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rs � • Response to Delay No Further Action Required Decision And Closure Request Moore Petroleum,Inc (Frank's Exxon), 14800 West Frontage Road,Manteca,California Page 3 AT123D fate and transport study considered the following scenarios 1) The two old domestic wells were not replaced and still in use both on and off site, and the screened depths of these old wells were at 50 feet bgs, 2) The two old wells were replaced by two new wells at their former locations, and the new wells are screened at 340 feet bgs each Both scenarios were simulated for a ten-year period, assuming the chemical releases occurred in 1997 The site-specific information for model input includes residual concentrations of MTBE and 1,2-DCA in both groundwater and soil, physical and chemical properties of MTBE and 1,2- DCA, site hydrogeological characteristics, and the distances of the domestic wells to the most impacted monitoring wells at the subject site The initial model run was performed in order to calibrate some of the site-specific parameters within their allowed boundaries The purpose of the calibration was to ensure that the simulated groundwater MTBE and 1,2-DCA concentrations at the locations of the old domestic wells conformed to the analytical results of the samples collected from the two old wells in the past After the model calibration, the potential groundwater impact at the locations of the newly- installed/proposed wells were evaluated by ATi23D The AT123D modeling results indicate that at the 340 feet bgs screen levels, the newly-installed/proposed domestic wells will not be impacted by the environmental conditions at the subject site in the next ten years Appendix C includes the AT123D modeling results reports Table A below summarizes the estimated MTBE and 1,2-DCA impact to the domestic wells on and off site from year 1997 to year 2006 Table A. AT123D Fate and Transport Modeling Results On-Site Domestic Well Off-Site Domestic Well MTBE MTBE 1,2- 1,2- MTBE MTBE 1,2- 1,2- in Old in New DCA in DCA in in Old in New DCA in DCA in Well Well Old New Well Well Old New Year (ppb) (ppb) Well Well (ppb) (ppb) Well Well (ppb) b b b 1997 036 000 009 000 002 000 006 000 1998 360 000 087 000 1 16 000 076 000 1999 596 000 151 000 369 000 143 000 2000 655 000 179 000 575 000 175 000 2001 626 000 185 000 681 000 186 000 2002 5 65 000 181 000 711 000 185 000 2003 496 000 174 000 695 000 180 000 2004 429 000 165 000 652 000 172 000 2005 369 000 156 000 597 000 163 000 • 2006 3 16 000 1 47 000 538 000 1 55 000 j JY C 1 PROJECTIE'SIERA02 009-Moore Petroleum,MantecalResponsetoRegionalBoardaesponse doe