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At least 487 records · Page 27Linked to original sources
USGS1996

Water-quality assessment of the Trinity River Basin, Texas - Nutrients in two coastal prairie streams draining agricultural areas, 1994-95

In 1991, the U.S. Geological Survey (USGS) began nationwide implementation of the National Water-Quality Assessment (NAWQA) Program. Long-term goals of NAWQA are to describe the status of and trends in the quality of a large, representative part of the Nation?s surface- and ground-water resources and to provide a sound, scientific understanding of the primary natural and human factors affecting the quality of these resources (Leahy and others, 1990). The Trinity River Basin in east-central Texas (fig. 1) was among the first 20 hydrologic areas, called study units, to be assessed by this program. The first intensive data-collection phase for the Trinity River Basin NAWQA began in March 1993 and ended in September 1995. Streams in the Trinity River Basin were assessed by sampling water, bed sediment, and tissue of biota and characterizing the aquatic communities and their habitat. Aquifers were assessed by sampling water from wells. The coastal prairie is a small part of the Trinity River Basin, but it is environmentally important because of its proximity to Galveston Bay and the extensive use of agricultural chemicals on many irrigated farms. Galveston Bay (fig. 1) was selected by Congress as an estuary of national significance and was included on a priority list for the National Estuary Program. The Trinity River is especially important because its watershed dominates the total Galveston Bay drainage area and because its flow contributes substantial amounts of freshwater and water-quality constituents to the bay. Historically, measurements of the quantity and quality of water entering Galveston Bay from the Trinity River Basin have been made using data from a station about 113 kilometers (70 miles) upstream from Trinity Bay, an inlet bay to Galveston Bay. With a focused objective of providing additional water-quality information in the intervening coastal prairie area and an overall objective of improving the understanding of the relations between farming practices and stream quality in the Trinity River Basin, a special study was conducted. This report provides a description of the occurrence and concentrations of nutrients in two streams in this intervening area. An earlier report by Brown (1996) describes the occurrence and concentrations of pesticides in these two streams. An overall analysis of nutrient data collected during 1974?91 in the Trinity River Basin is given by Van Metre and Reutter (1995).

Open-File Report↗
USGS2000

Organochlorine pesticides and PCBs in stream sediment and aquatic biota—initial results from the National Water-Quality Assessment Program, 1992–1995

One of the goals of the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey is to assess the status and trends in the nation's water quality and to understand the natural and anthropogenic factors that affect water-quality conditions. This report summarizes the occurrence and distribution of 33 organochlorine compounds in fluvial bed sediment and aquatic biota (whole freshwater fish and freshwater bivalves) sampled by NAWQA investigations between 1991 and 1994. These include historically used insecticides (DDT and metabolites, chlordane and its various components, and dieldrin), some currently used pesticides (permethrin and dacthal) and some industrial chemicals and byproducts (PCBs and hexaclorobenzene). Samples were collected at approximately 500 sites in 19 large hydrologic basins throughout the United States. Contaminant levels in bed sediment and aquatic biota are summarized, first on a national basis, and then by land-use classification (for example, urban, cropland, pasture and rangeland, and forest). Nationally, detection frequencies are highest in sediment and biota for the more persistent organochlorine compounds: total DDT, total chlordane, dieldrin, and total PCBs. Organochlorine compounds were detected more frequently in whole fish than in bivalves or bed sediment. Organochlorine pesticide concentrations were relatively high in agricultural regions with histories of high use. The highest organochlorine compound concentrations in both sediment and biota generally were associated with urban areas. Some organochlorine concentrations in sediment exceeded guidelines for the protection of aquatic organisms. A screening-level comparison of measured organochlorine concentrations in whole fish was made with human health guidelines that are applicable to edible fish. This comparison indicates stream sites at which additional sampling of game fish fillets may be warranted, depending on local patterns of fish consumption. A comparison of current national contaminant levels with previous studies of this scope suggests a gradual decrease in organochlorine contaminant levels, at least in fish.

