Laserfiche WebLink
1 <br /> ' Since no TPH as8 asoline was detected in any of the soil samples, the concentration of <br /> petroleum hydrocarbons can be based upon BTUX concentrations. Based on 1992 data, <br /> using an average concentration of 0.014 ppm (the concentration in sample MWI-35), the <br /> volume of hydrocarbons remaining in the soil is calculated to be 0.00003 gallons (or <br /> significantly less than a teaspoon). Therefore, the remaining impacted soil, if present, does <br /> not represent a significant threat to public health. <br /> 51 Groundwater Contamination <br /> ' Verylow concentrations of petroleum hydrocarbons continue to be detected in MW-1, MW- <br /> 4 <br /> P Y . <br /> 4 and MW-5, all down gradient of the former UST excavation. However, since the <br /> ' concentrations of hydrocarbons are so low, remediation would be ineffective. The <br /> concentrations present are often determined to be the point of "diminishing returns" for <br /> ' most remediation methods. <br /> The concentration of benzene in both MW-1 and MW-4 has decreased consistently over the <br /> past four quarters. Furthermore, only the concentration of benzene in MW-1 (5.5 ppb) <br /> ' exceeds the Maximum Contaminant Level (MCL) for drinking water in the state of <br /> California. <br /> tGeoAudit does not recommend the implementation of a groundwater treatment system at <br /> this time. It is unlikely that any treatment system (pump and treat, air sparging, <br /> bioremediation) would be effective in reducing hydrocarbons concentrations at the site. <br /> Monitoring wells MW-1, MW-4 and MW-5 should be sampled in September 1994. If <br /> ' hydrocarbon concentrations continue to indicate a consistent decrease, in our opinion, the <br /> PHS/EHD should grant site closure. <br /> ' 6.0 LIMITATIONS <br /> ' Our professional services were performed using that degree of care and skill ordinarily <br /> exercised by environmental consultants practicing in this or similar localities. The findings <br /> were mainly based upon analytical results provided by an independent laboratory. <br /> ' Evaluations of the geologic conditions at the site have been made from a limited number <br /> of available data points (i.e. monitoring wells), and subsurface conditions may vary away <br /> from these data points. No other warranty, expressed or implied, is made as to the <br /> ' professional recommendations contained in this report. <br /> I ' <br /> I11 <br /> Wakn list QR4I.9V--1.10 <br />