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At least 991 records · Page 55Linked to original sources
USGS2002

Analysis of nitrate (NO3-N) concentration trends in 25 ground-water-quality management areas, Idaho, 1961-2001

In Idaho, drinking-water supplies are pumped from relatively shallow ground-water zones where water quality has great potential for degradation by land- and water-use activities. One indicator of water quality, and one of the most widespread contaminants in Idaho ground water related to land and water uses, is dissolved nitrate. In December 2000, the U.S. Geological Survey, in cooperation with the Idaho Department of Environmental Quality, began a study to compile and assess nitrate data for ground water in 25 ground-water-quality management areas in Idaho. The primary objective of the study was to determine whether statistically significant trends in ground-water concentrations were discernible. Data included ground-water analyses but not analyses of water from springs, drains, or thermal water sources. A total of 8,465 nitrate analyses were compiled from 2,931 wells in the 25 priority areas; analyses dates ranged from June 1961 to February 2001. A time-period comparison was used to assess general trends in nitrate concentrations within individual priority areas. A time-series comparison was used to assess trends in nitrate concentrations from selected wells in each priority area. In time-period assessments, general trends in an area were evaluated by compiling nitrate data for selected time intervals to determine whether the population distributions were significantly different between one period and another. Data within each priority area were sorted into decades— 1970s, 1980s, and 1990s—for long-term trend assessment. The 1990s data also were divided into sets of selected years corresponding to Statewide Ambient Ground-Water Quality Program sampling cycles—1991 through 1994, 1995 through 1998, and a partial cycle, 1999 through 2000—for shortterm trend assessment. Data were analyzed by summary statistics, boxplots, and the Mann- Whitney statistical test. Long-term increasing trends in nitrate concentrations were evident for 6 of 25 priority areas, and long-term decreasing trends were evident for 4 of 25 areas. Short-term increasing trends were evident for 7 of 25 areas, and a short-term decreasing trend was evident for only 1 area. No long-term nitrate trends were evident for 7 of 25 areas, and no shortterm trends were evident for 15 of 25 areas. Data were insufficient for long-term trend assessment in 8 areas and for short-term assessment in 2 areas. Time-series trend analyses were conducted on data from wells with 7 or more nitrate analyses and longest periods of record, at least 10 years between oldest and most recent analyses. Because long-term records were available for so few wells and well construction data were not available for several of these wells, time-series analyses were not helpful to the nitrate trend assessment study. Trend results may be strongly affected by well construction, hydrogeologic environments, and changes in density and areal distribution of wells and analyses. The utility of nitrate trend assessments in priority areas would be improved by more consistent and specific well location descriptions between agencies; well construction and major water-yielding zone information to accompany the water-quality data for each well; and addition of historical nitrate data to data bases, particularly analyses prior to about 1990. Investigations of the possible effects of changing priority area boundaries and time periods on both long-term and short-term trend assessments are needed. Addition of these kinds of information would allow assessment of trends associated with hydrology and geology of each area and would provide a much stronger basis for trend assessment than currently possible.

Idaho↗
USGS2002

Geohydrology and ground-water quality, Big Elk Creek Basin, Chester County, Pennsylvania, and Cecil County, Maryland

A study of ground-water quantity and quality was conducted in the Big Elk Creek Basin, a rural area undergoing rapid growth. The 79.4-square mile study area is in the Piedmont Physiographic Province and is underlain almost entirely by crystalline rocks. Most of the basin in Pennsylvania is underlain by Wissahickon Schist, a fractured crystalline- rock aquifer. Yields of wells in the Wissahickon Schist range from 5 to 200 gal/min (gallons per minute); the median yield is 15 gal/min. Specific capacity ranges from 0.03 to 15 (gal/min)/ft (gallons per minute per foot) of drawdown; the median specific capacity is 0.4 (gal/min)/ft. Recharge to the basin occurs by infiltration of precipitation, and ground water discharges locally to streams. The median annual ground-water discharge to streams (base flow) for 1933-99 was 10.79 in. (inches) or 0.518 (Mgal/d)/mi 2 (million gallons per day per square mile), which was 63 percent of the median annual streamflow. The median annual ground-water discharge to streams ranged from 5.32 in. or 0.255 (Mgal/d)/mi 2 in 1966 to 17.98 in. or 0.863 (Mgal/d)/mi 2 in 1972. Estimated ground-water availability ranges from 0.127 to 0.535 (Mgal/d)/mi 2 , depending on the estimation method used. Annual water budgets were calculated for the Big Elk Creek Basin for 1998-99. The 1998-99 average annual streamflow was 15.38 in., change in ground-water storage was an increase of 1.32 in., ground-water exports were 0.03 in., and estimated evapotranspiration (ET) was 30.5 in. Despite a 12.27-in. difference in precipitation between 1998 and 1999, the percentage of precipitation as ET (65.6 and 64 percent, respectively) is similar. Estimated average annual recharge for 1998-99 was 12.12 in. [0.580 (Mgal/d)/mi 2 ]. For this study, water samples from 20 wells in the Big Elk Creek Basin were collected for analysis for inorganic constituents and pesticides. In addition, data were available from 44 additional wells. Major ions, in order of decreasing concentration, based on median concentrations for the Wissahickon Schist, are silica, calcium, chloride, sodium, sulfate, magnesium, and potassium. The Wissahickon Schist and Peters Creek Schist have similar water types; ground water from serpentinite, the basal unit of the Baltimore Mafic Complex that straddles the Pennsylvania-Maryland border, is distinctly different. For the Wissahickon Schist and Peters Creek Schist, no cation is predominant; calcium, magnesium, and sodium are in nearly equal concentrations expressed in milliequivalents per liter. Bicarbonate is the dominant anion. Water from serpentinite is of the magnesium bicarbonate type; magnesium is the dominant cation, and bicarbonate is the dominant anion. Water from 2 percent of sampled wells exceeded the U.S. Environmental Protection Agency (USEPA) secondary maximum contaminant level (SMCL) for total dissolved solids. None of the chloride or sulfate concentrations exceeded the USEPA SMCL. Water from 10 percent of sampled wells exceeded the USEPA maximum contaminant level (MCL) of 10 mg/L (milligrams per liter) nitrate as nitrogen. All of those wells are in the Wissahickon Schist. The median concentration of nitrate in water samples from the Wissahickon Schist was 3.6 mg/L, and the maximum concentration was 36 mg/L. Except for iron and manganese, metals and other trace inorganic constituents do not appear to pose a water-quality problem. Fourteen percent of water samples analyzed for iron and 29 percent of water samples analyzed for manganese exceeded the USEPA SMCL's. The median activity of radon-222 for all formations was 2,400 pCi/L (picoCuries per liter). The median activity for water from 35 wells sampled in the Wissahickon Schist in the Big Elk Creek Basin was 2,500 pCi/L. Water from 94 percent of sampled wells exceeded the proposed USEPA MCL of 300 pCi/L, and water from 25 percent of sampled wells exceeded proposed USEPA alternate MCL of 4,000 pCi/L. In addition to the 20 wells sampled for pesticides for this study, data were available for 20 other wells sampled for pesticides. The most commonly detected pesticides in the Big Elk Creek Basin are deethyl atrazine (71 percent of sampled wells), atrazine (35 percent of sampled wells), metolachlor (32 percent of sampled wells), carbaryl (19 percent of sampled wells), picloram (14 percent of sampled wells), simazine (13 percent of sampled wells), and carbofuran (11 percent of sampled wells). Most concentrations are extremely low and are in the parts per trillion range. Concentrations of pesticides detected did not exceed USEPA MCL’s. Out of 43 volatile organic compounds analyzed, only 4 were detected—chloroform, total phenols, tert-butyl methyl ether (MTBE), and toluene. None of the concentrations exceeded USEPA MCL’s.

