MS Comprehensive Exam (revised)
Saidet Saldutti
Geoenvironmental Department
July 11, 2009
INTRODUCTION
Most of us take safety of our drinking water for granted, whether it comes from our own
well or a public system. However, drinking water is sometimes contaminated beyond the limits of
safety. This is a particular concern for households that use an individual well, a spring or other
private drinking water source. The Safe Drinking Water Act of 1974 requires the U.S.
Environmental Protection Agency (EPA) to establish drinking water standards for America‟s
community water systems. The agencies in the state government therefore promote local water
supply solutions that will ensure system viability and hence compliance with quality standards.
Information on water quality of public systems is available from the water system manager to the
public. However, water quality for individual wells is the responsibility of the homeowner. It is the
responsibility of the private well owner to monitor and test their own water. Most local departments
or agencies have limited authority to impose or enforce standards for wells.
Contaminants can be both natural or human-induced. Naturally occurring contaminants are
present in the rocks and sediments. As groundwater flows through sediments, metals such as iron
and manganese are dissolved and may later be found in high concentrations in the water (USGS
2009). Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal or
waste all can affect ground water quality. Contaminants from leaking fuel tanks or fuel or toxic
chemical spills may enter the ground water and contaminate the aquifer. Pesticides and fertilizers
applied to lawns and crops can also accumulate and migrate to the water tables (Becher & Root
1981).
Performing a background water quality assessment of groundwater in Cumberland County,
Pennsylvania will help county and state legislators decide whether to support funding for the
expansion of regional water systems into areas of the county where residents and businesses are
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served by individual private water wells. By looking at forty water samples from wells in 1974 by
the USGS (shown in Figure 1), spatial trends and relationships can be examined with data on pH,
temperature, total dissolved solids (TDS), nitrate, and “hardness”.
Cumberland County, Pennsylvania
Figure 1. Sample well locations
BACKGROUND
Study Area
The general pattern of existing land uses in Cumberland County is characterized by high
density, mixed urban development and rural/agricultural. The geology of Cumberland County
consists of formations containing quartzite that dominate in the South Mountain region, while
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limestone and dolomite proliferate in the Great Valley, and shale is most abundant north of the
Conodoguinet Creek (Cumberland County Comprehensive Plan 2003). Of these groups, the
limestone and dolomite group appear to have the greatest impact on life in the County. These rocks
underlay the more level areas of the valley. They are the basis for the most productive farmland and
certain large ground water aquifers. Cumberland County geology and formations are shown below
in Figure 2.
Figure 2. Cumberland County geologic formations
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Hydrology
Cumberland County has a substantial groundwater supply largely due to the geology of the
region. The central portion of the County is composed mostly of limestone, which usually produces a
high groundwater yield and is overlain with the most productive agricultural soils in the County.
Cumberland County contains two of the highest yielding natural springs in Pennsylvania. Natural
groundwater quality is a result of interaction between the ground water and the bedrock with which
it is in contact. The more soluble bedrock types will allow more compounds to become dissolved in
the ground water. For example, groundwater in highly soluble limestone aquifers will commonly
have high hardness values (Becher & Root 1981).
Water Quality
Poor water quality is not always the result of human activities. Pure water, is often called the
universal solvent because it dissolves minerals from the rocks with which it comes into contact. The
dissolution of minerals in rocks occurs very slowly. The longer the groundwater flows through the
rocks (residence time), the more time it has to dissolve minerals. Deep groundwater, which has been
in the groundwater system longer than most shallow groundwater, is more likely to be higher in
dissolved solids. Some areas of Pennsylvania have rugged landscape, little groundwater penetrates
to deep levels in that area, resulting in a short residence time. The main rock types are sandstone
and shale, which are made of relatively insoluble minerals. Other areas of Pennsylvania have more
rock that is soluble and/or more of the groundwater penetrates to deeper levels increasing residence
time. The most common dissolved mineral substances are sodium, calcium, magnesium, potassium,
chloride, bicarbonate, and sulfate. In water chemistry, these substances are called common
constituents.
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In the U.S., the EPA limits the amounts of certain contaminants in tap water provided by
public water systems. The Safe Drinking Water Act authorizes the EPA to issue two types of
standards: primary standards, which regulate substances that potentially affect human health, and
secondary standards which prescribe aesthetic qualities, those that affect taste, odor, or appearance.
EPA recommends secondary standards to water systems but does not require systems to comply.
