Category: Research Sponsored by GWRI

Principal Investigator: Sydney T. Bacchus (University of Georgia)
Principal Investigator: George A. Brook (University of Georgia)

Sponsor: GWRI
Start Date: 1996-04-01; Completion Date: 1996-04-01;        
Keywords: Depressional wetlands, ground penetrating radar, groundwater mining, karst aquifers, southeastern Coastal Plain, subsidence, sustainable aquifer yield

Description:

The sustainable yield of the Floridan aquifer has been exceeded in west-central Florida. The Southwest Florida Water Management District (District), one of five regional water resource agencies in Florida, recently designated Water Use Caution Areas to reduce damage: 1) to private wells and property from lateral intrusion of saltwater, vertical upconing of mineralized water, and sinkhole formation, and 2) to depressional wetlands and other natural resources from hydroperiod perturbation. Aquifer characteristics vary dramatically from the shallow, semiconfined hydrogeologic system in the North Tampa Bay Water Use Caution Area (NTBWUCA) to a system described by the District as a well-confined, multi-layered aquifer system in the Southern Water Use Caution Area (SWUCA). However, similar damage is occurring in both areas. Destruction of depressional wetlands became apparent around North Tampa Bay municipal well fields in the mid 1980s. In response, the District initiated a geophysical evaluation of selected wetlands in two well fields to determine if structural differences could explain why some wetlands appeared to be more severely affected than others. Of the four geophysical approaches used in that study, ground penetrating radar (GPR) produced the best results. In conjunction with fracture trace analysis, GPR documented differences in geophysical characteristics between wetlands (ie. reflection free zones and dipping reflectors) that could increase the hydrologic connection between the depressional wetland and the production aquifer. A similar geophysical evaluation has not been conducted in depressional wetlands in the SWUCA or in Georgia, where extensive groundwater withdrawals occur for agricultural and other uses. This study was initiated to determine if wetlands in Georgia and well-confined areas in Florida exhibit subsurface discontinuities which could increase the hydrologic connection between the depressional wetland and the production aquifer. Results of geophysical characterization using GPR in this study suggest that depressional wetlands in Georgia and Florida exhibit subsurface discontinuities that invalidate the assumptions of homogeneity and isotropy commonly used in hydrologic models for determining responses to groundwater mining. These findings also suggest that standard approaches for groundwater monitoring, with wells installed in uplands and often in grid configurations, will provide limited information regarding how the hydroperiods of depressional wetlands are being influenced by anthropogenic groundwater perturbations or when the sustainable yield of the aquifer has been exceeded. Depressional wetlands appear to provide a more accurate tool for predicting the sustainable yield of a karst aquifer than the current approach, when using GPR analysis in conjunction with fracture trace analysis. The degree to which discontinuities associated with depressional wetlands are magnified by groundwater mining is unclear and should be investigated.

Principal Investigator: Heather L. Caudill (Georgia State University)

Sponsor: GWRI
Start Date: 1995-06-01; Completion Date: 1995-06-01;
Keywords: Fracture Analysis, Fractured Aquifers, Lineaments, Groundwater

Description:

With the recent growth trend in the metropolitan Atlanta, there is an increasing need for viable sources of water. Well siting in the fractured crystalline rocks of the Piedmont has always been an arduous task, often resulting in positioning of wells of variable productivity within meters of one another. Careful siting techniques can greatly increase the probability of encountering a high yielding hydrogeologic zone. The primary purposes of this project are to analyze well productivity in fractured rocks of the Piedmont in the Atlanta area and to propose procedures to better and more consistently locate sites for high yield wells.

Orientation and other characteristic features of mesoscopic fractures at the outcrop scale and lineaments at the 1: 24000, 1: 100000, and 1: 500000 scales were integrated with well data collected by the United States Geological Survey to delineate highly productive zones in the Atlanta Metropolitan area. The project utilized scanline techniques to quantitatively describe and measure fracture networks at the outcrop scale. Dominant fracture sets present on the outcrop scale were also detected at topographic map and satellite image scales, suggesting a similar distribution of the fractures over 6 orders of magnitude (10.2 m to l04 m).

