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Ms. Margaret Lagorio Page 2 December 29, 1994 BAE31604.AS.10 WORK PLAN ADDENDUM This work plan describes remedial investigation work planned for better defining the extent of contamination, installing additional monitoring wells, performing pump tests, developing a simple groundwater model, and evaluating hydraulic control with consideration for contaminant transport mechanisms and natural attenuation. Conduct Groundwater Investigation PHS/EHD has specified that Del Monte shall install one up-gradient monitoring well and two down gradient wells (one shallow and one deep) to better define the extent of contamination. They further require that pumping tests be performed to evaluate how to achieve hydraulic control of the gasoline plume. We interpret the county's requirement for up-gradient and down-gradient wells to mean that they would like to see non-detect levels in new monitoring wells closer to the source of contamination. Existing down-gradient monitoring wells MW-DIS-7 and MW-DIS-6 have � demonstrated non-detect levels. The new requirements will require off-site down-gradient wells. The up-gradient well will be placed on-site along the fence line, as it may not be possible to negotiate an encroachment easement with Caltrans for an off-site up-gradient monitoring well. PHS/EHD is aware of the historic pumping that has occurred at Del Monte's three production wells, and they are concerned that the vertical gradient created by production wells may be adding a vertical component to the movement of the gasoline plume. Thus they require a deep well that is down gradient. Defining the extent of contamination requires that groundwater samples collected from the up-gradient and down-gradient wells have non-detectable concentrations of gasoline constituents: Del Monte plans to collect discrete groundwater grab samples from a number of locations prior to installing the up-gradient and down-gradient wells. Figure 1 describes proposed drilling locations. The grab samples will tentatively define the extent of gasoline in the shallow groundwater. Monitoring wells can then be installed outside the area containing gasoline. All drill cuttings will be placed in a dumpster located on site rather than drums to avoid cost. Del Monte will dispose of cuttings either through on-site land spreading or landfill disposal. We propose to initially drill 3 holes with a 6 inch diameter hollow stem auger, along the west side of N. Filbert. We propose to use hollow stem auger with hydro-punch sampling. Sample collected will be analyzed over night. If we detect gasoline constituents along N. Filbert, we will continue to drill at 100 foot intervals westward along Weber Street until we reach the hAprojec \31604\pm\wp1nh1th.doc