irrigation feasibility study

APPENDIX F

IRRIGATION FEASIBILITY STUDY FOR THE POMBO PROPERTY

Irrigation Feasibility StudyFor The

Pombo Property

Gerry N. Kamilos, LLC

Gerry N. Kamilos, LLCPACIFIC ADVANCED

CIVIL ENGINEERING, INC.

17520 Newhope Street, Suite 200Fountain Valley, CA 92708

Job # 7862EPrepared for: Prepared by:

Revised April 23, 2004Revised January 23, 2004

January 13, 2004

Irrigation Feasibility Study

for the

Pombo Property

Prepared for

Gerry N. Kamilos, LLC

FINAL REPORT

Prepared by:

PACIFIC ADVANCED CIVIL ENGINEERING, INC.

17520 Newhope Street, Suite 200 Fountain Valley, CA 92708

#7862E

January 15, 2004

Required Reclaimed Water Disposal Acreage January 2004 Pombo Property Irrigation Feasibility Report 7862E

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Table of Contents I. Introduction……………………………………………………………………… 1 II. Site Description……………………………………………………………….… 1 III. Geotechnical Study…………………………………………………………….. 4 IV. Source Water………………………………………………………………….… 5 V. Supplemental Water………………………………………………………….… 5 VI. Proposed Site Layout………………………………………………………….. 7 VII. Basin Water Quality…………………………………………………………… 10 VIII. Permitting………………………………………………………………………. 10 IX. Determination of the Agronomic Irrigation Application Rate……………… 10 X. Results………………………………………………………………………..…14 XI. Preliminary Cost Estimate……………………………………………………. 15

Tables Table 1 Infiltration Rates and Groundwater Levels………………………………. 4 Table 2 Identification of Water Balance Parameters……………………………. 12 Table 3 Monthly Irrigation Volumes in a Year

with 100 Year Total Rainfall……………………………………………… 15

Figures Figure 1 Vicinity and Location Map ………………………………………………….2 Figure 2 Specific Plan Areas………………………………………………………… 3 Figure 3 Reclaimed Water Delivery Pipeline ……………………………………… 6 Figure 4 Fields and Infrastructure Plan – Alternative A…………………………... 8 Figure 5 Fields and Infrastructure Plan – Alternative B ……………………..…… 9

Appendix

Appendix A Geotechnical Report by ENGEO Appendix B Water Balances for the Pombo Property and Supporting

Documentation Appendix C Current Mountain House Discharge Permits #109 and #192 Appendix D Engineers Estimate of Probable Cost and Power Requirements


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I. Introduction This report is being prepared for Gerry N. Kamilos LLC (Kamilos), the principle developer within the proposed Specific Plan III, located in the southerly portion of the Mountain House Community. Figure 2 shows the location of the proposed Specific Plan III. There are currently two wastewater discharge permits that have been issued to the Mountain House Community Services District (MHCDS). Permit No. 192, which allows for 5.4 MGD year around discharge to the Old River, and Permit No. 109 which allows for land disposal of treated effluent, on an interim basis, until such time that permit conditions for full river discharge can be met. Copies of these permits are attached here-in as Appendix C. Specific Plan I was approved in 1994, and the project developer, Trimark Communities (Trimark), is currently developing Specific Plan I Trimark has constructed the present wastewater treatment plant (WWTP) to serve the first neighborhood, Neighborhood F. Complying with Discharge Permit No. 109, Trimark has constructed effluent disposal facilities of sufficient size to serve Neighborhood F. Two other neighborhoods in Specific Plan I will be developed soon and Trimark is currently expanding the treatment facilities to provide needed capacity. In addition, the land disposal facilities will need to be expanded to be able to handle the increased plant effluent. Any and all land disposal facilities constructed by Trimark will be sized to serve the needs of the Trimark development only. Other developers who construct within the Mountain House Community before full river discharge is achieved, will be required to provide for their own land disposal needs. Therefore, Kamilos has secured the Pombo property (approximately 140 acres) located east of Mountain House Parkway and south of Byron Road. For the time being, the Mountain House Community Services District (MHCSD) will be required to dispose of all treated effluent from the WWTP in a manner consistent with permit No. 109. To serve the needs of the Kamilos development, storage and irrigation facilities will be constructed on the Pombo property. The purpose of this report is to determine the amount of treated effluent that can be applied to the Pombo property based on agronomic rates. II. Site Description The approximately 140 acre Pombo property is situated immediately next to the east side of the community of Mountain House which is located north and west of the City of Tracy. The property lies on the southeast corner of Mountain House Parkway and Byron Road. Currently the property is farmed with the principal crop being alfalfa. The highest location found on the generally flat parcel is at the southwest corner.