Water-Resources Investigations Report↗
USGS2006

The Model Parameter Estimation Experiment (MOPEX): Its structure, connection to other international initiatives and future directions

The Model Parameter Estimation Experiment (MOPEX) is an international project aimed at developing enhanced techniques for the a priori estimation of parameters in hydrological models and in land surface parameterization schemes connected to atmospheric models. The MOPEX science strategy involves: database creation, a priori parameter estimation methodology development, parameter refinement or calibration, and the demonstration of parameter transferability. A comprehensive MOPEX database has been developed that contains historical hydrometeorological data and land surface characteristics data for many hydrological basins in the United States (US) and in other countries. This database is being continuously expanded to include basins from various hydroclimatic regimes throughout the world. MOPEX research has largely been driven by a series of international workshops that have brought interested hydrologists and land surface modellers together to exchange knowledge and experience in developing and applying parameter estimation techniques. With its focus on parameter estimation, MOPEX plays an important role in the international context of other initiatives such as GEWEX, HEPEX, PUB and PILPS. This paper outlines the MOPEX initiative, discusses its role in the scientific community, and briefly states future directions.

IAHS-AISH Publication↗
USGS2014

Optical sensors for water quality

Shifts in land use, population, and climate have altered hydrologic systems in the United States in ways that affect water quality and ecosystem function. Water diversions, detention in reservoirs, increased channelization, and changes in rainfall and snowmelt are major causes, but there are also more subtle causes such as changes in soil temperature, atmospheric deposition, and shifting vegetation patterns. The effects on water quality are complex and interconnected, and occur at timeframes of minutes (e.g., flash floods) to decades (e.g., evolving management practices). However, water-quality monitoring has historically focused on discrete samples collected weekly or monthly, and laboratory analyses that can take days or weeks to complete. Low-frequency data and delayed access hampers a timely response during events, limits the ability to identify specific causes or actions, and may result in poorly quantified effects on ecosystems and human health at local to regional scales. Recent advancements in commercially available in situ sensors, data platforms, and new techniques for data analysis provide an opportunity to monitor water quality in rivers, lakes, and estuaries on the time scales in which changes occur. For example, measurements that capture the variability in freshwater systems over time help to assess how shifts in seasonal runoff, changes in precipitation intensity, and increased frequencies of disturbances (such as fire and insect outbreaks) affect the storage, production, and transport of carbon and nitrogen in watersheds. Transmitting these data in real-time also provides information that can be used for early trend detection, help identify monitoring gaps, and provide sciencebased decision support across a range of issues related to water quality, freshwater ecosystems, and human health.

Lakeline↗
USGS2011

Ecosystem services provided by playas in the High Plains: potential influences of USDA conservation programs

Playas are shallow depressional wetlands and the dominant wetland type in the non-glaciated High Plains of the United States. This region is one of the most intensively cultivated regions in the Western Hemisphere, and playas are profoundly impacted by a variety of agricultural activities. Conservation practices promoted through Farm Bills by the U.S. Department of Agriculture (USDA) that influence playas and surrounding catchments impact ecosystem functions and related services provided by wetlands in this region. As part of a national assessment, we review effects of agricultural cultivation and effectiveness of USDA conservation programs and practices on ecosystem functions and associated services of playas. Services provided by playas are influenced by hydrological function, and unlike other wetland types in the United States, hydrological function of playas is impacted more by accumulated sediments than drainage. Most playas with cultivated catchments have lost greater than 100% of their volume from sedimentation causing reduced hydroperiods. The Conservation Reserve Program (CRP) has the largest influence on playa catchments (the High Plains has >2.8 million ha), and associated sedimentation, of any USDA program. Unfortunately, most practices applied under CRP did not consider restoration of playa ecosystem function as a primary benefit, but rather established dense exotic grass in the watersheds to reduce soil erosion. Although this has reduced soil erosion, few studies have investigated its effects on playa hydrological function and services. Our review demonstrates that the Wetlands Reserve Program (WRP) has seldom been applied in the High Plains outside of south-central Nebraska. However, this is the primary program that exists within the USDA allowing conservation practices that restore wetland hydrology such as sediment removal. In addition to sediment removal, this practice has the greatest potential effect on improving hydrologic function by reducing sedimentation in vegetative buffer strips. We estimate that a 50-m native-grass buffer strip could improve individual playa hydroperiods by up to 90 days annually, enhancing delivery of most natural playa services. The potential for restoration of playa services using USDA programs is extensive, but only if WRP and associated practices are promoted and playas are considered an integral part of CRP contracts.

