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ENVIRONMENTAL HEALTH DEPARTMENT PQ�,N SAN JOAQUIN COUNTY aj :< Donna K.Heran,R.E.H.S. Unit Supervisors Director 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. Mike Al Olsen,R.E.H.S. Stockton, California 95202-2708 Huggins,R.E.H.S.,R.D.I. Program Manager Douglas W.Wilson,R.E.H.S. �iFORa Laurie A.Cotulla,R.E.H.s. Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. Program Manager Fax: (209)464-0138 Robert McClellon,R.E.H.S. Mark Barcellos,R.E.H.S. PAUL SUPPLE ARCO PRODUCTS COMPANY [JAN 2 0 2004 P O BOX 6549 MORAGA CA 94570 RE: ARCO 225 Cherokee Lane Lodi, CA San Joaquin County Environmental Health Department(EHD) has reviewed Work Plan for Soil and Groundwater Assessment dated 13 January 2004, prepared by URS Corporation for the above referenced site. The work plan was prepared in response to the EHD directive letter dated 17 November 2003 to investigate the 1,2-dichloroethane (1,2-DCA) detected in ground water samples collected from the three on-site ground water monitoring wells at concentrations as high as 26 micrograms per liter(µg/1). The City of Lodi has a well within 1000 feet of the site that must be protected from this contaminant. URS proposes to advance four soil borings to collect soil and grab groundwater samples to assess for the lateral extent of 1,2-DCA. Based on the data obtained from these borings, URS will design an on-site deep groundwater monitoring well and up to four off- site shallow groundwater monitoring wells if needed. URS proposes to collect soil samples at 10-foot intervals and grab groundwater samples from first ground water. EHD approves the work plan with the following conditions: • Soil samples collected in the saturated zone should be taken at 5-foot intervals to adequately characterize the hydrogeological framework controlling the distribution and migration of the dissolved contaminant and to properly set well screens; • Well screens for all proposed wells should be set in a coarse-grained interval as verified by soil samples; • Care must be taken setting the shallow wells. The boring log for MW-1 indicates wet sand at 65 feet below surface grade (bsg), dry clayey silt at 70 feet bgs, and dry sand at 75 feet bsg. This suggests the possibility that first groundwater may be perched and that MW-1 may be providing a vertical conduit to the underlying sand. MW-2 and MW-3 were also terminated at 75 feet bsg, but soil samples were not collected below 70 feet bsg. The sand interval immediately underlying the existing monitoring wells should also be characterized and assessed onsite and off-site; • A shallow well between the potential source area and the municipal well should be set regardless of the analytical results of the grab ground water sample to act