Hydraulic Conductivity Estimates in Glacial Outwash A hazardous-waste-processing site was located on a level glacial outwash plain at Seymour in southern Indiana. There were two aquifers present in...

Hydraulic Conductivity Estimates in Glacial Outwash

A hazardous-waste-processing site was located on a level glacial outwash plain at Seymour in southern Indiana. There were two aquifers present in the unconsolidated glacial deposits. The upper aquifer consisted of a well-sorted fine to medium sand. There were 27 ground-water monitoring wells installed in this aquifer. The lower aquifer was a poorly sorted fine to coarse sand. There were 9 monitoring wells installed in this aquifer. The grain-size analyses of the sand samples from the screen zones of the wells in each aquifer are summarized in the following table:

The hydraulic conductivities of the sediments at each monitoring well were estimated by the Hazen method, using a coefficient of 100. The hydraulic conductivities of the sediments at each monitoring well were measured by means of a Hvorslev slug test performed on the well. The following table compares the results in centimeters per second.

The geometric means of the data sets were used to compare the Hvorslev test results with the Hazen method results in this chapter’s case study. Hydraulic conductivity values frequently vary by more than two orders of magnitude within the same hydrogeologic unit. An arithmetic mean of such a sample population tends to give more weight to the more permeable values. Some hydrogeologists believe that a more representative description of the average hydraulic conductivity of a hydrologic unit is the geometric mean. This is determined by taking the natural log of each value, finding the mean of the natural logs, and then obtaining the exponential (^x) of that value to arrive at the geometric mean.