SITE INFORMATION AND CORRESPONDENCE_1992

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0 3-D Model/RD Report Memorandum -2- 14 December 1992 DDRW, Sharpe compute recharge for the long-term calibration effort (pages 4-9, 5-3 and 5-16) . However, actual precipitation values were used for the 1989 to 1991 calibration period. The initial period for the model was selected using third quarter 1991 data which represents data collected during the fifth year of drought. This fact was not acknowledged in the RD Report. It is unclear whether the BC model , which used data collected and presented in 1985, were verified for the existing drought conditions. Therefore, I question whether the recharge values assigned to the model domain accurately reflect existing conditions during the initial time period for the 3-D model . Calibration The 3-D flow model was calibrated for steady state and transient (short- and long- term) state conditions (pages 5-5, 5-6 and 5-13) . Pumping tests were used for the short-term transient calibration and ground water fluctuations and declines during the 1989 to 1991 period were used for the long-term calibration (page 5-14) . My concern is that the existing data from the Sharpe site were not used to the fullest for the calibration effort. The RD Report acknowledges that ground water level data were collected beginning in 1983. Ground water levels continue to be collected by Sharpe to-date. It is unclear why the complete historical record was not used for the long-term calibration effort. Ground water levels from 1983 to 1992 would have reflected both pre-drought and current drought conditions as well as the seasonal variations that were simulated for the long-term transient state calibration. Design Objective The design objectives for the solute transport modeling included preventing the migration of the 5 microgram per liter (µg/1 ) trichloroethylene (TCE) contour beyond Roth Road to the north of the site and monitor well cluster 510 to the west. These objectives were referred to as plume containment (page 8-8) . Data from Second Quarter 1992 (April to June) show the TCE and total volatile organic constituent (VOC) concentrations to be as follows: Well Concentration (µg/1 ) Well Concentration (µg/1 ) TCE Total VOCs TCE Total VOCs Inside of 521A 12.0 13. 10 509A <0.5 <0.5 5 µg/l 5218 3.16 4.77 509B 0.83 18.21 Contour 521C 1 .56 3.24 509C 42.0 45.06 509CD Not yet sampled Outside of 505A <0.5 0.75 510A 0.56 2.66 5 µg/l 505B 1.2 1.78 5108 <0.5 1 .62 Contour 505C <0.5 0.72 510C <0.5 0.6 505D <0.5 1 . 16 These data indicate that the concentrations for TCE and total VOCs are generally less than the aquifer cleanup level for TCE (5 Ag/1 ) at the lateral limits established (Roth Road and the 510 well cluster) as part of the design objective. These data may imply one of two things: