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�� <br /> I r 1, , , , , a di>visiQn of **Ot <br /> ENVIRONMENTAL SOLUTIONS r ^„ 17 M n ` W <br /> k� J <br /> " -) P4 1. 05 <br /> April 8, 1998 <br /> Project 20805-146 010 <br /> Mr Ron Rowe <br /> San Joaquin County Public Health Department <br /> Environmental Health Division <br /> P O Box 388 <br /> Stockton, California 95201-0388 <br /> Re Results of Soil Vapor Extraction Assessment, Former ARCO Service Station No <br /> 2168, located at 441 West Charter Way, Stockton, California <br /> Dear Mr Rowe <br /> EMCON has prepared this letter on behalf of ARCO Products Company (ARCO) <br /> presenting the results from the evaluation of the soil vapor extraction (SVE) system <br /> performance at the Former ARCO Service Station No 2168, located at 441 West Charter <br /> Way, Stockton, California The work performed in this letter is based un our telephone <br /> conversation and letter dated January 27, 1998 and February 2, 1998, respectively <br /> As outlined in our February 2, 1998 letter, EMCON shut off the soil vapor extraction <br /> (SVE) system for a three week period to allow for soil vapor concentrations to rebound <br /> Commonly, during SVE activities at a site, the concentrations continue to decline during <br /> SVE operation only to rebound during non-operational periods EMCON has been <br /> operating the system at the site over the past few quarters in an intermittent pulse mode to <br /> account for and treat these episodes of higher concentrations The purpose of this <br /> evaluation was to (1) quantify the arnount of any rtbouna and if present, (2) assess the <br /> length of time required for it to decline back to pre-shutdown levels <br /> Previous Operational Data <br /> Prior to shutting down the SVE system to evaluate the response of petroleum hydrocarbon <br /> concentrations in the vadose zone, EMCON collected background influent samples at the <br /> site in January 1998 The analytical results indicated that influent concentrations were <br /> 1,200 part-per-million by volume (ppniv) for total petroleum hydrocarbons a5 gasoline <br /> (TPHG) and 2 8 ppmv for benzene Table 1 presents the analytical data for the pre- and <br /> post pulse sampling events <br /> t <br /> 5ACV7\F7LFS1ARC0121681JZ0WE2 DOC-951mt1 1 <br /> 3939 Cambridge Road Suite 220 Cameron Park California 95682 (530)676 6884 (530)676-6885 Fax <br />