HOME BACKGROUND STUDY AREAS PRODUCTS TIMELINE LINKS CONTACTS

NAWQA Study Units

NAWQA study units are major river basins and aquifers across the Nation. A study unit boundary frequently crosses state boundaries and usually encompasses more than 10,000 square kilometers (about 3,900 square miles). Study units are the building blocks of NAWQA and form the basis for national synthesis assessments.

TANC Study Areas

TANC study areas are smaller portions of the NAWQA study units and were selected for intensive study of the transport of urban, agricultural, and natural contaminants to public-supply wells in the most important principal aquifer within a study unit's boundary.

CONN - The TANC study area in Connecticut is within the Connecticut, Thames, and Housatonic Basins (CONN) study unit of the NAWQA program, which is located near the eastern edge of the region typified by sand and gravel aquifers of alluvial and glacial origin. The CONN TANC study area includes approximately 128 km2 of the Pomperaug River Basin where most water for public supply is obtained from wells completed in valley fill deposits. Characteristics of the selected aquifer system are similar to many valley-fill-aquifer systems in the Eastern Hills and Valley Fills hydrophysiographic region of Randall (2001) that encompasses much of the populated parts of New England, northern New Jersey, and eastern New York.

GAFL - The TANC study area in Florida is within the Georgia-Florida Coastal Plain (GAFL) study unit. It is located in west central peninsular Florida in the central-northern Tampa Bay region where two principal aquifers of the United States, the Surficial aquifer system and the underlying Floridan aquifer system, are present. The TANC GAFL study area covers approximately 5,400 km2, including the Tampa metropolitan area that relies heavily upon the Floridan aquifer system as a source of drinking water.

GRSL - The TANC study area in Utah is located on the western edge of the Great Salt Lake Basins (GRSL) study unit in the Salt Lake Valley. The study area is approximately 1,300 km2 in size and includes the metropolitan and industrial centers of the State. The principal aquifer in the GRSL TANC study area is the Basin and Range basin-fill aquifers, which is comprised of unconsolidated and semi-consolidated basin-fill materials deposited during the extension of the Basin and Range physiographic province. In 1990, the collective Basin and Range basin-fill and carbonate-rock aquifers ranked 3rd in terms of drinking water use within the principal aquifers of the United States.

HPGW - The TANC study area in Nebraska is within the High Plains Regional Ground Water (HPGW) study area of the NAWQA program and is located in east-central Nebraska around the City of York. The principal aquifer in the area is the High Plains aquifer, which is composed locally of Quaternary alluvial deposits. The aquifer serves as an important source of water for agricultural irrigation and drinking-water supply throughout the region. Although ground-water withdrawals for public supply account for less than 6 percent of the withdrawals in the HPGW TANC study area, ground water is the source of drinking water for 100 percent of the people in the area. The TANC study area covers approximately 390 km².

NVBR - The TANC study area in Nevada is within the Nevada Basin and Range (NVBR) study unit, which includes the Truckee and Carson River Basins that are characterized by high mountains surrounding valleys underlain by thick, unconsolidated deposits (Covay and others, 1996). Two locations within the NVBR study unit were included in the TANC study to address the affects of different rates of population growth and different potential sources of contaminants in otherwise similar hydrologic and geologic settings. The first area is Spanish Springs Valley, north of Sparks, located in the Truckee River basin. The second is Eagle Valley basin, which includes Carson City and is part of the Carson River basin. The Basin and Range principal aquifers are the source of water in both areas.

RIOG - The TANC study area in New Mexico is within the Rio Grande Valley (RIOG) study unit and is located near the city of Albuquerque, the most populous area within the state. Most public-supply wells in the RIOG TANC study area are completed in the middle and (or) upper units of the Santa Fe Group of the Rio Grande aquifer system. Ground water has been a primary source of household supply for residents of the Middle Rio Grande Basin since at least the early part of the twentieth century. The TANC study area covers approximately 2,300 km2.

SANJ - The TANC study area in California is within the San Joaquin-Tulare Basins (SANJ) study unit and is located in Modesto, CA, which typifies cities in the San Joaquin Valley with high growth rates resulting in gradual urbanization of adjacent farmlands. Although more than 90 percent of the 1995 water demands for the region were for irrigation, approximately half of the demand for municipal and industrial supply is met by ground water. Water in this area is produced from the Central Valley aquifer system. The TANC study area covers over 3,300 km².

SCTX - The TANC study area in Texas is within the South Central Texas (SCTX) study unit and is located near San Antonio, TX, where the karstic Edwards aquifer of the Edwards-Trinity aquifer system was the first to be declared a Sole-Source Aquifer. From 1950 to 2000, the city of San Antonio changed from the 25th to the 9th largest city in the United States, increasing demands on the local water supply.

SPLT - The TANC study area in Colorado is within the South Platte River Basin (SPLT) study unit and is located just south of metropolitan Denver, CO in the central part of the Denver Basin aquifer system. Rapid urbanization in the SPLT TANC study area has occurred in the past twenty years and several municipalities rely on ground water from this principal aquifer for their water supply.

WHMI - The TANC study area in Ohio is within the White River-Great and Little Miami River Basin (WHMI) study unit and is centered on the City of Dayton, OH. The area consists of sand and gravel aquifers of alluvial and glacial origin, which are primarily a result of glacial meltwater or outwash deposits left by retreating continental glaciers. The highly productive aquifer in the WHMI TANC study area was deposited in a buried-valley setting underlying the Great Miami River and has been designated a Sole-Source Aquifer by the U.S. Environmental Protection Agency. The TANC study area covers approximately 620 km2.

References

Covay, K.J, Banks, J.M., Bevans, H.E., and Watkins, S.A., 1996, Environmental and hydrologic settings of the Las Vegas Valley area and the Carson and Truckee River Basins, Nevada and California: U.S. Geological Survey Water-Resources Investigations Report 96-4087, 72 p.

Randall, A.D., 2001, Hydrogeologic framework of stratified-drift aquifers in the glaciated northeastern United States: U.S. Geological Survey Professional Paper 1415-B, 179 p.