bluuebunny/crossref_metadata_2025 huggingface dataset:
Screen Filters for Microirrigation
Authors: Haman Dorota Z.
Published: July 2005

Screen filters are simple and economical filtration devices of various shapes and sizes that are frequently used for the removal of physical contaminants. They can be made of metal, plastic, or synthetic cloth enclosed in a special housing. Screen filters are recommended for the removal of very fine sand or larger sized inorganic debris from irrigation water. It is normally not effective to use screen filters for the removal of heavy loads of algae or other organic material typical in surface water supply, since screens clog rapidly, requiring too frequent cleaning to be practical. Selection of a filter depends on the type and amount of contaminants in the irrigation water, the type of emitters, the size of the irrigation system, and the desired management practices. Screen filters should be a primary choice when water is pumped from a well where the only filtration requirement is to remove mineral particulate matter. They are sufficient in the absence of organic contamination and in addition they are usually inexpensive and easy to maintain.
Large Area Surface Energy Balance Estimation Using Satellite Imagery
Authors: Arasteh Peyman Daneshkar
Published: July 2005

All climatic and hydrologic phenomena in the atmosphere and on the earth's surface are affected by the energy balance at the surface. The energy balance is one of the main subjects in climatology, hydrology, civil and traffic engineering, biology, and health.

Photosynthesis and other metabolic processes in green plants, evaporation from free water and soil surfaces, and atmospheric and oceanic circulation are functions of the surface energy balance.

Due to the nonuniform properties of the earth's surface (albedo, heat capacity, soil cover, etc.), the Earth's surface, phenomena must be monitored on continuous and simultaneous spatial scales. Satellite imagery provides a large view of the earth's surface. Such a spatially continuous, but time discrete, data acquisition system provides a suitable framework for distributed modeling, provided that the phenomenon to be modeled has spectral behavior.

For energy balance processing, visible (VIS), near infrared (NIR), and thermal infrared (TIR) channels are used. Some primary surface parameters such as surface albedo, surface temperature, air temperature, surface roughness, land cover, and land use may be provided by remote sensing.

In this article, inferring energy balance components using remotely sensed data and some common methods in this respect are introduced. Then, the energy components of the Hamoon Wetlands are described as a case study, and some Internet sources of the satellite‐based global energy budget are introduced.
Measuring and Modeling Tree and Stand Level Transpiration
Authors: Vose J. M. , Harvey G. J. , Elliott K. J. , Clinton B. D.
Published: July 2005

Transpiration is a key process in the application of phytoremediation to soil or groundwater pollutants. To be successful, vegetation must transpire enough water from the soil or groundwater to control or take up the contaminant. Transpiration is driven by a combination of abiotic (climate, soil water availability, and groundwater depth) and biotic (leaf area, stomatal functions, root amount and distribution, and hydraulic characteristics) that need to be evaluated when considering appropriate site and species combinations. The protocols are not trivial, but transpiration can be measured at a variety of scales using techniques such as direct measurements of sap flow on individual trees, eddy flux gradient analyses, or gauged watersheds. Alternatively, models can be used to estimate transpiration, but these usually require on‐site calibration or parameterization to produce accurate predictions. Case study analyses across a range of site conditions and species indicate a maximum transpiration capacity of approximately 7.5 × 106liters of water per hectare per year (8 × 105gallons of water per acre per year), with a range of 1.5 × 106to 7.5 × 106liters per hectare per year (1.6 × 105to 8 × 105gallons per acre per year). Variation among sites is related to species, tree size, and stocking (i.e., vegetation density) differences. Application of a physiologically based and site‐specific parameterized model suggests reasonable agreement between measured and predicted transpiration estimates for the Air Force Plant 4 site in central Texas.
Plant and Microorganism Selection for Phytoremediation of Hydrocarbons and Metals
Authors: Mcintyre T. C.
Published: July 2005

Information on plants and other organisms that have the potential for phytoremediation of contaminants aids in the planning and establishment of removal and restoration projects for contaminated sites. Environment Canada is compiling databases on plants, bacteria, fungi, and other organisms that remediate petroleum hydrocarbons and accumulate metals and metalloids. The databases PHYTOPET (for PHYTOremediation of PETroleum hydrocarbon contaminants) and PHYTOREM (for PHYTOREmediation of Metals) are user‐friendly, searchable, and summarize all the known literature. Environment Canada has also drafted a Protocol, “Environmental Technology Verification (ETV) Protocol for Metal Contaminants.” The program provides suppliers of specified environmental technologies and services that meet the required criteria, with the right to use the licensed ETV verification mark.
Pesticide Occurrence and Distribution in Relation to Use
Authors: Chu Xuefeng
Published: July 2005

