SITE INFORMATION AND CORRESPONDENCE

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0 Paradise Point Marina -2- 9 January 2017 Stockton, San Joaquin County • For direct exposure to shallow soil (0-10 feet bgs)the Central Valley Water Board Site Cleanup Program uses the San Francisco Bay Regional Board Environmental Screening Levels for Direct Exposure. • Soil vapor will need to be evaluated against Office of Environmental Health Hazard Assessment (OEHHA) residential soil gas screening levels for current and future buildings; should vapor concentrations exceed screening levels, a human health risk assessment may need to be performed. • For groundwater, data should show that petroleum concentrations are decreasing and are not a threat to receptors such as the nearby supply wells, slough, or irrigation ditch. The well 200 feet southeast of the suspected release point supplies drinking water; therefore, California drinking water maximum contamination levels (MCLs) should be the target cleanup goal for groundwater. • While there are no underground storage tanks (USTs) known to have operated at the Site, the Central Valley Water Board in 2014 recommended that its staff consider the State Water Resources Control Board Low Threat UST Case Closure Policy(LTCP) when evaluating non-petroleum releases which exhibit similar attributes to those which the LTCP addresses; however, given the distance to nearby supply wells, the location adjacent to a surface water body, and the shallow nature of groundwater at many location across the Site, the LTCP groundwater and vapor intrusion to indoor air criteria may not be appropriate to be applied to the Site. Central Valley Water Board staff requests the following: 1. Beginning in the first calendar quarter of 2017 sample these two supply wells quarterly for the petroleum constituent suite listed in the 2015 Work Plan with laboratory analytical detection limits at or below drinking water MCLs. Submit quarterly analytical results for the supply well sampling to GeoTracker in Electronic Deliverable Format TM (EDF) upon reporting by the laboratory but at least within 30 days of the closure of each calendar quarter (i.e., by April 30, July 30, October 30, and January 30). The San Joaquin County Environmental Health Department(SJCEHD) regulates the distribution of water from "Well No. 2"for potable use and copies of the analytical data should also be mailed quarterly to: SJCEHD Attn: Small Public Water System 1868 East Hazelton Avenue Stockton, CA 95205 2. The 2015 Work Plan states that borings will be advanced to 20 to 25 feet bgs; however, given the proximity of the release to the nearby supply wells and the relatively shallow nature of these wells, you must define the Site lithology greater than 25 feet bgs in order to assess the threat to the supply wells and define the vertical extent of the plume. 3. By 1 May 2017, submit a report documenting the findings of your investigation. Should upcoming work proposed in the Investigation Report and Addendum fail to delineate the lateral and vertical extent of the release, the report of findings should propose further work to delineate petroleum impacts to soil and groundwater, which may include the installation of additional monitoring wells to fully delineate and monitor the lateral and vertical extent of the plume. The report of findings should also propose additional remediation strategies, as appropriate. 4. Beginning in the second calendar quarter of 2017 sample all Site monitoring wells for four consecutive quarters to establish trends in petroleum concentrations in groundwater and determine the groundwater gradient. Prepare quarterly monitoring reports due within 30 days of the closure of each calendar quarter(i.e., by April 30, July 30, October 30, and January 30) which contain the results of groundwater monitoring and sampling, plume map(s), supply well sampling results, and updates/documentation regarding activities conducted at the