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Understanding the dynamics and mechanisms of soil water movement and solute transport is essential for accurately estimating recharge rates and evaluating the impacts of agricultural activities on groundwater resources. In a thick vadose zone (0-15 m) under irrigated cropland in the piedmont region of the North China Plain, soil water content, matric potential and solute concentrations were measured. Based on these data, the dynamics of soil water and solutes were analysed to investigate the mechanisms of soil water and solute transport. The study showed that the 0-15 m vadose zone can be divided into three layers: an infiltration and evaporation layer (0-2 m), an unsteady infiltration layer (2-6 m) and a quasi-steady infiltration layer (6-15 m). The chloride, nitrate and sulphate concentrations all showed greater variations in the upper soil layer (0-1 m) compared to values in the deep vadose zone (below 2 m). The average concentrations of these three anions in the deep vadose zone varied insignificantly with depth and approached values of 125, 242 and 116 mg/L. The accumulated chloride, sulphate and nitrate was 2179 ± 113, 1760 ± 383 and 4074 ± 421 kg/ha, respectively. The soil water potential and solute concentrations indicated that uniform flow and preferential flow both occurred in the deep vadose zone, and uniform flow was the dominant mechanism of soil water movement in this study. The piston-like flow velocity of solute transport was 1.14 m/yr, and the average value of calculated leached nitrate nitrogen was 107 kg/ha∙yr below the root zone. The results can be used to better understand recharge processes and improve groundwater resources management. This article is protected by copyright. All rights reserved.

A sophisticated dual-permeability flow model of the T-tunnel complex, Rainier Mesa, Nevada National Security Site, was developed and calibrated to facilitate predictions of radionuclide transport from underground nuclear tests within a perched zone of saturation downward through a series of variably saturated, sparsely fractured and faulted Tertiary tuff units to a regional flow system. The hydrogeologic complexity of the site necessitated a multistage calibration effort to capture the dominant flow characteristics of the site including: laterally and vertically extensive saturation in the Tertiary volcanics, pressure heads consistent with water level measurements, variably saturated flow conditions involving a thin unsaturated zone situated between two saturated zones, unsaturated Paleozoic carbonates located immediately adjacent to saturated Tertiary volcanic units, and fracture saturations congruent with field observations that range from fully saturated to dry. The incorporation of discontinuous fault networks into the dual-permeability model played a key role in reproducing the salient hydrologic features of the site. Successful model reproduction of observed cumulative tunnel discharge volume and tunnel discharge rates before tunnel sealing served as a novel transient test of the ability of the discontinuous fault networks to realistically honor field-scale fault network connectivity and permeability. The excellent reproduction of field observations by the numerical model, and the uniqueness of the primary parameters used to calibrate the model, demonstrate the advantage of incorporating discontinuous fault networks over equivalent fracture properties in sparsely fractured, dual-permeability media.

Formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater. Extensive phreatic caves also occur, however, in eogenetic karst aquifers where fresh and saltwater do not mix, for example in the upper Floridan aquifer. These caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs. Alternatively, these caves have been hypothesized to have formed at lower water tables during sea level low-stands. These hypotheses have not previously been tested against one another. Analyzing morphological data and water chemistry from caves in the Suwannee River Basin in north-central Florida and water chemistry from wells in the central Florida carbonate platform indicates that phreatic caves within the Suwannee River Basin most likely formed at lower water tables during lower sea levels. Consideration of the hydrological and geochemical constraints posed by the upper Floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose CO2 gas into the groundwater. Sea level rise and a wetter climate during the mid-Holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table. When rising water tables reached the land surface, surface streams formed. Incision of surface streams breached the pre-existing caves to form modern springs, which provide access to the phreatic caves. Phreatic caves in the Suwannee River Basin are thus relict and have no causal relationship with modern surficial drainage systems. Neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers. Dissolution at water tables, potentially driven by vadose CO2 gas, offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks. Copyright © 2012 John Wiley & Sons, Ltd.

