minnesota nrcs guide to subsurface investigations october 2019 · map c1: simplified parent...

October 2019

Minnesota NRCS Guide to

Subsurface Investigations

October 2019

Table of contents Page Introduction ............................................................................................................................................. 1 I. General Guidance for Subsurface Investigations .............................................................................. 2

A. Reference Points, Markings and Site Map .................................................................................... 2 B. Investigation Methods .................................................................................................................. 2 C. Soil Profile Descriptions ................................................................................................................. 2 D. Bedrock Profile Descriptions ......................................................................................................... 3

II. Additional Requirements for Embankments with Storage A. Engineering Geology Risk Assessment ........................................................................................ 4 B. Borrow Area Investigation .......................................................................................................... 6 C. Types of Investigations 1. Geologic Reconnaissance ........................................................................................................ 6 2. Preliminary Site Investigation Level 1 ..................................................................................... 6 3. Preliminary Site Investigation Level 2 ..................................................................................... 7 4. Detailed Site Investigation ...................................................................................................... 8

III. Additional Requirements for Waste Storage Structures A. Engineering Geology Risk Assessment .......................................................................................... 9 B. Investigation Guidelines and Considerations .............................................................................. 10 C. Types of Investigations

1. Geologic Reconnaissance ...................................................................................................... 11 2. Preliminary Site Investigation ............................................................................................... 11 3. Detailed Site Investigation .................................................................................................... 11

D. Soils Testing for Soil Liners .......................................................................................................... 11 E. Bedrock Investigation Requirements for Liners .......................................................................... 12

October 2019

Appendix A: Investigation Report ......................................................................................................... 13 Appendix B: Charts for Using the Unified Soil Classification System (USCS) ......................................... 15 Appendix C: Soil Logs ............................................................................................................................ 17 Appendix D: Definitions ........................................................................................................................ 21 Table 1: Additional Investigation Requirements ..................................................................................... 1 Figure II‐1: Embankments with Storage Practice Risk Chart ................................................................... 4 Figure II‐2: Embankments with Storage Karst Risk Flow Chart ............................................................... 5 Figure II‐3: Embankments with Storage Engineering Geology (EG) Risk Assessment Matrix ................. 5 Figure II‐4: Boring Locations for Preliminary Site Investigation Level 1 .................................................. 7 Figure II‐5: Boring Locations for Preliminary Site Investigation Level 2 .................................................. 7 Figure III‐1: Waste Storage Structures Karst Risk Flow Chart ................................................................ 10 Figure III‐2: Waste Storage Structures Engineering Geology (EG) Risk Assessment Matrix .................. 10 Figure A‐1: Example Geologic Profile ..................................................................................................... 13 Figure B‐1: Laboratory Method for Classifying Soil Using the USCS System ........................................ 15 Figure B‐2: Field Method for Classifying Soils Using the USCS ............................................................. 16 Figure D‐1: Groundwater Geology ......................................................................................................... 21 Figure D‐2: Landscape Position .............................................................................................................. 22 Figure D‐3: Redoximorphic Features ..................................................................................................... 22

Introduction

October 2019 1

Types of engineering geologic investigations (NEM Part 531 – Geology, and NEH Part 631 Chapter 2 Engineering Geologic Investigations).

a. Geologic Reconnaissance b. Preliminary Site Investigation c. Detailed Site Investigation

Engineering geologic investigation requirements are defined in NEM 531 for Group A and Group B structures and practices.

Table 1 contains a summary of the sections where additional subsurface investigation requirements can be found in this guide for individual practice standards. Practices marked with an asterisk have soils and geology investigation requirements incorporated into the Practice Standard.

Table 1: Additional Investigation Requirements * Investigation requirements are included in the Practice Standard

Section I. General Guidance for Subsurface Investigations

Section I October 2019 2

A. Reference Points, Markings and Site Map.

1. Horizontal and vertical reference points (i.e., bench marks, landmarks, etc.) should be established when on‐site investigations are completed, including hand auger investigations.

2. The extent of the areas to be investigated should be marked by stakes, flags, tree markings, or shown on a plan view map of the site.

3. A legible site map drawn to scale is required. The scale should be 1:2,400 or larger. If applicable the map will identify the boring or test pit locations (in reference to the practice stationing), the footprint of the practice, the location of the borrow area, and the vertical and horizontal reference points.

