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1.
Determination of the nature, extent, and rate of off-site chemical migration are common objectives of hazardous waste site investigations. Chemical analyses of water samples from monitoring wells and measurements of hydraulic head and hydraulic conductivity provide the basis for making these determinations. Accurate site assessment, therefore, depends upon the appropriate monitoring well design and sampling and testing procedures.
During the course of remedial investigations in Niagara Falls, New York, it has been necessary to evaluate the ground water quality and hydraulic characteristics of 5- to 30-feet thick overburden formations. Many of the monitoring wells completed to these formations consist of a partially penetrating screen (5 feet at the base of the formation) with a fully penetrating sandpack. Questions regarding how this well design influences the source of sampled ground water and hydraulic tests were examined using an extremely fine axisymmetric grid with SATURN, a two-dimensional, finite-element ground water model, and a particle tracking post-processor.
A discrete sensitivity analysis was made to determine how flow patterns induced by pumping at 1 gpm are affected by: different screen and sandpack configurations, the ratio of sandpack to formation hydraulic conductivities, heterogeneity, anisotropy, and sandpack thickness. The simulations show that the source (and chemistry given a non-uniform chemical distribution) of ground water sampled will vary considerably depending on a number of factors. Analysis of simulated drawdowns in the monitoring well during purging shows that calculated transmissivities for the range of well designs and conditions modeled will be accurate to within one-half order of magnitude.  相似文献   

2.
Volatile organic compounds delected in ground water from wells at Test Area North (TAN) at the Idaho National Engineering Laboratory (INEL) prompted RCRA facility investigations in 1989 and 1990 and a CERCLA-driven RI/FS in 1992. In order to address ground water treatment feasibility, one of the main objectives, of the 1992 remedial investigation was to determine the vertical extent of ground water contamination, where the principle contaminant, of concern is trichloroethylene (TCE). It was hypothesized that a sedimentary interbed at depth in the fractured basalt aquifer could be inhibiting vertical migration of contaminants to lower aquifers. Due to the high cost of drilling and installation of ground water monitoring wells at this facility (greater than $100,000 per well), a real time method was proposed for obtaining and analyzing ground water samples during drilling to allow accurate placement of well screens in zones of predicted VOC contamination. This method utilized an inflatable pump packer pressure transducer system interfaced with a datalogger and PC at land surface. This arrangement allowed for real lime monitoring of hydraulic head above and below the packer to detect leakage around the packer during pumping and enabled collection of head data during pumping for estimating hydrologic properties. Analytical results were obtained in about an hour from an on-site mobile laboratory equipped with a gas chromalograplvmass spectrometer (GC/MS). With the hydrologic and analytical results in hand, a decision was made to either complete the well or continue drilling to the next test zone. In almost every case, analytical results of ground water samples taken from the newly installed wells closely replicated the water quality of ground water samples obtained through the pump packer system.  相似文献   

3.
Langseth DE  Smyth AH  May J 《Ground water》2004,42(5):689-699
Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.  相似文献   

4.
Ground water monitoring is considered to be a significant component of the geological service in the U.S.S.R. Currently, the total number of ground water monitoring wells exceeds 30,000. They are divided into two categories, which are the first class, or basic observation wells, and the second class, or auxiliary observation wells. The main objectives of both monitoring networks are briefly described. The general scheme of ground water monitoring organization is also presented.  相似文献   

5.
Modeling effects of multinode wells on solute transport   总被引：1，自引：0，他引：1  
Long-screen wells or long open boreholes with intraborehole flow potentially provide pathways for contaminants to move from one location to another in a ground water flow system. Such wells also can perturb a flow field so that the well will not provide water samples that are representative of ground water quality a short distance away from the well. A methodology is presented to accurately and efficiently simulate solute transport in ground water systems that include wells longer than the grid spacing used in a simulation model of the system and hence are connected to multiple nodes of the grid. The methods are implemented in a MODFLOW-compatible solute-transport model and use MODFLOW's Multi-Node Well Package but are generic and can be readily implemented in other solute-transport models. For nonpumping multinode wells (used to simulate open boreholes or observation wells, for example) and for low-rate pumping wells (in which the flow between the well and the ground water system is not unidirectional), a simple routing and local mixing model was developed to calculate nodal concentrations within the borehole. For high-rate pumping multinode wells (either withdrawal or injection, in which flow between the well and the ground water system is in the same direction at all well nodes), complete and instantaneous mixing in the wellbore of all inflows is assumed.  相似文献   

