Graves County, Kentucky

GEOLOGIC HAZARDS

Many concealed and exposed faults are located throughout Graves County. Currently, there is no evidence that these faults are active. Because of the proximity of Graves 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 saturated alluvium and other unconsolidated deposits are subject to liquefaction during a strong earthquake. Alluvium deposits are also subject to flooding. Soils derived from alluvium deposits have a moderate to high shrink-swell capacity, which 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/.

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 Graves County from depths of a few feet to below 700 feet; most wells set at the 100 foot range. Yields in some of the deeper wells (250 to 1,500 feet) are greater than 1,000 gallons per minute, which is sufficient for a community or industrial supply. A few wells obtain shallow, perched water from gravel or alluvial deposits. These zones often will not yield an adequate domestic supply during dry periods in late summer and fall.

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. Water from alluvium is generally hard to very hard with moderate to high levels of dissolved solids. Water from the sand or gravel, non-alluvium aquifers is considered soft and slightly acidic, with low dissolved solids content. In a few wells, harmful amounts of nitrate have been detected. Groundwater from the deeper zones sometimes contains naturally-occurring iron in objectionable amounts. In some formations with slightly acidic groundwater, a chemical reaction between the acidic groundwater, steel well casing, and pump equipment will produce a high iron content in the water. For more information on groundwater resources in the county, see Carey and Stickney (2001).

The well-drained soils in Graves County are conducive to the use of septic tanks with lateral lines. The unconsolidated sediment makes for easy excavation. In areas where the soils are not well-drained, unconventional methods to handle waste may be needed. Photo by Glynn Beck, Kentucky Geological Survey.

THE LAND

Agriculture is a major part of the Graves County economy. There are 356,224 acres in Graves County, and 124,200 of them were planted with either corn or soybeans in 2002 (Kentucky Agriculture Statistics 2002--2003). Photo courtesy of Jerry McIntosh, U.S. Department of Agricultural--Natural Resources Conservation Service.

Approximately 230 chicken houses are in Graves County. Each house holds about 27,000 birds. Chicken litter associated with these operations is used as a substitute for synthetic fertilizers on row crops. Photo by Glynn Beck, Kentucky Geological Survey.

Currently, 61 catfish ponds are in Graves County. After harvesting, the fish are trucked to the processing plant, located at the Purchase Area Aquaculture Cooperative. The processing plant is currently running at 30 percent capacity. To get the plant to 80 percent capacity 1000 more acres of ponds are needed. Photo courtesy of Roberta Bonk, Purchase Area Aquaculture Cooperative.

RESOURCES

The Kentucky-Tennessee Clay Company has been mining ball clay in Graves County since 1887and is currently one of three ball clay mining companies in the county. Ball clay has a high percentage of aluminum, which makes it suitable for the production of toilets, sinks, floor tile, bathtubs, and fine dinnerware. Photo by Glynn Beck, Kentucky Geological Survey.