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� v . A S S O C t A T E S I N C remaining pollutants in groundwater do not create or threaten to create risk to human health or safety — tjc,c , (ZPcA 4A 44A +, NZ<J,;, w,K so,( eft uSt.1, The City of Stockton operated a municipal well approximately 1,200 feet downgradient from the site until the late 1970s when it was shut down because of its brackish and salty content due to its proximity to the Stockton Deep Water Channel ATC contacted Cal Water, the entity that supplies drinking water and operates the municipal supply wells for ' the area of the site Mr Eric Mar, Field Supervisor, said that the water quality in the area of the site is very poor, due to inorganic pollutants from the Stockton Deep Water Channel (nitrates, sulfates, salinity, etc ), and that no future supply wells are planned for that area at this time Because the overall water quality of the basin is poor and no beneficial future use of the basin is planned by the local water provider, the II-year estimate of the MT31) model for contaminants reaching near MCLs in 2015 is acceptable ' —r2-1.7A"� f"� ts-s"-, fir ' e)""1+ "&,fly WJ ¢afL �luK IC rAlj o�5w,o Criterion G. The plume is stable and sufficiently limited in lateral and vertical extent and contaminant concentrations detected in groundwater show a decreasing ' trend with time One hydrologic cycle (four quarters) of monitoring after active remediation measures have ceased is usually considered to be the minimum necessary to determine site groundwater and plume conditions. The plume has been defined vertically and laterally since 1998 The MT313 model (u�shows that hydrocarbon contaminant concentrations will drop significantly for the first -0—f-7 three years followed by constant levels as the plume stabilizes It should be noted that _�,kwkt s•T laboratory analytical data from historical groundwater monitoring events shows that the -tit delre«<�e plume is decreasing in size and TPHg concentrations are decreasing more rapidly than ` W"7 sf ' predicted by the MT31) model This MT31) model simulation represents a very conservative estimation since the extents of the soil contaminant source 4 rbased on laboratory analytical collected in 1995 prior to the startup of soil vapor extraction 17V1 system Based on the results of the model, it is ATC's opinion that one hydrologic cycle of monitoring after active remediation measures have ceased is not necessary and ' the site should be immediately be granted NFA 7.2 Appendix A Check List ' Appendix A of the Tri-Regional Board's recommendations checklist of required data for site closure of USTs has been completed, as appropriate The checklist is included in this report as ' Appendix A 8.0 CONCLUSIONSIRECOMMENDATIONS ' The best available technology, vapor extraction, air sparge, groundwater extraction, and soil excavation and disposal, were used to remediate impacted soil and groundwater at the site Findings of our evaluation concluded that the project site does not appear to represent a W 1271421reportslclosure doc 22 ) 1 N