RFB936200-01 - CBC Geothermal Replacement - Exhibit A - Geotechnical Borings.pdf

ALLENDER BUTZKE ENGINEERS INC.

GEOTECHNICAL • ENVIRONMENTAL • CONSTRUCTION Q. C.

3660 109TH STREET • URBANDALE, IOWA 50322 • PHONE 515-252-1885 • FAX 515-252-1888

December 15, 2023

Dept. of Administrative Services

109 SE 13th Street

Des Moines, IA 50319

Attn: Mr. Brad Tonyan

RE:

Geotechnical Exploration

CBC District 2 Geothermal

1401 S 17th Ave

Marshalltown, Iowa

PN 231408

Dear Mr. Tonyan:

As authorized, Allender Butzke Engineers Inc. (ABE) has completed the soil borings for the above referenced project. The geotechnical exploration was conducted to evaluate the soil profile at this site for consideration of new geothermal wells. In general, the borings encountered clay fill, B-Horizon loess, and loess soils overlying eolian sand and sandy glacial till with thicker glacial outwash (sand) deposits. Weathered shale bedrock was encountered in all borings below depths between 25 and 31 feet. Details of our findings are described below and on the Boring Logs enclosed in the Appendix.

Three borings were conducted at this site to depths of 26 to 33.5 feet below existing grades on December 8, 2023. Approximate locations of the borings are shown on the enclosed Site Plan and were measured in the field from existing landmarks. The boring surface elevations, indicated on the enclosed Boring Logs, were determined by differential leveling and referenced to the finish floor elevation of the existing building at the north-central walk-in door. For reference in this letter, we have assigned this location an arbitrary elevation of 100.0 feet. Methods of drilling, sampling, standard laboratory testing, and classifying of subsurface materials are discussed in the Boring

Log Description/Legend pages of the Appendix.

Detailed descriptions of soils encountered by this exploration are provided on the Boring

Logs enclosed in the Appendix. The Profile of Borings (Plate A-1) presented in the Appendix depicts the relative deposit elevations in the borings. Following is a discussion of the subsurface materials encountered in the borings. Unless otherwise indicated, the depths of soil stratum and groundwater levels are referenced from below existing grade at the individual boring locations at the time of drilling.

PN 231408

Dark brown and brown sandy lean clay (CL) and sandy lean to fat clay (CL-CH) fill was encountered at ground surface in each of the borings. The damp to moist fill extended to depths of

2.5 to 10 feet.

Underlying the fill, Boring Nos. 1 and 3 encountered dark brown lean to fat clay (CL-CH)

B-Horizon loess which extended to depths of 4 to 4.5 feet. Brown-gray lean clay (CL) loess was encountered in Boring Nos. 1 and 2 underlying the fill and/or B-Horizon loess. The very moist loess extended to depths of 9 to 15 feet. Eolian sand consisting of brown-gray silty sand (SM) underlaid the loess in Boring No. 1 and the B-Horizon loess in Boring No. 3. The damp eolian sand extended to depths of 7 to 11 feet.

Brown-gray sandy lean clay (CL) and dark gray sandy lean to fat clay (CL-CH) glacial till was encountered in each of the borings underlying the loess and/or eolian sand. Brown-gray and red-brown clayey sand (SC) glacial outwash layers were encountered within the glacial till in

Boring Nos. 1 and 2. The glacial outwash layers were encountered near a depth of 14 feet in both borings and extended to depths of 22 and 20 feet in Boring No. 1 and 2, respectively. The moist glacial till extended to a depth of 27 feet in Boring No.1, 25 feet in Boring No. 2, and 31 feet in

Boring No. 3.

Light gray shale bedrock was encountered in each of the borings underlying the glacial till near depths of 25 to 31 feet. All borings terminated in the bedrock near depths of 26 to 33.5 feet.

The borings were monitored during and shortly after drilling operations to detect moisture seepage and groundwater accumulation. The results of our groundwater level observations are noted on the Boring Logs enclosed in the Appendix.

During drilling operations, moisture seepage was noted near depths of 14.5 to 21 feet below existing grades in each of the soil borings. Groundwater accumulation was observed between depths of 21.5 to 31.5 feet in each of the soil borings at the completion of drilling operation. It should be recognized that these short-term water levels are not necessarily a true indication of the groundwater table. Long-term observations would be necessary to accurately define the groundwater variations at this site. Fluctuation of groundwater levels can occur due to seasonal variations in the amount of rainfall, surface drainage, subsurface drainage, site topography, irrigation practices, and ground cover (pavement or vegetation).