Some commonly used parameters to determine water quality are temperature, hardness, total
dissolved solids, nitrate levels and pH.
Total Dissolved Solids
Dissolved solids refer to any minerals, salts, metals, cations or anions dissolved in water.
Total dissolved solids (TDS) are comprised of inorganic salts (calcium, magnesium, potassium,
sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that are
dissolved in water. As groundwater flows, it dissolves minerals in the soil and rock, and its
chemistry changes (World Health Organization 2004). TDS in drinking water originate from natural
sources, sewage, urban run-off, and chemicals used in the water treatment process, and the nature of
the piping or hardware used to convey the water. In the U.S., elevated naturally occurring TDS
levels have been due to natural environmental features such as mineral springs, carbonate deposits,
salt deposits, and sea water intrusion. Highly mineralized water may deteriorate domestic plumbing
and appliances. Under secondary standards, the EPA recommends TDS to be no greater than
500mg/L.
Hardness
The geologic makeup of an area usually determines the level of hardness. Soft water is often
seen in areas with igneous rocks, like granite, which don‟t release many ions. Hard water is often
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seen in areas with calcite rich soil or rock, such as limestone, which releases calcium when exposed
to slightly acidic water. Hardness affects the amount of soap that is needed to produce foam or
lather. Hard water requires more soap, because the calcium and magnesium ions form complexes
with soap, preventing the soap from sudsing. Water is considered soft if it contains 0 to 60 mg/L of
hardness, moderately hard from 61 to 120 mg/L, hard between 121 and 180 mg/L, and very hard if
more than 180 mg/L (DCNR 1999). Hard water can be softened at a fairly reasonable cost, but it is
not always desirable to remove all the minerals that make water hard. Extremely soft water is likely
to corrode metals, although it is preferred for laundering, dishwashing, and bathing. Hardness does
not pose a health risk for humans or aquatic life.
pH
pH is a measure of the relative acidity or alkalinity of water. The pH level can be affected by
several factors, including soil and bedrock, respiration and decomposition, and some forms of
pollution. Limestone bedrock neutralizes acid and raises the pH of a body of water, but granite
bedrock provides little neutralizing capacity and little effect on pH. The pH scale runs from 0-14.
Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher
than 7 indicate increasingly basic solutions. A one unit change in pH represents a 10-fold difference
in hydrogen-ion concentration. For example, water with a pH of 6 has 10 times more hydrogen-ions
than water with a pH of 7. Water that is basic can form scale; acidic water can corrode. According
to U.S. Environmental Protection Agency criteria, water for domestic use should have a pH between
6.5 and 8.5 (USGS 2009). Lethal effects of pH on aquatic life occur below pH 4.5 and above pH
9.5.
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Nitrate
Nitrate occurs naturally in mineral deposits, soils, seawater, freshwater systems, the
atmosphere, and biota. Nitrate levels should not be higher than 10 mg/L according to the EPA
primary standards. High nitrate may cause "blue baby disease" in infants who drink water or
formula made from water containing nitrate levels higher than recommended (U.S. Geological
Survey 2009). Adults can drink water with considerably higher concentrations than infants without
adverse affects. Nitrate is a major ingredient of farm fertilizer and is necessary for crop production.
When it rains, varying nitrate amounts wash from farmland into nearby waterways or to the
groundwater. Nitrates stimulate the growth of plankton and water weeds that provide food for fish.
This may increase the fish population. However, if algae grow too wildly, oxygen levels will be
reduced and fish will die.
Temperature
Temperature affects the solubility of many chemical compounds and can therefore influence
the effect of pollutants on aquatic life. Increased temperatures elevate the metabolic oxygen
demand, which in conjunction with reduced oxygen solubility, impacts many species. High water
temperature enhances the growth of microorganisms and may increase taste, odor, color and
corrosion problems. The Earth‟s temperature, and that of groundwater too, depends on depth
(World Health Organization 2004). Aside from places with volcanoes, geysers, and hot springs, the
temperature of groundwater within a hundred feet of the land surface is about the same as a region‟s
mean annual air temperature while surface waters are more subject to seasonal change. This rate of
increase is known as the geothermal gradient. Thermal pollution also causes increased water
temperature by adding warm water to a waterway. Industries may cause thermal pollution by
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discharging water that was used to cool machinery. It may also be caused by return flows from
irrigation systems and stormwater runoff that has traveled across heated surfaces like streets,
sidewalks, or parking lots.
