Water Balance Defined: A water blance, known also as a water or hydrologic budget, involves a quantitative evaluation of sources of water supply, storage, and discharge with respect to a defined drainage area. Changes in water input can directly affect water output and, thus, ultimately affect contaminant migration and wetland habitats.

In 2000, Rocky Flats initiated a site-wide water balance project to assist with the development of a detailed design basis for Site closure activities and to support future closure decision actions. The water balance will consist of an application of one or more integrated hydrologic models using available Site information and data to simulate pre- and post-closure hydrologic conditions. The water balance effort is being conducted by a project team consisting of modeling experts and on-site specialists in groundwater and surface water flow, collectively known as the Water Balance Working Group (WBWG).

Simplified water balance concept and resulting mass balance equation

Rocky Flats closure activities and final end-state configuration have the potential to significantly alter groundwater and surface water flow. Consequently, many Rocky Flats closure decisions are dependent on water balance information. The objectives of the water balance are to provide Rocky Flats with a management tool to:

Evaluate how the site-wide water hydrology changes from present to final Site configuration;

Predict surface water impacts from groundwater for present and final Site configuration;

Provide data for final Industrial Area configuration to protect surface water quality (cover design and land recontouring);

Provide information for the comprehensive risk assessment and final Rocky Flats Record of Decision; and

Guide the development of the wetlands conversion project.

Schematic showing major hydrologic components of RFETS Industrial Area water balance

The water balance project will be implemented in two phases and is scheduled for completion at the end of fiscal year 2001 (FY01). The first phase will be implemented in FY00 and includes: (1) preparing a work plan; (2) reviewing existing data; (3) collecting additional data, if needed; and (4) initiating the water balance evaluation/model(s).

Surface water gaging location (GS45) on Upper Church Ditch, 700 ft. east of the Site western boundary The second phase of the water balance project consists of calibrating the model(s) and completing “what-if” scenarios. This work, scheduled for FY01, will include: (1) evaluating the surface water hydrology to develop management options for the final Site configuration; (2) modeling the Site hydrogeology and impacts to surface water from current and future groundwater fluxes; and (3) evaluating closure options such as building foundation removals, pond operations, wetlands options, and final cap/cover configuration. The results of the modeling effort also have the potential to be used in future contaminant transport evaluations.

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