The application of aquifer testing evaluation techniques to oxidized till confining units in Central Iowa

Lemar, Tracy

doi:10.31274/rtd-180813-8372

Cited by 2 publications

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“…The till consists of 50-60% sand, 25-35% silt, and 15% clay. Pebbles are composed of granite, quartzite, basalt, greenstone, limestone, and dolomite (Foster, 1969 (Lemar, 1991). In the field research area, the till is considered to be subglacial till because the material is uniform in character and the bulk density value is 1.85g/cm^, which is close to the 1.89g/cm^ average value of subglacial till in Iowa as determined by Lutenegger (1983).…”

Section: Wisconsinan Till In Iowamentioning

confidence: 54%

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Repeatability of slug test results in Wisconsinan age Glacial Till in Iowa

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Slug and bail tests are commonly used for estimating hydraulic conductivity in low conductivity media. This research utilized two wells, 1.75 m. apart, near Boone, Iowa, to obtain hydraulic conductivity in glacial till. Slug and bail tests were repeated in order to obtain the range of hydraulic conductivity estimates. The effects of water level changes in one well on the other well, and of barometric pressure changes were also evaluated.Different slug/bail test methods were used, as were different mathematical methods of obtaining conductivity estimates from the observed data points, and the results were statistically evaluated.A graph of the natural log of water head versus time, using the Hvorslev and the Bouwer-Rice methods theoretically results in a single straight line. In this study, however, the data clearly results in two straight line segments, designated Type I and Type II lines.Type I lines were obtained from data taken early in sampling, whereas Type II lines were obtained from alter data. A third line fitting methods, designated as Best Fit Line, was also utilized, in which data obtained during the first 5000 seconds and after 80 percent well recovery were ignored in obtaining the best-fit line.Type II lines had smaller percentage range and standard deviation than either Type I or Best Fit Lines. This suggests that Type II lines provide more reliable and consistent determinations of hydraulic conductivity than the other two lines methods. Results of t-tests support the same conclusion. The amount of water added or withdrawn during slug/bail Vll tests did not have a significant effect on estimated hydraulic conductivity. Barometric pressure changes had significant effects on hydraulic conductivity estimates only for sampling intervals taken after about 80 percent recovery. Both Hvorslev and Bouwer-Rice methods give equally reliable results.

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Section: Wisconsinan Till In Iowamentioning

confidence: 54%

“…The upper 4 meters is oxidized Wisconsinan till. About 19 meters of unoxidized Wisconsinan till underlies the oxidized till zone (Lemar, 1991).…”

Section: Field Site Informationmentioning

confidence: 99%

Repeatability of slug test results in Wisconsinan age Glacial Till in Iowa

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Modeling the response of groundwater levels in wells to changes in barometric pressure

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The application of aquifer testing evaluation techniques to oxidized till confining units in Central Iowa

Cited by 2 publications

References 0 publications

Repeatability of slug test results in Wisconsinan age Glacial Till in Iowa

Repeatability of slug test results in Wisconsinan age Glacial Till in Iowa

Modeling the response of groundwater levels in wells to changes in barometric pressure

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