Colorado, Kansas, Nebraska, New Mexico, Oklahoma, ↗
USGS2020

Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and northern Chihuahua, Mexico

Changes in population, agricultural development and practices (including shifts to more water-intensive crops), and climate variability are increasing demands on available water resources, particularly groundwater, in one of the most productive agricultural regions in the Southwest—the Rincon and Mesilla Valley parts of Rio Grande Valley, Doña Ana and Sierra Counties, New Mexico, and El Paso County, Texas. The goal of this study was to produce an integrated hydrological simulation model to help evaluate water-management strategies, including conjunctive use of surface water and groundwater for historical conditions, and to support long-term planning for the Rio Grande Project. This report describes model construction and applications by the U.S. Geological Survey, working in cooperation and collaboration with the Bureau of Reclamation. This model, the Rio Grande Transboundary Integrated Hydrologic Model, simulates the most important natural and human components of the hydrologic system, including selected components related to variations in climate, thereby providing a reliable assessment of surface-water and groundwater conditions and processes that can inform water users and help improve planning for future conditions and sustained operations of the Rio Grande Project (RGP) by the Bureau of Reclamation. Model development included a revision of the conceptual model of the flow system, construction of a Transboundary Rio Grande Watershed Model (TRGWM) water-balance model using the Basin Characterization Model, and construction of an integrated hydrologic flow model with MODFLOW-One-Water Hydrologic Flow Model version 2 (referred to as MF-OWHM2). The hydrologic models were developed for and calibrated to historical conditions of water and land use, and parameters were adjusted so that simulated values closely matched available measurements (calibration). The calibrated model was then used to assess the use and movement of water in the Rincon Valley, Mesilla Basin, and northern part of the Conejos-Médanos Basin, with the entire region referred to as the “Transboundary Rio Grande” or TRG. These tools provide a means to understand hydrologic system response to the evolution of water use in the region, its availability, and potential operational constraints of the RGP. The conceptual model identified surface-water and groundwater inflows and outflows that included the movement and use of water both in natural and in anthropogenic systems. The groundwater-flow system is characterized by a layered geologic sedimentary sequence combined with the effects of groundwater pumping, operation of the RGP, natural runoff and recharge, and the application of irrigation water at the land surface that is captured and reused in an extensive network of canals and drains as part of the conjunctive use of water in the region. Historical groundwater-level fluctuations followed a cyclic pattern that were aligned with climate cycles, which collectively resulted in alternating periods of wet or dry years. Periods of drought that persisted for one or more years are associated with low surface-water availability that resulted in higher rates of groundwater-level decline. Rates of groundwater-level decline also increased during periods of agricultural intensification, which necessitated increasing use of groundwater as a source of irrigation water. Agriculture in the area was initially dominated by alfalfa and cotton, but since 1970 more water-intensive pecan orchards and vegetable production have become more common. Groundwater levels substantially declined in subregions where drier climate combined with increased demand, resulting in periods of reduced streamflows. Most of the groundwater was recharged in the Rio Grande Valley floor, and most of the pumpage and aquifer storage depletion was in Mesilla Basin agricultural subregions. A cyclic imbalance between inflows and outflows resulted in the modeled cyclic depletion (groundwater withdrawals in excess of natural recharge) of the groundwater basin during the 75-year simulation period of 1940–2014. Changes in groundwater storage can vary considerably from year to year, depending on land use, pumpage, and climate conditions. Climatic drivers of wet and dry years can greatly affect all inflows, outflows, and water use. Although streamflow and, to a minor extent, precipitation during inter-decadal wet-year periods replenished the groundwater historically, contemporary water use and storage depletion could have reduced the effects of these major recharge events. The average net groundwater flow-rate deficit for 1953–2014 was estimated to be about 1,090 acre-feet per year.

