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ftp©WN AND CALDWI:t.l. _— <br /> CONSULTING ENGINEERS <br /> I <br /> I i <br /> November 8, 1988 <br /> i <br /> 3 <br /> C <br /> Mr. Kyle Christie <br /> r- ARCO Products Company <br /> e 2000 Alameda de las Pulgas <br /> Post Office Box 5811 <br /> s San Mateo, California 94403 017-3214-I6/1 <br /> u <br /> P I ; <br /> {; 5ubject: Progress R;:port for ARCO Station 434, Lodi, California <br /> { Dear Mr. Christie: <br /> 1 f <br /> >. , . In April 1988, the California Regional Water Quality Control -Board, Central Valley Region <br /> I (Regional Board), requested ARCO Products Company (ARCO) to install monitoring wells <br /> 4- <br /> screened at discrete depth-specific intervals at the slbject site. The purpose of the <br /> Regional Board's mquest for depth-specific monitoring wells was to determine tho vertical <br /> VI. <br /> extent of dissolved hydrocarbons in the groundwater beneath Station 434 before approving <br /> Brown and Caldwell's (BC) planned extraction well and groundwater treatment system. <br /> Figure 1 shows the locations of all monitoring wells installed to date, benzene <br /> f <br /> concentrations in groundwater from these wells between April 1987 and June 1888, and the <br /> direction(s) of groundwater flow. <br /> i4i <br /> On June 15, 1988,.the Regional Board approved BC's work plan (Exhibit A) to install two <br /> depth-specific monitoring wells adjacent to monitoring well W-2. During each groundwater <br /> sampling event, the highest dissolved benzene concentrations in groundwater have been <br /> from monitoring well W-2. The two depth-specific wells were installed and sampled in <br /> z ry late June 1988. This report presents the results of the June 1988 work preceded by a <br /> i <br /> project states summary. <br /> Project Status Summary <br /> { ' P2t This summary includes a discussion of groundwater flow directions, dissolved hydrocarbon <br /> occurrence, the occlurence of free product in on-site monitoring wells, and the extent of <br /> } ' known soil contamination at the site. <br /> -- — - <br /> Groundwater Flow Directions. Measurements of water levels rn on= an off=site <br /> Erionitodng wells are included in Exhibit B. Five contour maps (at approximately quarterly <br /> intervals) constructed from these water level data are included as Exhibit C. Water level <br /> . . measurements from monitoring wells W-1 through W-8 were used in constructing these <br /> k contour maps, .ns these wells are all screened.across the same depth interval, from about <br /> - <br /> ' 7�3991Rf5T BACi?AMENTO,CALIFORNU95E11.7092•(916�M1.0123 <br /> I' A <br />