Geotechnical Final Report _ 04_29_2025.pdf

Report of Subsurface Exploration and Geotechnical Engineering Evaluation

Cartersville WPCP 25 MGD Expansion Walnut Grove Road Cartersville, Georgia Geo-Hydro Project Number 241227.20

Prepared for Hazen and Sawyer April 29, 2025

400 Chastain Center Boulevard, Suite 430 • Kennesaw, Georgia 30144 o: 770.426.7100 • www.geohydro.com

Mr. Fred P. Powell, P.E., S.E., F. ASCE April 29, 2025

Hazen and Sawyer

1300 Altmore Avenue, Suite 520

Atlanta, Georgia 30342

Report of Subsurface Exploration and

Geotechnical Engineering Evaluation

Cartersville WPCP 25 MGD Expansion

Walnut Grove Road

Cartersville, Georgia

Geo-Hydro Project Number 241227.20

Dear Mr. Powell:

Geo-Hydro Engineers, Inc. has completed the authorized subsurface exploration for the above referenced project. The scope of services for this project was outlined in our proposal number 241227.P0 dated

February 14, 2024, and our supplemental proposal number 241227.P0, dated December 12, 2024.

Project Information

The project consists of an expansion to the existing Cartersville Water Pollution

Control Plant located at 102 Walnut Grove Road in Cartersville, Georgia.

Figure 1 in the Appendix shows the approximate site location.

The expansion will include new construction on the east and west sides of

Walnut Grove Road. The table to the right lists the planned facility additions.

The project will also include a new stormwater detention pond. The planned construction area west of Walnut Grove Road is within the existing plant.

The area east of Walnut

Grove Road is currently mostly wooded, and the ground surface slopes up from west to east across the planned construction area.

We expect construction to involve as much as 25 to 40 feet of mass excavation, with greater excavation depths necessary for some specific below-grade structures.

Cartersville WPCP 25 MGD Expansion • Walnut Grove Road - Cartersville, Georgia Project Number 241227.20

April 29, 2025 | 2

The following table summarizes foundation bearing elevations and structural loading information provided by you.

Structure Current Ground

Elevation

Planned Bottom of Foundation Slab

Elevation

Approximate Excavation

Required (feet)

Average Foundation Bearing Pressure (psf)

Influent Pump Station Wet Well Area 677 651 26 2,000

Influent Pump Station Coarse Screening Area 681 660 21 3,200

Influent Pump Station Electrical Building 681 680 1 900

Headworks 745-750 732 13-18 2,500

Headworks Electrical Building 750 732 18 900

Headworks Odor Control Facility 748 732 16 1,200

Equalization Tanks 720-750 717 3-33 3,000

Main Electrical Building 683-693 682 1-11 900

Bioreactors 688-701 674 16-29 2,400

Blower Building 2 683 681 2 1,000

Clarifier Splitter Box 694 659 35 2,700

Final Clarifiers 694 667 27 1,500

Filter Facility 683 669 14 2,500

UV Disinfection 680 667 13 1,500

UV Electrical 680 678 2 2,200 All elevations in this table are approximate. The foundation bearing elevations have been rounded to the nearest foot.

Exploratory Procedures

Soil Test Borings

The subsurface exploration included 32 machine-drilled soil test borings performed at the approximate locations shown on Figures 2 and 3 included in the Appendix. The test borings were located in the field by

Geo-Hydro using a handheld GPS unit with preloaded coordinates and were offset where necessary to avoid existing utilities. The elevations shown on the test boring records were interpolated from the topographic site plan provided to us and have been rounded to the nearest foot. The topographic information is not certified as correct by Geo-Hydro. Users of this data do so at their own risk. In general, the boring locations and elevations should be considered approximate.

Standard penetration testing, as provided for in ASTM D1586, was performed at select depth intervals in the soil test borings. Soil samples obtained during the exploration were examined and classified in general accordance with ASTM D2488 (Visual-Manual Procedure for Description of Soils). Soil classifications include the use of the Unified Soil Classification System described in ASTM D2487 (Classification of Soils for Engineering Purposes). The soil classifications also include our evaluation of the geologic origin of the soils. Evaluations of geologic origin are based on our experience and interpretation and may be subject to some degree of error.

April 29, 2025 | 3

Descriptions of the soils encountered, groundwater conditions, standard penetration resistances, and other pertinent information are provided in the test boring records included in the Appendix.

Geophysical Testing

We used multi-channel analysis of surface waves (MASW) to develop profiles (one on each side of Walnut

Grove Road) of shear wave velocity for the site to a depth of 100 feet. This method consists of recording source seismic energy (active) and environmental source noise (background) utilizing an L-shaped array of multiple high-resonant-frequency geophones. The resulting data was combined and processed using proprietary, third-party software to produce a shear wave velocity profile. The shear wave velocity profiles are presented in Figures 3 and 4 in the Appendix.

Infiltration Testing

Test holes I-1, I-3, and I-5 were advanced to requested depths using a drill rig and continuous flight augers producing an approximately 7-inch diameter borehole. A 2-inch diameter PVC pipe with slotted screen was then placed in the borehole. The annular space was then backfilled with sand up to 2 feet above the screen, water was introduced to the hole and allowed to saturate the borehole for a minimum of four hours.

Subsequently, the drop in water level was measured over time. Percolation testing was performed in accordance with the Modified Taft Engineering Center Method. The percolation rate was converted to a vertical infiltration rate by using the equation below1.

