May, 2001

Ground-Water Supply Development

Many municipalities, and private and industrial entities utilize ground water as a source of water supply and are often faced with the need for additional supply for more service connections, backup supply or facility expansion. The question most suppliers are faced with is "where to find that new ground-water source?"

An evaluation for additional ground-water supply begins with assessing the existing sources to determine whether they are operating efficiently and are developing the maximum possible yield. Only after the evaluation results indicate available ground-water usage is maximized do we recommend assessing the feasibility of developing a new ground-water source on available land.

The initial feasibility assessment involves reviewing data from a variety of sources, including local and regional hydrogeologic data, watershed management plans, pumping test data from the existing ground-water sources, aquifer data and interference issues between existing supplies and potential future sources.

Once the hydrogeologic and resource data is reviewed, rough "target" development areas are defined based on land availability and favorable hydrogeologic conditions. Typically either a sand and gravel aquifer or a bedrock aquifer is targeted for development.

The detailed site selection process typically begins with the acquisition and review of remote sensing data such as black and white and infrared low-altitude aerial photography. Review of the aerial photography provides insight into the detailed local hydrogeology such as the location of sand and gravel deposits or zones of fractured bedrock.

In a bedrock aquifer, the development of a ground-water supply well is most favorable where water-filled bedrock fracture zones occur or intersect. These fracture zones are initially identified through remote sensing, and confirmed through the use of surface geophysical techniques.

In a sand and gravel aquifer, the procedures for developing a ground-water supply source involve either the use of surface geophysical techniques, or the installation of small-diameter borings to determine the location, extent and potential yield of the underlying sand and gravel aquifer.

Once a specific area on the ground is targeted for ground-water supply development, a "test" well is installed tapping the desired aquifer and short and long-term pumping tests are conducted to determine well yield and efficiency and aquifer yield. Detailed potential interference effects on neighboring supply wells is also determined from the pumping test results.

Many governmental agencies require permits for ground-water usage, either as a drinking water source and/or due to the volume of usage. The well installation and testing is typically conducted according to environmental agency or local health department rules and regulations. These agencies review the testing results and other pertinent site data as a basis for a decision in ground-water usage permits.

Requests for water rights have become increasingly controversial and contentious, as the density of ground-water development has increased nationwide. In many cases, diversion requests will be subject to public hearings and even litigation. Establishing the science behind a water diversion request has never been a more critical component of ground-water supply development project.

For over 57 years, Leggette, Brashears & Graham, Inc. has provided the expertise to determine optimal ground-water supply locations and has successfully permitted hundreds of new ground-water sources for our clients.