B. Investigation Methods.

1. Soil borings can be performed using hand equipment or power auger.2. When test pits are required to be excavated using a backhoe or excavator, they must meet OSHA

and NRCS safety standards found in NEM Part 503 and NEH part 645.

C. Soil Profile Descriptions.

1. Preliminary and detailed site investigations must be written in accordance with the descriptive procedures, terminology, and interpretations found in:a. ASTM D 2488 Standard Practice for Description and Identification of Soils (Visual‐Manual

Procedure)b. NRCS National Engineering Handbook, Part 650, Engineering Field Handbook, Chapter 4

Elementary Soil Engineering, and Field Identification and Description of Soilsc. National Engineering Handbook Part 631, Chapters 3, 4, and 5d. NRCS Field Book for Describing and Sampling Soils Version 3.0 (where applicable)

2. The soil logs in Appendix C or equivalent should be used to document each boring or test pit.a. Each log shall have inspectors name and date.b. Time should be entered when describing test pits.c. Boring/Excavation method should be noted.d. Other pertinent site information should be included.

3. The soil descriptions for each boring or test pit shall contain the following information:a. USCS group name or symbol with modifiers e.g., silt with sand or ML w/ sand.b. USDA texture (optional)c. Layer thickness (if >0.3’) as defined by changes in moisture, color, geologic material, or

texture (depth in feet and tenths)d. Estimate of boulders and cobbles by volume and gravel and sand by weight.e. Plasticity of fines: non‐plastic, slightly plastic, low, medium, highf. Moist soil color using the Munsell color under natural light conditions.g. Percent of redoximorphic features as defined by Munsell color. If multiple colors exist for

each feature type, log the most common. Feature type may be substituted for color. If applicable/possible, note location of features

4. The soil descriptions for each boring or test pit should contain the following information:a. In‐situ moisture content, i.e., dry, slightly moist, moist, very moist, or wet.b. Consistency (moist, fine‐grained soils only): very soft, soft, firm, hard, very hard. A pocket

penetrometer may be used in lieu of estimated value.c. Structure/stratification e.g., stratified, laminated, fissured, blocky, prismatic, massive.d. Geologic formation/type, parent material, and series.e. Seepage or water table depth. Information about subsurface saturation if encountered, such

as seepage from sand and gravel lenses, lens thickness, estimated flow rate, and associated depths should be noted. Estimated flow rate is for test pits and not applicable with other

Section I. General Guidance for Subsurface Investigations

Section I October 2019 3

equipment. The hole should not be refilled until a reasonable amount of time has passed and the water table is measured. Other pertinent information will also be noted.

f. Odor should be mentioned only if organic or unusual.g. Presence or absence of any other features that may influence the project. This may include,

but is not limited to: roots, gypsum, caving, unusual excavation difficulty, or krotovinas5. Frozen soil material must be thawed prior to conducting evaluations.

D. Bedrock Profile Descriptions.

1. If bedrock is encountered during the investigation that has the potential to adversely impact theplanned practice, consult with a geologist for further guidance.

2. Table 4‐27 in the NEH 631, Chapter 4 provides indicators on the excavatability of rock materials.3. The type of bedrock, if encountered, such as sandstone, limestone, dolomite, shale, or granite,

must be noted.4. The elevation of the top surface of bedrock will be recorded.5. For additional guidance on describing bedrock see National Engineering Handbook Part 631

Chapter 4.6. The soil logs or preapproved equivalent in Appendix C must be used to document the

descriptions when rock coring.

Section II: Additional Requirements for Embankments with Storage

Section II October 2019 4

These requirements apply to structures that provide permanent and temporary storage. It does not

apply to full flow structures where storage is not provided (such as 410 Grade Stabilization full flow open

and island type structures) or scrapes associated with wetland restoration projects.

A. Engineering Geology Risk Assessment

STEP 1: Log all information in the Minnesota Geology Ledger.

STEP 2: Determine the Practice Risk (Figure II‐1).

Figure II‐1: Embankments with Storage Practice Risk Chart

STEP 3: Make maps relevant for the site. These include maps for karst with sinkholes and stream sink (Map A1); bedrock (Map B1); and loose coarse‐grained deposits (Map C1 or C2). Include maps in producer file.