Maryland, Pennsylvania↗
USGS2002

Geophysical logging to determine construction, contributing zones, and appropriate use of water levels measured in confined-aquifer network wells, San Luis Valley, Colorado, 1998-2000

Geophysical logs were recorded in 32 wells in the confined-aquifer monitoring well network maintained by the Rio Grande Water Conservation District. Logging results were used to determine well construction, zones contributing water to the wells, and the purposes for which the ground-water levels measured in the wells can be used. The confined-aquifer well network consists of 42 flowing and nonflowing wells. This network consists of wells used to supply water for irrigation, household use, wildlife refuge supply, and stock use, and wells for water-level monitoring. Geophysical logs recorded in the wells included video, caliper, water specific conductance, water temperature, and water flow. Most wells in the confined-aquifer well network yield a composite water level representing water levels in multiple permeable zones in the confined-aquifer system of the San Luis Valley. A potentiometric-surface map constructed using November 2000 water levels indicates that water levels from most wells in the network are correlated with water levels from nearby network wells. Potentiometric-surface maps that are constructed from water levels measured in most of the wells in the network can be used to understand long-term local and regional changes in water levels in the confined-aquifer system. Water levels measured in 8 of the 42 wells in the confined-aquifer network are not representative of water levels in the confined-aquifer system.

Water-Resources Investigations Report↗
USGS2002

Effectiveness of three best management practices for highway-runoff quality along the Southeast Expressway, Boston, Massachusetts

Best management practices (BMPs) near highways are designed to reduce the amount of suspended sediment and associated constituents, including debris and litter, discharged from the roadway surface. The effectiveness of a deep-sumped hooded catch basin, three 2-chambered 1,500-gallon oil-grit separators, and mechanized street sweeping in reducing sediment and associated constituents was examined along the Southeast Expressway (Interstate Route 93) in Boston, Massachusetts. Repeated observations of the volume and distribution of bottom material in the oil-grit separators, including data on particle-size distributions, were compared to data from bottom material deposited during the initial 3 years of operation. The performance of catch-basin hoods and the oil-grit separators in reducing floating debris was assessed by examining the quantity of material retained by each structural BMP compared to the quantity of material retained by and discharged from the oil-grit separators, which received flow from the catch basins. The ability of each structural BMP to reduce suspended-sediment loads was assessed by examining (a) the difference in the concentrations of suspended sediment in samples collected simultaneously from the inlet and outlet of each BMP, and (b) the difference between inlet loads and outlet loads during a 14-month monitoring period for the catch basin and one separator, and a 10-month monitoring period for the second separator. The third separator was not monitored continuously; instead, samples were collected from it during three visits separated in time by several months. Suspended-sediment loads for the entire study area were estimated on the basis of the long-term average annual precipitation and the estimated inlet and outlet loads of two of the separators. The effects of mechanized street sweeping were assessed by evaluating the differences between suspended-sediment loads before and after street sweeping, relative to storm precipitation totals, and by comparing the particle-size distributions of sediment samples collected from the sweepers to bottom-material samples collected from the structural BMPs. A mass-balance calculation was used to quantify the accuracy of the estimated sediment-removal efficiency for each structural BMP. The ability of each structural BMP to reduce concentrations of inorganic and organic constituents was assessed by determining the differences in concentrations between the inlets and outlets of the BMPs for four storms. The inlet flows of the separators were sampled during five storms for analysis of fecal-indicator bacteria. The particle-size distribution of bottom material found in the first and second chambers of the separators was similar for all three separators. Consistent collection of floatable debris at the outlet of one separator during 12 storms suggests that floatable debris were not indefinitely retained.Concentrations of suspended sediment in discrete samples of runoff collected from the inlets of the two separators ranged from 8.5 to 7,110 mg/L. Concentrations of suspended sediment in discrete samples of runoff collected from the outlets of the separators ranged from 5 to 2,170 mg/L. The 14-month sediment-removal efficiency was 35 percent for one separator, and 28 percent for the second separator. In the combined-treatment system in this study, where catch basins provided primary suspended-sediment treatment, the separators reduced the mass of the suspended sediment from the pavement by about an additional 18 percent. The concentrations of suspended sediment in discrete samples of runoff collected from the inlet of the catch basin ranged from 32 to 13,600 mg/L. Concentrations of suspended sediment in discrete samples of runoff collected from the outlet of the catch basin ranged from 25.7 to 7,030 mg/L. The sediment-removal efficiency for individual storms during the 14-month monitoring period for the deep-sumped hooded catch basin was 39 percent.The concentrations of 29 in