Chihuahua, New Mexico, Texas↗
USGS2022

New projections of 21st century climate and hydrology for Alaska and Hawaiʻi

In the United States, high-resolution, century-long, hydroclimate projection datasets have been developed for water resources planning, focusing on the contiguous United States (CONUS) domain. However, there are few statewide hydroclimate projection datasets available for Alaska and Hawaiʻi. The limited information on hydroclimatic change motivates developing hydrologic scenarios from 1950 to 2099 using climate-hydrology impact modeling chains consisting of multiple statistically downscaled climate projections as input to hydrologic model simulations for both states. We adopt an approach similar to the previous CONUS hydrologic assessments where: 1) we select the outputs from ten global climate models (GCM) from the Coupled Model Intercomparison Project Phase 5 with Representative Concentration Pathways 4.5 and 8.5; 2) we perform statistical downscaling to generate climate input data for hydrologic models (12-km grid-spacing for Alaska and 1-km for Hawaiʻi); and 3) we perform process-based hydrologic model simulations. For Alaska, we have advanced the hydrologic model configuration from CONUS by using the full water-energy balance computation, frozen soils and a simple glacier model. The simulations show that robust warming and increases in precipitation produce runoff increases for most of Alaska, with runoff reductions in the currently glacierized areas in Southeast Alaska. For Hawaiʻi, we produce the projections at high resolution (1 km) which highlight high spatial variability of climate variables across the state, and a large spread of runoff across the GCMs is driven by a large precipitation spread across the GCMs. Our new ensemble datasets assist with state-wide climate adaptation and other water planning.

Alaska, Hawaii↗
USGS2008

Hydrogeology of the Islamic Republic of Mauritania

Hydrogeologic maps were constructed for the Islamic Republic of Mauritania. The ground-water flow system in the country can best be described as two interconnected regional systems: the porous Continental Terminal coastal system and the interior, fractured sedimentary Taoudeni Basin system. In these systems, ground-water flow occurs in fill deposits and carbonate, clastic, metasedimentary, and metavolcanic rocks. Based on an evaluation of the potentiometric surface, there are three areas of ground-water recharge in the Taoudeni Basin system. One region occurs in the northwest at the edge of the Shield, one occurs to the south overlying the Tillites, and one is centered at the city of Tidjikdja. In contrast to the flow system in the Taoudeni Basin, the potentiometric surfaces reveal two areas of discharge in the Continental Terminal system but no localized recharge areas; the recharge is more likely to be areal. In addition to these recharge and discharge areas, ground water flows across the country's borders. Specifically, ground water from the Atlantic Ocean flows into Mauritania, transporting dissolved sodium from the west as a salt water intrusion, whereas fresh ground water discharges from the east into Mali. To the north, there is a relatively low gradient with inflow of fresh water to Mauritania, whereas ground-water flow discharges to the Senegal River to the south. A geographical information system (GIS) was used to digitize, manage, store, and analyze geologic data used to develop the hydrogeologic map. The data acquired for map development included existing digital GIS files, published maps, tabulated data in reports and public-access files, and the SIPPE2 Access database. Once in digital formats, regional geologic and hydrologic features were converted to a common coordinate system and combined into one map. The 42 regional geologic map units were then reclassified into 13 hydrogeologic units, each having considerable lateral extent and distinct hydrologic properties. Because the hydrologic properties of these units are also influenced by depth and degree of fracturing, the hydraulic conductivity values of these hydrogeologic units can range over many orders of magnitude.

Open-File Report↗
USGS1973

Analog-model studies of the effects of recharge wells along the Houston Ship Channel on potentiometric surfaces of the Chicot and Evangeline aquifers, Houston, Texas

Because of increasing concern about the continuing decline of water levels in the Houston area, an electric analog model was used to determine the effects on the potentiometric surfaces resulting from recharging water through wells along the Houston Ship Channel into the two major aquifers, the Chicot and Evangeline. The model conditions simulated for this study are too complex to be described in detail. The upper model layer simulated the hydrologic conditions in the lower unit of the Chicot aquifer undifferentiated. The simulation included clay compaction and vertical leakage as well as transmissivity and storage. The lower model layer simulated the hydrologic conditions in the Evangeline aquifer which underlies the Chicot aquifer.