There are two dominant steeply-dipping sets of fractures with horizontal traces trending between 020°-070° and 300°-350°, and length and apertures that are greater than those of other steeply-dipping sets. These two major trends also occur as lineaments at the 1:24000, 1:100,000, and 1:500,000 scales. There is a third set of variably-oriented and gently-dipping fractures with large aperture and length relative to the two steeply-dipping sets. These pressure-relief fractures have horizontal traces that are subparallel to the two major trends and the trend of lineaments. The two dominant, steeply-dipping sets are sub-perpendicular to the gently-dipping set, and their intersection produces localized, high interconnectivity zones in the Piedmont.

An analysis of well data in the study area shows that well yield is a function of the following variables: local fracture lineament density and interconnectivity, well depth to tap the pressure-relief gently-dipping fractures, well distance from points of high intersection density of the steeply-dipping fractures, position of the well relative to the center of valleys, rock type, and lithostratigraphic contacts which control fracture/lineament densities. The Brevard fault zone and rocks belonging to the Sandy Springs Group and Clairmont Formation have the highest linear fracture and areal lineament densities at all the scales studied.

The results show that sites for high yield wells in the metropolitan Atlanta area within the Georgia Piedmont can consistently be located if geomorphologic, structural, and suatjgr.apJJk observations are made at several scales and integrated by analyzing the above-mentioned factors that control the well yield.

Principal Investigator: Yong Shi (Georgia Institute of Technology)
Principal Investigator: Pratyush Verma (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1995-05-01; Completion Date: 1995-05-01;
Keywords: Fractured Aquifers, Geostatistics, Aquifer Characteristics, Aquifer Parameters, Groundwater Hydrology, Groundwater Movement

Description:

Periodic droughts and localized industrialization in the Greater Atlanta area strain the available surface water supplies. The rising environmental concerns about over-use of surface water supplies have rendered groundwater resources in the Georgia Piedmont as a part of the solution to the water shortage problem. Aquifers in the Piedmont are traditionally viewed to have low permeability. However, this region includes wells with high yields up to 400 gpm. Tapping productive zones in the Piedmont region is considered as a difficult task driven by chance. This project attempts to use advanced statistical procedures to reliably locate, with high probability, zones for high-yielding wells in the Piedmont. In Part A (Babaie and Caudill, 1995) field fracture measurements at a number of locations in the greater Atlanta area were conducted. In Part B, attempts were made to determine the spatial distributions of collected data on fractures in the crystalline rocks of the Piedmont using geostatistical methods. The geostatistical outcomes were then compared with available regional groundwater discharge information. The results of these comparisons provided a means to relate surficial fracture features to the probability of siting high yield wells. The principal findings of Part B of this investigation are listed below:

(1)Among analyzed variables, density and number of fracture sets appear to be adequately representative of other fracture features.
(2)The resulting variograms of the above spatial features display well-defined structures with strong anisotropic tendencies.
(3)Based on the fitted variograms, contour maps of fracture density and the number of sets were produced. All kriged maps provided results consistent with available regional geologic maps.
(4)Available groundwater discharge information was then superimposed on the kriged maps. This led to the computation of conditional probability curves. These curves estimate the probability of siting a high yield well in zones with specific fracture feature values.

The conditional probability curve based on the composite indicator map, defined as the product of fracture density and set number, provide a promising measure to identify zones with high interconnectivity. This implies that geostatistical maps of composite fracture features can be viewed as reliable tools for siting high yield wells.

Principal Investigator: Rasheed Ahmad (Georgia Institute of Technology)
Principal Investigator: A. Amirtharajah (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1994-04-01; Completion Date: 1995-03-01;
Keywords: Water Treatment, Biofilms, Microbial Detachment, Hydrophobicity, Hydrophobic Interaction, Biological Filtration, Backwashing, Bed Expansions, Air Scour

Description:

