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1.
The maximum contaminant level for arsenic was reduced by the U.S. Environmental Protection Agency (U.S. E.P.A.) for Drinking Water Standards from 50 micrograms per liter (µg/L) to 10 µg/L, effective January 23, 2006. The subject site is a double-lined sanitary landfill facility located in the mid-Atlantic region of the United States. Arsenic was reported above the maximum contaminant level in a downgradient monitoring well (MW-18) in July 2005. Since July 2005, arsenic levels in MW-18 fluctuated above and below 10 µg/L. This research focuses on determining whether reducing conditions in groundwater, enhanced by subsurface landfill gas emissions, were causing naturally-occurring arsenic to mobilize from the native variably-saturated vadose zone soils into groundwater. The groundwater data collected from the impacted well (MW-18) were compared to an upgradient well (MW-8) to determine whether significant differences existed during the time period of April 2004 to April 2007. Linear regression analysis was also used to determine whether other parameters had a significant relationship with the arsenic concentrations detected in MW-18. The groundwater located in MW-18 was consistently more reduced than groundwater located in the upgradient/background well MW-8, and this was most likely attributed to the presence of subsurface landfill gas in the area. According to the U.S. E.P.A., oxidation-reduction potential (ORP) values in groundwater less than 50 millivolts (mv) suggest that a reducing environment may be present. The data presented in this study indicate that arsenic can mobilize into groundwater under moderately reducing conditions, with ORP measurements averaging 53 mv.  相似文献   

2.
Chloride contamination of groundwater in urban areas due to deicing is a well‐documented phenomenon in northern climates. The objective of this study was to evaluate the effects of permeable pavement on degraded urban groundwater. Although low impact development practices have been shown to improve stormwater quality, no infiltration practice has been found to prevent road salt chlorides from entering groundwater. The few studies that have investigated chlorides in permeable asphalt have involved sampling directly beneath the asphalt; no research has looked more broadly at surrounding groundwater conditions. Monitoring wells were installed upgradient and downgradient of an 860 m2 permeable asphalt parking lot at the University of Connecticut (Storrs, Connecticut). Water level and specific conductance were measured continuously, and biweekly samples were analyzed for chloride. Samples were also analyzed for sodium (Na), calcium (Ca), and magnesium (Mg). Analysis of variance analysis indicated a significantly (p < 0.001) lower geometric mean Cl concentration downgradient (303.7 mg/L) as compared to upgradient (1280 mg/L). Concentrations of all alkali metals increased upgradient and downgradient during the winter months as compared to nonwinter months, indicating that cation exchange likely occurred. Despite the frequent high peaks of chloride in the winter months as well as the increases in alkali metals observed, monitoring revealed lower Cl concentrations downgradient than upgradient for the majority of the year. These results suggest that the use of permeable asphalt in impacted urban environments with high ambient chloride concentrations can be beneficial to shallow groundwater quality, although these results may not be generalizable to areas with low ambient chloride concentrations.  相似文献   

3.
This research continues a 7-year study of oxygen-containing organic compounds present in groundwater at gasoline and diesel fuel release sites that are quantified as diesel-range “total petroleum hydrocarbons” when measured by methods utilizing solvent extraction and gas chromatography. Two-dimensional gas chromatography with time-of-flight mass spectrometry was used to tentatively identify 1162 compounds (TICs) in 113 groundwater samples from 22 sites. Samples were collected from wells either upgradient of the release, within the source zone, or downgradient of the source but still within the plume of dissolved organics associated with release. The names and formulas of all TICs found in samples from each well type are presented and the results from upgradient and downgradient locations are compared in detail. About 60% of the most frequently detected TICs in downgradient wells were also detected in upgradient wells. A majority of these were saturated straight chain alkyl acids, commonly called fatty acids, or fatty acid esters. Of TICs frequently detected in downgradient wells but not upgradient wells, over half were branched alkyl alcohols. Hierarchical cluster analysis results suggest about 80% of the chemical composition of downgradient samples is more similar to upgradient samples than to source area samples. This similarity is due to the presence of the same types of fatty acids and esters. Principal component analysis indicates a continuum of biodegradation between the source area and downgradient samples with the latter becoming more consistent with upgradient samples. Results suggest some TICs may not be petroleum degradation intermediates but compounds synthesized by microorganisms through secondary production and carbon cycling.  相似文献   

