B08_Solicitation_-_Attachment_8_-_Geotechnical_Report.pdf

ALLENDER BUTZKE ENGINEERS INC.

GEOTECHNICAL • ENVIRONMENTAL • CONSTRUCTION Q. C.

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

JULY 30, 2020 PN 191373

GEOTECHNICAL EXPLORATION

WATER TREATMENT PLANT BUILDING

EFFIGY MOUNDS NATIONAL MONUMENT VISITORS CENTER

MARQUETTE/HARPERS FERRY, IOWA

PERFORMED FOR

HDR ENGINEERING, INC.

703 MAIN STREET, SUITE 200

RAPID CITY, SD 57701

PN 191373

TABLE OF CONTENTS

PROJECT INFORMATION

FIELD EXPLORATION

SUBSURFACE CONDITIONS

Site Geology

Soil Profile Groundwater Level Observations

ANALYSIS AND RECOMMENDATIONS

Existing Fill Site Preparation and Grading

Excavation Stability and Dewatering

Foundation Design Floor Slab Support Lateral Earth Pressures

Pavement Subgrade Preparation Pavement Thicknesses

Frost Heave

GENERAL

APPENDIX

Boring Log Description/Legend

Profile of Borings

Boring Logs

Site Plan

July 30, 2020

PROJECT INFORMATION

The Effigy Mounds National Monument Visitors Center is planning the construction of a new water treatment plant building with design assistance from HDR Engineering, Inc. (HDR). It is our understanding the 1-story building will have exterior masonry walls up to 22 feet tall and a finish floor elevation of 683.0 feet. Chris Robinson, P.E. with HDR indicated the exterior footings will support a total load of 4,800 pounds per lineal foot (not including the weight of the footing).

An interior tank will be present inside the building and be supported on grade beams or continuous spread footings. Loads from the tank are expected to be on the order of 3,500 pounds per lineal foot.

The project site is located along Highway 76 at the base of a bluff near the junction of the

Yellow River and the Mississippi River south of Harper’s Ferry. Existing grades at the top of the bluff are near elevation 950 feet. LiDAR Elevation contours indicate the site near the base of the bluff varies between elevation 686 feet in the northern portion of the building area and slopes down to the southeast to near elevation 680 feet. Based on the proposed finish floor elevation of 683 feet we anticipate cut depths on the order of 4 feet and new fill thicknesses on the order of 2 feet or less will be required.

FIELD EXPLORATION

Two borings were conducted at this site to depths of 20 feet below existing grades on

December 27, 2019. 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 pump house, reported to be at elevation 983.50 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.

SUBSURFACE CONDITIONS

Site Geology

Allamakee County is located within a geomorphic region of Iowa referred to as the

Paleozoic Plateau. The landscape in the Paleozoic Plateau region is dominated by bedrock outcroppings and deep narrow valleys that have formed as result of erosion into Paleozoic age rock strata. Overburden soil materials at the site have been deposited by different geomorphic processes including water, wind, gravity, and ice. As a result, soil stratigraphy at the site varies by geographic position.

Soil stratigraphy in upland areas generally consists of discontinuous loess cover underlain by bedrock. The loess is an eolian (wind-blown) deposit derived from flood plain sediments and tends to have relatively uniform silt and clay particle sizes.

Colluvium is typically located on or near the base of steep to very steep side slopes along valley walls and is typically comprised of silt and clay materials with various sized rock fragments eroded or moved from the upland areas and deposited in lower positions on the slopes.

The overburden soils are underlain by weathered shale, sandstone, dolomite and limestone bedrock formations of the Devonian and Ordovician bedrock systems.

Soil Profile

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.

Dark brown sandy lean clay (CL) with varying amounts of sand and gravel was encountered the ground surface in Boring Nos. 1 and 2. The fill in Boring No. 1 extended to a depth of 1 foot; however, the fill in Boring No. 2 extended to a depth of 11 feet and contained rubble materials, i.e. brick, mortar, glass, and metal fragments. The soft to medium stiff fill exhibited a low in-situ dry density of 75 pounds per cubic foot in sample No. 3. Boring No. 2 appeared to be located near a former structure that may have occupied the southeastern portion of the site.

