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Ms. Marilyn Petruescu <br /> September 30, 2024 <br /> Soil Boring Advancement <br /> Three soil borings (BH-1 B, BH-21B, and BH-31B) are proposed in the vicinity of the UST excavation to confirm the <br /> current concentration of petroleum hydrocarbons in soil. Soil borings will be advanced by a C-57 licensed drilling <br /> contractor to an approximate depth of 35 feet bgs. The approximate proposed soil boring locations are shown on <br /> Figure 4. <br /> During soil boring advancement, soil will be continuously logged using the modified Udden-Wenworth grade scale <br /> and will be collected for field screening with a photo-ionization detector(PID). Soil screening procedures will <br /> involve measuring approximately 30 grams of soil from a relatively undisturbed soil sample and placing the soil in <br /> a resealable plastic bag. The bag will be warmed in the sun for approximately five minutes and the head space <br /> within the bag will be tested for total organic vapor, measured in parts per million (ppm). The PID results will be <br /> noted on the field boring logs. <br /> Soil samples will be collected from each boring every five feet and from the capillary fringe. Additional soil <br /> samples will be collected based on visual evidence of staining, odor, and/or elevated PID measurements, if <br /> necessary. <br /> Soil samples will be labeled, logged on a chain-of-custody form, and placed in an ice-chilled cooler for transport to <br /> a California-accredited analytical laboratory for analysis. The soil samples will be analyzed for: <br /> • TPHg TPHd, and TPH as motor oil (TPHo) by United States Environmental Protection Agency(USEPA) <br /> Test Method 8015B, and <br /> • BTEX, naphthalene, methyl tert-butyl ether(MTBE), and 1,2-dichloroethane (1,2-DCA) by USEPA Test <br /> Method 8260B. <br /> Field activities will be completed under the direct supervision of a State of California licensed Professional <br /> Geologist. <br /> Well Installation <br /> Two monitoring wells (MW-1 R and MW-4) are proposed to further characterize and evaluate concentrations of <br /> petroleum hydrocarbons in groundwater. Each 8-inch boring be advanced by a C-57 licensed drilling contractor to <br /> an approximate depth of 25 feet bgs, or approximately five feet into first encountered groundwater, via hollow <br /> stem auger drilling technique. The proposed monitoring well locations are shown on Figure 4. <br /> Similar to the soil borings, soil from each monitoring well boring will be continuously logged using the modified <br /> Udden-Wenworth grade scale and will be collected for field screening with a PID. The PID results will be noted on <br /> the field boring logs. <br /> Soil samples will be collected from each boring at depths of 5 and 10 feet, and from the groundwater capillary <br /> fringe. Soil samples will be labeled with a unique sample ID and placed into an ice-filled cooler for transportation <br /> to a State-certified laboratory under chain-of-custody protocol. The soil samples will be analyzed for: <br /> • TPHg TPHd, and TPHo by USEPA Test Method 8015B, and <br /> • BTEX, naphthalene, MTBE, and 1,2-DCA by USEPA Test Method 8260B. <br /> www.arcadis.com 4/7 <br /> Lathrop UST Site Investigation and Well Installation WP 9.30.24_final <br />