RECIRCULATING WELLS: GROUND WATER REMEDIATION AND PROTECTION OF SURFACE WATER RESOURCES1

ABSTRACT: Several chlorinated solvent plumes threaten the sole‐source aquifer underlying the Massachusetts Military Reservation at the western end of Cape Cod. Sensitive surface water features including ponds, cranberry bogs, and coastal wetlands are hydraulically connected to the aquifer. For one of the plumes (CS‐10 the original remedy of 120 extraction and reinjection wells has the potential for significant disruption of surface water hydrology, through the localized drawdown and mounding of the water table. Recirculating wells with in‐well air stripping offer a cost‐effective alternative to conventional pump‐and‐treat technology that does not adversely affect the configuration of the water table. Pilot testing of a two well system, pumping 300 gpm, showed a capture radius of > 200 feet per well, in‐well trichloroethylene (TCE) removal efficiencies of 92 to 98 percent per recirculation cycle, an average of three recirculation cycles within the capture zone, and no measurable effect on water table elevations at any point within the recirculation/treatment zone. During 120 days of operation, the mean concentration of TCE in the treatment zone was reduced by 83 percent, from 1,111 μg/l to 184 μg/l. Full‐scale design projections indicate that 60 wells at an average spacing of 160 feet, having an aggregate recirculation 11 MGD, can contain the CS‐b plume without ground water extraction or adverse hydraulic effects on surface water resources. The estimated capital costs for such a system are about $7 million, and annual operations‐and‐maintenance costs should be about $1.4 million, 40 percent of those associated with a pump and treat system over a 20‐year period.     

APPLICATION OF ENHANCED ANNEALING TO GROUND WATER REMEDIATION DESIGN1

ABSTRACT: A methodology for ground water remediation design has been developed that interfaces ground water simulation models with an enhanced annealing optimizer. The ground water flow and transport simulators provide the ability to consider site‐specific contamination and geohydrologic conditions directly in the assessment of alternative remediation system designs. The optimizer facilitates analysis of tradeoffs between technical, environmental, regulatory, and financial risks for alternative design and operation scenarios. A ground water management model using an optimization method referred to as “enhanced annealing” (simulated annealing enhanced to include “directional search” and “memory” mechanisms) has been developed and successfully applied to an actual restoration problem. The demonstration site is the contaminated unconfined aquifer referred to as N‐Springs located at Han‐ford, Washington. Results of the demonstration show the potential for improving groundwater restoration system performance while reducing overall system cost.     

SIMULATED ANNEALING WITH MEMORY AND DIRECTIONAL SEARCH FOR GROUND WATER REMEDIATION DESIGN1

ABSTRACT: Review of recent literature indicates an emergence in the use of combinatorial methods such as simulated annealing in ground water management during the past nine to ten years. While previous studies demonstrated the feasibility of using these methods, a general finding was that computational processing requirements were inordinately high relative to gradient‐based methods. An enhanced annealing algorithm was developed and used to demonstrate the potential for greatly improving the computational efficiency of simulated annealing as an optimization method for ground water management applications. The algorithm incorporates “directional search” and “memory” capabilities. Selecting search directions based on better understanding of the current neighborhood of the configuration space was shown to improve algorithm performance. Also, “memory” concepts derived from the Tabu Search Method show particular promise for improving the rate and quality of convergence. Performance of the enhanced annealing method was evaluated and the resultant management method was demonstrated using an example from the literature.     

