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45 days after the end of the monitoring period. The proposed groundwater monitoring scope is provided in Table 7. Specifics about the individual water-bearing zones are described below: A-Zone. Three monitoring wells (ST/MW-1, ST/MW-14, ST/MW-15) in the A-zone currently contain benzene and/or MTBE concentrations above proposed cleanup goals. These wells will be sampled semi-annually in the first and third quarters. In addition, thirteen wells (PS/P-11, PS/P-12, PS/P-13, PS/P-21, PS/P-23, PS/MW-17, PS/MW-19, PS/WC-2SR, PS/WC-3S, PS/WC-4S, ACA-1A, ACA-2A, ACA-3AB, and ACA-4AB) will be sampled annually in the third quarter to monitor the extent of the plume. A-zone wells will be accessed for groundwater elevation data semi-annually. B-Zone. Under current and reasonably likely future land uses, there are no complete exposure pathways for groundwater from the B-zone and residual dissolved-phase concentrations in the B-zone do not present an unacceptable risk. TPHg, BTEX and MTBE concentrations are below ESLs. TPHd concentrations sporadically exceed the ESL (Table 3, Appendix E); these concentrations are most likely the result of break down products or biogenic interference. Additionally, the hydrostratigraphy of the region supports that the B-zone is not laterally continuous and is effectively monitored by the existing A-zone well network. Therefore,we propose no further monitoring of B-zone groundwater. C-Zone. Under current and reasonably likely future land uses, there are no complete exposure pathways for groundwater from the C-zone. No monitoring wells have COC concentrations that are above the proposed cleanup goals. Three C-zone wells (ACA-26, ACA-4C and ACA-5C) are proposed for annual monitoring to confirm the extent of the dissolved phase plume in the C-zone remains stable or decreasing in extent. In addition, the C-zone wells listed in Table 7 will be accessed for groundwater elevation data to document that hydraulic gradients in the C-zone remain consistent with historical groundwater flow directions. D-Zone. Under current and reasonably likely future land uses, there are no complete exposure pathways for D-zone groundwater and dissolved-phase concentrations do not present a potential unacceptable risk. Benzene and MTBE concentrations were below proposed cleanup goals and the Basin Water Quality Objectives in the most recent sampling event. Therefore,we propose no further monitoring of the D-zone. �I �1 Revised Cleanup Plan Page 22 NuStar Stockton Terminal-Stockton,California November 7,2012 1014-12