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1 r <br /> 09 March 2005 <br /> AGE-NC Project No 95-0121 <br />' Page 6 of 7 { <br /> r ry <br />' southeast flow direction and steep ground water gradients encountered during third quarter <br /> 2004 appear to be anomalous to the usual low-hydraulic gradients and north to northeast flow <br /> directions at the site, and may be due to an error in depth-to-water measurement in well <br />' MW-1 - } <br /> • The core of the dissolved petroleum hydrocarbon plume appears to be located at depths <br /> between 25 feet and 53 feet below surface grade (bsg) in the area of wells MW-1 through <br /> IMW-4 and MW-7 (Figure 4) A review of current and previous ground water samples , <br /> suggests the core of the plume is impacted by TPH-g, BTEX, and MTBE (Table 5) <br />' The concentrations of TPH and BTEX compounds in well MW-1 have increased since April <br /> 2000, the contaminants in the remaining wells have remained stable BTEX compounds, <br /> MTBE and 1,2-DCA are present at concentrations exceeding the DHS' Maximum <br />' Contaminant Levels for these chemicals in drinking water <br /> • The lateral and vertical extents of dissolved petroleum hydrocarbons are not fully defined at <br />' the site,further assessment is warranted west-northwest of well MW-7,north of well MW-2, <br /> northeast of well MW-4 and southeast of MW-1 (Figure 4) <br /> 5.0. RECOMMENDATIONS <br /> rBased upon data collected during the third and fourth quarter 2004, AGE recommends <br /> I Continue operation of the SVE system, based on the vapor samples collected from the SVE <br /> system,continued operation should result in significant reduction of petroleum hydrocarbons <br /> in soil I Y <br />' • , Performance of a ground water monitoring event utilizing wells MW-1 through MW-8 and ' <br /> EW-1 Tlie'first quarter 2005 ground water monitoring event should take place in March <br /> 2005 ' <br /> IPreparation of a Site Conceptual Model{SCM}to provide a guide for future assessment and <br /> remediation - <br /> • <br /> Based on the well-defined, laterally continuous, sandy nature of soil encountered at depths <br /> of between 25 feet and 35 feet (HU2) and between 40 feet and 60 feet (HU4), any future <br /> feasibility studies (e g , ground water pump-and-treat versus ozone sparging technologies) <br /> I may require testing of both hydrogeologic units <br /> r <br /> f <br /> 1 <br /> Advanced GcoEnvironmental,Inc <br /> i <br />