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Site Investigation and No Further Action Request Repo Ta6w R&L Diesel Services, Project#051111 Since 1954 ' The area of impacted soil is estimated to be 8 to 10 ft. n diameter by 25 ft. deep, based on the site profile sketch included following section 3.3 of this report. Based on average concentration levels for diesel and VOCs, the remaining mass is estir iated to be 6Q0 0 654 ounds diesel, and 1-25 VOCs. No constituents have been removed or destroyed through excavation or remedial action. 16. Provide assumptions, parameters, calculations and the model used in any risk assessments. Based on the remaining concentrations and mass ins il, the lack of mobility of constituents in soil and the concentration of PCE detected in groundwater, which was below the established MCL, lack of preferential pathways for migration of constituents detected in soil and the concrete cap at the site, it was determined that the site falls within acceptable risk parameter ranges for no further action required status, therefore no additional risk assessment modeling F was performed. 17. Provide assumptions, parameters, calculations and the model used in fate and transport modeling. Based on results of subsurface investigations at the site which indicates the constituents found at the site are relatively immobile due to the concrete cap at the surface which prevents infiltration and a layer of silty clay at approximately 50 feet below grade which substantially retards downward migration of the petroleum hydrocarbons and chlorinated hydrocarbons, no F:� fate and transport modeling was conducted at the site. 18. Provide a rationale why the conditions remaining a the site will not adversely impact water Fquality, human health, and safety, or other benefici d uses. The rationale for NFAR must include a finding about present and future water use, and risks the site may still represent to Fhuman health and safety, and water quality. The groundwater sample collected directly below the area of impacted soil identified only one constituent (PCE) above laboratory detection limits, and that at a level below the relevant PMCL. The UST was closed in place in 1988- over 20 years ago. The area affected by prior leaks Ffrom the UST is immediately adjacent to and beneath the UST. The subsurface investigations conducted at the site provide strong evidence that the donstituents identified in soil adjacent to the UST are relatively immobile and not likely to impact groundwater at levels exceeding the relevant water quality goals. A dense silty clay layer at between 35 and 45 ft. bgs appears to be impermeable enough to prevent penetration by a push drill rig, and may also prevent constituents of concern from migrating vertically at a rate sufficient to impact groundwater. Utility corridors are not present at the site to provide preferential pathways for migration to , groundwater or other receptors. F10