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At least 379 records · Page 21Linked to original sources
USGS2002

Aquifer geochemistry and effects of pumping on ground-water quality at the Green Belt Parkway Well Field, Holbrook, Long Island, New York

Geochemistry, microbiology, and water quality of the Magothy aquifer at a new supply well in Holbrook were studied to help identify factors that contribute to iron-related biofouling of public-supply wells. The organic carbon content of borehole sediments from the screen zone, and the dominant terminal electron-accepting processes (TEAPs), varied by depth. TEAP assays of core sediments indicated that iron reduction, sulfate reduction, and undetermined (possibly oxic) reactions and microbial activity are correlated with organic carbon (lignite) content. The quality of water from this well, therefore, reflects the wide range of aquifer microenvironments at this site. High concentrations of dissolved iron (3.6 to 6.4 micromoles per liter) in water samples from this well indicate that some water is derived from Fe(III)-reducing sediments within the aquifer, but traces of dissolved oxygen indicate inflow of shallow, oxygenated water from shallow units that overlie the local confining units. Water-quality monitoring before and during a 2-day pumping test indicates that continuous pumping from the Magothy aquifer at this site can induce downward flow of shallow, oxygenated water despite the locally confined conditions. Average concentrations of dissolved oxygen are high (5.2 milligrams per liter, or mg/L) in the overlying upper glacial aquifer and at the top of the Magothy aquifer (4.3 mg/L), and low ( < 0.1 mg/L) in the deeper, anaerobic part of the Magothy; average concentrations of phosphate are high (0.4 mg/L) in the upper glacial aquifer and lower (0.008 mg/L) at the top of the Magothy aquifer and in the deeper part of the Magothy (0.013 mg/L). Concentrations of both constituents increased during the 2 days of pumping. The δ 34 S of sulfate in shallow ground water from observation wells (3.8 to 6.4 per mil) was much heavier than that in the supplywell water (-0.1 per mil) and was used to help identify sources of water entering the supply well. The δ 34 S of sulfate in a deep observation well adjacent to the supply well increased from 2.4 per mil before pumping to 3.3 per mil after pumping; this confirms that the pumping induced downward migration of water. The lighter δ 34 S value in the pumped water than in the adjacent observation well probably indicates FeS 2 oxidation (which releases light δ 34 S in adjacent sediments) by the downward flow of oxygenated water.

New York↗
USGS2001

Biodegradation potential of chlorinated solvents in ground water at the Naval Surface Warfare Center, Louisville, Kentucky, July 1999 to February 2000

The U.S. Geological Survey, in cooperation with the U.S. Department of the Navy, Southern Division Naval Facilities Engineering Command, investigated the potential for biodegradation of chlorinated solvents in ground water at the Naval Surface Warfare Center (also known as the Naval Ordnance Station, or the station), Louisville, Kentucky. The subsurface down to at least 100 feet at the station is characterized, from shallowest to deepest, by overburden deposits, a shale layer, and limestone. In general, all of the strata are poorly permeable. The permeable zones of the overburden and the limestone make up the overburden aquifer and the bedrock aquifer, respectively. Observed concentrations of redox-sensitive solutes suggest that the predominant anaerobic terminal electron accepting process in the overburden aquifer can shift between iron reduction and sulfate reduction, possibly as a result of rainfall-induced oxidation events. Daughter-product concentrations and laboratory experiments indicate that a variety of mechanisms, including reductive dechlorination and cometabolic oxidation, appear to be actively

Kentucky↗
USGS2003

Oxidation-reduction processes in ground water at Naval Weapons Industrial Reserve Plant, Dallas, Texas

Concentrations of trichloroethene in ground water at the Naval Weapons Industrial Reserve Plant in Dallas, Texas, indicate three source areas of chlorinated solvents?building 1, building 6, and an off-site source west of the facility. The presence of daughter products of reductive dechlorination of trichloroethene, which were not used at the facility, south and southwest of the source areas are evidence that reductive dechlorination is occurring. In places south of the source areas, dissolved oxygen concentrations indicated that reduction of oxygen could be the dominant process, particularly south of building 6; but elevated dissolved oxygen concentrations south of building 6 might be caused by a leaking water or sewer pipe. The nitrite data indicate that denitrification is occurring in places; however, dissolved hydrogen concentrations indicate that iron reduction is the dominant process south of building 6. The distributions of ferrous iron indicate that iron reduction is occurring in places south-southwest of buildings 6 and 1; dissolved hydrogen concentrations generally support the interpretation that iron reduction is the dominant process in those places. The generally low concentrations of sulfide indicate that sulfate reduction is not a key process in most sampled areas, an interpretation that is supported by dissolved hydrogen concentrations. Ferrous iron and dissolved hydrogen concentrations indicate that ferric iron reduction is the primary oxidation-reduction process. Application of mean first-order decay rates in iron-reducing conditions for trichloroethene, dichloroethene, and vinyl chloride yielded half-lives for those solvents of 231, 347, and 2.67 days, respectively. Decay rates, and thus half-lives, at the facility are expected to be similar to those computed. A weighted scoring method to indicate sites where reductive dechlorination might be likely to occur indicated strong evidence for anaerobic biodegradation of chlorinated solvents at six sites. In general, scores were highest for samples collected on the northeast side of the facility.

