SITE INFORMATION AND CORRESPONDENCE_FILE 2

Home Browse Search

Jamar Service Station Page 2 of 4 4075 East Main Street April 13, 2015 Stockton, California 95215 • Prior to collecting soil gas samples, collect a material blank employing manifolds, tubing, and plastic-screen-tip probes as will be used in the field and analyze the material blank for contaminants of concern by EPA Method TO-15; • Following installation of each soil vapor probe assembly, wait a minimum of two hours before performing a five-minute shut-in test; • Once the shut-in test has demonstrated that there is no leak in the above-ground sampling system, purge three volumes from the vapor probe assembly using a syringe; Cardno clarified that the purge volume calculations will be based on "the internal volume of tubing and annular space around the probe tip and the tubing volume of the above-ground assembly"; • Following purging of the vapor probe assembly, collect soil gas samples, including one duplicate, into a four-hundred milliliter Summa canister while using 1,1-difluoroethane (1,1-DFA) for a leak detector and analyze the soil gas samples by EPA Method TO-15; a trip blank will also be analyzed for contaminants of concern by EPA Method TO-15; • Remove the vapor probe assembly and all installed materials by either direct push drill technology or hand auger and backfill the borehole with neat portland cement from total depth to ground surface following the collection of soil gas samples; • Compare soil gas analytical results to values listed in Table 2 of Tier 1 Environmental Screening Levels (ESLs) published by the San Francisco Bay Regional Water Quality Control Board in November 2007, and California Human Health Screening Levels (CHHSLs) published by CA-EPA in January 2005; and if concentrations of contaminants of concern exceed the ESLs and/or CHHSLs, use the Johnson and Ettinger Vapor Intrusion Model for Soil Vapor Emission to Indoor Air Risk Assessment as appropriate for Residential Exposure Scenario for High Permeability (Sandy) Soils, Version 1.0 (2005) to evaluate the Hazard Quotient for carcinogens; and • Submit a report of findings. The EHD approves the Work Plan with the following conditions: • When constructing the vapor probe assembly, the probe tip, probe and probe connectors should all have the same diameters; place the probe tip midway in the sand pack consisting of a minimum thickness of six inches; emplace at least six inches of dry granular bentonite on top of each sand layer to prevent hydrated bentonite from infiltrating the sand pack, and use a shroud with the leak detector 1,1-DFA when collecting soil gas samples; • If equipment is reused, collect one equipment blank from the decontaminated equipment; • When calculating the purge volume, include the void space of the dry bentonite in addition to the void space of the sand pack around the probe tip;