4.
The concept of integrated constructed wetlands (ICW) promotes in‐situ soils to construct and line wetland cells. The integrity of soil material, however, may provide a potential pathway for contaminants to flow into the underlying groundwater. This study assessed the extent of groundwater quality deterioration due to the establishment of a full‐scale ICW system treating domestic wastewater in Ireland. The ICW is located at Glaslough in Co. Monaghan, Ireland. It consists of two sedimentation ponds and a sequence of five shallow vegetated wetland cells. The ICW cells were lined with 500‐mm thick local subsoil material, which comprised a mixture of alluvium, organic soils, tills, and gravel. Groundwater samples and head data were collected from eight piezometers, which were installed around the ICW cells. The groundwater and wetland water samples were analysed for water quality parameters such as bulk organic matter, nutrients, and pathogens. Overall, the quality of groundwater underlying the ICW system recorded some contamination with bulk organic matter and some inorganic nutrients. Significantly higher contaminant concentrations were recorded in monitoring wells upgradient and near to the distal wetland cells than downgradient ones, which were near to the proximal cells. For the downgradient piezometers, concentrations seldomly exceeded the natural background levels. Detailed analyses through the application of chemometrics models indicated that the source of contamination was largely of geogenic origin. Findings suggest that ICW systems pose a minimal risk to the groundwater quality; the greatest risk was associated with the distal wetland cells.  相似文献   

5.
A tracer test was conducted to characterize the flow of groundwater across a permeable reactive barrier constructed with plant mulch (a biowall) at the OU‐1 site on Altus Air Force Base, Oklahoma. This biowall is intended to intercept and treat groundwater contaminated by trichloroethylene (TCE) in a shallow aquifer. The biowall is 139‐m long, 7.3‐m deep, and 0.5‐m wide. Bromide was injected from an upgradient well into the groundwater as a conservative tracer, and was subsequently observed breaking through in monitoring wells within and downgradient of the biowall. The bromide breakthrough data demonstrate that groundwater entering the biowall migrated across it, following the slope of the local groundwater surface. The average seepage velocity of groundwater was approximately 0.06 m/d. On the basis of the Darcy velocity of groundwater and geometry of the biowall, the average residence time of groundwater in the biowall was estimated at 10 d. Assuming all TCE removal occurred in the biowall, the reduction in TCE concentrations in groundwater across the biowall corresponds to a first‐order attenuation rate constant in the range of 0.38 to 0.15 per d. As an independent estimate of the degradation rate constant, STANMOD software was used to fit curves through data on the breakthrough of bromide and TCE in selected wells downgradient of the injection wells. Best fits to the data required a first‐order degradation rate constant for TCE removal in the range of 0.13 to 0.17 per d. The approach used in this study provides an objective evaluation of the remedial performance of the biowall that can provide a basis for design of other biowalls that are intended to remediate TCE‐contaminated groundwater.  相似文献   

