Water Supply Solutions for Small Systems – Assessing the World of Options


  • Aaron Duke PE, BCEE - Hazen and Sawyer
  • Kinsey Downes PE
  • Colleen Rizzi PE

In addition to its Central System, Loudoun Water operates and maintains a number of small, community water and wastewater systems. These small systems are usually located in rural areas, have small customer bases to support infrastructure improvements, and often employ packaged treatment systems to meet water quality goals. Two of these systems are the focus of this project, Raspberry Falls and Selma Estates.

The Raspberry Falls Community Water System, one of the affected systems, has three active, offsite wells with a total well capacity of 400,000 gallons per day. All of the water supply wells are located in limestone geology, or karst. One of the water supply wells was removed from service because it was classified as Groundwater Under the Direct Influence of Surface Water (GUDI). Recent well sampling suggested that additional wells in the Raspberry Falls system, as well as its neighboring system of Selma Estates, were under risk of becoming classified as GUDI as well. Safe Drinking Water Act regulations require filtration treatment of GUDI water supply wells or switching to an alternative water supply. An evaluation ensued to assess the options available to these two communities to address the risk of a GUDI determination.

When one of the Raspberry Falls water supply wells was removed from service, the water distribution system in Raspberry Falls was interconnected with the neighboring Selma Estates system to reinforce water supply capabilities in emergency situations. This interconnection would prove to be an important aspect of the long-term solutions set to address supply risks for these communities.

One of the options considered was to cease use of groundwater wells for water supply and obtain finished water from a neighboring surface water utility treating water from the Potomac River. However, Town Council for the surface water utility voted not to support the initiative. This lack of support, coupled with disinfection by-product concerns due to the higher water age in the water supplied by the surface water utility at the point of connection to the community systems, resulted in this option being removed from consideration (among other factors).

The selected method to address supply issues was to expand the treatment capabilities of the Selma Estates WTP to include membrane filtration to address concerns around potential future GUDI determinations. This image depicts the rendering showing the building addition required to house the new membrane filtration treatment facilities. The Raspberry Falls treatment facility was converted into a pumping station, and the water from the Raspberry Falls groundwater supply wells will be pumped up to the Selma Estates WTP for treatment through the membranes.

As our economy recovers and development is reinvigorated, new small community water systems are beginning to spring up across the country. Water supply and treatment challenges are nothing new to our community water supplies, but when these challenges occur in small systems, they have a much greater impact. The water supplies available to these small community systems are much more susceptible to impacts, whether they be drought or water quality related. These systems also have more limited resources to address supply and treatment challenges, with costs of corrective actions spread across a much smaller customer base.

Loudoun Water operates 39 such small, community water and wastewater systems and is very familiar with the challenges faced in operating these types of community treatment facilities. Recently, water supply challenges arose at two neighboring groundwater systems related to potential groundwater under the direct influence of surface water (GUDI) concerns. One of the existing groundwater wells was confirmed to be GUDI, and the geology at both systems was such that there was a high likelihood that the remaining wells would become GUDI in the very near future. This prompted a holistic evaluation of source of supply and treatment options, ranging from interconnecting the two systems and drilling new groundwater wells to reaching out to neighboring surface water supplies to install a pipeline that could serve the small communities from the larger neighbor.

The various scenarios evaluated each had their own unique treatment challenges to be overcome. For example, the combining of the two systems and reliance on existing wells would require filtration treatment to be installed, which would involve new capital construction and the potential for increased operator time at the facility. Likewise, the surface water option carried with it a concern over DBP formation due to the long pipeline length to connect the two communities to the larger surface water system. One of the communities is adjacent to a golf course, so the application of herbicides and pesticides and potential occurrence in the groundwater also had to be addressed with the community.

For more information, please contact the author at aduke@hazenandsawyer.com.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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