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09 August 1999 <br /> AGE-NC Project No. 98-0466 . <br /> i— Page.10 of 10 <br /> AGE believes that the detected TPH-d poses little environmental concern because: <br /> The.are no established regulatory concentrations for diesel in ground water other than taste <br /> and odor thresholds. <br /> • The detected concentration is quite low despite being collected under the area that was most <br /> impacted by the release form the former UST system. It has been AGE's experience that the <br /> concentrations.of detected hydrocarbons in'gr b water samples obtained as described in," <br /> Section 3.2. above are commonly much higher than`samples subsequently obtained from <br /> monitoring wells established in the same area as the grab samples; <br /> • The detected TPH-d was not accompanied by detectable concentrations of BTEX compounds <br /> or MTBE' chemicals.for which concentration standards have been set by regulatory " <br /> 7 agencies; and <br /> 4 TPH-d has very low mobility in fine grained sal such as has been encountered on the site. <br /> 6.0. RECOMMENDATION <br /> Based on the results of previous work conducted on the site and the results of this investigation, <br /> AGE concludes that:, <br /> Approximately 3,200 lbs of diesel fuel has been removed from the site and that only minimal <br /> concentrations of TPH-d remain in soil.and,gro and water on the site, and that <br /> TPH-d remaining on the site has little potential to migrate and significantly impact arid". <br /> degrade beneficial use of ground Water in the area. <br /> AGE therefore recommends that the PHS=EHD consider granting site closure to UST No. 1 at 2901 <br /> North West Lane, Stockton, California Site Code-18822. <br /> 7.0. LIMITATIONS . <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br /> environmental consultants practicing in this or similar localities. The findings_were based mainly <br /> upon review of reports, notes and.data from previous investigations and-on "analytical results <br /> provided by an independent laboratory. Evaluations-of the geologic conditions at the site have been <br /> 4 made from a limited number of available data points(i.e. soil borings with discrete soil samples and <br /> 4 grab ground water samples), and subsurface conditions may vary away from these data points. No <br /> other warranty, expressed or implied, is made'as to the professional recommendations contained in <br /> �. this report. <br /> �'^, Advanced GeoEdvironmental,Inc. <br />