6.
The Dakar region is a mega city with multiple contaminant sources from urban expansion as well as industrial and agricultural activities. The major part of the region is underlain by unconfined sandy aquifer, which is vulnerable to contaminants derived from human land use. At present, the contaminated groundwater which extends over a large area in the suburban zone of Thiaroye poses a threat to the future of this valuable resource, and more specifically, a health threat. This study focuses on nitrate pollution occurrences and associated processes using nitrate isotope data (15NNO3, 18ONO3) combined with environmental isotopic tracers (18O, 2H, and 3H). Samples from 36 wells were collected to determine the level, distribution, and sources of contamination in relation to land use. Results indicate that shallow groundwater in the urbanized area of Thiaroye shows distinct evidence of surface contamination with nitrate as much as 300 mg/l NO3?. In rural area not serviced by water supply distribution network, much higher NO3? contents were found in few wells due to household and livestock feedlots. In most groundwater samples δ15N values ranged from + 10 to + 22‰, indicative of predominantly human and animal wastes. This was confirmed by environmental isotope data which suggest a mixture of polluted recharge waters. By using the dual δ15N vs δ18O as well as δ15N vs NO3? approach, denitrification may occur to some extent but it is blurred by mixing with new infiltrated nitrates and cycling derived from continuous leaky septic system. Results suggest that nitrate contamination of the aquifer is a consequence of unregulated urbanisation (homemade latrines), continuing contaminant transfer in shallow water depth where aerobic conditions prevail. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates, and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principal component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e., groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading. The pharmaceutical compounds migrate in both a deep semiconfined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2-km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modeling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semiconfined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long-lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.  相似文献   

8.
The stable isotope ratios of groundwater sulfate (34S/32S, 18O/16O) are often used as tracers to help determine the origin of groundwater or groundwater contaminants. In agricultural watersheds, little is known about how the increased use of sulfur as a soil amendment to optimize crop production is affecting the isotopic composition of groundwater sulfate, especially in shallow aquifers. We investigated the isotopic composition of synthetic agricultural fertilizers and groundwater sulfate in an area of intensive agricultural activity, in Ontario, Canada. Groundwater samples from an unconfined surficial sand aquifer (Lake Algonquin Sand Aquifer) were analyzed from multi-level monitoring wells, riverbank seeps, and private domestic wells. Fertilizers used in the area were analyzed for sulfur/sulfate content and stable isotopic composition (δ18O and/or δ34S). Fertilizers were isotopically distinct from geological sources of groundwater sulfate in the watershed and groundwater sulfate exhibited a wide range of δ34S (−6.9 to +20.0‰) and δ18O (−5.0 to +13.7‰) values. Quantitative apportionment of sulfate sources based on stable isotope data alone was not possible, largely because two of the potential fertilizer sulfate sources had an isotopic composition on the mixing line between two natural geological sources of sulfate in the aquifer. This study demonstrates that, when sulfate isotope analysis is being used as a tracer or co-tracer of the origin of groundwater or of contaminants in groundwater, sulfate derived from synthetic fertilizer needs to be considered as a potential source, especially when other parameters such as nitrate independently indicate fertilizer impacts to groundwater quality.  相似文献   

9.
This study applies an optimized phytoscreening method to locate a chlorinated ethene plume discharging into a stream. To evaluate the conditions most suitable for successful phytoscreening, trees along the stream bank were monitored through different seasons with different environmental conditions and hence different uptake/loss scenarios. Vinyl chloride (VC) as well as cis‐dichloroethylene (cis‐DCE), trichloroethylene (TCE), and tetrachloroethylene (PCE) were detected in the trees, documenting that phytoscreening is a viable method to locate chlorinated ethene plumes, including VC, discharging to streams. The results reveal, that phytoscreening for VC is more sensitive to environmental conditions affecting transpiration than for the other chlorinated ethenes detected. Conditions leading to higher groundwater uptake by transpiration than contaminant loss by diffusion from the tree trunks are optimal (e.g., low relative humidity, plentiful hours of sunshine and an intermediate air temperature). Additionally, low precipitation prior to the sampling event is beneficial, as uptake of infiltrating precipitation dilutes the concentration in the trees. All chlorinated ethenes were sensitive to dilution by clean precipitation and in some months, this resulted in no detection of contaminants in the trees at all. Under optimal environmental conditions the tree cores allowed detection of chlorinated solvents and their metabolites in the underlying groundwater. Whereas, for less ideal conditions there was a risk of no detection of the more volatile VC. This study is promising for the future applicability of phytoscreening to locate shallow groundwater contamination with the degradation products of chlorinated solvents.  相似文献   