PERMEABILITY OF AIR AND IMMISCIBLE ORGANIC LIQUIDS IN POROUS MEDIA1

ABSTRACT: The conductivity of air, mineral oil (relative viscosity 77), and a light nontoxic oil (relative viscosity 4.7) was measured in three porous media: a sand, loamy sand, and a silt loam. The measurements were made over a range of water contents for each porous medium. Small volumes of air were present as well as significant amounts of water during most of the oil conductivity measurements. The results were compared to two methods for calculating conductivities of immiscible fluids in water-wet porous media. A new equation that accounts for swelling and for the gas slippage effect in very small pores was formulated for use with these methods The observed conductivities, spanning seven orders of magnitude, agree reasonably well with calculated values. Only three soil parameters are required to calculate the conductivities: (1) the saturated conductivity of water, (2) the saturated conductivity of the immiscible fluid of interest, and (3) a pore size index value that is obtained from an estimate from the water release curve of the porous material. Remediation of organic liquid spills is briefly discussed to illustrate the practical applications of gas phase conductivities, as well as those for immiscible organic liquid phases. It is concluded that, in light of spatial variation under field conditions, the method presented for calculating values of three-phase conductivities will be useful in the management of immiscible organic liquid spills and leaks.     

CONTROLLING GROUND WATER DEGRADATION IN THE TULARE LAKE BASIN1

ABSTRACT This study examined the feasibility of extending the Accelerated Salt Transport (ASTRAN) method of groud water quality control to a complex, closed basin which is experiencing ground water quality degradation from irrigated agriculture (e.g., the Tulare Lake Basin in the Southern portion of the California Central Valley). A linear programming model was constructed and parametric analysis conducted which produced results with a “general appraisal” (or “level B”) degree of accuracy. The study concluded that a drainage water export drain is required in order to implement a long-term solution but that ground water degradation can be mitigated by a combination of the ASTRAN method and other measures even with existing entitlements and legal constraints.     

GROUND WATER SOLUTE TRANSPORT,OPTIMAL REMEDIATION PLANNING,AND DECISION MAKING UNDER UNCERTAINTY1

ABSTRACT: A groundwater quality modeling advisory system has been developed for the U.S. Air Force for use in investigating remediation alternatives for the cleanup of subsurface contamination. The system is capable of accounting for uncertainty, not only in the prediction of solute transport but also in the optimization of the remediation scheme through chance constraints. The system guides users in the selection of appropriate transport models through an algorithm independently tested with machine learning codes. An application to Hill Air Force Base, Utah, is presented for which different pump-and-treat strategies are considered: the results are evaluated in terms of the cumulative distribution of the contaminant concentration for each case and the tradeoff relationship between the cost of remediation and the probability that the remediation strategy exceeds an established maximum allowable contaminant concentration.     

DISSOLVED HEAVY METALS IN SHALLOW GROUND WATER IN A SOUTHEASTERN MICHIGAN URBAN WATERSHED1

ABSTRACT: The occurrence of dissolved heavy metal concentrations in shallow ground water were measured at 126 sites within an urban watershed in southeastern Michigan. A total of 1,140 samples were collected from the first saturated zone, and the mean concentrations of 11 heavy metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc) were obtained and compared to their corresponding mean concentrations within surface soil. The results suggest that former and current land use processes have resulted in significant adverse impacts on the study region. Levels of Cr 20 to 30 times the maximum contaminant level (MCL) have been detected in the ground water beneath industrial sites. In addition, Cd and Pb have been found at levels exceeding their MCLs where surface soils are clay‐rich, and in sandy soils at more than 10 times their MCLs. The high levels of Cr in ground water strongly suggest that the chromium is in a hexavalent form, and this likelihood is supported by current studies. Given the hydraulic connection between the watershed's surface waters and the Great Lakes, these findings raise significant ecological and public health concerns.     

MUNICIPAL RESPONSES TO VOLATILE ORGANIC COMPOUNDS IN WISCONSIN GROUND WATER1

ABSTRACT: Contamination of ground water supplies with volatile organic compounds is a new and significant problem. Municipalities and their community water systems are often the first to discover ground water contamination because of the monitoring programs they are required to carry out. When contamination exceeds standards, some action is required. The responses of Wisconsin municipalities to volatile organic compounds that exceed standards in their ground water sources is described. Actions to protect human health are prompt, but the survey results indicate plumes of contaminated ground water are usually not treated. They may continue to migrate and contaminate other private and public wells.     