Widespread use of a variety of pesticides has led to their occurrence in both surface and groundwaters. The occurrence and distribution of pesticides in the environment are closely related to their use and are determined by a series of pesticide transport and transformation processes. The occurrence and use of pesticides follow extremely complex and dynamic patterns that are affected by numerous factors related to pesticide properties, pesticide use, hydrology, and agricultural activities. The physical, chemical, and biological properties of pesticides affect their occurrence and distribution directly by altering their environmental persistence, mobility, and other fundamental transport processes. The way pesticides are used includes application amount, frequency, timing, and method has significant effects on pesticide occurrence and distribution. The quantity and frequency of application determine the overall exposure level of pesticides released into the environment, and the timing and method of application primarily change their environmental pathways and thus their occurrence as well as spatial and temporal distributions. Clearly, surface and groundwater systems have dissimilar patterns of pesticide use and occurrence due to their distinct hydrologic characteristics. The relationship of pesticide use and occurrence also varies with pesticide‐treated crops and agricultural management practices.
Supplemental Irrigation
Authors: Oweis Theib , Hachum Ahmed
Published: July 2005

Supplemental irrigation (SI) is the addition of a limited amount of water to otherwise rainfed crops, when rainfall fails to provide essential moisture for normal plant growth, in order to improve and stabilize productivity. It is widely practiced in arid, semiarid, and sub‐humid regions characterized by low or variable rainfall. The goal of SI is to achieve optimal instead of maximum yields. Maximizing return per unit water instead of yield per unit of land is a better strategy for SI practice in water limited areas. SI allows controlling the sowing date of field crops, resulting in improved growth, increased biomass production, favorable environmental conditions, and may help crops escape drought in rainfed farming. Due to its high flexibility, sprinkler irrigation, if coupled with an on‐demand water delivery system, would provide the best results.
Aquaculture Technology for Producers
Authors: Chen Shulin , Johnson Bill , Johnson Brit , Pan Qiang
Published: July 2005

The major limitations to the development of aquaculture in many regions are availability of water resources and environmental impact. Water is critical to aquatic animals, for it both serves as the medium that supplies the required oxygen and creates the physical environment that allows for movement of the animals. As world population has grown and industries have increased their production to meet the demands of the growing population, water has become a scarce resource that has had many conflicting demands placed upon it. Consequently, the major strategy for increasing aquaculture production with this limited water resource is production intensification. As fish biomass density increases, however, the amount of oxygen dissolved naturally in water becomes limited, thus necessitating supplemental aeration and oxygenation. In addition, the increased use of artificial feed as a means to developing a high density culture system leads to water pollution that stems from the facts that aquatic animals cannot completely utilize the feed and that the animals will excrete other metabolic products such as ammonia that are toxic to the aquatic animals at elevated levels. Internally, the waste produced deteriorates the water quality and makes the water unsuitable for fish to live in, while externally, discharge of the polluted water, if not properly managed, may lead to adverse effects on the environment.
Water Quality Management in an Agricultural Landscape
Authors: McHugh Marianne , Clarke Michelle , Duzant Julia
Published: July 2005

Water quality is important for a wide range of reasons including human health, food production, recreation, and biodiversity. Globally, agriculture exerts big demands and impacts on water supplies. In arid areas where groundwater may be the significant or sole source of water, agriculture can have profound effects on the rate and composition of groundwater recharge (1), while in tropical areas, high annual rainfall levels and the demands of tropical crops mean that water quality concerns are dominated by agrochemicals, untreated wastewater, and eroded sediment (2). In temperate zones, moderate rainfall throughout the year means there are few periods when agricultural activities can take place without some risk to water quality and, consequently, temperate water resources are also at constant risk of contamination from agriculture.
Crop Water Stress Detection Using Remote Sensing
Authors: Moran M. Susan , Zarco‐Tejada Pablo J. , Clarke Thomas R.
Published: July 2005

Remote sensing in the optical spectrum has potential to detect plant manifestations of both transient and chronic crop water stress. Crop water status and evaporation rate have been directly related to thermal indexes, such as the crop water stress index (CWSI), the water deficit index (WDI), and the thermal kinetic window (TKW) index. Measurements of surface reflectance in narrow visible and near‐infrared wavelengths have potential for monitoring crop photosynthesis and fluorescence. Surface reflectances in wide bands of the visible, near‐IR, and short‐wave IR spectrum have been used to detect plant manifestations of chronic crop water stress, such as phenological adaptations and leaf expansion and loss. To apply these approaches with satellite‐based sensors for farm‐scale irrigation scheduling and crop management, there are still needs for improved sensor design, timely image delivery, and reduced image cost.
Metal Tolerance in Plants: The Roles of Thiol‐Containing Peptides
Authors: Zhang Weihua , Cai Yong
Published: July 2005

Chelationand compartmentalization are important mechanisms for metal tolerance in plants. Thiol‐containing peptides, i.e.,glutathione(GSH),phytochelatins(PCs), and metallothioneins (MTs), are metal ligands and play important roles inmetal tolerancein plants. This article summarizes the present knowledge about the functions of these thiol‐containingpeptidesin plant heavy metal tolerance, especially for Cd, As, and Cu. GSH participates in the amelioration of metal‐induced oxidative stress. Metal‐GSH complexes are the substrate for PC synthesis. Thus, enhanced GSH synthesis can increase metal tolerance in plants. PCs, a set of thiol‐rich peptides with the general structure (γ‐GluCys)n‐Gly, play an essential role in constitutive Cd and tolerance, whereas PCs are not involved in adaptive Cd tolerance. In contrast, PCs are required for both constitutive and adaptive As tolerance in plants. PCs may play a role in constitutive Cu tolerance in some plants, but they are not involved in Ni or Zn tolerance. MTs may play an important role in constitutive Cu tolerance, and may be involved, to some extent, in Cd tolerance in plants.
Domestic Water Supply—Public–Private Partnership
Authors: Sohail Muhammad
Published: July 2005

This article addresses the question of how water—as a vital yet frequently limited natural resource—can be supplied for domestic use to the millions of people in developing countries who have poor or limited access to water for drinking and sanitation purposes. In particular, it looks at the potential for public–private partnerships (PPPs) to meet shortfalls in infrastructure and other forms of investment in water and sanitation services provision, and how such partnerships might lead to more effective and efficient provision for all, including people on low incomes.

Central to the entry are the questions of why and how PPPs can be an important tool in the provision of domestic water. There then follows a discussion on what key characteristics lead to successful and durable partnerships between the public and private sectors (and the community to be served), and what obstacles might be encountered and overcome along the way.

The final section looks at some of the challenges and opportunities faced by water services providers in terms of political and social acceptance of private sector involvement, the importance of community involvement and information sharing, appropriate technological and financial options, effective regulation, and creating trust among all stakeholders.
Roof Drainage Hydraulics
Authors: Arthur Scott , Wright Grant
Published: July 2005

Over the past decade, urban drainage systems have moved toward what are now commonly known as “sustainable urban drainage systems” (SUDS) or “best management practice” (BMPs). Fundamental to the implementation of these systems is addressing both runoff quantity and quality at a local level in a manner which may also have the potential to offer benefits to stakeholders. This has led to a change in the way new developments now look and interact within catchments. However, despite the availability of such tools to reduce, attenuate, and treat urban runoff, substantial areas of the urban environment are still 100% impermeable and drain rapidly, namely, roof surfaces. Normally, roof drainage systems do not always receive the attention they deserve in design, construction, and maintenance. Although the cost of a system is usually only a small proportion of a building's total cost, it can be far outweighed by the costs of the damage and disruption resulting from a failure of the system to provide the degree of protection required.

There are basically two different types of roof drainage system; conventional and siphonic (refer to Fig. 1). Conventional systems operate at atmospheric pressure, and the driving head is thus limited to the gutter flow depths. Consequently, conventional roof drainage systems normally require a considerable number of relatively large diameter vertical downpipes, all of which have to connect to some form of underground collection network before discharging to a surface drain. In contrast, siphonic roof drainage systems are designed to run full bore, resulting in subatmospheric pressures, higher driving heads, and higher flow velocities. Turbulent gutter conditions mean that there will always be a small percentage of entrained air within the system (typically 5%). Hence, siphonic systems normally require far fewer downpipes, and the depressurized conditions also mean that much of the collection pipework can be routed at high level, thus reducing the extent of any underground pipework.
Soil and Groundwater Geochemistry and Microbiology
Authors: Smith Stuart
Published: July 2005

Geochemistry
can be defined as the study of the chemical composition of, and of actual or possible chemical changes in, a geological matrix, including
soil
, that complex mixture of minerals, life, and organic material on the surface of the earth.
Groundwater
, of course, is water located in the saturated zone of the earth.
Microbiology
is the study of small forms of life, usually including the bacteria and archaea domains and protists and fungi of the eukaryaceae domain, and naturally also covers numerous subcategories.

The interdisciplinary studies of the interactions among microflora, earth materials, and chemical reactions are often linked under
geomicrobiology
or
biogeochemistry
.
Soil Water
Authors: Rasmussen Todd
Published: July 2005

Although water in saturated media is free to drain into openings such as wells, soil water is normally bound to soil surface by attractive forces and only freely drains into openings when the fluid pressure is positive. When soil water pressures are negative, water only partially fills soil pores—the remaining voids are filled with air or soil gasses. The negative water pressure is referred to as the soil tension. Water contents vary from very low values when the soil is dry and the soil tensions are large to saturated values when the soils are wet and the soil tensions are small. The negative pressure, or soil tension, and water contents of soils can be determined with a variety of field techniques, including tensiometers, time‐domain reflectometers, and psychrometers. The relationship between soil tensions and water contents is called the moisture characteristic curve, which is normally determined in a laboratory. Soil water samples can be collected with lysimeters.
Specific Gravity
Authors: Rasmussen Todd
Published: July 2005