Biological Filtration may become an essential part of drinking water treatment in the United States during the next several decades. Since biological granular activated carbon (GAC) filters accumulate both biological and non-biological particles on the filter bed, the differences in the detachment of these groups of particles during backwashing will be an important aspect of operation of these filters. Among mechanisms controlling attached biofilm reactor performance, biofilm detachment is one of the aspects of the process that is least understood and studied. This study presents the results of an analysis of the detachment of particles from biofilms in terms of a microscopic force model and the evaluation of this model with results from operation of a pilot filter. Experiments on attachment and detachment were completed in a packed glass column with GAC/sand media and an indigenous bacterial population. The operation of a biological filter was simulated by using filter influent (nonchlorinated) water from the nearby Water Treatment Plant with the addition of a carbon source. Bacterial hydrophobicity is an important factor in the study of microbial attachment and detachment from surfaces. To develop a valid microscopic force model for microbial detachment, the hydrophobic force must be included in the total force calculations. The microscopic force model for detachment includes electrostatic, van der Waals, Born repulsion and hydrophobic forces. In these calculations, hydrophobic colloids produce a deeper primary minimum as compared to hydrophilic colloids. Consequently, hydrophobic bacteria are far more strongly attached to the GAC surface as compared to hydrophilic clay particles. During backwash of a biological filter, the maximum turbidity occurs close to zero time in contrast to the maximum microbial detachment which occurs later. In biological filters, the location and degree of attachment of biological (bacteria) and non-biological (clay) particles to the GAC media surface are different. Hence, their mechanics of removal and times of detachment are different. The use of different bed expansions during backwash has a bearing on microbial detachment. A sixty percent bed expansion produced maximum bacterial removal. The optimum porosity expression for traditional filter backwash can be applied to biological filters in drinking water treatment. Water washed filters even at optimum porosity build up excessive headloss over successive filter runs. Hence, fluidization water wash alone is not an effective method to clean biological filters. Biological filters for drinking water treatment need air scour. The biological filters backwashed with a combination of air plus subfluidization water flow at collapse-pulsing followed by water wash with 20% bed expansion produced not only lower headloss but also little headloss build up over successive runs. The chemistry of the backwash water has an impact on biofilm detachment. Limited experiments suggest that chlorinated backwash is detrimental to biological filtration. The biofilm detachment model developed in terms of forces at the microscopic level, explains the detachment mechanism in biological filtration and is consistent with the experimental results.

Principal Investigator: Walter G. Knisel (University of Georgia)
Principal Investigator: Matt C. Smith (University of Georgia)
Principal Investigator: Stanley R. Wilkinson (U.S. Department of Agriculture)
Principal Investigator: Matt C. Smith (University of Georgia)

Sponsor: GWRI
Start Date: 1995-04-01; Completion Date: 1995-04-01;
Keywords: GLEAMS, leaching, management, modeling, nitrogen, poultry litter, runoff, water quality

Description:

The GLEAMS model was applied to represent 6 fertilizer and broiler litter management practices on Coastal bermudagrass with multiple cuttings for hay at Watkinsville, Georgia. Observed data from a 7 year study were used to validate GLEAMS with comparisons of runoff volumes, runoff nitrogen, N03-N leached, forage yield, and nitrogen yield. Simulated runoff volumes and runoff nitrogen losses compared well with observed values for the record period. NO3-N leached and maximum monthly weighted concentrations were compared with good representation of the timing of peaks for all treatments. The model over-estimated the mass of No3-N leached; but peak concentrations were both over- and under-estimated. Forage yield was simulated very well, but potential yield was found to be a very sensitive model input parameter. The model under estimated nitrogen yield in the forage very significantly. The optimum nitrogen concentration relations under-estimated N demand, but coefficients for lush nitrogen uptake were very sensitive interactively with potential yield. Lush nitrogen uptake could result in nitrogen deficiency and cause reduced yield which does not occur in observed data. GLEAMS represented the fertilizer and broiler litter management practices, and can be used effectively for relative comparisons. However, it should not be used for quantitative predictions. Model users are urged to se local site-specific data if at all possible to fine-tune values of sensitive parameters.

