management Project Initial Study and Proposed Negative Declaration.

USACE. 2004b. Farmington Groundwater Recharge Program Final Program Manual. Prepared by MWH.

USACE. 2006a. Farmington Groundwater Recharge Program Final Aquifer Test Evaluation. Prepared by MWH. June.

USACE. 2006b. Farmington Groundwater Recharge Program Final Technical Memorandum, Results of Pilot-Scale Recharge Testing, Stockton East Water District Northwest Site. Prepared by MWH. September.

USGS. 2013. Hantush USGS SIR 2010-5102-1110.xlsm tool. Available at: http://pubs.usgs.gov/sir/2010/5102/.


mwhglobal.com

3321 Power Inn Road, Suite 300 Sacramento , California 95826-3889

TEL 916 924 8844 FAX 916 924 9102

Appendix A

Data From Neighboring Wells

Date Completed:

USCS

feet bgs

Blow

Cou

nt

Project:Project Number:Logged by:Date Started:Surface Conditions:Well Location N/S:Well Location E/W:Reviewed by:

Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs

Water Depth After Completion:

Water Depth At Time of Drilling:

Class Lithologic DescriptionR

ecov

ery

%Sample

ID

Page:2 of 6

lbsfeet bgsfeet bgs

inches

inchesfeet bgsWell Screened Interval:

Screen Slot Size:Filter Pack Used:Surface Seal:Annular Seal:Monument Type:

Drilling Equipment:Sampler Type:Hammer Type/Weight:Total Boring Depth:Total Well Depth:State Well ID No.:

Notes/Comments:Well/Auger Diameter:Drilling Co./Driller:

15

20

25

30

--

B01

Stockton, California

--

08/10/2011G. Moore--

Farmland--

08/09/2011G. Moore /B. Copeland

MAR SI "North Site" (Bozanno Properties)S101-001-01

APN 10104022 86.45 acresSan Joaquin County

Soil boring only, no well installed.

--

--

------

----

--

Precision Sampling

98.6--Continuous Sample TubeCME 75

8 1/4

Same as above, moist.


Note: Root fibers, lenses of organic material, slightly darkerand more odorous than the rest of the SILT.

Boring paused at 1830.

Boring resumed at 0804 on 08/10/2011.

Clayey SILT (MH), dark brown (7.5 YR 3/2), moist.

(Note: organic-rich layer 2-3 inches thick at top of sample core,may be cave-in material.)

Clayey SILT (MH), dark brown (7.5 YR 3/4).

Note: Clay content decreasing with depth.

100

100

100

100

MH

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:3 of 6

lbsfeet bgsfeet bgs

inches





35

40

45

--

B01


--

08/10/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Silty SAND (SM), fine grain.

Silty SAND (SM), fine grained sand grading into a medium grainsand with gravel, color grades with increasing depth from darkbrown (7.5 YR 3/4) to brown (7.5 YR 4/4), moist.

Clayey SILT (MH), brown (7.5 YR 3/4) , dilatancy slow, drystrength low, toughness low.

Silty SAND (SM), brown (7.5 YR 4/4), fine grain, moist.

Clayey SILT (MH), brown (7.5 YR 4/4), moist.

Silty SAND (SM), medium grain, moist.

50

80

70

60

SM

SM

MH

SM

MH

SM

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:4 of 6

lbsfeet bgsfeet bgs

inches





50

55

60

65

--

B01


--

08/10/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Silty SAND (SM), medium to coarse grain, with fine to mediumgravel, well graded, moist to wet.

Same as above.

Silty SAND (SM), coarse grain, trace to no gravel.

1-2 inch clayey SILT (MH) lense, moist at 64.5 feet.

Same as above, no gravel.

70

100

80

SM

SM

SM

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:5 of 6

lbsfeet bgsfeet bgs

inches





70

75

80

--

B01


--

08/10/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Clayey SILT (MH), brown (7.5 YR 4/4).


Same as above.

Same as above.

50

100

100

100

SM

MH

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:6 of 6

lbsfeet bgsfeet bgs

inches





85

90

95

100

--

B01


--

08/10/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Same as above.

Note: Drill /auger working hard under increased formationresistance to drilling.

Same as above, moist to wet.

Change to 2-inch-diameter split spoon.Clayey SILT (MH), brown(7.5 YR 3/3), dilatancy slow to none, dry strength slow,toughness low to none, very dense.

