SITE INFORMATION AND CORRESPONDENCE_2004-2014

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Mr. Marshall Cloud September 18, 2007 Page 3 detected in piezometer P-10 which is down-gradient of EWCC3 indicating that a portion of the Central Area Plume has not been captured by EWCC3 and has potentially migrated farther down-gradient. The present monitoring well MW533C/CD is more than 600 feet down-gradient of EWCC3 and is too far down-gradient and potentially off-axis to currently determine the actual toe-of-plume. 5. Page 4-1, section 4.0, first bullet; DDJC-Sharpe requested that regulatory comments on the report be received by October 5, 2007 and therefore should indicate the pilot study will take place after this step and really occur in Fall 2007, rather than Summer 2007 as stated. Errata 1. Page 3-1, section 3.1.5, first sentence; The text for MW418C is misprinted and should be corrected. 2. Page 3-1, section 3.2.1.1, first sentence; See Errata comment No 1. Recommendations 1. DTSC recommends a time-critical delineation of both the horizontal and vertical extents of the persistent source area, P-5A, as this source is likely responsible for the persistent Central Area groundwater plume and increased TCE concentrations observed in MW437C and down-gradient monitoring points as far away as piezometer P-10. 2. DTSC recommends proceeding with the proposed nine month rebound period for MW418C to assess the contaminant concentrations trends prior to implementing the in-situ liquid potassium permanganate pilot test for the South Balloon. 3. DTSC recommends delineating the Central Area plume to define the actual "toe-of-plume" down-gradient of EWCC3 and P-10 with current TCE concentrations of 38 and 28 pg/L, respectively, prior to any installation of additional extraction wells. Plume delineation should occur until the contaminant concentrations are defined both laterally and vertically to the method detection limit to ensure the plume boundary is adequately characterized.