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Design |
The nationwide design for the NAWQA program is described by Gilliom and others (1995). NAWQA study units across the Nation share common protocols and goals (http://water.usgs.gov/nawqa/) for surface-water, ecological, and ground-water investigations. The study design of the Connecticut, Housatonic, and Thames River Basins NAWQA investigation includes national components and elements specific to this basin.
During Cycle I, 12 fixed sites (map 6; table 1) were established to examine differences in stream-water quality due to the environmental setting (land use, surficial deposits, and bedrock type) of the study area. One of the fixed sites, the Norwalk River at Winnipauk, CT (station 01209710) was an intensive fixed site and was sampled more frequently to determine seasonal variability in water quality and to test for pesticides. In addition, synoptic studies were completed that focused on sampling high and low flows at 56 sites (map 7; table 2) to characterize concentration and spatial distribution of nutrients, pesticides, sediment, and other water-quality characteristics. Streambed sediments from 43 sites (map 8; table 3) were analyzed for trace elements and hydrophobic organic compounds.
Intensive ecological assessments were done at 32 sites (map 9; table 4) to define existing biological communities and habitat to which future monitoring results will be compared and to assess temporal variations. A synoptic study was conducted in which selected fish species were sampled at the 10 fixed sites (map 10; table 5) for the presence of contaminants that can accumulate in fish tissues.
Following the 3-year (1993-95) high-intensity data-collection phase of Cycle I, low-intensity sampling was conducted at three CONN surface-water sites (map 11, table 6). These three stations were included in the National NAWQA Surface-Water Trends Network, and sampling frequency and analytical coverage increased at these sites in accordance with Cycle II high-intensity data-collection phase activity (water years 2002-2004). The following are brief descriptions of the sampling sites.
Green River near Colrain, Mass. -- 01170100 (Reference site): The Green River near Colrain, Mass., drains 58 mi2 of rural, mostly forested area in the northwestern parts of Massachusetts and southeastern Vermont. The Green River flows through mixed deciduous and hardwood forests and forested wetlands underlain by fractured crystalline bedrock mantled by generally thin glacial till deposits.
Norwalk River at Winnipauk, Conn. -- 01209710 (Urban intensive indicator site): The Norwalk River at Winnipauk, Conn., drains 33 mi2 of sandy surficial glacial deposits over crystalline bedrock in the largely urban southwestern Connecticut coastal corridor.
Connecticut River at Thompsonville, Conn. -- 01184000 (Integrator site): The Connecticut River at Thompsonville, Conn., drains 9,672 mi2 of mostly forested and agricultural uplands in the northern half of the study unit, but the station is also located less than 10 miles downstream from a major urban center (the Chicopee-Springfield-West Springfield-Westfield, Mass. metropolitan area). Surficial glacial and alluvial deposits overly crystalline and metacalcareous bedrock in the northern part of the study unit.
Aquatic biota community surveys (invertebrate, fish, and algae) were conducted at two of the three surface-water trend sites (Green River and Norwalk River) in the Cycle II high-intensity data-collection phase. The community surveys were conducted during mid-to-late summer as part of the trends sampling. Revised NAWQA biology field protocols (Fitzpatrick and others, 1998) were used for all community sampling. Multi-reach sampling information was collected only at the Green River site. Multi-reach sampling had not been previously conducted at any of the CONN surface-water trend sites. The Norwalk River site was not appropriate for multi-reach sampling due to the lack of three undisturbed reaches with the sampling section and numerous urban inputs.
Atmospheric deposition [figure 1] is generally accepted as the principal mechanism of mercury introduction into aquatic ecosystems. New England is thought to have one of the highest deposition rates anywhere in the United States. Major sources of mercury deposition in New England are emissions from municipal waste incinerators, coal and oil boilers, and medical waste incinerators. Through environmental processes, mercury (Hg) in its inorganic form can be transformed into methyl mercury (MeHg) and accumulate in aquatic organisms. Urbanization is postulated to affect the production and accumulation rates of MeHg. The major route of human exposure to mercury is through the diet, more specifically from consumption of fish. MeHg is the most toxic and bioaccumulative form of mercury in the environment, and comprises greater than 95 percent of the mercury in fish. Elevated mercury concentrations in fish have resulted in the issuance of fish consumption advisories [figure 2] in all states of New England and throughout the Northeastern United States. (from NECB NAWQA Mercury Surface Water Study)
Figure credits:
Figure 1. Modeled/predicted mercury deposition rates for the contiguous 48 states (from Russ Bullock, NOAA/EPA)
Figure 2. Fish consumption advisories for mercury (Krabbenhoft and Rickert, 1995)
During 2002, water, bed sediment and fish tissue samples were collected at eight sites in the CONN study unit (map 12; table 7). Sites were selected based on land use criteria and ranged from highly forested to urban. Wetland percentage was also taken into consideration for site selection. In water, concentrations of total mercury ranged from 0.00045 to 0.0043 micrograms per liter (µg/L) and concentrations of MeHg ranged from 0.00005 to 0.00262 μg/L. In fish, concentrations of total mercury ranged from 0.0599 to 0.3371 micrograms per gram (μg/g) wet weight. Criterion of 0.3 μg/g wet weight was established by the United States Environmental Protection Agency (USEPA) for human consumption (USEPA, 2001). This criterion was exceeded at three of the seven sites where fish were collected. To date, sediment concentrations have not been summarized.
