252021_20 _ Cobb _ Douglas County Health Reno.pdf

Report of Subsurface Exploration and Geotechnical Engineering Evaluation

Cobb & Douglas Health Renovation and Addition 6670 Selman Drive Douglasville, Georgia Geo-Hydro Project Number 252021.20

Prepared for Cobb & Douglas County Public Health July 2, 2025

400 Chastain Center Boulevard, Suite 430 • Kennesaw, Georgia 30144 o: 770.426.7100 • f: 770.426.5209 • www.geohydro.com

Ms. Destiny Davidson July 2, 2025

Cobb & Douglas Public Health

1650 County Services Parkway

Marietta, Georgia 30008

Report of Subsurface Exploration and Geotechnical Engineering Evaluation

Cobb & Douglas Public Health Renovation and Addition

6670 Selman Drive

Douglasville, Georgia

Dear Mrs. Davidson:

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 252021.P1 dated

June 10, 2025.

PROJECT INFORMATION

We understand that the Cobb & Douglas Public Health is planning an expansion and renovation to their existing facility at 6770 Selman Drive in Douglasville, Georgia. Figure 1 in the Appendix shows the approximate site location.

We have assumed that the additions will resemble the existing building, single-story structures with structural wood frames or masonry walls, At the time of this report, we have not been provided structural loading information for the additions. Based on our experience with similar projects, we have assumed that maximum column loads will be no greater than 30 kips with wall loads not exceeding 3 kips per lineal foot.

The areas of the planned building additions are currently occupied by asphalt parking lots, access drives, landscaping, grassed landscaping, and an outbuilding which will be demolished as part of the new construction. The annotated aerial photograph to the right shows current site conditions and the approximate addition footprints. We expect site grading to include less than 5 feet of mass excavation and structural fill placement.

Building Additions

Selman Drive

Cobb & Douglas Public Health Renovation and Addition • 6670 Selman Drive • Douglasville, Georgia Project Number 252021.20

July 2, 2025 | 2

EXPLORATORY PROCEDURES

The subsurface exploration consisted of five soil test borings performed at the approximate locations shown on Figure 2 included in the Appendix. Test boring B-5 was relocated about 20 feet west from it’s original intended location to avoid an existing gas line. The test borings were located in the field by Geo-Hydro using a handheld GPS unit with preloaded coordinates, and by measuring angles and distances from existing site features. In general, the boring locations should be considered approximate.

Standard penetration testing, as provided for in ASTM D1586, was performed at select depth intervals in the machine-drilled soil test borings. Soil samples obtained from the drilling operation 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 variation.

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.

REGIONAL GEOLOGY

The project site is located in the Northern Piedmont Geologic Province of Georgia. Soils in this area have been formed by the in-place weathering of the underlying crystalline rock, which accounts for their classification as “residual” soils. Residual soils near the ground surface, which have experienced advanced weathering, frequently consist of red brown clayey silt (ML) or silty clay (CL). The thickness of this surficial clayey zone may range up to roughly 6 feet. For various reasons, such as erosion or local variation of mineralization, the upper clayey zone is not always present.

With increased depth, the soil becomes less weathered, coarser grained, and the structural character of the underlying parent rock becomes more evident. These residual soils are typically classified as sandy micaceous silt (ML) or silty micaceous sand (SM). With a further increase in depth, the soils eventually become quite hard and take on an increasing resemblance to the underlying parent rock. When these materials have a standard penetration resistance of l00 blows per foot or greater, they are referred to as partially weathered rock. The transition from soil to partially weathered rock is usually a gradual one, and may occur at a wide range of depths. Lenses or layers of partially weathered rock are not unusual in the soil profile.

Partially weathered rock represents the zone of transition between the soil and the indurated metamorphic rocks from which the soils are derived. The subsurface profile is, in fact, a history of the weathering process which the crystalline rock has undergone. The degree of weathering is most advanced at the ground surface, where fine grained soil may be present. And, the weathering process is in its early stages immediately above the surface of relatively sound rock, where partially weathered rock may be found.