Texas↗
USGS2003

Processes affecting the trihalomethane concentrations associated with the third injection, storage, and recovery rest at Lancaster, Antelope Valley, California, March 1998 through April 1999

The formation and fate of trihalomethanes (THM) during the third injection, storage, and recovery test at Lancaster, Antelope Valley, California, were investigated as part of a program to assess the long-term feasibility of using injection, storage, and recovery as a water-supply method and as a way to reduce water-level declines and land-subsidence in the Antelope Valley. The program was conducted by the U.S. Geological Survey in cooperation with the Los Angeles County Department of Public Works and the Antelope Valley-East Kern Water Agency. The water used for injection, storage, and recovery must be disinfected before injection and thus contains THMs and other disinfection by-products. THMs (chloroform, CHCl3, bromodichloromethane, CHCl2Br, dibromochloromethane, CHClBr2, and bromoform, CHBr3) are formed by reaction between natural dissolved organic carbon that is present in water and chlorine that is added during the disinfection step of the drinking water treatment process. THMs are carcinogenic compounds, and their concentrations in drinking water are regulated by the U.S. Environmental Protection Agency. During previous cycles of the Lancaster program, extracted water still contained measurable concentrations of THMs long after continuous pumping had extracted a greater volume of water than had been injected. This raised concerns about the potential long-term effect of injection, storage, and recovery cycles on ground-water quality in Antelope Valley aquifers. The primary objectives of this investigation were to determine (1) what controlled continued THM formation in the aquifer after injection, (2) what caused of the persistence of THMs in the extracted water, even after long periods of pumping, (3) what controlled the decrease of THM concentrations during the extraction period, and (4) the potential for natural attenuation of THMs in the aquifer. Laboratory experiments on biodegradation of THMs in microcosms of aquifer materials indicate that aquifer bacteria did not degrade CHCl3 or CHBr3 under aerobic conditions, but did degrade CHBr3 under anaerobic conditions. However, the aquifer is naturally aerobic and CHCl3 is the dominant THM species; therefore, biodegradation is not considered an important attenuation mechanism for THMs in this aquifer. The alluvial-fan sediments comprising the aquifer have very low contents of organic matter; therefore, sorption is not considered to be an important attenuation mechanism for THMs in this aquifer. Laboratory experiments on formation of THMs in the injection water indicate that continued THM formation in the injection water after injection into the aquifer was limited by the amount of residual chlorine in the injection water at the time of injection. After accounting for THMs formed by reaction of this residual chlorine, THMs behaved as conservative constituents in the aquifer, and the only process affecting the concentration of THMs was mixing of the injection water and the ground water. The mixing process was quantified using mass balances of injected constituents, the sulfur hexafluoride (SF6) tracer that was added to the injected water, and a simple descriptive mathematical mixing model. Mass balance calculations show that only 67 percent of the injected THMs and chloride were recovered by the time that a volume of water equivalent to 132 percent of the injection water volume was extracted. Pumping 250 percent of the injection water volume only increased recovery of injected THMs to 80 percent. THM and SF6 concentrations in the extracted water decreased concomitantly during the extraction period, and THM concentrations predicted from SF6 concentrations closely matched the measured THM concentrations. Because SF6 is a conservative tracer that was initially only present in the injection water, parallel decreases in SF6 and THM concentrations in the extracted water must be due to dilution of injection water with ground water. The simple descriptive mixing mode

Water-Resources Investigations Report↗
USGS2003

Isotope geochemistry and chronology of offshore ground water beneath Indian River Bay, Delaware

Results of geophysical surveys in Indian River Bay, Delaware, indicate a complex pattern of salinity variation in subestuarine ground water. Fresh ground-water plumes up to about 20 meters thick extending hundreds of meters offshore are interspersed with saline ground water, with varying degrees of mixing along the salinity boundaries. It is possible that these features represent pathways for nutrient transport and interaction with estuarine surface water, but the geophysical data do not indicate rates of movement or nutrient sources and reactions. In the current study, samples of subestuarine ground water from temporary wells with short screens placed 3 to 22 meters below the sediment-water interface were analyzed chemically and isotopically to determine the origins, ages, transport pathways, and nutrient contents of the fresh and saline components. Apparent ground-water ages determined from chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), and helium isotopes (3He and 4He) commonly were discordant, but nevertheless indicate that both fresh and saline ground waters ranged from a few years to at least 50 years in age. Tritium-helium (3H-3He) ages, tentatively judged to be most reliable, indicate that stratified offshore freshwater plumes originating in distant recharge areas on land were bounded by relatively young saline water that was recharged locally from the overlying estuary. Undenitrified and partially denitrified nitrate of agricultural or mixed origin was transported laterally beneath the estuary in oxic and suboxic fresh ground water. Ammonium produced by anaerobic degradation of organic matter in estuarine sediments was transported downward in suboxic saline ground water around the freshwater plumes. Many of the chemical and isotopic characteristics of the subestuarine ground waters are consistent with conservative mixing of the fresh (terrestrial) and saline (estuarine) endmember water types. These data indicate that freshwater plumes detected by geophysical surveys beneath Indian River Bay represent lateral continuations of the active surficial nitrate-contaminated freshwater flow systems originating on land, but they do not indicate directly the magnitude of fresh ground-water discharge or nutrient exchange with the estuary. There is evidence that some of the terrestrial ground-water nitrate is reduced before discharging directly beneath the estuary. Local estuarine sediment-derived ammonium in saline pore water may be a substantial benthic source of nitrogen in offshore areas of the estuary.

