Task 6 — Data Synthesis and Evaluation

Data compiled, collected, and analyzed in other tasks will be synthesized and evaluated as integrated data sets to produce three primary products:

1. Estimates of basin water budgets,
2. A conceptual model of the regional ground-water flow system in White Pine County
3. A report documenting results of the study.

Water Budgets

Water budgets will be developed for the hydrographic basins in the study area along with a regionally balanced water budget. Estimates of basin recharge and discharge in the study area will be compiled and tabulated, along with estimates of recharge and discharge from previous studies, to develop a range of reasonable, representative values. Additionally, for areas where significant interbasin flow is thought to occur, an attempt will be made to quantify the magnitude of interbasin flow using Darcian calculations. For these areas, hydrogeologic data will be compiled and evaluated to determine cross-sectional areas and hydraulic properties of permeable units, and water-level gradients.

The principal tasks for estimating interbasin flow and developing basin water budgets are summarized below:

Previous water budget estimates - Literature searches will be performed to compile previous work on water budgets that have been estimated for basins or various areas within the primary study area. These estimates will be evaluated for accuracy and error and used where appropriate.

Hydrogeologic unit delineation - Lithostratigraphic units will be grouped into regional hydrogeologic units and coupled with hydrogeologic cross sections produced in task 1 to determine cross-sectional areas of permeable units. Three-dimensional modeling of the geometric relations of hydrogeologic units along selected basin boundaries may be performed to assist with cross-sectional area calculations.

Hydraulic Properties - Existing aquifer-test data will be compiled and evaluated to provide a quality-assured data base of hydraulic properties for hydrostratigraphic units of interest in the study area. Compiled aquifer-test data will be in addition to the oil and gas well information analyzed in task 1. Statistical distributions of hydraulic properties for rocks of similar hydrostratigraphic unit and structural setting will be developed and compared with distributions used for previous regional-scale modeling of areas in the carbonate-rock province.

Water level gradients along basin boundaries - Using the regional potentiometric-surface map produced for task 3, hydraulic gradients between selected basins within the study area will be calculated. For areas where water-level data are sparse, new water-level measurements will be collected during the study, if representative wells and (or) springs are available.

Estimates of Interbasin Flow - Two methods will be used to estimate flow across selected basin boundaries:

1. Calculations using Darcy's law, based on regional potential gradient, and cross-sectional areas and hydraulic conductivities of hydrogeologic units along boundary segments
2. Calculations from water budgets of contributing areas.

Darcy calculations will be based on data compiled and evaluated in this task; water-budget estimates of interbasin flow will be based on differences in mean annual recharge and discharge tabulated in task 2. Estimates of interbasin flow will be compared to previous estimates of flow from appropriate basin and regional studies.

Basin water budgets – Basin water budgets will be developed for 2005-2006 through an iterative process of integrating estimated recharge, discharge, and interbasin flow with pertinent geologic, hydrologic, and geochemical information that constrain or control ground-water flow. The iterative process will require adjusting estimates of recharge and interbasin flow in a manner consistent with geologic, hydrologic, and geochemical information to produce basin-tabulated and regional water budgets.

To help verify tabulated water budgets, a steady-state ground-water accounting model will be developed and applied. The mass-balance water-budget model will utilize an accounting “cell,” from which input and outputs will be defined rather than the standard ground-water flow equation used in numerical simulation. The level of uncertainty in the accounting model predictions will be evaluated by standard Monte Carlo techniques and Bayesian analysis.

Conceptual model of regional ground-water flow system

A hydrogeologic framework model (HFM) will be developed using cross sections and maps, compiled borehole lithologies, and available geophysical interpretations to provide a three-dimensional visualization of subsurface hydrogeology. The HFM will be developed using software such as Dynamic Graphics' Earthvision or Rockware's RockPlot 3D. Hydrologic spatial data sets, such as recharge and discharge areas, the distribution of pumping wells, or contours of ground-water flow will be incorporated in the HFM to provide a visual conceptualization of the regional ground-water flow system in the study area. The HFM also will be applied to help evaluate spatial data, such as determining hydrogeologic cross-sectional area for interbasin flow calculations. Additionally, the HFM will be used to test hydrogeologic conceptualizations of regional flow, present a broad picture of the study area's regional hydrogeology, and provide the initial foundation for a refined HFM that could be used for future numerical simulation applications.

Report Preparation and Publication

Draft reports prepared for each work package will be synthesized and organized into a USGS Scientific Investigations Report. Each section will be edited by team leads to ensure consistency in technical concepts and results and in presentation format. The SIR will include products outlined in the Lincoln County Land Act, including:

• A regional potentiometric surface map showing primary structural controls on ground-water flow,
  
  
• A tabular summary and electronic data base of compiled hydraulic properties and approximate volumes of water stored in aquifers,
  
  
• A series of maps showing the distribution of recharge and discharge, and areas of interbasin flow,
  
  
• A tabular summary showing ranges in the magnitude of basin recharge and discharge, and interbasin flow (water budgets), and
  
  
• A basic three-dimensional hydrogeologic framework model that shows a conceptualization of the regional ground-water flow system.