A former dry-cleaning site in Jackson, Tennessee, has undergone remediation to treat dense nonaqueous-phase liquid (trichloroethene [TCE] and tetrachloroethene [PCE]) contamination in the subsurface. The dry cleaning operation closed in 1977. In 2002, a series of injections were made at the site consisting of corn syrup, vegetable oils, and Simple Green®. In 2004, approximately 200 cubic yards of contaminated soil were excavated, and the bottom of the excavation was covered with sodium lactate. In 2009, the site was characterized using proprietary electrical resistivity imaging (ERI; commercially available as Aestus GeoTrax SurveysTM). Follow-up confirmation soil borings targeted anomalies detected via the geophysical work. The results indicate an extremely electrically conductive (less than 1 ohm-m) vadose zone downgradient from the injection wells, and extremely electrically resistive areas (greater than 10,000 ohm-m) in the phreatic zone near the injection area. The sample data indicate that the electrically resistive anomalous zones contain moderate to high concentrations of undegraded dry-cleaning compounds. Electrically conductive anomalous zones are interpreted to be areas of biological activity generated by the amendments injected into the subsurface based on the extreme conductivity values detected, the chemical composition (i.e., PCE degradates are present), and the dominant vadose-zone location of the conductive zones. © 2012 Wiley Periodicals, Inc.

Measurements of vadose zone water pressure using custom-made tensiometers provided insight into the dynamics of rainfall-induced infiltration events in a 22-m-thick sandy formation. The tensiometers, based on vadose zone sampling ports, were assembled in a vadose zone monitoring system that allowed in situ, real-time measurements of the temporal variation in vadose zone water content and pore water pressure. Results revealed the critical relationship between temporal variations in vadose zone water content and water pressure, as well as the dynamic connectivity of the vadose zone gas phase to the atmosphere. As expected, variation in the sediment water contents, induced by infiltration events across the vadose zone, resulted in corresponding variations in pore water pressure; however, the measured responses of sediment water pressure to wetting events were delayed compared with the measured variations in water content. The delay in the pressure response to a wetting process varied with location as well as between wetting events. Most of the time, the vadose zone gas phase was well connected to the atmosphere; however, this connectivity was limited during rain events and, therefore, compensation of the measured water pressure variation for the measured atmospheric pressure fluctuation is not straightforward. Connectivity of the vadose zone gas phase to the atmosphere was reestablished simultaneously across the entire vadose zone following redistribution of the percolating water in the upper part of the cross-section.

A better understanding of heat fluxes and temperature distribution in continental rocks is of great importance for many engineering aspects (tunnelling, mining, geothermal research, etc.). This paper aims at providing a conceptual model of temperature distribution in karst environments which display thermal ‘anomalies’ as compared with other rocks. In temperate regions, water circulation is usually high enough to ‘drain-out’ completely the geothermal heat flux at the bottom of karst systems (phreatic zone). A theoretical approach based on temperature measurements carried out in deep caves and boreholes demonstrates, however, that air circulation can largely dominate water infiltration in the karst vadose zone, which can be as thick as 2000 m. Consequently, temperature gradients within this zone are similar to the lapse rate of humid air (� 0.5 C 100 m )1 ). Yet, this value depends on the regional climatic context and might present some significant variations.

Groundwater assessment for environmental projects involves significant soil sampling to evaluate hydrologic and lithologic conditions. Soil samples in environmental investigations are typically collected at a minimum of every one to two meters and at changes of lithology or obvious signs of contamination, based on soil staining or discoloration of the soil or in the case of volatile organic compounds, organic vapor readings. Continuous coring is recommended for a minimum of at least one soil boring per site to characterize the subsurface adequately. Keywords: ASTM soil classification flow chart; capillary fringe zone; continuous coring; dense nonaqueous phase liquid (DNAPL); direct push coring; free-product; groundwater assessment; highly impacted soil zone (HISZ); hydrogeologic characterization; lithologic description; organic vapor readings; photoionization detector; phreatic zone; saturated zone; split-spoon samplers; united soil classification system (USCS); unsaturated zone; vadose zone; volatile organic compounds

The vadose zone is the geologic media between the land surface and the regional water table. The vadose zone includes the weathered soil horizon and the unconsolidated sediments and rocks below. The capillary fringe separates the water saturated zone from the unsaturated zone. The water saturated zone is often referred to as an aquifer if it allows significant amounts of water to be transmitted. Several processes take place in the vadose zone. The processes, which influence the vadose zone and the recharge to groundwater include precipitation, evapotranspiration, surface water runoff, and infiltration and groundwater recharge. Keywords: vadose zone; capillary fringe; material dependencies; models