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From this location, the slope is downward at approximately 0.6% to the east-northeast. Groundwater in the area is generally found relatively shallow, between 7.6 feet and 11.4 feet below existing grade. This condition is primarily attributed to the influence of farm irrigation drain water percolating into the ground and storm water runoff from the westerly adjacent hills that influence the groundwater level. Agricultural buildings occupy a small portion of the subject area and are not considered part of the 140-acre parcel. III. Geotechnical Study PACE subcontracted the geotechnical portion of this project to ENGEO Incorporated. ENGEO conducted seven infiltration tests for the subject site using double-ring infiltrometers. Groundwater exploration was also conducted to establish the level of groundwater at four different points on the property (D-1 through D-4). The results of the exploration are summarized in Table 1 below. The complete ENGEO report is included as Appendix A.

Table 1 Infiltration Rates and Groundwater Levels

Test Location Name Test Location Number

Infiltration Rate

(minutes/inch)

Infiltration Rate

(Inches/hour)

Stabilized Ground

Water Level Southwest corner (MH Parkway/open) D-1 113.2 0.5 8.4’

Southeast corner (open/open) D-2 >1,000 < 0.06 7.6’

Northwest corner (Byron/open) D-3 130.4 0.5 9.2’

Northeast Corner (MH Parkway/Byron) D-4 25.3 2.4 11.4’

West center (MH Parkway) D-5 37.0 1.6 -

Center of Property (open) D-6 146.3 0.4

North Center (Byron) D-7 111.1 0.5

ENGEO Recommended Design Percolation Rate:

125 minutes/inch = 0.48 in/hr (to be used with a safety factor)


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IV. Source Water The source of reclaimed water for this project will be from the Mountain House Wastewater Treatment Plant (WWTP). An expansion to this facility is currently being constructed to bring the average-day wastewater treatment capacity to 3.0 MGD. Two additional expansions are required to provide a final anticipated capacity of 5.4 MGD. A pump station at the WWTP site currently pumps reclaimed water to storage basins located adjacent to the WWTP on Trimark land. A proposed pipeline is anticipated to deliver reclaimed water to the Old River disposal location within the next couple of years; however this pipeline may not be used until clearance from the RWQCB is granted. Irrigation on the Pombo property is an option for disposal of a portion of the reclaimed water flow prior to river discharge. The current effluent pump station at the treatment facility contains two pumps for delivering treated water to the current Trimark storage ponds and eventually to discharge to the river. Two additional pump locations have been provided for future expansion of the pump station. In order to maintain a balance between Trimark irrigation, Pombo irrigation and the river discharge, PACE recommends that a new pump be placed in the existing effluent pump station to serve the Pombo property exclusively. This pump would deliver treated effluent to the subject property through a new dedicated force main. A flow meter on the new force main will be installed in order to determine whether the Pombo property is receiving (and disposing of) all reclaimed water contributed by related Specific Plan III homes. In the future, when discharge to the river is allowed, the Pombo pump could be combined with the other effluent pumps at the effluent pump station, to deliver water to the river. The preferred layout of the Pombo supply line is illustrated in Figure 3. This alignment provides the most direct route and requires the fewest number of easements. PVC or ductile iron pipe may be used for the force main, however, either material will be required to be color coded. Purple piping is required for all reclaimed water conveyances. The minimum recommended size for the pipeline is 8 inch. V. Supplemental Water In years where sufficient reclaimed water is not available for irrigation at the Pombo site, there is concern that the agricultural crops located there would suffer. Specifically, this situation may occur during community build-out, when few homes are producing wastewater for reclamation yet the field requires irrigation at normal or greater than normal levels due to below average rainfall. One effective remedy for this situation is to provide a supply of supplemental water to the reclaimed water storage basin. Two separate fill points, one for reclaimed water and one for supplemental water, discharge a minimum of 12” above the maximum water surface to provide the required air gap will be necessary.


