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"My well has an estimated 20 years of life left, but that's not going to happen," says Jack McCormick, a 20 -year resident of Plum Valley Heights, a 29 -home neigh- borhood tucked in the foothills between Sedalia and Highlands Ranch. "I don't think it'll go more than 10." McCormick and his neighbors rely on an aquifer in a marginal zone scientists predicted would be the first to show signs of the vast underground reserve's limits. How quickly wells in other areas of the basin will drop, and how long it will be economically feasible to pump this racniirra is rlahatahla UNDERSTANDING WHAT'S UNDERGROUND The Denver Basin is a geologic formation that stretches from Greeley south to Colorado Springs and from Limon west to Jefferson County. Four aqui- fers —the Dawson, Denver, Arapahoe and Laramie - Fox Hills —hold its water reserves. They're stacked and tilted like bowls. While in some areas the aquifer can be recharged — surface water can seep back into tiny pore spaces within or between rocks –it may take thousands of years. That makes this resource, while immense, essentially nonrenewable. Each year, groundwater measure- ments from select wells in the Denver Basin are published by the Colorado Division of Water Resources. The validity of these data is sometimes questioned. The wells measured are not dedicated to monitoring and vary significantly in age and how they are pumped, among other things. Consistent annual trends indicate that depending on the location of the well, water levels in the Denver Basin aquifers are either relatively stable, declining, or even rising. It all depends on the aquifer and the location of the measurement well. In the aquifers used predominately by the high - volume wells necessary for municipalities, specifically the Arapahoe and Laramie -Fox Hills, water level declines are significant. Between 1990 and 2000, ground- water levels in the Arapahoe aquifer declined from 100 to almost 300 feet. Municipalities relying almost exclusively on groundwater, such as Castle Rock or Parker, are concerned about how the aquifer will react and how long it will last, as pumping increases. Rural water users with private domes- tic wells are also concerned. If their water supply fails, they do not have the water utility managers or paid water brokers readily - available to help them find other sources of water. The issue becomes more complex as economics, water rights, legislation areas may have little to worry about. Similarly, the shallower Dawson and Denver aquifers which are more eas- ily recharged by irrigation and precipita- tion, remain steady or show water level increases in some areas. Homeowners with wells in those locations may not observe any decrease in well production for years, if ever. But the situation is very different for areas in Douglas County where high volume pumping from the Arapahoe aquifer has caused dramatic declines. In some areas, 40 feet drops per year have been recorded and it is anticipated well flow rates will diminish during the next decade. Jack McCormick is a 20 -year resident of Plum Valley Heights. The 29 -home community is between Sedalia and Highlands Ranch, on the western rim of the Denver Basin aquifers. As scientists predicted, groundwater levels in the area are dropping, necessitating new and deeper wells for homeowners, as well as the installation of cisterns. and advances in technology and sci- ence are stirred into the mix. And then there's growth: State projections fore- cast an additional 1.7 million people will call Colorado home by 2015 and more than 80 percent will live along the Front Range. They'll need water. LOCATION, LOCATION, LOCATION Although south metro municipal pro- viders can anticipate decreased well pro- duction, this isn't the case throughout the entire basin —a fact some well experts and water entrepreneurs like to reiterate. Much of the problem with dropping Denver Basin aquifers depends on loca- tion. Water tightly held in sandstone does not move very far, and if it does, it may take thousands of years. In loca- tions where demand is modest and the resource large, such as the eastern plains, these aquifers should provide many years of adequate supply. Private domestic wells tapping the Denver Basin in these AN EXHAUSTIBLE RESOURCE? Concern over the amount of water being pumped from deep non- renewable aquifers started decades ago. After a vari- ety of groundwater - related legislation in the 1950s and 1960s, in 1973 Senate Bill 213 set out to allocate who could use Denver Basin groundwater, and in what quantity. The act determined that the Denver Basin aquifers could be pumped at rates that might allow, based on the best available data, a minimum 100 -year life. Landowners overlying the Denver Basin groundwater would have the right to withdraw that water at the rate of 1 percent per year. Yet by the early 1980s, the population of south - Denver communities was grow- ing at a startling rate, accompanied by a spike in speculative groundwater claims. Developers were keen to pump the read- ily- available groundwater. Many people wanted to take advantage of the high - quality Denver Basin aquifers, but the state needed more guidance to ensure that the resource would be meted out fairly. In 1985, complex legislation com- monly known as Senate Bill 5 developed specific rules and a basic legal frame- work of how Denver Basin groundwater should be allocated. By enacting this legislation, the Colorado legislature agreed that it was acceptable to mine —or take out more water than is replaced —the Denver Basin HEADWATERS I SUMMER 2006 is