Catherine Schmidt
Environmental Geology
Groundwater Lab
Professor Johnson
Problem:
“Water containing both high levels of nitrate and high levels of benzene have
been found in a shallow well on the north side of campus. Those contaminants are being
carried by groundwater. The well in which the pollutants were found is a shallow well
near ground water. Thus, we must find the source of pollution so that it can be mediated
before it begins polluting surface water or comes in contact with wells for drinking
water.”
Benzene is a contaminant created by burning coal and oil. Short-term exposure to
humans may cause, “Drowsiness, dizziness, headaches, as well as eye, skin, and
respiratory tract irritation, and, at high levels, unconsciousness.”
(http://www.epa.gov/ttn/atw/hlthef/benzene.html). Long-term exposure to humans, “Has
caused various disorders in the blood, including reduced numbers of red blood cells and
aplastic anemia, in occupational settings. Reproductive effects have been reported for
women exposed by inhalation to high levels, and adverse effects on the developing fetus
have been observed in animal tests. Increased incidence of leukemia (cancer of the
tissues that form white blood cells) have been observed in humans occupationally
exposed to benzene. EPA has classified benzene as a Group A, human carcinogen.”
(http://www.epa.gov/ttn/atw/hlthef/benzene.html). It becomes hazardous when found in
levels greater than .05 mg/L.
Nitrate is often used as a fertilizer, however it still has serious health effects. The
maximum contaminant level established by the Environmental Protection Agency (EPA)
is 10 mg/L. Infants under the age of four months, and pregnant women are the most at
risk from nitrates. When deoxyhemoglobin is converted to methemoglobin, the most
clinical symptoms, such as, “Irritability, lethargy, cardiac dysrhythmias, and chocolate
brown blood,” appear. (http://aquaticpath.umd.edu/appliedtox/allison.pdf).
Besides the worry of pollutants reaching wells used for agriculture water systems
and then being inhaled by humans, they are also harmful to the ecosystems that rely on
that specific source for water.
Potential sources of pollution:
The well shows that ground water is flowing into the well and is at the water table
line. It is neither a gaining nor a losing stream, which means the water line remains at the
same level and the amount of water entering the well is equal to the amount of water
leaving the well. The water table mirrors the surface of the earth by loosely following
hills and valleys and it also decreases where rivers and streams decrease. It would be
smart to look for pollutant sources upstream, and at the places where major tributaries
join the main river.
The Krazy Nasty Consultants (TKNC) found two potential sources of pollution,
one for benzene and one for nitrate.
TKNC discovered that there was a high concentration of nitrate around the
baseball field located in between the sophomore apartments and Ridge Road. An area we
found even greater nitrate concentration is the varsity practice field located next to the
Post Office and physical plant shops and warehouse. The baseball field had a nitratenitrogen concentration of 25 and the practice field had a concentration of 27.
The greatest concentration of benzene that TKNC was able to locate was .025 and
it was in an area between Graham Road, Main Street, and Ridge Road.
Options for remediation:
There are many options for remediation, the majority of which are neither easy
nor cheap. While it is necessary to determine the location of the source, the actual
contaminants, the area the contaminants is affecting, and the chemical properties of the
pollutants, this should all be a prerequisite for remediation.
Removal of the source should be the first step, although this is difficult and
inconvenient, especially for the baseball and practice fields where there will be a
disruption to human schedules. However, this is an extremely important step because it
prevents more contaminants from entering groundwater. All the soil and water that has
been contaminated at the source should be removed.
The remediation for benzene that has the greatest success in the past is intrinsic
and enhanced bioremediation. Bioremediation is the same as biofiltration. Both use living
material to capture and degrade pollutants. Additionally, the EPA has approved Packed
Tower Aeration and granular activated charcoal for removing benzene.
Packed tower aeration (PTA) is a process that mixes water with air in a five to
twelve meter tower. Water is distributed evenly over a medium to create maximum airwater contact. The water is pumped upward, against the flow of water, through the tower.
At the base of the tower, there is a pump that collects and removes treated water.
Although these systems are often permanent installations, they can be temporarily
established. A major disadvantage is that this system is likely to clog, which then
increases the cost greatly.
Granular activated carbon (GAC) uses carbon filters to remove organic chemicals,
including benzene. The type of filter used greatly affects how many chemicals are
removed. One form of this is using activated carbon, or carbon with a slight
electropositive charge. This positive charge attracts the negative ions of chemicals and
contaminants. These filters require a lot of attention and need to be replaced often.
Distillation and reverse osmosis have the greatest success in treating nitrate.
Distillation separates compounds by heating a liquid until it boils, catching and
condensing the steam, and collecting the nitrate and other minerals remaining in the tank.
This is because different compounds have different boiling points and therefore separate
into volatile and non-volatile liquids.
Reverse osmosis forces water through a membrane filter, creating a higher
concentrate and a lower concentrate, and separating solvent from solute.