The remaining test holes were advanced using hand auger equipment producing an approximately 4-inch diameter borehole. The tests were then performed using an Aardvark constant head permeameter to measure the saturated hydraulic conductivity (Ksat) of the soil. The Aardvark Permeameter estimates soil hydraulic conductivity using the amount of supplied water measured at equal time intervals, which is the equivalent to the amount of water that was infiltrated by the soil. The tests were performed until the soil-water infiltration rate reached a steady value that did not change over time. Soil hydraulic conductivity

(Ksat) was then calculated using this steady flow rate (Q). The test procedure and model components are shown in the figure on the following page.

1 Appendix C of City of Atlanta Stormwater Management Practices for Small Commercial Development.

April 29, 2025 | 4

Saturated hydraulic conductivity was calculated using the Reynolds and Elrick Method. The saturated hydraulic conductivity of a soil under steady flow from a borehole was calculated using the following equation:

Where QS is the steady flow rate in volume of water (cm3) per time

(min), h is the height of water ponded in the borehole (cm), r is the radius of the hole (cm), α is the soil macroscopic capillary length

(cm-1), and C0 is a unitless geometric factor. The values of α and C0 are dependent on the texture and structure of the soil, and are fixed values predetermined by Reynolds and Elrick (1992)2.

Laboratory Testing

Three representative bulk samples of soil cuttings were collected from select borings. The following tests were performed on the bulk samples: Atterberg Limits (ASTM D4318), sieve analysis with hydrometer

(ASTM D422), pH (ASTM G51), soluble sulfates (AASHTO T290), chloride ion (AASHTO T291), electrical resistivity (ASTM G187), and oxidation/reduction potential (ASTM G200). We were unsuccessful in obtaining thin-walled tube samples for consolidation testing due to elevated groundwater conditions and borehole instability. Laboratory test results are included in the Appendix.

Temporary Piezometers

After borings SB-16 and SB-20 were completed, piezometers were installed in the boreholes to allow more reliable measurements of the stabilized groundwater levels by members of the project team. The piezometers were extended to a depth of 30 feet below the ground surface. The bottom 10 feet of each piezometer consisted of 0.010-inch screen with a sand pack installed in the annular space up to approximately 2 to 3 feet above the screen. A bentonite seal approximately 2 feet thick was then installed.

The annular space above the bentonite seal was backfilled with soil cuttings to the ground surface.

Regional Geology

The project site is located in the Appalachian Valley and Ridge Province of Georgia. Based on review of geologic maps, it appears that the site is located on or near the boundary of the Conasauga Group and Knox

Group Formations. These formations consist of dolomite, limestone, and shale.

2 Reynolds and Elrick (1992). Advances in measurement of soil physical properties: Bringing theory into practice (Vol. 30, pp. 1-24). Soil Science

Society of America.

April 29, 2025 | 5

The soils which form from the weathering of the parent rock are termed residual soils. Residual soils derived from limestone or shale are frequently clayey and may be highly plastic. Residual soils typically contain fragments of insoluble rock such as chert.

Solution activity within limestone and dolomite units occurs in the Valley and Ridge Province, particularly along joints, faults, and the bedding planes of the rock. Solution activity in areas where limestone and dolomite units are present directly under the overburden soils often results in the development of an extremely irregular rock surface that frequently has deep slots. The transition from soil to hard rock is generally rather abrupt, with the soils encountered immediately above the rock frequently having a much lower consistency than near the ground surface.

Solution activity can result in the formation of caverns within the limestone or dolomite, and the development of sinkholes and cavities within the overburden soils. Even in areas where deeper limestone or dolomite formations are overlain by shale or sandstones, a rock cavity collapse can occur within the upper rock unit. The adjacent figure3 illustrates a rock cavity collapse and the subsequent propagation of a void upward through the overburden soils to the surface.

Depending upon the stage of development of sinkholes, evidence of ground subsidence may be readily observable at the ground surface, or essentially no indication of impending sinkhole development may be present at the ground surface. The size and frequency of subsurface voids is highly variable and depends on several factors related to geology, climate, and man-induced conditions. The stability of subsurface voids is related not only to the structural characteristics of the subsurface void; but also to proposed site grading, the magnitude of structural loads, significant changes in groundwater levels, drought, and any number of other factors. No obvious signs of sinkhole formation were observed during our work on site.

Stream valleys and areas adjacent to rivers and streams may contain alluvial (water-deposited) soils, depending on ground surface topography, stream flow characteristics, and other factors. By nature, alluvial soils can be highly variable depending upon the energy regime at the time of deposition. Coarse materials such as sand or gravel are deposited in higher energy environments, while fine grained materials such as silt and clay are deposited in low energy environments. Alluvial soils may also contain significant organic materials, and are frequently encountered in a loose, saturated condition. In many cases, fine-grained alluvial soils will be highly compressible and have relatively low shear strength.

Overall geologic conditions at the project site have been modified by previous construction activities.

3 Correction and Protection in Limestone Terrane, George F. Sowers, Proceedings of the First Multidisciplinary Conference on Sinkholes, Orlando, Florida, 1984.

April 29, 2025 | 6

LABORATORY TESTING SUMMARY

The following tables summarize the results of laboratory testing performed for the project.