10.
The molecular and stable carbon isotopic compositions of contaminant polycyclic aromatic hydrocarbons (PAHs) at McMurdo Station, Antarctica were analyzed in samples collected from land and sub-tidal area. PAHs in the study areas were characterized by high amounts of naphthalene and alkylated naphthalenes from petroleum products introduced by human activities in the area. Principal component analysis (PCA) of PAH composition data identified multiple sources of PAH contamination in the study area. Compositional assignments of origins were confirmed using compound specific stable carbon isotopic analysis.  相似文献   

11.
A new method for the extraction of chlorinated solvents (CSs) from porewater with dimethylacetamide (DMA) used as a solvent and the determination of δ13C by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) with solid-phase microextraction (SPME) are presented. This method was used for the determination of δ13C of chloroethenes and chloromethanes. The extraction of the CSs from porewater with DMA led to a minimal loss of mass of solvent and chlorinated compounds. The accuracy of the method was verified with the analysis of the pure injected compounds using elemental analyzer—isotope ratio mass spectrometry (EA-IRMS). It has been effectively applied in a study area in saturated soil samples of a pollutant source zone of perchloroethylene (PCE) and trichloroethylene (TCE). The limit of quantification of the new method was 0.034 μg/g for PCE and TCE for 10–20 g of soil sample. This new method allows for compound-specific isotope analysis of CSs in porewater, which can be beneficial in sites where the identification of contamination sources and the behavior of the contaminants are not clear.  相似文献   

12.
In situ chemical oxidation (ISCO) with activated persulfate is commonly used for the remediation of petroleum impacted soil and groundwater because of its proven efficiency and the perception that reaction end products are completely innocuous. While the reaction products are less hazardous compared to the contaminants being treated, they may inadvertently prolong site closure in areas that have adopted the U.S. Environmental Protection Agency (EPA) Secondary Maximum Contaminant Levels (SMCLs) as enforceable standards. This study examines the occurrence and persistence of iron, manganese, sulfate, sodium, and total dissolved solids (TDS) in groundwater following persulfate ISCO. The concentrations of these chemicals were observed remaining above their respective regulatory criteria almost 3 years following the chemical application. Background concentrations and mobilization due to the petroleum contamination and ISCO application are also evaluated. Baseline sampling revealed substantially higher iron and manganese concentrations inside the plume area compared to the upgradient and downgradient wells suggesting mobilization due to redox reactions occurring inside of the plume. Iron was not a component in the applied chemical formula, yet the iron concentration spiked by 366% in the key monitoring well during the first post-remediation monitoring event. Ionic interactions between the ISCO amendment and native soils are believed to be responsible for displacing significant quantities of iron from the soil. Sulfate, sodium, and TDS exceedances are primarily associated with decomposition products of the ISCO amendments. The iron, manganese, sulfate, sodium, and TDS concentrations are trending downward over time, but still exceed regulatory criteria or pre-ISCO concentrations.  相似文献   

13.
Backward location and travel time probabilities, which provide information about the former location of contamination in an aquifer, can be used to identify unknown contamination sources. Backward location probability describes the possible upgradient positions of contamination at a known time in the past, and backward travel time probability describes the time required for contamination to travel from a known upgradient location to an observation point. These probabilities are related to adjoint states of resident concentration, and their governing equation is the adjoint of a forward contaminant transport model. Using adjoint theory to obtain the appropriate governing equation, we extend the backward probability model for conservative solutes to more general non-uniform and transient flow fields. In particular, we address three important extensions, spatially-varying porosity, transient flow and temporally-varying porosity, and internal distributed sources and sinks of solute and water. For the first time we learn that forward and backward location and travel time probabilities are not necessarily equivalent to adjoint states, but are related to them. The extensions are illustrated using a vertically-integrated groundwater model, creating transient flow by a step change in pumping and using areal recharge as an internal distributed source. Both the movement and spread of probabilities are affected. With internal sources of water, there are two interpretations of backward probability, depending on whether or not the source of water is also a source of solute. The results demonstrate how the backward probability model can be applied to other, perhaps more important, non-uniform and transient flow conditions, with time- and space-varying water storage, such as time-varying pumping or unsaturated (or saturated–unsaturated) flow and transport with spatially- and temporally-varying moisture content.  相似文献   

