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ENVIRONMENTAL HEALTHY)EPARTMENT <br /> aaU`" SAN JOAQUIN COUNTY <br /> �o.•`�}.coG Unit Supervisors <br /> '1 Donna K.Heran,R.E.H.S. 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> .� <br /> y: Director Mike Huggins,R.E.H.S.,R.B.t. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> • �.. �P • Program Manager Telephone. (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Qki....... Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 a MBarcellos,R.E.H.S. <br /> SEP 2 2002 <br /> Mike Wallace Mr. Jeffery Setness B <br /> nd F1 <br /> City of Stockton Redevelopment 2453 Grand Canal, 2 <br /> 305 North El Dorado, Suite 200 Stockton, CA 95207-8259 <br /> Stockton, CA 95202 <br /> RE: FORMER CHASE CHEVROLET FACILITY 423 MADISON <br /> 424 VAN BUREN <br /> STOCKTON, CA 95201 STOCKTON, CA 95201 <br /> Since removal of the underground storage tanks (UST) at the two above-referenced sites in <br /> 1989, a total of 27 monitoring wells have been installed on the sites. Earliest analytical <br /> results of groundwater samples collected from a monitoring well dated back to September <br /> 1990,and continuous quarterly sampling had been conducted since 1992. Concentrations of <br /> contaminants in groundwater samples have either fallen or stabilized over the years; <br /> however, some of the reduction may be attributed to the rise of groundwater and drowning <br /> of monitoring well screen. (Table 1) <br /> Table 1: Analytical Results of Total Petroleum Hydrocarbons as Gasoline (ITH-g) of MW6, <br /> MW-7,MW-1,MW-4 MW-4 <br /> Sam le location MW-6 MW-7 MW-1 <br /> 20' to 45' 20' to 45' �' 19' to 46' 20' to 45' <br /> Screen len th 710 <br /> 02/27/92 results/ 12,000 21,000 5,800 210 bs <br /> De th to Groundwater 27.73'bs 28.08' bs 27.32'bs ND <bs <br /> 11/06/96 results/ 5,100 14,000 1,300 <br /> 50 <br /> De th to Groundwater 21.08' bs 21.31'bs 21.46' bs ND2' bs <br /> <50 <br /> 02/05/97 results/ 830 6,700 850 <br /> De th to Groundwater 16.03' bs 16.25' bs 16.33'bs 16.30'bs <br /> 05/16/02 results/ 96 160 ND c50 ND c50 <br /> De th to Groundwater 16.46'bs 16.70' bs 16.82'bs <br /> 16.70'bs <br /> All results in micrograms per liter (µg/1) <br /> During a meeting at the Advanced GeoEnvirontnental,Inc. (AGE) office in Stockton on <br /> September 25,2002, San Joaquin County Environmental Health Department (EHD) and <br /> AGE agreed that continuous quarterly sampling of every monitoring well is neither <br /> necessary nor cost-effective, and the sampling schedule should be adjusted as follows: 1) <br /> Annual sampling of monitoring wells with historically non-detectable concentrations located <br /> in an upgradient direction or not in the critical flow path. 2) Semi-annual sampling of <br /> monitoring wells with consistent historically positive contaminant concentrations,and 3) <br /> i <br /> r <br /> I <br />