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v <br /> A S S O C I A T E S I N C <br /> unlikely that the on-site groundwater well or the adjacent downgradient wells will be impacted by <br /> dissolved petroleum hydrocarbons <br />' An on-site search for surface waters indicated there were no streams, P onds, or canals within <br /> 2,000 feet of the site <br />' It should be noted that um test data for the on-site and adjacent wells was not available for <br /> pump J <br />' review during the well survey <br /> 5.0 ASTM[ TIER 2 RBCA EVALUATION <br />' A human health risk assessment (HHRA) study was performed to address potential significant <br /> health risks associated with petroleum hydrocarbons at the subject site An American Standard of <br /> Testing Materials (ASTM) standard RBCA Tier 2 evaluation was performed following ASTM <br /> Standard E 1739-95 and the Tier 1 and Tier II Guidance Manuals for Risk Based Corrective <br /> Action published by Groundwater Services, Inc (GSI) of Houston, Texas (GSI, 1995) <br />' 5_1 ]Ex osure Pathway Evaluation <br /> Evaluation of the exposure pathways is the first step in the RBCA analysis There are four steps <br /> used to determine which exposure pathways are valid for the site These steps are described <br /> below <br /> Secondary Sources <br />' The first step is to identify the sources of contamination The primary source of the <br /> contamination at the site is the former USTs There are five potential secondary sources that <br /> must be evaluated when performing a RBCA analysis <br />' ® affected surface soils, <br />' ® affected subsurface soils, <br /> ® dissolved groundwater plume, <br /> ® free-phase liquid plume, and <br /> ® affected surface soils, sediments, or surface water <br /> Three of these five secondary sources are not present at the site, as described below <br /> ® Analytical results of soil samples and field observations indicated that surface soils at the site <br /> (less than 15 feet below bgs) were not impacted by the release <br /> • ® Evidence of free-phase liquid was not reportedly observed during the subsurface investigation <br /> performed at the site Free-phase liquid is not considered a secondary source <br /> w\148851repor \NFA-Request doe 6 <br />