Atterberg Limits (ASTM D4318)

Sample Liquid Limit Plastic Limit Plasticity Index

SB-10 (10-20 feet) 32 21 11

SB-21 (10-20 feet) 31 22 9

SB-27 (10-20 feet) 35 23 12

Sieve Analysis with Hydrometer (ASTM D422)

Sample %Gravel %Sand %Silt %Clay

SB-10 (10-20 feet) 6.5 23.5 46.6 23.4

SB-21 (10-20 feet) 11.8 25.4 50.8 12.0

SB-27 (10-20 feet) 3.5 17.2 51.2 28.1 pH (ASTM G51), Sulfate Ion Content (AASHTO T290), and Chloride Ion Content (AASHTO T291)

Sample pH Sulfate Ion Content (mg/kg-dry) Chloride Ion Content (mg/kg-dry)

SB-10 (10-20 feet) 6.6 77 4.12

SB-21 (10-20 feet) 5.4 <5 4.8

SB-27 (10-20 feet) 5.4 <5 4.13

Electrical Resistivity (ASTM G187) and Oxidation-Reduction Potential (ASTM G200)

Sample Electrical Resistivity (ohm-cm) Oxidation-Reduction Potential (mV)

SB-10 (10-20 feet) 4,381.8 355

SB-21 (10-20 feet) 31,758 334

SB-27 (10-20 feet) 49,848 328

Based on the results of the laboratory testing, corrosion does not appear to be a concern for the project.

For more detailed information on laboratory testing, please refer to the laboratory test results included in the Appendix.

Temporary Piezometer Readings

Well Number

Ground Surface

Elevation

Total Well

Depth (feet)

Screened Interval

(feet)

Select Measurement

Date

Groundwater Depth (feet)

Groundwater Elevation

SB-16 681 30 20 to 30 4-3-2025 14.75 666.25

SB-20 693 30 20 to 30 4-3-2025 13.5 679.50

April 29, 2025 | 7

Infiltration Test Results and Summary

The following table presents the results of the percolation tests and corresponding adjusted infiltration rates.

Infiltration Test Borehole Diameter

(inches) Ground Elevation Test Depth (feet) Test Elevation

Infiltration Rate (inches/hour)

I-1 7 750 20 730 0.61

I-2 4 733 6 727 0.00

I-3 7 732 11 721 1.49

I-4 4 722 8 714 0.08

I-5 7 742 27 715 0.82

I-6 4 700 3 697 0.54

I-7 4 701 4 697 0.03

I-8 4 710 5 705 0.00

I-9 4 720 4 716 0.15

I-10 4 719 5 714 0.14

All Dimensions, Depths, and Elevations in this Table are Approximate

All tests were performed in residual soils classified as clayey silt and silty clay. It is important to note that infiltration properties can vary horizontally and vertically, and the results of the infiltration tests may not be representative of the entire area where infiltration is intended. Appropriate judgement should be used when selecting values for design.

Soil Test Boring Summary

Brief summaries of the subsurface conditions encountered in each of the main areas of exploration are presented in the following sections. For more detailed descriptions of subsurface soil conditions, please refer to the Test Boring Records included in the Appendix. The table below summarizes all borings performed for the project.

Summary of Subsurface Conditions

Boring Approx.

Ground

Elevation

Groundwater 24-hours after drilling Bottom of Fill/Alluvium Top of PWR Auger Refusal

Boring Termination

Depth (feet)

Approx.

Elevation

Depth(feet) Approx.

Elevation Depth (feet)

Approx.

Elevation

Depth (feet)

Approx.

Elevation

Depth (feet)

Approx.

Elevation

PB-1 690 24 666 22 668 NE -- NE -- 50 640

PB-2 690 19 671 22 668 NE -- NE -- 50 640

PB-3 700 24 676 32 668 NE -- NE -- 50 650

PB-4 712 24 688 6 706 NE -- NE -- 50 662

PB-5 734 NE -- 6 728 42 692 11/47 723/687 11/47 723/687

PB-6 733 24 709 6 727 NE -- NE -- 50 683

PB-7 746 NE -- 8 738 27 719 31 715 31 715

April 29, 2025 | 8

Boring Approx.

Ground

Elevation

Groundwater 24-hours after drilling Bottom of Fill/Alluvium Top of PWR Auger Refusal

Boring Termination

Depth (feet)

Approx.

Elevation

Depth(feet) Approx.

Elevation Depth (feet)

Approx.

Elevation

Depth (feet)

Approx.

Elevation

Depth (feet)

Approx.

Elevation

SB-8 687 22 665 >50 <637 NE -- NE -- 50 637

SB-9 694 24 670 >50 <644 NE -- NE -- 50 644

SB-10 685 21 664 42 643 42 643 46 639 46 639

SB-11 694 NE -- >11 <683 NE -- 11 683 11 683

SB-12 682 19 663 >50 <632 NE -- NE -- 50 632

SB-13 695 33 662 57 638 57 638 68 627 68 627

SB-14 681 19 662 >50 <631 NE -- NE -- 50 631

SB-15 681 15 666 >50 <631 NE -- NE -- 50 631

SB-16 681 17 664 >50 <631 NE -- NE -- 50 631

SB-17 677 13 664 37 640 NE -- 37 640 37 640

SB-18 690 17 673 48 642 NE -- 48 642 48 642

SB-19 702 34 668 42 660 NE -- NE -- 50 652

SB-20 693 17 676 >50 <643 NE -- NE -- 50 643

SB-21 701 33 668 32 669 67 634 85 616 85 616

SB-22 719 NE -- 3 716 6 713 NE -- 50 669

SB-23 731 NE -- NE -- NE -- 42 689 42 689

SB-24 744 NE -- NE -- 17 727 37 707 37 707

SB-25 721 NE -- NE -- NE -- 37 684 37 684

SB-26 735 NE -- NE -- 42 693 47 688 47 688

SB-27 745 NE -- NE -- NE -- NE -- 50 695

SB-28 735 NE -- NE -- NE -- 37 698 37 698

SB-29 753 NE -- NE -- 22 731 26 727 26 727

SB-30 749 NE -- NE -- NE -- 27 722 27 722

SB-31 722 NE -- 6 716 17 705 36 686 36 686

SB-32 683 14 669 >50 <633 NE -- NE -- 50 633

All Depths and Elevations in this Summary Table are Approximate NE: Not Encountered PWR: Partially Weathered Rock # / #: Initial and offset auger refusal depth and elevation