Karst Prone Areas

Map A1: Minnesota Regions Prone to Surface Karst Feature Development: Series GW‐01 (MN DNR) with karst sinkholes and stream sink. MN DNR Karst Feature Inventory Points (Scale 1:24,000)

Bedrock Related Geologic Siting Risk

Map B1: Bedrock map was developed using the MN DNR County Atlas Status List or MN DNR (Scale 1:24,000). The geological risk was developed by MN NRCS Geologist.

Soil and Sediment Found on Site

Map C1: Simplified Parent Material (Scale 1:12,000). This dataset is not currently publicly available. As an alternate refer to Map C2 Surficial Sands of Minnesota.

o MN DNR MN DOT Borings o Soil Survey Field Documentation (MLRA Soil Science Division‐Available Online) o SDM_MGS.gdb

Map C2: Minnesota Hydrogeology Atlas (MHA) Water‐Table Elevation and Depth to Water Table HG‐03, Surficial Sands of Minnesota. (Scale 1:24,000)



STEP 4: Determine the Geological Siting Risk: low risk, soft sandstone, low karst, moderate karst,

high karst, or loose coarse‐grained deposits based on maps, Geological Siting Risk chart, and

Embankments with Storage Karst Risk Flow Chart (Figure II‐2).

I. Is it SOFT SANDSTONE (Map B1)? If yes, the Geological Siting Risk assessment is done and proceed to Step 5. If not, continue to II.

II. Is it KARST (Map A1)? If yes, follow Figure II‐2 Embankments with Storage Karst Risk Flow Chart below then proceed to Step 5. If not karst, continue to III.

III. Is it LOOSE COARSE‐GRAIN DEPOSITS (Map C1 or C2)? If yes, the Geological Siting Risk assessment is done and proceed to Step 5. If not, continue to IV.

IV. If no, it is LOW RISK and proceed to Step 5.

Figure II‐2: Embankments with Storage Karst Risk Flow Chart

STEP 5: Visit the site to verify geologic and soils conditions when possible. During the site visit, if a sinkhole, stream sink, seep or spring is found within 500 feet, then submit a brief report documenting the findings to the Area Engineer. The Area Engineer shall submit a request for assistance to NRCS Geologist if a sinkhole, stream sink, seep or spring is found within the pool area or embankment footprint.

STEP 6: Proceed to the Embankments with Storage Engineering Geology (EG) Risk Assessment Matrix (Figure II‐3). Determine the soil investigation requirement.

Figure II‐3: Embankments with Storage Engineering Geology (EG) Risk Assessment Matrix



STEP 7: Documentation

1. Log information in the Minnesota Geology Ledger. 2. Complete a risk assessment summary indicating the following: “The Practice Risk is ___. The

Geological Siting Risk is ____. The Engineering Geology Risk Assessment is approved by ______, Title, I &E EJAA.”

3. Document the Engineering Geology Risk Assessment summary in a design report (if provided or required by the type of investigation performed), NRCS‐CPA‐6 notes or an email from the approver.

B. Borrow Area Investigation

1. No borrow material will be removed from the planned pool area for structures located in a region prone to surface karst feature development.

2. Use boring(s) to locate approximately one and one‐half (1.5) times the needed fill. 3. Borings should extend at least three feet below the expected depth of removal of material,

unless consolidated material is encountered.

C. Types of Investigations

NOTE: If weathered sandstone is encountered during the investigation, complete a Preliminary 2 investigation.

1. Geologic Reconnaissance

a. Boring location, quantity, and depth: i. A minimum of one boring to verify information from the soil survey. Borings will be

taken near the low point along the centerline of the earth fill. Investigate to a depth equal to one‐half (0.5) the effective height or to unyielding foundation, i.e., competent bedrock.

ii. Walk the area of the proposed permanent pool with a tile probe check depth to bedrock or sand at significant grade breaks.

b. An investigation report is required for projects in Karst areas (Appendix A). No investigation report is required for projects in non‐Karst areas.

2. Preliminary Site Investigation Level 1

a. Boring location, quantity, and depth (Figure II‐4) i. One boring near the low point along the centerline of the earth fill. Investigate to a

depth equal to one‐half (0.5) the effective height or to unyielding foundation (i.e., competent bedrock). For sandstone sites, investigate to a depth equal to the effective height or to unyielding foundation.

ii. One boring near the control section of the auxiliary spillway, if applicable. Investigate a minimum of two feet below the control section elevation.

iii. One boring in the abutment opposite the auxiliary spillway. iv. Walk the area of the proposed permanent pool with a tile probe check depth to bedrock

or sand at significant grade breaks. v. If a layer of loose coarse grained materials greater than two feet thick (sand or gravel

lenses) are encountered, a Preliminary Site Investigation Level 2 must be performed. b. An investigation report is required (Appendix A).