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The recommended source of supplemental water is from the West Side Irrigation District. An existing irrigation supply line along the east side of Mountain House Parkway currently serves the Pombo property. Creating a piped connection from this line to the reclaimed water storage basin would be the most economical manner in which to supply supplemental water to the Pombo property. VI. Proposed Site Layout

Two site layouts were considered, the major difference between the two is the location of the reclaimed water storage basin. The first scenario places the reclaimed water storage basin at the highest point on the property, in the southwest corner. This results in the most advantageous profile for distribution to the irrigation fields. The second scenario locates the storage basin in the southeast corner of the property. This slightly reduces the elevation of the basin bottom; however it does have the advantage of removing the reclaimed water basin from the immediate vicinity of highly traveled Mountain House Parkway. In either location, groundwater resources will be protected by an HDPE liner. If the reclaimed water storage basin is located next to Mountain House Parkway, several measures may be taken to improve the aesthetics of the basin. Vegetating the exterior basin side slopes or providing a landscape buffer along the side adjacent to the roadway is suggested.

Border strip irrigation of the remaining acres is anticipated due to the prevalence of this method in other surrounding communities, the favorable grade (nearly level) of the land and the low capital cost associated with this irrigation method. Under border strip irrigation, water will be applied to one end of a rectangular strip of land that is slightly sloping. Water will advance down the vegetated slope with any unused water being collected and returned to the storage basin for reapplication. The gradual slope (0.6%) of the Pombo property facilitates this type of irrigation. This type of irrigation has the additional benefit of eliminating the risk of overspray and windblown mist.

To enable the irrigation layout described above, a pump station at the existing WRF will deliver water to the reclaimed water storage basin. From the storage basin a small pump system will be used to distribute the recycled water to individual fields for use. A gravity system has also been considered for this portion of the reclaimed water disposal system. In order to operate a gravity system the recycled water basin would need to be elevated above the irrigation application area. Due to the slope of the Pombo property this would require that the basins be elevated artificially by means of bringing in fill. The expense of the construction is likely to be significantly higher than the cost of the installation of a small pump station and a below grade basin as recommended.

Following irrigation, tail water collected at the north end of the fields would flow through a shallow ditch system to a collection point. From there it would be pumped back to the reclaimed water basin for redistribution to the irrigation fields. Figures 4 and 5 illustrate the two alternative locations of the proposed reclaimed water storage basin. Resulting irrigation fields and water conveyance requirements are also shown in the plan view.


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VII. Basin Water Quality

Maintaining basin water quality will be important. Poor water quality in the storage basin may produce odors and require additional maintenance of the distribution and tailwater recovery system components. Sub-surface aeration and mixing systems may be used to reduce the occurrence of these problems. However both of these items are most effective at basin depths greater than 8 feet. Therefore, these systems, if installed may only be effective in the winter months when basin water depths are expected to exceed 8 feet.

In addition to aeration, chemicals may also be used to control biological growth within the storage basin. VIII. Permitting Application of reclaimed water requires permitting from the Regional Water Quality Control Board. The existing land application permit does not identify irrigation of the Pombo property. Therefore, a permit application, a characterization of waste discharge and CEQA modification will be required. This property can be included into the existing land application permit, but will likely require a public hearing process be performed by the RWQCB. In addition, the current land disposal permit requires 12 months of groundwater monitoring prior to application of reclaimed water. Continued monitoring during irrigation is also required. Processing the required application will most likely take a minimum of six months and should be expected to take longer due to the current budget situation in the State of California and the requirements for public notice associated with the issuance of Waste Discharge Requirements. IX. Determination of the Agronomic Irrigation Application Rate Two basic requirements govern the application rate of reclaimed water for irrigation. These are hydraulic capacity and nutrient loading. Hydraulic capacity is determined by site-specific soil, ground water, and applied weather conditions. Nutrient capacity is determined by vegetation type and nutrient concentration, specifically nitrogen, contained in the effluent. Due to the high quality of effluent from the expanded Mountain House WWTP (i.e., Total Nitrogen < 5mg / L) and the relatively low permeability of the site soil, hydraulic capacity will govern the maximum application rate for the subject property. Upon completion of our hydraulic analysis, nutrient loading will be evaluated to verify this assumption.

Method and Assumptions The water balance modeling for the Pombo property was conducted for several rainfall return scenarios (i.e. 100-year and average year both with and without percolation). The water balance computations quantitatively account for each


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component of the hydrologic cycle with an equation representing the principle of conservation of hydraulic mass. The basic notion of the water balance model is as follows: Water Input (effluent production) – Water Withdrawals (pod evaporation, plant evapotranspriation, and soil percolation) = Water Storage The Regional Water Quality Control Board (RWQCB) requires that water balance calculations used to determine storage and irrigation requirements exhibit the following characteristics: 1. All values and calculations are computed annually and subdivided by

month. 2. The 100-Year Total Annual Rainfall is used as the precipitation value. 3. The average annual evapotranspiration is used as the expected

evapotranspiration 4. Percolation values are reduced to between 4 and 10% of their site-tested

values. 5. Irrigation may not occur during the months of November thru March A summary of the terms and data sources used to compile the Pombo Property water balance based on the conditions set by the RWQCB is presented in Table 2. Excerpts from these data sources are given in Appendix B.


