BWMA launches modeling projects to assess municipal groundwater supplies

For the past two years, the Columbia Basin Ground Water Area (GWMA) has been developing a sophisticated computational groundwater model of four Columbia Basin Counties – Adams, Franklin, Grant and Lincoln.

This year the state appropriated $1 million for GWMA “to use the model to help answer critical questions about ground water supply, recharge and aquifer storage,” according to Paul Stoker, GWMA Executive Director.

The 2011-2012 GWMA groundwater projects are:

• Construction of hydrologic assessment of each municipal water supply - GWMA will assess the future groundwater supply for each of the 25 cities and towns inside the four-county area.

• Identification of sustainable wells along east low canal - GWMA will assess wells along the east low canal to identify which farms wells may receive enough new water to be sustainable.

In describing the municipal water supply assessment modeling at the GWMA Administrative Board meeting on July 28 at Othello City Hall, Stoker remarked, “These assessments will simulate aquifer water budgets to allow evaluation of each community’s long-term water supply outlook. The assessment project will also evaluate the need for, and scope of, potential deep well injection – aquifer storage and recovery – projects that could reverse, or at least stabilize, the decline in local water levels,” pointing to a computer graphic of the cities and towns.

The graphic illustrated that only two of the 25 GWMA city wells listed contain a high percentage of young water.

GWMA has sampled most major municipal wells within city limits for geochemistry. By using a radiometric and multiple tracer approach and scientifically peer reviewed models, GWMA has determined years through Carbon 14 aging for those wells.

According to the graphic, “GWMA uses multiple lines of evidence to access municipal water sources, including geochemistry, in depth static water level analysis and personal interviews.”

The graphic lists the city where the wells are located, the well number and the Carbon 14 Age in years.

Lind’s well No. 8 is dated at 24,760 years while Ritzville’s well No. 18 is at 15,520 years. Washtucna’s well No. 3 is 11,240 years using Carbon 14 aging.

The only two with a high percentage of young water are Harrington’s well No. 3 and Mesa’s well No. 2, which are both new wells.

Carbon 14 aging was not provided for the wells in Hatton, Kahlotus or Wilson Creek.

Regarding the identification of sustainable wells along east low canal, hydrogeologist Dr. Kevin Lindsey, GSI Water Solutions, Inc. (GSI) explained how GWMA scientists “will test wells and develop model simulations of the potential impacts of recharge from alluvial systems on irrigation wells near the canal to identify wells that are, and are not, in hydrologic connection with the alluvial and canal systems.”

Stoker noted that the sustainability project originated during discussions with the Bureau of Reclamation on the agency’s interest in identifying wells that may not need surface water supply replacement due to a history of groundwater recharge from shallow water sources. “This project will improve the decision-making for the Odessa Special Study by increasing the number of acres currently receiving rechargeable water.”

Also at the GWMA Administrative Board meeting, board members and the attending public listened and watched as GWMA scientists and staff presented the final report of the GWMA Groundwater Hydrologic Modeling Project, focusing on the future value of the three-dimensional (3D) groundwater simulation tool in supporting local, state and federal decision-making.

“The model has already provided us with some important answers about local and regional ground water conditions, and now we have a ‘science tool’ to help us determine the most rationale water supply solutions for our communities. That’s another important step forward in determining our future sustainability,” said Roger Hartwig, Adams County Commissioner.

In describing the Hydrologic Modeling Project, Dr. Lindsey said it was “designed to help identify the locations, mechanisms and rates of groundwater recharge and discharge. The over-arching objective was to develop a quantitative tool for describing the groundwater system by sufficiently simulating the hydrologic processes. The Model will enable GWMA to evaluate historic and current impacts to the groundwater system from development, and support future water resource management projects and decisions as is planned with the municipal water supply assessments over the next 12 months.”

Adams County Commissioner Rudy Plager, in regard to the model and future ground water decision-making, noted, “The two GWMA projects are going to provide our area with new, critical groundwater information that will lead to real solutions, including in the Odessa sub-area. The GWMA model will be used to evaluate the sustainability of wells along the east low canal, which can be reduced from the number of acres requiring surface water replacement in the Odessa Special Study alternative evaluations.”

Stoker explained how the model is constructed to recognize the fact that the GWMA lies within a multiple state hydrologic setting that extends into both Idaho and Oregon.

The GWMA modeling approach includes two models: one that simulates conditions only within the GWMA (the GWMA Model), and a model that simulates conditions throughout the entire Columbia Plateau aquifer (the Watershed Model).

The Watershed Model ensures that calculations made using the GWMA Model are constrained by, and consistent with, the overall regional groundwater budget. Model development has been conducted under a GWMA contract by GSI Water Solutions, Inc. (GSI) and S.S. Papadopulos & Associates, Inc. (SSP&A).

To date, the following important inferences have been drawn from the model:

• The model displays the effects that geologic structures underground have on groundwater movement.

These structures provide barriers to groundwater movement, resulting in separate groundwater sub-basins.

• Because each sub-basin has experienced different development patterns, and is significantly isolated from adjacent basins, groundwater in these sub-basins is being lost at different rates.

The model depicts how each sub-basin has responded in the past and will respond in to the future.

• The model depicts how quickly groundwater is being depleted.

Unfortunately, in many areas groundwater is not replenished by recharge; and even in areas where a very small amount of recharge does occur, it is not sufficient to maintain the current rates of groundwater use.

Summarizing the report, hydrogeologist Dr. Kevin Lindsey, (GSI) stated, “The initial results consistently indicate that throughout the GWMA, demand for water from wells is met principally by storage depletion – and that because natural recharge has failed to keep pace with demand, ground water resources continue to decline.”

Lindsey went on to explain that, “Calculations of the ‘recoverable groundwater storage’ that remains suggest that over 50 percent of the storage that was available when development commenced has been removed and is not being replenished – and that in some groundwater sub-regions the situation is critical, with less than 40 percent of the initial recoverable storage remaining. Given that beneficial use of all ‘recoverable storage’ is impractical, it is likely that at current production rates, groundwater in storage throughout the GWMA may be depleted within two to three decades, and sooner within some groundwater sub-regions.”

The report includes the results of groundwater budget calculations for the entire GWMA area, and for four groundwater sub-regions (Odessa, Moses Lake, Royal Slope and Connell), which were completed as part of the modeling project. Groundwater budget calculations for the remaining 12 groundwater sub-regions have not been completed, although GWMA leaders sought state funding this year with expectations that the remaining sub-region water budget calculations would be completed next year.