Refusal at 98.6 feet.Standard Penetration Test by ASTM D1586(140 lb hammer)

3650/2

100

100

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:2 of 5

lbsfeet bgsfeet bgs

inches





15

20

25

30

--

B02


--

08/09/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Some white precipitate "banding", hydrochloric acid (HCL)reaction is strong.

Same as above with white precipitate "banding" present.

Same as above, no white precipitate visible.

Same as above, dry

100

100

100

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:3 of 5

lbsfeet bgsfeet bgs

inches





35

40

45

--

B02


--

08/09/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Clayey SILT (MH), yellowish brown (10 YR, 5/4) with gray clayclasts below, dry

Same as above, dry.

Note: Auger turning at increased rate, heating casing, soilcutting steaming.(increased formation resistance to drilling).

Same as above.

Note: Sampler (steel split spoon) very hot to touch.

Silty SAND (SM), fine grain, dense to very dense.

100

100

100

50

MH

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:4 of 5

lbsfeet bgsfeet bgs

inches





50

55

60

65

--

B02


--

08/09/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Silty SAND (SM), reddish, well graded, with trace gravel.

Clayey SILT (MH) grades to fine to coarse grain sand, verydense, wet.Silty SAND (SM), reddish, well graded, with trace gravel.

Silty SAND (SM), reddish, medium to coarse grained, withgravel, wet.

Same as above.

50

50

60

SM

SM

SM

MH

SM

SM

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:5 of 5

lbsfeet bgsfeet bgs

inches





70

75

80

--

B02


--

08/09/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Silty SAND (SM) to silty GRAVEL (GM), medium to coarsegrained sand, with 40% to 50% gravel, medium to coarsegrained.

Clayey SILT (MH), brown (7.5 YR 4/4) dilatancy slow to none,dry strength low, toughness low to none, very dense.

Note: Augers turning at high rate (increased formationresistance).

Refusal at 78.0 feet.

Bottom of boring at 78.0 feet.

60

60

SM

SM-GM

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:2 of 4

lbsfeet bgsfeet bgs

inches





15

20

25

30

--

B03


--

08/11/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Same as above.

Same as above, moist to wet.

with sand (sand fraction approximately 30%)

Same as above.

100

100

100

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:3 of 4

lbsfeet bgsfeet bgs

inches





35

40

45

--

B03


--

08/11/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above, no sand.

Same as above.

with medium to coarse gravel

Same as above, with sand and trace gravel.

100

100

100

100

MH

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:4 of 4

lbsfeet bgsfeet bgs

inches





50

55

60

65

--

B03


--

08/11/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Same as above, decreasing gravel content.

Same as above, very dense.Refusal at 61.5 feet.

Standard Penetration Test by ASTM D1586.(140 lb hammer)

Bottom of boring at 61.5 feet.

265050/3

100

100

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:2 of 7

lbsfeet bgsfeet bgs

inches





15

20

25

30

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above. White precipitate at 17 ft, hydrochloric acid(HCL) reaction none.

Same as above, no white precipitate.

Same as above.

Silty CLAY (CL), dark grayish brown (10 YR 4/2), dilatancy slow,dry strength medium, toughness medium, moist.

Same as above.

100

100

100

100

MH

MH

MH

CL

CL

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:3 of 7

lbsfeet bgsfeet bgs

inches





35

40

45

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Sample collected at 34 feet, 1310.

Same as above.

Clayey SILT (MH), brown (10 YR 4/3), moist.

Same as above.

Same as above.

100

100

100

CL

MH

MH

MH

B03ALT1-3420110808

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:4 of 7

lbsfeet bgsfeet bgs

inches





50

55

60

65

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above, but less clay.

Same as above.

Same as above.

SAND (SW), fine to coarse grained, little gravel, wet.

with fine sand

100

100

100

100

MH

MH

MH

SW

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:5 of 7

lbsfeet bgsfeet bgs

inches





70

75

80

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Clayey SILT (MH), dark yellowish brown (10 YR 4/4), dilatancynone to slow, dry strength low, toughness low, moist.

Same as above.

Same as above, no white precipitate but with trace gravelgrading into sand.

White precipitate, hydrochloric acid (HCL) reaction strong.

Sample collected at 69.5 feet, 1420.100

100

100

MH

MH

MH

B03ALT169.5-20110808

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:6 of 7

lbsfeet bgsfeet bgs

inches





85

90

95

100

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above.

Same as above.

Same as above.