6.
Regional ground water flow is most usually estimated using Darcy's law, with hydraulic conductivities estimated from pumping tests, but can also be estimated using ground water residence times derived from radioactive tracers. The two methods agree reasonably well in relatively homogeneous aquifers but it is not clear which is likely to produce more reliable estimates of ground water flow rates in heterogeneous systems. The aim of this paper is to compare bias and uncertainty of tracer and hydraulic approaches to assess ground water flow in heterogeneous aquifers. Synthetic two-dimensional aquifers with different levels of heterogeneity (correlation lengths, variances) are used to simulate ground water flow, pumping tests, and transport of radioactive tracers. Results show that bias and uncertainty of flow rates increase with the variance of the hydraulic conductivity for both methods. The bias resulting from the nonlinearity of the concentration–time relationship can be reduced by choosing a tracer with a decay rate similar to the mean ground water residence time. The bias on flow rates estimated from pumping tests is reduced when performing long duration tests. The uncertainty on ground water flow is minimized when the sampling volume is large compared to the correlation length. For tracers, the uncertainty is related to the ratio of correlation length to the distance between sampling wells. For pumping tests, it is related to the ratio of correlation length to the pumping test's radius of influence. In regional systems, it may be easier to minimize this ratio for tracers than for pumping tests.  相似文献   

7.
In this study, we use borehole temperature data and stable isotopes to delineate the flow system and estimate the effect of urbanization in the Nagaoka area of Japan. Temperature profiles were measured four times in observation wells during the period 2000-2001 and compared with those measured in the same wells during the period 1977-1983 (Taniguchi 1986). Water was sampled in both observation and pumping wells during the same period. The temporal and spatial variability in temperature indicate clearly the effect of urban warming and heavy pumping on the ground water system. Urban warming caused higher temperatures recently as compared to the older values, and pumping caused induced recharge from the river to the ground water. The stable isotope data show the ground water flow system is divided into shallow, intermediate, and deep systems, and that land use and infiltration rate are affecting the shallow flow system.  相似文献   

8.
State-of-the-art analytical techniques are capable of detecting contamination In the part per billion (ppb) range or lower. At these levels, a truly representative ground water sample Is essential to precisely evaluate ground water quality. The design specifications of a ground water monitoring system are critical in ensuring the collection of representative samples, particularly throughout the long-term monitoring period.
The potential interfaces from commonly used synthetic well casings require a thorough assessment of site, hydrogeology and the geochemical properties of ground water. Once designed, the monitoring system must be installed following guidelines that ensure adequate seals to prevent contaminant migration during the installation process or at some time in the future. Additionally, maintaining the system so the wells are in hydraulic connection with the monitored zone as well as periodically Inspecting the physical integrity of the system can prolong the usefulness of the wells for ground water quality. When ground water quality data become suspect due to potential interferences from existing monitoring wells, an appropriate abandonment technique must be employed to adequately remove or destroy the well while completely sealing the borehole.
The results of an inspection of a monitoring system comprised of six 4-inch diameter PVC monitoring wells at a hazardous well facility Indicated that the wells were improperly installed and in some cases provided a pathway for contamination. Subsequent down hole television inspections confirmed inaccuracies between construction logs and the existing system as well as identified defects in casing materials. An abandonment program was designed which destroyed the well casings in place while simultaneously providing a competent seal of the re-drilled borehole.  相似文献   

9.
A graphical method was devised for designing contaminant detection monitoring networks in aquifers. The approach eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network. In the equidistant configurations derived by the graphical approach, all wells are located the same distance from a landfill, but the distance is measured parallel to ground water flow, Measured perpendicular to ground water flow, there is also an equal spacing between wells in an equidistant network. A simulation model was used to compare an equidistant network to a peripheral monitoring configuration, in which wells were spaced evenly along the downgradient boundaries of a landfill. The equidistant network yielded a 12.4% higher detection efficiency and also facilitated earlier release detection. In practice, the graphical approach that yields equidistant configurations can be used to identify candidate monitoring networks to detect potential releases from landfills.  相似文献   

10.
Seepage from tailings ponds associated with an active uranium mill in Utah has resulted in contamination of ground water contained in the Dakota-Burro Canyon Formation. This aquifer is used in the area as a supply for domestic and industrial wells.
Results of very low-frequency electromagnetic surveys and ground water quality investigations at the site indicated that the flow of ground water and contaminants is primarily fracture-controlled. Pumping tests were conducted to determine the hydraulic characteristics of the fractured system. The extent of contaminant migration was then determined using an analytical model of transport in fractured aquifers.
Based on these investigations, a plan was designed to control future and remediate past ground water contamination. This plan consists of pumping from a single well intersecting the main fracture that transports contaminants off the site. The effectiveness of the plan was analytically modeled, taking account of the anisotropy of the ground water system. Subsequent monitoring of water levels in the area indicates that the plan has been effective since its inception in November 1983.  相似文献   