14.
Xenobiotic organic compounds can be discharged from contaminated groundwater inflow and may seep into streams from multiple pathways with very different dynamics, some not fully understood. In this study, we investigated the spatio-temporal variation of chlorinated ethenes discharging from a former industrial site (with two main contaminant sources, A and B) into a stream system in a heterogeneous clay till setting in eastern Denmark. The investigated reach and near-stream surroundings are representative of peri-urban settings, with a mix of high channel alteration and more natural stream environment. We therefore propose an approach for risk assessing impacts arising from such complex contamination patterns, accounting for potential spatio-temporal fluctuations and presence of multiple pathways. Our study revealed substantial variations in pathway contributions and overall contaminant mass discharge to the stream. Variable contaminant contributions arising from both groundwater seepage and urban drains were identified in the channelized part of the north stream, primarily from source A. Furthermore, variations in the hyporheic and shallow groundwater flows were found to enhance contaminant transport from source B. These processes result in an increase of the overall mass of contaminant discharged, correlating with the channels' flow. Thus, an in-stream control plane approach was found to be an effective method for integrating multiple and variable discharge contributions quantitatively, although information on specific contaminant sources is lost. This study highlights the complexity and variability of contaminant fluxes occurring at the interface between groundwater and peri-urban streams, and calls for the consideration of these variations when designing monitoring programs and remedial actions for contaminated sites with the potential to impact streams.  相似文献   

15.
Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.  相似文献   

16.
Thermal methods are promising for remediating fractured geologic media contaminated with volatile organic compounds, and the success of this process depends on the coupled heat transfer, multiphase flow, and thermodynamics. This study analyzed field‐scale removal of trichloroethylene (TCE) and heat transfer behavior in boiling fractured geologic media using the multiple interacting continua method. This method can resolve local gradients in the matrix and is less computationally demanding than alternative methods like discrete fracture‐matrix models. A 2D axisymmetric model was used to simulate a single element of symmetry in a repeated pattern of extraction wells inside a large heated zone and evaluate effects of parameter sensitivity on contaminant recovery. The results showed that the removal of TCE increased with matrix permeability, and the removal rate was more sensitive to matrix permeability than any other parameter. Increasing fracture density promoted TCE removal, especially when the matrix permeability was low (e.g., <10?17 m2). A 3D model was used to simulate an entire treatment zone and the surrounding groundwater in fractured material, with the interaction between them being considered. Boiling was initiated in the center of the upper part of the heated region and expanded toward the boundaries. This boiling process resulted in a large increase in the TCE removal rate and spread of TCE to the vadose zone and the peripheries of the heated zone. The incorporation of extraction wells helped control the contaminant from migrating to far regions. After 22 d, more than 99.3% of TCE mass was recovered in the simulation.  相似文献   

17.
Permeable reactive barriers (PRBs), such as mulch biowalls, have been installed at numerous groundwater cleanup sites, and laboratory and field studies have demonstrated biotic and abiotic processes that degrade chlorinated volatile organic compounds (CVOCs) in groundwater passing through these engineered remedies. However, the longevity of mulch biowalls remains a fundamental research question. Soil and groundwater sampling at seven mulch biowalls at Altus Air Force Base (AFB) approximately 10 years after installation demonstrated the ongoing degradation of CVOCs. Trichloroethene was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling established the presence of key dechlorinating bacteria and the abundance of genes encoding specific enzymes for degradation, high methane concentrations, low sulfate concentrations, and negative oxidation-reduction potential, all indicative of highly reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater, and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. These results demonstrate the ongoing and long-term efficacy of the mulch biowalls at Altus AFB. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.  相似文献   