Water-Resources Investigations Report↗
USGS2002

Surface-water characteristics and quality on the Osage Reservation, Osage County, Oklahoma, 1999

Concern about the effects of early oil-industry practices of surface disposal of produced-brine water prompted an investigation of the surface-water quality on the Osage Reservation. About 38,600 oil wells have been drilled on the Osage Reservation since drilling began in 1896. The Osage Reservation comprises three major drainage basins. The Caney River Basin is in the northeast, the Bird Creek Basin is in the southeast, and the Salt Creek Basin in the west. Variations in streamflow on the Osage Reservation during a year primarily result from variations in the quantity and frequency of rainfall, evapotranspiration, and reservoir operations. Most streams do not flow during low rainfall periods in late summer, early fall, and in winter. Percent of mean annual discharge is largest during March through June, averaging 54 to 62 percent and smallest during December, January, July, and August, averaging only 14 to 21 percent. The basin areas of Caney River in the reservation (251 square miles), Salt Creek (273 square miles), and Sand Creek (227 square miles) are about the same and the basin areas of the Bird Creek Basin (418 square miles) and Homily Creek Basin (383 square miles) are similar in area. One hundred forty surface-water sites were sampled once during either February, March or August 1999. The surface-drainage areas, incremental basins, between sample sites along a stream, range in size from 0.26 to 123 square miles with a median of 8.6 square miles. Total number of oil wells upgradient of the samples sites is 31,432 or 80 percent of the total in the reservation. The total number of oil wells in the Caney River Basin in the reservation (2,975 wells), Salt Creek Basin (4,619 wells), and Sand Creek Basin (3,858 wells) are about the same and the total number of oil wells in the Bird Creek Basin (8,858 wells) and Hominy Creek Basin (7,842 wells) are similar. The number of oil wells per square mile in the incremental basins ranges for 0.86 to 154. Surface-water quality monitoring had been conducted previously at two sites included in this study. Dissolved chloride concentrations for the two samples collected during 1999 were equaled or exceeded at both sites by the historical data. There is no statistically significant difference between the distribution of the dissolved chloride concentrations from the surface water and nearby ground-water samples. The surface-water quality samples had significantly lesser concentrations of dissolved solids, sulfate, and nitrite plus nitrate as nitrogen than the ground-water samples. Chloride yield, reported in tons per day per square mile, is the chloride load divided by the basin area upstream of the sample site. The mean of the chloride yields for all the samples was 0.07 ton per day per square mile. Many sample locations where yields were greater than 0.07 ton per day per square mile were areas where dissolved chloride concentrations from surface-water samples were greater than 250 milligrams per liter in an earlier water-quality investigation. An investigation of possible relations between the surface-water quality data and the oil-well construction data for the incremental basins and for 1-mile radial distance upstream in the incremental basins was conducted. The oil-well data also were grouped by the time periods of activity into pre-1930, 1930 to 1970, and post-1970. These groups attempt to account for differences in industry drilling and producing practices associated with various periods. No statistically significant correlations were found between the surface-water quality data and the oil-well construction data.

Oklahoma↗
USGS2002

Report of hydrologic investigations in the Three Sisters area of central Oregon, Summer 2001

An ongoing episode of crustal uplift centered in the Separation Creek drainage of the Three Sisters area, central Oregon Cascades, may result from a magmatic intrusion that began in 1998. An investigation of springs in this drainage in summer 2001 revealed slightly elevated water temperatures and chloride (Cl-) concentrations of up to about 5?C and 20 milligrams per liter (mg/L), respectively, above background. The total discharge of anomalous Cl- in Separation Creek was 9.2 grams per second, which in combination with the temperature-Cl- relation in the springs results in a total advective heat discharge of 16 MW (megawatts). Comparison with similar findings obtained a decade earlier suggests that total Cl- and heat discharges in the groundwater drainage are unaffected by the current uplift. However, the isotopic composition of the dissolved inorganic carbon (DIC) in the spring waters (delta carbon-13 (13C) = -9.03 to -11.6?; carbon-14 (14C) <25 pmC) combined with helium-3/helium-4 (3He/4He) ratios near 8 RA and C/3He ratios <1010 in two of the springs are indicative of a magmatic source. The high 3He/4He ratios indicate that the magmatic gas is derived from a relatively recent, if not ongoing, intrusion. The concentration of magmatic carbon is low, a few millimoles per liter (mmol/L) at most, with an average value of 1.53 mmol/L for all the springs sampled in the drainage. Combining this average with the late-summer water flow in Separation Creek suggests a discharge of 21 tonnes/day of magmatic carbon dioxide (CO2). The presence of magmatic carbon in the shallow groundwater system, and the fact that DIC is uncorrelated with Cl-, suggests that some magmatic gas could escape diffusely through the soils.