Figure II‐4. Boring Locations for Preliminary Site Investigation Level 1

3. Preliminary Site Investigation Level 2 (Figure II‐5)

a. Boring location, quantity, and depthsi. Along the centerline of the earth fill, take borings a minimum of every 100 feet and at

the low point and major grade breaks or changes in hillslope position.ii. For all sites except for sandstone sites, extend borings to a depth equal to one‐half (0.5)

the effective height of the structure. Where sufficient geology or soil survey data are available, the number of borings may be decreased.

iii. For sandstone sites the boring near the low point of the cross section will extend either a minimum of 10 feet, or to a depth equal to the effective height of the structure, or to an unyielding foundation. All other borings in sandstone sites will have a minimum depth of five feet or will extend to the gully bottom elevation.

iv. One boring near the control section of the auxiliary spillway, if applicable. Investigate a minimum of two feet below the control section elevation.

v. Walk the area of the proposed permanent pool with a tile probe check depth to bedrock or sand at significant grade breaks.

b. An investigation report is required (Appendix A).

Figure II‐5. Boring Locations for Preliminary Site Investigation Level 2.



4. Detailed Site Investigation (Initiated through MN‐ENG‐141):

a. Investigation requirements are determined by the State Geologist and the State Conservation Engineer and must meet or exceed the requirements for Group A or Group B structures as defined in NEM 531.

b. Identify geologic lithology and formation. c. An investigation report is required which follows the criteria located in NEH 631.

Section III: Additional Requirements for Waste Storage Structures

Section III October 2019 9

This section applies to waste storage structures which impound liquid manure or contaminated runoff and impoundment structures associated with a Level 3 Vegetated Treatment Area.

A. Engineering Geology Risk Assessment

STEP 1: Log all information in the Minnesota Geology Ledger.

STEP 2: Make maps relevant for the site. These include maps for karst with sinkholes and streamsink (Map A1); bedrock (Map B1); loose coarse‐grained deposits (Map C1 or C2); Depth to Bedrock(Map D1) and Depth to Seasonal High Water (Map E1) Include maps in producer file.

Karst Prone Areas

Map A1: Minnesota Regions Prone to Surface Karst Feature Development: Series GW‐01 (MN DNR) with karst sinkholes and stream sink. MN DNR Karst Feature InventoryPoints (Scale 1:24,000)

Bedrock Related Geologic Siting Risk

Map B1: Bedrock map was developed using the MN DNR County Atlas Status List or MNDNR (Scale 1:24,000). The geological risk was developed by MN NRCS Geologist.

Soil and Sediment Found on Site

Map C1: Simplified Parent Material (Scale 1:12,000). This dataset is not currentlypublicly available. As an alternate refer to Map C2 Surficial Sands of Minnesota.

o MN DNR MN DOT Boringso Soil Survey Field Documentation (MLRA Soil Science Division‐Available Online)o SDM_MGS.gdb

Map C2: Minnesota Hydrogeology Atlas (MHA) Water‐Table Elevation and Depth toWater Table HG‐03, Surficial Sands of Minnesota. (Scale 1:24,000)

Depth to Bedrock

Map D1: Statewide depth to Bedrock from the MN Geological Survey (1:24,000)

Seepage, Springs, Shallow Regional Water‐Table or Seasonal High Water‐Table

Map E1: Depth to Seasonal High Water Table (1:12,000).o NRCS SURGO Database

Map E2: Depth to Water Table (1:12,000)o Minnesota Hydrogeologic Atlas (MHA) Water Table Elevation and Depth to

Water Table HG‐03

Map E3: Groundwater Aquifer Sensitivity (1:24,000)o Minnesota Hydrogeologic Atlas (MHA) Pollution Sensitivity of Near‐Surface

Materials HG‐02

If the project is a waste storage structure located in a karst prone region, a karst inventory survey will also need to be completed which meets the requirements of Practice Standard 313 Waste Storage Facility.

STEP 3: Determine the Geological Siting Risk: low risk, soft sandstone, low karst, moderate karst, high karst, or loose coarse‐grained deposits based on maps, Geological Siting Risk chart, and Waste Storage Structures Karst Risk Flow Chart (Figure III‐1).

