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Water Boards <br />EDMUND C. BROWN J H. <br />COVE RHOS <br />MA1T HEY/ RODRIOUEZ <br />LdI SECRETARY FOR <br />FroARORIAERTAL PROS ECTtOti <br />Central Valley Regional Water Quality Control Board <br />12 August 2016 <br />David Guardino and Pat Guardino <br />Guardino and Crawford Construction <br />517 West Fremont Street <br />Stockton, CA 95201 <br />Soil Vapor Investigation Work Plan, Guardino-Crawford Construction, 517 West Fremont <br />Street, Stockton, San Joaquin County <br />California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br />Board) staff reviewed the Soil-Vapor Investigation Work Plan (Work Plan) dated 16 June 2016, <br />and the Semi-Annual Groundwater Monitoring Report — Fourth Quarter 2015 (4Q2015 Report) <br />dated 15 December 2015, both submitted on your behalf by Advanced GeoEnvironmental, Inc. <br />(AGE). I also reviewed the second quarter 2016 groundwater monitoring analytical data tables, <br />provided by AGE via email dated 3 August 2016. <br />In the Work Plan, AGE proposes to install two (2) soil borings for the installation of soil vapor <br />wells to allow for evaluation of risk to human health due to vapor intrusion to indoor air. AGE <br />proposes to install the soil vapor wells using a 3-inch diameter hand auger. Soil borings will be <br />advanced to a total depth of approximately 5.5 feet below ground surface (ft bgs). Soil vapor <br />wells are proposed to be constructed using a 1/4iinch diameter, 2-inch long polyethylene soil <br />vapor implants, and eight feet of %-inch diameter Teflon tubing. <br />AGE proposes to analyze soil vapor samples for: <br />Total petroleum hydrocarbons as gasoline (TPH-G). <br />Benzene, toluene, ethylbenzene, total xylenes (collectively BTEX), and naphthalene. <br />Fuel additives including methyl tertiary butyl ether (MTBE), tertiary-butyl alcohol (TBA), <br />di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), tertiary-amyl methyl ether <br />(TAME), ethylene dibromide (EDB), and 1,2-dichloroethane (1,2-DCA). <br />Percent oxygen. <br />Isopropyl alcohol, which will be used as the tracer compound. <br />I concur with the scope of work presented in the Work Plan. Therefore, by 30 December 2016, <br />submit a soil gas sampling report presenting results of the initial soil gas sampling event. <br />Collection of a second round of soil gas samples will be needed to confirm initial results and <br />should be collected approximately 6 months after the first sampling event. <br />Post remedial concentrations of benzene in well EW-1 continue to increase. Benzene was <br />detected in well EW-1 at 334 ug/L during the second quarter 2016. However, petroleum <br />hydrocarbon concentrations in wells MW-1 and MW-2 decreased between the fourth quarter <br />KARL E. LONGLEY ScD, P.E., CHAIR PAMELA C. CREEOON P.E., BC EE, EXECUTIVE OFFICER <br />11 020 Sun Center Drive #200, Rancho Cordova, CA 95670 I www.waterboards.ca.govicontralvalley <br />CARECYCLED PAPER