Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010

Abstract

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable scientific information that helps to enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the Nation's water resources is critical to ensuring long-term availability of water that is safe for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth and increasing demands for water make the availability of that water, measured in terms of quantity and quality, even more essential to the long-term sustainability of our communities and ecosystems. The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, State, and local information needs and decisions related to water-quality manage¬ment and policy (http:// water.usgs.gov/nawqa). The NAWQA Program is designed to answer: What is the quality of our Nation's streams and groundwater? How are conditions changing over time? How do natural features and human activities affect the quality of streams and groundwater, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of the Nation's river basins and aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/studies/ study_units.html). National and regional assessments are ongoing in the second decade (2001-2012) of the NAWQA Program as 42 of the 51 Study Units are selectively reassessed. These assessments extend the findings in the Study Units by determining water-quality status and trends at sites that have been consistently monitored for more than a decade, and filling critical gaps in characterizing the quality of surface water and groundwater. For example, increased emphasis has been placed on assessing the quality of source water and finished water associated with many of the Nation's largest community water systems. During the second decade, NAWQA is addressing five national priority topics that build an understanding of how natural features and human activities affect water quality, and establish links between sources of contaminants, the transport of those contaminants through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. Included are studies on the fate of agricultural chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on aquatic ecosystems, and transport of contaminants to public-supply wells. In addition, national syntheses of information on pesticides, volatile organic compounds (VOCs), nutrients, tra...

Using groundwater age distributions to understand changes in methyl tert-butyl ether (MtBE) concentrations in ambient groundwater, northeastern United States

“…All MtBE data are available on the USGS National Water Information System (U.S. Geological Survey, 2014). Raw age-dating tracer data are available from published USGS reports (Hinkle et al, 2010;Shapiro et al, 2012).…”

The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009

“…Groundwater ages can be estimated by measuring compounds and radioactive substances that enter the ground with recharge and that travel with the groundwater to the sampling point. All of the groundwater measured in aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions was young (less than 60 years old) compared to groundwater in most aquifers of the Nation (15)(16)(17)(18)(19)(20) because of abundant recharge and relatively short flow paths. In this report, groundwater ages are divided into two categories: less than 20 years and 20 to 60 years.…”

“…In all three types of aquifers, water with an age of less than 20 years was more likely to be oxic than water with an age of 20 years or more. (15)(16)(17)(18)(19)(20) Nitrate and some other contaminants are less likely to break down in oxic water than in anoxic water. Trace elements like iron and manganese are more likely to be mobile in anoxic water.…”