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. q SHP75 1-6-92 7, VE 1) �5 Stockton Cleanup Summary ` ¢ 992 103!North s street FNIVIRONMCNTAL HEALTH !'�:��MiT/SERl/10ES Tank Removals Two 5000 gallon underground gasoline tanks (C-14) and one 1000 gallon underground waste oil tank (WO-4) was removed on 1020-86. Calculations by Kleinfelder indicate that approximately 1700 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 installed 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 !delis 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 wells 4 and 5 are 50 feet deep and are also dry. Monitor wells 9, 10 and 11 are currently being used for quarterly sampling of the ground water. Monitor wells 9, 10 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. 2. There are no monitor wells located south of the tank 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 well(s) on the south border of the property. This will allow us to absolutely define the extent of ground water contamination if there is any.