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San Joaquin County DIRECTOR <br /> Donna Heran,REHS <br /> Environmental Health Depnartment <br /> OG M ASSISTANT DIRECTOR <br /> 2`' 2 600 East Main Street Laurie Cotulla, REHS <br /> :{ Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> • Carl Borgman, REHS <br /> Website: <br /> Mike Huggins, REHS, RDI <br /> FR� <br /> o. \P wwwsjgov.org/ehd Margaret Lagorio, REHS <br /> Phone: (209) 468-3420 Robert McClellon, REHS <br /> Fax: (209) 464-0138 .teff Carruesco,REHS,RDI <br /> Kasey Foley,REHS <br /> MR RUSSEL CHAPIN ?JUL 2 6 2007 <br /> CHAPIN BROTHERS, INC <br /> 1203 N CARLTON AVE <br /> STOCKTON CA 95203 <br /> RE: CHAPIN BROTHERS Site Code: 0850 <br /> 1766 MONTE DIABLO AVENUE <br /> STOCKTON, CA <br /> The San Joaquin County Environmental Health Department (EHD) has received <br /> and reviewed Quarterly Report— First Quarter 2007 (QR1), dated 04 June 2007, <br /> and Quarterly Report — Second Quarter 2007 (QR2), dated 10 July 2007, both <br /> prepared by Advanced GeoEnviron mental, Inc. (AGE). In both QR1 and QR2, <br /> AGE recommends continuation of quarterly monitoring and initiation of renewed <br /> groundwater extraction (GWE) utilizing the recently installed groundwater <br /> extraction wells EW-4, EW-5 and EW-6. AGE also recommended in QR2 <br /> additional site assessment "if required" through collection of soil, soil gas and <br /> groundwater samples from 'high-resolution' transects across the site and also, 'if <br /> needed', collection of soil gas samples under the structure on the site. <br /> QR1 included a vapor intrusion evaluation for your site and concluded that <br /> contaminant concentrations in soil and groundwater did not pose a significant risk <br /> of vapor intrusion into on-site structures. However, the benzene concentration of <br /> 5,200 micrograms per liter detected in the EW-4 groundwater sample in May <br /> 2007 does exceed the environmental screening level (ESL) for vapor intrusion <br /> into structures. <br /> The contaminant concentration trends in the wells monitored since the <br /> groundwater extraction system was turned off in May 2005 do not exhibit <br /> continual and constant declines and the newly installed wells are impacted by <br /> significant concentrations of the chemicals of concern (COC). Based on the <br /> dissolved benzene concentrations exceeding the vapor intrusion ESL and the <br /> persistent high dissolved COC concentrations the EHD concurs with the <br /> recommendations advanced by AGE. Provide a work plan to the EHD by 17 <br /> September 2007 to integrate the new extraction wells into the GWE system and <br /> initiate groundwater extraction and treatment. Continue the groundwater <br /> monitoring program. <br />