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KEI-P91-0202 .R7 March 18, 1993 Page 5 3 . Simulation #3 The third simulation was performed identically to the second simulation, except that the period of time modelled was extended from 10 to 20 years. The SESOIL model area for Simu- lation #3 is shown on Figure 2 . Input parameters used in Simulation #3 are included in Appendix A. SESOIL VADOSE ZONE MODEL - RESULTS The output of the SESOIL module of PCGEMS creates bar charts that show the depth of pollutant migration versus time, and the concen- tration of pollutant versus time for a specified depth. In this manner, a determination can be made of the probability and/or the degree of impact to the ground water. Results of Simulation #1 indicate that ground water is not impacted by this contamination source after ten years . The maximum depth of benzene migration for this conservative model was approximately 1400 centimeters (cm) or 46 feet. This corresponds to a total depth of 72 feet below grade since the source was assumed to begin at a depth of 26 feet below grade. Results of monitoring of the wells at the site indicate that ground water is approximately 75 feet below the surface. Therefore, according to Simulation #1 , ground water is not impacted in the ten year period simulated in this model. Results of the output from Simulation #1 are summa- rized in Table 1, and the bar charts for various benzene depth and concentration estimates are included in Appendix B. Results of Simulation #2 indicate that ground water is not impacted by this contamination source after ten years. The maximum depth of benzene migration for this more realistic model was approximately 1, 400 cm or 46 feet. This corresponds to a total depth of 72 feet below grade, which is still above the saturated zone. Results of the output from Simulation #2 are summarized in Table 1, and the bar charts for various benzene depth and concentration estimates are included in Appendix B. Results of Simulation #3 indicate that ground water is impacted by this contamination source after approximately 130 months (or ten years and ten months) . However, the maximum concentration of benzene that impacts ground water is approximately 0 . 0007 ppm (or 0. 7 ppb) , which is below the California Department of Health Services MCL level for benzene of 1 ppb. Furthermore, the concentration of benzene in the ground water is significantly reduced during the subsequent ten month period to a non-detectable level (<0. 5 ppb) . Results of the output from Simulation #3 are summarized in Table 1, and the bar charts for various benzene depth and concentration estimates are included in Appendix B.