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Table 2

Identification of Water Balance Parameters

Parameter Value Source Rainfall Data 100 Year Total Annual Rainfall (in/year)

Total Rainfall 23.15

(Assumed to fall at the same percentage per month as average

conditions)

100-year annual precipitation (Year’s worth of rainfall with 0.01 probability of occurring in any given year) for nearby Tracy Pump Station provided by CA Dept of Water Resources

Rainfall Data Average Annual Rainfall (in/month)

Jan 2.60 Jul 0.03 Feb 2.14 Aug 0.07 Mar 1.69 Sep 0.25 Apr 0.83 Oct 0.57 May 0.39 Nov 1.61 Jun 0.12 Dec 1.77

Average annual rainfall for nearby Tracy Pump Station provided by CA Dept of Water Resources

Evapotranspiration (in/month)

Jan 0.95 Jul 8.29 Feb 1.75 Aug 7.24 Mar 3.48 Sep 5.33 Apr 5.37 Oct 3.63 May 6.88 Nov 1.76 Jun 7.79 Dec 1.01

Average monthly evapotranspiration (ET) from 1988 to 2000 from California Irrigation Management Information System (CIMIS) of CA Dept of Water Resources for the Station at Tracy

Kc Factor (evapotranspiration adjustment factor) 1.0

Average value applied year round. Source: WATERIGHT for alfalfa cultivation beginning 3/1 and ending 2/28.

Percolation Rate (in/hr)

0.1

Results from reduction of the 0.48 value initially selected by the Geotechnical Engineer after double-ring infiltration testing performed by ENGEO. A safety factor of 4.8 was applied.

Percolation Reduction Factor 6%

Midrange value given by EPA publication entitled “Process Design Manual for Land Treatment of Municipal Wastewater”

To construct the water balance presented, PACE began each model in November with the storage basin assumed to be empty. This is practical, since sometime during the fall season, November specifically for the 100-year rain fall return, the storage basin will empty as the last of the stored water from the previous winter is used for irrigation and the rains associated with winter have not yet begun to fall. Treated effluent is then applied to the system at an average daily rate for each month. This effluent is either applied to the irrigation area or stored within the basin. Rainfall data is also applied evenly to the entire subject area, as it occurs, based on monthly total rainfall. Rainwater falling within the projected maximum surface area of the storage basin is directly accumulated within the storage basin. Rainwater falling outside the storage basin is applied uniformly to the irrigation areas and reduces or eliminates irrigation capacity.


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Due to the necessary inclusion of rainfall into the storage area and evaporation from the storage basin surface, it was necessary to develop a model to establish the relationship between storage volume and the resulting collection and storage basin surface areas. The model was based on similar basins within the region and used interior and exterior side slopes of 3:1 with berm heights of 12 ft above the natural ground surface. A level berm top section of 15 ft is provided for equipment access. The bottom of the basin is established 4 feet below the natural ground surface. This will allow 4 feet of separation between the bottom of the storage basin and groundwater which was found to be 8 feet below the surface. The total height of water in the storage basin (measured from the basin bottom) was limited to 14 ft in order to allow 2 ft of freeboard in the storage basins as mandated by the RWQCB. The freeboard is measured vertically from the water surface to the lowest point on the basin sidewall.

To complete the water balance accounting, both volumes (in ac-in) and depths (in inches) of reclaimed water were used. This simplified the calculations, helped illustrate the direction of flow into and out of the reclaimed water basin, and allowed terms to reflect values commonly encountered in the industry (i.e. inches of applied irrigation water and acre-in of storage volume). The relationship between the volume (i.e. of reclaimed water applied) and the depth of the applied water is dependent on the number of irrigation acres. Multiplying the depth of reclaimed water applied by the number of irrigation acres it is applied to, results in the acre-in value removed from the storage basin for the purposes of irrigation.

Next, the amount of reclaimed water that may be disposed of at the site was determined for the 100-year rainfall. Steadily increasing the reclaimed water flow whenever the selected flow rate resulted in an underutilized storage basin or irrigation site was the trial and error method used to accomplish this task.

