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<br />In the Fort Lupton area, the sediments making up slope-wash deposits are believed
<br />to be less than 10 feet thick and would probably not be an economically viable
<br />location for future municipal wells.
<br />The central portion of the City is underlain by the Kersey Terrace deposits that
<br />generally consist of interbedded clay, silt, sand, and gravel. The lower part of these
<br />deposits consists of rounded cobbles and boulders, some approximately 2 feet thick.
<br />The Kersey Terrace deposits are very porous and permeable and generally yield large
<br />quantities of water to irrigation, municiplil, industrial, domestic, and stock wells in
<br />Weld County. Sand and gravel deposits like the Kersey Terrace deposits have
<br />porosities that range from 10 to 35 percent (Groundwater and Wells, Second Edition,
<br />Fletcher G, Driscoll, pp. 66-68). During its PCE investigation for the EP A, Ecology
<br />and Environment, Inc., estimated the average porosity value for the Fort Lupton area
<br />to be 25 percent based on its field investigations (Report of Sampling Activities,
<br />Fort Lupton, Colorado, 1TD #T08-891O-010, Ecology and Environment, Inc., pg. 11),
<br />All of the City's seven existing wells are located in the Kersey Terrace deposits, which
<br />are overlain by approximately 2 to 5 feet of brown, loamy soil. A distinct layer of
<br />orange, medium- to coarse-grained sand about 5 to 10 feet thick is found
<br />approximately 5 to 10 feet below the surface.
<br />Underlying the City on its western boundaries are alluvial deposits which consist
<br />of interbedded clay, silt, sand, and gravel, along with some cobbles and boulders.
<br />These deposits are reported to yield moderate to large quantities of water to
<br />irrigation, municipal, industrial, domestic, and stock wells. The City's Pearson Park
<br />well is located in this alluvium.
<br />The ultimate source of all groundwater in the South Platte River basin is
<br />precipitation. Part of the snowmelt and rain is carried off by the streams, part
<br />evaporates, and the remainder infiltrates the ground. The water that is not consumed
<br />by vegetation or held by molecular attraction moves downward and is added to the
<br />zone of saturation. Water in the zone of saturation percolates laterally through the
<br />more permeable consolidated rock formations and through the unconsolidated rock
<br />materials that overlie the bedrock, ultimately discharging at the surface through wells,
<br />seeps, springs, and evapotranspiration, Tl1e principal bodies of groundwater within
<br />and around the Fort Lupton area are rechlirged chiefly by subsurface inflow through
<br />the unconsolidated rock materials, by seepage through streams, reservoirs, canals, and
<br />irrigated tracts, and by precipitation falling directly on the basin. The underflow from
<br />adjacent consolidated rocks may contribute minor amounts to recharge. The USGS
<br />
<br />25325,100; 12109/94
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