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V LTC <br /> {Jff� A S S O C I A T E S I N C <br /> 4,r <br /> f <br /> 4.0 RESULTS <br /> r: 4_1 Petroleum Hydrocarbons in Soil <br /> Results of laboratory analyses performed on selected soil samples indicate that TPHd was present <br /> fir= only in the samples collected between 14 and 15.5 feet bgs. Field observations indicated that the <br /> samples at these depths also exhibited the highest FID measurements. Soil samples SB11-15.5, <br /> ' SB 12-16.5 and SB13-14.0 contained detectable concentrations of TPHd at concentrations of 390 <br /> ppm, 290 ppm and 1,100 ppm, respectively. All the remaining soil samples were nondetect. <br /> Analytical results of soil samples are summarized in Table 1. <br /> 4.2 Petroleum Hydrocarbons in Groundwater <br /> Results of laboratory analyses performed on groundwater samples indicate that TPHd was <br /> detected in boring SB 11, located crossgradient from the former UST, at 75 ppb and in boring <br /> �- SB 12, located upgradient from the former UST, at 24,000 ppb. The sample collected from <br /> downgradient boring SB 13 was nondetect. Analytical results of groundwater samples are F <br /> ,f f summarized in Table 2. <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. <br /> Analytical results of the groundwater samples indicate that the highest concentrations are $ <br /> southwest of the former tank location which is consistent with results of previous investigations. <br /> TPHd was not detected in groundwater in the downgradient boring indicating that the plume <br /> appears to be stable. Based on field observations, no free product was detected in any of the <br /> rr� <br /> borings. <br /> ATC recommends performing two additional quarterly monitoring events to obtain current <br /> groundwater data. The monitoring events will each include collecting samples from all six wells, <br /> analyzing the samples for TPHd, and preparing a monitoring report. Following the completion of <br /> the two events, ATC will perform a fate and transport study and mass balance calculations of <br /> ` petroleum hydrocarbons in soil and groundwater. The results will be included in a comprehensive <br /> request for closure report. <br /> si <br /> wA149811149811repor1slpsi.doc 5 <br /> ��j <br />