Texas↗
USGS1991

Correlation of regional geohydrologic units to geological formations in southern Missouri

As part of the U.S Geological Survey's Regional Aquifer-System Analysis Program, geologic formations in southern Missouri (index map) were grouped into eight regional geohydrologic units on the basis of relative rock permeability and well yields (imes and Emmett, in press). Geohydrologic unit boundaries do not necessarily coincide with geologic unit boundaries or geologic time lines, but are determined by regional hydrologic properties, which may vary from one area to another. The geologic formaitons were grouped into the geohydrologic units to determine the hydrologic characteristics of regional aquifer systems and associated regional confining units in parts of Arkansas, Kansas,Missouri, and Oklahoma. This report presents a correlation of the regional geohydrologic units to corresponding geologic formations in southern Missouri. Included in the report is a brief geologic history of southern Missouri.

Missouri↗
USGS1994

Miocene and Pliocene lacustrine and fluvial sequences, Upper Ramparts and Canyon village, Porcupine river, east-central Alaska

Cenozoic strata exposed along the Porcupine River between the Upper Ramparts and Canyon Village, Alaska, can be divided into five unconformity-bounded units (sequences) which are: lower and middle Miocene unit A, the white sandy fluvial sequence with peat beds; middle Miocene unit B, the basalt sequence-part B1 is basalt, and part B2 is organic-rich sedimentary beds; upper Miocene unit C, mudrock-dominated lake sequence; late Miocene or Pliocene to Pleistocene unit D, terrace gravels, detrital organic matter and associated sediments, and Holocene unit E, mixed sand and gravel-rich sediment and other sedimentary material including peat and eolian silt. The sequence (unit A) of lower and middle Miocene fluvial deposits formed in streams and on flood plains, just before the inception of local volanism. Fossil pollen from unit A suggests conifer-dominated regional forests and cool temperate climates. Peat beds and lake deposits from unit B contain pollen that indicates a warmer temperate climate coinciding with the middle Miocene thermal maximum. The lake deposits (unit C) downstream from the basalts accumulated in a small basin which resulted from a hydrologic system that was dammed in the late Miocene but breached soon thereafter. The lower part of the terrace gravels (unit D) expresses breaching of the dammed hydrologic system (of unit C). The Porcupine River became a major tributary of the Yukon River in late Pleistocene time when Laurentide ice blocked drainage from the Yukon interior basins causing meltwater to spill over the low divide separating it from the Porcupine River drainage initiating erosion and capture of the Yukon interior basins. ?? 1994.

Quaternary International↗
USGS2010

Reclaiming freshwater sustainability in the Cadillac Desert

Increasing human appropriation of freshwater resources presents a tangible limit to the sustainability of cities, agriculture, and ecosystems in the western United States. Marc Reisner tackles this theme in his 1986 classic Cadillac Desert: The American West and Its Disappearing Water . Reisner's analysis paints a portrait of region-wide hydrologic dysfunction in the western United States, suggesting that the storage capacity of reservoirs will be impaired by sediment infilling, croplands will be rendered infertile by salt, and water scarcity will pit growing desert cities against agribusiness in the face of dwindling water resources. Here we evaluate these claims using the best available data and scientific tools. Our analysis provides strong scientific support for many of Reisner's claims, except the notion that reservoir storage is imminently threatened by sediment. More broadly, we estimate that the equivalent of nearly 76% of streamflow in the Cadillac Desert region is currently appropriated by humans, and this figure could rise to nearly 86% under a doubling of the region's population. Thus, Reisner's incisive journalism led him to the same conclusions as those rendered by copious data, modern scientific tools, and the application of a more genuine scientific method. We close with a prospectus for reclaiming freshwater sustainability in the Cadillac Desert, including a suite of recommendations for reducing region-wide human appropriation of streamflow to a target level of 60%.

