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Report: Groundwater-quality Monitoring—July 14-15,2006, 7500 West Eleventh Street, Tracy, CA. page 7 Repo 9 tY g diameter of Monitoring Well MW-7, SJC was concerned that the intermittent rounds of LNAPL purging from that well would not be successful in removing floating product from more than a limited area of the subsurface within close proximity to that well and that such any limited effect would be temporary. This assessment was supported by the steady increase in concentrations of fuel hydrocarbons in samples of groundwater recovered from MW-7 in the period following January 2004, when the quality of groundwater in that well was first analyzed following completion of the purging program. Unfortunately, despite quarterly purging of Monitoring Well MW-7 since that time; minor thicknesses of floating product, up to 0.14 ft., have periodically reappeared in that well (see Table 3). 1.6.2 Secondary Plume A secondary plume of diesel and gasoline, as shown on Figure 3, emanates from an area to the rear and slightly to the east of the Casa Mendoza restaurant on the 7500 West Eleventh Street property. Although no physical evidence of an underground or above- ground storage tank has been found there, it appears that, at some time in the past, there was a source of fuel hydrocarbons located in the vicinity of Monitoring Wells MW-12 and MW-12A (see Figure 3 for locations). When the 6,000 linear feet of underground piping that was found beneath the Navarra Site was removed in December 1998, a disconnected pipeline was discovered that ran from the general area of those monitoring wells toward the West Eleventh Street frontage of the property where the underground (� storage tanks that were removed at that time were located. As shown on Figure 2, underground fuel tanks were formerly located on the property at 24195 Chrisman Road, which adjoins the 7500 West Eleventh Street site to the south. They had contained diesel and were removed in December 1998. Although no additional investigation of the 24195 Chrisman Road site has been performed, SJC believes that because samples recovered from the bottom of the tank pit at the time of removal contained only low concentrations of diesel (Dietz Irrigation 1999b), it is likely that any contribution made by diesel migrating from the 24195 Chrisman Road site to the subject property would have had little, if any, deleterious effect on the environmental condition of the subsurface beneath the subject property. 1.6.3 Dispersed Petroleum Hydrocarbons in Shallow Soils Finally, there are dispersed, low concentrations of a variety of hydrocarbons affecting wide areas of shallow soil beneath the 7500 West Eleventh Street property and nearby land. Their presence can be attributed, in some instances, to hydrocarbons that have a vegetative source rather than being related to releases of fuels, while in others, they can be attributed to minor leaks and spills from vehicles using unpaved areas of the former service station and being parked on the shoulders of the streets over past decades. _ Evidence has also been found that fill used to bring West Eleventh Street, Chrisman Road and some of the adjoining sites to their present grade included some debris from bituminous macadam paving (The San Joaquin Company 2002). To provide for clarity of the presentation of the primary and secondary plumes of affected groundwater emanating sic