Modeling of Chemical Equilibrium using MINEQL+
The 1987 amendment of the Federal Clean Water Act requires that
heavy metal discharges into streams (i.e. NPDES permits) and waste
load allocations be conducted in such a way that heavy metals
do not exceed water quality standards adapted by individual state
environmental regulatory agencies using as quidance water quality
criteria published by the U.S. Environmental Protection Agency.
The Connecticut Department of Environmental Protection (CT DEP)
in an effort to conform with the Federal Law, has been conducting
toxicity tests of contaminated river water to examine its impact
to the biological community. CT DEP personnel have observed that
even though the water quality criteria are exceeded, the tested
water in many cases fails to produce an apparent impact to biota.
To illustrate the problem, I will use copper as an example. The
existing water quality criterion for copper is 5 ppb in stream
concentration. CT DEP is conducting toxicity testing in the form
of a Whole Effluent Toxicity (WET) program (using standard laboratory
reference water for dilution with discharge water at appropriate
ratios) to test whether a specific discharge will cause adverse
impacts to stream biota. Many of the tests fail to produce any
apparent toxicity impact to the testing organism, Daphnia pulex
that is considered to be highly sensitive to heavy metals,
even though the concentration exceeds the water quality criterion
level. According to the federal law, DEP can not issue a permit
to that particular discharger, even though the biological community
will not be affected by the effluent. This has the overall effect
of industries to be moving somewhere else (ie. more pristine areas)
and the economic growth of industrial belts to be slowing down.
Another example that further illustrates the economic impact to
the industrial and private sector of the State has to do with
municipal waste water treatment plants (MWWTP). Traditionally,
MWWTPs have been discharging higher than the water quality criterion
copper concentration into streams. Many of these treatment plants
do not serve any industries, but they still have high copper loads
from copper piping within the municipality. DEP could eliminate
this problem in several ways, such as requesting that MWWTPs install
ion exchange or reverse osmosis units to remove trace levels of
copper. Other possible alternatives include tighter limits on
industrial contributions to the MWWTPs, or perhaps operational
changes like pH control at the MWWTP. No matter how this problem
is dealt with it would impose an unnecessary burden on the municipality
or local industries during hard economic times, when this money
could be used to solve other urgent problems.
The scientific explanation of the apparent paradox of the above
illustrations (namely, high copper concentration without any adverse
biological impacts) lies on the fact that copper exists in various
complex forms that are not bioavailable. The U.S. Geological Survey
is conducting water quality monitoring surveys along the major
rivers in Connecticut. The data are published in a USGS goverment
publication and they are available to the public (UConn Library).
For this assignment, I want you to select a river of your interest,
find a USGS monitoring station where copper exceeds the water
quality criteria, and use these data to perform chemical speciation
(using MINEQL) in order to find the bioavailable copper concentration
in the river.
Instructor: Dr. Nikolaos P. Nikolaidis
Office: FLC Rm 318
e-mail: nikos@eng2.uconn.edu
Homepage: http://www.eng2.uconn.edu/cee/bio/Nikolaidis.html