The Snake River Plain aquifer owes its existence and abundance to a unique sequence of tectonic, volcanic, and sedimentologic processes associated with the migration of the North American tectonic plate southwestward across the Yellowstone hotspot, or mantle plume. The basalt lava flows that host the aquifer and comprise the overlying vadose zone are very porous and permeable due to emplacement processes and fracturing during cooling. Rubble zones between lava flows and cooling fractures allow very rapid flow of water in the saturated zone, rapid infiltration of water and contaminants, and deep penetration of air into the vadose zone. Alluvial, eolian, and lacustrine sediments interbedded within the basalt sequence are generally fine-grained, commonly serving as aquitards below the water table, and affecting infiltration and contaminant transport in the vadose zone. The subsiding eastern Snake River Plain (ESRP) and the high elevations of the surrounding recharge areas comprise a large drainage basin that receives enormous amounts of precipitation and feeds high-quality groundwater into the aquifer. Northeast–southwest directed extension of the ESRP produces significant anisotropy to the hydraulic conductivity of the rocks. High heat flow and upwelling of geothermal fluids from the crust beneath the aquifer affect geothermal gradients, aquifer temperatures, and solute chemistry.

The fate and transport of contaminants in the vicinity of septic fields remains poorly understood in many hydrogeomorphological environments. We report hydrometric data from an intensive hillslope-scale experiment conducted between 29 August and 11 November 1998 at a residential leach field in New York State. The objective of our study was to characterize water flux within the vadose zone, understand the physical controls on the flux, and predict how this ultimately will affect subsurface water quality. Soil-water flux was calculated using matric potential measurements from a network of 25 tensiometer nests, each nest consisting of three tensiometers installed to depths of 10, 50 and 130 cm. Unsaturated hydraulic conductivity curves were derived at each depth from field-determined time-domain reflectometry–tensiometry moisture-release curves and borehole permeametry measurements. Flownets indicated that a strong upward flux of soil water occurred between rainstorms. Following the onset of (typically convective) rainfall, low near-surface matric potentials were rapidly converted to near-saturated and saturated conditions, promoting steep vertical gradients through the near-surface horizons of the hillslope. Lateral hydraulic gradients were typically 10 times smaller than the vertical gradients. Resultant flow vectors showed that the flux was predominantly vertical through the vadose zone, and that the flux response to precipitation was short-lived. The flux response was controlled primarily by the shape of the unsaturated hydraulic conductivity curves, which indicated a rapid loss of conductivity below saturation. Thus, soil water had a very high residence time in the vadose zone. The absence of rapid wetting at 130 cm and the delayed and small phreatic zone response to rainfall indicated that water movement through macropores did not occur on this hillslope. These results are consistent with a Cl tracing experiment, which demonstrated that the tracer was retained in the vadose zone for several months after injection to the system. Copyright  2002 John Wiley & Sons, Ltd.

Geochemical data indicate that the Springfield Plateau aquifer, a carbonate aquifer of the Ozark Plateaus Province in central USA, has two distinct hydrochemical zones. Within each hydrochemical zone, water from springs is geochemically and isotopically different than water from wells. Geochemical data indicate that spring water generally interacts less with the surrounding rock and has a shorter residence time, probably as a result of flowing along discrete fractures and solution openings, than water from wells. Water type throughout most of the aquifer was calcium bicarbonate, indicating that carbonate-rock dissolution is the primary geochemical process occurring in the aquifer. Concentrations of calcium, bicarbonate, dissolved oxygen and tritium indicate that most ground water in the aquifer recharged rapidly and is relatively young (less than 40 years). In general, field-measured properties, concentrations of many chemical constituents, and calcite saturation indices were greater in samples from the northern part of the aquifer (hydrochemical zone A) than in samples from the southern part of the aquifer (hydrochemical zone B). Factors affecting differences in the geochemical composition of ground water between the two zones are difficult to identify, but could be related to differences in chert content and possibly primary porosity, solubility of the limestone, and amount and type of cementation between zone A than in zone B. In addition, specific conductance, pH, alkalinity, concentrations of many chemical constituents and calcite saturation indices were greater in samples from wells than in samples from springs in each hydrochemical zone. In contrast, concentrations of dissolved oxygen, nitrite plus nitrate, and chloride generally were greater in samples from springs than in samples from wells. Water from springs generally flows rapidly through large conduits with minimum water–rock interactions. Water from wells flow through small fractures, which restrict flow and increase water–rock interactions. As a result, springs tend to be more susceptible to surface contamination than wells. The results of this study have important implications for the geochemical and hydrogeological processes of similar carbonate aquifers in other geographical locations. Copyright © 2000 John Wiley & Sons, Ltd.