July 2, 2025 | 3

The thickness of the zone of partially weathered rock and the depth to the rock surface have both been found to vary considerably over relatively short distances. The depth to the rock surface may frequently range from the ground surface to 80 feet or more. The thickness of partially weathered rock, which overlies the rock surface, may vary from only a few inches to as much as 40 feet or more.

Stream valleys in the Piedmont Region 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.

SOIL TEST BORING SUMMARY

All borings encountered about 2 to 4 inches of topsoil at the ground surface. Detailed measurements necessary for quantity estimation were not performed for this exploration. For planning purposes, we recommend assuming an arbitrary surface material thickness of 8 inches. Additional topsoil will be encountered in poorly draining or generally low-lying areas.

Beneath the topsoil, borings B-1, B-3, and B-4 encountered fill material extending to depths of about 3, 12, and 8 feet, respectively. The fill materials were classified as sandy clay and clayey sand. Standard penetration test resistances recorded in the fill material ranged from 7 to 11 blows per foot.

Beneath fill materials, all borings encountered residual soils typical of the Piedmont region. The residual soils were classified as sandy silt and silty sand with varying amounts of mica content. Standard penetration test resistances recorded in the residuum ranged from 7 to 19 blows per foot.

Partially weathered rock was encountered in borings B-1 and B-2 at depths of about 12 feet. Partially weathered rock is locally defined as residual material having a standard penetration test resistance of 100 blows per foot or greater.

At the time of drilling, groundwater not encountered in any of the borings. The boreholes were backfilled with soil cuttings upon completion. It is important to note that groundwater levels will fluctuate depending on yearly and seasonal rainfall variations and other factors and may rise in the future.

For more detailed descriptions of subsurface soil conditions, please refer to the test boring records included in the Appendix.

July 2, 2025 | 4

Test Boring Summary

Boring Bottom of Fill

(feet) Top of PWR

(feet) Auger Refusal Depth

(feet) Depth to

Groundwater (feet)* Boring Termination

Depth (feet)

B-1 3 12 NE NE 20

B-2 NE 12 NE NE 20

B-3 12 NE NE NE 20

B-4 8 NE NE NE 20

B-5 NE NE NE NE 20

All Depths in this Summary Table are Approximate NE: Not Encountered PWR: Partially Weathered Rock *Groundwater level measured at time of drilling

EVALUATIONS AND RECOMMENDATIONS

The following evaluations and recommendations are based on the information available on the proposed construction, 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 small statistical sampling of subsurface conditions, it is possible that conditions different from those indicated by the test borings could be encountered during supplemental exploration and during construction.

Geotechnical Considerations

The following geotechnical characteristics of the site should be considered for planning and design:

• Fill materials were encountered in boings B-1, B-3, and B-4 extending to depths of about 3, 12, and 8 feet, respectively. Based on standard penetration resistances recorded in the fill material, moderate compactive effort was used at the time of placement. However, it should be noted that fill materials are inherently variable. Some management of poor-quality or loose fill may be necessary during grading and construction. Any loose, unstable fill material that cannot be readily densified in place should be removed and replaced with well compacted structural fill.

• The test borings indicate generally favorable excavation conditions within the anticipated excavation limits. Partially weathered rock was encountered in borings B-1 and B-2 at depths of about 12 feet. Fill materials and residual soils within the depths explored should be readily removable using conventional earth moving equipment. It is important to note that the depth to partially weathered rock and rock can vary drastically over relatively short distances. If encountered, removal of partially weathered rock will require the use of impact hammers.

• At the time of drilling, groundwater was not encountered in any borings. Based on the results of the borings and our understanding of the project, we do not expect groundwater to be a major hindrance to design or construction.

