There are over 158,000 public ground water systems. Almost 89 million people are served by community ground water systems and 20 million people are served by non-community ground water systems. The largest numbers of ground water systems are in the States of Wisconsin, Michigan, Pennsylvania, New York and Minnesota. Systems with service populations between 10,000 and 50,000 have mean revenues of 2.2 million dollars and mean expenses of over 1.9 million dollars per year. Small community ground water systems, those serving less than 10,000, typically have between one to three operators, one or two of which have been certified by the State.
Larger systems have more operators.
Ground water systems serving more than 100,000 people have an average of seventeen operators, thirteen of which have been State certified. Vulnerability Assessment Techniques. Approximately 158,000 PWSs rely on ground water as their source for drinking water supplies. Given this large number of systems, an essential task in developing a proposed ground water rule is how to prioritize wells for further action or analysis. Given the varying availability of site-specific information in different situations, the three approaches presented below are not universally applicable to all ground water systems yet there may be more than one approach that can yield a satisfactory result.