Groundwater Final Exam Fall 2010 (57+60=117/100)
Closed book portion: one page one side cheat sheet
1. (6) Sometimes wells are left open (uncased) and other times the screen is long or there are multiple well screens; casing can also become corroded, cracked, or not sealed at casing joints. This allows water to move between different depths when there are multiple aquifers (unconfined/confined, different confined layers). Draw arrows to show how the water is moving between the confined and unconfined aquifers and how it moves in each aquifer as a result of this water movement. Movement of this kind can spread contamination and is one reason unused wells are often filled with grout.
2. (3) Assuming this is all located above the water table, explain why the clay layers have lower resistivity than the gravel ones.
3. (3) When the barometric pressure rises, the water levels in confined aquifers ______
4. (3) Why does Grid 1 match the Theis Solution
(the correct solution) during early time periods but not at late time periods?
How could you change Grid 1 to improve the results?
5.(3) Show the change in hydraulic head for the labeled points, some of them may have the same head. Water is flowing into the stream.
6. (6) Show the change in hydraulic head for the labeled points, some of them may have the same head.
Draw what the flow lines will look like if the pumping rate at the well is doubled.
7. (3) Draw the water table between A and B if W (recharge) = 0.
8. (3) Explain what this figure shows.
9. (6) Draw flow lines, label discharge and recharge areas.
10. (6) Label confined and unconfined aquifers. Mark the direction of flow between the two aquifers shown.
11. (3) If q1>q2=q3=q4, what will happen to the energy per unit weight of the water in cell (I,j) during the next time step?
a) increase, b) decrease, c) no change
12. (3 ) Draw the flow lines.
13. (3) Which permeameter would be used to test the permeability of a clay? Why?
14. (6) Show flow lines, speculate on recharge and discharge areas as shown in your flow paths.
15. (3) Why are there two Theis type curves in this figure?
Open Book (60)
1. (15) The system is static (no flow). The capillary fringe is 25 cm thick, the intermediate zone is 50 cm thick, and the soil-water zone is 25 cm thick. If this is a loam soil, give the soil moisture content at the top and bottom of each interface.
2. (15) This is the soil moisture data from the Jornada station (just north of Las Cruces). All values are in mm of water in the first 1 meter of soil.
a) What month has the driest soil?
b) What month has the largest increase in soil moisture content?
c) What month has the largest soil moisture decrease?
d) What month has the wettest soil?
e) Why are AE and PREC so close in the summer?
Table 9.2
Water budget for: Latitude 32.5 Longitude 106.8
Field capacity 150.0 mm Resistance curve c
MON TEMP UPE APE PREC DIFF ST DST AE DEF SURP SMT SST
JAN 6 14 12 9 -3 23 0 10 2 0 0 0
FEB 9.4 27 23 6 -17 20 -2 9 15 0 0 0
MAR 13.8 49 50 4 -46 15 -5 10 41 0 0 0
APR 18.4 77 83 9 -74 9 -6 14 68 0 0 0
MAY 23.3 110 131 18 -113 4 -5 22 109 0 0 0
JUN 26 130 155 49 -106 2 -2 51 104 0 0 0
JUL 24.5 119 144 60 -85 1 -1 60 84 0 0 0
AUG 20.9 93 107 38 -68 1 0 39 68 0 0 0
SEP 14.8 55 56 24 -32 1 0 24 32 0 0 0
OCT 8.3 22 22 15 -7 1 0 15 7 0 0 0
NOV 3.8 7 6 21 15 16 15 6 0 0 0 0
DEC 3.5 6 5 13 8 23 8 5 0 0 0 0
Yearly Totals: 794 264 264 530 0
Explanation for water balance columns (all units are millimeters depth of water unless otherwise specified).
MON Month of the year
TEMP Mean monthly air temperature in degrees Celsius
UPE Unadjusted potential evapotranspiration
APE Adjusted potential evapotranspiration
PREC Precipitation
DIFF PREC minus APE
ST Soil moisture storage
DST Change in storage from preceding month
AE Actual evapotranspiration
DEF Soil moisture deficit
SURP Soil moisture surplus
SMT Snowmelt
SST Water equivalent held in snowpack
3. (20) A Curie of Technetium is placed in the well. If the retardation factor for Technetium is 2.2, the hydraulic conductivity is 25 m/yr, the porosity is 0.333, the depth to an impermeable clay layer is 40 m below ground surface, the numbers represent the elevation of the water table.
a) show flow paths on the diagram
b) estimate specific discharge, pore velocity near the well
c) estimate how long it will take for the Technetium to travel 1 km down gradient from the well
4. (10) Datum is the top of the figure. If the Water in well C rises to point F and the water in Well D rises to point E, find the hydraulic head in each.