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Recommendations for TCE Plume Action
Appendix 1: LDS Ballfield Solvent Mass Calculations

CH2M-Hill's (1994) ground water flux estimate from their computer model for the portion of the aquifer immediately south of Mink Creek is 1.35 x 106 cu. ft./day. This model flux represents conditions for November, 1993, and is equivalent to 3.69 x 109 gal/year or approximately 70% of the 5.3 x 109 gal/yr flux past Red Hill independently estimated by Welhan et al. (1996) for the April-November 1993 water balance period. At 28.32 liters/gallon, the CH2M-Hill model flux represents 14 x 109 liters/year.

For a conservative average TCE concentration over the LDS ballfield cross-section of 5 parts per billion (ppb) or 5 x 10-9 grams TCE per liter of ground water, this flux equates to 70 kg of TCE/year. At a specific gravity of 1.46, this represents 48 liters per year or about 13 gallons of equivalent liquid TCE flowing past the LDS ballfield per year. Therefore, since 1992 when recorded TCE concentrations first exceeded 5 ppb in Well 33, the equivalent of at least 90 gallons (335 liters) of liquid TCE have entered the aquifer and flowed past the LDS ballfield. If the ground water flux computed by Welhan et al. (1996) is used, at least 18 gallons (69 liters) of TCE per year or 130 gallons (480 liters) of liquid TCE have entered the aquifer and flowed past the LDS Ballfield since 1992.

In either case, these estimates are conservative because the average TCE concentration across the LDS ballfield is greater than 5 ppb. From the large amount of liquid TCE already accounted for that has entered the flow system, it is almost certain that a large amount remains suspended between soil particles at the source(s), and will continue to "bleed" dissolved TCE into the aquifer for a very long time to come. Thus, the likelihood that concentrations will decrease soon is extremely low.