18.
Enhanced reductive bioremediation (ERB) is effective for treating a broad range of groundwater contaminants, but does result in secondary water quality impacts (SWQIs). Monitoring data from 47 ERB projects were analyzed to gain a better understanding of the formation and extent of SWQIs. The database analysis revealed that SWQIs occur at virtually every site, including reduced levels of background aqueous electron acceptors (O2, NO3?, and SO42?), increases in dissolved‐phase metals (Fe and Mn), and the production of CH4. However, the SWQI “plume” that is produced is usually confined within the original contaminant plume. As a result, SWQIs from ERB are unlikely to adversely impact potable water supplies. SWQIs do attenuate with distance downgradient, with concentrations often returning to near background levels. The results of the database analysis were combined with previous research to develop a general conceptual model (CM) of SWQI production, mobilization, and attenuation. This CM can assist in identifying conditions where SWQIs may pose a concern. These can include sites with low iron/high sulfate (H2S mobilization), high groundwater velocity (SWQIs at distances far downgradient), and sites with low CH4 anaerobic oxidation rates (CH4 migration).  相似文献   

19.
Effective long‐term operation of soil vapor extraction (SVE) systems for cleanup of vadose‐zone sources requires consideration of the likelihood that remediation activities over time will alter the subsurface distribution and configuration of contaminants. A method is demonstrated for locating and characterizing the distribution and nature of persistent volatile organic contaminant (VOC) sources in the vadose zone. The method consists of three components: analysis of existing site and SVE‐operations data, vapor‐phase cyclic contaminant mass‐discharge testing, and short‐term vapor‐phase contaminant mass‐discharge tests conducted in series at multiple locations. Results obtained from the method were used to characterize overall source zone mass‐transfer limitations, source‐strength reductions, potential changes in source‐zone architecture, and the spatial variability and extent of the persistent source(s) for the Department of Energy's Hanford site. The results confirmed a heterogeneous distribution of contaminant mass discharge throughout the vadose zone. Analyses of the mass‐discharge profiles indicate that the remaining contaminant source is coincident with a lower‐permeability unit at the site. Such measurements of source strength and size as obtained herein are needed to determine the impacts of vadose‐zone sources on groundwater contamination and vapor intrusion, and can support evaluation and optimization of the performance of SVE operations.  相似文献   

20.
A simple algebraic equation is presented here to estimate the magnitude of groundwater velocity based on data from a single-well injection-drift test thereby eliminating the time-consuming and costly extraction phase. A volume of tracer-amended water was injected by forced-gradient into a single well followed by monitoring of the conservative solute tracers under natural-gradient conditions as their upgradient portions drifted back through the well. The breakthrough curve data from the single well during the drift phase was analyzed to determine the mean travel times of the tracers. The estimated mean upgradient travel distance back through the single well and the mean travel times of the tracers were used in a simple algebraic equation to estimate groundwater velocity. The groundwater velocity based on the single-well injection-drift test was estimated to be approximately 0.64 ft per day. Two transects of observation wells were used to monitor the natural-gradient tracer transport downgradient of the injection well. The one-dimensional, or dual-well, transport of the tracer from the injection well to the nearest downgradient observation well indicated that the groundwater velocity was 0.55 ft per day. The two-dimensional, or multi-well, transport of the center of mass of the tracers indicated that the groundwater velocity was 0.60 ft per day; the dual- and multi-well results were in excellent agreement with those from the single-well and validated the simple algebraic equation. The new single-well method presented here is relatively simple, rapid, and does not require an extraction phase.  相似文献   

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