11.
Monitoring well sand packs are theoretically capable of retarding metal ions and organic contaminants. If this retardation does indeed occur it may have a significant effect on the purging requirements of newly installed monitoring wells. Calculations based on mass balance and retardation concepts demonstrate that if common guidelines for well purging are followed, contaminants may not be detected or may be detected in lower concentrations than are actually present in the ground water. This problem is greatest in relatively shallow wells installed in low to moderate permeability materials. In most cases, the effect of solute retardation in the sand pack can be avoided simply by additional purging prior to the first sampling of the monitoring well. Common purging guidelines can then be applied to subsequent samplings. The methodology outlined in this paper can be used to calculate the purging requirements of existing monitoring wells or it may be applied to alternative monitoring well designs to test which will require the smallest volume of purged water.  相似文献   

12.
Robowell is an automated process for monitoring selected ground water quality properties and constituents by pumping a well or multilevel sampler. Robowell was developed and tested to provide a cost-effective monitoring system that meets protocols expected for manual sampling. The process uses commercially available electronics, instrumentation, and hardware, so it can be configured to monitor ground water quality using the equipment, purge protocol, and monitoring well design most appropriate for the monitoring site and the contaminants of interest. A Robowell prototype was installed on a sewage-treatment plant infiltration bed that overlies a well-studied u neon fined sand and gravel aquifer at the Massachusetts Military Reservation, Cape Cod, Massachusetts, during a time when two distinct plumes of constituents were released. The prototype was operated from May 10 to November 13, 1996, and quality-assurance/quality-control measurements demonstrated that the data obtained by the automated method was equivalent to data obtained by manual sampling methods using the same sampling protocols. Water level, specific conductance, pH, water temperature, dissolved oxygen, and dissolved ammonium were monitored by the prototype as the wells were purged according to U.S. Geological Survey (LJSGS) ground water sampling protocols. Remote access to the data record, via phone modem communications, indicated the arrival of each plume over a few days and the subsequent geochemical reactions over the following weeks. Real-time availability of the monitoring record provided the information needed to initiate manual sampling efforts in response to changes in measured ground water quality, which proved the method and characterized the screened portion of the plume in detail through time. The methods and the case study described are presented to document the process for future use.  相似文献   

13.
Hydrogeologic and ground water quality data obtained from a gas-driven multilevel sampler system and a polyvinyl chloride (PVC) monitoring well nest with the same aquifer communication intervals are compared. All monitoring points are in close proximity to each other. The study was conducted at an eight-acre uncontrolled hazardous waste site. The site is located in an alluvial valley composed of approximately 40 feet of alluvium overlying shale bedrock. The ground water at the site is contaminated with various organic constituents. A ground water monitoring network consisting of 26 conventional monitoring wells, nine observation well points, and six multilevel gas-driven samplers was established to characterize the hydrogeologic regime and define the vertical and horizontal extent of contamination in the vicinity of the abandoned chemical plant. As part of this study, a multilevel monitoring system was installed adjacent to a well nest. The communication zones of the multilevel samplers were placed at the same elevation as the sand packs of the well nest. The multilevel sampler system and well nest are located in a contaminated area directly downgradient of the site. A comparison of the vertical head distribution and ground water quality was performed between the well nest and the multilevel sampling system. The gas-driven multilevel sampling system consists of three gas-driven samplers that monitor separate intervals in the unconsolidated materials. The well nest, composed of two PVC monitoring wells in separate boreholes, has the same communication interval as the other two gas-driven samplers. Hydraulic head information for each multilevel sampler was obtained using capillary tubing. This was compared with heads obtained from the well nest utilizing an electric water level indicator. Chemical analyses from the PVC and multilevel sampler wells were performed and compared with one another. The analyses included organic acids, base neutrals, pesticides, PCBs, metals, volatile organics, TOX, TOC, CN, pH and specific conductance.  相似文献   

14.
Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole.  相似文献   

15.
As competition for increasingly scarce ground water resources grows, many decision makers may come to rely upon rigorous multiobjective techniques to help identify appropriate and defensible policies, particularly when disparate stakeholder groups are involved. In this study, decision analysis was conducted on a public water supply wellfield to balance water supply needs with well vulnerability to contamination from a nearby ground water contaminant plume. With few alternative water sources, decision makers must balance the conflicting objectives of maximizing water supply volume from noncontaminated wells while minimizing their vulnerability to contamination from the plume. Artificial neural networks (ANNs) were developed with simulation data from a numerical ground water flow model developed for the study area. The ANN-derived state transition equations were embedded into a multiobjective optimization model, from which the Pareto frontier or trade-off curve between water supply and wellfield vulnerability was identified. Relative preference values and power factors were assigned to the three stakeholders, namely the company whose waste contaminated the aquifer, the community supplied by the wells, and the water utility company that owns and operates the wells. A compromise pumping policy that effectively balances the two conflicting objectives in accordance with the preferences of the three stakeholder groups was then identified using various distance-based methods.  相似文献   

