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The protection of public health through quality public ground-water systems is the responsibility of the U. S. Environmental Protection Agency and the State of Missouri, through the Missouri Department of Natural Resources, Public Drinking Water Program. Approximately 95 percent of the public-water supplies in Missouri use ground water as their source of drinking water through more than 3,700 public wells. Karst terrain, intensive agricultural operations, extensive numbers of on-site sewage systems, and poor well construction can lead to chemical and microbiological contamination of the contributing aquifers. Sitespecific studies and routine regulatory monitoring have produced information on the overall quality and potability of the State's public-drinking-water supplies, but little is known about the presence of viruses. The U.S. Geological Survey, in cooperation with the Missouri Department of Natural Resources, sampled 109 public-water supplies to characterize the physical, chemical, bacterial, and viral conditions in southern Missouri. During April to July 1998, these wells were sampled for nutrients, total organic carbon, optical brighteners, indicator bacteria, enteric viruses, and ribonucleic acid and somatic coliphages. These constituents indicate possible surface contamination of the sampled aquifer. Selection of the wells to be sampled depended on the age of the well (pre-1970), land use, geohydrology, and well construction. None of the physical or chemical constituents measured or analyzed exceeded Missouri's Drinking Water Standards set by the Public Drinking Water Program of the Missouri Department of Natural Resources. The majority of ammonia plus organic nitrogen, nitrite, and phosphorus concentrations were below the laboratory's minimum reporting levels. There were a greater number of detects above the minimum reporting level with respect to the nitrite plus nitrate, ammonia, orthophosphate, and total organic carbon concentrations. Analyses included comparing and contrasting the data by grouping according to well age and construction, karst type, geohydrology, soil type, and land use. There was little variation in well construction between selected wells. The results indicated several groupings of similar and dissimilar concentrations, most expected because of hydrological, physical, or land use differences. Dissolved oxygen values indicated distinct variation in the different groupings. There were significant differences in dissolved oxygen values between the secondary and non-karst areas, the Ozark confined and Ozark unconfined geohydrologic groups, and between agricultural and other land uses. In groupings by soil and geohydrology, the Missouri bootheel region differed with respect to ammonia, total organic carbon, and phosphorus when compared with the other groups. Less than 10 percent of the wells sampled tested positive for bacterial contamination. E. coli was the most frequently detected bacterium. The public wells at Monett and West Plains, Missouri, Abstract 1 had plates with colonies too numerous to count for all three indicator bacteria. Further analyses by rRNA (ribosomal RiboNucleic Acid) hybridization techniques determined that much of the bacteria present were from ruminant and human sources. No enteric viruses were detected in the 109 samples. Both ribonucleic acid and somatic coliphage were detected at two wells. One additional well had ribonucleic acid coliphage and another had somatic coliphage for a total of four wells with coliphage selects. INTRODUCTION The U.S. Environmental Protection Agency (USEPA) and the Missouri Department of Natural Resources, Public Drinking Water Program (MDNRPDWP) have the responsibility to address public ground-water systems to assure the protection of public health. Section 1412(b)(l)(A) of the Safe Drinking Water Act requires that National Primary Drinking Water Regulations be established for contaminants that may have detrimental effects on public health. This requirement, along with an additional requirement under Section 1412(b)(8) that specifies that the USEPA develop regulations for the use of disinfectants for ground-water systems as needed, has prompted the development of a Ground Water Rule (GWR). The GWR is a method to prioritize drinking-water supplies by their vulnerability to be contaminated by pathogenic microorganisms. In Missouri, residents and commercial operations are greatly dependent on ground water as a clean source of drinking water. Approximately 95 percent of the public-water supplies in Missouri use ground water as their source of drinking water through more than 3,700 public wells. Karst terrain, intensive agricultural operations, extensive numbers of on-site sewage systems, and poor well construction can lead to chemical and microbiological contamination of the contributing aquifers. State resource managers are concerned about the impact of these conditions on the microbiological and chemical quality of the ground water in the State. Currently (1999), much