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Files - 4 - 10 August <br /> MONITORING WELL LOCATIONS: A clear rationale for location of the proposed monitoring wells <br /> is not given. I question the absence of wells proposed for the and northwest side of the ditch, <br /> considering the lack of knowledge of the ditch's relationship to the groundwater and the detection of <br /> COCs in the ditch. At least one well should be placed on the north side of the ditch, between the ditch <br /> and the gasoline tank area or between the ditch and the diesel tank area, in order to determine <br /> groundwater and flow direction and to allow for sampling. Additionally, the depth of the ditch and its <br /> relationship to groundwater(gaining or losing) and whether it contains water year-round, should be <br /> determined. <br /> GROUNDWATER MONITORING ANALYTES AND MONITORING DURATION: The work plan <br /> proposes monitoring for tph-g, BTEX, and MtBE for one year(four quarters). Analytes should include <br /> tph quantified as diesel and motor oil, in addition. The laboratory should report all peaks, and in the <br /> Method 8260 analysis for MtBE, all fuel oxygenates should be targeted. Monitoring for longer than one <br /> year may be required, depending on site conditions. <br /> CONCLUSIONS: Although extent of soil contamination appears limited, the impacts to groundwater <br /> are incompletely assessed. Present knowledge suggests that the contamination found in the ditch is <br /> probably from a surficial source (the truck washing area) that can be controlled by a change in practice. <br /> The site could become complicated if the ditch proves to be gaining from groundwater, and to still <br /> contain COCs, or if groundwater flow proves to be seasonally complex. <br /> I am concerned that all possible sources of contamination have not been recognized, and that the motor <br /> oil and diesel range hydrocarbons were not targeted in groundwater analyses. Upcoming analyses <br /> should include these compounds. Additional monitoring well locations should be proposed, or present <br /> ones modified to include coverage of the north side of the ditch and obtain a clear picture of <br /> groundwater hydrology. <br /> Attachment(s) <br /> GJW/C\volpi\riveTolder\mem <br />