A two-dimensional, field scale, finite-element ground water model was developed to simulate the ground water discharge process within an unconfined coastal aquifer. Model development was based on the density dependent fluid flow approach with water table and dynamic tidal boundary conditions. The performance of the model was compared against data collected from the Columbia Aquifer on the eastern shore of Virginia. The dynamic tidal boundary conditions were necessary to reproduce the surficial mixing zone observed within the ground water intertidal zone of the aquifer. The model was able to reproduce field data on the movement of the near-shore water table, ground water salt concentrations, and ground water discharge rates and patterns. The model was not able to replicate the short-term fluctuation in salt concentration observed within the surficial mixing zone. The inability to account for the wave action of the tides within the intertidal zone is believed to be responsible for this difficulty. The development of the model provided a new method to investigate ground water discharge to coastal systems.

This study examined a fractured carbonate aquifer that has a transition from porous media type (continuum) flow near the bedrock surface to discrete fracture (non continuum) flow at depth. Three depth zones were delineated using a borehole flowmeter, borehole video logs, and pumping tests. The upper zone is fractured to the degree where it behaves hydraulically as a continuum, the middle zone is less fractured and behaves as a discretely fractured aquifer, and the lower zone is least fractured, has no measurable fracture interconnection, and behaves as an aquitard. These zones were not related to lithologic boundaries, showing that monitoring well design based solely on lithology may be inappropriate in some fractured systems. The geometries of capture zones in this aquifer were determined by combining the field observations with numerical modeling. The capture zone geometries are very complex, containing thin a really extensive features around fractures in the middle zone which extend over an area 17.5 times greater than the capture area in the upper continuum zone. A capture zone computed with lumped aquifer parameters leads to inaccurate conceptualization of capture zone geometry at this site. The presence of open core hole monitoring wells affected the flow regime under both ambient and pumping conditions. The wells act as short circuits between otherwise isolated fractures and fracture zones. By connecting the continuum to the non continuum flow regime with the wells, ambient flow in the non continuum regime was increased by a factor of 20. Under pumping conditions, the presence of the monitoring wells alters the capture zone of the pumping well. Discrete fractures provide a connection between the pumping and observation wells at depth that causes separate cones of depression to be formed around observation wells in the upper aquifer, and thus, the capture zone in the near-surface aquifer may include multiple, isolated areas around monitoring wells.

In the long continental history of the Provence Basin which extended from Santonian to Oligocene times, a major period of palaeosol development occurred in the Danian. Dolocretes developed within floodplain silts, and partly from palustrine limestones. Dolocretes are overlain by pedogenic facies: calcretes and palustrine limestones. Gradational lower and upper limits of profiles, succession of nodular, coalescent and massive horizons, the epigenesis of quartz by dolomite, the unimodal crystal size and the euhedral dolomite fabric, as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone. The exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines, which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering. The term halo dolocrete is proposed to describe this type of dolocrete deposit. Subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization. Calcitization was either fabric-destructive (type I) or fabric-preserving (type II) and took place during very early diagenesis, i.e. concomitant with calcrete formation or palustrine limestone deposition. Fabric-destructive calcitization is attributed to a drop in the lake level, when the upper part of the dolocrete was subjected to vadose zone processes, whereas the fabric-preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level.

