Michael Kamrin and Jon Wyman Institute for Environmental Toxicology Michigan State University About half the population of Michigan depends on groundwater as the primary source of drinking water. Many of these individuals, especially those residing in rural areas, have their own wells. In light of recent reports of groundwater contamination in many areas of the state, much concern exists about the safety of well water. This bulletin is designed to address this concern and provide a guide to testing private wells. Groundwater initially fell to the earth as rain or snow and then percolated through the soil. It became trapped in underground layers called aquifers, which consist of sand, gravel and rock. Some of the aquifers are located near the surface, and others are far underground. They are irregular in shape, and wells drilled a few hundred feet apart may reach different aquifers. There may be several aquifers under a particular site, and wells may be drilled into any of these. Extensive regulations control the construction of wells. In addition, many local health departments require well-water testing before a new well is put into service. However, no regulations govern water quality in private wells. There are no enforceable limits for particular contaminants and no requirements for tests to be made on any regular basis. Often, health agencies will make recommendations as to the suitability of well water based on standards established for public drinking water supplies. These, however, are only recommendations. Many contaminants are natural. Where do these contaminants come from? Many are naturally occurring substances such as calcium, magnesium, silica and fluoride. As many

as 50 minerals may naturally occur in water; but these generally do not cause health problems, since they usually occur in such small amounts. More often they impact undesirable properties such as unpleasant taste, odor or hardness to the water. Some contaminants are living organisms, mainly soil bacteria. The ones which cause the most common odor, taste, smell and discoloration problems are the sulfur, iron and manganese bacteria. Occasionally, other types of bacteria, which indicate unsanitary conditions, are present. These may not affect the characteristics of water, but are indicators of the possible presence of disease-causing microorganisms. Other contaminants are man-made. These include a wide range of synthetic organic compounds, such as trichloroethylene, phenols, benzene and toluene. Other chemicals which may contaminate water are the heavy metals such as lead and cadmium, and salt or brine used on roads. In general, these contaminants pollute ground- water as a result of improper storage or disposal practices. Leaking underground storage tanks and leaking landfills are two common examples. At high-enough levels, these contaminants may render water unsuitable for drinking and may cause adverse effects on health. Contaminants which reach the groundwater generally move very slowly. In one sense this is a problem, since continued leakage in one spot will lead to gradually increasing levels of contaminants. With slow movement, there is little possibility of dilution. On the other hand, this slow movement means that most contaminants will be confined to a small area, and leakage in one place will not pollute a large region.

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