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<br />Page Five <br /> <br />To understand the characteristics of the -life- of bedrock aquifers in the <br /> <br />Denver Basin, it is important to distinguish between the actual volume of <br /> <br />nontributary groundwater within the four aquifers and the potentiometric head <br /> <br />(also referred to as the artesian, piezometric or pressure <br /> <br />head). <br /> <br />When a well driller penetrates the confining layer of one of the aquifers, <br /> <br />pressure forces water up the well until it reaches an equilibrium or static <br /> <br />water level. The distance that the water in a well will rise above the <br /> <br />aquifer is called the potentiometric head. The potentiometric head represents <br /> <br />two to five percent of the total quantity of water stored in anyone aquifer. <br /> <br />The majority of stored water (95% to 98%> occupies the spaces between <br /> <br />individual particles of an aquifer. Because the potentiometric head declines <br /> <br />as even small quantities of water are withdrawn, a perception has arisen that <br /> <br />we are rapidly approaching the end of the aquifer life. The fact is that the <br /> <br />potentiometric head may be falling, but, because this head only represents 2% <br /> <br />to 5% of the total volume in the aquifers, the amount of recoverable water <br /> <br />within the Denver Basin has not yet been affected to a significant degree. <br /> <br />Some publicity has emerged regarding water users whose nontributary <br /> <br />groundwater supplies are currently -running out.- Most of these situations, <br /> <br />however, are covered by two cases. Th~ first is wells -at the edge of the <br /> <br />saucer- which have a relatively thin portion of the aquifer directly beneath <br /> <br />them. In the second situation, the well construction does not allow for the <br /> <br />lowering of the pump as the potentiometric head declines. <br />