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October 26, 2020 Project No. 19-133605

David Lambert, Solid Waste Director Moore County Solid Waste 1 Courthouse Square Carthage, NC 28327

REPORT OF SOIL BORROW INVESTIGATION – RYHNE PUBLIC SAFETY CENTER STOCKPILE CARTHAGE, NORTH CAROLINA

Dear David,

Golder Associates NC, Inc. (Golder) is pleased to submit this report of a soil borrow investigation conducted on a soil stockpile on land adjacent to the County’s Rick Rhyne Public Safety Center (RPSC) in June of this year. The results were verbally communicated to you at that time but were not formalized in a written report until now.

PROJECT BACKGROUND Moore County’s Solid Waste Department plans to construct a new waste disposal area known as Cell 6 at the Moore County Construction and Demolition Landfill in Aberdeen, NC. The project will include preparation of an approximately 5.6-acre unlined landfill cell, including mass grading to establish cell base grades, soil stockpiling, and offsite hauling from the subject borrow site for subbase replacement (if required). This investigation was undertaken to determine the general characteristics of the stockpiled soil at the RPSC for possible use as subgrade replacement soil (to satisfy state requirements for subgrade soil classification) and as general backfill and landfill cover soil.

SUBSURFACE EXPLORATION PROGRAM

Subsurface Sampling Golder’s field technician advanced five shallow soil borings (designated BH-1 through BH-5) by hand auger to depths between 6 and 12 feet below ground surface (bgs) to explore, characterize, and describe shallow subsurface conditions at the designated borehole locations (see Drawing 01 attached). Three borings (BH-1 through BH-3) were located along the crest of the stockpile. The remaining two borings (BH-4 and BHG-5) were advanced on the east side of the stockpile at elevations approximately 10 feet below the top of the stockpile. All borehole locations were selected by Golder and located in the field without survey (locations shown are approximate).

Hand augering generates continuous disturbed samples of the soil at each location and allows for samples to be collected at any point within the boring based on the observations of the field technician. The retrieved auger cuttings were visually classified in the field by the technician and soil descriptions were noted on the field notes.

David Lambert, Solid Waste Director Project No. 19-133605

Moore County Solid Waste October 26, 2020

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Immediately after completion of hand augering, depths to water were recorded (where present). Note that water levels measured soon after hand augering in open boreholes may not be indicative of actual saturated or “phreatic” conditions, so this data should be considered preliminary and approximate.

All collected soil samples were returned to Golder’s office and visually classified by a Golder engineer. Refer to Table 1 (attached) for a summary of samples and descriptions for each boring based on the technician’s field notes and subsequent classification.

Geotechnical Laboratory Testing Selected soil samples were transported to Golder’s geotechnical laboratory in Atlanta, Georgia for classification and compaction testing. Table 2 below summarizes the types and number of tests performed:

Table 2: Scope of Laboratory Testing Program

Test Reference No. Tests

Grain Size Analysis ASTM D1140 9

Moisture Content ASTM D2216 9

Plasticity (Atterberg Limits) ASTM D4318 9

Standard Proctor Compaction

ASTM D698 2

Refer to Appendix A for geotechnical laboratory testing results, tabulated and individual.

INTERPRETED SUBSURFACE CONDITIONS Based on the soil boring information, the stockpile contains fine-grained soils with a predominant classification of Clayey Sand (USCS classification SC). One tested sample from boring BH-3 classified as a low-plasticity Clay (USCS classification CL). There was little to no evidence of non-soil material such as rock, trash or organic debris observed in the borings, but these could exist as only a miniscule percentage of the stockpile volume was observed. The soils were noted to be very moist to wet, as confirmed by the relatively high moisture contents measured in the lab-tested samples. The compacted maximum dry densities of the samples subjected to laboratory compaction tests were within the typical range for structural fill, but the as-received moisture contents were 2 to 4 percent above their respective optimum moisture contents for compaction.

Free water was noted in all three borings located along the crest of the stockpile at depths of 6 to 8 feet bgs, while water was observed in only one of the two lower borings at a depth of 2.5 feet bgs. It is presumed that the observed water is saturate or “perched groundwater” from rainfall infiltration, and is trapped or held by the low-permeability clayey soils, which retard drainage (flow in > flow out).

CONCLUSIONS Soil Availability and Excavation

The findings summarized above indicate that there is suitable soil available in the stockpile for borrow and use in landfill development and daily operations. A topographic survey of the stockpile was conducted for Golder by

David Lambert, Solid Waste Director Project No. 19-133605

Moore County Solid Waste October 26, 2020

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Fleming Engineering Inc. to estimate the volume of material in the stockpile. Based on that survey, roughly 17,700 cubic yards of material is available. It is unknown if all the material in the stockpile is soil similar to that sampled and tested, but it is a reasonable assumption that most or all is considering that the stockpile reportedly originated from excess soils generated during site preparation for the RPSC.

