SITE INFORMATION AND CORRESPONDENCE

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_ SUMMARY OF SITE CON`IjITIONS SITE INFORMATION RESPONSIBLE PARTY Singh's Unocal �{1 ,�� Mr. Satnam Singh Formerly Scotty's s ��l �_� ALJ 574 West Grant Line Road �J — Trac 574 West Grant Line Road Y, California 95376 Tracy, California 95376 O C T - 1 2003 REGULATORY AGENCY ENVIRONMENT HEAL VIRONMENTAL CONSULTANT San Joaquin County Public Health Services PERM IT/SER`VS cience Engineers, Inc. (ASE) Environmental Health Division 208 West El Pintado 304 East Weber Street, Third Floor Danville, CA 94526 Stockton, CA 95202 (925) 820-9391 Mr. Harlin Knoll (209) 468-3442 HISTORICAL EVENTS In March 1998, Aqua Science Engineers, Inc. (ASE) drilled 8 soil borings to assess the soil and groundwater around the underground storage tanks (USTs), dispensers, and piping. Elevated concentrations of total petroleum hydrocarbons as gasoline (TPH-G) and MTBE, benzene, toluene, ethylbenzene, and xylenes (collectively known as MBTEX) were identified in both soil and groundwater samples. In December 1998, the three 8,000 gallon gasoline USTs, dispensers and piping were removed from the site, along with approximately 300 tons of contaminated soil. In early 1999, two 10,000 gallon gasoline USTs were installed in a different portion of the property, along with new underground piping and dispensers. In October 2000, ASE installed five groundwater monitoring wells at the site. In August 2001, ASE installed one additional monitoring well. Since their installation, all six wells have been sampled by ASE on a quarterly basis. Two of these wells show elevated concentrations of TPH-G and MBTEX. The other four wells show only low or no concentrations of TPH-G and MBTEX. -� In August 2002, ASE installed and started an ozone-sparging remediation system to remediate groundwater polluted by petroleum-hydrocarbons and fuel-oxygenates. In February 2003, ASE prepared a report of the first 6-months operation of the ozone-sparging system. The conclusions of that report showed that the system had been effective at reducing the TPH-G and MBTEX concentrations in the groundwater on-site by one to two orders of magnitude, for the most part. In September 2003, ASE prepared a second 6-month report detailing the operation of the ozone- sparging system. Again, the conclusions of that report showed that the system had been effective at reducing or stabilizing the TPH-G and MBTEX concentrations in the groundwater on-site. RECOMMENDATIONS FOR E11111RE, REMEDIAL ACTIVITIES ASE believes that the pilot study has proven that ozone-sparging is an effective remediation tool for reducing petroleum-hydrocarbon and fuel-oxygenate concentrations in groundwater at this site. ASE recommends that the pilot study be concluded, and that the ozone-s p a r g i n g remediation system remain operating on-site until groundwater data confirms that hydrocarbon and oxygenate concentrations are at or below acceptable levels f o r long-term monitoring and eventual case closure. Should you have any questions or comments, please feel free to contact Robert Kitay, R.G. of Aqua Science Engineers, Inc. at (925) 820-9391.