Water-Resources Investigations Report↗
USGS2002

Delineation of the Troy Bedrock Valley and particle-tracking analysis of ground-water flow underlying Belvidere, Illinois

The U.S. Geological Survey, U.S. Environmental Protection Agency, and Illinois Environmental Protection Agency began a study of the hydrogeology, flow system, and distribution of contaminants in the aquifers underlying Belvidere, Ill., and vicinity in 1992. As part of the study, the ancestral Troy Bedrock Valley, located about 1.5 miles west of Belvidere, was identified as an important part of the ground-water-flow system. In the deepest parts of the valley, the basal Glenwood confining unit may be absent; thick deposits of sand and gravel that infill part of the valley may directly overlie the sandstone St. Peter aquifer, a regionally important source of water for public supply. With few deep wells open to the St. Peter aquifer present in the valley to provide necessary geologic information, tritium and other water-chemistry data were collected from eight wells to possibly delineate areas where the confining unit may be absent; the data also provide baseline water-quality information for an area expecting changes in land use and increases in water withdrawal. Also as part of the study, particle-tracking analysis was done using an available flow model to (1) identify possible discharge locations of ground water and contaminants and (2) delineate areas contributing recharge to the Belvidere municipal wells. This report presents and interprets water-chemistry data collected during December 2000 and presents results of particle-tracking analysis. Ground water in samples from two of four wells open to the St. Peter aquifer appears to have recharged after 1954, suggesting that the Glenwood confining unit may be absent near the wells. Other hydrogeologic and water-chemistry data, however, were inconclusive or contradictory. Concentrations of iron, manganese, and lead exceeded maximum contaminant levels in five or less samples, but materials associated with the water-distribution systems appear to contribute to the elevated concentrations above natural levels. Particle-tracking analysis indicates that most ground-water flow beneath possible contaminant-source areas discharges from the glacial drift aquifer to the Kishwaukee River. Most of the source areas are in or near Belvidere and are within 1,500 feet of the river. The analysis also indicates the possibility that in parts of the study area, some ground water does not discharge to the river, but flows beneath the Kishwaukee River in the underlying carbonate Galena-Platteville aquifer. Ground water that discharges to the one municipal well open to the glacial drift aquifer is estimated to travel over 1 mile in less than 25 years. Simulated residence (travel) times of ground water from the base of the glacial drift aquifer to the six municipal wells open, in part, to the Galena-Platteville aquifer, are estimated at less than about 40 years. Because fractures in this aquifer are unaccounted for in the flow model, actual areas contributing recharge are likely larger and travel times faster than those simulated for most of the municipal wells. Tritium data indicate that, in general, travel times from the land surface to the deepest parts of the Galena-Platteville aquifer are less than 46 years. Methyl tertiary-butyl ether data indicate that travel times to the upper part of the aquifer may be less than 16 years. The water-quality-based estimates of travel time generally are consistent with the estimates from particle-tracking analysis.

Illinois↗
USGS2002

Concentrations of pesticides and pesticide degradates in the Croton River Watershed in southeastern New York, July-September 2000

Thirty-seven pesticides and (or) pesticide degradates were detected in baseflow samples collected from 47 stream sites in the Croton River Watershed (374 square miles) in southeastern New York in the summer of 2000. The Croton Reservoir provides about 10 percent of New York City's water supply. Maximum concentrations of most pesticides detected did not exceed 0.1 μg/L (micrograms per liter). This study, by the U.S. Geological Survey in cooperation with the New York State Department of Environmental Conservation, was conducted from July through September 2000 and entailed analysis of the samples for more than 150 pesticides and their degradates. Nine compounds were detected at a concentration greater than 0.10 μg/L; three of these were insecticides (diazinon, carbaryl, and imidacloprid), one was a fungicide (mycobutanil), and five were herbicides (simazine, 2,4-D, diuron, hexazinone, and 2,4-D methyl esther). Only two of these compounds (simazine and 2,4-D) were detected at a concentration exceeding 1 μg/L; the simazine concentration exceeded the New York State surface-water standard of 0.5 μg/L. Two insecticides (diazinon and azinphos-methyl) exceeded aquatic-life-protection standard in one sample each. Concentrations of three insecticides (chlorpyrifos, carbaryl, and malathion) were more than 50 percent of the aquatic-life-protection standards in one sample each. Total concentrations of insecticides and herbicides (the sum of the concentrations, whereby all concentrations below the detection limit were set to zero), and the concentrations of the herbicide prometon and the insecticide diazinon, were highest in samples from watersheds with population densities greater than 510 per square mile (21 sites); therefore, the presence of these compounds is attributable to urban, residential, and other developed land uses. The data obtained in this study are useful for making general comparisons among watersheds with differing land uses, but the concentrations represent baseflow conditions and, thus, are probably lower than the annual maximum concentrations in these streams. A July baseflow sample had total insecticide and fungicide concentrations of less than 0.03 μg/L, whereas a stormflow sample collected at the same site 2 weeks later had a corresponding concentration greater than 0.10 μg/L. Total herbicide concentrations for the July baseflow and stormflow samples were around 0.03 μg/L, but that for a stormflow sample collected at the same site 2 months later was greater than 20 μg/L.

