Homework 8
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School
University at Buffalo *
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Course
414
Subject
Industrial Engineering
Date
Jan 9, 2024
Type
Pages
3
Uploaded by ChiefValorWombat16
Homework 8
Name:_________________________________
Due November 28, 2022
1.
The model below shows a confined aquifer with three wells and two
different hydrogeologic units. Water is flowing from left to right (q = 0.01
m/day) with observed heads shown in the table below. A simple model has
been built in Excel, which can be found on UBLearns.
Using this model,
please solve the inverse problem by adjusting the value of hydraulic
conductivity until your simulated heads match the observed heads (Green
Boxes).
Observed (m)
Well1
12
Well2
8.9
Well3
8.1
Report the values of hydraulic conductivity and your root mean square error.
Value
K in Unit 1 (m/day)
K in Unit 2 (m/day)
RMSE (Blue box)
2. You asked to review an old study looking at groundwater age in a sandy aquifer.
The aquifer contains two wells (MW1 and MW2) that are 500 meters apart, where
well MW1 is up gradient from MW2.
Tritium concentrations where taken in 1985
and 1998 and a single Helium sample was taken in 1998. Results are shown below.
Well
1985
3
H
1998
3
H
1998
3
He
MW1
208
25
47
MW2
142
31
A table of the tritium concentration at the time of groundwater recharge is given on
the UBLearn. Using these data, you will need to correct the concentration of tritium
to correspond to the 1985 and 1998 sampling dates; please assume a decay rate of
12.35 years. Based on these corrected concentrations, answer the following
questions.
A. What are the possible
ages
of the groundwater sampled, based on the 1985
tritium samples, for groundwater in well MW1 and MW2? Note that groundwater
age is the current year (i.e., 1985) minus the year the water was recharged; there
will be multiple possible ages.
B. Using the 1998
3
H data to help constrain the true age, try eliminating some of the
ages in part A above. Do this by calculating the ages based on the 1998 data and
then looking for ages matching the 1985 and 1998 data sets.
C. Finally, use the tritium/helium concentrations to further refine your estimate of
groundwater
age
in MW1.
3. Using CFC-11 measurements from four monitoring wells with concentrations of
1.9, 76.9, 176.1, and 430.4 pg/kg (data from Dunkle et al., 1993). Estimate when
recharge occurred (i.e., the year) assuming a 13 deg C recharge temperature. How
does this method differ from using Tritium to age data water, and what are the
advantages?
(Figure modified from Clark and Fritz 2000)
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