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LNThe output of annual summary contains the total pollutant mass inputs, hydrologic cycle components, the total pollutant mass removed from each layer, the average pollutant concentration distributions for each layer, and the maximum pollutant depths. The pollutant mass in the soil moisture, adsorbed on soil and in soil air and the total maximum pollutant depth are summarized in Tables 6 through 9. 5.4.2 Groundwater Impact Assessment After 10 years of simulated transport the maximum pollutant depth of benzene below the site is 9.8 feet (3 meters). At this time the residual concentrations of benzene are all less than 7 x le ppm. In fact after the second year concentrations have decreased to values less than the detection limit for benzene in soil. The model runs for toluene, ethylbenzene and xylenes produced similar results. The maximum pollutant depth of these constituents was seen for toluene which reached a depth of 26.5 feet at concentrations less than 1 x 10"'). Based upon the SESOIL results presented in the output files, no leaching of hydrocarbon constituents from the impacted soils to groundwater at the site is anticipated and constituents will naturally degrade to nondetectable levels over time. 6.0 SUMMARY AND CONCLUSIONS The fate and transport analysis resulted in the following conclusions. o The fate and transport analysis indicates a no-action remedial response provides protection of ` the beneficial uses of groundwater. o Petroleum hydrocarbon constituents will degrade to nondetectable levels over time 7.0 WORKPLAN FOR WELL ABANDONMENT Smith Environmental has prepared this workplan for the proposed well abandonment at the Stockton Police facility located at 22 East Market Street, Stockton, California(Figure 1). The location of well MW-1 is shown on Figure 2. A permit application and associated fee is contained in Appendix E. Upon receipt of the well destruction permit, Smith Environmental will schedule field activities. The well will be abandoned by a C57 licensed drilling company. The well will be abandoned by filling the well casing and filter pack with a neat cement/bentonite group utilizing a pressure grouting tool. For protection of the seal at the land surface, a hole at least two feet in diameter will be excavated around the outside of the well casing to a depth of approximately two feet below ground surface. The sealing grout will be allowed to spill over into the excavation. After the grout is set, the excavation will be filled with native soil and covered with an asphalt patch to restore the site. 6F 4 w-.W436 sVeportsLusoil.doc 11 Sion i.r