April 29, 2025 | 9

Influent Pump Station Wet Well Area, Influent Pump Station Coarse Screening Area, Influent Pump Station

Electrical Building (Borings SB-15, SB-16, SB-17)

Starting at the ground surface, borings SB-16 and SB-17 encountered approximately 2 inches of topsoil.

No measurable surface materials were encountered in boring SB-15. For planning purposes, we suggest a topsoil thickness of 6 inches.

Beneath the topsoil or starting at the ground surface, all borings encountered fill materials extending to depths ranging from about 6 to 12 feet. The fill materials were classified as sandy clay, clayey silt, and silty sand. Standard penetration test resistances recorded in the fill ranged from 5 to 37 blows per foot.

Beneath the topsoil or fill materials, all borings encountered alluvial soils extending to the termination depth. The alluvial soils were generally classified as silty sand, sandy silt, and clayey silt. Standard penetration resistances ranging from 6 to 30 blows per foot were recorded in the alluvial soils.

Materials causing auger refusal were encountered in boring SB-17 at a depth of 37 feet. Auger refusal is the condition that prevents advancement of the boring using conventional soil drilling techniques.

At the time of drilling, groundwater encountered in all borings at depths ranging from 19 to 22 feet. The borings were left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in all borings at depths ranging from 13 to 17 feet. The borings were backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Current Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depth

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

SB-15 681 680 Cut 1 foot <631 NE NE 666 631

SB-16 681 660 Cut 21 feet <631 NE NE 664 631

SB-17 677 651 Cut 26 feet 640 NE 640 664 640 All Depths and Elevations in this Summary Table are Approximate PWR: Partially Weathered Rock NE: Not Encountered Bold font indicates elevations within 5 feet of bearing elevation

April 29, 2025 | 10

Headworks, Headworks Electrical Building, Headworks Odor Control Facility (Borings PB-7, SB-29, SB-30)

Starting at the ground surface, boring SB-29 encountered approximately 2 inches of topsoil. No measurable surface materials were observed at PB-7 or SB-30. For planning purposes, we suggest a topsoil thickness of 6 inches.

Starting at the ground surface, fill materials were encountered in boring PB-7 extending to a depth of about

8 feet. The fill was classified as clayey silt and sandy silt with standard penetration resistances ranging from 14 to 33 blows per foot.

Beneath the topsoil, fill materials, or starting at the ground surface, residual soils typical of the Valley and

Ridge region were encountered in all borings. The residual soils were classified as clayey silt and sandy silt. Standard penetration resistances in the residual soils ranged from 10 to 53 blows per foot.

Partially weathered rock was encountered in borings PB-7 and SB-29 at depths of about 27 and 22 feet, respectively. Partially weathered rock is locally defined as residual material with a standard penetration resistance of 100 blows per foot or greater.

Materials causing auger refusal were encountered in all borings at depths ranging from 26 to 31 feet. Auger refusal is the condition that prevents advancement of the boring using conventional soil drilling techniques.

Twenty-four-hours after drilling, groundwater was not encountered in the borings. The borings were backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of Fill

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

PB-7 746 732 Cut 14 ft. 738 719 715 NE 715

SB-29 753 732 Cut 21 ft. NE 731 727 NE 727

SB-30 749 732 Cut 17 ft. NE NE 722 NE 722 All Depths and Elevations in these Summary Tables are Approximate **Groundwater level measured at time of drilling PWR: Partially Weathered Rock

Bold font indicates elevations within 5 feet of bearing elevation

April 29, 2025 | 11

Equalization Tanks (Borings PB-5, PB-6, SB-22, SB-23, SB-24, SB-25, SB-26, SB-27, SB-28, SB-31)

Starting at the ground surface, all borings encountered topsoil ranging in thickness from about 2 to 5 inches.

For planning purposes, we suggest a topsoil thickness of 6 inches.

Beneath the topsoil, borings PB-5, PB-6, SB-22, and SB-31 encountered fill materials extending to depths ranging from about 3 to 6 feet. The fill materials were classified as sandy clay, clayey sand, and silty sand.

Standard penetration test resistances recorded in the fill ranged from 9 to 30 blows per foot.

Beneath the topsoil or fill materials, residual soils typical of the Valley and Ridge region were encountered in all borings. The residual soils were classified as clayey silt, sandy silt, clayey sand, silty clay, and silty sand. Standard penetration test resistances recorded in the residual soils ranged from 10 to 53 blows per foot.

Partially weathered rock was encountered in five borings at depths ranging from about 6 to 42 feet. Partially weathered rock is locally defined as residual material with a standard penetration resistance of 100 blows per foot or greater.

Materials causing auger refusal were encountered in seven borings at depths ranging from 11 to 47 feet.

Boring PB-5 encountered materials causing auger refusal at a depth of 11 feet. An offset boring was made in attempt to reach the target exploration depth. Materials causing auger refusal were encountered in the offset borings at a depth of 47 feet. Auger refusal is the condition that prevents advancement of the boring using conventional soil drilling techniques.

