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Scott W. Ator

Publications and source records attributed to Scott W. Ator.

26 records · Page 2Linked to original sources
USGS2004

Water Quality in the Delmarva Peninsula, Delaware, Maryland, and Virginia, 1999-2001

This report contains the major findings of a 1999-2001 assessment of water quality in the Delmarva Peninsula. It is one of a series of reports by the National Water-Quality Assessment (NAWQA) Program that present major findings in 51 major river basins and aquifer systems across the Nation. In these reports, water quality is assessed at many scales?from local ground-water flow paths to regional ground-water networks and in surface water?and is discussed in terms of local, State, and regional issues. Conditions in the Delmarva Peninsula are compared to conditions found elsewhere and to selected national benchmarks, such as those for drinking-water quality and the protection of aquatic organisms. This report is intended for individuals working with water-resource issues in Federal, State, or local agencies; universities; public interest groups; or in the private sector. The information will be useful in addressing a number of current issues, such as the effects of agricultural and urban land use on water quality, human health, drinking water, source-water protection, hypoxia and excessive growth of algae and plants, pesticide registration, and monitoring and sampling strategies. This report is also for individuals who wish to know more about the quality of streams and ground water in areas near where they live, and how that water quality compares to the quality of water in other areas across the Nation. Other products describing water-quality conditions in the Delmarva Peninsula are available. Detailed technical information, data and analyses, methodology, models, graphs, and maps that support the findings presented in this report can be accessed from http://md.water.usgs.gov/delmarva. Other reports in this series and data collected from other basins can be accessed from the national NAWQA Web site (http://water.usgs.gov/nawqa).

Circular↗
USGS2004

Hydrologic and geochemical controls on pesticide and nutrient transport to two streams on the Delmarva Peninsula

Pesticides and nutrients move from application areas through ground water and surface runoff to streams on the Delmarva Peninsula. The relative importance of different transport media to the movement of these compounds in different watersheds is related to locally variable hydrologic and geochemical conditions among areas of regionally similar land use, geology, and soils. Consideration of such local variability is important to land-management efforts or future environmental investigations on the Peninsula. Chemical analyses of samples collected over a multiyear period from two streams on the Delmarva Peninsula were analyzed along with similar available analyses of ground water to document the occurrence of pesticides and nutrients, and illustrate important processes controlling their movement through watersheds to streams. The upper Pocomoke River and Chesterville Branch drain predominantly agricultural watersheds typical of the Delmarva Peninsula. Chesterville Branch drains a watershed of moderate relief, good drainage, and a permeable surficial aquifer that ranges in thickness from about 15 to 25 meters. The upper Pocomoke River Watershed, however, is extremely flat with poorly drained soils and abundant artificial drainage. Influences on the chemistry of water in each stream were determined from seasonal patterns in the concentrations of selected constituents from 1996 through 2001, and relations with streamflow. Nutrients and pesticides are detectable throughout the year in the upper Pocomoke River and Chesterville Branch. Water in both streams is typically dilute, slightly acidic, and well oxygenated, and nitrate and phosphorus concentrations generally exceed estimated natural levels. Pesticide concentrations are generally low, although concentrations of selected metabolites commonly exceed 1 microgram per liter, particularly in Chesterville Branch. Nitrate and metabolites of pesticide compounds are apparently transported to Chesterville Branch preferentially through ground water in the surficial aquifer, although selected pesticide parent compounds and less soluble nutrients move primarily in surface runoff. Conversely, the relative proportion of discharge from surficial and partially confined aquifers is the most important factor controlling the chemistry of water in the upper Pocomoke River. Surface runoff in the larger and predominantly flat upper Pocomoke River Watershed is apparently limited to particularly significant precipitation events. Transport of pesticides in surface runoff becomes important in both watersheds during such events. Instantaneous loads of pesticides in streams typically stabilize or continue to increase with increasing flow even after runoff begins, although in-stream concentrations may decrease due to dilution.

