PWC-Lesson2- Groundwater and Well Contamination

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© 2018 University of Illinois at Urbana-Champaign 11
2. Groundwater and Well Contamination
Why It’s Important
Now that we have an idea of how water is stored in the ground 
and how geology affects its movement and availability, we are 
going to look at how it moves to your well and what can hap-
pen as it does. In particular, we’ll discuss how water level, flow, 
and water quality can be affected when pumping a well. You’ll 
also learn how contaminants can move with groundwater, or 
be affected by groundwater flow and pumping. This lesson 
will give you the background to understand how pumping 
your well can influence groundwater flow. It will also give you 
a better idea of the value of source water protection. 
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Groundwater Flow
In a groundwater system, water 
flows naturally according to the 
hydraulic pressure put on the sys-
tem. The flow can be horizontal 
through a geologic unit, or verti-
cal through several different geo-
logic units, or sometimes some of 
both. In Lesson 1, we used Figure 
1.1 to show natural groundwater 
movement. The thin layers with 
horizontal dashes in Figure 2.1 
represent confining layers (aqui-
tards) that separate the aquifers, 
shown in blue. As you can see in 
the figure, because the high point 
of the water table is near the left 
edge, water is flowing downward 
from the high point toward areas 
of lower water levels in both direc-
tions (lower levels = less pressure).
If separated by confining layers, 
water levels in different aquifers 
at a single location can be very 
different. When an aquifer has the 
water table as its upper saturated 
surface, that aquifer is called a wa-
ter table aquifer. Water table aqui-
fers aren’t completely saturated: 
there is air in the pore spaces in 
the aquifer material above the wa-
ter table. In other words, the water 
level in a water table well is at the 
water table elevation, which is be-
low the top of the aquifer. 
When an aquifer is below a con-
fining unit, the situation is dif-
ferent. Wells in confined aquifers 
can have water levels above the 
top of the aquifer. This happens 
when the confined aquifer is get-
ting recharge from a location with 
a much higher water level. Figure 
2.2 shows a simple system with 
a water table well in a shallow 
Figure 2.1 Recharge. Waller, Roger M., Ground Water and the Rural Homeowner.
Figure 2.2 Example of a Confined Aquifer System. Source: Michigan Dept of Environmental Quality.
© 2018 University of Illinois at Urbana-Champaign 13
aquifer and two deeper wells in a 
confined aquifer. At the deep well 
labeled “artesian well,” the pres-
sure on the system forces water 
up into the well to nearly the same 
elevation as at the recharge area 
(the dashed line). When the water 
level in a well rises above the top 
of the aquifer, it is under artesian 
conditions. If it rises so high that it 
overtops a well, it is called a flow-
ing artesian well (labeled). The 
term “piezometric level” in Figure 
2.2 refers to the elevation that wa-
ter will rise to in a well due to the 
liquid pressure of the water in the 
aquifer.
Here is an analogy that will hope-
fully help make this clearer. Con-
sider a garden hose lying in your 
back yard. It has some water in it 
that you need to drain out so you 
can put it away. What do you do? 
You lift up one end and water runs 
out the other. Even if the other end 
of the hose is resting on a fence 
so that it is a few feet above the 
ground, water will still be forced 
out of it as long as you lift your 
end up higher. If you keep adding 
water to the end you are holding, it 
causes water to come out the other 
end, because your end is at a high-
er elevation (at a higher pressure). 
You could accomplish the same 
thing by blowing into your end of 
the hose. You are increasing the 
pressure in the hose on your end, 
which forces water to come out 
the other. In a well, similar kinds 
of pressure from an aquifer can 
cause the water level to rise. 
Why is this important? In some 
areas, well owners have never had 
a pump in their well because their 
well flows naturally. In other areas, 
heavy rains or flooding can cause 
wells to start flowing. Conversely, 
drought conditions, like we had 
in many parts of the US in 2012, 
can reduce recharge to the aquifer. 
This reduces the pressure head, 
which can cause some flowing 
wells to stop flowing. 
Understanding how the water lev-
el in your well can change because 
of natural factors will help you un-
derstand how your well works and 
if there are any risks of contami-
nation. For example, recharge can 
vary according to the seasons. In 
cold climates there is virtually no 
infiltration when the ground is fro-
zen, which limits recharge. 
For another example of seasonal 
differences, look at the water ta-
ble well in Figure 2.2. The water 
level in the well is clearly higher 
than the level of the stream (the 
solid line labeled “water table”). 
That means that groundwater flow 
in the water table aquifer is from 
right to left, from the well toward 
the stream. But what happens af-
ter heavy rainfall, when the stream 
elevation rises? It’s very possible 
that the flow direction could be 
reversed, short term, and water 
would flow from the stream into 
the aquifer and toward the well. 
This is important to understand 
if you have a shallow well that is 
close to a surface water body. Sur-
face waters have bacteria and or-
ganisms that can make us sick. 
Though the ground can act as a 
natural filter, if the well is close 
it may not have a chance to do 
so. Understanding the flow near 
and to your well is critical when 
it could potentially be affected by 
surface water sources.
Pumping and 
Groundwater Flow
When your pump kicks on and 
starts drawing water from your 
well, the water level in your well 
drops. This creates a pressure dif-
ference between the water in your 
well and the water in the surround-
ing aquifer. Water flows from the 
aquifer into your well to replenish 
what’s been withdrawn. The drop 
in water level in your well is affect-
ed by how fast water can move to 
your well from the aquifer. This 
drop is called the drawdown in 
your well. 