The soil profile immediately below the land surface and above the water table is called the unsaturated zone, where the pores contain both water and air. This zone differs from the saturated zone, where the pores are saturated with water. The unsaturated zone is sometimes called the vadose zone. The thickness of an unsaturated zone can range from zero (e.g., when a lake or marsh is at the surface) to hundreds of meters, as is common in arid regions. It is a zone of natural and human-induced activity. It experiences physical phenomena such as thermodynamic interactions, transport processes of various kinds, and chemical reactions involving both natural and artificial substances. Several biological activities involving plant roots, rodents, worms, microbiota, and other organisms also take place in this zone. The zone is used for cultivating plants, constructing structures, and disposal of waste. To a large degree, the unsaturated zone controls the transmission of water to aquifers (water bearing strata), as well as to the land surface, to water on the surface, and to the atmosphere. It also acts as a filter as it removes undesirable substances before they reach and affect aquifers. Keywords: unsaturated zone; soil water; soil water potential; moisture retention curve; measurement of soil water

The High Plains aquifer (HPA) is one of the largest aquifers in the world and is critical for agricultural production in the United States. In Kansas, irrigation using the HPA has resulted in steep groundwater declines. Unexpected water-level response to pumping recovery in the northwestern Kansas portion of the HPA was recently observed, indicating a previously unknown source of recharge. The goal of this research was to investigate water movement and vadose zone chemical inventories to constrain recharge pathways and rates to the aquifer. Detailed geochemical profiles at a cored site indicated displaced chloride, bromide, nitrate–nitrogen (NO 3 –N), and sulfate reservoirs—likely mobilized by the onset of on-site irrigation—believed to have commenced in 1984. Water in the vadose zone beneath the predevelopment water table (36–63 m below ground surface) is remnant groundwater left as the water table declined. Thus, assumptions of a chloride mass balance are not valid in this zone. These results indicate irrigation return flow has yet to travel through the vadose zone to recharge the aquifer at this location. Calculated chemical transit times through the profile to the predevelopment water table exceed the start of irrigation at the site, and groundwater radiocarbon ages on the order of 3000 yr BP provide further evidence against substantial irrigation return to the aquifer. These data establish evidence for complicated flow paths through the vadose zone to the aquifer and argue against broad, diffuse recharge to the aquifer. Future studies in the area should investigate focused recharge pathways to identify recharge sources.

Average-annual volumes of runoff, evapotranspiration, channel loss, upland (interchannel) recharge, and total recharge were estimated for watersheds of 53 channel sites in the Amargosa River basin above Shoshone, California. Estimates were based on a water-balance approach combining field techniques for determining streamflow with distributed-parameter simulation models to calculate transmission losses of ephemeral streamflow and upland recharge resulting from high-magnitude, low-frequency precipitation events. Application of the water-balance models to the Amargosa River basin, Nevada and California, including part of the Nevada Test Site, suggests that about 20.5 million cubic meters of water recharges the ground-water reservoir above Shoshone annually. About 1.6 percent of precipitation becomes recharge basinwide. About 90 percent of the recharge is by transmission loss in channels, and the remainder occurs when infrequent storms yield sufficient precipitation that soil water percolates beyond the rooting zone and reaches the zone of saturation from interchannel areas. Highest rates of recharge are in headwaters of the Amargosa River and Fortymile Wash; the least recharge occurs in areas of relatively low precipitation in the lowermost Amargosa River watershed.

The failure or “breaking up” of pavement in cuts in glacial till is a phenomenon commonly observed in northeastern Illinois and other areas in the midwest. Failure commonly follows periods of significant ground-water recharge, especially when such periods are concomitant with freezing and thawing conditions. Water levels in piezometers installed in glacial till in northeastern Illinois indicate that during periods of high precipitation or rapid snow melt, the potential surface normally occurs at shallow depths. Therefore, cuts of appreciable depth intersect the zone of saturation and establish local, gravity, ground-water flow systems with the bottom of the cut acting as a ground-water discharge zone. Such shallow gravity flow systems may bring about pavement failure by facilitating the growth of thick ice lenses or by developing high pressure beneath the pavement due to poor drainage.

