Outwash Aquifer Research Articles

Reductive Dissolution and Reactive Solute Transport in a Sewage‐Contaminated Glacial Outwash Aquifer

AbstractContamination of shallow ground water by sewage effluent typically contains reduced chemical species that consume dissolved oxygen, developing either a low oxygen geochemical environment or an anaerobic geochemical environment. Based on the load of reduced chemical species discharged to shallow ground water and the amounts of reactants in the aquifer matrix, it should be possible to determine chemical processes in the aquifer and compare observed results to predicted ones.At the Otis Air Base research site (Cape Cod, Massachusetts) where sewage effluent has infiltrated the shallow aquifer since 1936, bacterially mediated processes such as nitrification, denitritication, manganese reduction, and iron reduction have been observed in the contaminant plume. In specific areas of the plume, dissolved manganese and iron have increased significantly where local geochemical conditions are favorable for reduction and transport of these constituents from the aquifer matrix. Dissolved manganese and iron concentrations ranged from 0.02 to 7.3 mg/L, and 0.001 to 13.0 mg/L, respectively, for 21 samples collected from 1988 to 1989.Reduction of manganese and iron is linked to microbial oxidation of sewage carbon, producing bicarbonate and the dissolved metal ions as by‐products. Calculated production and flux of CO2 through the unsaturated zone from manganese reduction in the aquifer was 0.035 g/m2/d (12% of measured CO2 flux during winter). Manganese is limited in the aquifer, however. A one‐dimensional, reaction‐coupled transport model developed for the mildly reducing conditions in the sewage plume nearest the source beds showed that reduction, transport, and removal of manganese from the aquifer sediments should result in iron reduction where manganese has been depleted.

Meiofauna assemblages discharged by springs from a phreatic aquifer system in the Netherlands

Groundwater meiofauna washed out of springs was studied by means of spring water filtration. The principal interest was a quantitative analysis of the number and diversity of outwash fauna in relationship to hydrological conditions. In addition, a comparative analysis was made of outwash fauna of different outlets of the same hydrological system. The spring complex studied is part of the Centraal Plateau in the southern-most part of The Netherlands. This area is characterized by, for The Netherlands, relatively high hydraulic heads and large permeability of aquifers. Influence of human activities (agriculture) in the recharge area was demonstrated by elevated concentrations of nitrate, chloride, and sulphate in the spring waters. No traces of groundwater pollution by heavy metals or pesticides were found. Temporal variation of meiofauna outwash was studied in a single rheocrene spring during one year. This rheocrene had a relatively large and constant discharge (1300±8 ¦h−1). Meiofauna numbers fluctuated between 110–240 ind. m−3. Considerable differences in meiofauna numbers in a one-off analysis of different springs (rheocrenes and helocrenes) were found. Numbers ranged from 140 to 5800 org. m−3 and an inverse relationship with the amount of water discharged was shown. Organisms in the water filtrates were of multiple origin: aquifer(e.g. Niphargus, Parastenocaris), benthic spring head habitats (e.g. Gammarus, Chironomidae), and (saturated) soils near the outlets (e.g. Criconomatidae). Meiofauna abundance and composition is discussed in relation to hydrology and spring head morphology. A semi-quantitative analysis of outwash aquifer fauna was masked by the presence of epigean elements or elements of unclear origin. The outwash fauna of rheocrenes of large discharge supposedly is the most representative for the aquifer. Adaptations of hypogean populations to oligotrophic porous environments and the consequences for drift of juvenile stages is discussed.

A Comparison of Methods to Determine K in a Shallow Coastal Aquifer

AbstractFive methods (tidal damping, tracer, slug, permeameter, and grain‐size analysis) for the determination of hydraulic conductivity (K) were compared in both upland and shoreline regions of a sandy outwash aquifer adjacent to a shallow coastal embayment. The 7 m tracer test and tidal damping methods appeared to determine in situ K over sufficient horizontal scales to integrate the spatial variability of K within the aquifer, with the tracer test giving the most reproducible K estimates for the upland, 109 m/d. The tidal K measurements were similar to the tracer results, 106 m/d, integrating K over greater distances (30 to 85 m), but were highly variable due to the large aquifer storativity, small tidal amplitude, and irregular tides.The smaller scale methods yielded lower upland K estimates with the lowest value from permeameters, 29 m/d, only about one‐third of the other four methods. Estimates of upland K by both grain‐size and slug tests were comparable, 86 m/d and 71 m/d, respectively. However, the K derived from grain‐size methods was dependent not only upon the sediment but on the method selected, with consistently higher values of K generated by the Hazen equation than the Krumbein and Monk equation. Verification by in situ tests may be useful in removing this bias.Significant differences in K were found between shoreline and upland regions, though the relative magnitude of the difference was not constant: among the four methods where comparative measurements were possible, shoreline K ranged from 42% to 75% of upland values. Slug tests yielded the largest differences, 30 m/d and 71 m/d, with permeameter, 18 m/d and 24 m/d, the lowest. The lower K of shoreline sediments appears to be the result of processes associated with coastal embayments and should be addressed in the measurement and modeling of coastal ground‐water discharge.