Scientific Investigations Report↗
USGS1997

Nitrate and selected pesticides in ground water of the Mid-Atlantic region

Data from more than 850 sites were compiled and analyzed to document the occurrence of nitrate and pesticides in ground water of the Mid-Atlantic region as part of the Mid-Atlantic Integrated Assessment program of the U.S. Environmental Protection Agency. Only those data collected by the U.S. Geological Survey as part of regional networks between October 1985 and September 1996 (inclusive) were used in the analyses, and the data were examined to ensure analytical results are not biased toward sites at the same location or sites sampled multiple times during this period. Regional data are available for most of the Mid-Atlantic region but large spatial gaps in available data do exist. Nitrate was detected in nearly three-quarters of the samples for which it was analyzed, commonly at levels that suggest anthropogenic sources. Ten percent of samples contained nitrate at concentrations exceeding the Federal Maximum Contaminant Level (MCL) of 10 milligrams per liter as nitrogen. Pesticide compounds (including atrazine, metolachlor, prometon, simazine, and desethylatrazine, an atrazine degradate) were detected in about half of the samples for which they were analyzed, but rarely at concentrations exceeding established MCL?s. The most commonly detected pesticide compounds were desethylatrazine and atrazine. The occurrence of nitrate and pesticides in ground water of the Mid-Atlantic region is related to land cover and rock type. Likely sources of nitrate and pesticides to ground water include agricultural and urban land-use practices; rock type affects the movement of these compounds into and through the ground-water system. Nitrate concentrations in the compiled data set are significantly higher in ground water in agricultural areas than in urban or forested areas, but concentrations in areas of row crops are statistically indistinguishable from those in areas of pastures. Detection frequencies of atrazine, desethylatrazine, and simazine are indistinguishable among urban areas, row crops, and pastures. Prometon was most commonly detected in ground water in urban areas. Ground-water samples from forested areas typically contained the lowest concentrations of nitrate and detection frequencies of pesticides. Concentrations of nitrate and detection frequencies of pesticides were significantly higher in samples from carbonate rocks than in those from any other rock type. Most areas of the Mid-Atlantic region that are underlain by carbonate rocks have been developed for agricultural or urban use and the solution channels that are typical of carbonate rocks allow for relatively rapid transport of surficial contaminants throughout the ground-water system. Nitrate concentrations in unconsolidated aquifers were among the lowest for all rock types, possibly because of denitrification in organic-rich subsoils and shallow sediments.

Water-Resources Investigations Report↗
USGS1997

Pesticides in surface water of the Mid-Atlantic region

Water-quality data from 463 surface-water sites were compiled and analyzed to document the occurrence and distribution of pesticides in surface water of the Mid-Atlantic region as part of the Mid-Atlantic Integrated Assessment program of the U.S. Environmental Protection Agency. Those data collected by the U.S. Geological Survey from October 1973 through March 1997 were used in the analyses. Data are available for a large part of the Mid-Atlantic region, but large spatial gaps in the data do exist. USGS data bases contained analyses of surface-water samples for 127 pesticide compounds, including 12 degradates, but only 16 of the compounds were commonly detected. Atrazine, metolachlor, simazine, prometon, alachlor, tebuthiuron, cyanazine, diazinon, carbaryl, chlorpyrifos, pendimethalin, 2,4-D, dieldrin, DCPA, metribuzin, and desethylatrazine (an atrazine degradate) were detected in more than 100 of the samples analyzed. At least one pesticide was detected in about 75 percent of the samples collected and at more than 90 percent of the sites sampled. Concentrations greater than the Federal Maximum Contaminant Level (MCL) for drinking water of 3 micrograms per liter (ug/L) for atrazine were found in 67 of 2,076 samples analyzed; concentrations greater than the MCL of 2ug/L for alachlor were found in 13 of 1,693 samples analyzed, and concentrations greater than the MCL of 4 ug/L for simazine were found in 17 of 1,995 samples analyzed. Concentrations of four pesticides were greater than Federal Health Advisory levels for drinking water, and concentrations of nine pesticides were greater than Federal Ambient Water-Quality Criteria for the Protection of Aquatic Organisms. Streams draining basins with different land uses tend to have different pesticide detection frequencies and median concentrations. Median concentrations of herbicides tend to be highest in streams draining basins in which the major land use is agriculture, whereas median concentrations of insecticides tend to be highest in streams draining extensively urbanized basins. Concentrations of both herbicides and insecticides are usually highest during the spring and summer, although many pesticides are present at low concentrations in surface water throughout the year. Pesticide concentrations vary greatly seasonally and over different hydrologic conditions, with overall variation sometimes exceeding four orders of magnitude. During periods of pesticide application (typically spring and summer), the occurrence of selected pesticides in some streams in the Mid-Atlantic region is related to streamflow. Correlations between concentrations of selected pesticides and streamflow are statistically significant during spring and summer for small (draining less than 55 square miles) streams. Concentrations of selected pesticides in small streams increase during high flows in the growing season, up to 30 times the concentrations present during low-flow conditions in the growing season. In small streams draining urban areas, concentrations of atrazine decrease during high-flow events but concentrations of the insecticides diazinon and chlorpyrifos increase. This may be due to the differences in the pesticides used in agricultural and urban areas and the amounts applied.