At the time of drilling, groundwater encountered in boring PB-6 at a depth of 45 feet. The borings were left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in boring PB-6 at a depth of 24 feet. The borings were backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of Fill

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

PB-5 734 717 Cut 17 ft. 728 692 723/687 NE 723/687

PB-6 733 717 Cut 16 ft. 727 NE NE 709 683

SB-22 719 717 Cut 2 ft. 716 713 NE NE 669

SB-23 731 717 Cut 14 ft. NE NE 689 NE 689

SB-24 744 717 Cut 27 ft. NE 727 707 NE 707

SB-25 721 717 Cut 4 ft. NE NE 684 NE 684

SB-26 735 717 Cut 18 ft. NE 693 688 NE 688

SB-27 745 717 Cut 28 ft. NE NE NE NE 695

SB-28 735 717 Cut 18 ft. NE NE 698 NE 698

SB-31 722 --- --- 716 705 686 NE 686

All Depths and Elevations in these Summary Tables are Approximate Bold font indicates elevations above or within 5 feet of bearing elevation **Groundwater level measured at time of drilling PWR: Partially Weathered Rock NE: Not Encountered

April 29, 2025 | 12

Main Electrical Building, Blower Building 2 (Borings SB-18, SB-32)

Starting at the ground surface, the borings encountered approximately 4 inches of topsoil. For planning purposes, we suggest a topsoil thickness of 6 inches.

Beneath the topsoil, the borings encountered fill materials extending to a depth of about 12 feet. The fill materials were classified as clayey silt. Standard penetration test resistances recorded in the fill ranged from 4 to 22 blows per foot.

Beneath the fill materials, the borings encountered alluvial soils extending to the depth of auger refusal or the boring termination depth. The alluvial soils were classified as clayey silt with standard penetration test resistances ranging from 5 to 21 blows per foot.

Materials causing auger refusal were encountered in boring SB-18 at a depth of 48 feet. Auger refusal is

At the time of drilling, groundwater encountered in borings SB-18 and SB-32 at depths of 25 and 15 feet, respectively. The borings were left open overnight for stabilized groundwater level measurements.

Approximately 24 hours after drilling, groundwater was encountered the borings at depths of 17 and 14 feet, respectively. The borings were backfilled with soil cuttings after the final groundwater level check.

It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

SB-18 690 682 Cut 8 ft. 642 NE 642 673 642

SB-32 683 681 Cut 2 ft. <633 NE NE 669 633 All Depths and Elevations in this Summary Table are Approximate **Groundwater level measured at time of drilling

April 29, 2025 | 13

Bioreactors (Borings PB-1, PB-2, PB-3, SB-19, SB-20, SB-21)

Starting at the ground surface, all borings except PB-1 encountered approximately 3 to 4 inches of topsoil.

Boring PB-1 was performed in the pavement and encountered approximately 6 inches of asphalt underlain by about 4 inches of graded aggregate base. For planning purposes, we suggest a topsoil thickness of

6 inches, and a combined pavement thickness of 12 inches.

Beneath the topsoil, all borings encountered fill materials extending to depths ranging from about 6 to

27 feet. The fill materials were classified as clayey sand, silty sand, clayey silt, and silty clay. Standard penetration resistances in the fill ranged from 2 to 51 blows per foot.

Beneath the fill materials, all borings except PB-2 encountered alluvial soils extending to depths ranging from 22 to greater than 50 feet. The alluvial soils were classified as clayey silt, clayey sand, and silty sand.

Standard penetration test resistances ranging from 5 to greater than 100 blows per foot were recorded in the alluvial soils.

Materials causing auger refusal were encountered in boring SB-21 at a depth of 85 feet. Auger refusal is

At the time of drilling, groundwater encountered in all borings at depths ranging from 15 to 40 feet. The borings were left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in all borings at depths ranging from 17 to 34 feet. The borings were backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

PB-1 690 674 Cut 20 ft. 668 NE NE 666 640

PB-2 690 674 Cut 20 ft. 668 NE NE 671 640

PB-3 700 674 Cut 28 ft. 668 NE NE 676 650

SB-19 702 674 Cut 32 ft. 660 NE NE 668 652

SB-20 693 674 Cut 21 ft. <643 NE NE 676 643

SB-21 701 674 Cut 29 ft. 669 634 616 668 616 All Depths and Elevations in this Summary Table are Approximate PWR: Partially Weathered Rock

Bold font indicates elevations above or within 5 feet of foundation bearing elevation

April 29, 2025 | 14

Clarifier Splitter Box, Final Clarifiers (SB-8, SB-9, SB-10, SB-11, SB-13)

Starting at the ground surface, approximately 1 to 4 inches of topsoil were encountered in borings SB-8, SB-10, and SB-13. Borings SB-9 and SB-11 encountered approximately 1 and 2 inches of gravel, respectively. For planning purposes, we suggest a surface material thickness of 6 inches.

Beneath the surface materials, fill materials were encountered in all borings extending to depths ranging from about 11 to 27 feet. The fill materials were classified as clayey silt, silty clay, clayey sand, and sandy clay with standard penetration test resistances ranging from 4 to greater than 100 blows per foot. Boring

SB-11 encountered materials causing auger refusal within the fill at a depth of 11 feet.

Beneath the fill materials, all borings except SB-11 encountered alluvial soils extending to depths ranging from about 42 to 57 feet. The alluvial soils were classified as clayey silt and silty sand. Standard penetration test resistances ranging from 5 to 38 blows per foot were recorded in the alluvial soils. Boring SB-8 and

SB-9 were terminated in the alluvium at a depth of 50 feet.