This report is the result of a request by the State Board of Examiners of Water Well and Pump Installation Contractors. The Board is in the process of formulating a more reasonable set of guidelines which control the location of wells designed to produce water for human consumption and/or food processing with respect to potential or existing sources of ground-water pollution. The pollution of ground-water supplies is artfully treacherous. It appears belatedly and often is not recognized until a relatively large area has been contaminated and perhaps one or more individual water supplies have been rendered unfit for human consumption. It is known that soils and aquifer materials have capacity to remove or “filter” some types of contaminants, and something is also known of the limitations in this regard. It is with these thoughts upon which this report is based. The report is designed to briefly describe the results of several pertinent ground-water pollution investigations and present current and potential standards for governing “safe distances” between domestic-food processing wells and sources of potential or existing pollution. The recommendations are meant to emphasize the fact that no one set of distances are adequate and reasonable for ALL conditions. Whenever possible the “safe-distance” between a subject well and a source of potential or existing pollution should be based on local conditions. It is important that we develop knowledge that will permit continued use of the soil mantle as a waste-water treatment system and at the same time permit continued use of ground water for human consumption and/or food processing. Functional legal, administrative and engineering mechanisms must be developed to maintain this combined usage. The Colorado Board of Examiners of Water Well Drilling and Pump Installation Contractors was established in early 1968. By October the Board adapted a set of rules and regulations which provide minimum standards for location, construction, modification or repair of pumping equipment. The Board's current concern is with the sanitary quality of those waters which are to be used for domestic purposes; in particular. human consumption. Realizing that proper sanitary protection of domestic wells involves the prevention of the intake of contaminants, the Board of Examiners introduced a set of standards which provides for the location of wells and well casings with respect to sources of contamination. The standards were chosen arbitrarily and do not consider the differences between chemical and biological contaminants. It is the purpose of this report to briefly point out some of the past and current developments regarding the nature of ground-water pollution and, in particular, data related to studies of the length of travel of bacteria and virus-laden water when injected on both soil surfaces and in water wells. Two distinctly different aspects of pollution travel are considered. They are: (1) the movement of bacteria and viruses downward with percolating water; and (2) the lateral movement of identical pollutants once they have reached the zone of saturation.

In a steady-state condition the lateral flow rate through the unsaturated zone of an unconfined aquifer increases with a decreasing rate as the depth of the unsaturated zone increases while hydraulic gradient is kept constant. This flow rate reaches a maximum as the depth of the zone is increased. This maximum flow rate is computed by various methods such as an aquifer model, graphical integration of the characteristic hydraulic conductivity curve and a flow net diagram. Based on these calculations a simple method is outlined for estimation of steady-state flow rate through the unsaturated zone of an unconfined aquifer. It is also concluded that in shallow unconfined aquifers the contribution of the flow through the unsaturated zone to the total lateral flow can be significant.

Water-level declines in the principal artesian aquifer have created a head imbalance between the aquifer and an underlying brackish-water zone containing up to 4,550 mg/1 chloride. The brackish-water zone leaks brackish water into the aquifer through several breaks in a confining unit. A relief well tapping the brackish-water zone was drilled near a suspected break and pumped at about 3,000 gpm to lower the potential in the zone and bring it into hydrostatic equilibrium with the aquifer. The pumping apparently succeeded in decreasing the rate of brackish-water leakage into the aquifer. Successive samples of water from a well tapping the aquifer and downgradient from the relief well showed a decrease in the chloride content. Several more relief wells may be necessary to ultimately control chloride contamination of the aquifer.

The movement of bacteria-laden waters percolating through fractured crystalline bedrock in mountainous terrain was examined to determine whether effluent originating from domestic waste disposal systems could contaminate shallow ground-water supplies. Inoculated waters were injected into holes and/or wells at two geologically different test sites (granitic, metamorphic) to evaluate the extent of microbial filtration in or along bedrock fractures. Microbiological examination of tracer waters, sampled both above and below the zone of saturation, was made. Field studies showed that the direction and rate of movement of contaminated ground waters were controlled largely by the anisotropic nature of the geologic stratum, particularly by the orientation of major bedrock fracture sets. Inoculated waters were found to be readily transported by the ground-water gradient into a downslope well. At one test site, a tracer bacterium traversed a horizontal distance of 94 feet in 24-30 hours. Continued bacteriological analysis of the contaminated well found the organism to be present for at least five days after inoculation of the upslope well. In the zone of aeration, bacteria-laden effluent was found to percolate in or along fractures with inadequate filtration prior to entering the ground water. Studies conducted in metamorphic rock demonstrated that while fecal-type bacteria decreased slightly during percolation through bedrock fractures, total bacterial densities were generally unchanged. From the hydrogeological and microbiological data obtained at both test sites, it can be concluded that moderate percolation rates and minimum distances between water wells and leachfield type waste disposal units are inadequate to protect potable ground-water supplies from contamination in mountainous terrain.

