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1.
Ground water scientists engaged in assessment of contaminant occurrence and migration are faced with a number of practical problems. These problems include, but are not limited to, escalating drilling costs, labor costs for proper sampling of monitoring wells, collection of ground water samples that are representative of aquifer conditions and accurate delineation of hydrogeologic regimes and the areal and vertical distribution of ground water contaminants.
In response to these problems, a number of ground water sampling devices have been developed. One device is a gas-driven ground water sampler developed for multilevel installation. Use of these samplers have been shown to decrease project costs and allow easy collection of high quality samples. However, the currently available samplers are relatively expensive, some of them operate on a closed check valve system, which does not allow determination of piezometric heads in aquifers with fluctuating water tables and they are not adaptable to design changes in the field necessitated by site-specific hydrogeologic conditions.
GHR Engineering Associates Inc. has designed an effective gas-driven sampler, which accomplishes the same objectives as the commercially available models, but is on the average, one-tenth the cost of currently available samplers. It offers the advantages of being more cost-effective than commercially available models, has an open check valve system to allow measurements of water table fluctuation and is easily adaptable in the field to meet site-specific hydrogeologic conditions.  相似文献   

2.
A discrete point sampler has been developed that overcomes disadvantages inherent in several current small-volume samplers. It is designed to obtain ground water samples after a well has been purged with a pump. It consists of a sample chamber, two ports, and a stopcock for withdrawing sample aliquots. After lowering the sampler into a well, sampling is initiated by pulling on a line that sequentially removes the plugs in the lower and the upper level ports. The sample chamber fills from the bottom port and vents air from the top port. The device is suitable for sampling for volatile organic compounds in ground waters that are not subject to spontaneous bubble degassing. The upper port is sufficiently far above the lower port that none of the water that is sampled is exposed to the vented air. The sample chamber fills in such a way that the water that is taken from the chamber for analysis is not exposed to the headspace in the chamber.  相似文献   

3.
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   

4.
As part of an agricultural non-point-source study in the Conestoga River head waters area in Pennsylvania, different methods for collecting ground water samples from a fractured carbonate-rock aquifer were compared. Samples were collected from seven wells that had been cased to bedrock and drilled as open holes to the first significant water-bearing zone. All samples were analyzed for specific conductance, dissolved oxygen, and dissolved-nitrogen species. Water samples collected by a point sampler without pumping the well were compared to samples collected by a submersible pump and by a point sampler after pumping the well. Samples collected by using a point sampler, adjacent to major water-bearing zones in an open borehole without pumping the well, were not statistically different from samples collected from the pump discharge or from point samples collected adjacent to major water-bearing zones after pumping the well. Samples collected by using a point sampler without pumping the well at depths other than those adjacent to the water-bearing zones did not give the same results as the other methods, especially when the water samples were collected from within the well casings. It was concluded that, for the wells at this site, sampling adjacent to major water-bearing zones by using a point sampler without pumping the well provides samples that are as representative of aquifer conditions as samples collected from the pump discharge after reaching constant temperature and specific conductance, and by using a point sampler after pumping the well.  相似文献   

5.
The principal difficulties with determinations of volatile organic compounds (VOCs) in ground water are the reliability of sampling procedures and analytical methods. Two integrated methods have been developed for routine sampling, processing, and analysis of VOCs in ground water. These methods involve in situ collection of ground water using a modified syringe sampler from PVC piezometers or using dedicated glass syringes from stainless steel multilevel bores. The samples are processed in the syringe using purge and trap or microsolvent extraction and analyzed by GC/MSD.
The modified purge-and-trap method is time-consuming and limited to volatile organic compounds. However, it is extremely sensitive and flexible: the volume of sample used can be varied by the use of different-size glass syringes (sample volumes from 1 to 100 mL).
In cases where extremely low sensitivity (<10 mg 1−1) is not critical, the microextraction technique is a more cost-effective method, allowing twice as many samples to be analyzed in the same time as the purge-and-trap method. It enables less volatile compounds such as polynuclear aromatic hydrocarbons, phenol, and cresols to be analyzed in the same GC run. Also, the microextraction method can be used in the field to avoid delays associated with transportation of ground water samples to the laboratory.  相似文献   

6.
Lighter-than-water Non-Aqueous Phase Liquids (LNAPLs), such as jet fuels or gasolines, are common contaminants of soils and ground water. However, the total volume and distribution of an LNAPL is difficult to accurately determine during a site investigation. LNAPL that is entrapped in the saturated zone due to fluctuating water table conditions is particularly difficult to quantify. Yet, the amount of entrapped product in the saturated zone is theoretically higher, per volume of soil, than the residual product in the unsaturated zone, and small amounts of LNAPL in the saturated zone can contaminate large volumes of ground water.
The only method currently available to quantify the amount of LNAPL is direct soil-core sampling combined with laboratory analysis of the fluid extracted from the soil cores. However, direct sampling of saturated ground water systems with conventional samplers presents a number of problems. In this study, a new sampler was developed that can be used to retrieve undisturbed soil and pore fluid samples from below the water table in cohesionless soils. The sampler uses carbon dioxide to cool the bottom of a saturated soil sample in situ to near freezing. Results of a field study where a prototype sampler was tested demonstrate the usefulness of a cryogenic sampler and show that the amount of LNAPL entrapped below the water table can be a significant part of the total LNAPL in the soil.  相似文献   