Principal Investigator: Matt C. Smith (University of Georgia)
Principal Investigator: Jackie Sellers (University of Georgia)

Sponsor: GWRI
Start Date: 1994-06-01; Completion Date: 1994-06-01;
Keywords: agriculture, nonpoint pollution, nitrate contamination, wastewater

Description:

The Lake Lanier drainage basin covers approximately 665,600 acres in North Georgia and is the primary source of domestic water for the city of Atlanta. The drainage basin is located in the heart of the poultry producing region of the state with an estimated 274 million birds produced or housed within the basin. These birds could produce as much as 274,000 tons of litter per year. The objective of this study is to quantify any differences in specific water quality parameters between a forested watershed and similar watersheds whose land use is dominated by poultry production and open lands that receive applications of poultry litter. Automated water samplers were installed to collect samples from the outlet streams of four watersheds. The samples were analyzed for ammonia, nitrate, COD, total suspended solids, and orthophosphate. During the weekly sample collection, field measurements were made of pH, conductivity, and temperature. One additional sample was collected at this time for determination of BOD and fecal coliforms and streptococci. The four streams selected for monitoring were Little John, Mud Creek, East Little River, and West Little River. These sites were monitored from August, 1993 through March, 1994. The Little John site was selected as the control site, i.e. a watershed with no concentrated animal agriculture activities. Approximately 91 percent of the Little John watershed is forested and eight percent is in pasture. The East Little River and West Little sites were the same as used in a Clean Lakes Study of Lake Lanier. Mud Creek is the only site with a potential for significant influences from urban runoff and waste water treatment discharges. There are 87, 35, 43, and 0 chicken houses in the West Little, East Little, Mud, and Little John watersheds, respectively. For many of the measured parameters (dissolved oxygen, COD, BOD, total suspended solids, fecal coliforms, fecal streptococci, and temperature) there were no significant differences between watersheds. The parameters for which significant differences existed include ammonia, nitrate, electrical conductivity, pH, and orthophosphate. The data collected during this study do not provide strong evidence that the high concentrations of poultry houses and the associated land application of litter are contributing to a degradation of the water quality in the streams that were monitored. Almost all of the significant differences were associated with Mud Creek, and these differences are likely due to the discharge of municipal waste treatment plant effluent into the stream. High levels of fecal coliform and fecal streptococci bacteria have been noted previously in the streams in the Lake Lanier watershed. This study also showed high levels of bacteria in the water. The levels were high, however, for all of the sites, including Little John which is, on the whole, undeveloped.

Principal Investigator: D. E. Brune (University of Georgia)
Principal Investigator: H. D. Gunther (University of Georgia)
Principal Investigator: David E. Radcliffe (University of Georgia)
Principal Investigator: D. J. Drommerhausen (University of Georgia)

Sponsor: GWRI
Start Date: 1994-04-01; Completion Date: 1994-04-01;
Keywords: Nitrate, Animal Waste, Dairy, Electromagnetic Conductivity.

Description:

Nine dairies in north Georgia were surveyed using a ground electromagnetic (EM) conductivity meter to determine the source of high nitrate in dairy wells in the region. Ground EM conductivity increases with water and soluble salt content and has been used to map contaminant plumes from landfills and animal waste lagoons. A consistent pattern of EM readings was found at all of the dairies. There was evidence of seepage from lagoons at four of the seven dairies. However, it appeared that a more likely source of contamination in the wells was the unpaved loafing areas near the milking barns. EM readings in these areas were typically 15-20 mS m-l, whereas background readings were near 5 mS m-1. To supplement the EM readings, a total of seven groundwater observation wells were installed, five at one dairy (MO-l) and one each at two other dairies (MO-6 and PU-l). The wells at MO-l were installed at five locations: one next to the dairy barn, three in the loafing area, and one beyond the loafing area. Nitrate contents in the three wells in the loafing area ranged between 74- 96,60-105, and 83-120 mg L-1 N03-N. Concentrations in the well next to the barn and beyond the loafing area were between 12-43 and 12-16 mg L-\ respectively. The wells at MO-6 and PU-2 were located in loafing areas and had N03-N concentrations ranging from 53-83 and 105-135 mg L-1. We conclude that the loafing areas at the dairies we surveyed are a likely source of groundwater contamination by nitrate because of the high animal density and consequent high waste deposition rate.

