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4 5 xi <br /> ccologtralrrcknksln� i Page 16 <br /> Revised Site Conceptual Model Report <br /> Project No.507,2': <br /> April 3,2008 <br /> 7 <br /> Substituting: <br /> V = (0.69 ft/year)x (0.003 ft/ft) _ 4.5x 10"3 ft/year <br /> 0.4583 <br /> Using the value of 4.5x10"3 ft/year it can be theorized that the gasoline contamination would <br /> take 12,222 years to travel the 55"feet from the well MW-9 location to the down gradient <br /> . location of well MW-6 [12,222 x 4:5x10-3 ft/year= 55 feet]. Obviously the seepage velocity <br /> is an underestimate and preferential pathways within higher hydraulically conductive layers <br /> µ are present for more rapid contaminant transport. These calculations show that contaminant <br /> transport will occur but that predictingthe time at which nearby receptors will be impacted is <br /> Y P P <br /> problematic. ;There were no receptor wells utilized for domestic drinking water within the <br /> 2000' survey'radius for the plume to impact. Therefore, the groundwater plume poses <br /> negligible threat to human health for ingestion receptor pathway. <br /> a ' <br /> F The RWCQB-CVR developed the)Water Quality Control Plan for the San Joaquin River <br /> Basin and the plan includes numerical Water Quality Objectives (WQO). The WQO for the <br /> site's COC and their current maximum levels in groundwater are included in the table below: <br /> L COC February 22,2008 WQO <br /> [max. cont. (ig/1)] (RWQCB, Aril 1, 2004 <br /> Gasoline 114,000 : 5 <br /> x Benzene !� 3%200 0.15 <br /> Toluene 6,080 42 <br /> Ethyl benzene 4,600 29 <br /> X lens <br /> 15 000 1 <br /> 17 <br /> F The gasoline and BTEX concentrations exceed the RWQCB-CVR water quality objectives. <br /> L.. It is likely that the core soil plume documented in boring MW-9 soils will continue to <br /> contribute to groundwater contaminant levels above the WQO if not addressed. <br /> € 3.0 POTENTIAL OFF-SITE SOURCES OF CONTAMINATION <br /> I� <br /> GTI reviewed the State GeoTracker database for potential off site sources of contamination. <br /> Five parcels were identified in the immediate vicinity of the subject site with documented <br /> hazardous materials releases. The following list of nearby properties was identified as <br /> potential sources of contamination;from the GeoTracker database. The sites' report sheets <br /> and location map are included in Appendix I: <br /> • Independent Tracking(case closed), 1145 W Charter Way, Stockton, CA 95206 <br /> • Mid Cal Tractor(case closed), 1120 W Charter Way, Stockton, CA 95206 <br /> • Central Distributing (case closed), 1100 W Charter Way, Stockton, CA 95206 <br /> • Woolsey Oil (case open), 1501 W Charter Way, Stockton,CA 95206 <br /> • Stockton Scavenger Association(case open), 1240 Navy Drive, Stockton, CA 95205 <br /> - The above sites do not appear to contribute to the documented on site contamination. <br />