APPENDIX

BORING LOG DESCRIPTION/LEGEND

(page 1 of 3)

The material types encountered during the drilling operations were recorded on field logs. The profile represented on the

Boring Log is based on final classification performed by a geotechnical engineer using the field logs, laboratory observation and testing. The material stratigraphy demarcation lines shown on the Boring Logs indicate changes in soil characteristics, however, actual soil changes or variations may occur as a gradual transition. Soil profile discussion, Log Boring information, water levels and recommendations presented in this report are based upon measured depths below ground levels existing at time of the field exploration, unless otherwise specified.

DRILLING AND SAMPLING

The borings were conducted with either a truck or all-terrain rotary drill rig using the drilling methods indicated on each Boring Log. Soil sampling and/or in-situ testing such as Shelby Tube (ST), split-spoon (SS), drive cone (DC), or core (C) was conducted at depth intervals which were selected in consideration of the characteristics of the proposed construction. Generally undisturbed soil samples are taken at 5 foot depth intervals or change in soil types. Disturbed soil samples from the auger, either jar size or bulk size samples, may be taken at intermediate intervals for the purpose of soil classification or laboratory testing. Borings conducted for soil classification only, will show no designation of sampling although disturbed sampling is performed. Soil samples obtained in the field were identified and sealed for transportation to the laboratory for performance of pertinent physical testing and engineering classification.

Drilling Methods

CFA - Continuous Flight Auger: 4, 6, or 8-inch diameter (ASTM D1452).

RD - Rotary Drilling: Using drilling fluid in cased or uncased boring (ASTM D2113).

HSA - Hollow Stem Auger: 6 or 8-inch diameter, continuous flight auger remains in boring with soil removed from the hollow stem through which undisturbed sampling is conducted.

HA - Hand Auger: 4-inch or less diameter.

Sample Types

ST - Shelby Tube: Thin-walled tube samples of cohesive soils (ASTM D1587).

SS - Split Spoon with 140 lb. manual hammer: Standard penetration test and split-barrel samples (ASTM D1586).

SSA - Split Spoon with 140 lb. automatic hammer: Standard penetration test and split-barrel samples (ASTM D1586).

DC - Drive Cone: Dynamic in-place testing of soil using a 2-inch diameter cone with a 60 degree point driven into the soil for continuous 1-foot intervals in the same manner as Split Spoon, no sample is obtained.

C - Core: Sampling hard soil or bedrock with a diamond core barrel in a rotary drill boring (ASTM D2113).

SPT - Standard Penetration Test: Number of blows required to drive sampler (split spoon or drive cone) into the soil with a 140-pound weight dropping a distance of 30-inches (ASTM D1586), number of blows recorded for each 6-inch interval in an 18-inch (or more) penetration depth, values shown are for each 6-inch interval (if series of number sets are shown) or a total of the last two 6-inch intervals (if only one number is shown) which is commonly referred to as "N" in blows per foot. High resistance is indicated by a high number of blows for a lesser penetration depth listed in inches.

BS - Bulk Sample: Disturbed.

CPT - Cone Penetration Test: Quasi-static in-place testing of soils using a 60 degree cone and friction sleeve which are steadily pushed into the soil and measure skin friction and end bearing (ASTM D3441).

STANDARD LABORATORY TESTING

Representative undisturbed soil samples obtained by the Shelby Tube sampler were tested for moisture content (ASTM D2216), density (dry) and unconfined compressive strength (ASTM D2166) in the laboratory. Results of these tests appear on the respective Boring Logs. Additional soil testing including particle size analysis (ASTM D422) and Atterberg Limits (ASTM D4318) may be conducted, if necessary, to define in more detail pertinent soil characteristics for classification in accordance with the Unified Soil Classification System. Specialized laboratory tests (if conducted) to determine pertinent soil characteristics are discussed in the "Laboratory Testing" section of the report.

WATER LEVEL MEASUREMENT

Water levels indicated on the Boring Logs are the levels measured in the borings at the times indicated. In pervious soils, the indicated levels may reflect the location of groundwater. In low permeability soils, the accurate determination of groundwater levels is not possible with short term observations.

(page 2 of 3)

DESCRIPTIVE SOIL CLASSIFICATION

Soil description is based on the Unified Classification System as outlined in ASTM Designations D-2487 and D-2488. This classification is primarily based upon visual and apparent physical soil characteristics, comparison with other soil samples, and our experience with the soil. Additional laboratory testing may be conducted, if necessary to define in more detail pertinent soil characteristics. The Unified Soil Classification group symbol shown on the boring logs corresponds with the group names listed below. The description includes soil constituents, moisture conditions, color and any other appropriate descriptive terms.