• Based on the results of the soil test borings, and contingent upon proper site preparation and thorough evaluation of the foundation excavations, it is our opinion that the proposed building additions can be

July 2, 2025 | 5 supported using conventional shallow foundations and concrete slab-on-grade floors. Based on maximum column loads no greater than 30 kips and wall loads no greater than 4 kips per lineal foot, we recommend using an allowable bearing pressure of 3,000 psf for foundation design purposes.

Column footings should have a minimum width of 24 inches to prevent general bearing capacity failure and should bear at least 18 inches below the prevailing ground surface to avoid potential problems due to frost heave.

• It is our opinion that the soil test borings were not extended to a depth sufficient to characterize the upper 100 feet of the soil subsurface for the purposes of determining the seismic Site Class in accordance with the 2018 International Building Code (Chapter 20, ASCE 7-16). We recommend using a default Site Class of D as suggested in the code. The mapped and design spectral response accelerations are as follows: SS=0.195, S1=0.087, SDS=0.208, SD1=0.139.

The following sections provide recommendations regarding these issues and other geotechnical aspects of the project.

Existing Fill Materials

Fill materials were encountered in boings B-1, B-3, and B-4 extending to depths of about 3, 12, and 8 feet, respectively. We expect any fill encountered on site during construction to be highly variable, and some management of poor-quality or loose fill may be necessary during mass grading and construction.

There are several important facts that should be considered regarding existing fill materials and the limitations of subsurface exploration.

• The quality of existing fill materials can be highly variable, and test borings are often not able to detect all of the zones or layers of poor-quality fill materials.

• Layers of poor-quality fill materials that are less than about 2½ to 5 feet thick may often remain undetected by soil test borings due to the discrete-interval sampling method used in this exploration.

• The interface between existing fill materials and the original ground surface may include a layer of organic material that was not properly stripped off during the original grading. Depending on its relationship to the foundation and floor slab bearing surfaces, an organic layer might adversely affect support of footings and floor slabs. If such organic layers are encountered during construction, it may be necessary to “chase out” the organic layer by excavating the layer along with overlying soils.

• Subsurface exploration is simply not capable of disclosing all conditions that may require remediation.

General Site Preparation

Existing structures, pavement, trees, topsoil, landscaping and other deleterious materials should be removed from the proposed construction area. All existing utilities should be excavated and removed unless they are to be incorporated into the new construction. Additionally, site clearing, grubbing, and stripping should

July 2, 2025 | 6 be performed only during dry weather conditions. Operation of heavy equipment on the site during wet conditions could result in excessive rutting and mixing of topsoil and debris with underlying soils. All excavations resulting from demolition of underground structures or from rerouting of underground utilities should be backfilled in accordance with the Structural Fill section of this report.

We recommend, wherever possible, that areas to receive structural fill be proofrolled prior to placement of structural fill. Areas of proposed excavation should be proofrolled after rough finished subgrade is achieved. Proofrolling should be performed with multiple passes in at least two directions using a fully loaded tandem axle dump truck weighing at least 18 tons. Proofrolling must be avoided within 10 feet of the existing building and any other structures or hardscapes to remain. If low consistency soils are encountered that cannot be adequately densified in place, such soils should be removed and replaced with well compacted fill material placed in accordance with the Structural Fill section of this report. Proofrolling should be observed by Geo-Hydro to determine if remedial measures are necessary.

For planning purposes, we suggest considering that 15 percent of the new building additions will require undercutting and replacement extending to an average depth of 2 feet. The suggested site preparation approach is intended only as a tool to estimate a cost associated with managing unstable subgrade conditions. Ground stabilization may be accomplished by in-place densification, treatment with geosynthetics (grid or fabric) and crushed stone, or a combination of methods. The need for, extent of, location, and optimal method of stabilization should be determined by Geo-Hydro at the time of construction based on actual site conditions.

During site preparation, burn pits or trash pits may be encountered. All too frequently such buried material occurs in isolated areas which are not detected by the soil test borings. Any buried debris or trash found during the construction operation should be thoroughly excavated and removed from the site.

