ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb03727.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe potential for bioremediation of ground water polluted with various alkylpyridines was investigated. Aerobic bacteria, indigenous to the ground‐water aquifer, were utilized for biodegradation of the various contaminants. Laboratory experiments demonstrated that biodegradation occurred only under aerobic and not under anaerobic conditions. Analysis of the ground water in the site indicated that levels of oxygen were below 1 mg/l. Thus, it is suggested that oxygen limitation prevented the biodegradation of pollutants in the aquifer. Phosphate amendment (5 mg/1) into slurries of contaminated sediment and ground water resulted in enhanced degradation rates.Columns filled with aquifer material and leached with contaminated ground water were used to simulate possible in situ bioremediation. Reduction in concentration of the different compounds in column effluents ranged between 40 and 80%, with 2,3‐, 2,6‐, and 3,5‐lutidine degrading at lower rates than other contaminants. In addition to in situ treatment, the potential of using aboveground systems for treatment was explored. A mixed culture capable of degrading 14 different alkylpyridines was isolated from the subsurface sediment. This culture was used to seed a two‐stage fixed film reactor. The reactor was fed with a mixture of organic acids and alkylpyridines that simulated the ground‐water composition. The reactors were very effective in removing the pollutants from the waste stream. The efficiency of alkylpyridine removal was between 98 and 100% and overall COD removal was 97%, when operating at a loading rate of 4.32 g COD/L‐h and hydraulic retention time of 3 h. These results imply that a combined approach which utilizes both in situ and aboveground treatments should be used for the bioremediation of polluted

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01879.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractIn situ bioremediation of contaminated aquifers is often limited by the concentration of dissolved oxygen in the ground water. Various methods have been used to increase dissolved oxygen concentrations in ground water, but the effect of a trapped gas phase on the distribution and transport of dissolved oxygen needs to be understood. The two‐dimensional transport of dissolved oxygen is investigated in experiments conducted in a large‐scale physical aquifer model (2 m × 4 m × 0.2 m) where a gas phase is trapped in the pore spaces of an otherwise‐saturated porous medium. The transport of dissolved oxygen is shown to be retarded up to 11.2 times the transport of the bulk water due to the mass transfer of oxygen between the aqueous phase and the trapped gas phase. The theoretical model for dissolved gas transport in the presence of a trapped gas phase is evaluated in a two‐dimensional ground‐water flow field using the U.S.G.S. numerical model MOC. The results show that dissolved oxygen transport can be modeled with the advection‐dispersion equation with linear equilibrium mass transfer but only when the longitudinal dispersion is increased compared to the value determined using a bromide tracer of the water flow. Increased longitudinal dispersion of the dissolved oxygen plume may be due to a temporally or spatially varying retardation factor or rate‐limited mass transfer. The presence of even a small amount of a trapped gas phase in an aquifer will significantly affect the distribution and transport of dissolved oxygen (trapped gas filling only 5% of the pore space will cause a retardation factor for oxygen of 2.6 at T = 15°C) and thus should be considered when designing ways to increase the dissolved oxygen concentration in ground water for in sit

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01880.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractSurface application offers an inexpensive, noninvasive alternative to injection wells and infiltration galleries for in situ ground‐water bioreniediation applications. The technology employs artificial recharge to create favorable hydraulic conditions for mixing and vertical transport of supplemental electron acceptor and nutrients. A test plot infdtration test and a conservative tracer test at Eglin Air Force Base, FL confirmed the potential for transporting solutes to the subsurface via recharging water. These experiments demonstrated both the mounding hydraulics and vertical solute transport that occurs in response to surface application. Modeling provided quantitative estimates of site‐specific hydrogeologic and transport parameters. Experimental results also indicated that dilution may be a dominant attenuation mechanism associated with high surface application rates. The tests also served as the basis for the design of a pilot scale surface application system for delivery of nitrate to bioremediate a JP‐4 contaminated aquifer at the Eglin site. Models calibrated to data from the infiltration experiment were scaled up for design of the pilot scale surface application system. Preliminary tracer results from the pilot scale experiment confirm that surface application can adequately deliver chemicals to the subsu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01881.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractChlorinated organic solvents introduced to unlined lagoons at an industrial waste‐water treatment plant in the Inner Piedmont of South Carolina resulted in ground‐water contamination of a fractured‐rock aquifer. Part of the ground‐water contamination discharges to Little Rocky Creek, downgradient from the waste‐water treatment plant. Passive vapor collectors were buried in the bottom sediment of the creek to locate areas where ground water contaminated with volatile organic compounds was discharging to the creek. High concentrations of volatile organic compounds (VOCs) were found in passive vapor collectors in an area where VOCs were known to be discharging from ground water to surface water. This area was also a site where very low frequency electromagnetic anomalies (interpreted as fracture zones) intersected the creek or converged near the creek. The data show that passive vapor collectors in bottom sediment of Little Rocky Creek provided information on the location of fractures that were discharging contaminated ground water to surf

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01882.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA new technology called the In Situ Permeable Flow Sensor has been developed at Sandia National Laboratories. These sensors use a thermal perturbation technique to directly measure the direction and magnitude of the full three‐dimensional ground‐water flow velocity vector in unconsolidated, saturated, porous media. The velocity measured is an average value characteristic of an approximately 1 cubic meter volume of the subsurface. The sensors are permanently buried in direct contact with the formation at the point where the velocity measurement is to be made. While this deployment strategy means that the approximately $2500 instruments are not recovered, borehole effects which can negatively influence the quality of the measurement are avoided. The sensors can be connected to a data acquisition system which can be monitored remotely, via modem and telephone connection, for extended periods of time. The technology is able to measure flow velocities in the range of 5 × 10‐6to 1 × 10‐3cm/s, depending on the thermal properties of the medium in which it