The density of water and other materials varies with temperature as well as with the amount of dissolved and suspended matter within them. The specific gravity is the observed density of a material divided by a reference density, which is usually taken to be water at its maximum density, i.e., 1 kg/L. Thus, variations in the specific gravity are a direct measure of the variation in density. The specific weight of a material equals the product of its density and the gravitational constant. The specific gravity is important because it is needed to correct for the water density in wells to determine the freshwater head. Well construction also relies on the specific gravity of drilling muds to prevent the collapse of borehole walls in unconsolidated media.
Treatment for Nitrates in Groundwater
Authors: Loo Walter W. , Wen Jason J.
Published: July 2005

Common sources of nitrogen in the soil are fertilizers, livestock waste, and septic systems. Excess nitrate in the soil is most often found in rural and agricultural areas. Nitrate travels easily through the soil, carried by rain or irrigation water into groundwater supplies. The distribution of nitrate contamination in the United State is widespread. It is the largest amount of pollutant released into the environment. Infants under six months of age are susceptible to nitrate poisoning. The U.S. Environ‐mental Protection Agency (EPA) has established the maximum contaminant level (MCL) for nitrate at 10 milligrams per liter (mg/L). In addition, EPA has established an MCL for nitrite at 1 mg/L.

Biodenitrification treatment will probably be a very common technology used to come into compliance with the nitrate/nitrite regulation.

Reverse osmosis (RO) systems can often reduce nitrate from well water.

The following is a list of advanced studies for in‐situ groundwater treatment containing nitrate:

Mettallic ion treatment

Wetland treatment

In‐situ iron filing curtain treatment

In‐situ electrokinetic treatment.
Well Maintenance
Authors: Smith Stuart A.
Published: July 2005

Well maintenance consists of two overall problem‐preventing scopes of work: predictive and preventive maintenance (together comprising PM). Predictive maintenance involves tasks such as monitoring water quality, power, and other indicator data to detect evidence of deterioration prior to a fault and making necessary repairs. Preventive maintenance includes tasks such as maintaining lubrication, replacing components, and preventive well treatments conducted prior to deterioration of performance. By contrast, reactive maintenance repairs deteriorated components and performance conditions.
Well Screens
Authors: Williams Dennis E.
Published: July 2005

The well screen is the component of a well which provides an opening through which water enters the well casing from the aquifer, as well as stabilizing the material in the “near‐well zone” and preventing it from entering the well. Screens may be constructed with a variety of different materials and designs, as appropriate to the design of the well and its aquifers. Typical types of screen are:

Horizontal louver screens, a pipe‐based well screen with punch‐formed downward facing louver‐shaped openings.

Continuous wire wrap screens, manufactured by wrapping shaped wire around an internal array of rods.

Bridge slot screens, produced by rolling and welding perforated steel plates or sheets.

Machine‐slotted (milled) screens, manufactured by milling casing with axially oriented precision cutters.

Well casing perforated in place with a mills knife or a hydraulic perforator lowered down the cased borehole.

Different screens may by evaluated for a particular well design based on the material, size of perforations, percent of open area, cost, susceptibility to corrosion, and collapse strength. A properly designed screen allows sand‐free water to flow into the well with a minimum drawdown.
Radial Wells
Authors: Williams Dennis E.
Published: July 2005

Radial wells are wells whose screens have a radial or horizontal component. Types of radial wells include collector wells, horizontally directionally drilled wells, and slant or horizontal wells. Collector wells are the most common type of radial wells. The basic components of collector well design are a vertical shaft with horizontal screen laterals. These laterals typically extend up to tens of hundreds of meters and vary in number based on aquifer characteristics.

Radial wells take advantage of natural filtration through aquifer materials, which reduces treatment costs. Maintenance is reduced as the longer horizontal screens reduce water velocity, thereby reducing well head losses and clogging. Furthermore, lateral well screens are able to exploit the maximum saturated thickness of shallow aquifers. For example, up to 500 m of horizontal well screen can be developed in formations that would accommodate only 20 m of vertical well screen. Horizontal directionally drilled (HDD) wells, which are widely used in the oil and gas industry, are now being developed for groundwater applications.

Radial wells are used in applications such as municipal production wells, dewatering operations, desalination plant intake systems, and inducing surface water infiltration for groundwater recharge.
Horizontal Wells in Groundwater Remediation
Authors: Jacobs James A. , Vance David B.
Published: July 2005

Horizontal wells have been used in an increasing number of remediation projects. In addition to chemical and biological reactive barriers, horizontal borings can be used for groundwater extraction and control, air sparging, bioremediation, groundwater injection, for vadose zone soil vapor extraction or bioventing systems, and free product recovery. Although, in areas where there is a great deal of fluctuation in the groundwater table, use for free product recovery can be problematic.