Group Symbol

Group Name Group Symbol

Group Name Group Symbol

Group Name Group Symbol

Group Name

GW

Well-Graded

Gravel

SW

Well-Graded Sand

CL Lean Clay CH Fat Clay

GP

Poorly-Graded

Gravel

SP

Poorly-Graded Sand

ML Silt MH Elastic Silt

GM Silty Gravel SM Silty Sand OL Organic Clay Organic Silt

OH

Organic Clay Organic Silt

GC

Clayey Gravel

SC Clayey Sand PT Peat

RELATIVE PROPORTIONS

GRAIN SIZE TERMINOLOGY

Descriptive Term(s) (Of components also present in sample)

Sand and Gravel % of Dry Weight

Fines % of Dry Weight

Major Component of Sample

Size Range

Trace <15 <5 Cobbles 12 in. to 3 in.

(300mm to 75mm)

With 15-30 5-12 Gravel 3 in. to #4 sieve

(75mm to 4.75mm)

Modifier >30 >12 Sand #4 to #200 sieve

(4.75mm to 0.074mm)

Silt or Clay Passing #200 sieve

(.074 mm)

CONSISTENCY OF FINE-GRAINED SOILS

RELATIVE DENSITY OF

COARSE-GRAINED SOILS

Unconfined Compressive Strength, Qu, psf Consistency SPT, bpf SPT, bpf Relative Density

< 500 Very Soft 0-2 0-4 Very Loose

500-1,000 Soft 2-4 4-10 Loose

1,000-2,000 Medium Stiff 4-8 10-30 Medium Dense

2,000-4,000 Stiff 8-15 30-50 Dense

4,000-8,000 Very Stiff 15-30 50-80 Very Dense

8,000-16,000 Hard 30-100 80+ Extremely Dense

> 16,000 Very Hard >100

(page 3 of 3)

ABBREVIATIONS

COMMONLY USED ABBREVIATIONS

ft. or ' - feet elev. - Elevation

in. or " - inches

% - Percent psf - pounds per square foot

No. - Number plf - pound per lineal foot

TB - Test Boring pcf - pounds per cubic feet

N - blow count (SPT, bpf) kip - 1000 pounds

USCS - Unified Soil Classification System ksf - 1000 pounds per square foot

LL - Liquid Limit klf - 1000 pounds per lineal foot

PL - Plastic Limit tsf - tons per square foot

PI - Plasticity Index bpf - blows per foot (SPT, N)

Dark brown sandy lean clay, trace organics and gravel, damp to moist

FILL

Dark brown lean to fat clay, trace sand, moist

B-HORIZON LOESS

Brown-gray lean clay, trace fine sand, very moist

LOESS

Brown-gray silty fine to medium sand, damp

EOLIAN SAND

Brown-gray sandy lean clay, trace gravel, moist

GLACIAL TILL

Brown-gray clayey fine to medium sand, trace gravel, moist

GLACIAL OUTWASH

Moisture seepage near 21'

Dark gray sandy lean to fat clay, trace gravel, moist

GLACIAL TILL

Light gray weathered shale, moist

BEDROCK

Dense after 32' End of Boring

CL

CL-

CH

CL

SM

CL

SC

CL-

CH

2.5 88.6

87.1

82.1

80.1

77.1

69.1

64.1

32.8 58.3

BORING LOG NO. 1 Project No.: 231408

Project:CBC District 2 Geothermal Client:Dept. of Administrative Services

1401 S 17th Ave 109 SE 13th Street

Marshalltown, Iowa Des Moines, Iowa 50319

Surface Elevation: 91.1' Date Drilled: 12/08/2023 Drilling Method: 4" CFA Datum: North-Central Door Finish Floor = 100' Drilling Depth, ft.: 32.8 Page: 1 of

*The stratification lines represent the approximate boundary lines between material types: in-situ, the transition may be gradual.

Water Level Observation

ALLENDER BUTZKE ENGINEERS, INC.Time: at completion 3 hrs. days

Depth to Geotechnical | Environmental | Construction Q.C.water: 31.5 ft. 27 ft. ft.

