SITE INFORMATION AND CORRESPONDENCE

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(DHS) . Conversely, some have experienced marked decreases. Percentaget Well No. Parameter Increase/ (Decrease) LM-25 TCE (213) LM-963 TCE (670) LM-35 PCE 88 LM-41 TCE 79 LM-55 PCE 67 LM-62 TCE 137 PCE 256 LM-66 PCE 85 LM-70 TCE 92 tMay 1991 versus last reported analytical result. *Duplicate sample of LM-25. • In the final report, DDRW-Tracy should explain these changes in relation to the historical contamination around these wells, plume configuration and plume movement. 10. Because this is the first of many quarters of quarterly groundwater monitoring prudence would dictate a more comprehensive suite of chemicals be analyzed for. This would provide a firm foundation for a thorough site characterization and remediation. As an example, analyses for acetone and organophosphate pesticides, among others, have been limited to select wells or not performed at all. Consequently, it cannot be stated with any degree of certainty that these chemical constituents are not present throughout DDRW-Tracy. A skewed picture of the overall extent of contamination could result from limited chemical analyses. Because DDRW- Tracy is an uncontrolled hazardous waste site, a thorough assessment of the hazardous substances potentially present should be performed. This would involve analyzing for chemicals on the Target Compound List (TCL) , Target Analyte List (TAL) , as well as Dioxins and Tentatively Identified Compounds (TLCs) . (Dioxins are to be analytes of concern for some of the solid waste management unit investigations. ) • DDRW-Tracy will propose an interim sampling plan (to be followed by a formal plan, as was discussed at the Project Manager Meeting of October 11, 1991) , delineating parameters and locations for EPA and State review. 5