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Mr. Maurice Benson <br /> August 20, 2009 <br /> Page 3 <br /> Sites P-1 G and P-1 E VOC groundwater plumes appear to be co-mingled <br /> according to figure 8-1a of the comprehensive cone penetrometer test (CPT) <br /> report. Groundwater data and the cross-section provided in Figure 8-4 of the <br /> CPT report suggest that further delineation of the 530 pg/L TCE plume <br /> underneath Building 649 is warranted. Site P-1 E groundwater data taken <br /> immediately south of Building 649 reported TCE at 530 pg/L at 63.5 feet below <br /> ground surface with attenuating concentrations measured with depth indicating <br /> that a potential source may still be present in either the vadose zone or at the <br /> groundwater interface. Groundwater flow gradients in the vicinity of sites P-1 E <br /> and P-1G indicate a northwesterly groundwater flow direction and would cause <br /> TCE detected directly south of Building 649 to migrate underneath. The TCE <br /> plume that appears to originate south of Building 649 has not been delineated <br /> laterally or vertically and needs further delineation work before a NFA <br /> determination can be approved for P-1 E. <br /> Figure 8-4 of the CPT report identifies 500 pg/L and 1,000 pg/L TCE isopleths <br /> underneath Building 649's foundation shaped as a triskelion (three lobes). The <br /> upper lobe of the triskelion seems to emanate from the groundwater interface <br /> beneath Building 649 foundation. Increasing TCE concentrations with decreased <br /> depth appear to indicate a shallower release near the former locations of <br /> underground storage tanks. A total of eight (8) former USTs, five (5) on the <br /> south side and three (3) on north side of Building 649 were labeled as either <br /> solvent waste or waste oil and likely containing solvent rinseate, a mixture of <br /> water and solvents combined with petroleum hydrocarbons derived from <br /> maintenance operations. The combination of solvent with waste oil can both <br /> enhance the mobility of the combination during the initial spill, and act as a <br /> solvent stabilizer that hampers remediation, as shown by repeated contaminant <br /> rebounds after implementation of remedial measures more than 20 years after <br /> releases occurred. <br /> Site P-1G is the approximate location of In-situ technology (Solid Potassium <br /> Permanganate) currently in operation in the South Balloon in an attempt to <br /> remediate the persistent source responsible for TCE concentrations of 1,600 <br /> pg/L in groundwater. It is premature to eliminate or preclude additional remedial <br /> actions for both saturated and unsaturated soil when current technologies are still <br /> in operation and uncertainties still exist in the successfulness of their efforts, <br /> including contaminant mass locations remaining after completion. DTSC cannot <br /> support a NFA determination for Site P-1 G when active in-situ technologies are <br /> ongoing and uncertainties still remain on the levels of contaminants that exist in <br />