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California Department of Transportation June 29, 2001 <br /> Shop 10 Maintenance Station, Stockton, California Project No 400296001 <br /> i <br /> In well VM-1, TPH-G concentration decreased from 2,000 µg/1 to 1,200 µg/1 Benzene decreased <br /> from 574 µg/1 to 217 µg11 Toluene concentration decreased from 6 6 µg/1 to non-detectable lev- <br /> els Ethylbenzene concentration has decreased from 119 µg/1 to 94 µg11 Total xylenes <br /> concentration have decreased from 192 µg/1 to 15 µg/1 <br /> According to laboratory analytical data using EPA method 8260B, additional compounds were <br /> detected in samples from various on-site wells during the current groundwater sampling event <br /> These compounds include, 1,2-dichloroethane, tert-butylbenzene, 1,2,4-tnmethylbenzene, 1,3,5- <br /> tnmethylbenzene, and n-propylbenzene <br /> 6. RECOMMENDATIONS <br /> Based on the results of the First Quarter 2001 groundwater monitoring analytical results, which <br /> indicated elevated concentrations of TPH-G and/or BTEX, Ninyo & Moore recommends that <br /> quarterly groundwater monitoring continue at the site <br /> 7. LIMITATIONS <br /> The environmental services described in this report have been conducted to general accordance <br /> with current regulatory guidelines and the standard-of-care exercised by environmental consult- <br /> ants performing similar work in the project area No other warranty, expressed or implied, is <br /> made regarding the professional opinions presented in this report Please note that this study did <br /> not include an evaluation of geotechnical conditions or potential geologic hazards <br /> Our conclusions, recommendations and opinions are based on an analysis of the observed site <br /> conditions and the referenced literature It should be understood that the conditions of a site can <br /> change with time as a result of natural processes or the activities of man at the site or nearby <br /> sites In addition, changes to the applicable laws, regulations, codes, and standards of practice <br /> may occur due to government action or the broadening of knowledge The findings of this report <br /> may, therefore, be invalidated over time, in part or in whole, by changes over which Ninyo & <br /> Moore has no control <br /> 029601r ehap10 Drft IQO!doc 5 <br />