Sorption of Chlorobenzenes to Cape Cod Aquifer Sediments

Sorption of tetra- and pentachlorobenzene by sediment from a glacial outwash aquifer on Cape Cod, MA, was evaluated. Particle size and mineralogical fractions (separated based on paramagnetic susceptibility) were characterized with respect to sediment organic carbon (SOC), mineralogy, surface area, metal oxide coatings, and spatial variability. SOC increases by a factor of 10 as particle size decreases from 500-1000 to 25% in the <63-μm fraction, and SOC is preferentially associated with the magnetic minerals

Herbicide Leaching Potential Through Road Ditches in Thin Soils Over an Outwash Aquifer

Shallow glacial outwash aquifers provide water to farms, towns, and major cities. The fact that overlying soils are shallow and provide little protection from leachable chemicals suggests the need for careful management of chemical use. This research was conducted to provide data on the leaching potential of 2,4-D and picloram applied to road ditches over shallow aquifers. A comparison of soil profiles in the ditch and adjoining field indicated that an average of 0.3 m (1 ft) of soil was removed from road ditch soils, leaving very shallow soil profiles over the aquifer material. Cumulative infiltration of water into side slopes and ditch bottoms was measured on representative soils together with gravel road runoff to determine a water balance for the ditch. Undisturbed soil columns were brought into a greenhouse where leaching water could be collected and analyzed for the herbicides, 2,4-D and picloram, the currently used herbicides, which had been applied at recommended rates. The combination of extra leaching water from road runoff added to direct rainfall, and the naturally shallow soils that have been reduced in depth to build the roadbed resulted in two to five times the water passing through to groundwater than through adjoining fields. From 2 to 33% of the applied herbicides came through the undisturbed soil columns after the first storm event. The results indicate that caution should be exercised if the choice is made to use chemical methods of weed control in road ditches.

Crude oil in a shallow sand and gravel aquifer—II. Organic geochemistry

Crude oil spilled from a pipeline break in a remote area of north-central Minnesota has contaminated a shallow glacial outwash aquifer. Part of the oil was sprayed over a large area to the west of the pipeline and part of it accumulated in an oil body that floats at the water table to the east of the point of discharge. Total dissolved organic carbon (TDOC) concentrations in shallow groundwater collected in the oil spray area reach 16 mg/l. This is nearly an order of magnitude higher than the TDOC concentrations of native groundwater (∼2–3mg/l). The additional TDOC derives from the partial degradation of petroleum residues deposited at the land surface and transported to the aquifer by vertical recharge. In the vicinity of the oil body, TDOC concentrations in groundwater are 48 mg/l, 58% of the TDOC being composed of non-volatile organic C. The majority of the volatile DOC (63%) is a mixture of low-molecular-weight saturated, aromatic and alicyclic hydrocarbons derived from the oil. Downgradient from the oil body along the direction of groundwater flow, concentrations of all measured constituents of the TDOC pool decrease. Concentrations begin to decline most rapidly, however, in the zone where dissolved O 2 concentrations begin to increase, ∼50m downgradient from the leading edge of the oil. Within the anoxic zone near the oil body, removal rates of isometric monoaromatic hydrocarbons vary widely. This indicates that the removal processes are mediated mainly by microbiological activity. Molecular and spectroscopic characterization of the TDOC and its spatial and temporal variation provide evidence of the importance of biogeochemical processes in attenuating petroleum contaminants in this perturbed subsurface environment.

Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties

AbstractTo study the effect of spatial variability of sediment hydraulic properties on multiphase flow, oil infiltration into a hypothetical glacial outwash aquifer, followed by oil extraction, was simulated using a cross‐sectional multiphase flow model. The analysis was simplified by neglecting capillary hysteresis. The first simulation used a uniform mean permeability and mean retention curve. This was followed by 50 Monte Carlo simulations conducted using 50 spatially variable permeability realizations and corresponding spatially variable retention curves. For the type of correlation structure considered in this study, which is similar to that of glacial outwash deposits, use of mean hydraulic properties reproduces the ensemble average oil saturation distribution obtained from the Monte Carlo simulations. However, spatial variability causes the oil saturation distribution in an individual oil lens to differ significantly from that of the mean lens. Oil saturations at a given location may be considerably higher than would be predicted using uniform mean properties. During cleanup by oil extraction from a well, considerably more oil may remain behind in the heterogeneous case than in the spatially uniform case.

Laboratory Column Measurement of VOC Retardation Factors and Comparison with Field Values

AbstractA laboratory column technique was developed to measure retardation factors (Rf) of volatile organic compounds (VOC) using geological material obtained from an outwash aquifer. The site is a former solvent disposal pit near Ottawa, Canada. The experimental column was designed as a closed system from introduction of the sample to the collection and analysis of effluent samples to prevent loss through volatilization of the VOCs. The retardation of the volatile compounds 1,4‐dioxane, tetrahydrofuran, diethyl ether, 1,2‐dichloroethane, chloroform, 1,1‐dichloroethene, and benzene was measured. The centers of mass of both the contaminant and conservative tracer breakthrough curves were compared to determine Rf. The measured Rf values ranged from 1.1 (1,4‐dioxane) to 14.3 (benzene) compared with values of 1.6 and 8.8 derived from contaminant plume lengths. Considering the uncertainty of the disposal history at the site, the values are of reasonable agreement in comparison.

Interim pump‐and‐treat remediation of a hydrocarbon‐contaminated aquifer

AbstractThe continuous and discontinuous release of petroleum hydrocarbons from an oil refinery in Alaska resulted in the contamination of an unconfined glacial outwash aquifer. Geologic conditions at the site allowed for the vertical migration of hydrocarbon product to the water table and subsequent formation of an areally extensive floating product layer. Since the petroleum hydrocarbon phase would provide a major source of BTX (benzene, toluene, xylene) contamination to the groundwater, interim product and groundwater recovery measures were initiated to limit aquifer degradation. Phase I remedial activities involved the operation of nine well pairs, with one well used for groundwater extraction and the other for product recovery. Phases II and III involved expansion of the recovery well network and use of a two‐pump system. Petroleum product recovered was reprocessed at the refinery. Contaminated groundwater was initially treated using the refinery's wastewater treatment system, but treatment inefficiencies and continued system expansion necessitated use of a separate treatment unit. Performance evaluations indicate that the remedial phases have been successful in halting further contaminant migration and in recovering a significant volume of the released petroleum hydrocarbons.

Hydrogeology and historical assessment of a classic sequential-land use landfill site, Illinois, U.S.A.

The Blackwell site in northeastern Illinois was a classic sequential-use project combining land reclamation, a sanitary landfill, and a recreational park. This paper adds a recent assessment of leachate generation and groundwater contamination to the site's unfinished record. Hydrogeological studies show that (1) the landfill sits astride an outwash aquifer and a till mound, which are separated from an underlying dolomite aquifer by a thin, silty till; (2) leachate leaks from the landfill at an estimated average rate between 48 and 78 m3/d; (3) the resultant contaminant plume is virtually stagnant in the till but rapidly diluted in the outwash aquifer, so that no off-site contamination is detected; (4) trace VOC levels in the dolomite probably indicate that contaminants have migrated there from the landfill-derived plume in the outwash. Deviations from the original landfill concepts included elimination of a leachate collection system, increased landfill size, local absence of a clay liner, and partial use of nonclay cover. The hydrogeological setting was unsuitable for the landfill as constructed, indicating the importance of detailed geological consideration in landfill and land-use planning.

A Remedial Investigation of an Organically Polluted Outwash Aquifer

AbstractA glacial outwash aquifer underlying the Gloucester Landfill near Ottawa, Canada, has become polluted with various organic chemicals following the disposal of laboratory solvents in shallow trenches immediately above the aquifer. Several remedial alternatives have been considered by the government of Canada. Impermeable barrier walls were rejected as being unsuitable given the permeable nature of the underlying bedrock. It appears improbable that pools of liquid organic chemicals (DNAPLs) exist within the aquifer, although ganglia are likely present. Therefore, much of the contaminant plume can be removed hydraulically over a period of five years by the operation of four purge wells discharging to an on‐site treatment plant from which the purified water is returned to the aquifer by recharge wells. The residual contamination is anticipated to be cleaned up by in situ biorestoration techniques currently under development.

