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Emergency Remediation 2480 Tracy Blvd., Tracy, CA. • Page 2 BACKGROUND Structures and appurtenances that housed a car wash located at 2480 Tracy Boulevard, Tracy, California were demolished in March of 1996 in preparation for construction of a new car wash and automobile-lubrication service center. During excavation for the foundations and basement of the new facility, gasoline contaminated soil was encountered and identified as such on April 2, 1996. On the same day, a drain field and pump sump were installed in preparation for dewatering during construction and subsequent continuous dewatering during the operating life of the facility. The dewatering system was designed to prevent groundwater seeping into the working area of the lubrication center. A Chevron gas station was previously located on the northeast corner of the intersection of Grant Line Road and Tracy Blvd. That location is approximately 100 feet south and up the groundwater gradient from the 2480 Tracy Blvd. property and is the most likely source of the gasoline encountered in the excavation opened for the new construction on the latter site. No underground storage tanks are present on the 2480 Tracy Boulevard property and an initial review of past uses of the site revealed no evidence of the previous presence of any underground storage tanks or operations involving the use or storage of hydrocarbon fuels at the location. Prior to construction of the car wash facilities that were demolished in March 1996, a small house and corral were located on the property. GEOLOGY AND HYDROGEOLOGY The subject property and the surrounding area are situated on level terrain on the distal, northern slope of an alluvial fan. The underlying alluvial sediments are of Quaternary to Recent age. Observations in the excavation opened for construction of the new car wash and lubrication facilities revealed that the soil beneath the site to a depth of approximately eight feet is a silty clay. Similar clastic materials including: clays, silty clays, sandy clays, silty sands, sands and sands with gravel are known to dominate the regional, near-surface strata to a considerably greater depth than has been exposed by the excavations completed on the site to date. These soil types are distributed in complex lenticular structures over a wide area around the subject property The depth to groundwater in the general area is known to range from 7 to 9 feet. Seasonal variations in the elevation of the groundwater table are typically on the order of one foot. The direction of the groundwater flow beneath the site is to the north. The groundwater gradient at the specific property location is presently unknown.