Delaware↗
USGS1976

Nitrogen and phosphorus uptake in the Everglades Conservation Areas, Florida, with special reference to the effects of backpumping runoff

In much of the water pumped into the northern Everglades, Florida, concentrations of inorganic nitrogen and phosphorus are relatively high. These nutrients are transported in the canals or into the peripheral marshes. Concentrations decrease sharply within 330 feet or less of the canals, whereas specific conductance remains essentially unchanged within this distance. The sharp decrease in inorganic nitrogen and phosphorus near the canal edge indicates net uptake in these shallow waters. Concentrations of nitrogen and phosphorus also decrease as water moves through the conservation areas in canals. This decrease is due partly to dilution by rainfall and runoff, and partly to net uptake in the canals and their peripheral marsh. The large canals of the northern and eastern parts of the conservation areas often have relatively low concentrations of dissolved oxygen which show little fluctuation within 24 hours. Backpumping 50 percent of the total annual canal runoff in southeast Florida would add from 990 to 6,160 tons of nitrogen and from 10 to 62 tons of phosphorus to the conservation areas. The bottom sediments of the Everglades are a sink for nitrogen and phosphorus. They can, however, be a source of these nutrients when anaerobic conditions exist at the water-sediment interface or when bottom material becomes resuspended. (Woodard-USGS)

Florida↗
USGS1979

Water-quality conditions in the New River, Imperial County, California

The New River, when entering the United States at Calexico, Calif., often contains materials which have the appearance of industrial and domestic wastes. Passage of some of these materials is recognized by a sudden increase in turbidity over background levels and the presence of white particulate matter. Water samples taken during these events are usually extremely high in organic content. During a 4-day reconnaissance of water quality in May 1977, white-to-brown extremely turbid water crossed the border on three occasions. On one of these occasions , the water was intensively sampled. The total organic-carbon concentration ranged from 80 to 161 milligrams per liter (mg/l); dissolved organic carbon ranged from 34 to 42 mg/l, and the chemical oxygen demand was as high as 510 mg/l. River profiles showed a dissolved-oxygen sag, with the length of the zone of depressed dissolved-oxygen concentrations varying seasonally. During the summer months, dissolved-oxygen concentrations in the river were lower and the zone of depressed dissolved-oxygen concentrations was longer. The largest increases in dissolved-oxygen concentration from reaeration occurred at the three drop structures and the rock weir near Seeley. The effects of oxygen demanding materials crossing the border extended as far as Highway 80, 19.5 miles downstream from the international boundary at Calexico. Fish kills and anaerobic conditions were also detected as far as Highway 80. Standard bacteria indicator tests for fecal contamination showed a very high health-hazard potential near the border. (Woodard-USGS)

California↗
USGS1984

Phenolic contamination in the sand-and-gravel aquifer from a surface impoundment of wood treatment wastes, Pensacola, Florida

Creosote and pentachlorophenol wastewaters discharged to unlined surface impoundments have resulted in groundwater contamination in the vicinity of an industrial site near Pensacola, Florida. Total phenol concentrations of 36,000 microgm/liter have been detected 40 ft below land surface in a test hole 100 ft south of an overflow impoundment but less than 10 microgm/liter 90 ft below land surface. Samples collected in test holes 1,350 ft downgradient from the surface impoundments and 100 ft north of Pensacola Bay, above and immediately below a clay lens, indicate that phenol contaminated groundwater may not be discharging directly into Pensacola Bay. Phenol concentrations exceeding 20 microgm/liter were detected in samples from a drainage ditch discharging directly into Bayou Chico. Microbiological data collected near the test site suggest that an anaerobic methanogenic ecosystem contributes to a reduction in phenol concentrations in groundwater. A laboratory study using bacteria isolated from the study site indicates that phenol, 2-methylphenol, and 3-methylphenol are significantly degraded and that methanogenesis reduces total phenol concentrations in laboratory digestors by 45%. Pentachlorophenol may inhibit methanogenesis at concentrations exceeding 0.45 milligm/liter. (USGS)

