Coliform Bacteria and Nitrate Contamination of Wells in Major Soils of Frederick, Maryland.Introduction Groundwater supplies drinking water drinking water supply of water available to animals for drinking supplied via nipples, in troughs, dams, ponds and larger natural water sources; an insufficient supply leads to dehydration; it can be the source of infection, e.g. leptospirosis, salmonellosis, or of poisoning, e.g. to over 100 million people in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. (1). Approximately 90 to 95 percent of rural Americans use well water as a source for their drinking water supply; in municipal areas, 75 percent of the water supply systems use some groundwater (2,3). Therefore, the quality of groundwater supplies is an important public health concern. Since soil can treat microbial microbial pertaining to or emanating from a microbe. microbial digestion the breakdown of organic material, especially feedstuffs, by microbial organisms. contaminants in water that percolates from the ground surface, groundwater is normally assumed to be free of pathogenic microorganisms (3). Nevertheless, many waterborne disease outbreaks have been caused by contaminated contaminated, v 1. made radioactive by the addition of small quantities of radioactive material. 2. made contaminated by adding infective or radiographic materials. 3. an infective surface or object. groundwater (4). One potential source of well contamination is effluent from septic systems. When septic system effluent moves through soil for a sufficient period of time, bacteria and viruses are likely to be removed by straining, adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). , and die-off (3). If absorption fields are too close to a high water table, permeable sand and gravel, or fractured rock, adequate sewage attenuation Loss of signal power in a transmission. Attenuation The reduction in level of a transmitted quantity as a function of a parameter, usually distance. It is applied mainly to acoustic or electromagnetic waves and is expressed as the ratio of power densities. may not occur, and microorganisms may enter the groundwater (5). If the soil is very impermeable impermeable /im·per·me·a·ble/ (-per´me-ah-b'l) not permitting passage, as of fluid. im·per·me·a·ble adj. Impossible to permeate; not permitting passage. , the sewage effluent may not be absorbed by the ground, and it may emerge onto the surface of the ground. Poorly constructed wells near such sewage flow can be contaminated by surface water infiltration (6). Kross et al. reported that 44.6 percent of private water systems in Iowa tested positive for total coliform bacteria coliform bacteria Rod-shaped bacteria usually found in the intestinal tracts of animals, including humans. Coliform bacteria do not require but can use oxygen, and they do not form spores. They produce acid and gas from the fermentation of lactose sugar. , and nitrate contamination was more significant in wells less than 99 feet deep (7). In addition, Risch and Cohen cohen or kohen (Hebrew: “priest”) Jewish priest descended from Zadok (a descendant of Aaron), priest at the First Temple of Jerusalem. The biblical priesthood was hereditary and male. reported a general increase in nitrate concentrations in Indiana groundwater from 1973 to 1991 (8). The presence of coliform bacteria is an indicator of possible sewage pollution and is the principal microbiological parameter used in determining water quality; high levels of coliform bacteria may indicate contamination by fecal coliform bacteria (7,9). Noncoliform pathogens such as Staphylococcus aureus Staphylococcus au·re·us n. A bacterium that causes furunculosis, pyemia, osteomyelitis, suppuration of wounds, and food poisoning. Staphylococcus aureus Staphylococcus pyogenes and Salmonella can also be present in sewage (10). Nitrates are also an important septic system contaminant contaminant /con·tam·i·nant/ (kon-tam´in-int) something that causes contamination. contaminant something that causes contamination. . The standard set by the U.S. Environmental Protection Agency Environmental Protection Agency (EPA), independent agency of the U.S. government, with headquarters in Washington, D.C. It was established in 1970 to reduce and control air and water pollution, noise pollution, and radiation and to ensure the safe handling and (U.S. EPA EPA eicosapentaenoic acid. EPA abbr. eicosapentaenoic acid EPA, n.pr See acid, eicosapentaenoic. EPA, n. ) for nitrates is 10 milligrams per liter (mg/L) nitrate-nitrogen ([N[O.sub.3]-N) (11). This standard was chosen to prevent methemoglobinemia Methemoglobinemia Definition When excessive hemoglobin