Horizontal well technology was first used in the late 1920s by the petroleum industry to increase oil reservoir thickness per well and greatly increase oil production. In the 1970s, the technology was applied by utility companies to cross rivers and other natural or manmade barriers such as highways. The use of horizontal drilling technology for environmental applications began in the late 1980s and has escalated ever since.
The Environmental Impact of Iron in Groundwater
Authors: Vance David B. , Jacobs James A.
Published: July 2005

Iron is a common constituent in soils and groundwater. It readily participates in subsurface redox reactions and under some conditions can cause taste, odor, and flow problems with drinking water wells and can precipitate and plug up
in situ
groundwater remediation systems. In other geochemical conditions, iron can aid in the remediation of certain chemicals undergoing chemical transformations associated with Redox reactions. Ferrous iron is used as a terminal electron acceptor for anaerobic bioremediation processes that play a dominant role in the natural attenuation process.
Dating Groundwaters with Tritium
Authors: Testa Stephen M.
Published: July 2005

Tritium (
3
H) is one of the most common radioisotopes used to identify the presence of modern groundwater recharge and estimate apparent groundwater ages (1). Tritium, a short‐lived radioactive isotope of the element hydrogen, has one proton and two neutrons. Tritium emits only a very weak beta particle and has a half‐life of 12.43 years. Although tritium can occur as a gas, its most common form is in water because, like nonradioactive hydrogen, radioactive tritium readily reacts with oxygen to form water, which allows groundwater to be dated. As tritium replaces one of the stable hydrogens in the water molecule, (H
2
), it is referred to as the molecule HTO, or tritiated water (T
2
0). Similarly to water, tritium is colorless and odorless.

Tritium is produced naturally in both the atmosphere and hydrosphere of the earth when cosmic rays strike air molecules, notably by the interaction of
14
N with cosmic ray neutrons.
Groundwater and Mercury: Chemical Behavior and Treatment
Authors: Jacobs James A. , Johnson Silvia
Published: July 2005

Mercury is a naturally occurring element named after the planet Mercury. It cycles in the environment as a result of both natural and anthropogenic activities. Mercury appears as elemental vapor mercury in the atmosphere and as inorganic mercury salts and organic mercury in water, plants, and land. Mercury enters the environment from natural sources such as volcanoes and the weathering of rocks. Mercury is also a by‐product of gold and zinc mining. The environment is impacted by the use of mercury in mining operations and other industries and from the burning of fossil fuels at coal‐fired power plants and smelting metals.
Groundwater and Uranium: Chemical Behavior and Treatment
Authors: Jacobs James A. , Smalling Ricardo
Published: July 2005

The element uranium, symbol U, is a chemically reactive radioactive metallic element. It is the main fuel used in nuclear reactors. Uranium has atomic number 92, which places it in the actinide series of the periodic table. The German chemist Martin Heinrich Klaproth discovered uranium in 1789 in pitchblende. He named it after the planet Uranus. Uranium was first isolated in the metallic state in 1841and the radioactive properties were first demonstrated in 1896 by the French physicist Antoine Henri Becquerel (1).
High
p
H
Groundwater— The Effect of The Dissolution of Hardened Cement Pastes
Authors: Shi Caijun , Spence Roger
Published: July 2005

The pH value of the hardened portland cement and concrete ranges from over 12.5 to values as high as 13.5, due to the presence of alkalis in cement. Partial replacement of portland cement with supplementary cementing materials such as coal fly ash, blast furnace slag, silica fume, and natural pozzolan can decrease the pH value depending on the characteristics and dosage of the material used.

The dissolution and leaching of hydration products of cement can affect the pH value of groundwater. Increased pH of groundwater can be expected around the surface of concrete but is not expected to penetrate far into the groundwater matrix, because the transport rate from the concrete is low. The width of the affected zone is mainly controlled by the rate of flow of the groundwater around the surface of the concrete.
Water/Rocks Interaction
Authors: Teng Henry
Published: July 2005

Water–rock interactions encompass primarily three types of reactions, namely adsorption, dissolution, and precipitation, that take place at the mineral‐fluid interfaces. Adsorption reactions occur because of the formation of surface complexes and can be described by a chemical and an electrostatic interaction between adsorbates and surface species on minerals. Although the chemical (intrinsic) reaction of adsorption can be evaluated by equilibrium thermodynamics, theories of electrochemistry, such as the diffuse double layer model, have to be invoked to encounter the coulombic interactions. Dissolution and precipitation are solution saturation‐driven reactions. The direction of dissolution‐precipitation reactions can be accessed by the relative level of solute chemical potential in solid and liquid phases. Whereas a higher potential in solid phase leads to dissolution, a reversed situation results in precipitation. Precipitation cannot be regarded as a mirror reaction of dissolution because the former is a two‐step process, nucleation and growth, and each step has its unique thermodynamic and kinetic characteristics. Kinetics of dissolution/precipitation may be controlled by the rate of the actual interfacial chemical reactions or the transport process that moves reactants and products. It is general agreed that most mineral‐water interactions are surface reaction controlled processes.
Process Limitations of
In Situ
Bioremediation of Groundwater
Authors: Vance David B. , Jacobs James A.
Published: July 2005

