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Response to Delay No Further Action Required Decision And Closure Request Moore Petroleum,Inc (Frank's Exxon), 14800 West Frontage Road,Manteca,California Page 4 The AT123D modeling results also indicate that even though the old domestic wells would be impacted by MTBE and 1,2-DCA if they are still in use, the concentrations of MTBE and 1,2- DCA would generally start to decline in the 4th or 6th year after chemical releases at the subject site The newly-installed/proposed domestic wells on and off site would not be impacted by MTBE and 1,2-DCA in the next ten years Please refer to Appendix C, Charts 1 through 4 for detailed illustrations Site-Specific Soil Characteristics The AT123D modeling used properties of silty sand in the chemical fate and transport study In addition, the amounts of chemical releases used in the modeling are several times greater than the residual chemical mass calculated based on the actual analytical data Therefore, the AT 123D fate and transport evaluation is conservative in nature The drill log prepared by the driller during the new domestic well installation, indicates that a layer of clay exists at the site from 175 feet bgs to 278 feet bgs This 100-foot clay layer, combined with interbedded clay layers above 175 feet bgs, should confine the remaining groundwater impact on-site to the shallow water aquifer and prevent the impacted groundwater from migrating downward Apex therefore believes that the new domestic well on site will not likely be impacted by the subsurface environmental conditions at the site Appendix D includes the new domestic well drill log Water Sampling Results for the Existing Off-Site Domestic Well On April 30, 1998, Apex personnel collected water samples from the existing off-site domestic well at the trailer park The water samples were submitted, under chain-of-custody documentation, to Sparger Technology, Inc , a state-certified analytical laboratory for chemical analyses The samples were analyzed for TPHg, TPHd, benzene, toluene, ethylbenzene, xylenes, MTBE and 1,2-DCA by EPA Methods 8020, 8015 and 601, respectively The laboratory analytical results indicate all constituents of concern are below the standard laboratory detection limits Appendix E includes the laboratory analytical report and chain-of-custody form 3. INFORMATION ON THE PROPOSED OFF-SITE NEW DOMESTIC WELL Apex has submitted a Pre-Approval package to the State Underground Storage Tank Cleanup Fund (UST Fund) for the construction of the proposed new domestic well at the off-site trailer park Once the Cleanup Fund approves the proposed work,the new off-site domestic well will be installed The new off-site domestic well will be identical in its construction details to those of the newly installed on-site domestic well (Appendix D) Information concerning the location and construction details of the proposed off-site new domestic well will be submitted to you upon completion of the work JY C 1 PROJECM'S\ERA02 009-Moore Petroleum,Manteca\ResponsetoRegionalBoard\Response doc