2022-154-E-DEAPR-S&ME, INC-Additional remedial investigation at former Hillsborough landfill

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DocuSign Envelope ID: FC9986C3-F179-4A3D-BACO-D8CA9F8B93A7 Proposal for Additional Remedial Investigation Hillsborough Dump l: &meow ID No. NONCD0000483 Task Orders 483DP-19 thru 25 S&ME Project No.4305-17-061G S&ME will subcontract a North Carolina Licensed Professional Land Surveyor(McKim &Creed) to survey the 9 groundwater monitor wells (including the top of casing and ground surface elevations). Sampling Groundwater Monitor Wells(9): Ground water samples will be collected, and the samples analyzed according to the methods presented in Task 483DP-22 above. Landfill Gas Probe Installations (12) Twelve additional permanent gas probes (GP-11 through GP-22) are proposed to be installed at the approximate locations shown on Figure 1. The gas probes will be installed as follows: A decontaminated 3 '/4" or 4'/4"diameter auger will be extended with a Geoprobe unit up to eleven feet bgs.The bottom of the PVC well screen will be installed at least two feet or more above the estimated groundwater table elevation. If the estimated groundwater table is expected to be less than 13 ft. bgs, adjustments to the length of well screen will be made. (If the depth to the estimated groundwater is too shallow to allow at least a five-foot distance between the bottom of the bentonite seal and the top of the ground surface, a gas probe will not be installed. The Unit Project Manager will be contacted in this case and a Flux Chamber may be installed (if requested) instead of a gas probe. A one to five-foot long 1-inch diameter,0.010-inch slot screen with 1-inch diameter PVC well casing will be placed into the open boring. o If the well screen is shortened to accommodate shallow groundwater, a push cap will be placed onto the cut bottom of the well screen. o Each gas probe will be fitted with a slip cap outfitted with a quick connect fitting to facilitate sample collection. The inside end of the quick connect fitting will be connected to a section of dedicated Teflon lined tubing that will extend down to the screened interval of each probe. o Coarse sand (#3 sand)will be tremmied into the annulus around the PVC screen and casing from the bottom of the boring up to approximately one foot above the top of the screen. o A one-foot thickness of bentonite pellets will be poured into the boring around the PVC casing from the top of the sand to one foot above the sand. The landfill gas probe will be installed to ensure that there is at least four feet from the top of the bentonite to the ground surface. Approximately one gallon of clean water will be poured into the boring to hydrate the bentonite seal. o Soil from the drill cuttings will be packed into the boring from the top of the bentonite layer to the ground surface. This soil layer will be at least four feet thick. The gas probes will be finished as permeant sampling points with concrete pads, stick-up protective steel casings and locks. Landfill Gas Probe Sampling (12): Landfill gas probes will be sampled and analyzed according to the methods presented in Task 483DP-22 above. Investigative Derived Waste Investigative derived waste (IDW)extracted from a boring will be placed back in the boring unless groundwater was encountered. Per the OCHD Rules, grout will be used to backfill borings that intersect the water table. March 10, 2022 8