U.S. Department of the Interior 

 U.S. Geological Survey 

 Fact Sheet 2005-3013 

 May 2005 Printed on recycled paper

 In the second decade (or “Cycle 

II”) of the U.S. Geological Survey’s 

National Water-Quality Assessment (NAWQA) Program, a major 

focus is on regional assessments of 

ground-water quality conditions and 

trends. The assessments will evaluate those conditions and trends in 

19 aquifers, most of which underlie 

multiple States (see map inside). 

 These regional ground-water 

assessments will build on NAWQA 

findings from 1991 to 2001 (“Cycle 

I”) in 51 “Study Units” across 

the Nation. (Summary reports of 

findings from the Study Units are 

available online; see back page). 

Regional assessments will complement and extend the findings of the 

Study Units to fill critical gaps in 

our understanding of ground-water 

quality and flow over broad regions, 

and determine trends at sites that 

have been monitored for more than 

a decade. The assessments will 

increase our understanding of how 

natural features and human activities affect ground-water quality. 

For example, regional differences 

in climate, geology, land use, and 

other factors can lead to regional 

differences in water quality among 

aquifer systems. Such regional 

variations can be analyzed using the 

large data set from NAWQA’s 

Cycle I. 

 Water-quality information in 

a regional context will be useful 

for regional monitoring councils, 

States, and localities in addressing 

priority water-quality and drinking-water issues in their areas. For 

example, regional-scale analyses, 

models, and other scientific tools 

will help with extrapolating findings 

to unmonitored, comparable areas 

in other parts of the regions. Data 

sets from multiple States representing similar hydrogeologic settings 

can be used by States and localities 

to assess, protect and manage their 

water resources more cost effectively. 

 Other activities planned during Cycle II include regional 

assessments of streams and rivers; 

continuing national syntheses of 

information on pesticides, volatile organic compounds (VOCs), 

nutrients, and selected trace elements; and national topical studies 

of mercury, the fate of agricultural 

chemicals, effects of urbanization 

on stream ecosystems, nutrient 

enrichment, and the transport of 

contaminants to drinking-water 

wells (Gilliom and others, 2001; 

see back page for on-line sources of 

information about these activities 

and information). 

 Selection of aquifers for 

assessment 

 A total of 62 principal aquifers 

underlie the United States (U.S. 

Geological Survey, 2003); the 

19 aquifers selected for regional 

 National Water-Quality Assessment Program — Cycle II

Regional Assessments of Aquifers 

 by Wayne W. Lapham, Pixie A. Hamilton, and Donna N. Myers 

assessment account for about 75 

percent of the estimated withdrawals of ground water for drinkingwater supply. 

 Each of the regional assessments 

focuses on water-quality issues of 

concern within a particular aquifer, 

and addresses one or more general issues. The studies will vary 

in scope and complexity and will 

be implemented at different stages 

throughout Cycle II. New topics 

may be added as the studies progress. 

 USGS personnel measure water levels 

and water quality in wells tapping major 

aquifers. 
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 Nineteen aquifers selected for regional assessment 
 Regional assessments build 

on Cycle I findings 

 Selected findings of NAWQA 

studies from 1991 to 2001 include: 

 • Contaminants in shallow 

ground water are widespread, 

often in mixtures but at low 

concentrations, across a wide 

range of landscapes and land 

uses. 

 • Concentrations of contaminants 

generally are lower in water in 

the deeper parts of the aquifers 

than in shallow ground water 

underlying agricultural and 

urban areas. Deep aquifers generally are more protected than 

shallow aquifers by relatively 

impermeable materials. Contaminants are most prevalent 

in aquifers where the geology 

allows water to move rapidly 

downward from the shallow 

ground-water system, such as 

in carbonate (karst) settings. 

 • Natural features—including 

soils, aquifer characteristics 

(such as geology, hydrology, 

mineral composition, and oxygen-reducing conditions), and 

the properties of the chemicals themselves (such as their 

tendency to dissolve, attach 

to sediment or bedrock, and 

persist in the environment)—

affect the movement of water 

and associated chemicals into 

and through the aquifer. For 

example, water and chemicals 

can move relatively rapidly into 

and throughout sand and gravel 

aquifers, alluvial fans, and 

carbonate settings with highly 

permeable sediment and open 

conduits in the bedrock. 

 • Contaminants found in ground 

water underlying agricultural 

and urban lands are closely 

related to the chemicals that 

are applied to the land. Nitrate 

and selected herbicides were 

frequently detected in shallow 

ground water underlying agricultural land, and VOCs were 

frequently detected in shallow 

ground water underlying urban 

land. 

 Issues addressed by the 

regional assessments 

 Contaminants in aquifers 

 Assessments of the occurrence 

of nutrients, pesticides, volatile 

organic compounds (VOCs), trace 

elements, and radionuclides are 

planned in, for example, the carbonate Biscayne and Floridan, the 

unconsolidated Surficial, the carbonate Basin and Range, the Piedmont, and the Hawaiian aquifers. 

