In 2007, in response to declining groundwater levels in the cretaceous aquifers throughout eastern North Carolina, the General Assembly passed the Central Coastal Plain Capacity Use Area (CCPCUA) rule. The rule heavily regulates large withdrawals from those aquifers and ultimately requires withdrawals to be reduced by 25% in 2008, 50% in 2013, and 75% in 2018.
Groundwater users reacted by seeking a variety of alternative water sources. Some users formed water authorities and water districts with the intent of combining resources to develop surface water sources in lieu of groundwater. Other users looked to groundwater sources that excluded the cretaceous aquifers. After considering an interconnection with an adjacent system as well as the other two options mentioned above, and the Town of La Grange chose to develop additional wells not in the cretaceous aquifers.
To determine the feasibility of drilling new wells, a preliminary engineering study and water quality testing of a nearby irrigation well was carried out. The testing revealed the presence of iron, which had been expected. The Town developed a scope of work and budget for the project that included iron removal, and then sought and obtained funding from the North Carolina Rural Center and the U.S. Department of Agriculture Rural Development.
Once construction began, however, test wells at the specific production well locations revealed the presence of not only iron, but also aluminum, which was above the EPA’s secondary limit. With no additional funding available from the Town or government agencies, the Town needed a creative engineering solution to remove the aluminum to carry out its CCPCUA reduction plan while staying within the previously established budget.
WithersRavenel personnel researched and conceived a filtration solution that would not only remove iron, but also attempt to remove the aluminum and raise the pH. After selecting suitable filter media, WithersRavenel personnel constructed a pilot scale filter to run via a small well pump for six months; the results were analyzed by a laboratory.
The pilot test proved successful, and while the project was significantly delayed as a result of this additional engineering, the Town was able to build a full-scale iron and aluminum removal system within budget, which ultimately allowed the Town to drill two new wells and provide an additional 150,000 GPD with a quality that exceeded the existing water sources.