Proceedings of the National Academy of Sciences of↗
USGS2022

Hydrogeology and simulation of groundwater flow in the Lucerne Valley groundwater basin, California

The Lucerne Valley is in the southwestern part of the Mojave Desert and is about 75 miles northeast of Los Angeles, California. The Lucerne Valley groundwater basin encompasses about 230 square miles and is separated from the Upper Mojave Valley groundwater basin by splays of the Helendale Fault. Since its settlement, groundwater has been the primary source of water for agricultural, industrial, municipal, and domestic uses. Groundwater withdrawal from pumping has exceeded the amount of water recharged to the basin, causing groundwater declines of more than 100 feet between 1917 and 2016 in the center of the basin. The continued withdrawal has resulted in an increase in pumping costs, reduced well efficiency, and land subsidence near Lucerne Lake. Although the volume of pumping has declined in recent years, there is concern that new agricultural growth and limits on imported water will continue to strain the sustainability of the groundwater system. To address these concerns, the U.S. Geological Survey entered into a cooperative agreement with the Mojave Water Agency to develop a better understanding of the Lucerne Valley hydrogeologic system and provide tools to help evaluate and manage the effects of future development in the Lucerne Valley. The objectives of this study were to (1) improve the understanding of the aquifer system, (2) improve the understanding of subsidence in the basin, and (3) incorporate the understanding into a groundwater-flow model that can be used to help manage the groundwater resources in the Lucerne Valley. The model developed for this study covers the period of 1942–2016 and can help evaluate various proposed water-management scenarios during different climatic and hydrologic conditions. The aquifer system consists of a shallow aquifer, a confining unit, and middle and lower aquifers. These layered water-bearing units were identified based on geologic units of the mostly unconsolidated sediments and hydrologic properties. These alluvial deposits consist of clay, silt, sand, and gravel; some places also contain clay and silty clay lacustrine deposits. Several faults act, at least in part, as barriers to groundwater flow on the eastern, southern, and western edges of the basin. Present-day natural recharge is primarily from the infiltration of runoff from the San Bernardino Mountains to the south; however, stable and radioactive isotopes show that groundwater from the middle of the Lucerne Valley was older than about 10,000 years and probably was recharged as infiltration from streams draining the mountains in the Mojave Desert to the north, which probably does not occur under present-day climatic conditions. The annual average natural recharge for 1942–2016, estimated by a Basin Characterization Model, was about 635 acre-feet per year; the average amount of treated wastewater effluent transferred to the Lucerne Valley for artificial recharge annually ranged from about 1,500 to 4,000 acre-feet per year during 1980–2016. Pumpage estimates for 1942–2016 ranged from about 3,000 acre-feet in 1942 to about 18,300 acre-feet in 1984. The total cumulative amount of groundwater removed from the basin by pumping between 1942 and 2016 was estimated to be about 700,000 acre-feet, which was about 10 times greater than the cumulative amount of recharge to the entire Lucerne Valley groundwater basin. Before groundwater development, the direction of groundwater flow was from the southern part of the basin northward to discharge areas near Lucerne Lake, where it discharged through springs along the Helendale Fault and by evapotranspiration. Since the early 1900s, groundwater-level declines have mostly eliminated the areas where natural discharge occurred and exceeded 100 feet in the middle of the basin between the early 1950s and mid-1990s, and as much as 25 feet near the margins from about the mid-1950s to 2000s. A decrease in the rate of pumping after the mid-1990s lessened the hydraulic stress on the middle and lower aquifers and enabled hydraulic heads in the middle of the basin to recover slightly as groundwater near the margins of the basin moved toward the pumping depression. Although trends in groundwater levels in the center of the basin have reversed since the mid-1990s, levels at the basin margins continue to decline as the movement of groundwater from the margins fills the pumping depression and gradually flattens the groundwater table throughout the basin. The long-term extraction of groundwater and associated dewatering of the fine-grained sediments present within the aquifer system has resulted in aquifer compaction and consequently land subsidence, primarily near Lucerne Lake. Analysis of interferometric synthetic aperture radar data shows that almost 11 inches of land subsidence has occurred south of Lucerne Lake between April 1992 and November 2009; less subsidence occurred elsewhere in the basin during this period. This differential land subsidence has caused fissures and cracks in the ground surface, which have buckled the pavement and undercut roads in several locations. The Lucerne Valley Hydrologic Model was developed using the finite-difference groundwater modeling software One Water Hydrologic Model to represent the hydrologic conditions and stresses during 1942–2016. The model has a uniform grid of approximately 92 acres per cell (2,000 feet by 2,000 feet) and has four layers representing the water-bearing units. The results from the calibrated model simulations indicated that groundwater pumpage exceeded recharge, resulting in an estimated net cumulative depletion of groundwater storage (discharge minus recharge) of about 465,000 acre-feet from 1942 to 2016. The model simulated as much as 7.5 feet (90 inches; 2,286 millimeters) of aquifer compaction, which indicates the extensive fine-grained deposits and measured subsidence near Lucerne Lake.

