Developing A National Drinking Water Regulation for Disinfection of Ground Water

The Safe Drinking Water Act directs EPA to promulgate requirements for disinfection of ground water-based drinking water systems. The Ground- water Disinfection Rule regulatory workgroup, made up of representatives from EPA, the states, and other interested parties, is actively considering the issues for the wide range of elements necessary to ensure a regulation that will protect public health and can be feasibly implemented. This regulation is likely to require disinfection of ground water sources and systems found to be contaminated or vulnerable to contamination.     

Ground Water Monitoring at Wellhead Protection Areas

Wellhead protection programs implemented to this date have not, in general, included a comprehensive ground water monitoring strategy. This is due both to the relatively recent introduction of the wellhead protection concept into the ground water field and also to the complexity of the monitoring problem. A well-planned monitoring program, however, can contribute significantly to the success of a wellhead protection program. The elements of wellhead protection, important from a monitoring perspective, are the management objectives, the types of potential contaminant sources, and the locations of those sources with respect to the wellhead protection area boundary. General monitoring strategies applicable to wellhead protection are derived from the relationships between these elements.     

Long-Term Confidence in Ground Water Monitoring Systems

State-of-the-art analytical techniques are capable of detecting contamination In the part per billion (ppb) range or lower. At these levels, a truly representative ground water sample Is essential to precisely evaluate ground water quality. The design specifications of a ground water monitoring system are critical in ensuring the collection of representative samples, particularly throughout the long-term monitoring period.
The potential interfaces from commonly used synthetic well casings require a thorough assessment of site, hydrogeology and the geochemical properties of ground water. Once designed, the monitoring system must be installed following guidelines that ensure adequate seals to prevent contaminant migration during the installation process or at some time in the future. Additionally, maintaining the system so the wells are in hydraulic connection with the monitored zone as well as periodically Inspecting the physical integrity of the system can prolong the usefulness of the wells for ground water quality. When ground water quality data become suspect due to potential interferences from existing monitoring wells, an appropriate abandonment technique must be employed to adequately remove or destroy the well while completely sealing the borehole.
The results of an inspection of a monitoring system comprised of six 4-inch diameter PVC monitoring wells at a hazardous well facility Indicated that the wells were improperly installed and in some cases provided a pathway for contamination. Subsequent down hole television inspections confirmed inaccuracies between construction logs and the existing system as well as identified defects in casing materials. An abandonment program was designed which destroyed the well casings in place while simultaneously providing a competent seal of the re-drilled borehole.