Water-Resources Investigations Report↗
USGS1987

Water-quality assessment of Arvada Reservoir, Denver metropolitan area, Colorado

Water quality data were collected from Arvada Reservoir, Colorado, and from its major inflows, Ralston Creek and Croke Canal, to assess the water quality of the reservoir, to evaluate the effect of water from various sources on the reservoir, and to estimate the trophic state of the reservoir. Data were collected at five sites in Arvada Reservoir, one site in Ralston Creek, and two sites in Croke Canal. The study began in June 1983 (just before filling in May 1984) and continued through September 1985. The reservoir was thermally stratified on most sampling dates from April through September. Dissolved-oxygen concentrations ranged from 0 to 12.0 milligrams per liter, and the reservoir was anaerobic below the 10-meter depth during most of the summer. Secchi-disk-depth measurements ranged from 0.9 to 5.5 meters and generally increased during the study period, possibly because of decreases in nonalgal turbidity after the reservoir was filled. Water from the reservoir generally is of suitable quality for a raw-water-supply source and for maintenance of aquatic life. Total-nitrogen and total-phosphorus concentrations were small, and both were growth-limiting factors in the reservoir. The phytoplankton community was diverse, and the most dominant taxa were diatoms. Phytoplankton densities ranged from 1,400 to 29,000 cells per millimeter, and chlorophyll alpha concentrations ranged from 0.0 to 20.4 micrograms per liter. (USGS)

Colorado↗
USGS1989

US Geological Survey Toxic Substances Hydrology Program: Proceedings of the technical meeting, Phoenix, Arizona, September 26-30, 1988

Crude oil floating at the surface of a shallow aquifer of glacial outwash, near Bemidji, Minnesota, is altered by geochemical processes. Hydrocarbons from the oil are attenuated by several reactions that include aerobic and anaerobic microbial degradation. These degradation reactions result in the development of geochemical facies in the shallow groundwater system. Groundwater most affected by the presence of organic compounds is anoxic, and concentrations of methane, dissolved organic carbon, and total inorganic are high--0.76 millimole/L, 2.9 millimole/L, and 12.3 millimole/L, respectively. The concentrations of chemical species and delta-(13)C isotope values indicate that the plume near the oil lens has become progressively more reducing. Over a 4-year period (1984 through 1987), the concentrations of methane and iron have increased by a factor of > 25. The data suggest that sequential degradation occurs, as predicted by thermo-dynamics: manganese is reduced before iron is reduced, which occurs before methanogenesis. These data provide field evidence that reduction of iron and manganese is an important mechanism of decomposition of organic matter in aquifers. The delta-(13)C values of inorganic carbon of the native groundwater range from -12 ppt to -15 ppt as a result of mixing of soil CO2 with CO2 from the dissolution of carbonates. Non methanogenic biodegradation of oil constituents adds isotopically light CO2 to the groundwater because the oil has a delta-(13)C value of 28 ppt. The delta-(13)C value of inorganic carbon in the reducing zone have become progressively heavier from 1985 through 1987. The maximum change occurs 15 m downgradient from the oil lens, where the delta-(13)C values increased from -21.6 ppt to -5.35 ppt. This change indicates that the plume has become more reducing and methanogenic over time.

Water-Resources Investigations Report↗
USGS1989

Hydrologic environments and water-quality characteristics at four landfills in Mecklenburg County, North Carolina, 1980-86

A water-quality study was conducted during 1980-86 at four landfills in Mecklenburg County, North Carolina. Each landfill has a three-layered hydrogeologic system typical of the Piedmont, consisting of (1) the regolith; (2) a transition zone; and (3) unweathered, fractured crystalline bedrock. As much as 7.6 inches per year of rainfall enters the ground-water system and has the potential to generate leachate within landfill cells. Ground water and leachate discharge to tributaries within the landfill sites or to streams adjacent to them. Water-quality samples were collected from 53 monitoring wells and 20 surface-water sites. Samples were analyzed for selected physical and biological characteristics, major inorganic ions, nutrients, trace elements, and organic compounds. Selected indicators of water quality, including specific conductance; hardness; and concentrations of chloride, manganese, dissolved solids, total organic carbon, and specific organic compounds were analyzed to determine the effects of each landfill on ground- and surface-water quality. Increases in concentrations of inorganic constituents above background levels were detected in ground water downgradient of the landfills. The increases were generally greatest in samples from wells in close proximity to the older landfill cells. In general, the increases in concentrations in downgradient wells were greater for calcium, magnesium, and chloride than for other major ions. Manganese exhibited the largest relative increase in concentration between upgradient and downgradient wells of any constituent, and manganese concentration data were effective in defining areas with extensive anaerobic biological activity. Differences between upgradient and downgradient concentrations of total organic carbon and specific organic compounds generally were not as apparent. The most frequently identified organic contaminants were the herbicides 2,4-D and 2,4,5-T. Chlorofluoromethanes were identified in three of four ground-water samples analyzed for volatile organic compounds. Landfills affected the water quality of several smaller streams but did not noticeably affect larger ones. Apparent effects on water quality were greatest at the oldest landfill, located on Statesville Road, where waste is in cells that are partly below the water table.

