DEPARTMENT OF CIVIL & ENVIRONMENTAL ENGINEERING; LAFAYETTE COLLEGE
Homework Assignment 1, due Thurs, Sept 4
CE 321, Fall 2008
1. Our country’s many environmental regulations create an alphabet soup of acronyms for the
environmental professional to wade through. Two important ones are CWA and RCRA. Look
these up in your text and describe briefly what they are and what they regulate.
2. Use the www to find a Superfund National Priorities List (NPL) waste site somewhere near
your hometown, describe the contamination at the site, and briefly discuss cleanup activities that
have occurred there. (If you are an international student, pick a site somewhere near Easton)
3. In a mass balance problem, the situation where the total rate of change in the control volume is
zero is referred to as _____________________________. In a mass balance problem, a chemical
that does not undergo any reactions to add or reduce mass is known as
_____________________________.
4. Five million gallons per day (MGD) of a conservative substance, with concentration 10.0
mg/L, is released into a stream having an upstream flow of 10 MGD and concentration of 3.0
mg/L of the same substance. Assume complete mixing in the stream.
a. What is the concentration in ppm just downstream?
b. How many pounds of substance per day pass a given spot downstream?
5. A river with 400 ppm of salts (a conservative substance) and an upstream flow of 25 m3/s
receives an agricultural discharge of 5.0 m3/s carrying 2000 mg/L of salts. The salts quickly
become uniformly distributed in the river. A municipality just downstream withdraws water and
mixes it with enough fresh water (20 ppm) from another source to deliver water having no more
than 500 ppm salts to its customers. What should the mixture ratio of fresh water to the river
water be to achieve this?
6. The two-pond system shown in the following figure is fed by a stream with a flow rate of 1.0
MGD and organic matter (nonconservative pollutant) concentration of 20 mg/L. The first order
rate of decay of the organic matte is 0.30/day. The volume of the first pond is 5.0 million gallons
and the second is 3.0 million gallons. Solve for C1 and C2 in mg/L.