SummaryCH2M Hill Plateau Remediation Company (CHPRC) is currently assessing aquifer characterization needs to optimize pump-and-treat remedial strategies (e.g., extraction well pumping rates, pumping schedule/design) in the 200-ZP-1 operable unit (OU), and in particular for the immediate area of the 241-TX-TY Tank Farm. Specifically, CHPRC is focusing on hydrologic characterization opportunities that may be available for newly constructed and planned ZP-1 extraction wells. These new extraction wells will be used to further refine the 3-dimensional subsurface contaminant distribution within this area and will be used in concert with other existing pump-and-treat wells to remediate the existing carbon tetrachloride contaminant plume. Currently, 14 extraction wells are actively used in the Interim Record of Decision ZP-1 pump-and-treat system for the purpose of remediating the existing carbon tetrachloride contamination in groundwater within this general area. As many as 20 new extraction wells and 17 injection wells may be installed to support final pump-and-treat operations within the OU area.The addition of new, high-pumping capacity, extraction wells to the 200-ZP-1 pump-and-treat system provides the opportunity of generating areal hydrologic responses that may be analyzed for determining large-scale information for a wide-range of hydrologic properties (i.e., transmissivity, hydraulic conductivity, vertical and horizontal anisotropy, and storativity). This type of aquifer test characterization information is important for the detailed modeling of contaminant capture and the optimal use of the pump-and-treat system. Large-scale information can be obtained that is more reflective of ZP-1 pumpand-treat system operations by performing a constant-rate pumping test of longer duration (e.g., ~1 to 3 months). To conduct extended hydrologic tests of this duration without adversely impacting remedial activities of the pump-and-treat system requires that 1) the pumping tests be conducted within the framework of the existing 200-ZP-1 operational system and 2) the observed areal hydrologic response be monitored primarily with the existing monitor well networks.Analytical simulations of areal test responses based on representative aquifer properties within the area and anticipated pumping rates indicate that the radius-of-influence (i.e., drawdown of ≥ 0.01 m) from large-scale, new ZP-1 extraction well tests would be extensive, and for test durations of ≥1 month extend to distances of ≥ 1,000 m from the pumping well location. Simulations of barometric effects on monitor well water-level responses during extended large-scale pumping tests indicate a potential well water-level response change of ≤ 0.3 m. The simulated magnitude of potential barometric pressure effects underlies the need to effectively remove barometric effects from surrounding well water level responses monitored during the extended, large-scale, pumping test. While no universal, large-scale test conclusions can be made from these general simulation evaluatio...