North Carolina↗
USGS1995

Ground-water flow and effects of agricultural application of sewage sludge and other fertilizers on the chemical quality of sediments in the unsaturated zone and ground water near Platteville, Colorado, 1985-89

From fall 1985 through 1989, 6,431 dry tons of anaerobic, digested, sewage sludge were applied as a fertilizer on about 1 square mile of sandy farm- land near Platteville, Colorado. Mean nitrite plus nitrate as nitrogen concentrations in the surficial aquifer increased during the period of sewage- sludge application. However, the effects of municipal sewage sludge applied to the soil in section 16 are difficult to ascertain because anhydrous ammonia and cattle and chicken manure were applied to section 16 prior to sewage-sludge application and anhydrous ammonia was applied during the period of sewage-sludge application. Mostly ammonia plus organic nitrogen was detected in the unsaturated zone while nitrite plus nitrate as nitrogen predominated in the surficial aquifer. The areas of largest concentrations of nitrite plus nitrate as nitrogen were in the northeastern and southwestern quarter sections os section 16. Changes in nitrite plus nitrate as nitrogen concentrations with depth and time were detected in water samples from the multilevel ground-water sampling devices in the surficial aquifer. Nitrogen probably entered the saturated zone in the irrigated areas and low temporarily ponded areas and moved to the northeast with water in the surficial aquifer.

Water-Resources Investigations Report↗
USGS1996

Initial effects of Stagecoach Reservoir on discharge, water-quality characteristics, and suspended-sediment loads in the Yampa River, northwestern Colorado

The construction and filling of Stagecoach Reservoir on the Yampa River during 1988-91 were done to enhance water management and to use local water resources. To assess the initial effects of the reservoir on the hydrology of the upper Yampa River, physical, chemical, and biological data were collected at a site upstream (YR-1) during water years 1989-92 and a site downstream (YR-2) from the reservoir during water years 1985-92 and at two sites in the reservoir during 1990-92. Annual suspended-sediment loads were determined for the Yampa River for water years 1985-92, and sediment retention in Stagecoach Reservoir was estimated. The initial filling of the 33,275-acre-foot reservoir proceeded slower than expected because inflow from the Yampa River was about 50 to 73 percent of average during water years 1989-91. Secchi-disk measurements in Stagecoach Reservoir ranged from 2.5 to 18 feet. Algal growth and sediment transport during stormy weather decreased water clarity, and possible algal grazing by zooplankton and sediment deposition improved water clarity. Water temperature in the reservoir ranged from 0 to 22 degrees Celsius, and thermal stratification was maintained during summer. Values of pH ranged from 7.2 in the hypolimnion to 8.9 in the epilimnion. Changes in pH were related to photosynthesis and respiration. Concentrations of dissolved oxygen in the reservoir ranged from 0 milligram per liter in the hypolimnion to 13 milligrams per liter in the epilimnion. Average 5-day biochemical-oxygen-demand rates ranged from 0.33 to 0.46 milligram per liter per day. Oxygen production from photosynthesis was greatest in the epilimnion; oxygen depletion from respiration was characteristic in the hypolimnion. Near or above average inflow might decrease the incidence of anaerobic conditions. Specific conductance in the reservoir ranged from 414 to 520 microsiemens per centimeter at 25 degrees Celsius, depending on the specific conductance of inflow from the Yampa River. The water was a very hard, calcium bicarbonate type. Nitrogen input to the reservoir was mostly as organic nitrogen that ranged in concentration from less than 0.18 to about 1.0 milligram per liter. Concentrations of dissolved phosphorus in the inflow of the Yampa River ranged from less than 0.01 to 0.06 milligram per liter. Decomposition of organic material and release of nutrients from sediments under reducing conditions were probable causes for dissolved-ammonia concentrations near the reservoir bottom to increase to maximum values of 0.9 to 1.6 milligrams per liter as nitrogen during thermal stratification in summer. Dissolved phosphorus also increased in the same conditions to a range of 0.32 to 0.35 milligram per liter. Except for concentrations of total recoverable manganese that ranged from 210 to 440 micrograms per liter near the reservoir bottom, most concentrations of 20 trace constituents were measured at or near analytical detection limits. A total of 119 phytoplankton from 7 phyla was identified in Stagecoach Reservoir during 1990-92. Cyanophyta (blue-green algae) accounted for most of the cell counts. Cyanophyta blooms of Aphanizomenon and Aphanocapsa developed during 1990-92, and photosynthesis caused concentrations of dissolved oxygen to exceed 150-percent saturation in the epilimnion. Diversity index values for phytoplankton ranged from 0.05 to 3.06. Values of diversity index during the summer of 1992 indicated that the community diversity of algae could be greatest in spring and least in fall. All colony counts of fecal coliform bacteria in the reservoir during 1990-92 were less than criteria limits set by the State of Colorado. During water years 1985-88 (preconstruction period), at a site on the Yampa River downstream from the proposed damsite, and water years 1989-92 (post-construction period), at a site upstream from the dam, annual loads of suspended sediment ranged from 2,480 to 22,650 tons. The average annual suspended-sediment load for th

