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U IV�Pp'17O A 9c THS SAN JOAQ ll�l CD 4602 U 1 1 20 HOLLYWOOD VENUF.SUITE 3,QAK1-ANL?,CA'IFO IJ NOV U 7 2001 San Joaquin County Public Health Services ENVi; ,!i1;. ; HEALTH Environmental Health Division PEP,10i 1,_,jqV10ES Third Floor 304 East Weber Avenue Stockton,CA 95202 Date: November 2, 2001 Attn.: Ms. Rebecca Setliff, EHS Your Reference: Site Code 1392 SUBJECT: Work Plan for Extended Site Characterization: Navarra Property, 7500 Eleventh Street, Tracy,California 95376 Dear Ms. Setliff: We have received a copy of your letter of October 26, 2001 that was addressed to our client, Mr. Carl Navarra, regarding our Work Plan for Extended Site Characterization at Former Fueling Station, 7500 West Eleventh Street, Tracy, California, which was submitted to your office for review on October 17,2001. We have the following comments regarding the items in your letter. TWO DISCRETELY-SCREENED WELLS AT LOCATION OF PROPOSED WELL MW-I 1 We doubt that installation of two wells at the location of proposed well MW-11 described in the work plan will be cost effective in providing significant additional information of import ppears to ance to an understanding of the characteristics of the secondary plume of contamination that a have originated in that area. However, to be responsive to your request, we will modify the design Of well MW-11 as it is currently proposed so that it will have a total depth of 23 ft. and will be screened in the interval between 7 and 22 ft. In addition, we now plan to install an additional well - to be designated well MW-IIA — in close proximity to MW-I 1. MW-1 IA will have a total depth of 36 ft. and will be screened over the interval 30 to 35 ft. LOCATION OF PROPOSED WELL MW-9 You recommend that MW-9 be located further south than the location shown on Figure 2 of the work plan because, it appears, you believe such location would be useful in assessing the J potential for contaminated groundwater to affect the water-supply well at 23950 Chrisman Road. As was discussed in Section 6.3.3 of the work plan, our reasoning for installing monitoring well MW-9 in the location shown on Figure 2 was to investigate whether or not the down-gradient migration of the contaminant plume had reached that distance along its axial direction of flow, which, to within a reasonable degree of confidence, has been established from the characteristics of the hydrogeologicaI regime and the soil and groundwater chemistry that have been obtained from the site characterization work completed to date. Those data indicate that the central axis of the contaminant plume (i.e., the line along which contaminant concentrations will be at their highest compared to those on either side of that line at any given down-gradient distance from the TELEPHONE: OAKLAND,CALIFORNIA(51 O)336-91 IS TRACY. CALIFORNIA(209)832-29 1 O