Water-Resources Investigations Report↗
USGS1996

Radon in ground water of the lower Susquehanna and Potomac River basins

Ground-water samples collected from 267 wells were analyzed for radon as part of a water-quality reconnaissance of subunits of the Lower Susquehanna and Potomac River Basins conducted by the United States Geological Survey (USGS) as part of the National Water-Quality Assessment (NAWQA) program. Radon is a product of the radioactive decay of uranium. Airborne radon has been cited by the Surgeon General of the United States as the second-leading cause of lung cancer and the United States Environmental Protection Agency (USEPA) has identified ground-water supplies as possible contributing sources of indoor radon. Eighty percent of ground-water samples collected for this study were found to contain radon at activities greater than 300 pCi/L (picocuries per liter), the USEPA's proposed Maximum Contaminant Level for radon in drinking water, and 31 percent of samples contained radon at activities greater than 1,000 pCi/L. The 10 subunits where samples were collected were grouped into three classes - median ground-water radon activity less than 300 pCi/L, between 300 pCi/L and 1,000 pCi/L, and greater than 1,000 pCi/L. Subunits underlain by igneous and metamorphic rocks of the Piedmont Physiographic Province typically have the highest median ground-water radon activities (greater than 1,000 pCi/L); although there is a large variation in radon activities within most of the subunits. Lower median radon activities (between 300 pCi/L and 1,000 pCi/L) were found in ground water in subunits underlain by limestone and dolomite. Of three subunits underlain by sandstone and shale, one fell into each of the three radon-activity classes. The large variability within these subunits may be attributed to the fact that the uranium content of sandstone and shale is related to the uranium content of the sediments from which they formed.

lower Susquehanna and Potomac River basins↗
USGS1995

Nitrate in ground water in the Great Valley carbonate subunit of the Potomac River Basin

Agriculture is the major land use in the carbonate part of the Great Valley of the Potomac River Basin. Applied fertilizer and manure are potential sources of nitrate that can contaminate Groundwater. Nitrate concentrations in Groundwater increased with increasing percentage of cropland but did not decrease with increasing well depth, as has been found in previous studies elsewhere. Samples from 28 wells contained nitrate concentrations ranging from 0.29 to 29 mg/L (milligrams per liter) as nitrogen, with a median concentration of 4.55 mg/L, compared to a median of 1.8 mg/L for 1,056 Groundwater samples from the entire Potomac River Basin. Median nitrate concentrations in Groundwater samples were higher in the Maryland, Pennsylvania, and West Virginia part of the valley, and were lower in the Virginia part (7.45 and 2.95 mg/L, respectively), probably as a result of differences in agricultural land-use patterns; this geographical difference was also noted in surface-water samples (6.65 and 2.3 mg/L, respectively). The area of contribution to each well could not be delineated by surface topography or distance to the well, because Groundwater flow and nitrate transport can be unpredictable in the carbonate region because of fractures and solution channels present.

Water-Resources Investigations Report↗