California↗
USGS1994

National Water-Quality Assessment Program: The Sacramento River Basin

In 1991, the U.S. Geological Survey (USGS) began to implement a full-scale National Water-Quality Assessment (NAWQA) program. The long-term goals of the NAWQA program are to describe the status of and trends in the quality of a large, representative part of the Nation's surface- and ground-water resources and to identify the major natural and human factors that affect the quality of those resources. In addressing these goals, the program will provide a wealth of water- quality information that will be useful to policy makers and managers at the national, State, and local levels. A major asset of the NAWQA program is that it will allow for the integration of water-quality information collected at several scales. A major component of the program is the study-unit investigation-the foundation of national- level assessment. The 60 study units of the NAWQA program are hydrologic systems that include parts of most major river basins and aquifer systems of the conterminous United States. These study units cover areas of 1,000 to more than 60,000 square miles and represent 60 to 70 percent of the Nation's water use and population served by public water supplies. Investigations of the first 20 study units began in 1991. In 1994, the Sacramento River Basin was among the second set of 20 NAWQA study units selected for investigation.

Fact Sheet↗
USGS2010

Groundwater Hydrology and Chemistry in and near an Emulsified Vegetable-Oil Injection Zone, Solid Waste Management Unit 17, Naval Weapons Station Charleston, North Charleston, South Carolina, 2004-2009

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated the hydrology and groundwater chemistry in the vicinity of an emulsified vegetable-oil injection zone at Solid Waste Management Unit (SWMU) 17, Naval Weapons Station Charleston, North Charleston, South Carolina. In May 2004, Solutions-IES initiated a Phase-I pilot-scale treatability study at SWMU17 involving the injection of an edible oil emulsion into the aquifer near wells 17PS-01, 17PS-02, and 17PS-03 to treat chlorinated solvents. The Phase-I injection of emulsified vegetable oil resulted in dechlorination of trichloroethene (TCE) to cis-1,2-dichloroethene (cDCE), but the dechlorination activity appeared to stall at cDCE, with little further dechlorination of cDCE to vinyl chloride (VC) or to ethene. The purpose of the present investigation was to examine the groundwater hydrology and chemistry in and near the injection zone to gain a better understanding of the apparent remediation stall. It is unlikely that the remediation stall was due to the lack of an appropriate microbial community because groundwater samples showed the presence of Dehalococcoides species (sp.) and suitable enyzmes. The probable causes of the stall were heterogeneous distribution of the injectate and development of low-pH conditions in the injection area. Because groundwater pH values in the injection area were below the range considered optimum for dechlorination activity, a series of tests was done to examine the effect on dechlorination of increasing the pH within well 17PS-02. During and following the in-well pH-adjustment tests, VC concentrations gradually increased in some wells in the injection zone that were not part of the in-well pH-adjustment tests. These data possibly reflect a gradual microbial acclimation to the low-pH conditions produced by the injection. In contrast, a distinct increase in VC concentration was observed in well 17PS-02 following the in-well pH increase. Adjustment of the pH to near-neutral values in well 17PS-02 may have made that well relatively favorable to VC production compared with much of the rest of the injection zone, possibly accounting for acceleration of VC production at that well. Following a Phase-II injection in which Solutions-IES, Inc., injected pH-buffered emulsified vegetable oil with an improved efficiency injection approach, 1,1-dichloroethene, TCE, and cDCE rapidly decreased in concentration and are now (2009) undetectable in the injection zone, with the exception of a low concentration (43 micrograms per liter, August 2009) of cDCE in well 17PS-01. In August 2009, VC was still present in groundwater at the test wells in concentrations ranging from 150 to 640 micrograms per liter. The Phase-II injection, however, appears to have locally decreased aquifer permeability, possibly resulting in movement of contamination around, rather than through, the treatment area.

North Carolina↗