Brown lean clay (CL) colluvium with trace amounts of limestone fragments was present underlying the existing fill in Boring No. 1. The colluvium was moist to very moist and medium stiff. Below a depth of 8 feet lean to fat clay (CL-CH) colluvium was encountered.

Brown fractured dolomite was encountered below depth of 10 and 11 feet in Boring Nos.

1 and 2. The fractured dolomite was medium dense to dense and extended to the boring depths of

20 feet.

Groundwater Level Observations

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

During drilling operations, moisture seepage was noted near a depth of 9 feet in Boring

No. 2. Groundwater accumulation was observed near a depth of 10.5 feet in Boring No. 2 while

Boring No. 1 remained dry shortly after completion of drilling operations. 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.

Past seasonal high-water tables may have been within 5 feet of existing grades perched within the colluvium and existing fill above the denser weathered dolomite bedrock. In this area of Iowa it is not uncommon to encounter natural springs in exposed bedrock formations on hill side slopes. 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).

ANALYSIS AND RECOMMENDATIONS

Existing Fill

Existing fill consisting of dark brown lean clay (CL) was encountered at the ground surface in Boring Nos. 1 and 2. The fill in Boring No. 1 extended to a depth of 1 foot while the fill in

Boring No. 2 extended to a depth of 11 feet and contained rubble materials such as brick, glass, mortar, and metal fragments. Higher concentrations of brick and mortar were encountered between depths of 6.5 and 7 feet and between depths of 9 and 11 feet. Historical aerial photos indicate a structure occupied a portion of this site in the past which was previously demolished. It appears that backfilling of the below grade structures was conducted in a controlled manner, i.e. with material selection, moisture content, and density control. By supporting the new structures over the existing fill there is a high risk of excessive total and differential settlements which could cause cracking of walls, foundations, floor slabs, plumbing issues, doors and windows that are difficult to open/shut, and building envelope leakage.

In our opinion, the existing fill encountered at this site would not provide reliable support for the proposed building foundations and floor slabs due to the fill’s variable material content and consistency, and the associated structural support uncertainties. Therefore, we recommend the existing fill be completely removed from beneath proposed structures and replaced with engineered compacted fill. We recommend that extensive geotechnical probing, testing, and observations be conducted by an ABE geotechnical engineer during over-excavation to assist in identifying unsuitable materials requiring removal and replacement. Care should be taken during the over-excavation process to avoid undermining existing adjacent building footings.

Over-excavations should extend 9 inches laterally in each direction beyond the foundation edges for each foot of over-excavation depth (see the following Figure No. 1) or on the order of 6 feet beyond the outside exterior footing edges near Boring No. 2 where fill depths of up to 7.5 feet are expected below the footing. Deeper fill soils could be encountered in other unexplored areas of the site.

Figure No. 1 – Typical Over-Excavation Detail

Due to the amount of rubble material (brick, mortar, etc.) portions of the existing fill materials will not be suitable for reuse as engineered compacted fill beneath buildings and some import of suitable low plasticity borrow materials for backfill may be required.

As an alternative to an over-excavation procedure, if the location of the former structure is known, the proposed building could be moved away from the footprint of the former building such that new footings and floor slabs would be supported on natural soils. Test pits could be conducted to better define the footprint of the former building. Boring information suggests and historical aerial photos indicate the former structure may be located on the southeastern portion of the new building site but due to the inaccuracy of the historical images, the exact location of the structure is not known to ABE.

Other options to support the proposed building and water tank over the existing fill soils without requiring a deep over-excavation may include helical pier mini piles or compacted aggregate pier ground improvement systems. These options are further discussed in the

Foundation Design section of this report. Due to the possibility of buried rubble causing installation difficulties, the feasibility of these support options should be discussed with the specialty contractor.

Site Preparation and Grading

Prior to the placing of concrete floors or pavements on this site, or before any fill is placed, the organic and loose materials in addition to all vegetation must be stripped. We expect that a minimum stripping depth of 6 inches will be required. The stripping depths may vary due to localized variations in vegetation cover and subgrade stability. The strippings could be used for landscaping purposes in non-critical areas where support for foundations, floor slabs, and pavements is not required. The subgrade should then be proof-rolled to delineate zones of soft soils present near the surface which may require additional removal or compaction.