The history of groundwater remediation of hydrocarbon‐related compounds illustrates a variety of technologies and methods used over time. Starting in the late 1970s, and continuing to the present,
in situ
bioremediation has been a cost effective adaptation to the process for both petroleum hydrocarbons and synthetically produced chlorinated solvents and other xenobiotic compounds such as MTBE.
Modeling ofDNAPLMigration in Saturated Porous Media
Authors: Mohan Kumar M. S. , Mathew Mini
Published: July 2005

Nonaqueous phase liquids (NAPLs) such as the homogenate hydrocarbons used in dry cleaning and industrial degreasing (DNAPLs), hydrocarbon fuels and aromatic solvents (LNAPLs), and neutrally buoyant coal tars and creosotes are widespread in our environment. Because of their low solubility, NAPL sources can emit toxic contaminants to groundwater for many decades if not managed properly. The migration of dense nonaqueous phase liquids (DNAPLs), which are immiscible with water, through the saturated porous media is an important part of contaminant hydrology and in petroleum engineering. Protection and remediation of groundwater resources require an understanding of processes that affect the fate and transport of such contaminants in the subsurface environment. To implement appropriate remedial schemes in the contaminated area, it is necessary to evaluate the extent of the contaminated area. This information can be obtained by extensive field investigation, which generally is expensive and time consuming. Field investigation can be reduced or made more cost effective, if the migration pattern of the DNAPLs can be evaluated by using numerical models accurately.
Groundwater Vulnerability to Pesticides: Statistical Approaches
Authors: Gurdak Jason J. , McCray John E.
Published: July 2005

Groundwater vulnerability to pesticides is the potential for contamination of groundwater by pesticides from a nonpoint source or aerially distributed point sources. Due to widespread pesticide use and detection in groundwater, assessments that evaluate and estimate pesticide vulnerability have increasingly proven valuable during decisions regarding groundwater management, conservation, and remediation because of the significant costs of such actions. To predict groundwater vulnerability and understand factors that affect the transport of pesticides to groundwater resources, a variety of approaches have been developed that are broadly classified into three general categories: (1) overlay and index, (2) statistically based, and (3) process based. Often the selection of an appropriate approach for assessing groundwater vulnerability to pesticides is determined by the type and scale of the problem and by the available resources. This article provides an overview of the approaches and methods of evaluation for assessing groundwater vulnerability to pesticides.
Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in
U
.
S
. Streams
Authors: Buxton Herbert T. , Kolpin Dana W.
Published: July 2005

A recent study by the Toxic Substances Hydrology Program of the U.S. Geological Survey (USGS) shows that a broad range of chemicals found in residential, industrial, and agricultural wastewaters commonly occurs in mixtures at low concentrations downstream from areas of intense urbanization and animal production. The chemicals include human and veterinary drugs (including antibiotics), natural and synthetic hormones, detergent metabolites, plasticizers, insecticides, and fire retardants. One or more of these chemicals were found in 80 percent of the streams sampled. Half of the streams contained 7 or more of these chemicals, and about one‐third of the streams contained 10 or more of these chemicals. This study is the first national‐scale examination of these organic wastewater contaminants in streams and supports the USGS mission to assess the quantity and quality of the Nation's water resources. A more complete analysis of these and other emerging water‐quality issues is ongoing.
Phytoremediation of MethylTertiary‐Butyl Ether
Authors: Winnike‐McMillan S.K. , Zhang Q. , Davis L. C. , Erickson L. E. , Schnoor J. L.
Published: July 2005

The capability of plants to remediate methyltertiary‐butyl ether (MTBE) at contaminated sites is promising to the point that at least one field test is underway and others anticipated. Both hybrid poplar (Populus deltoides × Populus nigra‘DN34’ ‘Imperial Carolina’) cuttings and alfalfa (Medicago sativa) facilitate the removal of MTBE from saturated soil in the laboratory. The primary removal of MTBE is by soil volatilization facilitated by plant transpiration. Very little of the contaminant is metabolized or accumulated in laboratory studies. The MTBE that volatilizes and the small amount that diffuses from stems or transpires through leaves do not represent a risk in the atmosphere due to the rapid dispersion and degradation. Despite the different behavior of MTBE in groundwater, plants, and the atmosphere, concurrent phytoremediation of gasoline spills containing MTBE and other contaminants is expected to be very useful in the future.
Genetics of Metal Tolerance and Accumulation in Higher Plants
Authors: Datta Rupali , Sarkar Dibyendu
Published: July 2005

