Cedar Valley
Aquifer
IronCounty, Utah
CeLena Clough
Spring 2010
GO 571 Hydrogeology
(Danis, 2010) Picture of Cedar City within the Cedar Valley.
Introduction
The Cedar Valley aquifer is located in southwestern Utah, on the
southeastern edge of the Basin and Range Province. The valley
encompasses about 170 square miles of land. Several fairly steep
mountains and hills surround Cedar Valley, as shown in figure 1.
The towns of Enoch and Cedar City depend on the Cedar Valley
aquifer for their water supply. Ground water issues in the Cedar
Valley area include contamination from septic systems and
agricultural fertilizers. Nitrate contamination is the main
contaminant in this area.A significant increase in population has
lead to over-pumping of groundwater for irrigation and for public
use(Eisinger, 1998).
Figure 1. Map of Cedar Valley aquifer drainage basin with
surrounding landforms (Eisinger, 1998).
GEOLOGIC SETTING
The geology of Cedar Valley is quite complex with
previousvolcanic activity and many faults. Normal faulting in this
region caused the valley to form. The lowest section of the valley
consists of Middle Proterozoic up to Permian age sedimentary
rocks. Above these sedimentary rocks lie Tertiary volcanic,
intrusive volcanic, and more sedimentary rocks.
InterbeddedQuaternary alluvium and lacustrine deposits sit
above the Tertiary volcanic rock. Quaternary lakes once occupied
the valley floor and deposited the alluvium and lacustrine
deposits. Alluvium also originated from alluvial fans within Cedar
Valley. The alluvium consists of coarse-grained material ranging
from pebble to boulder size. The alluvial sediments cause the
aquifer medium to have a high permeability. Alluvium in the
aquifer ranges from poorly sorted to well sorted. Poorly sorted
material begins on the edges of the basin near alluvial fans and
increases to well sorted near the center of the basin (Eisinger,
1998).The composition of the alluvium is quartzite, limestone, and
some volcanic rock. Lacustrine deposits are composed of fine clay
with some trace amounts of silt and sand (Hurlow, 2004).
Most groundwater in Cedar Valley is drawn from the basin-fill
aquifers, although bedrock aquifers are also present in the area.
Figure 2 shows a diagram of a basic basin-fill aquifer.
Figure 2. Diagram of basin-fill aquifer.(Banta and Robson, 1995)
(http://pubs.usgs.gov/ha/ha730/ch_c/jpeg/C034.jpeg)
HYDROLOGIC SETTING
REGIONAL CLIMATE
Cedar Valley experiences warm, dry summers and fairly cold
winters. During the summer, temperature can vary significantly
between night and day. Fluctuation in temperature can be up to
40˚F. The average high temperature is 100˚F and the average
low temperature is 0˚F (Eisinger, 1998). Precipitation ranges
from 8 to 14 inches per year in Cedar Valley(UtahDivision of
Water Resources, 1995). The majority of precipitation in spring
and winter is created from humid air masses moving through the
area. Snowfall occurs from December to March and even up
through April and May (Eisinger, 1998).
SURFACE WATER
Surface water in Cedar Valley consists of perennial and
ephemeral streams, and also two lakes. These streams generally
enter the basin from the east. Coal Creek is the major stream in
Cedar Valley, discharging 23, 830 acre-feet annually. Quichapa
and Shurtz Creeks are two other significant sources of surface
water, however, Quichapa Creek is used diverted for irrigation.
Other ephemeral streams rapidly infiltrate the alluvium or
evaporate quickly. The alluvial fan created by Coal Creek also
formed two lakes, Rush and Quichapa Lakes, which both
contribute significantly to recharging the basin-fill aquifer
(Eisinger, 1998).
RECHARGE AND DISCHARGE
The source of most recharge into the Cedar Valley aquifer is
from streams. Snowmelt from surrounding mountains causes
streams to drain into the basin.The average amount of
precipitation in Cedar Valley is 452,000 acre-feet per year, but
the amount of recharge to the aquifer is only approximately
40,000 acre-feet per year. A large amount of precipitation that
falls in Cedar Valley is evaporated or transpired, and therefore
does not reach the water table(Eisinger, 1998).
