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• petroleum hydrocarbons. Hydrocarbons in the diesel range were detected at a concentration of 590 Mg/1. Twelve soil samples were collected on February 3 , 1992 from the sidewalls of the excavation. No hydrocarbons were detected, confirming the successful removal of contaminated soil . Due to the presence of groundwater in the excavation and the detection of hydrocarbons, the investigation proceeded to an assessment of groundwater contamination. 2 .4 Groundwater Assessment Monitoring wells were installed in May 1992 , and groundwater samples were collected in June. Samples were analyzed for total petroleum hydrocarbons in the gasoline and diesel ranges, and for volatile aromatic hydrocarbons (BTEX) . Diesel was detected in all three wells. Groundwater flow was to the southeast. In the Preliminary Investigation and Evaluation Report dated July 17, 1992 , GeoAudit recommended that groundwater be monitored again within two months . 2 .5 Groundwater Monitoring The second monitoring event took place in September 1992 . Again, groundwater flow was to the southeast. Diesel contamination was again detected in MW-1 , but not in MW-2 or MW-3 . Gasoline-range hydrocarbons were detected in MW-2 . Based on these results, the next monitoring event was scheduled for December 1992 . In the December 1992 monitoring event, the groundwater flow was very similar to that in previous events. However, in contrast to the previous events, no contamination was detected in any of the water samples. The fourth monitoring event occurred in March 1993 . No contamination was detected in any of the samples, and groundwater flow continued to be toward the southeast. Following discussions between Mr . John Urrutia of the Bank of Stockton, Mr. Ron Rinehart of Ned Pepper, Inc. , Mr. Robert Marty and Dr. Victor Cherven of Geological Audit, and Ms. Mary Meays of San Joaquin PHS/EHD over the next few months, a decision was made to continue the groundwater monitoring program for an additional two quarters. 3.0 PROCEDURES 3. 1 Well Purging The fourth monitoring event was conducted on September 15, 1993 . A solznist water level meter was used to measure the depth to water in the three monitoring wells. The standing water was purged using a three--stage purge pump. Water samples were collected after 12 to 14 gallons (approximately six well volumes) of water had been removed and temperature, pH and conductivity of the ground water 4