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. Discussion - Third Quarter Data Groundwater movement is north-northwesterly at a low flow gradient and the flow direction is consistent with historically observed trends The large groundwater mound previously observed at MW-9 has disappeared Concentrations of TPHG were observed in the Wells MW-2, MW-3, MW-6 and MW-9 were slightly lower than the previous sampling round MTBE was not observed in any well "Concentrations at MW-9 decreased roughly to half of the previously observed quarter's amount This supports the increase and decrease of concentrations at MW-9 when groundwater levels rise or fall, indicating residuals are localized at the capillary fringe Contaminant concentrations fluctuation are attributed to winter precipitation recharge and rising water levels which allow more desorption of residual contaminants In our opinion, these concentrations are a degraded fuel and fluctuating concentrations of volatile components which are anticipated to continue an overall declining trend The occurrence of contaminants in MW-6 is currently attributed to an offsite source (presumably from south across East Eleventh Street) since MW-6 is upgradient of the known on-site contaminant source Discussion -Work to Date Overview The contaminants appear to have migrated in a northerly direction from the former tank pd area, with some northeasterly movement Field evidence indicates that the migration in the aquifer has occurred along or just below the capillary fnnge A dissolved plume has moved to the north and crossed the Tracy High School property line, the downgradient edge of which has been defined just across the property line A subsurface imgation line occurs on both the Tracy High and Cox properties and may have influenced the plume migration to move to the north, somewhat parallel to the pipeline course The most elevated TPHG and BTEX concentrations occur roughly in the center of the site This would support a relatively slow northerly movement Again, these concentrations indicate a highly degraded volatile components in the gasoline product, with concentrations declining about one order of magnitude north Chemical analysis of total organic carbon (TOC) indicates that roughly 0 049% TOC occurs in the aquifer, some of which may be related to hydrocarbons The TOC test does not discriminate between indigenous carbon (such as from reduced plant matter) and possible hydrocarbon input The low TOC value is consistent with young (10,000-100,000 years before present) semi-and alluvial sedimentary deposits These environments usually contain only traces of organic carbon due to geologic TOC degradation processes (Hunt, 1972 pp 278-279) A calculation for a site specific retardation factor is not considered feasible since 0 049% TOC falls below 3% TQC (total in soil threshold value considered necessary) for valid retardation computations (Dragun, 1988, pp 242-251) Aquifer Strata A relatively slow groundwater movement is inferred from the groundwater monitoring and boring data Overall site groundwater movement is consistently northerly This shallow aquifer is not known to be a dnnking water source and no pumping wells are known to draw water from this aquifer in the vicinity A relatively low gradient, together with the clayey sand aquifer strata, appear to have limited plume Migration Some northeasterly flow movement may be due to a coarsening of sand which is surmised to have locally increased hydraulic conductivity Sieve analysis and hydrometer data indicate that the aquifer strata are composed of fine to very fine sand A hydraulic conductivity estimate for this material may range into the 0 001 to 0 00001 centimeter per second range, supporting this interpretation (Fetter, 1988) On the basis of this most recent field work, the plume has moved about 275 feet north of the source and was not detected roughly 350 feet Page 6