Water-Resources Investigations Report↗
USGS1996

Hydraulic characteristics and nutrient transport and transformation beneath a rapid infiltration basin, Reedy Creek Improvement District, Orange County, Florida

The Reedy Creek Improvement District disposes of about 7.5 million gallons per day (1992) of reclaimed water through 85 1-acre rapid infiltration basins within a 1,000-acre area of sandy soils in Orange County, Florida. The U.S. Geological Survey conducted field experiments in 1992 at an individual basin to examine and better understand the hydraulic characteristics and nutrient transport and transformation of reclaimed water beneath a rapid infiltration basin. At the time, concentrations of total nitrogen and total phosphorus in reclaimed water were about 3 and 0.25 milligrams per liter, respectively. A two-dimensional, radial, unsaturated/saturated numerical flow model was applied to describe the flow system beneath a rapid infiltration basin under current and hypothetical basin loading scenarios and to estimate the hydraulic properties of the soil and sediment beneath a basin. The thicknesses of the unsaturated and saturated parts of the surficial aquifer system at the basin investigated were about 37 and 52 feet, respectively. The model successfully replicated the field-monitored infiltration rate (about 5.5 feet per day during the daily flooding periods of about 17 hours) and ground-water mounding response during basin operation. Horizontal and vertical hydraulic conductivity of the saturated part of the surficial aquifer system were estimated to be 150 and 45 feet per day, respectively. The field-saturated vertical hydraulic conductivity of the shallow soil, estimated to be about 5.1 feet per day, was considered to have been less than the full-saturation value because of the effects of air entrapment. Specific yield of the surficial aquifer was estimated to be 0.41. The upper 20 feet of the basin subsurface profile probably served as a system control on infiltration because of the relatively low field-saturated, vertical hydraulic conductivity of the sediments within this layer. The flow model indicates that, in the vicinity of the basin, flow in the deeper, saturated zone was relatively slow compared to the more vigorous flow in the shallow saturated zone. The large radial component of flow below the water table in the vicinity of the basin implies that reclaimed water moves preferentially in the shallow part of the saturated zone upon reaching the water table. Therefore, there may be some vertical stratification in the saturated zone, with recently infiltrated water overlying ambient water. The infiltration capacity at the basin would be unaffected by a small (less than 10 feet) increase in background water-table altitude, because the water table would remain below the system control on infiltration. However, water-table rises of 15 and 20 feet were estimated to reduce the infiltration capacity of the basin by 8 and 25 percent, respectively. Model simulations indicate that increasing ponded depth within the basin from 4 to 12 inches and from 4 to 24 inches would increase basin infiltration capacity by less than 6 and 11 percent, respectively. A loading strategy at the basin that relies on long, uninterrupted flooding was shown to offer the possibility of inducing a more anaerobic environment conducive to denitrification while maintaining reclaimed-water disposal capacity. Field measurements indicated that transient, elevated concentrations or "spikes" of nitrate (as high as 33 milligrams per liter as nitrogen) occurred at the leading edge of the infiltrating water and in the shallow saturated zone following a prolonged basin rest period. This phenomenon probably is the result of mineralization and nitrification of organic nitrogen retained within the subsurface during earlier basin loading events. The organic nitrogen was retained in the shallow soil (due to adsorption/straining) and the shallow saturated zone (due to deposition under slacking pore-water velocity). The magnitude of the nitrate spikes appears to be influenced by the scheduling of basin loading, with short flooding and resting periods being most favorable to minimization of nitrate spikes. Removal of nitrogen by denitrification from the percolating reclaimed water is minimal in the vicinity of the basin, probably because of the lack of reducing conditions and a relative paucity of organic carbon substrates. It is speculated that longer flooding periods could induce reducing conditions that would be favorable for nitrogen removal from the system, but probably would lead to more pronounced nitrate spiking. Phosphorus concentrations were decreased by about 90 percent from concentrations in reclaimed water after moving through the upper 15 feet of the soil profile. This most likely was a result of adsorption onto abundant iron and aluminum hydrous oxyhydroxide coatings on sand grains. However, some phosphorus (coarse fraction, organic) passes through the shallow soil and accumulates below the water table under slacking pore-water velocity. This phosphorus is immobilized by adsorption, fixation, or precipitation reactions during basin rest periods.