Groundwater

At the time of drilling, groundwater was not encountered in the test borings. It is important to note that the groundwater levels recorded in the borings were measured at the time of drilling. Stabilized groundwater levels are typically higher than those measured at the time of drilling.

Based on our understanding of the project, we do not expect groundwater to be a major hindrance to design or construction. Regardless of groundwater conditions, the contractor should be prepared to manage surface runoff during rain events and subsurface drainage should be included behind all below-grade walls.

Excavation Characteristics

The test borings indicate generally favorable excavation conditions within the anticipated excavation limits.

Partially weathered rock was encountered in borings B-1 and B-2 at depths of about 12 feet. It is important to note that the depth to partially weathered rock and rock can vary drastically over relatively short distances. If encountered during utility installation, we expect impact hammers to be necessary to remove partially weathered rock.

July 2, 2025 | 7

For construction bidding and field verification purposes it is common to provide a verifiable definition of rock in the project specifications. The following are typical definitions of mass rock and trench rock:

• Mass Rock: Material that cannot be excavated with a single-tooth ripper drawn by a crawler tractor having a minimum draw bar pull rated at 56,000 pounds (Caterpillar D-8K or equivalent), and occupying an original volume of at least one cubic yard.

• Trench Rock: Material occupying an original volume of at least one-half cubic yard which cannot be excavated with a hydraulic excavator having a minimum flywheel power rating of 123 kW (165 hp);

such as a Caterpillar 322C L, John Deere 230C LC, or a Komatsu PC220LC-7; equipped with a short tip radius bucket not wider than 42 inches.

The foregoing definitions are based on large equipment typically utilized for mass grading. Retail excavations for building foundations, retaining walls, and underground utilities are often performed with smaller equipment such as rubber-tired backhoe/loaders or even mini-excavators. Contractors will often request additional payment for mobilizing larger equipment than that which was anticipated during preparation of their construction bid. The amount of additional compensation, if any, and the minimum equipment size necessary to qualify for any additional compensation should be defined before the start of construction.

Reuse of Excavated Materials

Based on the results of the test borings and our observations, residual soils and fill materials appear to be suitable for reuse as structural fill. However, it is possible that some fill materials will be encountered that will not be suitable for reuse. Geo-Hydro should observe the excavation of materials to evaluate their suitability for reuse. Routine adjustment of moisture content will be necessary to allow proper placement and compaction of excavated soils.

It is important to establish as part of the construction contract whether soils having elevated moisture content will be considered suitable for reuse. We often find this issue to be a point of contention and a source of delays and change orders. From a technical standpoint, soils with moisture contents wet of optimum as determined by the standard Proctor test (ASTM D698) can be reused provided that the moisture is properly adjusted to within the workable range. From a practical standpoint, wet soils can be very difficult to dry in small or congested sites and such difficulties should be considered during planning and budgeting. A clear understanding by the general contractor and grading subcontractor regarding the reuse of excavated soils will be important to avoid delays and unexpected cost overruns.

Structural Fill

Materials selected for use as structural fill should be free of organic matter, waste construction debris, and other deleterious materials. The material should not contain rocks having a diameter over 4 inches. It is our opinion that the following soils represented by their USCS group symbols will typically be suitable for use as structural fill and are usually found in abundance in the Piedmont: (SM), (ML), and (CL). The

July 2, 2025 | 8 following soil types are typically suitable but are not abundant in the Piedmont: (SW), (SP), (SP-SM), and

(SP-SC). The following soil types are considered unsuitable: (OL), (OH), and (Pt).

If encountered, highly plastic silt or clay, (MH) or (CH) soils, should be used with extreme caution. Such soils will require protection against desiccation or inundation during the construction process. Soils which have a liquid limit greater than 60 and a plasticity index greater than 35 will require blending with less plastic materials to result in lower Atterberg limits.

Laboratory Proctor compaction tests and classification tests should be performed on representative samples obtained from the proposed borrow material to provide data necessary to determine acceptability and for quality control. The moisture content of suitable borrow soils should generally be no more than 3 percentage points below or above optimum at the time of compaction. Tighter moisture limits may be necessary with certain soils.