INTERACTIONS BETWEEN GROUND WATER AND SURFACE WATER IN THE SUWANNEE RIVER BASIN,FLORIDA1

ABSTRACT: Ground water and surface water constitute a single dynamic system in most parts of the Suwannee River basin due to the presence of karst features that facilitate the interaction between the surface and subsurface. Low radon-222 concentrations (below background levels) and enriched amounts of oxygen-18 and deuterium in ground water indicate mixing with surface water in parts of the basin. Comparison of surface water and regional ground water flow patterns indicate that boundaries for ground water basins typically do not coincide with surface water drainage subbasins. There are several areas in the basin where ground water flow that originates outside of the Suwannee River basin crosses surface water basin boundaries during both low-flow and high-flow conditions. In a study area adjacent to the Suwannee River that consists predominantly of agricultural land use, 18 wells tapping the Upper Floridan aquifer and 7 springs were sampled three times during 1990 through 1994 for major dissolved inorganic constituents, trace elements, and nutrients. During a period of above normal rainfall that resulted in high river stage and high ground water levels in 1991, the combination of increased amounts of dissolved organic carbon and decreased levels of dissolved oxygen in ground water created conditions favorable for the natural reduction of nitrate by denitrification reactions in the aquifer. As a result, less nitrate was discharged by ground water to the Suwannee River.     

PESTICIDES IN GROUND WATER: DO ATRAZINE METABOLITES MATTER?1

ABSTRACT: Atrazine and atrazine-residue (atrazine + two metabolites - deethylatrazine and deisopropylatrazine) concentrations were examined to determine if consideration of these atrazine metabolites substantially adds to our understanding of the distribution of this pesticide in groundwater of the midcontinental United States. The mean of atrazine.residue concentrations was 53 percent greater than that of atrazine alone for those observations above the detection limit (> 0.05 μg/l). Furthermore, a censored regression analysis using atrazine-residue concentrations revealed significant factors not identified when only atrazine concentrations were used. Thus, knowledge of concentrations of these atrazine metabolites is required to obtain a true estimation of risk of using these aquifers as sources for drinking water, and such knowledge also provides information that ultimately may be important for future management policies designed to reduce atrazine concentrations in ground water.     

EMERGENCY WATER SUPPLIES FROM GROUND WATER IN HUMID REGIONS1

ABSTRACT: This paper focuses on the development and testing of a mathematical model of an emergency ground water supply operated principally during periods of low streamflow. The process of ground water withdrawal and recharge is simulated taking account of streamflow, water demand, evapotranspiration, natural and artificial recharge and increased evapotranspiration due to artificial recharge, ground water pumpage, and streamflow contribution to pumped water. The model determines whether natural recharge is possible in less time than the return period of drought and also whether artificial recharge is needed. By simulating operation over a long period of time, the model can examine different droughts of short and long duration and can test the operating rules for ground water storage development in an area. Submodels analyze the components of the operating process including ground water flow into the stream, seepage losses, stream portion of well discharge due to induced infiltration and recharge from rainfall or water spreading. The model has been tested for areas in the humid northeastern United States.     

EFFECT OF SEMI‐PERCHED GROUND WATER ON MONITORING OF GROUND WATER LEVELS IN A DEVELOPED AQUIFER1

ABSTRACT: Interpretation of ground water level changes in a developed aquifer usually relies on reference to some benchmark such as “predevelopment” ground water levels, changes from fall to fall and/or spring to spring, or to determination of maximum stress during the pumping season. The assumption is that ground water levels measured in the monitoring well accurately reflect the state of the ground water resource in terms of quantity in storage and the effects of local pumping. This assumption is questionable based on the patterns shown in continuous hydrographs of water levels in monitoring wells in Nebraska, and wells installed to determine vertical gradients. These hydrographs show clear evidence for vertical ground water gradients and recharge from overlying parts of the aquifer system to deeper zones in which production wells are screened. The classical concept of semi‐perched ground water, as described by Meinzer, is demonstrated by these hydrographs. The presence of semi‐perched ground water (Meinzer definition, there is no intervening unsaturated zone) invalidates the use of measured ground water levels in regional observation programs for detailed numerical management of the resource. Failure to recognize the Meinzer effect has led to faulty management. The best use of data from the observation well network would be for detection of trends and education unless it is clearly understood what is being measured.     