We recommend that low plasticity (Liquid Limit (LL) of 45 or less and Plasticity Index

(PI) of 23 or less) cohesive or cohesionless soils, free of rubble and organics, be used as compacted fill. Inorganic existing soil such as the lean clay (CL) colluvium would be suitable soil types for general fill applications. The following Table A lists recommended minimum compaction requirements for cohesive and cohesionless fill materials in specific applications. For cohesive soils, moisture contents within a range of -1 to +4 percent of the material's optimum moisture content are necessary to achieve the desired fill qualities. Soils compacted closer to optimum moisture content would exhibit greater stability under repeated construction traffic loading.

TABLE A

RECOMMENDED DEGREE OF COMPACTION GUIDELINES

Construction

Application

Standard Proctor

(ASTM D698)

Cohesive Soil

Standard Proctor

(ASTM D698)

Cohesionless Soil

*Relative Density

(D4253 & D4254)

Cohesionless Soil

Class 1 95% 98% 70%

Class 2 90% 93% 45%

Class 3 85% 88% 20%

Class 1 - Subgrade for building foundations, slabs-on-grade, pavements and other critical backfill areas.

Class 2 - Backfill adjacent to structures not supporting other structures - Minor subsidence possible.

Class 3 - Backfill in non-critical areas - Moderate subsidence possible.

*Use Relative Density technique (ASTM D4253 & D4254) where Standard Proctor technique (ASTM D698) does not result in a definable maximum dry density and optimum moisture content.

The on-site soils can be excavated utilizing conventional excavation equipment. Larger debris may be present requiring heavier excavation equipment or breakers. Granular soils can generally be suitably compacted with vibratory compaction equipment whereas cohesive soils are more suitable for compaction with sheepsfoot or pneumatic type compactors. Care should be exercised in properly backfilling and compacting all trenches, especially utility trenches under or adjacent to the pavement. Loosely compacted or sand backfilled trenches can collect surface water and inadvertently direct it to the pavement subgrade and cause softening of the soil as well as increasing frost heave potential.

Excavation Stability and Dewatering

Boring information indicates shallow excavations at this site will encounter predominately cohesive soils with the possibility of granular fill in other unexplored areas. If excavations encounter only cohesive soils with no wet sand seams or layers, it is expected that the water seepage can be controlled by permitting it to drain into temporary construction sumps and be pumped outside the perimeter of the excavations. More extensive dewatering such as sand points and wells may be required for excavations which extend down into water bearing sand layers. We recommend that prior to excavating in saturated sand, water levels be lowered and maintained 2 feet or more below the bottom of excavations in saturated sand to prevent upward seepage forces which could reduce subgrade support.

The extent of bracing or sloping of open cut excavations will be dependent upon depth of cut, groundwater conditions, soils encountered, length of time the excavation will be open, area available for excavation and local governing regulations. Predominately cohesive soils may appear to stand nearly vertical in shallow excavations for short periods of time. However, soil creep, surcharge loads, precipitation, subsurface moisture seepage, construction activity vibrations and other factors may cause these soils to cave within an unpredictable period of time. Excavations encountering sand may tend to cave rapidly, especially if water is flowing through the sand.

Unstable granular excavation walls may also cause surrounding cohesive soils to become unstable.

Stability of excavation in existing fill containing miscellaneous debris is unpredictable.

Temporary shoring, flattening of the excavation slopes or use of trench boxes may be required to maintain a safe condition. Determining the appropriate OSHA classifications of the soil types encountered and implementing the required provisions for sloping, shoring, and bracing of excavations throughout the project during construction are the responsibility of the contractor per OSHA.

Foundation Design

As discussed in the Existing Fill section of this report, the deep existing fill is not suitable for support of the proposed structures. If relocating the structure to avoid the deep existing fill is not possible, then we recommend one or a combination of the following options be considered to support the proposed structures.

