Question

B. Under certain conditions the Thiem equation (5-43) for confined aquifers, is equivalent to the Cooper-Jacob equation (5-58) for confined aquifers. What are the conditions? (This exercise is easier than Problem A.) C. If an analysis is made of the hydraulic conductivity of a site using permeameter tests of core samples, slug tests of monitoring wells, and pumping tests of production wells, it is often observed that the hydraulic conductivity as measured by each method is different. Which method would be most likely to have the greatest hydraulic conductivity, and which the least? What are some possible reasons why this would be true?

Answer 1

1) Homogeneous Aquifer : Both equations are equivalent when confined aquifer is homogeneous which means that the properties of the aquifer such as hydraulic conductivity are uniform throughout the aquifer. 2) Steady-State Flow : The equations apply to steady-state flow conditions where the groundwater flow remains constant over time. This assumption implies that there are no changes in the groundwater recharge or discharge rates over the duration of interest. Both equations are equivalent in this case also.3) Radial Flow : The Thiem equation and the Cooper-Jacob equation yields same result in radial flow where groundwater flow occurs towards a well or pumping point in a circular pattern. In other words, the equations are equivalent if the flow is primarily in the radial direction from the well towards the surrounding aquifer.4) Confined Aquifer : This means that there is a relatively impermeable layer both above and below the aquifers. Both equations can be considered equivalent under this case. The confining layer prevents vertical flow and confines the groundwater within the aquifer.

Slug method K is as low as 1.0 x 10-5 m/yrConstant-head conductivity test K> 1.0 × 102m/yr.Falling-head conductivity K < 1.0 × 102 m/yr.Pumping test K larger than 1.0 x 100 m/yr, to relatively clean sand or sandy gravel with K <1.0 × 104 m/yr.Greatest conductivity is in permeability test Least conductivity is in slug test.Possible reasons: When Soil gets compacted k values varies in various test. The size of the grain is also affects its value.