T use of ground water for irrigation and public potable-water supplies has long been recognized. These are but two of a multitude of uses, however, to which the United States has put its underground water resources. Most of these applications generate little attention; and when compared to large scale reclamation and impoundment projects their scope and cost seem insignificant. As the intensity of water development increases, the numerous uses for ground water must be recognized, not only by the general public but by professional planners and engineers as well. Only by this total recognition can the nation be sure that its total water resources will be utilized for the greatest good, for the greatest number of people over the longest period of time. It is intended that the term "beneficial use" be viewed in its broad sense -that is, to include all uses that benefit man or his environment. Most beneficial uses require development by man; some, however, operate as an integral part of the hydrologic cycle and are given recognition for the purpose of showing the interrelationship of all water resources. In the past, and even today, many persons adhered to an elaborate classification of subsurface waters. From both a scientific point of view and a utilitarian approach, such systems are neither justified nor necessary. All water in the zone of saturation is basically ground water, which moves in accordance with well-known laws of physics. If these principles are accepted as fact, all those associated with water supply must be persuaded that certain descriptions and opinions included in judicial decisions are not compatible with the present state of knowledge. For example

Shallow aquifers, commonly the most important sources of ground water, are also those most susceptible to contamination. The mode of entry of contaminants to shallow aquifers is (1) directly, via wells or secondary openings in consolidated rocks, (2) percolation through the zone of aeration, (3) induced infiltration through the zone of saturation, and (4) interaquifer leakage or flow through open holes. Natural removal or degradation of contaminants is by filtration, dispersion, sorption, ion exchange, oxidation, and various biochemical processes. These phenomena are controlled by the physical environment, structure; mineralogy, and hydraulic characteristics of the earth materials contacted by the liquid wastes. When liquid wastes enter an aquifer directly, there is little or no natural treatment by filtration, sorption, or oxidation. Purification is only by those processes that operate within the aquifer under anaerobic conditions. Contaminants from natural sources that enter aquifers under saturated-flow conditions are degraded primarily by dilution. The natural processes effective in reducing contamination from surface-water sources depend on the hydraulic regimen involved, which vary with individual cases. Liquid wastes percolating through the zone of aeration are those most likely to be purified by natural environment processes. Natural processes, however, do not effectively remove or degrade all contaminants, especially some of the many highly stable compounds that have gained widespread use in recent years, such as synthetic detergents. Comprehensive interdisciplinary research into the ability of various earth materials to remove many types of contaminants under varying hydrologic conditions is needed.

This study of the geometry of limestone solution is based on the following conditions: (1) the limestone is impermeable but contains and transmits water in joints, fractures, bedding-plane partings, and solution channels; (2) at depth, the limestone aquifer is underlain by impermeable rock; (3) ground water in the limestone is under water-table conditions; (4) recharge to the limestone is by infiltration of precipitation through the overlying rock to the zone of saturation; (5) discharge from the aquifer is by seeps and springs; and (6) ground water dissolves the limestone through which it flows, continuously modifying the flow pattern and the hydrologic properties of the medium. These conditions commonly are found in limestone terranes in the eastern and central United States. An electrical analog was constructed conforming to this description of the ground-water flow system and has been used to define the pattern, velocity, and density of ground-water flow and the relative length of time of contact of water with the aquifer. Successive models are used to illustrate progressive limestone solution and changes in ground-water flow in the aquifer. The initial analog indicates a strongly convex water table with the greatest density of flow at shallow depths beneath the water table near the point of discharge. Successive models indicate greater concentration of flow near and on the level of ground-water discharge, an overall lowering of the water table, and a pronounced flattening of the water table near the discharge point. Results of the analog study support the following conclusions: (1) The most active zone of solution is at shallow depths beneath the water table and near the point of ground-water discharge. Consequently, the size of channels generally decreases with depth and increases with proximity to the point of ground-water discharge. (2) Generally, solution channels have a greater lateral than vertical extent.