SITE INFORMATION AND CORRESPONDENCE

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Ms. Kathleen Minahan - 4 - 31 January 2007 Regional Water Board staff conceptually concur with the installation of monitoring wells, and the range of analytes proposed for monitoring, although two monthly events is not sufficient to evaluate groundwater movements. Please provide a more detailed workplan for the monitoring wells. The monitoring well workplan should be provided to San Joaquin County Environmental Health and Regional Water Board staff, and should include proposed locations, proposed installation procedures, a construction diagram, tentative schedule, and any other pertinent details. Since some of the groundwater quality questions that need to be answered include the portion of pollutants that are reasonably attributed to adjacent off-site operations, obtaining off-site groundwater data would be to Lesco's advantage. Review of the monitoring well applications provided in the Investigation Report and review of files at the Regional Water Board office suggests that there may be monitoring wells at Riverside Cement Company, the Port of Stockton maintains a monitoring well at West Washington Blvd., and the Port of Stockton may have other wells nearby that Lesco could access. If monitoring wells are not available, Lesco may want to consider installing an off-site monitoring well. Health Risk Assessment In the Investigation Report, Lesco offered to conduct a simple health risk assessment to determine if the compounds identified in groundwater pose a risk to human health or the environment. The primary threat to ecological receptors exists in the transport of site groundwater to the San Joaquin River, and the primary pathway to human health is through vapor transport of ammonium. In order to determine if these are complete pathways, additional information will need to be collected, such as the hydraulic connectivity between groundwater and river water, and soil properties such as bulk density, porosity, and water content. Groundwater surface elevation monitoring in relation to tidal fluctuations at the Port of Stockton will be needed, as will undisturbed soil samples. The undisturbed soil samples can be obtained during the monitoring well installation and can be analyzed for the pertinent properties. A health risk assessment should not be undertaken until the soil and hydraulic properties at the site are better understood. Summary The soil sample data show that a few shallow locations at the facility contain nitrate and ammonium that exceed the cleanup goal 100 mg/kg, and only SB-13 and SB-15 exceed this goal at the deeper sample interval. Lesco should remove nitrate and ammonium that exceeds 100 mg/kg in and about borings SB-13 and SB-15. If Lesco believes that the soil cleanup goal of 100 mg/kg nitrate-N plus ammonium-N is too stringent, it may propose an alternate cleanup goal that is protective of groundwater. An alternate cleanup goal must be derived from leachability tests performed on site soils in accordance with the Designated Level Methodology. Constituents of concern in groundwater are nitrate, ammonium, sulfate, and possibly nickel and petroleum hydrocarbons. A monitoring well workplan needs to be provided to Regional Water Board staff and to San Joaquin County Environmental Health Department. The monitoring well workplan