Phytoremediation of metals is rapidly developing as a cost‐effective and environmentally friendly solution for cleaning up heavy‐metal‐contaminated sites. The most important requirements for effective phytoremediation are fast‐growing, high biomass plants that uptake and accumulate large amounts of toxic metals in their aboveground harvestable parts. A relatively small group of hyperaccumulator plants sequesters metals in their shoot tissues at high concentrations. In recent years, major scientific progress has been made in understanding the physiological mechanisms of metal uptake and transport in these plants. The majority of metal hyperaccumulators are slow growing and typically have low biomass, so bioengineering of nonaccumulators that have high biomass is essential for more effective phytoremediation. Biotechnology offers the opportunity to transfer hyperaccumulator phenotypes into fast‐growing, high biomass plants that could be highly effective in phytoremediation. However, comprehensive knowledge of the genetics of metal tolerance and accumulation is essential to design transgenic plants capable of phytoremediation. After an initial focus on plants with an immediate promise of application, research is now being directed at understanding the underlying mechanisms involved in heavy metal hyperaccumulation in plants. Once the rate‐limiting steps for uptake, translocation, and detoxification of metals in hyperaccumulator plants are identified, more informed construction of transgenic plants could become rather routine, which will help tremendously in more effective use of phytoremediation technology for cleaning up heavy‐metal‐contaminated sites.
Geochemical Modeling‐Computer Codes
Authors: Gonçalves Mário Abel
Published: July 2005

Geochemical modeling practices are increasingly using a wealth of available computer codes specifically designed for such purposes. Although obtaining the codes is fairly easy nowadays, the uncritical use of these codes should be avoided at all cost. Each of the computer codes presented has their own limitations. Users must also critically evaluate the thermodynamic databases available for each program. Among the codes described, one puts more emphasis on the hydrogeochemical codes developed by the United States Geological Survey (USGS) and US Environmental Protection Agency (USEPA) mostly because these institutions provide a wide range of codes, an important number of which are regularly updated. Besides, codes available from other institutions are also referred to, a few of them being commercial programs. A final note is given about a new class of object‐oriented platform‐independent programs, whose main objective is to provide a framework for building specialized geochemical models.
Geochemical Modeling—Computer Code Concepts
Authors: Thyne Geoffrey
Published: July 2005

The formalism that allows us to relate mass actions equations (balanced chemical reactions) to actual solutions is called chemical thermodynamics or, more precisely, equilibrium thermodynamics. The basic idea is that elements, molecules, and compounds all contain some internal energy and that all systems try to reach a state where that energy is minimized (equilibrium). Natural systems, particularly low‐temperature systems, do not always reach equilibrium, but they do move in that direction. The internal energy of an element, molecule, or compound is expressed as its enthalpy or internal heat. The free energy of an element is an element, molecule or compound is the sum of its internal heat and its internal tendency toward disorder (entropy).
Geochemical Models
Authors: Gonçalves Mário Abel
Published: July 2005

Geochemical models are considered as an abstract representation of natural processes of a system, represented by a set of master variables and described by mathematical equations. The output data of these models is a quantitative representation of an outcome that can be either observable in the natural system or subject to experimental validation. From this definition, the importance of defining proper boundary conditions, and using reliable experimental data on models is discussed. Geochemical models may have as components, chemical reactions (inorganic and/or biological), transport of chemical elements by advection and dispersion, fluid flow, and heat transport. These are the building blocks of geochemical models, which can be divided as: speciation‐solubility, reaction‐path, inverse mass balance, and coupled reaction‐transport models. Finally, model validation and usefulness is shortly discussed.
Resistivity Methods
Authors: Jahani Hamid R.
Published: July 2005

In nature, groundwater is stored in geologically formed pore spaces. When these pores are interconnected, the groundwater moves from a high potential to a low potential zone. The rock layers at different depths have different “porosities” and consequently different water content. The more water in a formation, the lower the electrical resistivity, provided there is no other conducting layer such as clay or shale. If the contained water is brackish or saline, the resistivity of that layer drops even further (1).

The conductivity of an underground formation also varies as its homogeneity varies. The variation in conductivity affects the flow density, which in turn affects the distribution of the potential difference under the ground. The size of this effect depends on the size, shape, position and resistivity of the heterogeneity.

Thus, by measuring or determining the resistivities of earth layers at different depths, it is possible to infer indirectly the hydrogeologic character of a particular subsurface layer and also the quality of water it contains. The most applicable geoelectrical methods are resistivity methods in which an electrical current is passed into the ground so that the current distributes itself according to the conductivities of the geologic materials coming under the influence of the current.
Groundwater Flow in Heterogenetic Sediments and Fractured Rock Systems
Authors: Jacobs James A. , Vance David B.
Published: July 2005

Groundwater flow in heterogenetic sediments and fractured rock systems is highly complex. Contaminants within these types of subsurface conditions are relatively common. Similarities and differences exist in flow characteristics of heterogenetic sediments and fractured rock systems, which influence contaminant fate and transport and subsequent remediation efforts at environmentally impacted properties.
Groundwater Remediation byIn SituAeration and Volatilization
Authors: Vance David B. , Jacobs James A.
Published: July 2005

Soil venting is a term used for anin situaeration process that is a powerful remediation technology for the treatment of soils exposed to a variety of hydrocarbons. The practice of soil venting includes the following variations in application:

Soil vapor extraction (SVE) systems are designed to exploit hydrocarbons potential for volatilization.

Air sparging is an aeration process in which volatilizing air is injected into the saturated zone beneath the water table. Soil venting is used to recover the vapor laden air as it exits the water table.