Hydrologic and water-quality characteristics of a Wetland receiving wastewater effluent in St. Joseph, Minnesota

Hydrologic and water-quality characteristics were determined for a wetland being used for tertiary treatment of wastewater in St. Joseph, Minnesota. The wetland consists of spruce-tamarack fen and a cattail marsh, with the wastewater being discharged into the fen, and the fen draining into the marsh. The wetland is underlain by flat-lying glacial outwash that ranges from 0 to greater than 20 m in thickness. Horizontal ground-water movement in the outwash aquifer is toward the wetland from the south, east, and west. There is a strong upward vertical hydraulic gradient (about 0.1) in the ground-water flow system beneath and around the wetland. Regionally, the glacial-outwash aquifer is unconfined, but it is confined or partly confined locally by peat deposits under the wetland. Analysis of the hydrologic balance of the fen from October 1985 through September 1986 indicates that the inflow was 44 percent ground water, 38 percent wastewater, 11 percent runoff (storm sewer), and 7 percent precipitation. The fen outflow was 93 percent surface water and 7 percent evapotranspiration. Inflow to the marsh was 74 percent surface water, 21 percent ground water, and 5 percent precipitation. Outflow from the marsh was 94 percent surface water and 6 percent evapotranspiration. Wastewater contributed 74,996, and 81 percent of the total suspended solids, total phosphorus, and total ammonia plus organic nitrogen in the fen, respectively. Other chemical inputs were from the storm sewer, ground water, and atmospheric deposition. The fen was found to retain 34, 14, and 14 percent of the suspended solids, total phosphorus, and total ammonia plus organic nitrogen, respectively. The marsh retained 44, 18, and 22 percent of these three constituents, respectively.

Retardation of Toxic Chemicals in a Contaminated Outwash Aquifer

Organic chemicals disposed between 1969 and 1980 in a “Special Waste Compound” at the Gloucester Landfill near Ottawa, Canada, are migrating through a confined outwash aquifer. The subsurface distribution of the chemicals down gradient from the disposal site suggests that chromatographic dispersion (i.e. aqueous phase solute transport plus sorption) is the major process controlling migration. Retardation factors calculated on the basis of relative lengths of contaminant plumes agree closely with those determined independently during a purge-well test and indicate a linear relationship with the logarithm of the octanol/water partition coefficient (Kow): The slope, 0.50, of this relationship is at the low end of the range of values reported for other expressions of the same form determined principally on the basis of laboratory experiments. This lower slope may reflect the fact that in aquifers flow is predominantly through the coarser, less organic-rich units. The relatively low range of Kow values (log Kow from −0.27 to 2.83) represented by the contaminants may also be a factor contributing to a smaller slope value.

Geology of Indianapolis, Indiana, United States of America

The engineering geology of Indianapolis, Indiana, is strongly influenced by glacial drift, which covers Marion County with a thickness varying from 10 to 350 ft (3.1 to 106.7 m), averaging 140 ft (42.7 m). Nearly all major structures are supported on spread footings bearing either on overconsolidated Wisconsin till or on dense sand and gravel outwash deposits along White River or Fall Creek. Spread footings supporting high rise buildings (up to 38 stories) in downtown Indianapolis are typically designed for bearing pressures of 8 to 12 kips/ft 2 (3.9 to 5.9 kg/cm 2 ). For the relatively small number of structures supported on deep foundations, pressure-injected footings, auger cast piles and drilled piers are the most common types. The main geologic resources of commercial importance in Marion County are sand and gravel, which are obtained from outwash deposits along major streams, and, to a lesser degree, mined limestone. Ninety-five percent of the water withdrawn by the Indianapolis Water Company is from surface sources, as three water supply reservoirs have been formed by constructing dams across major streams. Recent studies have shown that significant quantities of ground water are available within outwash aquifers along White River and Fall Creek.