Over-Excavation and Replacement – In our opinion, newly placed engineered compacted fill required to replace all existing fill, as discussed in the Existing Fill section of this report, and suitable natural soils can provide adequate support for the proposed structure. We recommend that continuous spread foundations bearing on suitable soils be proportioned for a maximum net allowable soil bearing pressure of 1,500 pounds per square foot. We estimate long-term total settlement due to structural loads will be less than 1 inch and differential settlement may be on the order of ½ of the total settlement when foundations bear on newly placed engineered compacted fill and suitable natural soils.

Continuous foundations should be adequately reinforced to limit deflections caused by non-uniform soil support characteristics. All exterior foundations and foundations in unheated areas should be placed a minimum of 4 feet below final grade to provide protection against frost penetration and reduce movements associated with changes in soil moisture content. The on-site natural cohesive soils and newly placed cohesive fill would be suitable for trench foundations.

Footing excavations should be kept free of water accumulation to prevent softening of subgrade soils. Observations and test probing of the foundation subgrade soils should be conducted by an

ABE geotechnical engineer to determine that the soils are compatible with the design criteria.

Helical Piers – Helical piers extending through the fill to bear in the deeper weathered bedrock can also be used to support footings and floor slabs over the deep existing fill. Helical piers are a design-build system which involves hydraulically screwing several square or round steel shafts with 2 to 4 helical plates spaced several feet apart welded to the bottom section into reliable bearing materials. Subsequent shaft sections are added as the pier is screwed into the ground. Typical individual safe load carrying capacities of 30 to 60 kips, possibly more, are capable with helical piers. Helical piers will likely extend to depths of 8 to 10 feet or deeper depending on the elevation variations of the weathered bedrock. Production pier capacities can be estimated during installation by monitoring torque hydraulic pressures. Feasibility of this option should be discussed with a specialty contractor as penetration into the weathered bedrock may be limited.

Compacted Aggregate Piers – Compacted aggregate piers (CAP) could be installed beneath footings and floor slabs over the deep existing fill by augering 18- to 24-inch diameter holes through the fill to bedrock and backfilling the holes with thin lifts of compacted aggregate to densify the surrounding variable existing fill. Alternatively, a displacement approach may be used by driving a hollow mandrel into the ground, feeding aggregate through the mandrel, and compacting in thin lifts. The CAP ground improvement system serves to reduce settlement by replacing some of the variable existing fill below footings and slabs as well as densifying the remaining existing materials into a stiffer composite soil matrix. CAPs would be designed and installed under the direction of a specialty contractor. Spread foundations for proposed buildings could be proportioned for a bearing pressure of about 3,000 to 4,000 pounds per square foot, dependent upon the specialty contractor pier design. The aggregate pier design/installer should be consulted regarding the impact of vibrations of their system on adjacent structures and utilities during installation.

Floor Slab Support

Interior floor slabs can be adequately supported on a minimum of one foot of reworked inorganic existing soils, engineered compacted fill required to replace existing fill, as discussed in the Existing Fill section of this report, or new engineered compacted fill required to achieve desired grades. The slab could also be supported over the deep fill soils on helical piers or compacted aggregate pier ground improvement system.

The floor slabs can be designed for a modulus of subgrade reaction value of 100 pounds per cubic inch when bearing on a minimum of one foot of prepared subgrade. Testing, observations and probing should be conducted during construction to delineate zones of soft soils which may require repair prior to concrete placement.

Lateral Earth Pressures

Walls constructed to retain soil should be designed to accommodate unbalanced lateral earth pressures. Estimated lateral earth pressures for cohesive and cohesionless (granular) backfill are presented in the following Table B. Cohesionless (granular) backfill lateral earth pressure parameters may be used where granular backfill is installed behind the subsurface wall in accordance with Figure No. 2. The granular backfill should have a minimum width of 2 feet and be wide enough to accommodate the back slope limit line of 2:1 (vertical to horizontal) or flatter.

The area between the required minimum zone of granular material and the actual limits of excavation may be backfilled with either cohesive or granular soils.