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01883.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe application of dissolved stable gases as injected ground‐water tracers is a relatively new area of study, and the transport behavior of dissolved gases in a comprehensive range of saturated porous media types is poorly understood. Gas tracers, and sulphur hexafluoride (SF6) in particular, possess many of the characteristics of an ideal conservative, nonreactive tracer. SF6is a volatile, nontoxic, inorganic gas that, when dissolved in water, behaved similarly to bromide in an idealized highly uniform saturated medium, exhibiting little physical nonequilibrium. For sand possessing significant intragranular porosity, SF6did not show persistent tailing as a result of physical nonequilibrium transport to the same degree as bromide. This is consistent with less mass transfer of SF6to immobile porosity due to its lower diffusion coefficient. This nonequilibrium is enhanced by the high pore‐water velocities employed. SF6is slightly hydrophobic, with a measured octanol‐water partitioning coefficient of 13.8. This raises the question of whether SF6would be slightly retarded in media with significant organic carbon, but no evidence of retardation was seen in sand with focas high as 2.

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01884.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractConcentrations of222Rn in ground water may vary considerably within megascopically homogeneous rocks over relatively short distances. Calculations indicate that different hydraulic apertures of water‐bearing fractures may account for variations in dissolved222Rn concentration measured in domestic water wells completed in fractured Pikes Peak Granite, assuming that all other factors influencing dissolved222Rn concentrations are constant. Concentrations of dissolved222Rn range from 124 to 840 kBq m‐3[3,360 to 22,700 picocuries per liter (pCi L‐1)] within a 2.5 km2well field. Aquifer tests show that transmissivities range from 0.072 to 160 m2day‐1within the well field. Acoustic televiewer and heat‐pulse flow meter logging of four wells reveals that, despite tens to hundreds of fractures that intersect each well, a single fracture supplies all the flow to three wells, and one fracture provides 65% of the flow to the fourth well. Aquifer tests indicate that two pairs of the four wells are hydraulically connected. Type‐curve interpretation of early‐time data from aquifer tests reveals classic half‐slope behavior on log‐log plots of drawdown versus time for two wells, suggesting linear flow to a single fracture. Drawdown versus time for the other two wells indicates radial or pseudo‐radial flow, which suggests a higher degree of fracture interconnectivity near those boreholes.Hydraulic apertures calculated using the cubic law are 0.024 and 0.038 cm for producing fractures in the first hydraulically connected well pair and 0.011 and 0.020 cm for flowing fractures in the second well pair. Assuming uniform distribution of226Ra along fracture walls and long residence time of water relative to222Rn decay, the ratio of fracture apertures should equal the inverse ratio of222Rn concentration in each well. Assuming 50% error in hydraulic aperture estimation and 10% analytical uncertainty in222Rn measurement, differences in222Rn concentration between wells in the hydraulically connected pairs can be attributed solely to differences in hydraulic aperture. Different hydraulic apertures, however, do not explain different222Rn concentrationsbetweenwell pairs. Allowing for measurement error, a cubic meter of rock transfers from 1.3 to 20 times more222Rn to ground water in the first pair of wells than in the second pair. Nonuniform distribution of226Ra along fracture walls, heterogeneous emanating power in the rock‐water system, or short ground‐water residence time along the transmissive fracture network may account for the differ

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01885.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe results of a field experiment comparing water‐quality constituents, specific conductance, geophysical measurements, and well‐bore hydraulics in two long‐screen wells and adjacent vertical clusters of short‐screen wells show bias in ground‐water data caused by well‐bore flow in long‐screen wells. The well screen acts as a conduit for vertical flow because it connects zones of different head and transmissivity, even in a relatively homogeneous, unconfined, sand and gravel aquifer where such zones are almost indistinguishable. Flow in the well bore redistributes water and solutes in the aquifer adjacent to the well, increasing the risk of bias in water‐quality samples, failure of plume detection, and cross‐contamination of the aquifer. At one site, downward flow from a contaminated zone redistributes solutes over the entire length of the long‐screen well. At another site, upward flow from an uncontaminated zone masks the presence of a road salt plume.Borehole induction logs, conducted in a fully penetrating short‐screen well, can provide a profile of solutes in the aquifer that is not attainable in long‐screen wells. In this study, the induction‐log profiles show close correlation with data from analyses of water‐quality samples from the short‐screen wells; however, both of these data sets differ markedly from the biased water‐quality samples from the long‐screen wells. Therefore, use of induction logs in fully cased wells for plume detection and accurate placement of short‐screen wells is a viable alternative to use of long scre

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01886.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractLaboratory and field experiments have shown that cationic surfactants can be used to modify aquifer materials, and thereby form zones of enhanced sorption for hydrophobic organic contaminants (HOC's) migrating in ground water. Coupled to a contaminant degradation or removal process, this concept has potential as a remediation technology. In order to apply enhanced sorption in a remediation scheme, an ability to predict the transport and partitioning behavior of cationic surfactants in the subsurface is necessary. In this paper we present the results of a numerical modeling study in which the transport and partitioning behavior of the cationic surfactant hexadecyltrimethylammonium chloride (HDTMA) in porous media is investigated. Modeling of previously published batch and column HDTMA sorption experimental results for Columbus Air Force Base aquifer material indicates that, under certain conditions, kinetic effects will dominate the transport process with slow desorption of HDTMA being the likely rate‐controlling step. The results suggest that a significant departure from equilibrium will exist under natural gradient conditions for the Columbus aquifer material. Low aqueous surfactant concentrations can be expected to persist within a surfactant‐enhanced sorption zone, even after considerable flushing with surfactant‐free ground water. The low aqueous concentration may have implications in terms oftoxicityto microorga

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb01887.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY