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1 . encountered in the groundwater. Minor levels of gasoline, 2,700 ppb, are described in Advanced's report to be at the volatile end of diesel 1 The USTs, which were the focus of the Advanced's investigation, were removed in February and October of 1998 The diesel UST located in the southern portion of the property was removed in February of 1998, and the USTs located in the UST farm situated in the northern portion of the property were removed in October of 1998 Elevated levels 1 of contamination, 240,000 ppb diesel, were encountered in the southern diesel UST area As groundwater is at approximately nine feet below ground surface(bgs), the groundwater sample was collected directly from the UST pit excavation Elevated levels of hydrocarbons were also found in the soil and groundwater in the northern UST pit area Water samples were collected directly from the UST pit and the results were as follows 100,000 ppb TPH gasoline, 31,000 ppb MTBE,4,600 ppb Benzene, 16,000 ppb Toluene, 3,000 ppb Ethyl Benzene, and 170,000 ppb Xylenes. Additionally, a small hole was discovered in the unleaded UST during the removal In November of 1998, Avalon, drilled fifteen geoprobe borings on the subject property a and tested soil and groundwater. Elevated levels of MTBE were found in the groundwater in the area of the former, northern UST area While the southern UST area did contain some contamination it appeared to be-minor in nature. The detections of MTBE in the northern UST area prompted the initiation of a groundwater investigation on the subject property - i In March of 2000, Avalon, installed six groundwater monitoring wells on the subject property This investigation was undertaken in order to determine the groundwater gradient direction and to determine the levels of MTBE and other Oxygenates in the groundwater The results of the groundwater investigation and subsequent four quarters of monitoring indicate a north/northeast gradient direction The groundwater monitoring wells confirm that the primary area of impact is the northwest portion of the subject property in the area of the former gasoline USTs referred to as the northern UST area Due to the elevated levels of MTBE along the northern boundary of the subject property, the Sanjoaquin County Environmental Health Department requested that offsite sampling be initiated to determine if an offsite impact had occurred In April 2001, Avalon, drilled ten geoprobe borings both on the subject property and offsite Four geoprobe borings were drilled on the subject property and six were drill offsite and to the northeast of the subject property All borings were advanced to depths of 20 feet bgs All of the borings were continuous cores with plastic liners Groundwater samples were collected from nine of the ten borings. Laboratory analytical results showed detections of MTBE in all samples analyzed Additionally, select groundwater samples also contained Toluene, TAME, Tert Butanol, Methanol, and Ethanol Levels of MTBE Avalon Environmental Consultants 9627-001-7 Joe's Truck Plaza May I5,2002 15600 S Harlan Road Lathrop,California 2