METHODOLOGY
The water quality data used in this analysis was collected by the USGS in 1974. In order to
transfer the data from Excel into GIS, the latitude and longitude coordinates were changed to
decimals. By „adding xy data‟ in ArcMap, the selected data was transferred to examine for spatial
trends. The background imagery and prime agricultural land was downloaded from PASDA and the
geologic map from PA Geological Survey. The projection used is Lambert Conformal Conic,
NAD83 PA South.
SPSS was used to explain some of the trends between datasets. To see how well TDS
„residue at 180 C‟ and „sum of constituents‟ are correlated, the data was tested for normality. Using
SPSS, the data was considered not normal according the Shapiro-Wilks test. Knowing that the data
was not normal, a Spearman‟s Ranked Correlation was performed.
ANALYSIS OF DATA
By mapping out the parameters given by the USGS, spatial trends can be shown. Also, by
comparing parameters using graphs and statistics, relationships can be speculated. The data can also
be compared to EPA primary and secondary standards to find out the water quality of the individual
private water wells and whether the expansion of regional water systems into these areas is
necessary. The following parameters are analyzed to determine the water quality of these private
wells.
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pH
The pH of the water samples varied throughout the Cumberland Valley, and ranged from 6.6
to 8.0, which meant that all of the wells were safe for domestic use and wouldn‟t be lethal to aquatic
life since the EPA suggests a pH between 6.5 and 8.5. There was no spatial pattern besides a few
wells along the base of South Mountain that are shown in Figure 2.2 that had higher pH values
ranging from 7.6-8.0, which is basic water and can form scale.
Figure 3. pH of samples wells
Temperature
Average groundwater temperature is typically the same as mean annual air temperature. In
the Cumberland County, mean annual air temperature is around 11.5°C. The data shown in Figure 3
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ranges from 11.5°C to 18.5°C, which means that some of sample wells have other factors that
influence the groundwater temperature. Figure 4 shows sampling depth (ft) vs. water temperature
(°C). There is little or no association (R²= 0.022) between the two parameters, which means that the
sample wells that had the highest groundwater temperatures weren‟t necessarily the deepest wells.
However, there were several cases where a deep well also contained warmer groundwater than the
mean annual air temperature, which could be a result of the geothermal gradient. For example, one
well was sampled at 300 feet and had a groundwater temperature of 15.5°C. On the other hand,
there was one well that was only 80 feet but had the highest groundwater temperature of 18.5°C out
of all 40 wells. This is most likely a result of geothermal pollution or runoff from a storm event that
had a shorter residence time. In this case, it would be because the Valley contains karst terrain
which have high rates or permeability and water is not filtered.
Figure 3. Water temperature (°C) of sample
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Figure 4. A comparison of water temperature (°C) and sampling depth (ft)
Total Dissolved Solids
Figure 5 shows that there is a spatial pattern with total dissolved solids (TDS) in the
Cumberland County. TDS values are higher in the Valley than in the South and North Mountains.
The Valley contains limestone and dolomite which are composed of minerals that easily dissolve in
groundwater, which would explain higher TDS values. Soluble rock that allows groundwater to
penetrate to deeper levels also has increasing residence time which allows for groundwater to pick
up more dissolved solids than areas with insoluble rocks and a lower residence time. There were
three wells that exceeded the EPA recommendation of TDS <500 mg/L, all found at the base of
North Mountain. Another observation was that some sample wells that were deeper groundwater
samples, also contained higher levels of TDS.
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Figure 5. Total dissolved solids (mg/L), residue at 180°C of sample wells
A graph was made to see if there was a relationship between depth of sampling and TDS.
Looking at Figure 6, the depth of sampling does not control TDS. The R² is 0.071, which is almost
no association. The rate of change in TDS per depth unit is 231.31 mg/L. There are a variety of
ways to measure TDS. The simplest is to filter the water sample, and then evaporate it at 180°C in a
pre-weighed dish until the weight of the dish no longer changes. The increase in weight of the dish
represents the TDS, and it is reported in mg/L. Finally, TDS can be calculated by measuring
individual ions and simply adding them together.
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Figure 6. The amount of total dissolved solids and depth of sampling
Using SPSS, a normality test and Pearson‟s Correlation were performed to see if there was a
correlation between solids (residue at 180°C) and solids (sum of constituents). Normality test results
are shown below:
Tests of Normality
a
VAR000
03
VAR00001
Kolmogorov-Smirnov
Statistic
df
Shapiro-Wilk
Sig.