TABLE B

LATERAL EARTH PRESSURE PARAMETERS

Condition

Cohesive Soil

(non-expansive clay)

Cohesionless Soil

(granular-sand)

Assumed Backfill Characteristics

Approximate Total Density

Approximate Friction Angle

Active Pressure Coefficient, Ka

At-Rest Pressure Coefficient, Ko

Passive Pressure Coefficient, Kp

130 pcf

15o - 20o

0.5

0.7

120 pcf

30o - 35o

0.3

0.5

3.3

Estimated Lateral Earth Pressure1 (Equivalent Fluid Pressures)

Active - Drained

Active - Undrained2

65 pcf

95 pcf

35 pcf

80 pcf

At-Rest - Drained

At-Rest - Undrained2

90 pcf

110 pcf

60 pcf

90 pcf

Passive - Drained

Passive - Undrained3

260 pcf

135 pcf

400 pcf

190 pcf

1) Assumes no safety factor, negligible wall friction, vertical wall, level backfill, zero surcharge loads and ignores cohesion shear strength.

2) Combined buoyant backfill unit weight and hydrostatic (water @ 62.4 pcf) loading.

3) Excludes hydrostatic loading.

Coefficient of sliding friction values of 0.3 may be used for Portland cement concrete on a cohesive subgrade. This ultimate value assumes no safety factor and design with this ultimate value should include a minimum factor of safety of 1.5.

Figure No. 2 – Lateral Earth Pressures Example Section

Active earth pressure design assumes that the wall can rotate and deflect at the top. If the wall is rigidly fixed, higher lateral earth pressures will develop against the wall and at-rest pressure parameters should be used for design. Increased earth pressures can also develop from restricted soil drainage, surcharge loads adjacent to the wall, and compaction of the adjacent backfill.

Expansive materials (CH), either natural or backfill, should not be within 3 feet of below grade walls.

Walls retaining fine-grained soils, and subjected to seasonally depressed temperatures, may be subject to long-term accumulative movement due to soil creep and freeze-thaw action. It is desirable to use free draining granular backfill behind such walls to reduce this movement. We recommend that a chimney of clean granular material (similar to Iowa DOT Specification 4131) be placed directly against the back of these walls and that the chimney be connected to a drain system. An acceptable drain system may be constructed using perforated pipe encased in clean granular material and sloped to sumps or storm drains.

Pavement Subgrade Preparation

Uniform subgrade support is critical in pavement performance. As discussed in the Existing

Fill section of this report, there is risk of settlement and cracking associated with constructing new pavements over the existing fill encountered at this site. The risk of pavement settlement and cracking may be acceptable to the owner for economic reasons, as pavements are more easily repaired than footings and floor slabs.

If the owner chooses to accept the risk of future pavement settlement by constructing new pavements over existing fill, we recommend proof-rolling and technical observations be conducted by an ABE geotechnical engineer during subgrade preparation. As a minimum, we recommend that the prepared subgrade depth be at least 1 foot deep after fine grading or trimming and extend

2 feet beyond the edge of the pavements. The recommended 1 foot of compacted subgrade may necessitate undercutting and reworking soils in cut areas. Subgrade preparation to 1-foot depths for some soil types may not be suitable under repeated heavy construction vehicle loads and may require stabilization to greater depths.

Subgrade preparation should be completed shortly before paving operations commence and is to be maintained in suitable condition until paved. Damages caused by construction traffic or deterioration due to adverse weather are to be repaired prior to paving.

Depending upon conditions encountered at the time of construction, it may be necessary to moisture condition existing soils to achieve the recommended moisture content range of -1 to +4 percent of optimum moisture content. Soils compacted closer to optimum moisture content will exhibit greater stability under construction traffic loading. Suitable cohesive soil compacted to a minimum of 95 percent of maximum dry density determined by ASTM D698 would provide a design support capability equivalent to a CBR value of 3 or a modulus of subgrade reaction value of 100 pounds per cubic inch. Subgrade compaction, moisture content and depth should be verified by an ABE representative.

Pavement Thicknesses

Either rigid (Portland cement concrete, PCC) or flexible (hot mix asphalt, HMA) pavement types could be constructed on the prepared cohesive subgrade. The following Table C summarizes alternate pavement thicknesses for typical lightly-loaded, moderately-loaded and heavily-loaded paved areas. A more specific pavement evaluation can be provided if traffic volume and loading information is available.