 The occurrence of particular 

contaminants of concern will be 

assessed, such as arsenic and deicing chemicals in the glacial deposits 

aquifers; radon and uranium in the 

New York and New England crystalline rocks and glacial deposits 

underlying the Northeast and upper 

Midwest; salinity in aquifers underlying the Basin and Range and California Coastal Basins; and mixtures 

of urban pesticides in ground-water 

discharge from the glacial deposits, 

the Cambrian-Ordovician in the 

upper Midwest, and the New York 

and New England crystalline rocks 

in the Northeast. 

 Water quality in domestic and 

public-supply wells 

 The occurrence of anthropogenic 

chemicals, such as fertilizers and 

pesticides, in domestic and publicsupply wells will be assessed in 

aquifers that cover a large part of 

the Nation, including areas served 

by ground-water supplies from the 

Floridan, Northern Atlantic Coastal 

Plain, and the glacial deposits aquifers. Effects of long-term withdrawals (1950-2000) on ground-water 

quality in the Floridan aquifer 

system also will be assessed. 

 Processes affecting water quality 

and contaminant transport 

 Chemical and hydrologic processes that control the transport of 

contaminants will be assessed in the 

Northern Atlantic Coastal Plain, the 

glacial deposits, Basin and Range, 

and High Plains aquifers. In addition, studies will assess the effects 

on water quality of hydrologic alterations and controls—such as pumping, artificial recharge, and irrigation—in the High Plains, Hawaiian, 

Basin and Range, California Coastal 

Basin, and Central Valley aquifers. 

 Effects of land use on water 

quality 

 The relation of ground-water 

quality to land use will be examined 

in the Northern Atlantic Coastal 

Plain, Basin and Range, Central 

Valley, California Coastal Basin, 

High Plains, glacial deposits, and 

the Piedmont aquifers. Selected 

topics include the effects of chemical use and agricultural practices in 

four agricultural settings in Florida 

and the southeastern Coastal Plain; 

and effects on ground water used for 

drinking water from urban development in the Mississippi embaymentTexas coastal uplands and Piedmont 

aquifers. 
 For additional information 

about regional assessments of 

aquifers, contact: 

 Wayne Lapham 

wlapham@usgs.gov 

(703) 648-5805 

 For online information, reports, 

and data from the NAWQA 

Program: 

 Summary reports of assessments 

conducted during the first decade 

in the 51 Study Units: 

 http://water.usgs.gov/nawqa/

nawqa_sumr.html

 Information and publications 

from the national synthesis 

teams: http://water.usgs.gov/

nawqa/

natsyn.html 

 How the study results can 

be used 

 Resource managers and scientists 

can use the results of these studies in assessing the vulnerability 

of ground water to contamination 

across different regions. By identifying natural and human factors and 

processes affecting the occurrence 

and transport of contaminants, the 

assessments will allow managers 

and scientists to apply findings to 

broader classes of contaminants and 

to newly identified contaminants. 

 Regional-scale models and other 

decision-support tools, which integrate aquifer characteristics, land 

use, and water-quality monitoring 

data, will help water managers to 

assess conditions in unmonitored 

areas and the sustainability of water 

resources for future supply, as well 

as to develop cost-effective groundwater monitoring programs. 

 References 

 Gilliom, R.J., Hamilton, P.A., and 

Miller, T.L., 2001, The National 

Water-Quality Assessment Program—Entering a new decade of 

investigations: U.S. Geological 

Survey Fact Sheet 071-01, 6 p. 

 U.S. Geological Survey, 2003, 

Principal aquifers of the 48 conterminous United States, Hawaii, 

Puerto Rico, and the U.S. Virgin 

Islands, available online at 

http://www.nationalatlas.gov/mld/

aquifrp.html . 

 A pilot regional assessment — the High Plains aquifer 

 In 1999, NAWQA began a pilot regional assessment of the High Plains aquifer, which 

underlies an area of about 174,000 square miles in parts of eight states. Ground-water 

age in this aquifer ranges from less than 10 to more than 10,000 years. Studies through 

2004 assessed spatial and temporal variability in water quality in the aquifer, including 

concentrations of nutrients, volatile organic compounds, pesticides, trace elements, 

and radon. Tritium and radiocarbon concentrations were used to assess ground-water 

ages and the timing of recharge to the ground-water system, and therefore, the vulnerability of the water to contamination from recent human activities. 

 Besides providing a broad assessment of water-quality conditions, the studies help 

us understand the factors that control the vertical transport of chemicals. A key finding 

was that chemical travel times through the thick unsaturated zone under irrigated farm 

fields ranged from about 50 to 375 years. These travel times suggest that it could be 

many decades before we can detect improvements in ground-water quality that result 

from implementing best-management practices on land. 

 Plans for 2005-06 include use 

of a USGS model to further assess 

ground-water quality and transport 

of chemicals. 

 Selected results from the High 

Plains studies are available online 

at http://co.water.usgs.gov/nawqa/

hpgw/HPGW_home.html .