100

100

100

MH

MH

MH

Date Completed:

USCS

feet bgs

Blow

Cou

nt


Dep

th

Gra

phic

Inte

rval

(feet

bgs)

LOGBORING

Site Address:

feet bgs




ecov

ery

%Sample

ID

Page:7 of 7

lbsfeet bgsfeet bgs

inches





100

105

110

--

B03ALT1


--

08/08/2011G. Moore--

Farmland--





--

--

------

----

--

Precision Sampling


8 1/4

Same as above, very dense.

Refusal at 103.0 feet. Bottom of boring at 103.0 feet.

MH

10’ 20’ 30’ 40’ 50’ 60’

70’ 80’ 90’ 100’ 110’ 120’

130’ 140’ 150’ 160’ 170’ 180’

190’200’

210’ 220’230’

240’

250’ 260’ 270’ 280’ 290’ 300’

310’ 320’ 330’ 340’ 350’ 360’

370’ 380’ 390’ 400’ 410’ 420’

430’ 440’450’ 460’ 470’

480’

490’ 500’ 510’ 520’ 530’ 540’

550’ 560’ 570’ 580’ 590’ 600’

610’ 620’ 630’ 640’ 650’ 660’

670’ 680’

0’-20’ 20’-40’ 40’-60’ 60’-80’ 80’-100’ 120’-140’100’-120’

660’-680’640’-660’620’-640’600’-620’580’-600’

560’-580’

540’-560’520’-540’500’-520’480’-500’460’-480’440’-460’420’-440’

400’-420’380’-400’360’-380’340’-360’320’-340’300’-320’280’-300’

260’-280’240’-260’220’-240’200’-220’180’-200’160’-180’140’-160’

SITE ID: 375805121121101-04 STATION NAME: 001N/007E-03D002-5MUSGS SITE NAME: STK7 Stockton-7 COMPLETION DATE: 03/29/2012

TOTAL DEPTH: 680’

WELL OWNER: Northeastern San Joaquin County Groundwater Banking Authority

DRILLER: USGS RESEARCH DRILLING UNIT DRILL TYPE: MUD ROTARYCASING TYPE: SCHED 80 PVC, 20’ SECTIONS SCREEN TYPE: SCHED 80 PVC 2”-->1.5" X 0.020" SLOTSEALS: PUREGOLD GROUT @ 30% SOLID except: Pel-Plug TR30 1/4” pellets 119’-125‘ & 245’ - 250’ FILTER PACK: CEMEX #3 MONTEREY SANDBOREHOLE DIA.: 14.75: 0’-20’; 9.875”: 20’-680’

WELL FINISH: Vault

CEMENT

BOREHOLE FILL KEY

SCREENSAND

1

Water Level (03/29/2012)#1: 76.37’ bls#2: 72.75’ bls#3: 55.30’ bls#4: 38.61’ bls

2

GROUT PELLETSVault

N

34

Depth

1ft:900ft

Well Construction

0101

Summary LithCALIPER

5 20INCH

SP

0 150MVTEMP

75 80DEG F

GR(EM)

0 200CPS

RES(16N)

0 100OHM-M

RES(64N)

0 100OHM-M

LATERAL

0 50OHM-MRES

0 50OHM-M

DELTAT

100 400USEC/FT

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

520

540

560

580

600

620

640

660

680

Sandy silt

Gravelly Sand

Sandy silt

Silty clay

Clayey silt withsand

Sand

Clayey silt

Sand

Clayey silt withsand

Silty clay

Sandy silt

Clayey silt

Sand with clayeysilt

Sandy silt

Silty gravellysand

Silt

Gravelly sand

Silty gravellysand

Silt

TD: 680’

Well #1: 545’ - 565’ w

ith sump to 665’

Well #3: 270’ - 290’

588’

465’

388’

305’

183’

Well #2: 415’ - 435’

125’

Well #4: 145’ - 165’

524’

250’245’

119’

Surface Casing: 0’ - 20’

Appendix B

Pilot-Scale Field Recharge Plan

TECHNICAL MEMORANDUM

DRAFT

TO: North Site Study Team DATE: 20 February 2013

FROM: MWH Team CC:

SUBJECT: DRAFT Pilot-Scale Field Recharge Plan REF: 10502262

1. Introduction On January 29, 2013, MWH was authorized by Stockton East Water District (SEWD) to begin the North Site Groundwater Banking Project Feasibility Study. The study consists of four tasks, including;

(1) analysis of surface water supply availability and limitations,

(2) assessment of the feasibility of developing the North Site (Bozanno Property) and existing 35-Acre of SEWD property into a groundwater banking site,

(3) preparing a project implementation plan, and

(4) preparing a groundwater banking feasibility study report.

