SITE INFORMATION AND CORRESPONDENCE

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o - San Joaquin County Environmental Health Department DIRECTOR _,•' r�� G 600 East Main Street Donna Heran,REHS Stockton, California 95202-3029 PROGRAM COORDINATORS Robert McClellon,REHS Jeff Carruesco,RENS,RDI cgtfko'a�'�P Website: www.sjgov.org/ehd Kasey Foley,REHS Phone: (209) 468-3420 Fax: (209)464-0138 March 2, 2010 Mr. Gerald L. Thiemann 327 Blossom Drive Ripon, California 95366 Subject: Former Thiemann's Service Station 106 West Second Street Ripon, California 95366 Dear Mr. Thiemann: The San Joaquin County Environmental Health Department (EHD) has reviewed Additional Investigation Work Plan (work plan), dated January 14, 2010, prepared by ATC Associates, Incorporated (ATC) for the above-referenced site on your behalf. The work plan was submitted in response to EHD's letter dated September 24, 2009, and following a meeting at the site attended by you and personnel from the EHD and ATC where the EHD communicated the need to define the petroleum hydrocarbon plume north of monitoring well MW-2 and cone penetration test (CPT) boring CPT3-35. In the work plan, ATC proposes to advance two adjacent borings, one to approximately thirty-eight feet below surface grade (bsg), and one to approximately sixty-three feet bsg using a CPT rig, and collect grab groundwater samples at total depth. The proposal is based on soil lithology from previous CPT bore logs that indicates the presence of a sand layer (and potentially a migration pathway for contaminants) at approximately thirty-eight and sixty-three feet bsg. The paired borings will be advanced at two locations in the grassy area between the curb and sidewalk on the north side of Second Street, opposite the above-referenced site. A third pair of borings, located in the driveway of the Former Madsen's Sunrise Dairy at 239 South Stockton Street, is proposed if contaminants of concern are detected while collecting groundwater samples in the initial four borings. The three locations for the proposed paired borings are illustrated on Figure 2 of the work plan. The EHD approves the work plan as submitted; however, since the work plan inadvertently omitted the analyses proposed for the grab groundwater samples, EHD directs that the samples be analyzed for benzene, toluene, ethylbenzene, and total xylenes (BTEX); and total petroleum hydrocarbons quantified as gasoline (TPHg). In addition to the items to be included in the report of findings and listed as bullets in the work plan, include the comparison of residual contaminant concentrations of TPHg and BTEX to Environmental Screening Levels (ESLs) and California Human Health Screening Levels (CHHSLs) as first requested by the EHD by letter dated September 24, 2009.