Principal Investigator: Valentine A. Nzengung (Georgia Institute of Technology)
Principal Investigator: Evangelos A. Voudrias (Georgia Institute of Technology)
Principal Investigator: J. M. Wampler (Georgia Institute of Technology)
Principal Investigator: Charles E. Weaver (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1993-04-01; Completion Date: 1994-03-31;
Keywords: Organoclays, Quaternary ammonium ions, Clay minerals, Montmorillonite, Sorption, Sorption kinetics, Adsorption and exchange, Aromatic hydrocarbons, Organic wastes, Wastewater treatment

Description:

The second year of a two-year research project was used to complete a series of experiments on the sorptive properties of organoclays prepared from Wyoming montmorillonite by replacing the natural exchange ions of the clay by the quaternary ammonium ions TMA (tetramethylammonium), TMPA (trimethylphenylammonium), HDTMA (hexadecyltrimethylammonium), and BDTDA (benzyldimethyltetradecylammonium). Experiments on the kinetics of sorption of naphthalene and diuron by two of the organoclays show that equilibrium is attained quickly, in most cases within one or two hours. Of the organoclays studied, TMP A-montmorillonite has the greatest sorptive ability for naphthalene and is followed in order of decreasing sorptive ability by BDTDA-, HDTMA-, and TMA-montmorillonite. Naphthalene molecules are too large to penetrate the interlayers of TMA-montmorillonite. TMA-montmorillonite is much more effective as a sorbent for benzene than it is for naphthalene. For benzene sorption, TMP A-montmorillonite is most effective, followed in order by TMA-, BDTDA- and HDTMA-montmorillonite. Diuron molecules are too large to penetrate the interlayers of TMA- and TMPA-montmorillonite, so sorption of diuron by the organoclays is increasingly effective in the order TMA-, TMPA-, HDTMA-, and BDTDA-montmorillonite, the same as the order of increasing organic carbon content of the organoclays. The presence of methanol as a cosolvent reduces the sorption coefficients roughly in the manner predicted by the solvophobic theory of Rao et al. (1985), that is, the sorption coefficients decrease approximately in log-linear fashion as the methanol content increases, but there are irregularities in some of these relationships owing to swelling of the organoclays in the presence of the cosolvent. The swelling of these organoclays in methanolwater mixtures has been quantified by x-ray diffraction analysis of samples equilibrated with the solvent mixtures. Differences in the apparent value of the empirical constant, a, for different sorbate-sorbent pairs point to other interactions not accounted for by the solvophobic theory. Experiments with radiolabelled HDTMA-montmorillonite indicate that organoclays are stable in methanol-water mixtures and that appreciable loss of organic ions by exchange with inorganic cations is appreciable only if the concentration of inorganic cations is relatively large (~1 N).

Principal Investigator: Thomas N. Debo (College of Architecture, Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1993-04-01; Completion Date: 1994-03-31;
Keywords: Computer model, Design procedures, Infiltration, Stormwater management, Urban runoff, Water quality control

Description:
This research has focused on the development of a personal computer model which was designed to assist in the design and analysis of infiltration systems. The systems included in the model are infiltration basins, infiltration trenches, dry wells, porous asphalt pavement and vegetated swales with check dams. This report outlines the data needed and procedures that must be followed to use the model, possible applications, and a computer slide show which can be used to assist in training professionals in the use of the model. Model limitations and anticipated problems in using the model are discussed. The Infiltration Computer Model is designed for use on personal computers that run MS DOS. The model is interactive in that the user is prompted for all input data by answering questions given on the computer screen. The user then has several choices in running the different design options and obtaining output on the screen or in printed format. Menus are given to allow the user to select options for design and analysis. Following are some of the other characteristics of the model. (1)Each portion of the model has on-screen editing capabilities to correct errors in data input and allow the user to change specific data values.

Principal Investigator: Robert E. Carver (University of Georgia)

Sponsor: GWRI
Start Date: 1993-04-01; Completion Date: 1993-04-01;
Keywords: Ground water, groundwater, aquifer, artesian, storativity, coefficient of storage, storage coefficient, limestone aquifer, Floridan aquifer, Georgia, Atlantic Coastal Plain, southeast Atlantic Coastal Plain

Description:

The role of storativity in production of water from the artesian portion of the Floridan aquifer in Georgia was examined from three standpoints: Expected change in water and aquifer volume under the observed historic pressure change, storage coefficients derived from historic production and observed aquifer pressure change, and the change in aquifer volume required to supply historic water production.