ECONOMICS OF SCREENING FOR PESTICIDES IN GROUND WATER1

ABSTRACT: In the United States, millions of dollars are currently spent to monitor water quality for a whole suite of organic compounds. However, results of several surveys conducted in the past decade indicate that only a few pesticides occur in a small proportion of wells. Screening methods based on historical evidence of contamination patterns and knowledge of the locales will have significant potential to reduce these costs and effectively identify contamination problems. In this paper, the economics of utilizing two screening methods, sequential analysis and sample compositing, in the design of monitoring strategies is captured In the form of mathematical models and illustrated for a state-level monitoring program. When the two methods are adopted, the total analytical cost to conclusively identify contaminated wells in a network of 4,000 wells is shown to range from $12,500 to $1,575,000 depending on the extent of contamination. In contrast, the total analytical cost of a conventional program where all the wells in the network are sampled and tested for a standard suite of pesticides at a cost of $250/sample is one million dollars. Given such wide range in costs, it is prudent to incorporate the screening concepts presented in this paper in the development of cost-effective monitoring programs.     

GROUND WATER MONITORING FOR TEMIK (ALDICARB) IN FLORIDA1

ABSTRACT: Over 700 community drinking water supplies were sampled for the pesticide Temik (aldicarb and its oxidative metabolites aldicarb sulfoxide and aldicarb sulfone) in Florida. All community supply wells sampled for Temik were located in counties where Temik was reported to have been used and approximately one-half of the wells were located in counties where ground water was determined to be highly susceptible to contamination by Temik. Susceptibility was determined using ranking criteria that incorporated ground water recharge characteristics, water use, and Temik use patterns. Temik was not detected in any of the community supply wells sampled during the study. However, Temik was detected in shallow, private wells, as was the pesticide ethylene dibromide in counties with ground water characterized as highly susceptible to contamination.     

RADIUM - 226 IN GROUND WATER OF WEST CENTRAL FLORIDA1

ABSTRACT: Principal U.S. phosphate production is from central Florida where mining, processing, and waste disposal practices intimately associate the industry with water resouces. Available radium-226 data from 1966 and from 1973–1976 in mined and unmined mincralized areas and nonmineralized areas in the primary study area in Polk, Hardee, Hillsborough, Manatee, and De Soto counties were studied using log-normal probability plots and nonparametric statistical tests for significant difference as functions of time, depth, and location. Plots of radium in the water table and Floridan aquifers for mineralized and nonmineralized areas indicate that neither phosphate mineralization nor the industry is a probable factor. For the Lower Floridan aquifer, three separate radium populations are indicated with geometric means of 0.7, 3, and 10 pCi/1. Geometric mean radium-226 content of the water table aquifer is 0.17 pCi/1. Radium in the Floridan aquifer in Manatee and Sarasota Counties is elevated relative to that in the water table and in other areas of Florida. For Sarasota County, geometric mean radium content of the water table is 15 pCi/l versus 7.5 pCi/l in the Floridan. Potential sources include shallow phosphate sediments and monazite sands and possibly crystalline basement rocks or other strata unrelated to phosphatic zones of current economic interest. The existing radium-226 data base is rather marginal in terms of number and spatial distribution of analyses, particularly for the water table and Upper Floridan aquifer. Existing radium data do not substantiate widespread contamination of ground water as a result of the phosphate industry. However, local contamination associated with specific operations has occurred.     