The main source of groundwater discharge in the Cedar Valley
aquifer is from municipal and irrigation usage, due to the rapid
increase in population. Little discharge occurs through
evapotranspiration and springs. In the year 2000, the estimated
withdrawal was 36,000 acre-feet per year. This is a drastic
increase from the average 13,200 acre-feet per year in
1938(Eisinger, 1998).
AQUIFER PROPERTIES
Confined and unconfined conditions appearwithin the Cedar Valley
basin-fill aquifer. The thickness of the basin-fill aquifer ranges
from 249 feet up to 3,000 feet in the center of the
aquifer(Brooks and Mason, 2005). Figure 3 illustrates the
variation in thickness of alluvial deposits within the aquifer.
Hydraulic conductivity, transmissivity, specific yield, and
storativity vary throughout the aquifer as a function of thickness
and type of sediments. Hydraulic conductivity ranges from 5 to
180 feet per day. Figure 4 shows different hydraulic
conductivities of the aquifer. Transmissivity ranges from 12,000
to 90,000 feet per day, depending on the thickness of
sediments(Brooks and Mason, 2005). Specific yield of the
aquifer was estimated to be 0.2, according to Eisinger in 1998.
Storativity values derived from multiple wells range from 0.0005
to 0.013 for confined and semi-confined conditions, with semiconfined values at the higher end of the range(Lohman, 1972).
Figure 3. Map of thickness of alluvial deposits in basin-fill aquifer
(Brooks and Mason, 2005).
Figure 4. Hydraulic conductivities within Cedar Valley aquifer
(Brooks and Mason, 2005).
WATER CHEMISTRY
Water chemistries of various wells in Cedar Valley are displayed
by a piper diagram in Figure 5.On the eastern boundary of the
aquifer, water type can be classified as Ca-SO4, Ca-Mg-HCO3SO4, or Ca-Mg-SO4-HCO3. The sulfate and calcium in the water
originates from a dissolved gypsum layer located with the
MarkaguntPlataeu (see figure 1). Bicarbonate, Magnesium, and
calcium in the water also originate from dissolution of carbonate
rocks in the area (Brooks and Mason, 2005).
The water type on the western and northern sides of the aquifer
is slightly different than the eastern side. Primary ions on the
west side are calcium and bicarbonate, while primary ions in the
north are sodium and chloride. The sodium and chloride ions are
thought to be derived from underlying playa deposits(Bjorklund
and others, 1978).
Figure 5. Groundwater composition at different wells within
Cedar Valley (Brooks and Mason, 2005).
CEDAR VALLEY AQUIFER AS A
WATER RESOURCE
In recent years, the land use of Cedar Valley has changed. Most
of the area was used for agriculture, but an increase in population
has shifted the use of the aquifer towards public use, also. The
current population of Cedar City and Enoch together is 43, 575.
By the year 2060, the population is expected to grow to 240,
456. As population increases, so does the demand for water.
Many agencies are responsible for protecting groundwater in the
area. In 1997 under The Utah Water Conservancy District Act,
the Central Iron County Water Conservancy District (CICWCD)
was formed as a local agency. The purpose of the CICWCD is to
conserve and stabilize existing water sources and formulate plans
for new water supplies (CICWCD, 2009). The Utah Division of
Water Resources and Utah Division of Water Rights are state
agencies that help manage water in this area. The Department of
Environmental Quality is another state agency that is responsible
for protecting water quality (National Water Rights Digest). The
EPA is a federal agency that aids in protecting and clean up of
contaminants in groundwater.
GROUNDWATER CONTAMINATION
The quality of groundwater in most of the Cedar Valley aquifer is
good. There are, however, some issues with nitrate contamination
on the eastern edge of the basin near the city of Enoch.In 1979,
the concentration of nitrate in groundwater wells ranged from
0.06 mg/L to 57.4 mg/L. High concentrations are spread out
throughout Cedar Valley, but seem to be higher on the eastern
edge. Nitrate contamination is believed to come from fertilizers,
septic tank soil-absorption systems, sewage lagoons, and possibly
from natural sources (Eisinger, 1998). One solution to keeping
nitrate contamination low in Cedar Valley is to limit the number of
septic tank systems installed (Lowe, Wallace, and Bishop, 2000).