The purpose of this document is to provide recommendations for pilot-scale field recharge testing (recharge testing) including testing locations, testing methods, and monitoring. The purpose of recharge testing is to assist in the evaluation of aquifer properties at the North Site and the feasibility of proposed future groundwater recharge and banking operations.

The North Site property consists of 230 acres in two lots adjacent to and northwest of The Stockton East Water Treatment Plant (Figure 1). Information from this recharge testing is intended to provide additional data to evaluate the feasibility of long-term aquifer recharge and banking at the North Site and 35-Acre site.

2. Pilot-Scale Field Testing Recommended recharge testing includes construction of two test recharge basins, testing methods, installation of groundwater monitoring wells, and monitoring as described in the following sections.

MWH Pilot-Scale Field Recharge Plan

PAGE 2

2.1. Test Recharge Basin Design and Operation

Based on recommendations in the Farmington Groundwater Recharge Program Manual (USACE, 2003), 100-foot by 100-foot spreading basins are proposed, with a 5-foot excavation depth and ponding depths between 1 and 3 feet.

To evaluate the North Site recharge characteristics, MWH recommends recharge tests at two locations within the North Site property, one on the east parcel and one on the west parcel (Figure 1). Locations for the recharge tests were selected to fill data gaps where infiltration rates were not previously measured (SoundEarth Strategies, 2011). There is flexibility to move the proposed locations if an alternative site appears better suited after field inspection or coordination with the landowner. Suitability of these sites are subject to completion of the Phase 1 Environmental Site Assessment and confirmation there are no preexisting concerns with the North Site.

MWH proposes that each recharge test be conducted for a minimum of 45 days or until water levels measured in monitoring wells are no longer increasing, indicating that the system has reached a pseudo-equilibrium state. The volume of water entering the recharge test basins will be metered and the flow will be regulated manually or by a float valve to maintain a constant head in the basin. If the infiltration rate at a recharge basin remains below 0.1 feet per day for five consecutive days during testing, then MWH will terminate the test at that recharge basin. As recommended by the Farmington Groundwater Recharge Program Manual (USACE, 2003), infiltration rates less than 0.1 feet per day are considered the least desirable for artificial groundwater recharge. Thus, sustained rates below the least desirable condition would be considered infeasible for long-term recharge.

2.2. Monitoring

Table 1 summarizes the types of monitoring and data to be collected, the frequency at which measurements are to be collected, and responsible party for collecting the data. Further description is provided below.

2.2.1. Wells MWH recommends three single-completion monitoring wells be installed to support the evaluation of recharge tests on the North Site. The borings from the monitoring wells will


PAGE 3

be used to help characterize the soil and hydrogeologic characteristics of the recharge test sites and surrounding areas. The monitoring wells will also be used to collect groundwater levels and quality to help evaluate the aquifer response to recharge.

The monitoring wells will be installed along a line between the pilot recharge basins, with one approximately 20 feet east of the westernmost basin, one approximately 20 feet west of the eastern most basin, and one approximately at the midpoint between basins as shown on Figure 1. Preliminary analytical calculations using parameters from existing studies (SoundEarth Strategies, 2011; MWH, 2006a; MWH 2006b) indicate that changes in groundwater elevations could potentially be as much as 1 inch approximately 850 feet away, the approximate distance from the center of each recharge test basin to MW-NS03.

Boreholes for the monitoring wells will be drilled using hollow-stem auger drilling methods with continuous collection of soil samples using a split-spoon sampler. Soil samples will be logged by the on-site geologist using the Unified Soil Classification System (USCS). Well screen intervals will be selected based on field observation of several factors, including soil type, depth to first groundwater, and expected seasonal water table fluctuations. Based on data provided by SEWD to MWH, the expected depth to the water table will be 60 to 65 feet. However, depth to water as recent as 2009 was 85 feet below ground surface. MWH will consider seasonal and annual variability in groundwater depths when selecting total well depths and screen intervals. Monitoring wells will be constructed with 2-inch diameter PVC screens and casings. Surface completions will be above grade and will include a standpipe with lockable lid. Once well construction activities are complete, monitoring wells will be instrumented with pressure transducers to collect continuous measurements of groundwater levels throughout the test. Data will continue to be collected for at least 30 days following completion of the test.

