MOD-12_Groundwater Lab
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Northern Virginia Community College *
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105
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Geography
Date
Dec 6, 2023
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docx
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Name ____________________
Name: Saurav Bhattarai
Module 12 Part 2 Groundwater Lab
Objective:
This lab will familiarize you with the basic techniques and terminology of groundwater analysis, including the concepts of hydraulic head, hydraulic gradient, flow nets and their use in understanding underground contaminant flow or plume flow.
Introduction:
In this lab, you will be asked to plot the groundwater elevation data provided in Table 1 on the map of Arsenic Springs provided (Figure 2). You will then create contour lines showing the elevations of the local groundwater table and then draw in the flow nets indicating the direction of flow of the subsurface groundwater. Based on this map, you will predict the direction of contaminant flow in the subsurface groundwater.
Directions:
1)
Read section 17.2 Groundwater and the Water Table
in your textbook. Pay particular attention to Figure 17.7 Mapping the Water Table.
2)
Plot the elevations of the water table (provided in Table 1) on the map of Arsenic Springs (Figure 2)
3)
Draw in lines connecting each of the wells, similar to the dashed blue lines in Figure 1a. This will be the basis for extrapolating the groundwater elevations between each of the wells.
4)
You are now going to estimate the surface elevation of the water table between the
wells, along each of these drawn lines. Since we will be contouring the water table in 5 ft. contours, you should estimate the location of each 5 ft elevation (for example, 170 ft. 175 ft, 180 ft, etc…) similar to the blue dots in Figure 1b with the itaicized elevations next to them.
5)
Draw in the contours of the water table surface by connecting numbers of equal value, similar to the red lines in Figure 1b. Be sure to label the elevations of each line that you draw. You have now completed the contour map of the water table. Since water always flows dowhill, the groundwater will flow downslope from regions of high elevation to regions of low elevation. This is termed the hydraulic
head of the groundwater table.
6)
Draw in the flow net for the ground groundwater table in Figure 2. Groundwater will flow along lines that run perpendicular to the contour that you just drew. The
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flow lines do not necessarily need to be parallel to each other, but they can not cross each other. See the blue arrow lines in Figure 1b. 7)
Answer the questions below Table 1.
8)
Complete the accompanying Groundwater Lab Exercise (part I). This exercise consists of 17 multiple choice questions based on the information in the “Chapter 17: Groundwater
” in your textbook and the work you completed on the Arsenic Springs sketch map.
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Table 1
Well
ID
Elevation of water
table (ft)
Contaminant
B-1
171
arsenic
B-2
178
none
B-3
172
none
B-4
168
none
B-5
163
none
B-6
181
none
B-7
162
none
B-8
166
none
B-9
176
none
B-10
177
none
B-11
171
none
B-12
164
none
B-13
168
none
B-14
173
none
Questions:
Will the arsenic in well B-1 likely contaminate the water in Clearwater Lake? Why or why not?
- Arsenic present in Well B-1 will not contaminate the water in Clearwater Lake. The movement of arsenic in Well B-1 is directed toward the southeast, where it is descending to lower altitudes. Arsenic will disperse towards the southeast of Clearwater Lake as a result of variations in elevation and gravitational forces. Consequently, the water in Clearwater Lake will remain uncontaminated by arsenic due to its more significant elevation compared to Well B-1. As a result, the arsenic will naturally flow downhill from
Well B-1 towards lower elevations in a south-easterly direction.
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In which direction is the contaminated water in well B-1 moving? Which well will most likely show contamination of arsenic next?
The water in Well B-1 that has been contaminated is flowing in a path that is both southward and eastward. The subsequent well that is very probable to exhibit indications
of contamination is Well B-8. The reason for this is that Well B-1 has an elevation of 171 ft., and the closest well in the south-easterly direction with a lower height than Well B-1 is Well B-8, which has an elevation of 166 ft. Page 4
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How to draw a groundwater flow net
a)
B
(81 ft)
A
(64 ft)
D
(63 ft)
C
(73 ft)
Figure 1
b)
65
65
65 ft
70 ft
75 ft
80 ft
D
(63 ft)
C
(73 ft)
B
(81 ft)
A
(64 ft)
65
65
70
70
70
70
75
75
75
80
80
80
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Arseni
c B-8
B-1
B-13
B-2
B-14
B-6
B-7
B-5
B-12
B-4
B-11
B-3
B-10
N
B-9
Clearwater
Pond
Figure 2
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Figure 2:
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