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s possible detection limits. Report the results of your investigation to this agency within 30 days of completion of the approved scope of work. Conventional monitoring well networks currently installed at this fuel leak site are insufficient to properly locate and define the extent or existence of MTBE/Additive plumes at this site recognizing that only one monitor well has been installed to date. Therefore, PHS/EHD directs you to perform a detailed, expedited site assessment using depth discrete and continuous core sampling to define and quantify the full three- dimensional extent of MTBE and other additives, Total Petroleum Hydrocarbons, Benzene and other contaminants in groundwater. You are requested to properly characterize the hydrogeology and groundwater flow conditions in the vicinity of your site. Sampling protocol shall include the following components in your next work plan; During SWI activities, we request that you gather detailed lithologic information using borings, continuous core sampling, dual tube expedited site assessment methods, or cone penetrometer together with other methods to understand the hydrogeology at your site. You are requested to determine and report the historic high and low ground water elevations during the operational period of this facility.Collection of soil and ground water samples from each significantly different lithological unit shall be analyzed by a qualified laboratory for permeability, porosity, bulk density, moisture, and organic carbon content. You may substitute cone penetrometer or equivalent data where appropriate. Samples from each significantly different lithologic unit encountered in vertical assessment efforts shall be submitted to a state certified analytical laboratory for chemical analyses following the guidelines presented above (See Analytical Chemistry Protocol). This data shall be employed in determining the potential rate at which contaminants may migrate in this hydrogeologic setting and shall be considered in the process of positioning and constructing monitoring well networks and sampling strategies. This data shall also be utilized to provide a rationale for determining the radius of receptor, conduit, and well surveys. Report the results of your investigation to this agency within 30 days of completion of the approved scope of work. In constructing your site conceptual model you shall include the potential for plumes to dive vertically considering recharge and pumping influences in the area. We also request that you evaluate local groundwater flow conditions and establish a site-specific localized flownet that is dependent on geologic conditions and is reflected on geologic cross sections and fence diagrams. Additionally, you are required to prepare a rose diagram for groundwater gradient at this site, plot it on the groundwater contour maps, and update this diagram in all future reports submitted for your site. Discuss your proposal for performing this work in the work plan addendum requested below. Report the results of your investigation to this agency within 30 days of completion of the approved scope of work. We request that you employ approaches to estimating MTBE/Additive contaminant mass flux across plume transects or fences located perpendicular to the MTBE/Additive plume. We request the use of expedited site assessment tools and/or appropriately screened monitoring wells to provide data for these estimates. In deciding the location of transects and developing mass flux estimates, please consider the variable dissolution of MTBE from the source. We request that you install permanent monitoring wells and/or monitoring well clusters(screened at appropriate discrete depths with appropriate length of screen) to monitor the plume. Include your proposal for the installation of these wells in the work plan requested below. Please report your results in the SWI Report requested below. Please note, you are requested to immediately pursue any off-site access agreements that you may need to complete your investigation activities. You are requested to evaluate the probability of the plume encountering preferential conduits that could spread the contamination particularly in the vertical direction and identify receptors in the vicinity of this site. Report your results in the SWI Report requested below. We request that you perform a conduit study that details the potential migration pathways and potential conduits (sewers, storm drains, etc.) that may be present in the vicinity of the site. Provide a map showing the location and depth of all utility lines and trenches including sewers and storm drains within and near the plume area. The conduit study is to include a detailed survey reporting the positions and use patterns of all wells. Please contact the Department of Water Resources (DWR) for procedures to request well location information. The 2