Reducing the Risks of Pathogens in Groundwater–The Groundwater Disinfection Rule, Part 2
By Kelly A. Reynolds, MSPH, PhD
A highlight in environmental health protection in 2006 was the promulgation of the EPA’s Ground Water Rule, (GWR) published in the Federal Register on November 8, 2006. The rule is aimed at reducing risks of microbial disease in drinking water by targeting all systems that utilize ground water sources (the source linked to 76 percent of the 183 waterborne disease outbreaks since 1991). Under the 1996 amendments of the Safe Drinking Water Act (SDWA), the EPA was required to promulgate regulations for disinfection of surface water and, as needed, groundwater supplies. Groundwater treatment, as needed, is expected to reduce waterborne illnesses due to viruses by more than 42,000 cases per year. This article is the second of two parts (see Part I in On Tap, WC&P, December 2006) reviewing the GWR.
A targeted approach
Unlike the regulations under the Surface Water Treatment Rule, not all groundwater systems will be required to disinfect under the GWR but rather only those that are identified as being at risk of fecal contamination. Surveys will be conducted to determine ‘at-risk’ supplies using fecal indicator organisms. Classical fecal indicator organisms, such as the non-pathogenic E. coli, enterococci or coliphage, have been used for decades to monitor drinking water quality and have been criticized for their lack of correlation with the presence of viral (norovirus) and protozoan (Cryptosporidium and Giardia) pathogens in water, but they can be used to determine if a particular environment is subject to fecal contamination.
Groundwater contaminated with fecal indicators also has the potential to be subject to the presence of other fecally transmitted pathogens. Viruses, such as norovirus, echovirus, coxsackievirus, rotavirus and hepatitis A and E are a primary concern due to their small size, easy transportability in the subsurface (i.e., soil) and low infectious dose (typically less than 10 viruses can initiate an infection). The presence of fecal indicators also suggests possible pathways of groundwater contamination where bacteria may reach the subsurface supplies. Bacteria of primary concern include the pathogenic E. coli strain O157:H7, Salmonella, Shigella, and Vibrio cholerae.
Since a major goal of the GWR is to identify and target groundwater systems that are susceptible to fecal contamination, high-risk suppliers will have to routinely monitor source waters and, when necessary, take corrective action. The type of action to be taken depends on existing state programs and a flexible approach toward public health protection has been accepted. According the EPA, corrective action can include a variety of possible responses, including:
- correction of all significant deficiencies
- provide an alternative water source
- eliminate the source of contamination
- provide treatment capable of removing 99.99 percent of viral contaminants
The 1986 SWDA originally required all public water systems to disinfect their supplies, regardless of whether or not they utilized a surface or groundwater source. Following the SDWA amendments in 1996, the EPA developed a risk-based approach that targets only groundwater supplies that ‘need’ additional treatment primarily due to the challenge of requiring all of the approximately 147, 000 public groundwater systems to implement the change.
Previously, no Federal regulation was in effect that required monitoring of groundwater. Although some systems did monitor for fecal contamination, no guidelines were in place regarding corrective efforts and no follow-up protocols were utilized. According to a report by the US Government Accountability Office (GAO) in 1993, even follow-up on “major problems” was often lacking and problems, when identified, often remained uncorrected. The GWR, however, provides requirements for treatment technologies (i.e., achieving a 99.99 percent reduction rate for viruses) and establishes subsequent compliance monitoring requirements to make sure the applied treatment is effective over time. Specific requirements include periodic sanitary surveys, routine monitoring, optional hydrogeological assessments, corrective actions and compliance monitoring.
