Water: Drinking Water Standards
GROUND WATER RULE: Ground Water Monitoring BACKGROUND ON MONITORING TOOLS
Draft April 23, 1998
EPA has the responsibility to develop a ground water rule which not only specifies the appropriate use of disinfection but, just as important, addresses other components of ground water systems to assure public health protection. Section 1412(b)(1)(A) of the Safe Drinking Water Act (SDWA) requires EPA to establish National Primary Drinking Water Regulations for contaminants that may have an adverse public health effect and that present a meaningful opportunity for health risk reduction. This general provision is supplemented with an additional requirement under Section 1412(b)(8) that EPA also develop regulations specifying the use of disinfectants for ground water systems as necessary. To meet these requirements EPA is working with stakeholders to develop a Ground Water Rule (GWR) proposal by March 1999, and a final rule by November 2000.
Assurance that the drinking water is not fecally contaminated is the key issue for any drinking water system. Fecally contaminated waters are likely to contain enteric pathogens, which can cause gastrointestinal illness (diarrhea, fatigue, cramps, etc.), hepatitis A, meningitis, ulcers, myocarditis, typhoid fever, cholera, and a host of other diseases. Identifying which ground waters are, or may be, vulnerable to fecal contamination is a critical issue for the GWR. Monitoring plays an important role both in detecting fecal contamination in source waters, as well as in assessing best management practices and disinfection in place.
Two approaches for determining whether a well is contaminated is to monitor for the presence of either pathogens or their surrogates. Individual pathogen monitoring, however, is impractical because the large number and variety of pathogens makes a comprehensive search for all extremely time-consuming, expensive, and difficult. Moreover, methods are not available for some pathogens; some microbes have not yet even been recognized as being pathogens; and pathogen concentrations in water are usually sufficiently small to require analysis of large-volume samples, which significantly increases analysis costs. For these reasons, EPA is focusing on indicators of fecal contamination rather than on individual pathogens, themselves, as a screening tool to identify vulnerable or at-risk wells. Under this approach, if a well is fecally contaminated, the system will be required to take corrective action.
The Agency is evaluating several promising indicators of fecal contamination. Analytical methods for the several bacterial indicators being considered (E. coli, enterococci, Clostridium perfringens) are simple, reliable, inexpensive, and commercially available. EPA is also considering the coliphage, which are viruses that infect the bacterium E. coli. Methods for the two major groups of coliphage being considered -- the somatic phage and the male-specific phage -- are relatively simple and inexpensive. The Agency is focusing especially on E. coli, enterococci, and male-specific coliphage as the candidate indicators. In evaluating the utility of microbial indicators of fecally contaminated ground water, EPA is considering factors such as method cost, feasibility, performance, and availability, as well as occurrence data on the ground water surveys currently being conducted.
Currently, all ground water systems must comply with the Total Coliform Rule (TCR). Total coliforms are a group of closely related bacteria that are used to determine the effectiveness of water treatment, evaluate the integrity of the distribution system, and serve as a rough screen for fecal contamination. Under the TCR, total coliform samples are tested at the tap. This means that, for an untreated ground water supply, the system cannot easily determine whether the presence of a total coliform-positive (or E. coli-positive) sample represents a contaminated source water or a problem in the distribution system itself. Another issue is the low monitoring frequency required under the TCR for small systems. For example, community water systems serving 1,000 people or fewer only need to monitor once per month (once per quarter in certain cases); a similar size non-community water system needs to monitor only once per quarter or less.
DATA SUMMARY and ANALYSIS
Information in the published literature about the occurrence of some pathogens and potential indicators in ground water is available, and indicates that pathogenic viruses and bacteria can be present in ground water (see microbial occurrence fact sheet). Additional data exist on the occurrence of microbial indicators in human stool samples and in sewage, and their association with fresh fecal contamination.
Table 1 represents a summary of some promising indicators of fecal contamination in undisinfected ground waters. EPA is also examining the utility of total coliforms and measurement of enteroviruses (polioviruses, echoviruses, and coxsackieviruses) with the assistance of the polymerase chain reaction (AWWSC is conducting this investigation).
As Table 1 indicates, the bacterial indicators are typically found in all human stool samples and in sewage at high densities (106 - 109+/L in sewage). Coliphage are also common in sewage (106/L), at least in large communities, but are not found in all human stool samples (50% for somatic phage, <5% for male-specific phage).
Table 2 indicates that analytical methods are available for the indicators identified above. There is an issue of sample volume for the bacterial indicators; increasing the volume from 100 mL to 1L will increase the sensitivity of the indicators ten-fold. Enteric virus methods are available, but are currently expensive (about $250-$1,000/sample). All costs are estimates, and will vary (costs in parentheses refer to the sample volume in parentheses, i.e., a larger sample volume will be more expensive)
EPA is awaiting more results from on-going ground water occurrence studies so that indicator selection is based on as much information as possible regarding the co-occurrence of various indicators with pathogens. The Agency is also awaiting the results of research on somatic and male-specific coliphage to determine the utility and cost of these two groups as monitoring tools.