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A relatively slow groundwater movement is inferred from the groundwater monitoring and reconnaissance data Overall site groundwater movement is consistently northerly A relatively low gradient, together with the clayey sand aquifer strata, appear to have limited migration of the plume Some northeasterly flow movement at PB-7 may be due to a coarsening of sand which is surmised to have locally increased hydraulic conductivity On the basis of this most recent field work, the plume has moved a total of about 275 feet north of the source and was not detected roughly 300 feet north This plume configuration and length is in our opinion typical for petroleum fuel dissolved plumes in shallow alluvial deposits Sieve analysis and hydrometer data indicate that fine to very fine sand composes the aquifer The hydraulic conductivity estimate for this material may range into the 0 001 to 0 00001 centimeter per second range, supporting this interpretation (Fetter, 1988) Data from PB-9 shows that contaminants were not detected on an assumed northwesterly flow direction from the tank pit Soil samples collected outside of the tank pit vicinity of the former tank location show that contaminants were not detected in the vadose zone soil or near the capillary fringe (at about 8- feet) Previous excavation in the tank area apparently removed vadose zone contaminated sod Wright interprets this data to indicate that the leakage under the tanks probably arrived very near the capillary fringe and then moved away as dissolved components This agrees with the Remediation Risk Management (1993) data and observations of the excavation adjacent to the building during tank removal Remediation Risk Management borings SB-1 and SB-2 revealed that contaminants were not detected in groundwater upgradient of the former tank pit area Conclusions and Recommendations Soil exploratory borings were used to further define the extent of petroleum contaminants in the vicinity of a former underground storage tank location Exploratory soil borings and reconnaissance groundwater sampling show that highly degraded TPHG and BTEX occurs downgradient of the former tank area, with the highest concentrations at PB-4, PB-7 and PB- 8 Contaminant distribution is indicative of a slowly moving plume to the north in groundwater with some north-northeasterly movement near PB-7 The anomalous occurrence of contaminants is not typical of gasoline ranges according to the analytical laboratory, and is therefore interpreted to have arisen from another source other than this site Cleanup actions of further soil excavation do not appear to be warranted given the data presented herein Soil and groundwater extraction and treatment do not appear to be cost effective for the degraded contaminant composition and distribution and pending changes in State guidance Given the degraded BTEX volatile component chemistry of the dissolved plume, Wright feels that natural biologic action will continue to decompose the gasoline, however, continued groundwater monitoring is warranted and the existing groundwater monitoring array may need to be expanded for this purpose Wright recommends that two groundwater monitoring wells be placed downgradient of the former tank location in the following locations, one on Tracy High property, about 75 feet north of the property line (near PB-5), and the other on Heinz property, at the property line (roughly in line with PB-7) (See Figure 3) These wells would be monitored at quarterly .� Mr Ed's Muffler Project No 4090-P Page 6