TABLE C

TYPICAL PAVEMENT THICKNESSES

Traffic Volume Rigid: PCC 1 Flexible: HMA 2

Lightly-Loaded 3 5" 6"

Moderately-Loaded 6" 7"

Heavily-Loaded 4 7" 8"

1) PCC - Flexural strength of 550 psi

2) Type A HMA - Structural coefficient of 0.44/inch

3) Automobile and 1 to 2 trucks average daily traffic.

4) Entrances, delivery areas, dumpster areas or other areas of heavier truck traffic

(25 trucks or less per day).

The above pavement thicknesses are considered to be typical and would require periodic maintenance. This maintenance would consist of sealing cracks and replacement of isolated distressed areas. Thicker pavement sections would reduce maintenance and increase the pavement service life. Likewise, thinner sections would be expected to have a shorter service life that still may satisfy particular project needs but may require more maintenance. Other criteria which influence pavement service life include surface drainage, subsurface drainage, paving material quality, reinforcement, and joint design. Construction procedures involving placement, finishing, curing, jointing and weather protection can significantly impact pavement performance.

Frost Heave

Key elements contributing to frost heave including freezing temperatures, available water, and fine-grained frost susceptible soils are generally present at sites in Iowa. As a result, frost heave problems are generally common (and most noticeable) in pavements or sidewalks adjacent to non-frost susceptible elements such as manholes, light poles, and exterior doors or frost protected stoops. Frost heave can cause pavement cracks to develop parallel to and several feet from curbs. This generally occurs where cleared paved areas exposed to freezing temperatures heave more than adjoining paved areas insulated by piled snow. Areas cleared of snow not exposed to periodic sunshine during the winter, such as under canopies, on the north shaded side of buildings and other shaded areas may experience more frost heave than other sunshine exposed areas. Sometimes it is not readily apparent why frost heave problems occur at one location and not at another seemingly similar location.

While it is appropriate to implement measures to reduce frost heave such as insulation, replacing frost susceptible soils with less frost susceptible soils, void forms, sealing cracks/joints to reduce surface water infiltration, or drainage improvements (surface and subsurface), these measures may simply move the frost heave problem to a different location where preventative measures have not been implemented. Having a smooth transition between heaved and non-heaved areas is desirable, but may be difficult and/or costly to accomplish. We are available to consult with you to discuss options for your consideration to reduce frost heave potential on this project.

GENERAL

The analyses and recommendations in this report are based in part upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations then appear evident, it will be necessary to reevaluate the recommendations of this report.

It is recommended that the geotechnical engineer be provided the opportunity to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and observation during earthwork and foundation construction phases to help determine that the design requirements are fulfilled.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, expressed or implied, is made. In the event that any changes in the nature, design or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed and the conclusions of this report modified or verified in writing by the geotechnical engineer.

The scope of our service was not intended to include any environmental assessment or exploration for the presence of hazardous or toxic materials in the soil, surface water, groundwater or air on, below or adjacent to this site.

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)

BEDROCK

CLASSIFICATION

LIMESTONE

Light to dark colored, crystalline to fine-grained texture, composed of CaCO3, reacts with HCl.

DOLOMITE

Light to dark colored, crystalline to fine-grained texture, composed of MgCO3, slightly harder than limestone, reacts with

HCl when powdered.

CHERT

Light to dark colored, smooth, very fine-grained texture, composed of micro-crystalline quartz (SiO2), brittle, breaks into angular fragments, will scratch glass.

SANDSTONE

Usually light colored, coarse to fine texture, composed of cemented sand-sized grains of quartz, feldspar, etc.

SHALE

Light to dark colored, very fine-grained texture, composed of consolidated mud, silt, or clay, usually bedded in thin layers.

The unlaminated equivalent is frequently referred to as siltstone, claystone, or mudstone.

COAL

Usually black graphite-like material composed of carbonaceous matter (decomposed organics) and clay, brittle.

Rock Quality Designation, RQD is based on a modified core recovery procedure which, in turn, is based indirectly on the number of fractures and amount of softening or alteration in the rock mass as observed in the rock cores from a drill hole. Instead of counting the fractures, an indirect measure is obtained by summing up the total length of core recovered but counting only those pieces of core which are 4 inches in length or longer, and which are hard and sound.

