SITE INFORMATION AND CORRESPONDENCE FILE 2

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WWI -Wo San Joaquin County Environmental Health Department DIRECTOR ).• —,.�� .O Donna Heran,RENS Z.' i 600 East Main Street Q. PROGRAM COORDINATORS U). :� Stockton, California 95202-3029 Robert McClellon, REHS Jeff Carruesco,REHS, RDI r` Kase Foley,REHS cq�iFo'Rc'�P Website: www.sjgov.org/eiid v y' Phone: (209) 468-3420 Fax: (209) 464-0138 April 15, 2010 Mr. Dan Silva Ms. Tina Mayhew West Clay Properties Post Office Box 6152 Stockton, California 95206 Subject: West Clay Properties 639 West Clay Street Stockton, California 95206 Dear Ms. Mayhew and Mr. Silva: The San Joaquin County Environmental Health Department (EHD) has reviewed Monitoring Well Installation Work Plan, dated February 22, 2010, prepared and submitted by Advanced GeoEnvironmental, Inc. (AGE) on your behalf for the above-referenced site. In the work plan, AGE proposes to install two monitoring wells at locations illustrated on Figure 2. Proposed well MW-27 will be screened from approximately forty to sixty feet below surface grade (bsg), and proposed well MW-28 will be screened from approximately sixty-five to seventy-five feet bsg, contingent upon hydrogeologic/geologic conditions observed during the well installations. The EHD approves the installation of the two proposed monitoring wells as described in the work plan to delineate the lateral extent of groundwater contamination down-gradient of MW-14B and east of MW-1; however, the EHD believes an additional monitoring well, screened between approximately forty and sixty feet bsg, is needed in the area of MW-5 to delineate the contaminant plume in the hydrological unit identified by AGE as HU2. Monitoring wells MW-1 and MW-2, the two most impacted wells at this site, are both screened within hydrological unit HU2, with screen intervals from approximately forty to sixty feet bsg. MW-5 is screened within hydrological unit HU1, with a screen interval from approximately fifteen to thirty-five feet bsg. Since 2001, the groundwater samples collected from MW-5 have been non-detect. Also, soil samples collected in the hydrological unit HU1 at twenty-five and thirty feet bsg, during the advancement of borehole B6 near MW-5, were non-detect for chemicals of concern; however, two additional borings, B14 and B15, advanced in the same area as MW-5 and B6, had positive results for petroleum hydrocarbon contaminants in soil samples collected in hydrological unit HU2 at approximately fifty feet bsg. The EHD first proposed installing additional wells in the area of B15 and north of MW-8B by letter dated May 19, 2009. The FHn still hP.IIPVPs a well is needed near MW-5 and will decide if an additional well.