Suitable fill material should be placed in thin lifts. Lift thickness depends on the type of compaction equipment, but in general, maximum lifts of 8 inches loose measurement are recommended. The soil should be compacted by heavy compaction equipment such as a self-propelled sheepsfoot roller. Within small excavations such as in utility trenches, around manholes, or behind retaining walls, we recommend the use of “wacker packers” or “Rammax” compactors to achieve the specified compaction. Maximum loose lift thicknesses of 4 to 6 inches are recommended in small area fills.

We recommend that structural fill be compacted to at least 95 percent of the standard Proctor maximum dry density (ASTM D698). The upper 12 inches of floor slab subgrade soils should be compacted to at least 98 percent of the standard Proctor maximum dry density. Following Georgia DOT guidelines, the upper 12 inches of pavement subgrade soils should be compacted to at least 100 percent of the standard

Proctor maximum dry density. Additionally, the in-place maximum dry density of structural fill should be no less than 90 pcf. Geo-Hydro should perform density tests during fill placement.

Earth Slopes

Temporary construction slopes should be designed in strict compliance with OSHA regulations. The exploratory borings indicate that most soils at the site are Type B and Type C as defined in 29 CFR 1926

Subpart P. This dictates that temporary construction slopes in fill materials, or any soil type below the groundwater level, for excavation depths of 20 feet or less should be no steeper than 1.5H:1V. Excavations in residual soils above the groundwater level should be no steeper than 1H:1V. Temporary construction slopes should be closely observed on a daily basis by the contractor’s “competent person” for signs of mass movement: tension cracks near the crest, bulging at the toe of the slope, etc. The responsibility for excavation safety and stability of construction slopes should lie solely with the contractor.

We recommend that extreme caution be observed in trench excavations. Several cases of loss of life due to trench collapses in Georgia point out the lack of attention given to excavation safety on some projects.

We recommend that applicable local and federal regulations regarding temporary slopes, and shoring and bracing of trench excavations be closely followed.

July 2, 2025 | 9

Formal analysis of slope stability was beyond the scope of work for this project. Based on our experience, permanent cut or fill slopes should be no steeper than 2H:1V to maintain long term stability and to provide ease of maintenance. The crest or toe of cut or fill slopes should be no closer than 10 feet to any foundation or to the edge of any pavement that will support truck traffic. The crest or toe should be no closer than 5 feet to the edge of any pavements supporting cars or light truck traffic or parking. Erosion protection of slopes during construction and during establishment of vegetation should be considered an essential part of construction.

Earth Pressure (Cast-in-Place Structures)

Three earth pressure conditions are generally considered for retaining wall design: "at rest", "active", and

"passive" stress conditions. Retaining walls which are rigidly restrained at the top and will be essentially unable to rotate under the action of earth pressure (such loading dock walls) should be designed for "at rest" conditions. Retaining walls which can move outward at the top as much as 0.5 percent of the wall height

(such as free-standing walls) should be designed for "active" conditions. For the evaluation of the resistance of soil to lateral loads the "passive" earth pressure must be calculated. It should be noted that full development of passive pressure requires deflections toward the soil mass on the order of 1.0 percent to 4.0 percent of total wall height.

Earth pressure may be evaluated using the following equation:

ph = K (DwZ + qs) + Ww(Z-d) where: ph = horizontal earth pressure at any depth below the ground surface (Z).

Ww = unit weight of water

Z = depth to any point below the ground surface d = depth to groundwater surface

Dw = wet unit weight of the soil backfill (depending on borrow sources). The wet unit weight of most residual soils may be expected to range from approximately 115 to 125 pcf.

