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00 <br /> V � <br /> ASSOCIATES I N C . <br /> 4_2 Petroleum Hydrocarbons in Groundwater <br /> Results of laboratory analyses performed on groundwater samples indicate that TPHd was <br /> detected in boring SB17, located downgradient from the former UST, at 98 ppb. The sample <br /> collected from the remaining downgradient borings were nondetect. Analytical results of <br /> groundwater samples are summarized in Table 3. The estimated extent of TPHd in groundwater <br /> is shown on Figure 3. <br /> 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> Analytical results for soil samples are generally consistent with field observations and FID <br /> readings. Impacted soil appears to be limited to depths less than approximately 18 feet bgs and is <br /> not present in any of the site borings. Analytical results of the groundwater samples indicate that <br /> the highest concentrations are southwest of the former tank location which is consistent with <br /> results of previous investigations. TPHd was not detected in groundwater in any of the off-site <br /> borings and was detected only at a low concentration in the on-site downgradient boring <br /> indicating that the plume appears to be stable. Based on field observations no free product was <br /> detected in any of the borings. <br /> ATC recommends the installation of one monitoring well near boring SB 17 and performing four <br /> additional quarterly monitoring events to obtain groundwater data. The monitoring events will <br /> each include collecting samples from all seven wells, analyzing the samples for TPHd, and <br /> preparing monitoring reports. Following the completion of the events, if the data show the plume <br /> is stable ATC will prepare an addendum to the previous request for closure report. <br /> 12-' <br /> w:162574162574.021repotislsup sub_inv.doc 6 <br /> rr� <br /> �s <br />