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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ from the Arapahoe aquifer. Most ground water supplies developed to date have come from the compressible portion of this water supply since the aquifer has been and remains at most locations in a confined condition. That is. water is being pumped from the artesian head that raises water levels well above the top of the aquifer when a well penetrates the water bearing strata. The available head in the aquifer effectively assists in bringing these supplies to the surface by reducing the total dynamic head required to deliver the supplies into potable water systems. Over particularly the last twenty years, as the aquifer has been actively mined, the artesian head in the Arapahoe Formation has been dropping at a rate approaching thirty feet per year. This means that the total dynamic head required to produce these supplies is increasing by approximately thirty feet year, requiring larger pumps and motors to produce the supply with increasing energy usage. As aquifer water levels drop, water drains more slowly to the well, and production rates drop off. As the regional head continues to decline in the future, additional wells will be required by the water suppliers to maintain historic pumping rates. This will add substantially to the cost of producing the same water supply. Therefore, ground water production costs will increase in the future both due to the operation costs associated with higher pumping heads and the increased capital costs as additional wells are necessary to meet the same demands. As water demands continue to expand with development, the water suppliers have generally fust maximized their production of Arapahoe aquifer supply and have then tapped their additional sources of supply. Generally, the water supplier will look to the next most economical supply available. In many cases, the development of additional water supplies tIuough water augmentation plans, where water returned to the stream is exchanged for additional withdrawals, or through large customer (golf courses and parks) non-potable irrigation has been the next economic choice over wells developed in the other aquifers. As the economical choices of water augmentation and non-potable supplies are exhausted, the water providers then turn to their next most economical aquifer which is generally the Denver or the Laramie-Fox Hills Formation, depending on location. In general, the Districts have used the Dawson Aquifer very sparingly because oflow production rates and potential affects on nearby domestic well production rates. Even though the water supplies in each of these aquifers generally requires some level of treatment, these supplies are free of bacteria and pathogens and the treatment required to produce potable water supplies is generally much less extensive than that required for surface waters available to these providers. Therefore, water treatment is a factor in the development of ground water supplies which adds both capital and operating costs, but does not limit its development. 1.4 Water Supply Summary Today, the districts of the South Metro Area are stretching their supplies to meet demands and are searching for and developing additional water supplies. Because of rapid development of the South Metro Area, these water suppliers have generally maximized their use of available surface water supplies and Arapahoe Aquifer non-tributary supplies, and have some level of reuse water supply development either tIuough water augmentation plans or non-potable irrigation. The next sources of supply which are already being utilized to some degree, are the waters of the other non-tributary aquifers, the importation of additional non-tributary ground water from outside the Page 1-] I