Figure 1 North Site Study Area Showing Locations of Available Data and Proposed Testing and Monitoring Well Locations

Table 1Testing Phase Monitoring and Data Collection

Testing Phase Data Type Collected By Collection Frequency Collection Point Comments

MW-NS01

MW-NS02

MW-NS03

Manual (electric sounder): weekly Additional existing wells TBD

MW-NS01MW-NS02MW-NS03Source Water

MW-NS01

MW-NS02

MW-NS03


Pond Height SEWD Daily Staff GaugesTotal Inflow SEWD Daily Flow TotalizerAlgae\Plant Growth SEWD Weekly Visual observation

Evaporation MWH Daily CIMIS Gauge (via internet) CIMIS is the California Irrigation Management Information System, Station 70 (Manteca)

Precipitation MWH Daily CIMIS Gauge (via internet) Station 70 (Manteca)

Air Temperature MWH Daily CIMIS Gauge (via internet) Station 70 (Manteca)Field measured source water quality - water temperature, pH, TDS, EC, turbidity MWH Weekly Discharge point into pond

and in pond

MW-NS01

MW-NS02

MW-NS03


Shallow, middle and deep monitoring wells to be determined.MW-NS01MW-NS02MW-NS03Source Water

Groundwater Quality (Lab analysis listed in Table2) MWH Groundwater samples collected at completion of well

development.1 Time

Automated (transducer): every 30 minutesManual (electric sounder): weekly

Reference point for measurement of groundwater level using sounder is the top of well casing (north side of rim). Groundwater level will be measured weekly with sounder. Well will also be equipped with pressure transducer that will collect measurements every 30 minutes. Data will be downloaded from pressure transducers weekly.





Post – Test(30 days)

Groundwater Quality (Lab analysis listed in Table2)

Recharge Testing Period

(6 weeks)

Groundwater Elevation

Groundwater Elevation MWH

MWH

Pre - Test (1 week)

Groundwater Elevation MWH

MWH 1 Time Groundwater samples collected at completion of well development.


PAGE 6

2.2.1. Groundwater Elevation Groundwater elevations in the monitoring wells will be measured every 30 minutes with a pressure transducer and datalogger. Dataloggers will be downloaded weekly. Groundwater elevation data will be supported with manual sounder readings, collected weekly.

2.2.2. Groundwater Quality Groundwater quality samples will be collected from each of the three monitoring wells prior to recharge testing and following the test. Three other samples will be taken from adjacent monitoring wells to characterize ambient shallow, middle, and deep aquifer water quality. The samples will be sent to an analytical lab for analysis of parameters as presented in Table 2.

2.2.3. Source Water Quality Source water quality samples will be collected prior to recharge testing for a suite of constituents presented in Table 2. Source water quality will be monitored weekly for field parameters during the test (see Table 1).

Table 2 Water Quality Analysis Constituents

Source Water and

Groundwater Monitoring pH Metals Anions Dibromochloropropane (DBCP) Pesticides Pesticides, Nitrogen/Phosphorus Herbicides VOCs Sodium Absorption Ratio (SAR) Total Dissolved Solids Total Coliform Fecal Coliform Alkalinity Hardness Specific conductance


PAGE 7

The metals group in Table 2 includes: boron, calcium, copper, iron, potassium, magnesium, manganese, sodium, zinc. Alkalinity includes total alkalinity, bicarbonate, and carbonate. Anions include chloride, nitrate, nitrite, and sulfate

2.2.4. Recharge Test Basin Monitoring The primary purpose of the recharge test basin (source water) monitoring is to collect the data necessary for calculating infiltration rates. Consistent and accurate data collection is necessary to maximize the overall effectiveness of the tests. Table 1 lists a summary of the data being collected by SEWD associated with the tests (see Recharge Test Period). MWH will provide data collection forms and data collection procedures to SEWD. MWH will use the data collected to calculate daily infiltration rates.

References MWH. 2006a. Stockton East Water District Site, Final Aquifer Test Evaluation. Farmington Groundwater Recharge Program. Prepared for U.S. Army Corps of Engineers and Stockton East Water District. June 2006.

MWH. 2006b. Final Technical Memorandum - Results of Pilot-Scale Recharge Testing, Stockton East Water District Northwest Site. Farmington Groundwater Recharge Program. Prepared for U.S. Army Corp of Engineers and Stockton East Water District. September 2006.

SoundEarth Strategies California, Inc. 2011. Report of Managed Aquifer Recharge, Characterization and Site Assessment for the Bozanno Property (Also Known as the North Site in the Farmington Groundwater Recharge Program), Stockton, California. October 2011.

U.S. Army Corps of Engineers, 2003. Farmington Groundwater Recharge Program. Project Management Plan, Contract No. DACW05-01-D-0013, August, 2003.

final preliminary feasibility study technical memorandum...

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