Statistic
df
Sig.
1.00
.103
40
.200
*
.931
40
.017
2.00
.112
40
.200
*
.932
40
.019
The Shapiro-Wilk test is best to use since the dataset is more than 50. The data are
significantly different from normal because .017 and .019 are smaller than .05. This means a
Spearman‟s Ranked Correlation 2-tailed test is best to use for this dataset. Using SPSS again, the
test results are shown on the next page:
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Correlations
VAR00001
Spearman's rho
VAR00001
Correlation Coefficient
1.000
Sig. (2-tailed)
N
VAR00004
Correlation Coefficient
Sig. (2-tailed)
N
VAR00004
.978
**
.
.000
40
40
**
1.000
.000
.
40
40
.978
**. Correlation is significant at the 0.01 level (2-tailed).
Spearman‟s Ranked Correlation test showed that there is a positive strong correlation
between TDS „residue at 180°C‟ and „sum of the constituents‟ (rs=.978) with an alpha level of 0.05.
TDS „residue at 180°C‟ appears to be an important predictor of „sum of constituents‟, and vice
versa. The probability value of .000 is <.05, so our hypothesis is supported. There is a positive
relationship between the two variables.
Nitrate
The spatial trend of nitrate levels in the groundwater is clear from looking at Figure 7.
Nitrate levels are higher in agricultural areas located in the Valley and lower in non-agricultural
areas. Also, 25 of the 40 water samples exceeded the EPA recommended limit of 10 mg/L of
nitrate. One water sampling was tested at 84 mg/L of nitrate located in the Valley and was also the
deepest sample at 490 feet. These amounts are not natural, but are caused by man‟s activities in the
area. Crop fertilizers, cattle feedlots, barnyard wastes, and on-lot sewage disposal systems can
contribute nitrates to the groundwater.
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Figure 7. Nitrate (mg/L) levels in groundwater and prime agriculture land.
Hardness
A trend similar to the nitrate map is shown in Figure 8 of water hardness. Values are lower
in the mountains and higher in the valley. There were 24 wells contained very hard water (>180
mg/L). The more soluble bedrocks, such as the limestone in the Valley, allow more compounds to
become dissolved din the ground water and will commonly have higher hardness values. Hard water
is often seen in areas with limestone, which releases calcium when exposed to slightly acidic water.
When comparing the parameters Ca+Mg and hardness, there was a strong positive association
between the two (R²=.989).
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Figure 8. Groundwater “hardness” (mg/L) of sample wells
Figure 9. Ca+Mg vs. hardness of sample wells
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CONCLUSION
Performing a background water quality assessment using the well sampling data from the
USGS gives incite on whether to expand regional water systems to individual private well owners.
By looking at pH, temperature, TDS, nitrate, and hardness spatially distributed throughout the
Cumberland County, it was easier to see which parameters displayed a spatial trend and which
didn‟t. TDS, hardness, and nitrates showed spatial patterns with values higher in the Valley than in
the South and North Mountains. Temperature and pH parameters, however, did not show any spatial
trends. There are private wells where EPA primary and secondary standards are exceeded. These
are areas where regional water systems should be expanded because of the health risks and poor
water. While the areas especially located in South and North Mountains seem to currently have
good water quality.
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REFERENCES
Becher AE, Root SI. 1981. Groundwater and geology of the Cumberland valley, Cumberland
county, Pennsylvania. Pennsylvania Geological Survey, Fourth Series.
Cumberland County Comprehensive Plan. [Internet]. Cumberland County; c2003 [cited 2009 May
16]. Available from http://www.ccpa.net/index.asp?NID=3086
Ground-water Quality. [Internet]. U.S. Geological Survey; c2009 [cited 2009 May 16]. Available
from http://ga.water.usgs.gov/edu/earthgwquality.html
Quality of Groundwater. [Internet]. U.S. Geolgical Survey; c2009 [cited 2009 May 15]. Available
from http://pubs.usgs.gov/gip/gw/quality.html
The Geology of Pennsylvania Groundwater. [Internet]. DCNR; c1999 [cited 2009 May 15].
Available from http://www.dcnr.state.pa.us/topogeo/education/es3.pdf
Water Quality Standards. [Internet]. U.S. Environmental Protection Agency; c2009 [cited 2009 May
15]. Available from http://www.epa.gov/waterscience/standards/
World Health Organization. Guidelines for Drinking-water Quality: third edition. Volume 1: 2004.
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