The water table is the upper surface of the saturated zone, below which all interstices in the soil or rock are filled with water. The position of the water table in an aquifer is indicated by the water levels in wells. The water table fluctuates in response to changes in the rate of recharge to or discharge from the aquifer. It will rise as infiltrated water from precipitation percolates to the water table, and it will fall as groundwater is pumped or as groundwater drains to points of discharge along streams. Where subsurface materials are relatively uniform areally, the shape of the water table generally reflects the topography, and the water table intersects the land surface at stream level. In the relatively uniform alluvium in the Kansas and Delaware River valleys, the water table slopes obliquely toward the stream in those localities where groundwater discharge helps to sustain streamflow during dry periods.
In localities where the land surface is irregular and has considerable relief, and where subsurface materials are not uniform, as in much of Jefferson County, the water table is discontinuous. In most of the smaller valleys in the county, the streams have little or no flow except during and immediately after periods of precipitation. The lack of streamflow is a general indication of the poor availability of groundwater and the general absence of extensive aquifers in the upland areas of the county.
Depth to Water
The depth to water in the upland areas in Jefferson County generally is less than 30 feet; in the alluvial materials in the valleys, it generally is less than 20 feet. Depths to water, as measured in wells and test holes (table 3), indicate levels at a point in time regardless of the season or the effects of pumping.
Availability of Groundwater
The largest quantities of groundwater are available from wells in alluvium in the Kansas River valley. Yields of as much as 1,350 gpm (gallons per minute) have been reported from properly constructed wells that penetrate as much as 50 feet of saturated coarse sand and gravel underlying the Newman terrace and the flood plain of the Kansas River valley. Because the use of groundwater for irrigation is seasonal, and because pumping for municipal or public-supply use is small (1970) compared with the amount of groundwater available, the natural slope of the water table in the area essentially is unaffected. Groundwater discharges to the Kansas River at about the same rate as it would if there were no pumping. Hydrologic conditions in the valley are suitable for the development of large industrial and municipal water supplies, especially if well fields are located near the Kansas River so that pumping will induce movement of river water into the aquifer.
Moderate to large supplies of water (see footnote 2, table 1) are available from wells in alluvium in the Delaware River valley. Municipal wells and other public-supply wells drilled in alluvium adjacent to the new (1970) Perry Reservoir yielded as much as 150 gpm prior to filling of the reservoir. Larger yields should be available when the reservoir attains conservation-pool stage (altitude of 892 feet), because groundwater levels will rise in the alluvium along the reservoir border and because infiltration from the reservoir to the aquifer will be possible. In the alluvium in the valley north of the conservation pool, moderate supplies of water are available. Periodic, but temporary, rises of reservoir level to flood-pool stage (altitude of 921 feet) may increase the yields of wells in this area as the result of recharge to the aquifer and a raised groundwater level. Possible changes in reservoir stage should be considered in the location and construction of wells in the Delaware River valley.
House lots in new subdivisions surrounding Perry Reservoir are reported by newspaper accounts to number 70,000. Further development of water supplies for these subdivisions probably will be by rural water districts having supply wells in alluvium of the Kansas and Delaware Rivers, or surface-water intakes in the reservoir. Sewage disposal systems are being installed by a number of subdivisions.
Small amounts of water generally are available to wells in alluvium in the smaller valleys. In the 1930s, the Kansas Emergency Relief Committee installed a number of large-diameter, shallow, dug wells in alluvium adjacent to stream channels. Many of these wells are still used as a source of water for domestic and stock supply; the water is hauled in tanks to points of use.
The remnants of terrace deposits of Kansan and Illinoisan age, which border the valley walls in the Kansas and Delaware River valleys, generally yield only small quantities of water to wells. These deposits generally are thin and have low permeability.
In the north-central part of Jefferson County, in the vicinity of Nortonville, small to moderate supplies of water locally are available to wells. Wells that have penetrated coarse glaciofluvial material of Nebraskan and Kansan age beneath the "Nortonville clay" are reported to yield as much as 60 gpm; some wells penetrate as much as 165 feet of saturated material. Locally, however, the yield of a well may be much less, because the glaciofluvial deposits are discontinuous and have a considerable range in thickness and water-bearing characteristics.
In the upland areas of Jefferson County, other than in the vicinity of Nortonville, glacial drift and thin loess overlie bedrock. In northeastern Jefferson County, where the drift is more than 30 feet thick, one or more of the thin sand or gravel lenses incorporated in the drift generally will be penetrated by a well and may yield small to moderate amounts of water. Where the drift is less than 30 feet thick, the chances of penetrating a sand or gravel lens are remote, and wells may obtain small quantities of water only from the weathered zone at the bedrock surface. Because the glacial drift yields water slowly, a large-diameter dug well provides the advantage of storage within the well. It is for this reason, and because water can enter the permeable well wall at all levels, that about half of the wells inventoried in Jefferson County are large-diameter dug wells.
In many places in the upland areas where glacial drift is thin, domestic and stock wells are in draws or small valleys, and water is piped to points of use. Here, the yield from wells in combined colluvium and alluvium may provide an adequate supply of water. In localities where the groundwater supply is inadequate to meet needs, a supplementary supply may be obtained by collecting precipitation from roofs of buildings and storing it in cisterns, or by purchasing water delivered by tank truck.
The rocks of Pennsylvanian age generally yield only small quantities of water to wells-a few gallons per hour or less. Wells drilled or dug into the bedrock derive most of their yield from weathered material in the upper few feet of the bedrock. The part of the well beneath the bedrock surface serves to store water for intermittent periods of pumping at rates higher than the average yield of the well. Wells cased tightly into the bedrock generally are reported to be dry or to yield only small quantities of water that usually has an objectionable flavor or odor.
Kansas Geological Survey, Jefferson County Geohydrology
Web version July 2002. Original publication date Dec. 1972.
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