Bioventing is an aeration process designed to deliver oxygen to the subsurface for use by indigenous bacteria to degrade hydrocarbons; the focus is on minimizing hydrocarbon volatilization.

Biosparging is a variant of air sparging in which oxygen stimulated biodegradation is the aim rather than volatilization. As with air sparging, soil venting is used to recover gas discharged through the water table.
Groundwater Flow Properties
Authors: Babel Mukand Singh
Published: July 2005

Groundwater constitutes a large component of the freshwater cycle. It moves more or less continuously from areas of recharge to areas of discharge through interconnected void spaces in porous media, fractured media, and large passages. Groundwater flow results mainly from precipitation that infiltrates into the soil; it also originates from influent streams, seepage from reservoirs, artificial recharge, seepage from oceans, etc. It often augments streamflow, eventually moving through the soil to the stream channel, also referred to as baseflow, or dry‐weather flow.

The driving force for groundwater movement is measured in terms of hydraulic head, which represents the fluid pressure potential and elevation potential. It is also referred to as the piezometric or potentiometric head. Contour maps of hydraulic head (piezometric or potentiometric maps), which can be constructed from water‐table elevations, can be used to infer directions of groundwater flow.
Groundwater Modeling
Authors: Holzbecher Ekkehard
Published: July 2005

In the first part the basics of groundwater flow and transport modeling are outlined. Starting from the fundamental differential equations for water flow and heat and mass transport, a groundwater problem is stated in the form of an initial boundary‐value problem. Next, the problem is discretized in order to carry out the analysis on a computer. Major discretization methods—finite differences, finite elements, and finite volumes—are explained briefly. A brief outline follows of the different steps in the task of modeling: preprocessing, processing, and postprocessing. Finally, inverse modeling is tackled briefly. References to standard textbooks are given for the different topics. Graphical input and output are illustrated in two examples. Special features are explained for some software products.
Horizontal Wells
Authors: Beljin Milovan
Published: July 2005

Horizontal wells are a new technology for solving problems in the environmental industry. Due to interest in horizontal wells for oil production, a large number of technical papers have been published regarding the reservoir engineering aspects of horizontal drilling and reservoir simulation. In the groundwater supply industry, the first theoretical analysis of groundwater flow to horizontal drains (collector wells) can be traced back to the early 1960s. In recent years, however, there has been renewed interest in horizontal wells for subsurface remediation. Horizontal wells offer significant advantages over vertical wells in environmental remediation and protection in many hydrogeologic scenarios. Horizontal well‐screen orientation complements common site logistics, typical aquifer geometry, and groundwater flow patterns. A single horizontal well can replace many closely spaced vertical wells.
What Is a Hydrochemical Model?
Authors: Lee Kung‐Yao , Fisher Thomas R.
Published: July 2005

A hydrochemical model is a set of mathematical algorithms that calculate water, sediment, and nutrient fluxes from a defined watershed. A hydrochemical model is usually developed from a “hydro” submodel that calculates water balance, followed by erosion and nutrient submodels that simulate export of sediments and nutrients (e.g., nitrogen and phosphorus). Hydrochemical models can be categorized into lumped parameter models and distributed parameter models. Lumped parameter models simplify the watershed properties and ignore the spatial heterogeneity, whereas distributed models can explicitly represent the spatial effects of topography or the spatial variations of properties. Before conducting hydrochemical modeling, a hydrochemical model has to be calibrated by selecting values of parameters that represent the current conditions in the watershed using observed flow and water chemistry. In addition, a model should be validated with independent observed data to investigate the model's ability to simulate natural conditions and to estimate model errors at several time scales. Numerous models are available, each with its limitations and assumption, and it is important to evaluate several hydrochemical models to choose the best for each situation.
Treatment of Arsenic, Chromium, and Biofouling in Water Supply Wells
Authors: Loo Walter W. , Wen Jason J.
Published: July 2005

Arsenic is naturally occurring and also is a component of pesticides and may enter streams or groundwater through waste disposal or agricultural drainage. An EPA MCL level of 50 ug/l established in 1976 by US EPA and now lowered down to 10 ug/l. Five arsenic treatment methods are recommended for small systems users ‐ ion exchange, activated alumina, and the membrane technologies (reverse osmosis, nanofiltration, and electrodialysis reversal).

Chromium can contaminate drinking water sources through discharges from industries, leaching from hazardous waste sites, or it may occur naturally from the erosion of natural deposits. The U.S. EPA classified chromium 6 as a human carcinogen by inhalation. Ion exchange and the membrane technologies (reverse osmosis, nanofiltration, and electrodialysis reversal) are effective chromium treatment method but may be very costly.

Iron and manganese biofouling (usually associated with “iron bacteria”) is common in water supply wells. Biofouling sometimes cause clogging, corrosion, and water quality degradation. Combinations of disinfectants, selected acids and dispersants (wetting agents) have become a part of the arsenal of weapons being used to rehabilitate problems in a well.

In‐situ electrokinetic treatment of chromium, arsenic and biofouling may provide cost effective solution.