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MEMORANDUM - : � . - •F � <br />: CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENT <br /> RAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 255-3000 <br /> Sacramento, California 95827-3098 CALNET: 8-494-3000 it <br /> TO: EAT,GLB FFI OM: AEG <br /> Underground Tank Unit <br /> k, <br /> DATE: 29 June 1995 SIGNATURE: D• ..— �,✓ <br /> >. <br /> SUBJECT: REQUEST FOR CLOSURE, FORMER UNOCAL STATION,'3778 TRACY' <br /> BOULEVARD, TRACY, SAN JOAQUIN COUNTY <br /> _ ,�- - - .�;....,. -- ,....-_._. •,-,-- -'mow...... �.'.,......�...-. . _ _. ---� <br /> A closure report was submitted by Mittelhauser Corporation (Mittelhauser) in March 1995, which <br /> contained all the information required in Appendix B to the Tri-Regional Guidelines. Three <br /> underground storage tanks were removed from the site. One 550 gallon waste oil'tank was <br /> removed in June 1990. The pit was excavated to 14.5 feet, where ground water was encountered. <br /> One sample, taken during the excavation, showed halogenated volatile organics at 10 feet. One <br /> bottom soil sample indicated 3.7 parts per million (ppm)Total Extractable Petroleum <br /> Hydrocarbons (TEPH) at 14 feet and three sidewall samples showed up to 270 ppm TEPH at 12.5 <br /> feet. Ground water in the pit was not sampled at that time. <br /> Two 10,000 gallon gasoline USTs, associated piping and two dispenser islands were removed in <br /> December 1992. Over excavation of the pit was performed in January 1993. Approximately <br /> 1,900 cubic yards of soil was removed. Mittelhauser calculated the mass balance of gasoline at <br /> approximately 100 gallons, from excavated soil: Confirmation samples indicated up to 43 ppm <br /> TPHg at 3 feet, benzene at up to .070 ppm at 8.5 feet and .009 ppm at 12.5 feet, and up to 16 ppm <br /> total oil and grease at 8.5 feet remain. <br /> An area used to store oil drums was also excavated to approximately 10 feet below grade. Five <br /> -- �. confirmation samples were taken, indicating less that 20 ppm total oil and grease. <br /> = - . <br /> Five monitoring wells were installed on-site. The depth to ground water has fluctuated between 8 <br /> to 10 feet below grade. The last recorded ground water flow direction was north/northeast, but <br /> flow direction has been recorded to fluctuate almost 90° between northeast and northwest. Ground <br /> water samples from the monitoring wells showed non-detect for all petroleum constituents during <br /> four consecutive quarters from December 1993 to September 1994. <br /> In February 1995, four confirmation'soil borings and one Hydropunch® were drilled at the site. <br /> The borings were sampled at 5 and 10 feet and were analyzed for chlorinated halocarbons by EPA <br /> Methods 8240 and 8270, TPHg, benzene, toluene, ethylbenzene, xylenes and total`oil and grease. <br /> All sampled showed non-detectable concentrations. The ground water sample from the' <br /> Hydropunch® was analyzed for chlorinated hydrocarbons and indicated non-detectable <br /> concentrations. <br /> WEG <br />