Cleaning Well by Pump and Treat
Dr. D.G. Zeitoun
ED Technology
Groundwater contamination
About 1/2 of the people in the U.S.
depend on groundwater for their
domestic water supply. Groundwater
may become inadequate for human or
animal consumption if concentrations of
undesirable materials (contaminants)
exceed safe levels.
Potential sources of contaminants include:
septic tanks
landfills and illegal dumps
mining operations
industrial discharge (used waters)
urban runoff
pesticides and fertilizers
underground storage tanks
waste-water treatment plants
saltwater, etc.
Contaminants may have
undesirable health or ecological
effects.
Once contaminants enter the
groundwater systems, they
disperse as a result of groundwater
flow, producing an ever-growing
contaminant plume, if not
remediated.
Types of contaminant
sources
Groundwater contamination
occurs when contaminants enter
the groundwater system by
infiltration, or injection, or any
other mean.
Contaminants may infiltrate from
point sources (e.g., underground
tank, dump) or non-point
sources (e.g., pesticides,
fertilization, urban runoff, etc.).
Common types of contaminants in
ground and surface water:
• pesticides
• nutrients
• volatile organic compounds
• microbes
• trace elements, heavy metals
• radioactive materials
These different types of contaminants are undesirable for a variety of
reasons, including human and animal health risk, effects on
ecosystems, poisoning of crops, etc.
In accordance with the Safe Drinking Water Act, the US Environmental
Protection Agency sets guidelines, including maximum contaminant
levels (MCLs) for human consumption.
Microbes
Various water-borne microbes
which pose a threat to human
and/or animal health can make
their way into surface water and
groundwater systems.
These included cryptosporidium,
giardia, cholera, forms of
hepatitis, etc.
cryptosporidium cyst (1 mm = .001 mm)
Many of these microbes reside in human and
animal excrements. When water comes in contact
with these, the microbes can enter and be
transported into the water system.
E. coli coliform
E. coli is a fecal microbe (coliform) which is used
as an indicator of the possible presence of other
harmful, microbes in the water (because the
concentration of E. coli is relatively easy and cheap
to determine).
Pesticides
Pesticides (herbicides, insecticides and fungicides) are used in
agriculture to curb the development of organisms that negatively impact
crop productivity or quality (weeds, insects, fungi, etc.). Improper or
excessive use of such products can lead to their entering the ground and
surface water systems.
Frequency of occurrences of atrazine (herbicide) in groundwater wells in
the U.S., from National Water Quality Assessment project (NAWQA)
Trace elements, heavy metals
Toxic trace elements, including heavy metals such as lead, arsenic,
uranium, etc., can be released into the groundwater systems from a number
of sources, including landfills, buried pipes, industrial waste, mine drainage
(above), etc.
Nutrients
Plants need nutrients such as nitrogen (N) and phosphorus (P) to grow. Farmers
spread commercial fertilizers or animal manure to enrich their soils in these
nutrients, and stimulate plant growth. These nutrients are also released after waste
water treatment, and found in certain commercial products (e.g., phosphorus in
detergents).
Excessive addition of these nutrients have health risks for human and animals. In
additions, excess nutrients can enter surface water bodies where they stimulate
excessive plant growth which can significantly alter ecosystems.
The nitrogen
cycle
Excessive release of
nutrients to streams
and lakes
Release of nutrients to
surface water bodies
either from groundwater
discharge or surface runoff
leads to enhanced plant
and algae growth. When
the plants and algae die,
their decomposition takes
up oxygen dissolved in the
water, leaving oxygendepleted (anoxic)
conditions. Such
environmental changes
stress certain species
(fish, shell fish, etc.) which
may die out.
Nutrients in
Chesapeake Bay
Excessive use of fertilizers and
release of waste water
treatment byproducts in the
Chesapeake Bay drainage has
led to enhanced influx of
nutrients in Bay waters.
This, in turn, has led to
declining populations of certain
species, such as oysters, Bay
crabs, striped bass, etc.
A decline in these species leads
to a decline of the species that
feed on them (e.g., shorebirds).
Overall, nutrient contamination
may produce permanent
destruction of ecosystems and
loss of biodiversity in
Chesapeake Bay.
Remediating groundwater
contamination
Several options exist when groundwater
has been found to contain unacceptable
levels of contaminants. They can generally
be divided into two approaches:
- Source control, e.g., remove the source, or
isolate source from groundwater
- Plume treatment, e.g., contaminant
flushing, contaminant extraction (pump and
treat), in situ degradation of contaminants
by action of added biological
(bioremediation) or chemical catalysts
Plume treatment:
Source control
In some cases, as for leaky underground
tanks, it is practical to remove the source
of the contaminant. Further treatment of
contaminated ground may also be
necessary.
removal of leaky gas tank
Properly designing potential
sources of groundwater
contamination can result in
effective isolation of the
contaminants from the
groundwater systems.
Lined landfill with collection and treatment of leachate
Plume treatment: Pump and treat
In many cases, to remove, or at least contain, a contaminant plume, it is necessary
to pump the contaminated water out of the aquifer. This water is typically treated
and purified, than put back into the surface water system. This approach is costly
and may not necessarily result in complete removal of the contaminant.
Plume treatment:
bioremediation
Contaminants may break down over time if
left to themselves, solely by chemical
reactions, or by biologically-mediated
reactions (natural bioremediation).
microbes breaking down oil (black)
injection of air and bio-catalyst to contaminant plume
Artificial bioremediation involves
the addition of appropriate
microbes or microbe nutrients to
the contaminant plume. Over time,
these organisms break down the
contaminant in-situ.
Bioremediation can also be done
ex-situ, in pump-and-treat
schemes, or wetlands for instance.
FRTR Groundwater Remediation
Case Studies
Ex Situ Groundwater Treatment
In Situ Groundwater Treatment
Bioremediation (32)
Permeable Reactive
Barrier (13)
Pump and
Treat (44)
Air Sparging (11)
Chemical
Oxidation (8)
Multi-Phase
Extraction (7)
Monitored Natural
Attenuation (6)
Flushing (6)
Drinking Water
Treatment (3)
Other (12)
In-Well Air Stripping (3)
Phytoremediation (3)
Thermal Treatment (3)
Bioslurping (1)
Constructed Wetlands (1)
Membrane Filtration (1)
Soil Vapor Extraction/Air
Sparging System
Electrokinetics
Pneumatic Fracturing
Land Treatment

Contaminated soil is
removed from the site
and applied to surface
soil where natural
biological action
removes the
contaminants or
converts them to
harmless chemicals
In Situ Chemical Oxidation
Passive Treatment Wall
Pump-and-Treatment System at Commencement Bay
Tacoma, Washington