Connecticut, New York↗
USGS2002

Concentrations of Escherichia coli in streams in the Ohio River Watershed in Indiana, May—August 2000

Water samples collected from 40 stream sites in the Ohio River Watershed in Indiana from May through August 2000 were analyzed for concentrations of Escherichia coli (E. coli) bacteria. Each site was sampled five times in a 30-day period. Concentrations of E. coli in 72 of the 200 samples exceeded the State of Indiana single-sample standard of 235 colonies per 100 milliliters for waters used for recreation. A five-sample geometric mean of concentrations was computed for each site. Concentrations in samples from 24 of the 40 sites exceeded the State of Indiana standard for a five-sample geometric mean of 125 colonies per 100 milliliters for waters used for recreation. Samples collected from 34 sites had E. coli concentrations that exceeded either or both the single-sample standard and the five-sample geometric mean standard. Five of the 40 sampling sites were at or near U.S. Geological Survey streamflowgaging stations. On the basis of records from these stations, 16 percent of the samples from these sites were collected at streamflows above the median daily mean discharge for each station. E. coli concentrations and turbidity measurements collected during 2000 were analyzed in concert with E. coli concentration and turbidity data collected in 1999 at streams within the Kankakee and Lower Wabash River Watersheds in Indiana and in 1998 at streams within the Upper Wabash River Watershed in Indiana. These data were grouped together to investigate the relation between concentrations of bacteria and turbidity. The resulting analysis indicated a statistically significant correlation between concentrations of E. coli and turbidity.

Indiana↗
USGS2002

The effects of atmospheric nitrogen deposition in the Rocky Mountains of Colorado and southern Wyoming— A synthesis and critical assessment of published results

The Rocky Mountain region of Colorado and southern Wyoming receives as much as 7 kilograms per hectare per year ((kg/ha)/yr) of atmospheric nitrogen (N) deposition, an amount that may have caused changes in aquatic and terrestrial life in otherwise pristine ecosystems. The Rocky Mountain National Park, in its role of protecting air-quality related values under provisions of the Clean Air Act Amendments of 1977, has provided support for this synthesis and critical assessment of published literature on the effects of atmospheric N deposition. Results from published studies indicate a long-term increase in the rate of atmospheric N deposition during the 20th century, but no region-wide increase during the past 2 decades, although the rate of atmospheric N deposition has increased at three sites east of the Continental Divide in the Front Range region since the mid-1980s. Much of the increase in atmospheric N deposition at all three sites has resulted from an increase in the ammonium concentrations of wet deposition; this suggests an increase in contributions from agricultural areas or from vehicle traffic east of the Rocky Mountains. Lakes at two study sites in the Front Range (Loch Vale and Green Lakes Valley) had NO 3 - concentrations of 30 to 40 micromoles per liter (µmol/L) during early spring snowmelt and remained at 5 to 10 µmol/L during summer. Retention of N in atmospheric wet deposition in some sub-catchments of these lakes was less than 50 percent, which reflects an advanced stage of N saturation. Nitrate concentrations in surface waters west of the Continental Divide were lower—often less than 10 µmol/L during snowmelt and less than 2 µmol/L during summer -- than surface waters east of the Divide, except in areas such as the Mt. Zirkel Wilderness that receive elevated amounts of atmospheric N deposition of 4 to 5 (kg/ha)/yr. Atmospheric N deposition in the Front Range east of the Divide may have altered the composition of alpine tundra-plant communities and lake diatoms, but additional studies would be needed to definitively demonstrate the hypothesized cause-and-effect relations. Rates of N-mineralization and nitrification in soils of the Front Range have increased in response to increased atmospheric N deposition. Projected future population growth and energy use in Colorado and the west increase the likelihood that the subtle effects of atmospheric N deposition now evident in the Front Range will become more pronounced and widespread in the future. The likelihood of future increased N emissions along the Front Range warrants a continuation of existing long-term precipitation and surface-water chemistry monitoring programs, and an expansion of the networks into areas that receive large amounts of atmospheric N deposition, but currently lack adequate monitoring. Long-term study and expanded sampling are needed to address uncertainties about the effects of atmospheric N deposition on terrestrial plant communities, nutrient limitation in lake plankton, shifts of dominant species within diatom communities, and on amphibian response to episodic surface-water acidification.

Colorado, Wyoming↗
USGS2002

Water quality, sediment quality, and stream-channel classification of Rock Creek, Washington, D.C., 1999-2000