in the blood is converted to another chemical that cannot deliver oxygen to tissues, called methemoglobin. in infants (12). Some investigators have hypothesized that nitrates are carcinogenic carcinogenic having a capacity for carcinogenesis. , although there is currently no definitive evidence that they are responsible for the development of cancer or other disorders (11,13,14). Because of the potential public health impact of groundwater contaminated with coliform bacteria and nitrates, the hypothesis [TABULAR DATA FOR TABLE 2 OMITTED] that septic systems may be a source of well contamination was tested in Frederick County, Maryland Frederick County is located in the western part of the U.S. state of Maryland, bordering the southern border of Pennsylvania and the northeastern border of Virginia. It is a part of the Washington-Baltimore Metropolitan Area, and is often recognized as part of Western Maryland. . The prediction that well contamination increases as lot size decreases was tested first. Septic system contamination may occur more readily when a well is located on a small lot, since the well and septic system may be close to one another. Also, wells on smaller lots are usually close to septic systems on other lots. As a result, less soil may be present for treatment of coliform bacteria.
TABLE 1
Soil Groups (5)
Soil Group Parent material
Chandler/Talledaga Hard talcose schist and mica schist
Chester Micaceous schist; white quartzite present
on uplands
Edgemont Quartz schist, quartzitic sandstone,
quartzite conglomerate, pure quartzite
Glenelg/Chester Micaceous schists
Hagerstown/Duffield Limestone
Highfield Metabasalt with considerable quartzite
Linganore Hard slaty schist or phyllite
Manor/Glenelg Thin, platty schistose rock
Myersville/Fauquier Metabasalt
Penn/Readington/Croton Red, Triassic-age sandstone and shale
A second prediction was also tested - that as casing length in wells increases, there will be a decrease in coliform bacteria and nitrate contamination. The well casing and grouting grout n. 1. a. A thin mortar used to fill cracks and crevices in masonry. b. A thin plaster for finishing walls and ceilings. 2. Chiefly British Sediment; lees. Often used in the plural. function as a barrier against the entry of contaminated groundwater and surface water. Longer lengths of casing may be more likely to exclude undesirable groundwater from the well borehole bore·hole n. A hole that is drilled into the earth, as in exploratory well drilling or in building construction. . Methodology The coliform bacteria and nitrate level test results for 832 wells were obtained from Frederick County, Maryland, Health Department records. All well samples collected between 1983 and 1991 from wells that were grouted and cased (casing is extended above the surface of the ground) and that were located in an area not being used for commercial agriculture at the time of sampling were analyzed. Approximately 60 percent of these 832 wells were newly constructed and were analyzed within a short period after construction. The multiple-tube fermentation technique, with 10 mL of water in five separate tubes, was used to measure the presence of coliform bacteria. The five-tube test is a measurement of the most probable number (MPN MPN Master Promissory Note MPN Most Probable Number MPN Medical Provider Network MPN Mobil Producing Nigeria MPN Manufacturer's Part Number MPN Military Personnel, Navy MPN Mobile Private Network MPN Managed Private Network MPN Mode Partition Noise ) of bacteria per 100 mL (9). The number of positive tubes was the independent variable used in the statistical analysis for this study (one positive tube indicated the lowest degree of contamination, and five positive tubes indicated the greatest contamination). Nitrate levels were determined using the cadmium reduction method, and are reported in milligrams per liter as nitrate-nitrogen (N[O.sub.3-N) (9). Lot size and well construction information were obtained from well completion reports, tax records, and building permits. Soil types were determined using the Frederick County, Maryland, Soil Survey; property maps; subdivision [TABULAR DATA FOR TABLE 3 OMITTED] plats; site plans; well permits; and well completion reports. The wells were sorted by soil type, and those with similar parent material (e.g., limestone soils) were combined into groups (5). Ten soil groups were defined (Table 1). A Spearman spear·man n. A man, especially a soldier, armed with a spear. rank-order correlation coefficient Noun 1. rank-order correlation coefficient - the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables rank-difference correlation, rank-difference