ROCK QUALITY DESIGNATION (RQD)

RQD Description of Rock Quality

0 – 25 Very Poor

25 – 50 Poor

50 – 75 Fair

75 – 90 Good

90 – 100 Excellent

SSA

25.0

SSA

27.1

ST

31.2

ST

21.2

SSA

12.2

SSA

10.5

SSA

21.3

ST

24.0

ST

32.4

SSA

SSA

SSA

11.5

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 Clay

Lean to Fat Clay

Fractured Dolomite

Fill with Rubble

Misc. Symbols

Water table at completion

PROJECT NO.:

191373

DATE:

7/31/2020

PROJECT: Water Treatment Plant Building Effigy Mounds Nat. Mon. Visitors Center Hwy 76, Marquette/Harpers Ferry, Iowa

PLATE:

A-1

SCALE:

4 feet/in.

ALLENDER BUTZKE ENGINEERS, INC.

SSA

SSA

ST

ST

SSA

SSA

25.0

27.1

31.2

21.2

12.2

10.5

Dark brown sandy lean clay, trace gravel, trace organics, moist

FILL

Brown lean clay, trace sand and limestone fragments, moist Very moist after 2'

COLLUVIUM

Brown lean to fat clay after 8'

Brown fractured dolomite with lean clay, damp

WEATHERED BEDROCK

Less clay after 15' Hard dolomite stringers 1 to 2 inches thick after 16'

End of Boring

CL

CL

CL-

CH

683.5

674.5

664.5

BORING LOG NO. 1 Project No.: 191373

Project: Water Treatment Plant Building Client: HDR

Effigy Mounds Nat. Mon. Visitors Center 703 Main Street, Suite 200

Hwy 76, Marquette/Harpers Ferry, Iowa Radpid City, South Dakota 57701

Surface Elevation: 684.5' Date Drilled: 12/27/2019 Drilling Method: 4" CFA Datum: Pump House F.F.E. = 683.50' Drilling Depth, ft.: 20 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: Dry ft. ft. ft.

E le va tio n ft

D e p th ft

S a m p le N o

T yp e

S P

T b p f

M o is tu re C o n te n t, D ry

D e n si ty p cf

U n co n fin e d C o m p re ss iv e S tr e n g th p sf Material Description*

G ra p h ic L o g

U S

C S

W a te r

L e ve l

D e p th

E le va tio n ft

SSA

ST

ST

SSA

SSA

SSA

21.3

24.0

32.4

11.5

Dark brown lean clay with sand, brick, glass, limestone, and metal fragments, moist

FILL

Brick and mortar from 6.5' to 7' With limestone from 7' to 9'

Moisture seepage near 9' Brick and mortar fragments after 9'

Brown fractured dolomite with lean clay, moist

Less clay after 13'

WEATHERED BEDROCK

End of Boring

CL

BORING LOG NO. 2 Project No.: 191373

Project: Water Treatment Plant Building Client: HDR

Effigy Mounds Nat. Mon. Visitors Center 703 Main Street, Suite 200

Hwy 76, Marquette/Harpers Ferry, Iowa Radpid City, South Dakota 57701

Surface Elevation: 683.0' Date Drilled: 12/27/2019 Drilling Method: 4" CFA Datum: Pump House F.F.E. = 683.50' Drilling Depth, ft.: 20 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: 10.5 ft. ft. ft.

E le va tio n ft

D e p th ft

S a m p le N o

T yp e

S P

T b p f

M o is tu re C o n te n t, D ry

D e n si ty p cf

U n co n fin e d C o m p re ss iv e S tr e n g th p sf Material Description*

G ra p h ic L o g

U S

C S

W a te r

L e ve l

D e p th

E le va tio n ft

B 1 B 2

18 ft.

12 ft.

42 ft.

6 ft.

Approximate Boring Location

ALLENDER BUTZKE ENGINEERS INC.

B #

Urbandale, IA 50322 3660 - 109th Street

Site Plan Water Treatment Plant Building

Effigy Mounds Visitor Center Hwy 76, Marquette/Harpers Ferry, Iowa

PN 191373

Base Plan Provided by HDR Engineering, Inc.

0 20 40

Scale (feet)

AutoCAD SHX Text N

NOTES