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i <br /> i <br /> 12 December 1995 <br /> I AGE-NC Project No 95-0134 <br /> Page 4 of 6 <br /> Isites A description of the SESOIL modeling program and the potential for soil leaching was <br /> presented in the May 1995 Quarterly Report <br /> i A request was made to examine the potential impact to ground water if ground water were to return <br /> to the 1986 seasonal high of 35 feet Approximately 5 feet of impacted soil would be in contact with <br /> ground water <br /> The volume of hydrocarbons was calculated for impacted soils below a depth of 35 feet The total <br /> I volumes of toluene, ethyl benzene and xylene were defined as an instantaneous release to ground <br /> water over the area of impacted soils No degradation rate was used for the first model The <br /> concentrations of contaminants in ground water at the down-gradient edge of the release was <br /> Ipredicted using the AT123D A second model was run using the degradation rates from an example <br /> model supplied in the SESOIL program <br /> I <br /> 4.0. FINDINGS <br /> 4 1 RELATIVE GROUND WATER ELEVATION AND GRADIENT <br /> The relative elevation of the ground water in each well was calculated by subtracting the depth to <br /> water from the surveyed relative casing elevation(Table 1) Comparison of the measurements indicate <br /> that groundwater at the site rose an average of 0 14 feet between the May and September 1995 <br /> f monitoring events <br /> The ground water gradient was calculated to be 0 0016 ft/ft directed N 84° E (Figure 3) The <br /> September 1995 represents a return to the historically more shallow gradients The flow direction is <br /> directed more easterly than in previous monitoring events <br /> 4 2 ANALYTICAL RESULTS OF GROUND WATER SAMPLES <br /> No petroleum hydrocarbons were detected in the samples collected during this quarterly monitoring <br /> event The analytical results are summarized in Table 2 The laboratory report and chain-of-custody <br /> form are included in Appendix B <br /> 43 SESOIL MODELING <br /> The predicted concentrations for ethyl benzene, toluene and xylene for the first year were 11 7, 3 9 <br /> and 789 ppb, respectively All concentrations should immediately decrease to approximately 57% of <br /> the initial year values and then maintain a steady decrease The predicted concentrations for ethyl <br />