Bottom Area

15 ft Wide Top Section

Plan View Section View

3

1 3

1

Water Level 12 ft

4 ft

2 ft

Ex. Ground

Exterior Side Slope

Interior Slope

Berm Top SectionGround Water

4 ft


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Once the acceptable amount for disposal was determined, the balance of irrigation and basin acres was fine tuned. At the end of this process, the water balance demonstrated that the basin water level achieved its maximum allowable height of 14 ft in March and was emptied continuously over the summer. Of the 140 acre parcel, 130 acres were utilized in order to allow sufficient equipment access to the irrigation fields. Prior to November, the storage basin is expected to empty in preparation for the following year’s storage requirements. The final water balance for the 100-year total annual rainfall is included in Appendix B.

Once the number of storage and irrigation acres was established for the 100-year rainfall, an additional rainfall scenario was considered in the manner described above to illustrate an average rainfall year. However, since the number of irrigation and storage basin storage acres are fixed by the values determined for the 100-year water balance, these values were held constant in subsequent modeling. The amount of supplementary water required during the average rainfall year was found as a result of this water balance.

Finally, based on previous actions of the RWQCB an additional ‘worst case scenario’ water balance was constructed for the property. This water balance represents the amount of irrigation and storage basin acreage required if the RWQCB requires that percolation of recycled water be removed from the water balance entirely. Recent correspondence with the RWQCB suggests that this scenario will not be instituted for future irrigation sites; however it is important to recognize and prepare for the possible ramifications that this conditions may have.

X. Results

Using a 100-year total rainfall event, the size of the storage basin bottom and irrigation acres was determined. The storage basin, which is based initially on the model detailed above, was found to require a bottom area of 18.0 acres and a volume not including that dedicated to freeboard of 279 acre-ft. The resulting total storage basin area is 27 acres. 103 acres will be used for irrigation.

In a year in which the 100 year annual rainfall occurs, 670 acre-ft of reclaimed effluent may be disposed of through evaporation and irrigation. This equates to an average of 1.8 acre-ft or 562,000 gallons a day. An average monthly disposal rate of 55.8 acre-ft is expected, however, the actual amount acceptable for disposal on a monthly basis varied based on weather and crop growth patterns. Table 3 summarizes the expected monthly application rates.


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Table 3 Monthly Irrigation Volumes in a Year with 100 Year Total Rainfall

Once the storage basin and irrigation acreages were established, the water requirement for a year with average rainfall was determined. The 140 acre Pombo property is able to consistently accept an annual average daily flow of 1.9 acre-ft of water. It has been established that eventually, reclaimed water may be permitted to contribute at least 1.8 acre-ft. During an average year, the remaining 0.1 acre-ft per day will need to be supplied by a supplemental water source. In years with less than average rainfall, additional water will be required to sustain healthy crop growth. XI. Preliminary Cost Estimate Based on the conclusions laid out in this report a preliminary construction cost of $3,334,500 was determined. The cost estimate breakdown is included in Appendix 4. It is important to note that only those items indicated in the breakdown are included, all other items which may later be determined necessary will likely increase the cost of the project. The estimated annual power cost of the reclaimed water disposal system was determined from an estimate of the required pump horsepower. The calculation for this item is detailed below.

Existing Effluent Pump Station: Given: Flow = 560,000 GPD (average) = 388 GPM Total Dynamic Head = 60 feet Pump Eff. = 75% Calculate Pump Break Horsepower: BHP = (GPM x TDH) / (3960 x Eff.) = 388 x 60 / 3960 x 0.75 = 7.9 HP kW = 7.9 HP x 0.8 = 6.3 kW

Month Acre-ft Month Acre-ft Jan 2 Jul 119 Feb 3 Aug 109 Mar 6 Sep 86 Apr 76 Oct 61 May 93 Nov 2 Jun 110 Dec 1


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Calculate Cost Per Day (average): Cost per Day = 6.3 x 24 hours x $0.12 / kW = $18.20 Irrigation Pump Station: Given: Flow = 388 GPM TDH = 20 feet Pump Eff. = 75% Cost per Day = $18.20 x 20 /60 = $6.07 Total: Total Cost per Day = $18.20 + $6.07 = $24.27 Total Estimated Annual Power Cost = $24.27 x 365 days = $8857.33

PACIFIC ADVANCED CIVIL ENGINEERING, INC.

17520 Newhope Street, Suite 200Fountain Valley, CA 92708

irrigation feasibility study

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