GROUND WATER HYDRAULICS CONSIDERATIONS REGARDING LANDFILLS1

ABSTRACT: Landfill siting and design guidelines or regulations differ from state to state. Most include hydrogeological criteria, referring to hydraulic conductivities, aquifers, ground water flow patterns, contaminant travel times, and distance between landfill and sensitive targets for contaminants, etc. However, almost all of the existing hydrogeological guidelines are incomplete, inconsistent, or both. The aquitard between landfill and regional aquifer frequently offers less resistance to leachate migration than compliance with regulations may suggest. Residence times of leachate, that makes it through the landfill liner, is often overestimated. Monitoring wells in the regional aquifer are unreliable detectors of local leaks in a landfill. If a landfill does leak, costly aquifer restoration is called for. For traditional landfill designs, ground water monitoring considerations suggest the siting over homogeneous sand and gravel aquifers, rather than over complex till environments. An alternative landfill design criterion is suggested, which is based on a negative hydraulic gradient underneath the landfill. This design guarantees ground water protection, simplifies landfill monitoring, and generally enhances the landfill economy.     

LOW-INPUT AGRICULTURE AS A GROUND WATER PROTECTION STRATEGY1

ABSTRACT: Protection of ground water quality is of considerable importance to local, state, and federal governments. This study uses a 15-year mathematical programming model to evaluate the effectiveness of low-input agriculture, under alternative policy scenarios, as a strategy to protect ground water quality in Richmond County, Virginia. The analysis considers eight policy alternatives: cost-sharing for green manures, two restrictions on atrazine applications levels, chemical taxation, a restriction on potential chemical and nitrogen levels in ground water only and in surface and ground water, and two types of land retirement programs. The CREAMS and GLEAMS models were used to estimate nitrate and chemical leaching from the crop root zone. The economic model evaluates production practices, policy constraints, and water quality given a long-term profit maximizing objective. The results indicate that low-input agriculture alone may not be an effective ground water protection strategy. The policy impacts include partial adoption of low-input practices, land retirement, and the substitution of chemicals. Only mandatory land retirement policies reduced all chemical and nutrient loadings of ground water; however, they did not promote the use of low-input agricultural practices.     

THE USE OF LANDSAT IMAGERY IN GROUND WATER EXPLORATION1

ABSTRACT: Water supplies in Arizona are becoming increasingly limited because municipal, industrial, and agricultural consumption depletes ground water reserves by three million acre-feet annually. Additional demands are being created by electric power generation, particularly in northeastern Arizona where ground water pumpage is expected to escalate by sixfold during the next 10 years. The results of a study to determine the ease and feasibility of using satellite imagery as a tool in exploring for new sources of ground water are reported. Lineaments detected on Landsat images of two sites were mapped and correlated with well data in the two study areas by means of well centered grid model. The correlations developed between lineament density and water well data in the two study sites support the hypothesis that a relationship exists between regional geologic structure and the presence of ground water.     

FACTORS INVOLVED IN EVALUATING GROUND WATER IMPACTS OF DEEP COAL MINE DRAINAGE1

ABSTRACT: The determination of probable ground water impacts of proposed deep coal mining is required as part of permit applications. Impact prediction generally involves well production test analysis and modeling of ground water systems associated with coal seams. Well production tests are often complicated due to the relatively low permeabilities of sandstones and shales of ground water systems. The effects of the release of water stored within finite diameter production wells must be considered. Well storage capacity appreciably affects early well production test time drawdown or time recovery data. Low pumping rates, limited cones of depression, and length of required pumping periods ate important well production test design factors. Coal seam ground water system models are usually multilayered and leaky artesian. Mine drafts partially penetrate the ground water system. Simulation of coal mine drainage often involves the horizontal permeability and storage coefficient of the coal seam zone, vertical permeabilities of sandstones and shales (aquitard) above and below the coal seam zone, and the hydrologic properties of the source bed above the aqultard overlying the coal seam zone. Ground water level declines in both the coal seam zone and source bed near land surface are necessary factors in impact analysis. An example of evaluation studies in southwest Indiana will illustrate factors involved in deep coal mine drainage modeling efforts.