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Quantifying Hydraulic Conductivity: Slug Test

Objectives: Quantify hydraulic conductivity in an unconfined aquifer based on slug test data of changes in water levels over time.

1.  The biggest unknown in groundwater problems is knowing the hydraulic conductivity of an aquifer.  While there are multiple methods available for quantifying hydraulic conductivity one of the most popular methods is the slug test.  This method artificially changes the water level in a well and monitors the response back to the static level.  Using the data provided below and foldable aquifer model address the following problems.

Table1. Time vs drawdown data.

Time (sec) H-h/(H-Ho)
1 1
10 0.89
20 0.75
30 0.64
50 0.3
100 0.28
120 0.2
180 0.08
200 0.05
300 0.02

A. Quantify the hydraulic conductivity using the Hvorslev method.   

B. Based on the value of hydraulic conductivity above determine if this geologic unit makes a better aquifer or confining unit.   Please explain your answer.

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Below is a second class problem (PDF)
Slug Test Class Problem II
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Effective Hydraulic Conductivity: The basics

Objectives: Determine the effective hydraulic conductivity of a heterogeneous aquifer in the horizonal and vertical directions.

1. When aquifers are heterogenous there is a simplification that can sometimes be made in order to calculate a bulk or effective hydraulic conductivity across the whole aquifer.  This assumption only works if water is flowing parallel or perpendicular to the bedding planes (see figure below).  When these conditions are met, it is possible to then calculate an effective hydraulic conductivity where the hydraulic conductivity of an individual layer is weighted based on the layer thickness.  Then each of the products of layers and thickness are summed. The equations used to calculate this effective hydraulic conductivity are given below.  Using the foldable aquifer model address the following problems.

For groundwater flow parallel to the bedding plane.

Where

                Kxi is the hydraulic conductivity of a layer i in the x direction

                di is the thickness of layer i

For groundwater flow perpendicular to the bedding plane.

Where

                Kxi is the hydraulic conductivity of a layer i in the z direction

                di is the thickness of layer i

A. Determine effective hydraulic conductivity for horizontal flow in aquifers A, B, and C. 

B.  Determine effective hydraulic conductivity for vertical flow in aquifers A, B, and C.

C.  Explain why the effective hydraulic conductivity is different when flow is in the horizontal directions as compared to when flow is in the vertical direction.

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Heterogeneity and Wells

Objectives: Determine the effective hydraulic conductivity of a heterogeneous aquifer to quantify groundwater discharge.
1. The world of geology is complex and aquifer are typically not made up of homogeneous materials.  As a result, we must find ways to approximate aquifer heterogeneity in order to quantify groundwater discharge.  In this problem there are two wells drilled into two different aquifer materials.  For illustrative purposes there is a sharp vertical interface between the two materials.  Using the foldable aquifer model address the following problems.

A. Determine effective hydraulic conductivity of the total aquifer in the direction of groundwater flow. 

B.  Calculate the groundwater discharge (Q) across the aquifer.

C.  Draw the equipotential lines between the wells with an increment of 5 m.

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