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Emergency Remediation - 2480 Tracy Blvd., Tracy, CA. • Page 7 property. These soil types are distributed in complex lenticular structures over a wide area around the site. 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 general direction of the groundwater flow beneath the site is to the north toward the Old River anastomotic branch of the San Joaquin River. The Old River watercourse is approximately 2.75 miles down gradient. The precise site-specific groundwater gradient is presently unknown. Soil Sampling To investigate the areal extent over which the subsurface of the 2480 Tracy.Boulevard site is affected by hydrocarbons and to confirm that the gasoline has migrated there from the adjacent up-gradient property, which is an officially-recognized site of an unauthorized release of hydrocarbon fuels, a total of nine sampling locations were selected. Six of these were on the subject property and, with the consent of the owner, three were located on an unpaved area on the former site of the Chevron station at 575 West Grant Line Road. The sampling locations are shown on Figure 2. ' The soil samples were recovered from depths between seven and ten feet by a 0.5 in- internal diameter push-probe sampler advanced by a drill rig operated by Spectrum Exploration Inc. of Stockton, California. That company holds the requisite C57 license issued by the California Contractors State License Board. The relative elevations of the maximum depths of penetration of the probe were determined from the length of the drill-string and the surface elevation, measured relative to a temporary benchmark established by the general construction contractor's surveyor on a concrete curb running along the north perimeter of the site. Following sample recovery, each 18 in.-long, plastic push-probe sample liner was cleaned externally and its ends closed by plastic caps secured with adhesiveless tape. The top of each liner was marked so that the in-situ, vertical orientation of the samples could be identified. Each sample liner was then labeled for identification, entered into chain-of- custody control, and packed on chemical ice for transport to Chromalab Inc.'s laboratory in Pleasanton, California for analysis. Before the drill rig was moved from one sampling location to another, the sampling tools and the drill stem were steam cleaned. Upon completion of sampling, the push probe holes were sealed with hydrated bentonite. Mr. Harlan Knoll of the SJCPHS was present to observe the sampling operations and approve the probe-hole seals.