Below the groundwater level, Dw must be the buoyant weight.

qs = uniform surcharge load (add equivalent uniform surcharge to account for construction equipment loads)

K = earth pressure coefficient as follows:

Earth Pressure Condition Coefficient

At Rest (Ko) 0.53

Active (Ka) 0.36

Passive (Kp) 2.77

The groundwater term, Ww(Z-d), should be used if no drainage system is incorporated behind retaining walls. If a drainage system is included which will not allow the development of any water pressure behind the wall, then the groundwater term may be omitted. The development of excessive water pressure is a common cause of retaining wall failures. Drainage systems should be carefully designed to ensure that long term permanent drainage is accomplished.

July 2, 2025 | 10

The above design recommendations are based on the following assumptions:

• Horizontal backfill

• 95 percent standard Proctor compactive effort on backfill (ASTM D698)

• No safety factor is included

For convenience, equivalent fluid densities are frequently used for the calculation of lateral earth pressures.

For "at rest" stress conditions, an equivalent fluid density of 68 pcf may be used. For the "active" state of stress an equivalent fluid density of 46 pcf may be used. These equivalent fluid densities are based on the assumptions that drainage behind the retaining wall will allow no development of hydrostatic pressure; that native sandy silts or silty sands will be used as backfill; that the backfill soils will be compacted to

95 percent of standard Proctor maximum dry density; that backfill will be horizontal; and that no surcharge loads will be applied.

For analysis of sliding resistance of the base of a cast-in-place concrete retaining wall, the coefficient of friction may be taken as 0.35 for the soils at the project site. This is an ultimate value, and an adequate factor of safety should be used in design. The force which resists base sliding is calculated by multiplying the normal force on the base by the coefficient of friction. Full development of the frictional force could require deflection of the base of roughly 0.1 to 0.3 inches.

Foundation Design

After general site preparation and site grading have been completed in accordance with the recommendations of this report including thorough evaluation of foundation bearing surfaces and remediation of any loose or soft soil as described below, it is our opinion that the proposed building additions can be supported using conventional shallow foundations. We recommend that footings be designed using an allowable bearing pressure of 3,000 psf. This recommendation is based on maximum column loads of 30 kips with wall loads no greater than 4 kips per lineal foot. If actual foundation loads exceed these estimated limits, please allow us to review, and if necessary, revise the foundation design recommendations provided in this report.

In addition, we recommend a minimum width of 24 inches for column footings and 18 inches for continuous wall footings to prevent general bearing capacity failure. Footings should bear at a minimum depth of

18 inches below the prevailing exterior ground surface elevation to avoid potential problems due to frost heave.

The recommended allowable bearing pressure is based on an estimated maximum total foundation settlement no greater than approximately 1 inch, with anticipated differential settlement between adjacent columns not exceeding about ½ inch. If the architect or structural engineer determines that the estimated total or differential settlement cannot be accommodated by the proposed structure, please contact us.

Because some foundation excavations may occur adjacent to the existing building, care should be taken to avoid undermining existing foundations and floor slabs. Generally, new footings located adjacent to

July 2, 2025 | 11 existing footings should be constructed to bear at the same elevation as the existing footings. The responsibility for preserving foundation support for the existing building should lie solely with the contractor.

Because of natural variation, it is possible that some of the soils at the project site may have an allowable bearing pressure less than the recommended design value. Likewise, existing fill materials can be highly variable, and may have an allowable bearing pressure less than the recommended design value. Therefore, foundation bearing surface evaluations will be critical to aid in the identification and remediation of these situations.

Foundation bearing surface evaluations should be performed in all footing excavations prior to placement of reinforcing steel. Geo-Hydro should perform these evaluations to confirm that the design allowable soil bearing pressure is available. Foundation 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 as much as 2 times the footing width, depending on the actual conditions. For budgetary purposes, we suggest considering that as much as 30 percent of the foundation excavations will require overexcavation and stone replacement extending to a depth of 2 feet below bearing elevation. The actual quantity of stone replacement will be different and may exceed the provided estimate.