correlation coefficient, rank-order correlation (RHO Rho The rate at which the price of a derivative changes relative to a change in the risk-free rate of interest. Rho measures the sensitivity of an option or options portfolio to a change in interest rate. ) was calculated for the relationship between lot size and both coliform bacteria and nitrate contamination using the SYSTAT statistical program 15). The Spearman RHO [TABULAR DATA FOR TABLE 4 OMITTED] was used to test the association between these variables because the data were not normally distributed and various transformations did not yield a normal distribution. The Spearman RHO was calculated within each soil group and for all data combined. If the probability of the value of RHO was less than .05, the correlation was considered significant. A sign test was used to determine if there was a random distribution of positive and negative correlations for each pair of variables across the different soil groups (16). TABLE 5 The Effect of Casing Length on Coliform Bacteria and Nitrate Contamination in Wells (Unsewered Areas) Casing Range % Wells % Coliform Bacteria % N[O.sub.3]-N (feet) in Range Contamination Contamination 20 3.2 51.9 59.3 21-30 15.1 45.1 69.7 31-40 14.5 38.4 70.4 41-50 25.2 32.4 71.0 51-60 9.1 35.5 67.1 60+ 32.7 31.6 22.8 To determine which lot-size categories exhibit nitrate contamination potential, soil groups that showed a significant correlation between lot size and nitrate contamination level were categorized by size. Selection of size categories was based on the range of lot sizes found in each soil group. The percentage of wells contaminated with [N[O.sub.3]-N at the 5 mg/L level (the level at which U.S. EPA has determined that increased monitoring will occur in public water supplies) was calculated for each category (11). A Spearman RHO was also calculated for both coliform bacteria and nitrate contamination in relation to length of well casing for all wells in unsewered areas. A sign test was used to determine if the directions of the correlation coefficients were random among soil types (16). Results A significant negative correlation between coliform bacteria contamination and lot size was found only in the Edgemont soil group (Table 2). The two smallest lots in this soil group were contaminated with fecal coliform bacteria. In nine of the 10 soil groups, however, the correlation coefficient was negative (sign test p [less than] .05) (Table 2). If there were no overall relationship between lot size and contamination with coliform bacteria, there would be an equal number of positive and negative RHO values. For three of the soil groups, a significant negative correlation was found between nitrate contamination and lot size (Table 2). The significant negative correlation found for all wells was probably due primarily to the large sample for the Manor/Glenelg soil group. A negative correlation between nitrate level and lot size was present in seven of the 10 soil groups (sign test p [greater than] .05). In the Manor/Glenelg soil group, nitrate contamination levels clearly decreased as lot size increased (Table 3). Although nitrate levels in Highfield soil were relatively low, the contamination level may still be related to lot size. In the Penn/Readington/Croton soil group, the pattern of nitrate contamination in relation to lot size was not as tight as in the other two soil groups. A significant negative correlation was found between coliform bacteria and casing length in the Manor/Glenelg soil group. The significant negative correlation found in all wells was also probably due to the large sample size of the Manor/Glenelg soil group. In seven of the 10 soil groups, there was a negative correlation between coliform bacteria contamination and casing length (sign test p [greater than] .05). Table 4 shows a negative significant correlation between nitrate contamination and well casing length for all wells combined and for the Penn/Readington/Croton soil group individually. A negative correlation was found in seven soil groups (sign test p [greater than] .05). When the wells were grouped by casing length regardless of soil type, there was an inverse relationship A inverse or negative relationship is a mathematical relationship in which one variable decreases as another increases. For example, there is an inverse relationship between education and unemployment — that is, as education increases, the rate of unemployment between the percentage of coliform bacteria contamination and casing length (RHO = -0.94, df = 5, p [less than] .01) (Table 5). There was not, however, a significant correlation between nitrates and casing length (RHO = 0.2, df = 5, p [greater than] .05). Discussion Nine of the 10 soil groups exhibited a negative correlation between lot size and coliform coliform /col·i·form/ (kol´i-form) pertaining to fermentative gram-negative enteric bacilli, sometimes restricted to those fermenting lactose, e.g., Escherichia, Klebsiella, or Enterobacter. contamination of wells, suggesting that septic systems contributed to coliform contamination of wells on small lots. In addition, the significant negative correlation between lot size and coliform contamination in the Edgemont soil group and the presence of fecal coliform bacteria in wells located on the two smallest lots indicate that the wells in this soil group were particularly vulnerable to contamination. Exner and Spalding also reported that wells located near a point source (intermittently used barnyards) were more frequently contaminated with coliform bacteria (17). Coliform bacteria attenuation may be increased when shallow disposal systems and sand filters are Used on lots less than one acre (10). The negative correlation between lot size and nitrate contamination for all wells and for wells located in three soil groups suggests that nitrate contamination of wells in these soil groups originated from septic systems and was not due to residual nitrogen from past agricultural land use (Table 2). Studies by Exner and Spalding and Tjostem et al. suggested that elevated levels of nitrates in groundwater are due to point-source contamination (e.g., barnyards and septic systems) and are not caused by the past agricultural use (17,18). The observations of this study that indicate that septic systems contribute to the contamination of wells are also supported by Tinker, who found that nitrate levels were higher in wells located on the down-gradient side of a subdivision in Wisconsin, and by Ford et al. who found that nitrate levels decreased in wells as their distance from septic systems increased (19,20). A buffer strip of trees planted below a septic system may sequester sequester v. to keep separate or apart. In so-called "high-profile" criminal prosecutions (involving major crimes, events, or persons given wide publicity) the jury is sometimes "sequestered" in a hotel without access to news media, the general public or their the nitrates from a septic system and thus reduce nitrate entry into wells located in a down-gradient area. Also, sewage effluent denitrification de·ni·tri·fy tr.v. de·ni·tri·fied, de·ni·tri·fy·ing, de·ni·tri·fies 1. To remove nitrogen or nitrogen groups from (a compound). 2. methods could be used to reduce nitrate loading rates when septic systems on small lots are repaired or upgraded (21). Ford et al. found that improper well construction, not well depth, was a factor that caused increased levels of coliform bacteria contamination in wells (20). The clear inverse relationship between coliform bacteria contamination and casing length found in this study and observed by Tjostem et al. suggests that coliform contamination may be reduced by using longer well casing lengths (18). Specifically, a minimum length of 40 feet of casing should be used when wells are constructed in the Manor/Glenelg soil group (Table 5). Conclusion The relationship between 1 bacteria and nitrate contamination and lot size suggests that septic systems may cause increased levels of well contamination as lot sizes decrease. Installation of adequate septic systems is needed on existing small lots to ensure attenuation of coliform bacteria. A long-range study is needed to determine what changes septic system use causes in nitrate concentrations in wells in a subdivision. Information from such a study could show the long-term nitrate contribution to the groundwater caused by septic systems and could be used in making zoning decisions about minimum residential lot size in unsewered subdivisions. Coliform bacteria contamination was highest when casing lengths were shortest, suggesting that coliform bacteria contamination in deep wells may be caused by inadequate casing length. Examining coliform bacteria contamination in wells of different depths with the same casing length and in the same geological area would further test the effect of casing length. Did you know ... Aquifers from which much of the nation draws its drinking water are shrinking faster than they can be replenished. As this happens, they become increasingly vulnerable to toxic contamination. (Source: U.S. Dept. of Health & Human Services, Public Health Service) Acknowledgement: The authors thank the Environmental Health staff of the Frederick County Frederick County is the name of several counties in the United States.