I. Is it LOOSE COARSE‐GRAIN DEPOSITS (Map C1 or C2)? If yes, the Geological Siting Risk assessment is done and proceed to Step 4. If no, continue to II.

II. Is it SOFT SANDSTONE (Map B1)? If yes, Geological Siting Risk assessment is done and proceed to Step 4. If not, continue to III.



III. Is it KARST (Map A1)? If yes, follow Figure III‐1 Waste Storage Structures Karst Risk Flow Chart below then proceed to Step 4. If not karst, continue to IV.

IV. It is LOW RISK and proceed to Step 4.

Figure III‐1: Waste Storage Structures Karst Risk Flow Chart

STEP 4: Verify geological siting risk with a site walkover (if possible). During the site walkover, if a sinkhole, stream sink, seep or spring is found within 1000 feet of the proposed waste storage structure, then submit findings to Area Office. The Area Office shall submit a request for assistance to the NRCS Geologist if assistance is needed to ensure the proposed project will meet state Karst Locational Restrictions.

STEP 5: Proceed to the Waste Storage Structure Engineering Geology Risk Assessment Matrix (Figure III‐2). Determine the geologist involvement.

Figure III‐2: Waste Storage Structures Engineering Geology (EG) Risk Assessment Matrix

STEP 6: Documentation for non‐Geologist involvement.

a. Log information in Minnesota Geology Ledger.b. Complete risk assessment summary indicating the following: “The Practice Risk is HIGH. The

Geological Siting Risk is ____. The Engineering Geology Risk Assessment is approved by ______,Title, EJAA.”

B. Investigation Guidelines and Considerations

1. MN Pollution Control Agency (MPCA) Guidelines for Design and Construction of (LMSA)2. NEH 651 Agricultural Waste Management Field Handbook (AWFMH), Chapter 7 Geologic and

Groundwater Considerations



C. Types of Investigations:

1. Geologic Reconnaissance a. Geologic Reconnaissance investigations are conducted during the development of a facility

assessment for a site with a waste storage structure or an impoundment associated with a Level III vegetated treatment area. It is used to assess the characteristics of the site, including geomorphology, topography, drainage, and other conditions that might affect the suitability of the site for its intended use.

b. Verify the accuracy or adequacy of existing information and identify significant gaps in information needed to continue with the design.

c. Data gathered during the reconnaissance level subsurface investigation is primarily descriptive of the site and the nature of the project. Additional sources of information may include; well logs, topographic maps, aerial photography and soil survey.

d. No investigation report is required for sites in non‐karst areas. Provide a brief interpretation of geologic and soils maps and other available resources.

2. Preliminary Site Investigation

a. Preliminary site investigations are conducted during the design phase of a project which includes a waste storage structure or Level 3 vegetated treatment area. They can be completed using test pits, disturbed soil borings, or by obtaining a continuous undisturbed sample. Testing locations are referred to as borings in this section, regardless of the method of testing used.

b. Boring location, quantity, and depths i. Borings should be within the footprint of the practice. ii. A minimum of 2 borings are required for up to half acre in surface area (top inside

dimensions) plus 1 more additional boring for each additional acre of surface area. Complete additional borings as needed to confirm continuity of soils and to document soil transitions.

iii. Depth of the boring(s) will be the greater of either: a) The depth required to meet the requirements of Practice Standard 313 Waste

Storage Facility, for separation to bedrock. b) Bedrock separation requirements in the MPCA Liquid Manure Storage Areas

guidelines. c) Depth required to determine the vertical separation to groundwater, as required in

Practice Standard 313 Waste Storage Facility. c. An investigation report is required (Appendix A).

3. Detailed Site Investigation a. Sites with elevated risks of groundwater contamination due to underlying geology or other

site conditions will require a detailed site investigation. Investigation requirements are determined by the State Geologist and the State Conservation Engineer and must meet or exceed the requirements of NEM 531.

b. An investigation report is required which follows the criteria located in NEH 631.

D. Soils Testing for Soil Liners:

1. Conduct index testing on each soil which will potentially be used as a liner material. Run Atterberg Limits (ASTM D4318) and Gradation tests (ASTM D422) to determine the Plasticity Index (PI), the percent passing the #200 sieve and percent retained on the #4 sieve, and the lab defined Unified Soil Classification System Symbol (USCS) (ASTM D2487).