Beneath the alluvial soils, partially weathered rock was encountered in borings SB-10 and SB-13 at depths of about 42 and 57 feet, respectively. Partially weathered rock is locally defined as residual material with a standard penetration resistance of 100 blows per foot or greater.

Materials causing auger refusal were encountered in borings SB-10, SB-11, and SB-13 at depths ranging from 11 to 68 feet. Boring SB-11 encountered materials causing auger refusal at a depth of 11 feet within the fill. Auger refusal is the condition that prevents advancement of the boring using conventional soil drilling techniques.

At the time of drilling, groundwater encountered in all borings except SB-11 at depths ranging from 22 to

41 feet. The borings were left open overnight for stabilized groundwater level measurements.

Approximately 24-hrous after drilling, groundwater was encountered in all borings except SB-11 at depths ranging from 21 to 33 feet. The borings were backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

SB-8 687 667 Cut 20 ft. <637 NE NE 665 637

SB-9 694 667 Cut 27 ft. <644 NE NE 670 644

SB-10 685 667 Cut 18 ft. 643 643 639 664 639

SB-11 694 659 Cut 35 ft. <683 NE 683 NE 683

SB-13 695 667 Cut 28 ft. 638 638 627 662 627 All Depths and Elevations in this Summary Table are Approximate PWR: Partially Weathered Rock

Bold font indicates elevations above or within 5 feet the foundation bearing elevation

April 29, 2025 | 15

Filter Facility (Boring SB-12)

Starting at the ground surface, the boring encountered approximately 1 inch of topsoil. For planning

Beneath the topsoil, fill materials were encountered extending to a depth of about 17 feet. The fill materials were classified as silty clay and clayey silt. Standard penetration resistances in the fill ranged from 7 to

16 blows per foot.

Beneath the fill materials, the boring encountered alluvial soils extending to the planned termination depth of 50 feet. The alluvial soils were classified as clayey silt with standard penetration resistances ranging from 6 to 14 blows per foot.

At the time of drilling, groundwater encountered at a depth of 23 feet. The boring was left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in the boring at a depth of 19 feet. The boring was backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors, and may rise in the future.

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

SB-12 682 669 Cut 13 ft. <632 NE NE 663 632

All Depths and Elevations in these Summary Tables are Approximate

UV Disinfection, UV Electrical (Boring SB-14)

Starting at the ground surface, the boring encountered approximately 1 inch of topsoil. For planning

Beneath the topsoil, the boring encountered fill materials extending to a depth of about 12 feet. The fill materials were classified as silty sand with standard penetration test resistances ranging from 7 to 24 blows per foot.

Beneath the fill materials, alluvial soils were encountered extending to the boring termination depth of

50 feet. The alluvial soils were classified as clayey silt. Standard penetration test resistances ranging from

6 to 12 blows per foot were recorded in the alluvial soils.

At the time of drilling, groundwater encountered at a depth of 32 feet. The boring was left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in the boring at a depth of 19 feet. The boring was backfilled with soil cuttings after the final

April 29, 2025 | 16 groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of

Fill/Alluv.

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

SB-14 681 667 Cut 14 ft. <631 NE NE 662 631 All Depths and Elevations in this Summary Table are Approximate PWR: Partially Weathered Rock

Bold font indicates elevations above or within 5 feet the foundation bearing elevation

Proposed Detention Pond (Boring PB-4)

Starting at the ground surface, the boring encountered approximately 4 inches of topsoil. For planning

Beneath the topsoil, the boring encountered fill materials extending to a depth of about 6 feet. The fill materials were classified as clayey sand with a standard penetration test resistance of 6 blows per foot.

Beneath the fill materials, residual soils typical of the Valley and Ridge region were encountered. The residual soils were classified as clayey silt and sandy silt. Standard penetration test resistances in the residual soils ranged from 15 to 51 blows per foot.

At the time of drilling, groundwater encountered at a depth of 30 feet. The boring was left open overnight for stabilized groundwater level measurements. Approximately 24 hours after drilling, groundwater was encountered in the boring at a depth of 24 feet. The boring was backfilled with soil cuttings after the final groundwater level check. It should be noted that groundwater levels will fluctuate depending on yearly and

Existing Ground

Elevation

Foundation Bearing

Elevation

Foundation Cut/Fill Depths

Bottom of Fill

Elevation

Top of

PWR

Elevation

Auger Refusal

Elevation

24-Hour Groundwater

Elevation

Boring Termination

Elevation

PB-4 712 --- --- 706 NE NE 688 662

All Depths and Elevations in this Summary Table are Approximate

April 29, 2025 | 17

Evaluations and Recommendations - Specific Structures

The following evaluations and recommendations are based on the information available regarding the proposed construction, our observations, the data obtained from the test borings, and our experience with soils and subsurface conditions similar to those encountered at this site. Because the test borings represent a very small statistical sampling of subsurface conditions, it is possible that conditions may be encountered during construction that are substantially different from those indicated by the borings. In these instances, adjustments to the design and construction may be necessary.

The following sections present discussions of subsurface conditions and specific design recommendations for each of the proposed structures. Following the individual sections, we present general evaluations and recommendations that typically apply to all construction.