Rock Creek Park is within the National Capital Region in Washington, D.C., and is maintained by the National Park Service. Part of Montgomery County, Maryland, and part of the District of Columbia drain into Rock Creek, which is a tributary of the Potomac River. Water quality in Rock Creek is important to biotic life in and near the creek, and in the Potomac River Basin and the Chesapeake Bay. The water quality of the Rock Creek Basin has been affected by continued urban and agricultural growth and development. The U.S. Geological Survey, in cooperation with the National Park Service, investigated water quality and sediment quality in Rock Creek over a 2-year period (1998?2000), and performed a stream-channel classification to determine the distribution of bottom sediment in Rock Creek. This report presents and evaluates water quality and bottom sediment in Rock Creek for water years 1999 (October 1, 1998 to September 30, 1999) and 2000 (October 1, 1999 to September 30, 2000). A synoptic surface-water assessment was conducted at five stations from June 23 to June 25, 1999, a temporal surface-water assessment was conducted at one station from February 18, 1999 to September 26, 2000, and bed-sediment samples were collected and assessed from three stations from August 17 to August 19, 1999. The synoptic surface-water assessment included pesticides (parent compounds and selected transformation products), field parameters, nutrients, and major ions. The temporal surface-water assessment included pesticides (parent compounds and selected transformation products) and field parameters. The bed-sediment assessment included trace elements and organic compounds (including low- and high-molecular weight polycyclic aromatic hydrocarbons, poly-chlorinated biphenyls, pesticides, and phthalates). Some, but not all, of the pesticides known to be used in the area were included in the synoptic water-quality assessment, the temporal water-quality assessment, and the bed-sediment assessment. In addition to the water-quality and sediment-quality assessments, a Rosgen stream-channel classification was performed on a 900-foot-long segment of Rock Creek. In the synoptic water-quality assessment, two pesticides were found to be above published criteria for the protection of aquatic life. In the temporal water-quality assessment, four pesticides were found to be above published criteria for the protection of aquatic life. In the bed-sediment assessment, 8 trace elements, 14 polycyclic aromatic hydrocarbons, 6 pesticides, and 1 phthalate compound were found to be above published criteria for the protection of aquatic life. In the Rosgen classification, a comparison to a previous classification for this segment showed an increase in sands and other fine-grained sediments in the creek bed.

Water-Resources Investigations Report↗
USGS2002

Relation of Environmental characteristics to the composition of aquatic assemblages along a gradient of urban land use in New Jersey, 1996-98

Community data from 36 watersheds were used to evaluate the response of fish, invertebrate, and algal assemblages in New Jersey streams to environmental characteristics along a gradient of urban land use that ranged from 3 to 96 percent. Aquatic assemblages were sampled at 36 sites during 1996-98, and more than 400 environmental attributes at multiple spatial scales were summarized. Data matrices were reduced to 43, 170, and 103 species of fish, invertebrates, and algae, respectively, by means of a predetermined joint frequency and relative abundance approach. White sucker (Catostomus commersoni) and Tessellated darter (Etheostoma olmstedi) were the most abundant fishes, accounting for more than 20 and 17 percent, respectively, of the mean abundance. Net-spinning caddisflies (Hydropsychidae) were the most commonly occurring benthic invertebrates and were found at all but one of the 36 sampling sites. Blue-green (for example, Calothrix sp. and Oscillatoria sp.) and green (for example, Protoderma viride) algae were the most widely distrib-uted algae; however, more than 81 percent of the algal taxa collected were diatoms. Principal-component and correlation analyses were used to reduce the dimensionality of the environmental data. Multiple linear regression analysis of extracted ordination axes then was used to develop models that expressed effects of increasing urban land use on the structure of aquatic assemblages. Significant environmental variables identified by using multiple linear regression analysis then were included in a direct gradient analysis. Partial canonical correspondence analysis of relativized abundance data was used to restrict further the effects of residual natural variability, and to identify relations among the environmental variables and the structure of fish, invertebrate, and algal assemblages along an urban land-use gradient. Results of this approach, combined with the results of the multiple linear regression analyses, were used to identify human population density (311-37,594 persons/km2), amount and type of impervious surface cover (0.12-1,350 km2), nutrient concentrations (for example, 0.01-0.29 mg/L of phosphorus), hydrologic instability (for example, 100-8,955 ft3/s for 2-year peak flow), the amount of forest and wetlands in a basin (0.01-6.25 km2), and substrate quality (0-87 percent cobble substrate) as variables that are highly correlated with aquatic-assemblage structure. Species distributions in ordination space clearly indicate that tolerant species are more abundant in the streams impaired by urbanization and sensitive taxa are more closely associated with the least impaired basins. The distinct differences in aquatic assemblages along the urban land-use gradient demonstrate the deleterious effects of urbanization on assemblage structure and indicate that conserving landscape attributes that mitigate anthropogenic influences (for example, stormwater-management practices emphasizing infiltration and preservation of existing forests, wetlands, and riparian corridors) will help to maintain the relative abundance of sensitive taxa. Complementary multiple linear regression models indicate that aquatic community indices were correlated with many of the anthropogenic factors that were found to be significant along the urban land-use gradient. These indices appear to be effective in differentiating the moderately and severely impaired streams from the minimally impaired streams. Evaluation of disturbance thresholds for aquatic assemblages indicates that moderate to severe impairment is detectable in New Jersey streams when impervious surface cover in the drainage basin reaches approximately 18 percent.

Water-Resources Investigations Report↗
USGS2002

Ground-water levels in the Floridan-Midville aquifer in the Breezy Hill area, Aiken and Edgefield Counties, South Carolina, April 1999-November 2000

