CASE STUDY: POTOMAC RIVER - BETTER OR WORSE? 
by 
Drs. James P. Bennett and Edward Callender 
United States Geological Survey 
Abstract 
In the 30 years preceding 1985, approximately $1 billion was 
spent on upgrading sewage treatment plant performance in an 
effort to improve water quality conditions in the tidally 
influenced Potomac River near Washington, D.C. Although algae 
blooms can still occur when hydrologic and weather conditions 
are favorable, dissolved oxygen conditions in the tidal-fresh 
portion of the river sire greatly improved. The greater than 
natural present-day supply of nutrients to the estuary has 
aggravated the naturally-occurring phenomenon of summertime 
bottom water anoxia. It is not clear that recent cleanup 
efforts have had any effects on the phenonmenon, and in fact the 
large reservoir of nutrients in the bottom sediments should 
prevent the effects of cleanup from becoming evident for some 
time. The recent resurgence of submersed vegetation in the 
tidal-fresh portion of the river has a potential to alter 
nutrient budgets throughout the influenced portion and appears 
to have had a positive effect on the tidally water quality. 
Dr. Bennett: A number of the very difficult technical is¬ 
sues that I was concerned about being able to present in 20 min¬ 
utes have been brilliantly covered earlier; therefore, I will 
proceed right to the heart of the issues. 
I will address three different topics in this presentation. 
First, better or worse in the tidal river; second, better or 
worse in the estuary; and third, some recent developments that 
may well invalidate extrapolating these conditions into the 
future. In the USGS study, the tidal river extends from Chain 
Bridge near D.C. to Quantico; and the estuarine zone extends 
from Morgantown, Maryland, to the mouth on the Chesapeake Bay. 
In the past 20 years, approximately one billion dollars have 
been spent on construction and improvement of the sewage treat¬ 
ment plant capabilities in the District of Columbia. As you saw 
in one of the earlier presentations this morning, probably the 
most advanced waste treatment facility, certainly the largest 
advanced waste treatment plant in the Chesapeake Bay watershed, 
is in the District of Columbia. Although Figure 1 shows an ap¬ 
proximate 2.5 fold increase in waste-water flow in the last 30 
years, 5 day B.O.D. and total phosphorous, both, have decreased 
markedly over that time span. At the same time, total nitrogen 
loading has been essentially constant since 1970. Now looking 
at the River, what has that billion dollars bought us? 
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