E le v a tio n ft

D e p th ft

S a m p le

N o

T y p e

S P

T b p f

M o is tu re

C o n te n t, D ry

D e n s ity p c f

U n c o n fin e d

C o m p re s s iv e S tr e n g th p s f

Material Description*

G ra p h ic

L o g

U S

C S

W a te r L e v e l

D e p th

E le v a tio n ft

Dark brown sandy lean to fat clay, trace gravel, damp to moist

FILL

Moist after 7.5'

Brown-gray lean clay, trace sand, moist to very moist

LOESS

Moisture seepage near 14.5' Dark gray sandy lean to fat clay, trace gravel, moist

GLACIAL TILL

Light gray shale, moist

BEDROCK

End of Boring **Auger Refusal at 26'

CL-

CH

CL

CL-

CH

83.2

78.2

68.2

67.2

BORING LOG NO. 2 Project No.: 231408

Project:CBC District 2 Geothermal Client:Dept. of Administrative Services

1401 S 17th Ave 109 SE 13th Street

Marshalltown, Iowa Des Moines, Iowa 50319

Surface Elevation: 93.2' Date Drilled: 12/08/2023 Drilling Method: 4" CFA Datum: North-Central Door Finish Floor = 100' Drilling Depth, ft.: 26 Page: 1 of

*The stratification lines represent the approximate boundary lines between material types: in-situ, the transition may be gradual.

Water Level Observation

ALLENDER BUTZKE ENGINEERS, INC.Time: at completion 1.5 hrs. days

Depth to Geotechnical | Environmental | Construction Q.C.water: 23.8 ft. 18.3 ft. ft.

E le v a tio n ft

D e p th ft

S a m p le

N o

T y p e

S P

T b p f

M o is tu re

C o n te n t, D ry

D e n s ity p c f

U n c o n fin e d

C o m p re s s iv e S tr e n g th p s f

Material Description*

G ra p h ic

L o g

U S

C S

W a te r L e v e l

D e p th

E le v a tio n ft

Brown sandy lean to fat clay, trace gravel, damp to moist

FILL

Brown-gray lean to fat clay, trace sand, moist

B-HORIZON LOESS

Brown-gray silty fine sand, damp

EOLIAN SAND

Brown-gray sandy lean clay, trace gravel, moist

GLACIAL TILL

Red-brown clayey fine to medium sand, trace gravel, moist

GLACIAL OUTWASH

Moisture seepage near 18'

Dark gray sandy lean to fat clay, trace gravel, moist

Boulder near 22.3'

GLACIAL TILL

Light gray weathered shale, moist

BEDROCK

End of Boring **Auger Refusal at 33.5'

CL-

CH

CL-

CH

SM

CL

SC

CL-

CH

2.5 97.2 4.5 95.2

92.7

85.7

79.7

68.7

33.5 66.2

BORING LOG NO. 3 Project No.: 231408

Project:CBC District 2 Geothermal Client:Dept. of Administrative Services

1401 S 17th Ave 109 SE 13th Street

Marshalltown, Iowa Des Moines, Iowa 50319

Surface Elevation: 99.7' Date Drilled: 12/08/2023 Drilling Method: 4" CFA Datum: North-Central Door Finish Floor = 100' Drilling Depth, ft.: 33.5 Page: 1 of

*The stratification lines represent the approximate boundary lines between material types: in-situ, the transition may be gradual.

Water Level Observation

ALLENDER BUTZKE ENGINEERS, INC.Time: at completion hrs. days

Depth to Geotechnical | Environmental | Construction Q.C.water: 21.5 ft. ft. ft.

E le v a tio n ft

D e p th ft

S a m p le

N o

T y p e

S P

T b p f

M o is tu re

C o n te n t, D ry

D e n s ity p c f

U n c o n fin e d

C o m p re s s iv e S tr e n g th p s f

Material Description*

G ra p h ic

L o g

U S

C S

W a te r L e v e l

D e p th

E le v a tio n ft

E L

E V

A T

IO

N

I N

F E

E T

E L

E V

A T

IO

N

IN

F

E E

T

PROFILE OF BORINGS

Strata symbols

Lean Clay Fill

Lean to Fat Clay Loess

Lean Clay

Silty Sand

Sandy Lean Clay

Clayey Sand

Sandy Lean to Fat Clay

Weathered Clay Shale

Clay Shale

PROJECT NO.:

231408

DATE:

12/15/2023

PROJECT: CBC District 2 Geothermal 1401 S 17th Ave Marshalltown, Iowa

SCALE:

6 feet/in.

ALLENDER BUTZKE ENGINEERS, INC.

PLATE:

A-1

NOTES