2. Standard proctor compaction testing of proposed compacted soil liner material is required for all earthen liners. Proctor compaction tests will be conducted by a certified lab or an individual qualified to perform testing according to ASTM D698 Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort.

3. Permeability of less than 1x10‐7 used for design will require permeability testing. Permeability tests will be conducted by a certified lab according to ASTM D5084, Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials using a Flexible Wall Permeameter or through in‐field permeability testing.

4. Liners that are located in a region prone to surface karst feature development as designated by the MN DNR in series GW‐01 should be investigated using excavator test pits so the true depth and nature of the bedrock surface can be observed. These sites shall also be reviewed by a qualified geologist to determine if additional geologic investigations with geophysics are needed on that site.

E. Bedrock Investigation Requirements for Liners

1. For purposes of making the determination as to the depth to bedrock, the point at which the soil profile/epikarst contains a majority of rock (less than 50% soil) will be considered the start of bedrock. In some instances, MPCA may request to be present to establish the elevation at which bedrock begins (MPCA LMSA 3.2.4).

2. Standard penetration testing is recommended for sandstone bedrock and may be required by MPCA.

Appendix A: Investigation Report

Appendix A October 2019 13

A. The report shall contain a legible site map, drawn to scale, no smaller than 8.5 inches by 11 inches, showing the boring or test pit locations, the footprint of the practice and the borrow area, and the vertical and horizontal reference point(s) provided by the designer.

B. A soil log shall be prepared for each boring or test pit containing all the information described in section I.

C. A narrative summary of the soil logs shall be included with the investigation report. This summary shall contain a narrative discussing the conclusions that can be drawn from an analysis of the investigations.

1. The summary shall note limiting features (e.g., depth to bedrock, water table observations) found during the investigation.

2. These limiting factors as well as the geologic material name and USCS group name and modifier will be used by the investigator and / or designer to construct a geologic profile as seen in figure 5‐1 of NEH Part 631, Chapter 5 – Engineering Geology‐ Logging, Sampling, and Testing:

Figure A‐1: Example Geologic Profile

D. Additional Requirements for Waste Storage Facility and Vegetated Treatment Area Level 3.

1. Method used to complete the investigation shall be noted.

2. The designer shall indicate the elevation of the bottom of the waste storage structure on each of the soil logs.

3. Evaluate the potential impacts that groundwater intrusion may have on the liner.

Appendix A: Investigation Report

Appendix A October 2019 14

Engineering Geology Risk Assessment Investigation Report Cover Sheet

Producer name:

Primary Practice:

Estimated EJC: Latitude:

Location: Longitude:

County:

Engineering Geology Risk Assessment

This site was reviewed by the engineering and soils staff under the guidance of the MN NRCS Geologist

on______________________ by _____________________________.

Practice Risk: ________________________

Overall Height: ft Dry/Wet Structure:

Effective Height: ft Existing/New Structure:

Storage: ft

Geological Siting Risk: _________________

Bedrock Formation:

Number of verified and unverified sinkholes or stream sinks within 1 mile:

The practice risk was determined by the Overall Height, Effective Height, Storage, Dry/Wet Structure, and Existing/New Structure.

The Geological Siting Risk was determined by reviewing the Minnesota Regions Prone to Surface Karst Feature Development (MN DNR Series GW‐01), the state or county bedrock map, loose coarse‐grained deposits (surficial sands), and sinkholes and stream sinks within 1 mile of the site. The maps are documentation whether there is karst, sandstone, loose coarse‐grained deposits on site, or sinkholes and stream sinks within 1 mile of the site.

Soils Investigation Requirement: _____________________________________

In Summary: As a result, the NRCS Geologist is willing to give you a variance for any additional field based geologic investigation on this site at this time. If during field work on site you find additional sinkholes, stream sinks, springs, seep, or bedrock within 5 feet in the structure footprint, please discuss with the NRCS Geologist. Prepared by: ________________________________________________________________________ Signature, Printed name, Title, Date Approved by: ________________________________________________________________________ Signature, Printed name, Title, I&E EJAA, Date

Appendix B: Charts for Using the Unified Soil Classification System (USCS)

Appendix B October 2019 15

Figure B‐1: Laboratory M

ethod for Classifying Soil Using the USCS System

Appendix B: Charts for Using the Unified Soil Classification System (USCS)

Appendix B October 2019 16

Figure B‐2: Field M

ethod for Classifying Soils Using the USCS

Appendix C: Soil Logs

Appendix C October 2019 17

Appendix D: Definitions

Appendix D October 2019 21

Aquiclude: A layer of soil, sediment, or rock that may or may not be saturated, that is incapable of transmitting significant quantities of water under ordinary hydraulic gradients.

