Todd Engineers

Mojave Water Agency (MWA) and Bighorn-Desert View Water Agency (BDVWA) face the challenge of providing sustainable water supply in an era of increasing competition. The agencies -— having used groundwater historically from the Ames, Means, and Johnson Valley Basins -- are seeking the multiple benefits of conjunctive use of surface water and groundwater resources.

In 2007, the agencies took major step along the critical pathway from science to management, retaining Todd Engineers and Kennedy/Jenks Consultants (Kennedy/Jenks/Todd) to assimilate hydrogeologic data and findings from previous investigations and provide the technical foundation for management decisions, including possible managed aquifer recharge (MAR) projects.

Key Issues
Identification of areas with available storage, favorable lithology and good water quality for Managed Aquifer Recharge (MAR) Assessment of MAR in light of water supply and demand

The effort was organized in two interrelated components: the development of a basin conceptual model and the analysis of water supply and demand that includes projections of future use.

For each basin, hydrogeologic data were used to estimate groundwater storage and available storage and identify areas with coarse-grained lithology and favorable groundwater quality. Major inflows, outflows, and changes in storage were estimated to determine basin perennial yield. Groundwater supply was compared to existing and projected water demands under average and drought scenarios to quantify the need and potential benefit of a MAR project.

Upon preliminary identification of the southwest Ames Valley basin as a suitable location for a MAR project, Kennedy/Jenks/Todd assisted BDVWA and MWA to develop a focused geophysical investigation program, including 20,000 feet of electrical resistivity surveys and 32 time-domain electromagnetic (TEM) surveys, to identify geologic faults and confirm their impacts on subsurface flow.

The study found that communities in the Ames Valley basin would benefit most from a MAR project. Coarse-grained sediments beneath two major washes downgradient of geologic faults appear ideal for the sustainable percolation of imported water.

Services Provided
Evaluation of lithology Geophysical investigations Documentation of water quality, including septic tank impacts Assessment of water supply and demand Calculation of potential groundwater mounding Provision of a comprehensive report

Groundwater quality in the basin generally meets drinking water standards; however, the extent and concentrations of naturally- occurring nitrate and high-nitrate septage in the unsaturated zone are not well understood and require further investigation.