FRAC3D Groundwater Model
PTRAX Particle Tracking Model
Hydraulic Conductivity Assessment
Grain Size Analysis
From April 1995 to July 1996, provided OpTech with groundwater modeling to support the design of well networks capable of containing six of the largest groundwater plumes in the vicinity of the MMR facility for Otis Air National Guard Base, Massachusets (OTIS).. Final review and acceptance of the well network design rested with Stakeholders, which included the NGB, USEPA, MDEP, and the public residents of Western Cape Cod. As modeling results became available and the complexities associated with plume containment were better understood by the Stakeholders, the modeling and design objectives originally provided to ECE and OpTech were modified and expanded. Several DSM models were based on the groundwater flow code FRAC3DVS (Therrein et al., 1994). Each model was calibrated using the 1993 stream fluxes and water levels in 330 wells. The calibration of each model was checked by simulating the migration of the six plumes using the particle-tracking code PTRAX (ECE, 1995a) . The major differences among the codes involve the recharge rates, the three-dimensional K-fields, and the numerical representation of surface water bodies and domestic pumping wells. DSM I has a K-field based on a trend of decreasing K-values with depth as obtained from aquifer pumping tests, a uniform recharge of 29 in/yr, constant-head boundary nodes to represent streams and ponds, and no domestic water supply wells. The DSM II model has the DSM I K-field scaled at 75%, uniform recharge of 26.5 in/yr, water supply wells with a total pumpage of 4.7 MGD, and high-K three-dimensional and two-dimensional elements to represent ponds and streams, respectively. The DSM III model uses the same the numerical representation for ponds and streams the DSM II model, a uniform recharge rate of 21.6 in/yr, water supply wells with a total pumpage of 4.7 MGD, and a K-field based on the USGS WCC model (Masterson et al., 1996) scaled at 89%. Modeling results used to develop the 60% Design were based on the DSM I model, which was completed in December 1995. DSM I served as the primary model until April 1996 when improved estimates for fluxes through surface water bodies were required to address potential adverse risks. After April 1996, DSM I and DMS II models were used extensively to help design well networks for 97% or better capture of the contaminant mass associated at with the FS-12 and SD-5 plumes. Toward the completion of the FS-12 and SD-5 numerical simulations, DSM III was created to help with a sensitivity analyses. Provided refinements of the systems, the CS-10 plumes and improvement of the overall western Cape Cod groundwater and surface water conceptual model to optimize plume containment of the seven large contaminant plumes.