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3. Bouwer, H. (1984), "Elements of Soil Science and Groundwater Hydrology hydrology, study of water and its properties, including its distribution and movement in and through the land areas of the earth. The hydrologic cycle consists of the passage of water from the oceans into the atmosphere by evaporation and transpiration (or ," Groundwater Pollution Microbiology, G. Bitton and C.P. Gerba, eds., New York: John Wiley and Sons, Inc., pp. 9-37. 4. Moore, A.C., R.L. Calderon, C.F. Craun, B.L. Herwaldt, A.K. Highsmith, and D.D. Juranek (1994), "Waterborne Disease in the United States, 1991 and 1992,"Journal of the American Water Works Association American Water Works Association (AWWA) is an international nonprofit professional organization dedicated to the improvement of drinking water quality and supply. It was founded in 1881 and, as of 2007, there are approximately 60,000 AWWA members world-wide. , 86(2):87-99. 5. The Catoctin and Frederick Soil Conservation Districts (1985), Frederick County Maryland Soil Survey Supplement Text and Tables, USDA USDA, n.pr See United States Department of Agriculture. , pp. 16-34, 131. 6. Miller, J.C. (1972), Nitrate Contamination of the Water-Table Aquifer in Delaware, Delaware Geological Survey, pp. 1-2. 7. Kross, B.C., D.R. Bruner, G.R. Hallberg, R.D. Libra, et al. (1990), The Iowa State-Wide Rural Well-Water Survey. Water-Quality Data: Initial Analysis, Iowa Department of Natural Resources The Iowa Department of Natural Resources (Iowa DNR or IA DNR) is a department/agency of the U.S. state of Iowa charged with maintaining state parks and forests; protecting the environment; and managing energy, fish, wildlife, land resources, and water resources of Technical Information Series 19, pp. 43-45, 97, 99, 102. 8. Risch, M.R., and D.A. 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(1991), "Potential health consequence of ground-water contamination by nitrates in Nebraska," Nitrate Contamination: Exposure, Consequence, and Control, I. Bogardi and R.D. Kuzelka, eds., NATO NATO: see North Atlantic Treaty Organization. NATO in full North Atlantic Treaty Organization International military alliance created to defend western Europe against a possible Soviet invasion. ASI ASI, n See Anxiety Sensitivity Index. Series G: Ecological Sciences 30, Berlin:. Springer-Verlag pp. 309-315. 15. SYSTAT Statistical Program (1990), Evanston, Ill.: SYSTAT, Inc. 16. Seigel, S. (1956), Nonparametric Statistics for the Behavioral Sciences behavioral sciences, n.pl those sciences devoted to the study of human and animal behavior. , New York: McGraw-Hill Book Co. 17. Exner, M.E., and R.F. Spalding (1985), "Groundwater Contamination and Well Construction in Southeast Nebraska," Groundwater, 23 (1): 26-34. 18. Tjostem, J.L., C. Hoilien, and R.E. Iverson, and J. Young (1985), "Bacterial and Nitrate Contamination of Well Water in Northeast Iowa," Proceedings of the Iowa Academy of Sciences, 84(1):14-22. 19. Tinker, J.R., Jr., (1991), "An Analysis of Nitrate-Nitrogen in Groundwater Beneath Unsewered Subdivisions," Groundwater Monitoring Review, 11 (l): 141-150. 20. Ford, K.L., T.J. Keefe, and J.H. Schott (1980), "Mountain Residential Development and Minimum Well Protective Distances - Well Water Quality," Journal of Environmental Health, 43(3): 130-133. 21. Piluk, R.J. (1988), "Field Study of an Innovative On-Site Wastewater Disposal System for Nitrogen Reduction," Master's thesis, College Park: University of Maryland University of Maryland can refer to:
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