The Breezy Hill area in Aiken and Edgefield Counties of west-central South Carolina is a rapidly growing region in need of increasing amounts of ground water. From 1995 to 1998, the local water utility increased ground-water withdrawals in the Breezy Hill area from 1.4 to 2.1 million gallons per day to meet water-supply demands. As development continues, future demands for ground water will likely put stress on the surfaceand ground-water resources of the area. To address this issue, the U.S. Geological Survey, in cooperation with Aiken County, compiled and interpreted geologic and hydrologic data needed to map the ground-water system in the Breezy Hill study area. The Breezy Hill study area consists of four interfluvial areas comprising the regions between Horse and Little Horse Creeks, Little Horse and Hightower Creeks, Hightower Creek and Franklin Branch, and Franklin Branch and Mims Branch. Across the interfluvial areas, the average elevation of the water-level surface ranged from 200 to 480 feet above sea level, and the average saturated thickness of the Floridan-Midville aquifer ranged from less than 20 to 70 feet thick. A water-level contour map of the surface of the Floridan-Midville aquifer indicates that recharge to the aquifer occurs mainly within the interfluves. Recharge is derived principally from precipitation, although there is some potential for ground-water recharge from underlying crystalline rocks. Ground water discharges along the flanks of the interfluves into the bounding streams where the elevations of the ground water and streams coincide. From April 1999 to November 2000, calculated long-term normal precipitation totaled about 84.0 inches; however, actual recorded precipitation totaled 69.2 inches, representing about a 17.6 percent decrease in precipitation during this period. Published estimates of annual evapotranspiration range from 30 to 35 inches. A U.S. Geological Survey surface-water gaging station located near the center of the study area on Little Horse Creek monitors runoff from a drainage area of 26.6 square miles. Average annual flow for the station for water years 1990-2000 was 33.8 cubic feet per second. From April 1999 to November 2000, the monthly average flow was less than the average monthly flow for the longterm record, excluding December 1999 to March 2000 when no data were collected. Monthly average flow for Little Horse Creek exceeded the normal monthly flow during June and July 1999. Ground water in the Breezy Hill area is principally withdrawn from the unconfined Floridan- Midville aquifer. Ground-water withdrawals by the local water utility increased 37 percent from 1989 to 2000 (315.2 to 500 million gallons, respectively). From January 1999 to December 2000, the utility exceeded the long-term monthly average groundwater withdrawals for every month except September and December 2000. Calculated long-term monthly ground-water withdrawals by the utility for a 20-month period from April 1999 to November 2000 totaled 674 million gallons; however, actual ground-water withdrawals totaled 883 million gallons, which is 31 percent more than the long-term average ground-water withdrawals for the production wells. Published estimates of average annual ground-water recharge rates for the study area range from 13 to 15 inches per year. A base-flow recession analysis of streamflow data for Little Horse Creek provided an estimated recharge rate of 14.9 inches per year for the drainage area. Using an estimated average porosity ranging from 30 to 35 percent observed in sand-aquifer cores, the average annual recharge of 13 to 15 inches would cause a 3.6- to 4.1-foot water-level change to the saturated thickness of the aquifer, if applied instantaneously. The water-level declines observed in wells from April 1999 to November 2000 approximated an average decline of 4 feet. From November 1999 to November 2000, ground-water levels in six wells near utility pumping centers declined 2 to 5 feet. Long-term waterlevel declines of 10.27 and 11.50 feet were measured in two wells between May 1992 and April 2000, respectively.

South Carolina↗
USGS2002

Changes in ground-water quality in the Canal Creek Aquifer between 1995 and 2000-2001, West Branch Canal Creek area, Aberdeen Proving Ground, Maryland

Since 1917, Aberdeen Proving Ground, Maryland has been the primary chemical-warfare research and development center for the U.S. Army. Ground-water contamination has been documented in the Canal Creek aquifer because of past disposal of chemical and ordnance manufacturing waste. Comprehensive sampling for volatile organic compounds in ground water by the U.S. Geological Survey in the West Branch Canal Creek area was done in June?October 1995 and June?August 2000. The purpose of this report is (1) to compare volatile organic compound concentrations and determine changes in the ground-water contaminant plumes along two cross sections between 1995 and 2000, and (2) to incorporate data from new piezometers sampled in spring 2001 into the plume descriptions. Along the southern cross section, total concentrations of volatile organic compounds in 1995 were determined to be highest in the landfill area east of the wetland (5,200 micrograms per liter), and concentrations were next highest deep in the aquifer near the center of the wetland (3,300 micrograms per liter at 35 feet below land surface). When new piezometers were sampled in 2001, higher carbon tetrachloride and chloroform concentrations (2,000 and 2,900 micrograms per liter) were detected deep in the aquifer 38 feet below land surface, west of the 1995 sampling. A deep area in the aquifer close to the eastern edge of the wetland and a shallow area just east of the creek channel showed declines in total volatile organic compound concentrations of more than 25 percent, whereas between those two areas, con-centrations generally showed an increase of greater than 25 percent between 1995 and 2000. Along the northern cross section, total concentrations of volatile organic compounds in ground water in both 1995 and 2000 were determined to be highest (greater than 2,000 micrograms per liter) in piezometers located on the east side of the section, farthest from the creek channel, and concentrations were progressively lower at piezometer locations closer to the creek channel. Total volatile organic compound concentrations increased more than 25 percent in some areas in the middle depths of the aquifer; however, it could not be determined if a defined plume was moving farther downgradient along ground-water flow paths toward the creek channel, or vertically downward because of density differences within the aquifer.