Under the GWR, at-risk systems will be identified based on the results of sanitary surveys conducted by the state. If a significant deficiency is identified from the sanitary survey, the system has up to 120 days to implement corrective action. To the extent that it is applicable, sanitary surveys target eight critical components of a water system including:
- Source water
- Distribution system
- Finished water storage
- Pumps, pump facilities, and controls
- Monitoring, reporting and data verification
- System management and operation
- Operator compliance with state requirements
States have until December 31, 2012 to complete the initial sanitary survey on non-community water systems, exclusive of those that already meet the performance criteria which have until 2014 to conduct the initial survey, as do noncommunity water systems. The survey must be repeated every three years in community water systems and every five years in noncommunity systems and those community systems that meet the performance criteria.
Briefly, systems that do not already provide a disinfectant treatment barrier are required to monitor a minimum volume of 100 ml of source water for the presence of fecal indicator organisms. Additionally, under the already-implemented Total Coliform Rule, systems are monitoring the distribution system for total coliforms. A positive total coliform sample would trigger additional monitoring of the source water for fecal indicator organisms. If the source is positive for fecal indicators, the system must notify the state and the public. Unless immediate corrective action is directed by the state, the system operators must collect another five samples and re-test within 24 hours of the initial positive result. If another sample is positive, the state and public must be notified and a corrective action must be initiated. States have the ability to require systems to conduct source water assessment monitoring at any time in order to identify high risk systems.
Optional hydrogeological assessements are aimed at identifying aquifers that are sensitive to fecal – and thus potentially microbial – contamination. The EPA estimates that 15 percent of wells are located in sensitive hydrogeology;, for example, they have a high rate of permeability and are more likely to be contaminated with viruses. Specifically, the EPA identifies karst, gravel, sand and fractured rock aquifer settings as sensitive. Tracer studies could be used to determine groundwater flow velocities in sensitive versus non-sensitive aquifers. Shallow wells are also a concern, regardless of the hydrogeological assessment.
Corrective action technologies
Although non-treatment actions are available to systems that are identified as high risk, technologies that rely on treatment would be able to eliminate existing problems and are expected to preempt future waterborne disease outbreaks. Provided the appropriate concentration and contact time, chemical treatments identified to provide a 99.99 percent (4-log reduction) of viruses include disinfectants such as chlorine, chlorine dioxide, ozone or anodic oxidation. Membrane filtration technologies with an absolute molecular weight cut off are also available for virus removal, keeping in mind that viruses range in diameter from 20-900 nanometers. Ultraviolet (UV) inactivation may also provide the required removals; however, adenovirus, a recognized waterborne human pathogen, has recently been identified as being extremely resistant to UV treatment (1.); thus this technology is not considered an effective stand-alone treatment but may be very useful in combination with other technologies to achieve the overall 4-log removal required.
Approximately 114 million people in the US are served by a public water system with a groundwater source. About 100 million are on community water systems, while about 14 million receive water from a non-community water system. A total of 70.1 million people are served groundwater that is either not disinfected or is treated to less than a 99.99 percent efficacy for virus removal. Contamination often occurs intermittently and thus routine monitoring is key to effective targeting of high-risk systems.
Routine monitoring will also help with the assessment of the burden of waterborne disease, the likelihood of source water contamination and the efficacy of a single-treatment barrier (disinfection) for the mitigation of microbial contamination. There are many additional details and concerns associated with the Ground Water Rule that are beyond the scope of this review. The rule is, however, generally considered to be a comprehensive and proactive approach to reducing the risks of waterborne disease, from groundwater sources, in the public.
- Thurston-Enriquez JA, Haas CN, Jacangelo J, Riley K, Gerba CP (2003) Inactivation of feline calicivirus and adenovirus type 40 by UV radiation. Appl Environ Microbiol 69:577-582.
- USEPA (2006) Prepublication of ground water rule federal register notice. national primary drinking water regulations: ground water rule. 40 CFR Parts, 9, 141, and 142. EPA-HQ-OW-2002-0061; FRL-RIN-2040- AA97.
- USGAO (1993) Drinking water key quality assurance program is flawed and underfunded. GAC/RCED-93-97.
About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at firstname.lastname@example.org.