is known about the status of bacterial contamination of the public-water supplies through studies and monitoring efforts, but little is known about viral contamination or the effects of leaking septic systems on the contributing aquifers. Virus populations fluctuate with the natural conditions of aquifers, which tend to make their detection a hit-or-miss opportunity. Since the early 1900's, drinking water disinfection has been used to decrease the risks of waterborne pathogens. Widespread outbreaks of typhoid fever, cholera, and other bacterial diseases prompted the need to disinfect drinking-water supplies. Enteric viruses have caused epidemics, even when the drinking water has met all of the water-quality standards for coliform bacteria, turbidity, and chlorine residuals. Results from a recent study of gastroenteritis suggested that drinking water was responsible for one-quarter to one-third of all such illnesses reported, even though the drinking water met all required standards (Sobsey, 1995). Animal or human sewage or pasture runoff can contain detrimental microorganisms such as E. Co//, Salmonella, and enteric viruses, and can cause gastroenteritis. Enteric viruses are indicators of materials associated with the digestive tract such as sewage. Viruses are composed of genetic material that survive and reproduce by attacking or invading other living cells. As they take over another cell, they destroy the original cell's genetic material and replace it with its own. This ability enables the viruses to survive and flourish. Coliphages are viruses that infect coliform bacteria specifically. Two types of coliphages are RNA (ribonucleic acid) coliphage (also know as Male Specific), and somatic coliphage. These coliphages differ in how they infect the host bacteria. The RNA coliphage infects the bacteria cells by entering through the sex pili; the somatic coliphage enters the cells through the cell wall. The U.S. Geological Survey (USGS), in cooperation with the MDNR-PDWP, has completed two phases of a study to characterize the bacterial and viral conditions in the ground water of southern Missouri. The first phase (Phase I) of the study is documented in Davis and Witt (1999). The data from the two sampling periods of the Phase I study indicate that microbiological contamination of public-water-supply wells drilled after 1970 is not widespread in the Ozark Plateaus. A small percentage (10 to 14) of the wells sampled in Phase I are contaminated by potentially pathogenic viruses or other pathogen indicator organisms. Also, results from the two periods of sampling varied considerably. More than a single sampling opportunity is needed to definitively address the presence or lack of viruses in the drinking-water-supply aquifers. Microbiological and Chemical Quality of Ground Water Used as a Source of Public Supply in Southern Missouri-Phase II The objectives of the Phase II study were to determine if the chemical and microbiological quality of the ground water is affected by land use, soil, geohydrology, karst type, well construction or well age; to use optical brighteners as an indicator of onsite sewage migration to the sampled aquifer; the effectiveness of the USEPA Ground Water Disinfection Rule (GWDR) Vulnerability Assessment Plan (VAP) (U.S.Environmental Protection Agency, written commun., 1998) to categorize wells into vulnerability classes; and the type of microbiological contamination in affected wells. The purpose of this report is to describe the study and to present the data, analyses, and conclusions derived from the data collected for this study. This report includes a description of the study area and sampling network, design, and methods. Also included are discussions of the chemical and physical data, the use of optical brighteners as a detection method, microbiological data, and the usefulness of the VAP in southern Missouri. During this second phase (Phase II) of the study, 109 public-water-supply wells were sampled to characterize the physical, chemical, bacterial, and viral conditions in southern Missouri (table 1, at the back of this report). These wells were sampled from April to July 1998 for nutrients, total organic carbon, optical brighteners, indicator bacteria, enteric viruses, and RNA and somatic coliphages. The presence of these constituents indicate possible surface contamination of the sampled aquifer. Selection of the wells to be sampled depended on well age, land use, geohydrology, and well construction. Phase II studied older wells, drilled before 1970, to determine if age and construction would contribute to susceptibility to surface contamination. DESCRIPTION OF STUDY AREA The study area is located in the southern one-half of Missouri and consists of parts of three major physiographic provinces (fig. 1). The Ozark Plateaus is the dominant physiographic province in southern Missouri. The Mississippi Alluvial Plain physiographic section

Microbiological and chemical quality of ground water used as a source of public supply in southern Missouri — Phase II, April–July, 1998