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Building 16 Former USTs GW Workplan - 2 - 31 August 2004 Former NCTS Stockton, Rough and Ready Island 1. Beneficial Uses. The Workplan includes general statements in Section 2.2.1 regarding the suitability of Rough and Ready Island surface and groundwaters as potable waters. This section refers to the potential and future use of these waters that may be allowed under the Water Quality Control Plan (Basin Plan) for the Sacramento River Basin and the San Joaquin River Basin. References are made to exceptions allowed under the Basin Plan to the Municipal and Domestic Supply(MUN) designation. As discussed in the Basin Plan, beneficial uses are critical to water quality management in California. Beneficial uses are defined under California Law and designated by the Regional Board in the Basin Plan. The Regional Board has taken no action to modify the Basin Plan or de-designate MUN for the waters at Rough and Ready Island. Unless otherwise designated by the Regional Board, the MUN beneficial use designation applies to all groundwaters and surface water at Rough and Ready Island. For clarity, all future documents that discuss the beneficial uses of Rough and Ready Island waters should reflect the current applicable MUN and other beneficial use designations. 2. Groundwater Sampling. Monitoring data presented in the Workplan indicate that groundwater contamination may be limited to shallow groundwater in the vicinity of the former USTs; however, groundwater monitoring data from downgradient of the known source areas and from deeper hydrostratigraphic zones are limited. The on-site monitoring wells are screened in shallow groundwater [from the ground surface to approximately 10 feet below ground surface (bgs)]. Groundwater at depths below 19 feet bgs, where contaminants were detected, have not been investigated. A majority of the proposed groundwater samples will be collected at approximately 20 feet bgs with three borings proposed to be extended to approximately 35 feet bgs. In general, Board staff concur with the proposed sampling locations and depths and support the approach of using an on-site mobile laboratory to evaluate the need for additional groundwater samples. However, the proposed investigation should be conducted in phases with flexibility to allow for adjusting these sampling locations and depths as necessary to define both the lateral and vertical extent of cont uAination. In particular, a deeper sample in addition to the proposed shallow C3, C4, and C5 samples may be necessary to define the vertical extent of MTBE contamination detected immediately downgradient of UST 16-3. The locations and depths of proposed CI I through C14 should be moved more immediately downgradient of the source areas to define the extent of contamination based on results of samples collected from the C8 through C10 borings. Depending on the results of the proposed investigation, installation of at least one deeper groundwater monitoring well, and replacement of any shallow wells destroyed as part of future roadway construction activities, may be required to provide for continued evaluation of impacts to groundwater at the site over time. Board staff understands that the Port intends to continue to conduct at least quarterly groundwater sampling and analyses at each on-site monitoring well for each of the contaminants detected at the Building 16 site thus far. As discussed in the Workplan, regular reports should be submitted, at least quarterly, to further assess groundwater quality and to determine what additional actions are necessary to address the impacts to groundwater at the site. 3. Groundwater Analysis. The Workplan proposes groundwater samples be analyzed for benzene, toluene, ethyl-benzene, and total xylenes (BTEX) using EPA Method 8020 and for Methyl-T-Butyl Ether(MTBE)using EPA Method 8260. EPA Method 8260B may be used to analyze for all these constituents depending upon how the laboratory is requested to report the results. We request that all groundwater samples sent to the laboratory be analyzed for the presence of MTBE and other oxygenates using EPA Method 8260B. Some laboratories do not routinely report results for particular volatile