As water flows into your well, it 
also lowers the water level in the 
surrounding aquifer, creating a 
cone-shaped area of lower water 
levels around your well. This is 
called the cone of depression. Fig-
ure 2.3 shows a pumping well with 
3 additional wells to the right. The 
water table surface is shaped like a 
cone pointing downward with your 
well at the center. In this example, 
the two wells closest to the pump-
ing well are in the cone of depres-
sion, but the third well is not. The 
size and extent of the cone of de-
pression depends on the pumping 
rate, permeability, and available 
water in the aquifer. 
Pumping can have a significant 
effect on groundwater flow. Re-
ferring back to Figure 2.2, if we 
were to pump the water table well 
at a high enough rate, we could 
reverse the flow in the aquifer, 
causing water from the stream to 
flow into the aquifer and toward 
the well. There are many other sit-
uations where this is important. 
Wells and aquifers near an ocean 
could induce salt water migration 
into the aquifer if the water levels 
drop too much. Lowering water 
levels in a well could induce flow 
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from a shallower or deeper aqui-
fer that has differing water qual-
ity. Though these are important 
considerations, in most cases nor-
mal household use won’t result in 
pumping your well hard enough to 
cause significant changes in flow, 
except for very near your well.
Groundwater Flow and 
Contamination
Water is a natural solvent. Because 
of this, all groundwater generally 
has dissolved minerals and other 
constituents in it. These added 
minerals are what can give it a par-
ticular taste, odor, or, in some cas-
es, smell. This is why some people 
feel their well water tastes better 
than (treated) city water. However, 
water’sability to dissolve material 
also means that water can some-
times “pick up” contaminants 
from the surface and transport 
them down into your groundwa-
ter system. In other cases, liquid 
contaminants at the surface can 
infiltrate directly into the ground-
water. Then, depending on their 
density, these contaminants ei-
ther sit on top of the water table 
(less dense than water), or create a 
pool of contaminant at the bottom 
of an aquifer (more dense than 
water) (Figure 2.4). The problem 
with groundwater contamination 
is that we have learned the hard 
way that it’s much cheaper to pro-
tect groundwater in the first place 
than it is to try to remove the con-
taminant from the aquifer. Many 
communities and individual well 
owners have had to abandon their 
wells because their source aquifer 
became contaminated and it’s too 
expensive to treat or clean up.
We’re going to deal with the is-
sue of groundwater contaminants 
several times in this class. For Les-
son 2, today, we are going to limit 
the discussion to some common 
sources of contamination. Later, 
in Lesson 8, we’ll talk about source 
water protection and how to help 
prevent these things from getting 
in your well. In Lesson 10, we’ll 
talk about what you can do if you 
have any of these contaminants in 
your well. 
Contaminants that can get into 
groundwater are of two types, nat-
urally occurring and anthropogen-
ic. Anthropogenic simply means 
the result of human activities. 
Both natural and anthropogenic 
contaminants fall into two catego-
ries, nuisance or of possible health 
risk. We care about both. Nuisance 
contaminants like iron can cause 
staining, for example, and sedi-
ment can cause taste problems 
or possibly pump wear. Those 
that pose a health risk speak for 
themselves. We all need to be con-
cerned about ensuring our well 
water is free of any unwanted con-
stituent. 
Figure 2.3 Well Drawdown. Source: Oregon Water Resources Department.
Figure 2.4 Contaminant Movement. Source: New York State Water Resources Insti-
tute.
© 2018 University of Illinois at Urbana-Champaign 15
Anthropogenic 
Contaminants
The permeability of the soil and 
shallow earth materials above 
an aquifer will affect surface in-
filtration of both water and con-
taminants (Figure 2.5). That said, 
creating a dump for waste allows 
contaminants to infiltrate over 
time. So whether slowly or not, im-
properly dumped waste will even-
tually contaminate the ground wa-
ter system. This is why it’s always 
important to dispose of waste 
materials properly (Figure 2.6). If 
you aren’t sure what to do, call the 
manufacturer or your local health 
department for advice on dispos-
ing of materials that could become 
groundwater contaminants.
Naturally Occurring 
Contaminants
The problem with naturally occur-
ring contaminants is that if they 
are in the ground and part of the 
groundwater system, there isn’t a 
lot you can do. In Wisconsin, for 
example, they have identified a 
certain bedrock layer that is espe-
cially high in arsenic. Now they 
require new wells to be sealed 
from that geologic unit. In cases 
like this, the contaminate is just 
there. Then the only solutions 
are to treat the water, if feasible, 
or else not use the aquifer. Many 
naturally occurring contaminants 
represent a nuisance, rather than a 
health risk. Iron, Chloride, Sulfur, 
Manganese, and Hardness are all 
examples. But some have health 
risks too, including Arsenic, Bari-
um, Chromium, Nitrate, Selenium, 
Radium, and Uranium. For more 
details on these and other natu-
rally occurring contaminants, con-
tact your local health department, 
cooperative extension, or state 
water resources agency. They will 
be able to tell you which, if any, 
of these contaminants are preva-
lent in your area. The USEPA has 
a page that allows you to click on 
your state to find private well info, 
especially contacts. An excellent 
description of types of groundwa-
ter contamination can be found 
in the “Groundwater Contamina-
tion” bulletin available from the 
New York State Water Resources 
Institute and Cornell Cooperative 
Extension. We highly recommend 
you take a look at it. 
Additional Steps
The message for everyone is com-
mon sense. Whether you are on 
a farmstead, in a rural subdivi-
sion, or in a community that uses 
private wells, consider what you 
might be doing that can affect the 
infiltration of contaminants into 
your source aquifer. 
Figure 2.5 Surface Vulnerability. Source: 
NY State Water Resources Institute. 
Figure 2.6 Landowner is burying his waste so it won’t be a problem. Source: Cornell Cooperative Extension
All references used to develop 
this lesson, as well as additional 
resources mentioned in the text, 
can be found on our website at: 
privatewellclass.org/lesson-2
http://privatewellclass.org/lesson-2