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31 January 2013 <br />AGE-NC Project No. 02-0926 <br />Page 8 of 21 <br />Results from periodic groundwater monitoring events generally indicate that the primary <br />constituents of concern at the site are TPH-g, TPH-d, BTEX, TAME, with the lead <br />scavenger EDB and 1,2-DCA. Historically, the most intense hydrocarbon-impact has <br />generally been reported in samples collected from shallow well MW-5. Intermittent <br />detections of hydrocarbon constituents have been reported in shallow and deep <br />monitoring well MW-6 (Table 4). <br />Based on groundwater data collected from wells MW-1 through MW-6 and grab <br />groundwater samples collected from borings B4, B5, B6 and CPT-1 through CPT-3, the <br />lateral and vertical extent of the dissolved hydrocarbon plume is generally defined_at the <br />site. Sporadic detections of petroleum hydrocarbon constituents have been reported in <br />both shallow perimeter well MW-3 and deep well MW-6 water samples. Additionally the <br />plumghtly undefined to the east of monitoring well MW-5. However, based on the <br />limited detedtions, grbffridWater Iloinrdifebtions and generally low concentrations of <br />constituents reported during periodic monitoring, further assessment of the hydrocarbon <br />plumes does not appear warranted at this time. <br />Figures 11 and 12 depict the estimated extent of dissolved TPH-g impact to shallow and <br />deep monitoring zones at the site. <br />Utilizing the above figures, the mass of dissolved TPH-g in groundwater was determined <br />by splitting the groundwater plume into different isocontours based on concentrations <br />reported during the most recent ground water monitoring event (July 2012) and grab <br />groundwater samples collected at the site. The screening interval of the shallow and deep <br />monitoring zones (i.e. 20 feet for shallow zone and 5 feet for deep zone) were use in <br />determining the thickness of the dissolved hydrocarbon plume. <br />The volume of each was determined by the following formula: <br />V = Area (A) multiplied by the height (h) <br />A= Area as determined using computer area inquiry tool (Figures 11 and 12) <br />h = thickness (screened intervals) <br />Using the above calculations and the analytical results for groundwater samples as <br />described above, approximately 4.4 gallons (equivalent to 25 lbs.) of TPH-g impact is <br />estimated in groundwater at the site. The assumptions for the calculations of hydrocarbon <br />mass in groundwater are presented in Appendix E. <br />Advanced GeoEnvironmental, Inc.