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s. f 1 5HP75 t Ed C.ti CEIVE 1-&92 ��SS Stockton Cleanup Summary �� } 1992 M North a SUM ENVIK)NMENTAL HEALTH PERMIT/SERVICES 'rank Removals Two 5000 gallon underground gasoline tanks (C-14) and one 1000 gallon underground waste oil tank (WO-4) was removed on 10-20-86. Calculations by Neinfelder indicate that approximately 170G gallons of gasoline leaked into the surrounding soil. 'there was approximately 1700 cubic yards of soil which was excavated and remediated. Remediation of this soil was completed on 5-17-88. Prior to backfilling the area excavated, vapor extraction pipes were:ns;alled for future use if needed. Soil borings installed on 12-9-86 indicated significant TPH contamination to a depth of 35'. Since this time, sixteen soil borings have been installed to assess the horizontal and vertical extent of soil contamination. Eight monitoring wells have also been installed to assess the possibility and extent of any ground water contamination. One 10000 gallon underground gasoline tank (C-12) was removed on 8-11-88. There was minor contamination around the tank fill. The tank hole was overexcavated around the tank fill end and the soil was remediated. Remediation of this soil was completed on 5-21-88. Monitoring Wells Monitoring.wells 1 and 2 were destroyed when contaminated soil was excavated on 9-31-87. Monitor well 3 is about 35 feet deep and is dry due to a dropping water table. Monitor webs 4 and 5 are 50 feet deep and are also dry. Monitor wells 9, 10 and 1 i are currently being used for quarterly sampling of the ground water. frlonitor wells 9, and 11 have been sampled four times since they were installed on 3-20-90. Monitoring of the ground water has been complicated by frequent changes in the ground water gradient. This is probably because of three large neighboring production wells located within a 3000 foot radius. Problems 1. Trace amounts of benzene showed up three times during"the quarterly samplings. 1 2. There are no monitor wells located south of the tans removal area. In order to prove that their is absolutely no contamination,extending south of the tank removal area, San Joaquin Public Health Services is requesting that we install a monitor -- --- — — --------------- wells) on the-south-border of the property:—This-w1•'.I allow-us tr.absolutely-define- --- the extent of ground water contamination if there is any. r r. ai