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1 <br />Even when a septic tank appears to be operating adequately from the <br />surface, the effluent may be short-circuiting to the groundwater. This is <br />' of particular concern when septic tanks are near a well field. The <br />increased rate of induced groundwater flow within the well field caused by <br />pumping operations enhances the probability of contaminants which emanate <br />' from septic tanks to leach into shallow water supply wells. <br />' The most widely used indicator of septic tank contamination is the coliform <br />bacteria. The coliform bacteria is not pathogenic itself, but its presence <br />' indicates the possibility of pathogenic bacteria and viruses. High <br />concentrations of total coliform bacteria may or may not indicate that the <br />water is contaminated by septic tanks since other sources of coliforms <br />' include plants, soil, and animals. The presence of fecal coliform bacteria <br />strongly suggests that the water is contaminated. Because these bacteria <br />' come from the feces of warm-blooded animals, they indicate that pathogenic <br />bacteria such as Salmonella (typhoid fever) and Shigella (shigellosis) may <br />be present in the groundwater. <br />' <br />Inasmuch as neither total coliform or fecal coliform indicate human <br />contamination conclusively, fecal streptococci can substantiate the source <br />' <br />of pollution. Fecal streptococci are also found in the intestines of <br />warm-blooded <br />animals. Fecal streptococci do not multiply in surface waters <br />and are rarely found in natural soil or vegetation. However, the <br />' <br />quantities of fecal coliform (FC) and fecal streptococci (FS) discharged by <br />humans differ significantly from quantities discharged by animals. Because <br />' <br />of this difference, the ratio of FC to FS can be used to show whether <br />suspected contamination is from human or animal wastes. Typical FC to FS <br />' <br />ratios for humans and other animals are as follows: <br />' <br />Ratio <br />Animal <br />FC/FS <br />chicken 0.4 <br />' <br />cow 0.2 <br />duck 0.6 <br />' <br />human 4.4 <br />IRC.VB4 <br />6/4/87 <br />