Influent Pump Station Wet Well Area, Influent Pump Station Coarse Screening Area, Influent Pump Station

Electrical Building (Borings SB-15, SB-16, SB-17)

Site preparation for the Influent Pump Station Wet Well Area and Influent Pump Station Coarse Screening

Area will involve mass excavation extending to depths of about 20 to 30 feet below current grades. Mass grading for the Electrical Building will involve less than 5 feet of excavation. Fill materials and alluvial soils should be readily removable using conventional earth moving equipment such as backhoes and loaders. Based on the results of the test borings, we do not expect difficult excavation conditions to be encountered.

The stabilized groundwater level within the Influent Pump Station Wet Well Area and Influent Pump

Station Coarse Screening Area was measured at approximate elevation 664. Stabilized groundwater levels will range from about 5 to 15 feet above the foundation bearing elevation. Dewatering should be performed to maintain the groundwater level approximately 2 to 3 feet below the lowest prevailing excavation depth.

The Influent Pump Station Wet Well Area and Influent Pump Station Coarse Screening Area structures should benefit from significant overburden relief. There should be a negligible net increase in pressure applied at bearing elevation. A properly prepared bearing surface should result in little or no net settlement of the structures. Because the structures are connected and have different foundation bearing elevations, to reduce the risk of differential settlement, we recommend the Screening Area be backfilled with well-compacted Graded Aggregate Base. The plan excerpt below shows the approximate GAB backfill area outlined in red.

April 29, 2025 | 18

Prior to placing GAB or crushed stone, the soil subgrade should be evaluated. If weak areas are detected, remedial measures may be required. Generally, subgrade evaluation involves proofrolling, hand probing, and visual observations.

All excavations beneath/within the Influent Pump Station Wet Well area, Influent Pump Station Coarse

Screening area, and Influent Pump Station Electrical Building footprint should be backfilled with well compacted GAB or “Select Fill” as outlined in the project specifications.

Contingent upon proper subgrade preparation, it is our opinion that a monolithic reinforced concrete mat can be supported on a properly prepared subgrade including a 6- to 12-inch thick course of open-graded stone such as #57 stone meeting Georgia DOT specifications for gradation, or in the case of the Wet Well and Coarse Screening area, the compacted GAB that will be required for general backfill purposes will be suitable for placing the reinforced concrete mat.

The electrical building will be constructed after the Wet Well and Screening area. The excavation surrounding these structures should be backfilled with well-compacted structural fill. An allowable bearing pressure of 2,500 psf can be used for design of the Electrical Building.

Because of natural variation, it is possible that some of the soils may have an allowable bearing pressure less than the recommended design value. Therefore, bearing surface evaluations will be critical to aid in the identification and remediation of these situations. Bearing surface evaluations should be performed prior to placement of reinforcing steel. These evaluations should be performed by Geo-Hydro to confirm that the design allowable soil bearing pressure is available. Bearing surface evaluations should be performed using a combination of visual observation, hand augering, and portable dynamic cone penetrometer testing (ASTM STP-399).

Remedial measures should be based on actual field conditions. However, in most cases we expect the use of the stone replacement technique to be the primary remedial measure. Stone replacement involves the removal of soft or loose soils, followed by replacement with well-compacted graded aggregate base (GAB) meeting Georgia DOT specifications for gradation. Stone replacement is generally performed to depths ranging from a few inches to several feet, depending on the actual conditions.

Estimated Settlement

(inches) Design Groundwater Elevation

Modulus of Subgrade Reaction (pci)

Influent PS Wet Well Less than ¼-inch 664 80

Influent PS Screening Area

Less than ¼-inch 666 80

Influent PS Electrical Building

Less than 1 inch 666 40

April 29, 2025 | 19

Headworks, Headworks Electrical Building, Headworks Odor Control Facility (Borings PB-7, SB-29, SB-30)

Site preparation for the Headworks, Headworks Electrical Building, and Headworks Odor Control Facility will involve mass excavation extending to depths ranging from 10 to 20 feet below current grades. Partially weathered rock and materials causing auger refusal were encountered within 5 feet of the foundation bearing elevation within the Headworks building (boring SB-29). Fill materials and residual soils should be readily removable using conventional earth moving equipment such as backhoes and loaders. However, difficult excavation conditions requiring ripping and blasting may be encountered in isolated areas at elevations above the target grade. The construction budget should include a modest allowance for rock excavation in the Headworks areas.

Prior to placing crushed stone, the soil subgrade should be evaluated. If weak areas are detected, remedial measures may be required. Generally, subgrade evaluation involves proofrolling, hand probing, and visual observations.

Contingent upon proper subgrade preparation, it is our opinion that a monolithic reinforced concrete mat can be supported on a properly prepared subgrade including a 6- to 12-inch thick course of open-graded stone such as #57 stone meeting Georgia DOT specifications for gradation. An allowable bearing pressure of 3,000 psf can be used for design for the Headworks, Headworks Electrical Building, and Headworks

Odor Control Facility.