Seismic Design

It is our opinion that the soil test borings were not extended to a depth sufficient to characterize the upper

100 feet of the soil subsurface for the purposes of determining the seismic Site Class in accordance with the 2018 International Building Code (Chapter 20, ASCE 7-16). We recommend using a default Site Class of D as suggested in the code. The mapped and design spectral response accelerations are as follows:

SS=0.195, S1=0.087, SDS=0.208, SD1=0.139.

Based on the information obtained from the soil test borings, it is our opinion that the potential for liquefaction of the residual soils at the site due to earthquake activity is relatively low.

Floor Slab Subgrade Preparation

The soil subgrade in the area of concrete slab-on-grade support is often disturbed during foundation excavation, plumbing installation, and superstructure construction. We recommend that the floor slab subgrade be evaluated by Geo-Hydro immediately prior to beginning floor slab construction. If low consistency soils are encountered that cannot be adequately densified in place, such soils should be removed and replaced with well-compacted fill material placed in accordance with the Structural Fill section of this report or with well-compacted graded aggregate base (GAB).

July 2, 2025 | 12

Assuming that the top 12 inches of floor slab subgrade soils are compacted to at least 98 percent of the standard Proctor maximum dry density, we recommend that a modulus of subgrade reaction of 120 pci be used for design.

Moisture Control for Concrete Slabs

To prevent the capillary rise of groundwater from adversely affecting the concrete slab-on-grade floor, we recommend that slab-on-grade floors be underlain by a minimum 4-inch thickness of open-graded stone.

Use of #57 crushed stone meeting Georgia DOT specifications for gradation is suggested. The stone must be covered by a vapor retarder. We suggest polyethylene sheeting at least 10 mils thick as a minimum vapor retarder.

We appreciate the opportunity to serve as your geotechnical consultant for this project and are prepared to provide any additional services you may require. If you have any questions concerning this report or any of our services, please call us.

Sincerely, GEO-HYDRO ENGINEERS, INC.

Austin J. Kuehler, E.I.T. Brian K. Ingram, P.E

Staff Engineer Georgia Operations Manager akuehler@geohydro.com bingram@geohydro.com

AJK/BKI/252021.20 - Cobb & Douglas County Health Renovation and Additions - Geotech Report

APPENDIX

Figure 1: Site Location Plan

Approximate Scale, Miles

0 0.25 0.5 1 1.5

Cobb & Douglas Public Health Renovation and Addition Douglasville, Georgia

Site

B-1

B-2

B-3

B-4

B-5

Selm an

D r

Approximate Scale: 1"=40'

Cobb & Douglas Public Health Renovation and Addition Douglasville, Georgia Geo-Hydro Project Number 252021.20

Figure 2: Boring Location Plan

20 40 80 120

LEGEND: Soil Test Boring

Cobb & Douglas Public Health Renovation and Addition Douglasville, Georgia Geo-Hydro Project Number 252021.20

LEGEND: Soil Test Boring Approximate Scale: 1"=60'

0 30 60 120 180

Figure 3: Boring Location Plan

B-1

B-2

B-5

B-4

B-3

Selman Dr

I:Main/Geo/Misc/Symbols&Nomenclature

Symbols and Nomenclature

Symbols ▐ Thin-walled tube (TWT) sample recovered

Thin-walled tube (TWT) sample not recovered

● Standard penetration resistance (ASTM D1586)

50/2” Number of blows (50) to drive the split-spoon a number of inches (2)

65% Percentage of rock core recovered

RQD Rock quality designation - % of recovered core sample which is 4 or more inches long

GW Groundwater

Water level at least 24 hours after drilling

Water level one hour or less after drilling

ALLUV Alluvium

TOP Topsoil

PM Pavement Materials

CONC Concrete

FILL Fill Material

RES Residual Soil

PWR Partially Weathered Rock

SPT Standard Penetration Testing

Penetration Resistance Results Approximate Number of Blows, N Relative Density Sands 0-4 very loose

5-10 loose 11-20 firm 21-30 very firm 31-50 dense Over 50 very dense

Approximate Number of Blows, N Consistency Silts and 0-1 very soft Clays 2-4 soft 5-8 firm 9-15 stiff 16-30 very stiff 31-50 hard Over 50 very hard

Drilling Procedures Soil sampling and standard penetration testing performed in accordance with ASTM D 1586. The standard penetration resistance is the number of blows of a 140-pound hammer falling 30 inches to drive a 2-inch O.D., 1.4-inch I.D. split-spoon sampler one foot. Rock coring is performed in accordance with ASTM D 2113. Thin-walled tube sampling is performed in accordance with ASTM D 1587.