Water-Resources Investigations Report↗
USGS2002

Streamflow gains and losses along San Francisquito Creek and characterization of surface-water and ground-water quality, southern San Mateo and northern Santa Clara counties, California, 1996-97

San Francisquito Creek is an important source of recharge to the 22-square-mile San Francisquito Creek alluvial fan ground-water subbasin in the southern San Mateo and northern Santa Clara Counties of California. Ground water supplies as much as 20 percent of the water to some area communities. Local residents are concerned that infiltration and consequently ground-water recharge would be reduced if additional flood-control measures are implemented along San Francisquito Creek. To improve the understanding of the surface-water/ground-water interaction between San Francisquito Creek and the San Francisquito Creek alluvial fan, the U.S. Geological Survey (USGS) estimated streamflow gains and losses along San Francisquito Creek and determined the chemical quality and isotopic composition of surface and ground water in the study area.Streamflow was measured at 13 temporary streamflow-measurement stations to determine streamflow gains and losses along a 8.4-mile section of San Francisquito Creek. A series of five seepage runs between April 1996 and May 1997 indicate that losses in San Francisquito Creek were negligible until it crossed the Pulgas Fault at Sand Hill Road. Streamflow losses increased between Sand Hill Road and Middlefield Road where the alluvial deposits are predominantly coarse-grained and the water table is below the bottom of the channel. The greatest streamflow losses were measured along a 1.8-mile section of the creek between the San Mateo Drive bike bridge and Middlefield Road; average losses between San Mateo Drive and Alma Street and from there to Middlefield Road were 3.1 and 2.5 acre-feet per day, respectively.Downstream from Middlefield Road, streamflow gains and losses owing to seepage may be masked by urban runoff, changes in bank storage, and tidal effects from San Francisco Bay. Streamflow gains measured between Middlefield Road and the 1200 block of Woodland Avenue may be attributable to urban runoff and (or) ground-water inflow. Water-level measurements from nearby wells indicate that the regional water table may coincide with the channel bottom along this reach of San Francisquito Creek, particularly during the winter and early spring when water levels usually reach their maximum. Streamflow losses resumed below the 1200 block of Woodland Avenue, extending downstream to Newell Road. Discharge from a large storm drain between Newell Road and East Bayshore Road may account for the streamflow gains measured between these sites. Streamflow gains were measured between East Bayshore Road and the Palo Alto Municipal Golf Course, but this reach is difficult to characterize because of the probable influence of high tides.Estimated average streamflow losses totaled approximately 1,050 acre-feet per year for the reaches between USGS stream gage 11164500 at Stanford University (upstream of Junipero Serra Boulevard) and the Palo Alto Municipal Golf Course, including approximately 595 acre-feet per year for the 1.8-mile section between San Mateo Drive and Middlefield Road. Approximately 58 percent, or 550 acre-feet, of the total estimated average annual recharge from San Francisquito Creek occurs between the San Mateo Drive and Middlefield Road sites.The chemical composition of San Francisquito Creek water varies as a function of seasonal changes in hydrologic conditions. Measurements of specific conductance indicate that during dry weather and low flow, the dissolved-solids concentrations tends to be high, and during wet weather, the concentration tends to be low owing to dilution by surface water. Compared with water samples from upstream sites at USGS stream gage 11164500 and San Mateo Drive, the samples from the downstream sites at Alma Street and Woodland Avenue had low specific conductance; low concentrations of magnesium, sodium, sulfate, chloride, boron, and total dissolved solids; high nutrient concentrations; and light isotopic compositions indicating that urban runoff constitutes most of the streamflow

Water-Resources Investigations Report↗
USGS2002

A National survey of methyl tert -butyl ether and other volatile organic compounds in drinking-water sources: Results of the random source-water survey

Methyl tert -butyl ether (MTBE) was detected in source water used by 8.7 percent of randomly selected community water systems (CWSs) in the United States at concentrations that ranged from 0.2 to 20 micrograms per liter ( μ g/L). The Random Survey conducted by the U.S. Geological Survey, in cooperation with the Metropolitan Water District of Southern California and the Oregon Health & Science University, was designed to provide an assessment of the frequency of detection, concentration, and distribution of MTBE, three other ether gasoline oxygenates, and 62 other volatile organic compounds (VOCs) in ground- and surface-water sources used for drinking-water supplies. The Random Survey was the first of two components of a national assessment of the quality of source water supplying CWSs sponsored by the American Water Works Association Research Foundation. A total of 954 CWSs were selected for VOC sampling from the population of nearly 47,000 active, self-supplied CWSs in all 50 States, Native American Lands, and Puerto Rico based on a statistical design that stratified on CWS size (population served), type of source water (ground and surface water), and geographic distribution (State). At a reporting level of 0.2 μ g/L, VOCs were detected in 27 percent of source-water samples collected from May 3, 1999 through October 23, 2000. Chloroform (in 13 percent of samples) was the most frequently detected of 42 VOCs present in the source-water samples, followed by MTBE. VOC concentrations were generally less than 10 μ g/L 95 percent of the 530 detections and 63 percent were less than 1.0 μ g/L. Concentrations of 1,1-dichloroethene, tetrachloroethene, trichloroethene, vinyl chloride, and total trihalomethanes (TTHMs), however, exceeded drinking-water regulations in eight samples. Detections of most VOCs were more frequent in surface-water sources than in ground-water sources, with gasoline compounds collectively and MTBE individually detected significantly more often in surface water. Use of personal and commercial motorized watercraft on surface-water bodies that are drinking-water sources is probably the reason for the elevated detections of gasoline contaminants relative to ground water. MTBE detections demonstrated a seasonal pattern with more frequent detections in surface water in summer months, which is consistent with seasonal watercraft use. The detection frequency of most VOCs was significantly related to urban land use and population density. Detections of any VOC, non-trihalo-methane compounds, gasoline compounds collectively, the specific gasoline compounds benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE, solvents, and refrigerants were significantly greater in areas with more than 60 percent urban land use and (or) population density greater than 1,000 people per square mile than in source waters from less urbanized or lower population-density areas. MTBE detections were five times more frequent in source waters from areas with high MTBE use than in source waters from low or no MTBE use, but, unlike other gasoline compounds, MTBE detections were not significantly related to the density of gasoline storage tanks near drinking-water sources.

Water-Resources Investigations Report↗