Aquifer: A saturated, permeable geologic unit of sediment or rock that can contain or transmit sufficient quantities of water to wells or springs.

Figure D‐1: Groundwater Geology

Bedrock: A general term for the solid rock that underlies the soil and other unconsolidated material or that is exposed at the surface.

Dry Structure: One that does not have a permanent pool AND dewatering time is less than 48 hours. This definition is only being used for the EG risk assessment.

Effective Height: the difference in elevation in feet between the auxiliary spillway crest and the lowest point in the original cross section on the centerline of the dam. If there is no auxiliary spillway, the (settled) top of dam becomes the upper limit (NEM 520).

Engineering Geology (EG) Risk Assessment: The process of integrating the practice risk and geological siting risk to maximize due diligence in assessing and prioritizing the intensity of engineering, geology, and soils investigations.

Embankment: a linear man‐made structure created by the placement and compaction of soil or other materials. An embankment is typically perpendicular to the watercourse. It may temporarily or permanently impound water

Existing Structure: Any embankment that has been constructed. This includes structures known as push‐ups.

Geological Siting Risk: The potential geological hazards that appear on a particular site that is assessed during this process in order to appropriately locate and design conservation practices.

Aquiclude



Landscape Position: A generic term for the steeper part of a hill between its summit and the drainage line, valley flat, or depression floor at the base of the hill (Part 629 – Glossary of Landform and Geologic Terms). Is also referred to as the Hillslope.

Figure D‐2: Landscape Position

Karst Area: A type of topography that is formed on limestone, gypsum, and other soluble rocks, primarily by dissolution. It is characterized by closed depressions, sinkholes, caves, and underground drainage. For the purpose of this document karst is defined as the region prone to surface karst feature development as designated by the MN DNR in series GW‐01 and adjacent areas with surface karst features.

Outcrop: That part of a geologic formation or structure that appears at the surface of the earth.

Overall Height: the difference in elevation in feet between the settled top of dam and the lowest downstream elevation at the toe (NEM 520).

Practice Risk: The potential risk associated with engineering practices.

Redoximorphic: Features formed by the processes of redox, translocation, and/or oxidation of Fe (iron) and Mn (manganese) oxides. Formally called mottles and low chroma colors.

Figure D‐3: Redoximorphic Features



Seasonal High Water Table: The maximum elevation of free water at any time of the year at the location. This is typically interpreted by the presence of redoximorphic features during the soils investigation.

Storage: the capacity of the reservoir in acre‐feet below the auxiliary spillway crest, or the top (settled) of the dam if there is no auxiliary spillway (NEM 520).

Soil Investigation: The process where borings or test pits are used to classify soils for engineering practices defined in this guide as geologic reconnaissance, preliminary, and detailed investigations.

Site Walkover (Engineering Geologic Investigation): A field based investigation to look for sinkholes, stream sinks, sieves, springs, seeps and sandstone bedrock within a specified radius of the practice site. The results of this may increase the geological siting risk which may change the soil investigation required on site and design considerations. The purpose is to assess the actual site conditions present in relation to the potential geological siting risk.

Sinkholes: A closed, circular or elliptical depression, commonly funnel‐shaped, characterized by subsurface drainage and formed either by dissolution of the surface of underlying bedrock (e.g., limestone, gypsum, salt) (solution sinkhole) or by collapse of underlying caves within bedrock (collapse sinkhole).

Stream Sink or Sieve: An area of a stream where water disappears underground at a distinct point. Hydrologically, it is a recharge site. In this document it will be referred to as a stream sink.

Spring or Seep: An area, generally small, where water naturally outflows at the land surface. Volume may be variable, but the surface will be saturated during dry periods. Hydrologically, it is a discharge site and in this document it will be referred to as a spring.

Water Table: The elevation where there is free water at the time of the soils investigation, well drilling, and/or geologic investigation.

Wet Pool: one that has a permanent pool OR does not have a permanent pool AND the dewatering time is greater than 48 hours. This definition is only being used for the EG risk assessment.

minnesota nrcs guide to subsurface investigations october 2019 · map c1: simplified parent...

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