Topsoil (Approximately 3 inches) Loose gray-brown and orange clayey fine to medium sand (SC) (FILL)

Loose to firm orange to gray, tan, and white silty fine to medium sand (SM) (RESIDUUM)

Partially weathered rock sampled as tan, white, and black silty fine to coarse sand

(SM)

Firm tan, gray, and white silty fine to medium sand (SM)

Boring Terminated at 20 feet

50/5"

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 6/23/25

GWT at 24 hrs: N/A (Boring Backfilled) Logged By: HB

Method: HSA- ASTM D1586

Project No: 252021.20Project: Cobb & Douglas Public Health Renovation and Addition

Location: 6670 Selman Road, Douglasville, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-1

G.S. Elev:

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G D

T

6/

/2

Topsoil (Approximately 2 inches) Loose to firm orange to tan and gray silty fine sand (SM) (RESIDUUM)

Partially weathered rock sampled as orange and tan-brown silty fine to coarse sand (SM)

Firm gray-brown, white, and black silty fine to medium sand (SM)

Boring Terminated at 20 feet

50/6"

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 6/23/25

GWT at 24 hrs: N/A (Boring Backfilled) Logged By: HB

Method: HSA- ASTM D1586

Project No: 252021.20Project: Cobb & Douglas Public Health Renovation and Addition

Location: 6670 Selman Road, Douglasville, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-2

G.S. Elev:

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G

Firm orange fine sandy clay (CL) (FILL)

Loose orange clayey fine sand (SC) (FILL)

Firm gray-brown and orange fine sandy clay

(CL) (FILL)

Firm tan and orange fine sandy silt (ML)

(RESIDUUM)

Firm tan and orange silty fine sand (SM)

Boring Terminated at 20 feet

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 6/23/25

GWT at 24 hrs: N/A (Boring Backfilled) Logged By: HB

Method: HSA- ASTM D1586

Project No: 252021.20Project: Cobb & Douglas Public Health Renovation and Addition

Location: 6670 Selman Road, Douglasville, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-3

G.S. Elev:

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G

Firm to stiff dark gray and orange fine sandy clay (CL) (FILL)

Loose to firm orange and tan slightly micaceous silty fine sand (SM) (RESIDUUM)

Boring Terminated at 20 feet

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 6/23/25

GWT at 24 hrs: N/A (Boring Backfilled) Logged By: HB

Method: HSA- ASTM D1586

Project No: 252021.20Project: Cobb & Douglas Public Health Renovation and Addition

Location: 6670 Selman Road, Douglasville, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-4

G.S. Elev:

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G

Topsoil (Approximately 4 inches) Loose to firm orange to tan and gray slightly micaceous silty fine to medium sand (SM)

Boring Terminated at 20 feet

E le v.

(F t)

0 30 40 100

S ym bo l

Test Boring Record D ep th

(F t)

G W

T

GWT at Drilling: Not Encountered

50 70

Date: 6/23/25

GWT at 24 hrs: N/A (Boring Backfilled) Logged By: HB

Method: HSA- ASTM D1586

Project No: 252021.20Project: Cobb & Douglas Public Health Renovation and Addition

Location: 6670 Selman Road, Douglasville, Georgia

Remarks:

Standard Penetration Test (Blows/Foot)

B-5

G.S. Elev:

Description

Driller: GCD (Auto-Hammer)

N

T E

S T

B O

R

IN

G R

E C

O R

D L

O G

S .G

P J

G E

O H

Y D

R O

.G