The same way water gets contaminated from the guts of any animal - bacteria live in your gut and your excreta and if they get in your drinking water can make you sick. Water levels are likely shallow there so whatever enters at the surface isn't sufficiently worked over by soil microbes before reaching the aquifer. How long to boil usually depends on your elevation, but about 10 minutes is probably a good rule of thumb, unless you're at pretty high elevation.
In Maine, Usually, the 300 foot mark circle around a well head/well is meant (desired) to be undisturbed or used. Potential sources of contamination (PSC) would include any “activities” that might introduce bacteria, viruses and contaminants into the water. We have a common list of about 80 common PSCs, it includes everything from water bodies, grazing, tanks, roads, parking lots, establishments, cemeteries, septics, gas lines and on and on. So if something is within the 300 foot radius, the chances for contamination are higher, regardless of the depth of the well. Gray water and guts/fecal matter certainly is a concern.I believe EPA has now set the time criteria at 1 minute ROLLING BOIL for disinfection of water.
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