Florida↗
USGS1996

Geology, hydrogeology, and potential of intrinsic bioremediation at the National Park Service Dockside II site and adjacent areas, Charleston, South Carolina, 1993-94

A long history of industrial and commercial use of the National Park Service property and adjacent properties located in downtown Charleston, South Carolina, has caused extensive contamination of the shallow subsurface soils and water-table aquifer. The National Park Service property is located adjacent to a former manufactured-gas plant site, which is the major source of the contamination. Contamination of this shallow water-table aquifer is of concern because shallow ground water discharges to the Cooper River and contains contaminants, which may affect adjacent wildlife or human populations. The geology of the National Park Service property above the Ashley Formation of the Cooper Group consists of two Quaternary lithostratigraphic marine units, the Wando Formation and Holocene deposits, overlain by artificial fill. The Wando Formation overlies the Ashley Formation, a sandy calcareous clay, and consists of soft, organic clay overlain by gray sand. The Holocene deposits are composed of clayey to silty sand and soft organic-rich clay. The artificial fill, which was placed at the site to create dry land where salt marsh existed previously, is composed of sand, silt, and various scrap materials. The shallow hydrogeology of the National Park Service property overlying the Ashley Formation can be subdivided into two sandy aquifers separated by a leaky, black, organic-rich clay. The unconfined upper surficial aquifer is primarily artificial fill. The lower surficial aquifer consists of the Wando sand unit and is confined by the leaky organic-rich clay. Aquifer tests performed on the wells screened in these aquifers resulted in hydraulic conductivities from 0.1 to 10 feet per day for the upper surficial aquifer, and 16 feet per day for the lower surficial aquifer. Vertical hydraulic gradients at the site are typically low. A downward gradient from the upper surficial aquifer to the lower surficial aquifer occurs throughout most of the year. A brick-lined storm-water-drainage archway located in the study area is a conduit for the overflow of seawater into the surficial aquifer during exceptionally high tides. The efficiency of intrinsic bioremediation to reduce contaminant migration in the upper surficial aquifer at the National Park Service site was assessed to determine if, and at what concentrations, contaminants are being transported to the Cooper River. This assessment required incorporating hydrologic, geochemical, microbiologic, and demographic information into a predictive solute-transport model to determine rates of contaminant transport to the Cooper River. The transport of toluene and naphthalene was modeled as a surrogate for the transport of aromatic and other hydrocarbon compounds at the study area. Laboratory estimates of the adsorption coefficients for sediments of the upper surficial aquifer suggest preferential adsorption of naphthalene over toluene. The adsorption coefficient of naphthalene is at least two orders of magnitude greater than that determined for toluene. Laboratory microbial-biodegradation experiments indicate that microorganisms present in the shallow aquifer have the potential to degrade toluene under anaerobic and aerobic conditions, and naphthalene primarily under aerobic conditions. Rates of microbial biodegradation are similar for both compounds under aerobic conditions. Flow-model calibration to the January 1994 water-table surface of the upper surficial aquifer was achieved by specifying appropriate hydrogeologic boundary conditions and using hydraulic conductivity values determined in the field. The brick-lined storm-water drainage archway located in the study area was modeled to account for ground-water discharge through this drain. An exploratory modeling approach was used to evaluate the range of possible solutions that approximate the transport of contaminants to the observed distributions. Approximate toluene solute-transport conditions for January 1994 were estimated using velocity dist

South Carolina↗
USGS1998

Dissolved organic carbon concentrations and compositions, and trihalomethane formation potentials in waters from agricultural peat soils, Sacramento-San Joaquin Delta, California; implications for drinking-water quality

Water exported from the Sacramento-San Joaquin River delta (Delta) is an important drinking-water source for more than 20 million people in California. At times, this water contains elevated concentrations of dissolved organic carbon and bromide, and exceeds the U.S. Environmental Protection Agency's maximum contaminant level for trihalomethanes of 0.100 milligrams per liter if chlorinated for drinking water. About 20 to 50 percent of the trihalomethane precursors to Delta waters originates from drainage water from peat soils on Delta islands. This report elucidates some of the factors and processes controlling and affecting the concentration and quality of dissolved organic carbon released from peat soils and relates the propensity of dissolved organic carbon to form trihalomethanes to its chemical composition. Soil water was sampled from near-surface, oxidized, well-decomposed peat soil (upper soil zone) and deeper, reduced, fibrous peat soil (lower soil zone) from one agricultural field in the west central Delta over 1 year. Concentrations of dissolved organic carbon in the upper soil zone were highly variable, with median concentrations ranging from 46.4 to 83.2 milligrams per liter. Concentrations of dissolved organic carbon in samples from the lower soil zone were much less variable and generally slightly higher than samples from the upper soil zone, with median concentrations ranging from 49.3 to 82.3 milligrams per liter. The dissolved organic carbon from the lower soil zone had significantly higher aromaticity (as measured by specific ultraviolet absorbance) and contained significantly greater amounts of aromatic humic substances (as measured by XAD resin fractionation and carbon-13 nuclear magnetic resonance analysis of XAD isolates) than the dissolved organic carbon from the upper soil zone. These results support the conclusion that more aromatic forms of dissolved organic carbon are produced under anaerobic conditions compared to aerobic conditions. Dissolved organic carbon concentration, trihalomethane formation potential, and ultraviolet absorbance were all highly correlated, showing that trihalomethane precursors increased with increasing dissolved organic carbon and ultraviolet absorbance for whole water samples. Contrary to the generally accepted conceptual model for trihalomethane formation that assumes that aromatic forms of carbon are primary precursors to trihalomethanes, results from this study indicate that dissolved organic carbon aromaticity appears unrelated to trihalomethane formation on a carbon-normalized basis. Thus, dissolved organic carbon aromaticity alone cannot fully explain or predict trihalomethane precursor content, and further investigation of aromatic and nonaromatic forms of carbon will be needed to better identify trihalomethane precursors.