Source-Water Quality Assessment (SWQA) Study
The primary objective of SWQAs is to determine the occurrence of about 280 primarily unregulated anthropogenic organic compounds in source water used by community water systems. Source
water is the raw (ambient) water collected at a supply well or surface-water intake prior to water treatment used to produce finished water. A secondary objective is to understand occurrence patterns
in source water and determine if these patterns also occur in finished water prior to distribution. The NAWQA Program is planning as many as 30 surface-water and 30 ground-water assessments through
2013 (http://water.usgs.gov/nawqa/fsSWQ.pdf). The findings are not intended to comprehensively portray the quality of our Nation’s source waters owing to the relatively small number of water supplies studied. They are, however, intended to improve understanding of ambient resource conditions in a drinking-water-supply context. The CONN completed both a surface-water SWQA and a ground-water SWQA.
In addition to water-supply vulnerability, other national priority topics being addressed by the NAWQA Program in its second decade, effects of urbanization on stream ecosystems (USGS Fact Sheet 042-02); ecological effects of nutrient enrichment USGS Fact Sheet 118-03; mercury in stream ecosystems USGS Fact Sheet 016-03; and sources, transport, and fate of agricultural chemicals USGS Fact Sheet 2004-3098.
In Cycle I, three ground-water land-use studies were conducted in the study unit that focused on the occurrence and distribution of natural and anthropogenic contaminants in shallow ground water beneath agriculture (map 13; table 9), forested (map 14; table 10), and mixed urban (map 15; table 11) land-use areas. The land-use studies documented and compared the influences of the three prevalent land uses on shallow water quality and identified differences in natural chemical composition of water in glacial aquifers in relation to lithogeochemical provenance of the glacial deposits (Grady and Mullaney, 1998). A study of ground-water quality conditions along a flowpath through a glacial deposits aquifer underlying the urban Manchester, Conn. area (map 16; table 12) was also conducted in Cycle I (Mullaney and Grady, 1997). Additional ground-water sampling in Cycle I included a major aquifer study in the fractured crystalline bedrock aquifer (map 17; table 13) and special studies of ground-water/surface-water interactions in agricultural and urban settings (map 18; table 14).
In Cycle II, four additional ground-water quality assessments were conducted, including a more detailed study of contaminant transport in the contributing areas to public-supply wells at both regional and local scales. The glacial aquifer was chosen as the host aquifer for these studies because it is one of the most used aquifers in the study area and is one of the 16 principal aquifers chosen for study by NAWQA. http://water.usgs.gov/nawqa/studies/praq/glacaq/index.html.
The Major Aquifer Study (MAS) consists of a study of 30 domestic wells (map 19; table 15) in the stratified glacial deposits in the Connecticut, Housatonic, and Thames River basins (CONN) study unit. Five wells in the MAS were chosen for quarterly sampling and water-level monitoring in 2005 as part of the NAWQA Ground-Water Trends Network, and will be resampled in 2007 as part of ongoing biennial monitoring.
The Urban Land-Use Study (ULUS) targets “new” development (circa 1975 to 1997) in residential and commercial areas in towns of the Hartford-Springfield area by constructing and sampling 27 wells in unconfined glacial aquifers (map 20; table 16). Twenty-seven monitoring wells were installed in 2002 and 2003 and sampled in 2003. Five of these wells were chosen for quarterly sampling and water-level monitoring in 2005, and will be resampled again in 2007 as part of ongoing biennial monitoring. Two monitoring wells that were installed during Cycle I (1992) in a similar hydrogeologic setting with undeveloped, forested land use are being similarly monitored as reference wells.
Ground-Water Source-Water Quality Assessment (SWQA) Study (map 21, table 17): In late 2002, a water-supply study was begun that included eleven ground-water source-water quality assessments (GW-SWQA) of source water from about 165 community water system (CWS) wells. Untreated ground-water samples were analyzed for a comprehensive list of primarily anthropogenic organic constituents. A second year of sampling was based primarily on results from the first year of sampling at the ten sites where source water was treated. Samples were collected from both untreated source water and finished water. Although major cities in the CONN study unit generally rely on surface water drawn from a number of small to medium-sized reservoirs, many of the secondary towns and cities, including some of the most rapidly developing suburban areas, obtain their drinking water from ground water, principally the glacial aquifers. Implementation of the SWQA study in the CONN augments the glacial aquifer MAS and is nested to some extent with the previous land-use studies and the TANC study. Nine of these supply wells are located in the Pomperaug Basin area and overlap with the large area TANC (see below) study; the remainder of the wells are located in a separate but similar glacial aquifer setting in the towns of Southington, Plainville, Farmington, and Cheshire, Connecticut http://pubs.usgs.gov/sir/2007/5171/.