16.
Chen X 《Ground water》2001,39(5):721-728
Analysis of stream-aquifer interaction due to ground water extraction has traditionally focused on the determination of the amount of water depleted in the stream. Less attention has been paid to the movement of infiltrated stream water inside aquifer, particularly for agricultural areas. This paper presents a method of using particle-tracking techniques to evaluate the transport of the leaked stream water in the nearby aquifers. Simple stream-aquifer conditions are used to demonstrate the usefulness of the analysis. Travel times, pathlines, and influence zones of stream water were determined between a stream and nearby pumping wells for seasonal ground water extraction areas. When water quantity is a concern, the analyses provide additional information about stream depletion; when water quality is an issue, they offer information for wellhead protection. Analyses were conducted for transient conditions, and both pumping and nonpumping periods were considered. According to the results from the simulation examples, migration of infiltrated stream water into the nearby aquifers is generally slow and most infiltrated stream water does not arrive at the pumping well at the end of a 90-day irrigation season. Infiltrated stream water may remain in the aquifer for several years before arriving at the pumping well. For aquifers with a regional hydraulic gradient toward streams, part of the infiltrated stream water may discharge back to streams during a recovery period.  相似文献   

17.
Previous site-specific studies designed to assess the impacts of unsewered subdivisions on ground water quality have relied on upgradient monitoring wells or very limited background data to characterize conditions prior to development. In this study, an extensive monitoring program was designed to document ground water conditions prior to construction of a rural subdivision in south-central Wisconsin. Previous agricultural land use has impacted ground water quality; concentrations of chloride, nitrate-nitrogen, and atrazine ranged from below the level of detection to 296 mg/L, 36 mg/L, and 0.8 microg/L, respectively, and were highly variable from well to well and through time. Seasonal variations in recharge, surface topography, aquifer heterogeneities, surficial loading patterns, and well casing depth explain observed variations in ground water chemistry. This variability would not have been detected if background conditions were determined from only a few monitoring wells or inferred from wells located upgradient of the subdivision site. This project demonstrates the importance of characterizing both ground water quality and chemical variability prior to land-use change to detect any changes once homes are constructed.  相似文献   

18.
AGalerkin finite-element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high-capacity irrigation well. The model was used to compute the head distribution around the pumping well, to determine the area of influence, and to define ground water flowlines during short-term pumping periods typical of those used to collect water quality samples from high-capacity wells. In addition to hypothetical example results, the model was used to qualitatively analyze data obtained from pump-and-sample experiments conducted in an unconfined alluvial aquifer within the Platte River valley of south-central Nebraska where nitrate-nitrogen (NO3-N) contamination is prevalent.
Simulation results of both the hypothetical and field cases suggest that short-term pumping events, impact a limited volume of aquifer. The area of influence and flowlines are affected by aquifer anisotropy, pumping rate, and well construction characteristics). Ground water above or below the screened intervals does not enter a partially penetrating well in anisotropic aquifers. In aquifers where NO3-N concentration varies vertically and horizontally, waler quality samples from an irrigation, or other high-capacity, well provide only limited information about ground water contamination. A numerical model is thus recommended for calculating the area of influence and determining flowlines around high-capacity wells so that information derived from water quality samples collected at the wellhead can be better interpreted.  相似文献   

19.
本文采用调和分析的方法,处理了全国地下水观测井网中18口井孔的水位和气压资料,求出了水井水位中固体潮体应变各分波群的潮汐系数和位相滞后,对这些结果作了分析和讨论。重点对映震能力较好的滇01井潮汐系数及位相滞后这二个参量与地震的关系,作了较详细的研究。  相似文献   

20.
Temporal Variations of Chlorinated Solvents in Abstraction Wells   总被引：1，自引：0，他引：1  
Data obtained during an organic water quality survey of abstraction (pumping) wells in the Triassic Sandstone Aquifer of Birmingham (U.K.) indicate that there are important variations of chlorinated solvent concentrations with time. Short-term observation of solvent concentrations with elapsed pumping time indicates widely differing well responses; such observations are important in establishing good sampling protocols. Long-term monitoring indicates that solvent concentrations, particularly trichloroethene, are often stable with time. When large solvent variations do occur, these are shown to be due to the variation in the abstraction history of the well or significant migration of solvent plumes during the monitoring period. The latter effect is particularly exemplified by rising trends in 1,1,1-trichlroethane concentrations. The changes observed in solvent concentrations during long-term monitoring of the Birmingham Aquifer are slow to occur, but often large.  相似文献   

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