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Former Beacon Station No.474 April 20, 2000 Stockton California Groundwater Monitoring Report were reported in wells MW-7 and MW-9. A concentration of 28 ppb TBA was detected in monitoring well MW-10. Concentrations of ethanol were detected in groundwater samples from monitoring wells MW-5 MW-12 and air-sparge well AS-1 at 6.0, 36,000, and 69,000 ppb, respectively. Methanol was not detected in any groundwater sample. The lead scavenger compound EDC was detected in monitoring wells MW-3, MW-7, MW- 9, MW-10, MW-11 and vapor well VW-I at concentrations ranging from 0.98 to 1,500 ppb. The EDC concentration in the groundwater sample from monitoring well MW-3 has decreased compared to December I999 analytical results. The EDC concentrations in the groundwater samples from monitoring well MW-7 and MW-9 have increased slightly compared to December 1999 analytical results. The lead scavenger compound EDB was detected in vapor well VW-I at a concentrations of 5,800 ppb. Recommendations Horizon recommends continued quarterly monitoring at the site including groundwater monitoring wells MW-10, MW-11, MW-12 and air-sparge well AS-I installed in October 1999. Horizon shall submit a report describing the well installations and recommendations for additional work, if needed, to complete delineation of gasoline constituents in groundwater. A Problem Assessment Report/Remedial Action Plan shall subsequently be completed to define the problem and recommend remedial actions. Report Distribution We recommend a copy of this report be forwarded to: Mr. Michael J. Infurna Environmental Health Division San Joaquin County Public Health Services P.O. Box 2009 Stockton, California 95201 Mr. Gordon Boggs CRWQCB - Central Valley Region 3443 Routier Road, Suite A Sacramento, California 95827-3098 A:\474\431474QMR00Ql.doc Job No. 1474.43 3 HORIZON ENVIRONMENTAL INC.