Calloway County, Kentucky

GEOLOGIC HAZARDS

Several shallow, concealed, and exposed faults are located throughout Calloway County. Currently, there is no evidence suggesting these faults are active. Because of the proximity of Calloway County to the New Madrid Seismic Zone, however, strong earthquake activity is a possibility. Soil creep, slumps, and landslides along steep slopes may occur from erosion or ground motion associated with a strong earthquake. Areas associated with alluvium material are subject to liquefaction during a strong earthquake. These areas are also subject to flooding. Soils derived from alluvium deposits have a moderate to high shrink-swell capacity that may affect structural foundations and roads. Flood information is available from the Kentucky Division of Water, Flood Plain Management Branch, www.water.ky.gov/floods/.

Surficial materials in Calloway County are unconsolidated and generally saturated with water, which can make these materials prone to collapse during excavation. Shallow excavation through these surficial materials is needed in order to construct water and sewage pipelines. Photo by Glynn Beck, Kentucky Geological Survey.

EARTHQUAKE HAZARDS

Peak ground acceleration at the top of rock that will probably occur in the next 500 years in Kentucky

Although we do not know when and where the next major earthquake will occur, we do know that an earthquake will cause damage. Severity depends on many factors, such as earthquake magnitude, the distance from the epicenter, and local geology. Information on earthquake effects is obtained by monitoring earthquakes and performing research. Such information is vital for earthquake hazard mitigation and risk reduction.

The most important information for seismic-hazard mitigation and risk reduction is ground-motion hazard. One way of predicting ground-motion hazard is by determining the peak ground acceleration (PGA) that may occur in a particular timeframe. The map above shows the PGA at the top of bedrock that will likely occur within the next 500 years in Kentucky (Street and others, 1996). It shows, as expected, that PGA would be greatest in far western Kentucky near the New Madrid Seismic Zone. Ground-motion hazard maps for the central United States and other areas are available from the U.S. Geological Survey. These maps are used to set general policies on mitigating damage. For example, maps produced by the USGS in 1996 were used to determine seismic design in building codes. For additional information pertaining to earthquake hazards visit the Kentucky Geological Survey website at www.uky.edu/KGS/geologichazards/geologichazards.html

GROUNDWATER

Abundant quantities of groundwater are available for domestic, irrigation, and industrial uses in Calloway County. Water is obtained from depths ranging from a few feet to below 700 feet; most wells are less than 100 feet deep. A few wells may intercept shallow perched water from gravel or alluvial deposits, but these zones often will not yield sufficient water for an adequate domestic supply during periods of low rainfall, which are typical in late summer and fall. Groundwater from alluvium and limestone in the county is generally hard to very hard, with moderate (200-500 milligrams per liter) to high (more than 500 milligrams per liter) levels of dissolved solids. Groundwater from unconsolidated sand or gravel, non-alluvium aquifers are considered soft and slightly acidic with low dissolved solids. Water quality generally is good except in areas where downward percolation of surface water and fluids from domestic sewage-disposal systems and other sources of domestic or industrial pollution have contaminated the aquifer. In a few wells harmful amounts of nitrate have been detected. Groundwater sometimes contains naturally occurring iron and manganese in objectionable amounts from the deeper zones. In some formations with slightly acidic groundwater, a chemical reaction between the acidic groundwater, steel well casing, and pump equipment will produce high iron content in the water, which is not naturally occurring. For further information on groundwater resources in the county, see Carey and Stickney (2001).

The City of Murray and portions of Calloway County use groundwater as their drinking-water source. The municipal water well above, one of five, is approximately 200 feet deep and pumps about 1000 gallons per minute. Photo by Glynn Beck, Kentucky Geological Survey.

Groundwater is used in pivot irrigation of traditional crops such as corn. Pivot irrigation is used to sustain crop growth during periods of drought. Photo by Glynn Beck, Kentucky Geological Survey.

Groundwater is also used for drip irrigation of nontraditional agricultural crops such as ornamental trees, cabbage, watermelons, and cantaloupes. Photo by Glynn Beck, Kentucky Geological Survey.

SURFACE WATER

Slow-flowing streams, such as the East Fork Clarks River shown above, are prevalent in the Loess Plains Ecoregion (Woods and others, 2002) of Calloway County. Because of the large percentage of flat to gently sloping areas, developments such as subdivisions can cause flooding if proper drainage designs are not implemented. These streams are susceptible to impairment from improper sewage treatment and agricultural, urban, and industrial runoff contamination. Allowing natural vegetation to thrive along the stream bank is an excellent way to maintain good surface water quality. Photo by Glynn Beck, Kentucky Geological Survey.

CONSTRUCTION

When building a road in Calloway County, rock excavation is generally not needed. Because of the large number of small streams and wetlands associated with those drainages, however, cut and fill techniques are required. Cut and fill techniques are used to remove unsuitable soil, such as saturated clays. The new Ky. 80 running through Calloway County is an example of how multiple bridges are used, as well as cut and fill methods. Photo by Glynn Beck, Kentucky Geological Survey.