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e� C• x- I The nondetectable levels of BTER.. TPHG, 0&G, chlorinated hydrocarbons and semivolitile organics in water samples from MW-1 indicates groundwater quality has not been adversely affected by these constituents. The presence of low levels of dissolved diesel hydrocarbons in two samplings suggest 1) the former waste oil tank has contributed to this groundwater contamination 2) leakage from the former diesel tanks has contaminated groundwater and migration to the location beneath the waste oil tank occurred 3) sampling and/ or laboratory error has led to the detection of these low levels of diesel contaminations It should be noted that the first sample was 150 ppb above the detection limit and the second sample just 4 ppb above the detection limit. There is no Maximum Contaminant Level (MCL) for TPHD in - drinking water as established by DOHS. Nuisance conditions related to taste and/or odor would have to be considered. Under current State Water Quality Control Board criteria the presence of dissolved diesel hydrocarbons represents net degradation of natural (background) groundwater quality. The concentration of metals Cd, Cr, Pb and Zn in groundwater sampled are all below the MCL for drinking water. Based on the data collected to date, soil and groundwater have been impacted by varying concentrations of diesel hydrocarbons and waste oil constituents. The limited extent of soil contamination in the former diesel tank pit is supported by the low to non-detectable levels of TEX, TPHG and TPHD in soil samples collected during the original tank pull and after re-excavation of the west end of the -- middle tank. Although the original waste oil tank pit sample recorded 4500 ppm TPH-D, the low to non-detectable levels of TPHD and nondetectable levels of other organic w constituents tested suggests the greatest contamination is limited laterally to the the boundaries of the excavation and vertically to less than 15 to 20 feet. The presence of dissolved diesel hydrocarbons in the well adjacent to the waste oil tank indicates a slight net degradation of groundwater quality has probably occurred. 7.0 RECOMMENDATIONS Because the evidence that groundwater contamination by diesel hydrocarbons is not completely conclusive due to quantification of contaminant concentrations near method detection limits and the potential for inducing these low levels during sampling or analysis we recommend well MW1 be sampled with duplicate samples submitted to two different ---_-_--laboratories._-In- addition-a-travel--blank-from -each--lab and - -- field blank should be submitted for analysis. These samples should be tested for TPHD by appropriate state or EPA methodology. Pending the return of these laboratory test results the need for additional monitoring well would be assessed. 8