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Geospte& consultants groundwater, and monitoring well groundwater sample locations. A Sampling Plan Summary is provided in Table 1 which identifies the proposed sampling depths. Geosyntec will contract with a California-licensed C-57 drilling contractor to advance the boring locations using a direct push technology (DPT) drilling rig. At each location, existing asphalt or concrete surfaces, if applicable, will be cored to provide access to the underlying soil. If there is any indication of sub-surface utilities based on the USA markings or private utility survey, the first five feet of the borings will be advanced using a hand auger to safeguard against potential subsurface utilities. If USA and the private utility survey do not indicate the presence of subsurface utilities, borings will be advanced from ground surface with the DPT drilling rig. Borings may require relocation within a five-foot radius if sub-surface obstructions are noted or drilling refusal is encountered. Borings advanced may serve multiple purposes; soil, grab groundwater, and soil vapor samples may be collected from a single boring. Samples will be labeled, handled, and analyzed as described in Section 4.2.5. Sample container requirements, holding times, and preservation requirements are outlined in Table 2. Quality assurance/quality control (QA/QC) samples will be collected as outlined in Section 3.3. 4.2.1 Soil Sampling Soil samples are proposed to be collected from a total of 11 borings. Soil samples will be collected from the vadose zone at depths of 2, 4, and 6 feet bgs. If a hand auger is utilized to advance the upper five feet of the boring, the hand auger will be advanced to a depth of 2 and 4 feet bgs, and an undisturbed soil core sample will be collected into a stainless-steel sleeve via a slide hammer. The remainder of the borehole will be advanced via DPT drilling rig. Where DPT drilling is utilized, soil cores will be collected from the borings using dual-tube direct-push technology. The dual-tube sampling involves advancing a 2-inch- diameter, hollow steel direct-push rods fitted with an acetate liner. The recovered soil will be field-screened for VOCs using a photoionization detector(PID) and visually logged using the Unified Soil Classification System(USCS)by a Geosyntec field geologist or engineer, under the supervision of a California-licensed Professional Geologist. Soil samples will be analyzed as outlined in Table 1. Soil samples for analysis of VOCs and TPH-g will be collected directly from the stainless-steel sleeve or acetate liner using disposable, laboratory-supplied Terra-CoreTM samplers, and placed into 40-milliliter vials in accordance with the United States Environmental Protection Agency (USEPA) Method 5035A. A new Terra- CoreTM plunger will be used to collect each soil sample. Soil samples to be analyzed for TPH-d will be collected directly from the stainless-steel sleeve or acetate liner and placed into laboratory-supplied glass jars. 4.2.2 Grab Groundwater Sampling A total of five grab groundwater samples will be collected as outlined in Table 1. Borings will be advanced with DPT to a minimum depth of five feet past first encountered groundwater to facilitate the collection of grab groundwater samples. The sampling method will include installing temporary polyvinyl chloride (PVC) casing in the boring that is slotted across the saturated zone. The perforated portion of the well screen or screen-point sampler is anticipated to Investigation Work Plan—UST 817B 7 December 2024