The stockpiled material should be readily removable with a track excavator or other conventional earthmoving equipment. The high moisture contents and free water observed will likely make handling, transport and placement more difficult than normal for acceptable productivity. Moisture conditioning (drying) should be anticipated as being necessary before placement in final locations where load support and stability is required.

Additional investigation using test pit methods could provide more information on the feasibility of dewatering, excavating, hauling and placing the stockpiled materials using conventional means.

Use as Low-Permeability Landfill Subbase

The fine-grained soils observed and sampled will satisfy the state criteria for use as a landfill subbase if subgrade replacement is needed during new cell construction. The maximum volume of soil potentially available for this use is roughly the same as the maximum that would be needed if the entire Cell 6 area (5.6 acres) required replacement to a depth of 2 feet (about 18,000 cubic yards).

Use as Daily, Intermediate and Final Landfill Cover

The soils encountered should be suitable for use as daily and intermediate landfill cover; however, the low permeability materials could create undesirable water-holding layers inside the landfill if used near slopes or over large areas without interruption. The clayey soils should also be suitable for use in the final cover low permeability soil layer, but the quantity will fall well short of the amount needed for that application.

Use as Backfill and Structural Fill

Most of the soils should be suitable for use as general backfill and structural fill, though moisture conditioning (drying) will likely be required prior to compaction. Standard Proctor compaction tests performed on bulk samples from borings BH-1 and BH-2 produced results with relatively high compacted maximum dry densities, both about 120 pounds per cubic foot (pcf). This suggests satisfactory shear strength for typical structural fill applications such as low embankments, roadway fills, and building pads; however, specific applications of planned structural fill should be evaluated for suitability before use.

LIMITATIONS This report was prepared in a manner consistent with that level of care and skill ordinarily exercised by geotechnical engineering professionals currently practicing in the same locality under similar conditions and subject to the same time limits and financial and physical constraints imposed on Golder.

Judgment has been applied in interpreting and presenting the report findings, results, and conclusions. There will be variations in stockpile conditions beyond and between the investigated locations. Subsurface data only indicate conditions at specific locations and to depths penetrated, and the boreholes referenced herein do not reflect soils strata or groundwater conditions and/or variations elsewhere. If subsurface conditions and/or water conditions are found to differ from those described herein, Golder should be notified, and the conclusions presented herein should be re-evaluated by Golder.

David Lambert, Solid Waste Director Project No. 19-133605

Moore County Solid Waste October 26, 2020

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CLOSURE Golder appreciates the opportunity to prepare this report for Moore County Solid Waste. If you have any questions or require additional information, please feel free to contact the undersigned at (336) 398-2821.

Sincerely,

Golder Associates NC, Inc.

Mark Taylor, PE Senior Consultant

Reviewed By: James Gardner, PE

Attachments: Drawing 01 – Rhyne PSC Stockpile Site Plan Table 1 – Soil Stratification in Hand Auger Borings Appendix A – Geotechnical Laboratory Test Results

https://golderassociates.sharepoint.com/sites/131919/project files/5 technical work/site prep & geotech/report of rpsc soil borrow study_final.docx

June 2020 Project No. 19133605.200

Borehole ID DescriptionDepth

(ft bgs)Samples

takenDriller's Notes

Brown Silty Clay, Sand, Moist 0-2Reddish Brown, Clayey Sand, Moist 2-8 B-1(4')Tan, Clayey Sand, Moist 8-10 B-1(9')Tan, Clayey Sand, Wet 10-11 B-1(10.5') Too wet to continue. Water

Level = 5.6 ft bgs

Brown Silty Sand, Moist 0-1Reddish brown, Clayey Sand, some gravel

1-7 B-2(4') Some rocks up to 1 inch in size

Tan, more moist, some gravel 7-8.5 B-2(8')Brown some Red, Clayey Sand, Moist 8.5-10

Brown some Red, Clayey Sand, Wet 10-11 B-2(11') Too wet to continue. Water Level = 8.1 ft bgs

Brown silty sand, moist 0-1Tan Sandy Clay, moist 1-3 B-3(3')Reddish Clayey Sand, moist 3-4.5Reddish brown Clayey Sand, moist 4.5-6Same, more moist/wet at ~10 feet 6-10 B-3(9')Tan, Clayey Sand, Wet 10-12 B-3(12') Too wet to continue. Water

Level = 8.0 ft bgs

Brown, Silty Sand, moist 0-2.5 B-4(2.5') Auger refusal. No water encountered

Reddish Brown, Clayey Sand, Moist 0-3

Brown, Clayey Sand, More moist 3-6 B-5(3.5') B-5(6')

Terminated at 6 ft. Water Level = 2.5 ft bgs

Table 1: Soil Stratification in Hand Auger Borings, Moore County Stockpile

BH-1

BH-2

BH-3

BH-4

BH-5

1

APPENDIX A

Geotechnical Laboratory Test Results