California↗
USGS1999

Ground-water quality in the eastern part of the Silurian-Devonian and upper Carbonate aquifers in the eastern Iowa basins, Iowa and Minnesota, 1996

Ground-water samples were collected from 33 domestic wells to assess the water quality of the eastern part of the Silurian-Devonian and Upper Carbonate aquifers in the Eastern Iowa Basins National Water-Quality Assessment Program study unit. Samples were collected during June and July 1996 and analyzed for major ions, nutrients, pesticides and pesticide metabolites, volatile organic compounds, tritium, radon222, and environmental isotopes. Calcium, magnesium, and bicarbonate were the dominant ions in most samples and were likely derived from the solution of carbonate minerals (calcite and dolomite) present in the aquifer materials. The dominance of sulfate in samples from several wells suggests the dissolution of evaporite minerals. Ammonia and orthophosphorus were the most commonly detected nutrients. Nitrate was detected in about half of the samples and exceeded the U.S. Environmental Protection Agency maximum contaminant level (10 milligrams per liter) in 6 percent of samples. Atrazine and metolachlor were the only pesticides detected and were present in 18 percent and 12 percent of samples, respectively. Alachlor ethanesulfonic acid and deethylatrazine were the most commonly detected pesticide metabolites and were present in 16 percent and 9 percent of samples, respectively. Radon-222 was detected in all samples, and 47 percent had concentrations in excess of the U.S. Environmental Protection Agency previously proposed maximum contaminant level (300 picocuries per liter). Radon-222 concentrations were significantly higher in samples from wells that produced recently recharged water. This relation suggests that uranium-bearing glacial deposits (Schumann, 1993) may be a source of radon-222 in the underlying aquifers. The presence of regional confining units and thick overlying Quaternary-age deposits have an effect on water quality in the Silurian-Devonian and Upper Carbonate aquifers in the study area. Tritium-based ground-water ages were significantly older, and dissolved-solids concentrations were significantly higher in relatively well protected areas (where the aquifers are overlain by a bedrock confining unit or more than 100 feet of Quaternary-age deposits). Ammonia concentrations were significantly higher in relatively well protected areas and in samples from wells that produced older water. Higher ammonia concentrations also were observed in ground water with dissolved-oxygen concentrations of 0.5 milligram per liter or less, allowing for the anaerobic reduction of nitrate to ammonia. Nitrate concentrations were significantly higher in relatively poorly protected areas (where the aquifers are not overlain by a bedrock confining unit or are overlain by less than 100 feet of Quaternaryage deposits) and in samples from wells that produced recently recharged water. Pesticide and metabolite concentrations were significantly higher in samples from wells that produced recently recharged water. Atrazine, metolachlor, and deethylatrazine were not detected in any samples from relatively well protected areas of the aquifers.

Iowa, Minnesota↗
USGS1999

Storage Capacity and Water Quality of Lake Ngardok, Babeldaob Island, Republic of Palau, 1996-98

A bathymetric survey conducted during March and April, 1996, determined the total storage capacity Lake Ngardok to be between 90 and 168 acre-feet. Elevation-surface area and elevation-capacity curves summarizing the current relations among elevation, surface area, and storage capacity were created from the bathymetric map. Rainfall and lake-elevation data collected from April 1996 to March 1998 indicated that lake levels correlated to rainfall values with lake elevation rising rapidly in response to heavy rainfall and then returning to normal levels within a few days. Mean lake elevation for the 22 month period of data was 59.5 feet which gives a mean storage capacity of 107 acre-feet and a mean surface area of 24.1 acre. A floating mat of reeds, which covered 58 percent of the lake surface area at the time of the bathymetric survey, makes true storage capacity difficult to estimate. Water-quality sampling during April 1996 and November 1997 indicated that no U.S. Environmental Protection Agency primary drinking-water standards were violated for analyzed organic and inorganic compounds and radionuclides. With suitable biological treatment, the lake water could be used for drinking-water purposes. Temperature and dissolved oxygen measurements indicated that Lake Ngardok is stratified. Given that air temperature on Palau exhibits little seasonal variation, it is likely that this pattern of stratification is persistent. As a result, complete mixing of the lake is probably rare. Near anaerobic conditions exist at the lake bottom. Low dissolved oxygen (3.2 milligrams per liter) measured at the outflow indicated that water flowing past the outflow was from the deep oxygen-depleted depths of the lake.

Water-Resources Investigations Report↗