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LW (4010gkAl TeAIIXS Inc. Page 15 Revised Site Conceptual Model Report Project No.507.2 c.. April 3,2008 W To meet the survey objective,the following tasks were performed: o Geological Technics Inc. personnel reconnoitered the site on September 18, 2000 to make a physical search for any wells in the area. o Specific well logs were requested from the State of California Department of Water Resources (DWR) both to aid in identifying local wells and to specify their construction details. The DWR well logs that were available for this area(all outside the 2000' radius) are included in Appendix H. o The California Water Services Company (CWSC) was contacted regarding municipal wells serving the area. Only one active well was located just at the 2,000-foot radius search area (1963 S. Argonaut Street). The commercial, industrial and residential properties in the area are serviced by CWSC. Well details are shown in Table H1, Appendix H and the approximate well positions are plotted on Figure H1, Appendix H. 2.$ Potential Effects of Residual Contamination The contamination described in Section 2.0 will persist in the environment if left in place. +� When petroleum hydrocarbons are released to the soil, it moves deeper under the primary influences of gravity, groundwater flow patterns, and capillary action. As the product reaches a fine grained unit or the water table it concentrates on the top of the clay or on the groundwater surface due to its lesser density. In groundwater, petroleum constituents then dissolve from the pool into the groundwater to form a dissolved contaminant plume that migrates under the control of the groundwater gradient. At the same time the dissolved LW plume is forming and migrating, non-dissolved petroleum product remains in the pore spaces in the soil due to capillary forces. These forces make it difficult to remove the non-aqueous phase liquids (NAPL) trapped in the pore spaces. Fresh water moving through the soil can 6- eventually flush a portion of the NAPL out,but this process can take a very long time and can contribute to an extensive groundwater plume. +- The plume has migrated down gradient to the location of well MW-6. If a seepage velocity is calculated for the site, a contaminant transport velocity can be approximated: Seepage Velocity Seepage velocity(v)=permeability(K)x gradient(i) = Ki porosity(n) n K= 6.7X10- cm/sec (site average from table above Section 2.2.1) = 1.9X10`3 ft/day = 0.69 ftlyear i=0.003 (average water table gradient for the site in "fttft") n=0. 1583 (average porosity as above)