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IVIr. Little 2 18 August 1999 <br /> contamination during well drilling is a concern, perhaps conductor casing should be employed. Actual <br /> as-built construction of monitoring wells, including screen intervals and filter pack, should be <br /> determined by conditions encountered in the field, and rationale for as-built well design and any field <br /> decisions should be documented in the work report. If site conditions warrant screen coverage at <br /> shallower or deeper depths, staff recommends well clusters be installed, possibly as a later phase of <br /> work. <br /> 4. Monitoring well locations: A clear rationale for location of the proposed monitoring wells is not <br /> given. Staff questions the lack of wells on the north side of the ditch, considering the detection of total <br /> petroleum hydrocarbons as diesel (tph-d), as motor oil (tph-mo), and gasoline-related compounds (tph-g <br /> and BTEX) in the ditch water, and the detection of all of these in soil from the west side of the gasoline <br /> tank building. Groundwater samples from Trench 1 also contained gasoline-related compounds, but the <br /> groundwater was not analyzed for tph-d and tph-mo. As discussed in the attached memo,the source of <br /> the diesel and motor oil contamination is uncertain, and it is not established that diesel and motor oil are <br /> absent in the groundwater. <br /> On this basis, and because of the lack of groundwater hydrologic information, staff requests that at least <br /> one monitoring well be placed on the north side of the ditch near the leaking gasoline lines and the truck <br /> wash area and/or on the northwest near the diesel tank. Additionally, the depth of the ditch, its <br /> relationship to groundwater(gaining or losing) and whether it contains water year-round, should be <br /> determined. <br /> 5. Analyses: Staff requests that total petroleum hydrocarbons as diesel and motor oil be added to the <br /> analyses, and that for all analyses, all peaks be reported. Monitoring and sampling should continue on a <br /> quarterly basis until no further actions status is achieved, which may require more than one seasonal <br /> round(more than four quarters) of sampling. <br /> If you have any questions, please call me at(916) 255-3119. <br /> 7 <br /> FJAIL WIGGETT,i1C.E.G. <br /> Aboveground Tanks Program <br /> Enclosure(s): memo with attachments <br /> cc: Ms. Margaret Lagorio, San Joaquin County PHS-EHD, Stockton <br /> Ms. Nancee Volpi, c/o Herum, Crabtree, Dyer, Zolezzi, and Terpstra, LLP, Stockton <br /> GJW/C\volpAwkpinitr <br />