Because of natural variation, it is possible that some of the soils may have an allowable bearing pressure less than the recommended design value. Therefore, bearing surface evaluations will be critical to aid in the identification and remediation of these situations. Bearing surface evaluations should be performed prior to placement of reinforcing steel. These evaluations should be performed by Geo-Hydro to confirm that the design allowable soil bearing pressure is available. Bearing surface evaluations should be

Remedial measures should be based on actual field conditions. However, in most cases we expect the use of the stone replacement technique to be the primary remedial measure. Stone replacement involves the removal of soft or loose soils, followed by replacement with well-compacted graded aggregate base (GAB) meeting Georgia DOT specifications for gradation. Stone replacement is generally performed to depths

(inches) Design Groundwater Elevation

Modulus of Subgrade Reaction (pci)

Headworks Less than 1 inch 725 40

Headworks Electrical Building

Less than 1 inch 725 40

Headworks Odor Control Facility

Less than 1 inch 725 40

April 29, 2025 | 20

Equalization Tanks (Borings PB-5, PB-6, SB-22, SB-23, SB-24, SB-25, SB-26, SB-27, SB-28, SB-31)

Site preparation for the Equalization Tanks will involve mass excavation extending to depths ranging from

5 to 35 feet below current grades. Partially weathered rock was encountered above or within 5 feet of the foundation bearing elevation in borings SB-22 and SB-24. Materials causing auger refusal were encountered in boring PB-5 at a depth of 11 feet. An offset boring was advanced in an attempt to reach the target boring depth at PB-5. The offset boring encountered materials causing auger refusal at a depth of

47 feet. Fill materials and residual soils should be readily removable using conventional earth moving equipment such as backhoes and loaders. Difficult excavation conditions requiring ripping and the use of impact hammers/blasting may be encountered at elevations above the target grade. The construction budget should include a modest allowance for rock excavation.

Based on the results of the test borings, subsurface conditions are suitable for support of the Equalization

Tanks using a mat foundation or a ringwall foundation. The tanks will impose a bearing pressure of about

2,400 psf under gravity loading conditions. We estimate that total settlement will not exceed 1 inch, and planar tilt and dish-type settlement should be no greater than about ½ inch.

Because of natural variation, it is possible that some of the soils may have an allowable bearing pressure less than the recommended design value. Therefore, bearing surface evaluations will be critical to aid in the identification and remediation of these situations. Bearing surface evaluations should be performed prior to placement of reinforcing steel. These evaluations should be performed by Geo-Hydro to confirm that the design allowable soil bearing pressure is available. Bearing surface evaluations should be

Remedial measures should be based on actual field conditions. However, in most cases we expect the use of the stone replacement technique to be the primary remedial measure. Stone replacement involves the removal of soft or loose soils, followed by replacement with well-compacted graded aggregate base (GAB) meeting Georgia DOT specifications for gradation. Stone replacement is generally performed to depths

(inches) Design Groundwater Elevation

Modulus of Subgrade Reaction (pci)

Equalization Tanks Less than 1 inch 710 40

Main Electrical Building, Blower Building 2 (Borings SB-18, SB-32)

Site preparation for the Main Electrical Building and Blower Building 2 will involve mass excavation extending to depths ranging from about 5 to 15 feet below current grades. Fill materials and alluvial soils should be readily removable using conventional earth moving equipment such as backhoes and loaders.

Based on the results of the test borings, we do not expect difficult excavation conditions to be encountered during mass excavation.

April 29, 2025 | 21

Prior to placing crushed stone, the soil subgrade should be evaluated. If weak areas are detected, remedial measures may be required. Generally, subgrade evaluation involves proofrolling, hand probing, and visual

The buildings will impose a bearing pressure of about 1,000 psf under gravity loading conditions.

Contingent upon proper subgrade preparation, it is our opinion that a monolithic reinforced concrete mat can be supported on a properly prepared subgrade including a 6- to 12-inch thick course of open-graded stone such as #57 stone meeting Georgia DOT specifications for gradation. An allowable bearing pressure of 2,000 psf can be used for design for the Main Electrical Building and Blower Building 2; as well as generator pads.

Because of natural variation, it is possible that some of the soils may have an allowable bearing pressure less than the recommended design value. Therefore, bearing surface evaluations will be critical to aid in the identification and remediation of these situations. Bearing surface evaluations should be performed prior to placement of reinforcing steel. These evaluations should be performed by Geo-Hydro to confirm that the design allowable soil bearing pressure is available. Bearing surface evaluations should be

Remedial measures should be based on actual field conditions. However, in most cases we expect the use of the stone replacement technique to be the primary remedial measure. Stone replacement involves the removal of soft or loose soils, followed by replacement with well-compacted graded aggregate base (GAB) meeting Georgia DOT specifications for gradation. Stone replacement is generally performed to depths

(inches) Design Groundwater Elevation

Modulus of Subgrade Reaction (pci)

Main Electrical Building Less than 1-inch 675 40

Blower Building 2 Less than 1-inch 670 40

Bioreactors (Borings PB-1, PB-2, PB-3, SB-19, SB-20, SB-21)

Site preparation for the Bioreactors will involve mass excavation extending to depths of about 20 to 35 feet below current grades. Fill materials and alluvial soils should be readily removable using conventional earth moving equipment such as backhoes and loaders. Based on the results of the borings, we do not expect difficult excavation conditions to be encountered during mass excavation.

The stabilized groundwater levels measured in the borings and the piezometer installed in borehole SB-20 ranged from approximate elevations 666 to 680. The groundwater level data suggests that the stabilized groundwater levels will range from about 5 feet above to 5 feet below bearing elevation. Dewatering should be performed to maintain the groundwater level approximately 2 to 3 feet below the lowest prevailing excavation depth.

April 29, 2025 | 22

The Bioreactors should benefit from significant overburden relief. There should be a negligible net increase in pressure applied at bearing elevation. A properly prepared bearing surface consisting of 12-inches of

#57 stone meeting Georgia DOT specifications for gradation or 9-inches of #57 stone with a 3-inch thick

“mud mat” should result in little or no net settlement. The Bioreactors will impose a bearing pressure of about 2,400 psf under gravity loading conditions.

Because of natural variation, it is possible that…