Transport of Anthropogenic and Natural Contaminants (TANC) to Supply Wells: This NAWQA study focused on the sources, transport, and fate of selected anthropogenic contaminants from urban and agricultural sources, as well as contaminants from natural sources, within that part of the ground-water system that contributes water to public-supply wells http://pubs.usgs.gov/fs/2005/3022/. The study also considers how the operation of public-supply wells can affect their vulnerability to contamination. Consistent methods are used to collect and analyze data, and investigations are being conducted at both regional (tens to thousands of square miles) and local scales (less than 10 square miles).
Large-Area TANC Study
(map 22, table 18)
The Pomperaug aquifer in west-central Connecticut is one of seven such study sites nationally that are performing a large-area characterization. This aquifer lies within the towns of Woodbury and Southbury and typifies a New England valley-fill glacial stratified aquifer that is both susceptible and vulnerable to contamination. The study will assemble and analyze information of aquifer properties, sediment geochemistry, age and patterns of ground-water circulation, water quality, water use, population density, land use (map 22a), and locations of contaminant sources to identify those factors that are associated with the greatest risk of ground-water contamination. In addition to the obvious importance of anthropogenic sources and transport mechanisms http://oh.water.usgs.gov/tanc/pubs/Kauffman_lj_2007_ground_water_summit.pdf, a major focus of the study is to identify the source, distribution, and mobility of natural contaminants, including arsenic, uranium, and other trace elements of concern that could affect the quality of water in public supply wells http://oh.water.usgs.gov/tanc/pubs/Hinkle_NWQMC_Abstract.pdf. Because consistent methods are being used to collect and analyze data and investigations at both regional and local scales, we can compare and contrast results from different settings, and then identify the most important processes or factors to include in vulnerability assessments applied at different scales and in a variety of water-supply aquifers. A Professional Paper presents the hydrogeologic settings and documents the ground-water flow models for each of the NAWQA TANC regional study areas that began work in 2001. Methods used to compile retrospective data, determine contributing areas of public-supply wells, and characterize oxidation-reduction (redox) conditions also are presented. This Professional Paper Chapter provides the foundation for future susceptibility and vulnerability analyses in the TANC study areas and comparisons among regional aquifer systems. The report is organized in sections. In addition to the introductory section (Section 1) are seven sections that present the hydrogeologic characterization and ground-water flow model documentation for each TANC regional study area (Sections 2 through 8). Section 6 provides the summary and major findings for the regional study area in the Pomperaug River Basin http://pubs.usgs.gov/pp/2007/1737a/Section6.pdf.Small-Area TANC Study
(map 23; table 18)
Six of the 10 large-area TANC sites were selected for more detailed study of the processes associated with the mobilization and transport of contaminants in the area of ground-water contribution to a single public supply well (PSW-1). One of the small-area study sites selected includes a supply well in the Pomperaug aquifer of Woodbury, CT, in a contributing area that includes both the glacial stratified deposits in the valley, and till-covered bedrock in the uplands. A monitoring-well network was installed that consists of 34 monitoring wells, including 23 screened in stratified glacial deposits, 6 in underlying or adjacent glacial till deposits, and 4 in underlying or adjacent bedrock. Drill core samples were collected for analysis of mineralogy, grain-coatings analysis of Fe, Mn, As, U, and other trace elements, carbon forms, stable isotopes, sulfides, and sediment properties. Sorption experiments were conducted to determine sorption behavior and equilibrium constants for arsenic and uranium. Water samples were analyzed for major and trace constituents, radionuclides, stable isotopes, dissolved gases, VOCs, pesticides, ground-water age tracers. The findings of the study will be presented in two comprehensive reports, including one that focuses on ground-water flow modeling (http://pubs.usgs.gov/sir/2007/5210/) and one that focuses on aquifer chemisty and ground-water quality (Brown and others, in review), http://oh.water.usgs.gov/tanc/pubs/Brown_NWQMC_Abstract.pdf, http://oh.water.usgs.gov/tanc/pubs/Brown_cj_2007_NatContam.pdf, http://oh.water.usgs.gov/tanc/pubs/BrownZielinski04.htm.
The small-area TANC studies are to be published as scientific investigation reports for Connecticut, Florida, Nebraska, and California by 2008, and for Texas and New Mexico by 2009. In addition, data from these TANC sites will be analyzed in national synthesis studies of ground-water drinking water aquifers in papers that achieve the following objectives:
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