Electrical resistivity—hydraulic conductivity relationships in glacial outwash aquifers

Empirical field relationships between the apparent formation factors from surface resistivity soundings and hydraulic conductivity from pumping tests in fresh water granular aquifers usually show positive correlations. These relationships can be adequately explained by theory if consideration is taken of in situ field conditions. A sound theoretical basis for relating apparent formation factor to pertinent hydrogeophysical parameters in homogeneous isotropic sand is a three‐phase parallel resistor model which explicity includes parameters of porewater resistivity, grain size and shape, porosity, tortuosity, and intergranular surface conductance. The veracity of the theoretical model is supported by data from laboratory tests. The model demonstrates that intergranular surface conductance is an important factor at small grain sizes and high porewater resistivities, operating to lower the apparent formation factor. The model further shows that direct relationships between hydraulic conductivity and formation factor are weak in the normal range of porewater resistivity, being strongly dependent on porosity. When systematic variation of in situ porosity and aquifer layering effects are considered, a simulated field curve relating the apparent formation factor to hydraulic conductivity is shown to compare favorably with the comparable curve from field data for thirteen pumping test sites in southern Rhode Island. Both theoretical and empirical results demonstrate a useful positive correlation between aquifer apparent formation factor and hydraulic conductivity. Quantitative interpretation, however, is imprecise because of nonuniqueness of interpretation and inherent variation in important aquifer parameters, especially porosity.

THE USE OF A GAMMA LOGGER TO DELINEATE GLACIAL AND BEDROCK STRATIGRAPHY IN SOUTHWESTERN OHIO

Abstract. An evaluation was made of the usefulness of the gamma‐ray logger in delineating glacial‐drift and bedrock stratigraphy in southwestern Ohio. The logger was useful in delineating gross stratigraphic units in a glacial outwash aquifer. The gamma log also provided a clearer indication of the clay content of sand and gravel units than did the driller's log.On the uplands, away from the valleys filled with glacial outwash, the logger could not be used to locate the thin, poorly‐sorted, interstadial sand and gravel deposits between thicker till sheets. It could, however, be used to distinguish formational contacts in the upper Cincinnatian Series.

Aquifer Transmissivity from Surficial Electrical Methods

ABSTRACTRecent advances in the automatic inversion of vertical electrical sounding data offer the opportunity to describe the relationship of the resistivity of a granular aquifer to its hydraulic conductivity. This type of relationship, together with aquifer thickness, can be used to determine the transmissivity of the aquifer.Vertical electrical soundings and pump‐test data along the axis of a glacial outwash aquifer in central Illinois have indicated an inverse relationship between aquifer resistivity and hydraulic conductivity. This relationship has been attributed to differences in sorting of the outwash sediments. But studies of granular aquifers deposited in other geologic environments are needed before meaningful generalizations can be made.

Effects of a Concentrated Acid on Water Chemistry and Water Use in a Pleistocene Outwash Aquifera

AbstractA break in a waste‐discharge line associated with a 49‐foot rise in stage of the Ohio River in March 1967 allowed an undetermined volume of 22 percent hydrochloric acid to enter the Pleistocene outwash aquifer used by a Kentucky industry. Chloride concentrations in excess of 30,000 mg/l (milligrams per liter) were observed in the water discharged from the industrial well nearest the break in the waste‐discharge line. Chlorides ranged from 5–26 mg/l in water pumped from this area prior to intensive development. Other changes in water chemistry such as an increase in iron from 5 mg/l to 9,600 mg/1 indicate a dissolution of the aquifer materials. Movement of the highly mineralized water in response to river stage and pumping of the industrial wells has forced the industry to change its water‐supply system. Three wells, approximately 600 feet from the river, were the primary water source prior to March 1967. By March 1968, the well nearest the acid source was abandoned, the remaining two wells near the river were used in a supplemental capacity and a fourth well 1,500 feet from the river plus a new well were the primary water sources. Fluctuations of chlorides in an industrial well near the river for a 16‐month period indicate a persistent body of highly miner alized water near the acid source. Movement of this water body appears to be regulated at low river stages by the inclined surface of the New Albany Shale bedrock.

Use of Type Curves Developed from Electric Analog Studies of Unconfined Flow to Determine the Vertical Permeability of an Aquifer at Piketon, Ohioa

AbstractA type‐curve method for determining anisotropy of unconfined aquifers, developed from electric analog simulation, is applied to drawdowns observed near, a well pumping from a glacial outwash aquifer at Piketon, Ohio. The coefficient of vertical permeability, P z'averaged 365 gpd per square foot. Computed drawdown for the pumped well, based on this value, differed by only a small amount from the observed drawdown. The coefficient of storage, determined from type curves for an image well system, averaged 0.20, typical of unconfined aquifers. Application of the method required a thorough knowledge of geohydrologic controls operating at the test site.