A recent issue associated with possible groundwater
contamination to the alluvial aquifer is earth fissures. Earth
fissures are deep surface fractures in the soil resulting from
subsidence of the land as groundwater is being pumped from the
aquiferat a faster rate than the aquifer can be recharged. Once
a fissure forms, it can quickly become eroded. One major fissure
near the city of Enoch extends 2.25 miles. Damage to existing
roads and buildings may result from earth fissures, but the main
concern with earth fissures is that some may extendto the water
table. In essence, any surface contaminants such as fertilizers,
could be introduced directly through these fractures and
contaminate groundwater. Figures 7 and 8 show examples of
earth fissuresin the basin (Lund, 2009).
Figure 6. Nitrate concentration in mg/L (Brooks and Mason,
2005).
Figures 7 and 8.Pictures of earth fissures in Cedar Valley (Lund,
2009).
CONCLUSION
The primary concern with the Cedar Valley aquifer in Iron County
Utah is associated with water supply for the growing population.
The alluvial aquifer will continue to be pumped more than the
aquifer can be recharged as the population increases. The overall
quality of groundwater is good, however there is some nitrate
contamination in certain areas. Agencies such as the CICWCD
are working to regulate and sustain water resources in the
future.
REFERENCES
Brooks, Lynette E. and Mason, James L. 2005. Hydrology and
Simulation of Ground-Water Flow in Cedar Valley, Iron County,
Utah.U.S. Geological Survey Scientific Investigations Report
20055170.(http://pubs.usgs.gov/sir/2005/5170/PDF/SIR2005_5170.p
df) Retrieved on 23 April, 2010.
Banta, E.R, Robson, S.G. 1995. Groundwater Atlas of the United
States Arizona, Colorado, New Mexico, Utah HA 730-C. US
Geological Survey. (http://pubs.usgs.gov/ha/ha730/ch_c/Cbasin.html) Retrieved on 27 April, 2010.
“CICWCD, 2009”. Central Iron County Water Conservancy
District. (http://cicwcd.org/ ) Retrieved on 28 April, 2010.
Danis, Juli 2010. Cedar City Real Estate. Century 21.
(http://www.julidanis.com/CEDAR_CITY/page_2215457.html)
Retrieved on 28 April, 2010.
Eisinger, Chris, 1998. A Summary of the Geology and
Hydrogeology of the Cedar Valley Drainage Basin, Iron County,
Utah.Utah Geological Survey Report 360.
(http://geology.utah.gov/online/ofr/ofr-360.pdf) Retrieved on 29
April, 2010.
Hurlow, H.A., 2002, The geology of Cedar Valley, Iron County,
Utah, and its relation to ground-water conditions: Utah Geological
Survey Special Study 103, 74 p.Counties, Utah: U.S. Geological
Survey Water-Supply Paper No. 277, 162 p.
(http://pubs.usgs.gov/sir/2005/5170/PDF/SIR2005_5170.pdf)
Retrieved on 25 April, 2010.
Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological
Survey Professional Paper 708, 70 p.
(http://pubs.usgs.gov/sir/2005/5170/PDF/SIR2005_5170.pdf )
Retrieved on 28 April, 2010.
Lowe, Mike. Wallace, Janae. and Bishop, Charles E. 2000.Analysis
of Septic-Tank Density for Three Areas in Cedar Valley, Iron
County, Utah- A Case Study for Evaluations of Proposed
Subdivisions in Cedar Valley. Utah Geological Survey Water
Resource Bulletin 27.(http://geology.utah.gov/online/wrb/wrb27.pdf ) Retrieved on 27 April, 2010.
Lund, W.R, 2009. Enoch Earth Fissures.Central Iron County
Water Conservancy District Board Meeting.Utah Geological
Survey.(http://www.xmission.com/~cicwcd/presentations/earthfi
ssures.pdf) Retrieved on 25 April, 2010.
“National Water Rights Digest”.Ridenbaugh Press.29 April, 2010.
(http://www.ridenbaugh.com/nwrd/nwref/nwref.htm) Retrieved
on 29 April, 2010.