7.
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   

8.
Observations of colloidal movement under natural conditions and during pumping were conducted at several field sites. Results indicate that several modifications to present sampling protocols may improve the representativeness and cost effectiveness of obtaining ground water samples for assessing the total mobile contaminant load. These modifications include the installation of dedicated sampling devices, limited purging of the well prior to sampling, sampling at a flow rate of 100 mL/min, and no filtering of samples. This sampling approach can result in significant cost savings while providing the best possible water samples.  相似文献   

9.
In order to avoid contamination of ground water samples by stagnant water in the well bore, it is generally recommended that the well be purged prior to sampling. There is however, a divergence of opinion both on the need for purging and the best methods of purging. This paper describes detailed field tests in which non-reactive tracers were used to examine, from a well hydraulics point of view, the need for purging and also the effectiveness of various purging procedures. Results show that in the permeable geologic materials of the test site, and for the non-reactive tracers, the water within the screened interval will be purged by the natural flow of water through the screen, while the water above will remain stagnant. The volume of water above the screen is referred to here as one bore volume. It,is suggested that with consideration of the required sample volume, the volume of water stored in the screen, the sampling rate, and the position of the sampler intake, dedicated samplers could be used to obtain representative ground water samples without prior purging of the well.
Of the purging procedures tested, pumping from just below the air-water interface in the well, or the method of "complete removal" of the water within the well bore were the only effective means for complete removal of the stagnant water. Using these procedures, it appeared that representative samples could be obtained with the removal of only two to three bore volumes of water.  相似文献   

10.
Loss of volatile organics during sampling is a well-recognized source of bias in ground water monitoring; sampling protocols attempt to minimize such loss. Such bias could be enhanced for ground water highly charged with dissolved gases such as methane. Such ground water was the object of this study. A positive-displacement bladder pump, a momentum-lift pump and a suction-lift, peristaltic pump were employed in sampling both methane-charged ground water for volatile aromatic hydrocarbons and a CO2-charged reservoir water for volatile chlorinated hydrocarbons. In both cases, the suction-lift pump produced samples with a significant negative bias (9 to 33 percent) relative to the other methods. Little difference between samples produced by the other pump Systems was noted at the field site, but in sampling the reservoir, the bladder pump produced samples that were 13 to 19 percent lower in halocarbon concentration than were samples from the momentum-lift pump.
These negative biases are tentatively interpreted as losses due to volatilization during sampling. Slightly greater negative biases occur for compounds of higher volatility as estimated from their Henry's law constants. Additional studies appear to be warranted in order to adequately establish the scientific basis for recommending protocols for sampling ground water in which degassing could enhance the loss of volatile organics during sampling.  相似文献   

11.
Molecular hydrogen (H(2)) is an important intermediate product and electron donor in microbial metabolism. Concentrations of dissolved H(2) are often diagnostic of the predominant terminal electron-accepting processes in ground water systems or aquatic sediments. H(2) concentrations are routinely measured in ground water monitoring wells but are rarely measured in saturated aquatic sediments due to a lack of simple and practical sampling methods. This report describes the design and development (including laboratory and field testing) of a simple, syringe-based H(2) sampler in (1) saturated, riparian sediments, (2) surface water bed sediments, and (3) packed intervals of a fractured bedrock borehole that are inaccessible by standard pumped methods.  相似文献   

12.
Lawrence Livermore National Laboratory (LLNL) uses a cost-effective sampling (CES) methodology to evaluate and review ground water contaminant data and optimize the site's ground water monitoring plan. The CES methodology is part of LLNL's regulatory approved compliance monitoring plan (Lamarre et al. 1996). It allows LLNL to adjust the ground water sampling plan every quarter in response to changing conditions at the site. Since the use of the CES methodology has been approved by the appropriate regulatory agencies, such adjustments do not need additional regulatory approval. This permits LLNL to respond more quickly to changing conditions. The CES methodology bases the sampling frequency for each location on trend, variability, and magnitude statistics describing the contaminants at that location, and on the input of the technical staff (hydrologists, chemists, statisticians, and project leaders). After initial setup is complete, each application of CES takes only a few days for as many as 400 wells. Effective use of the CES methodology requires sufficient data, an understanding of contaminant transport at the site, and an adequate number of monitoring wells downgradient of the contamination. The initial implementation of CES at LLNL in 1992 produced a 40% reduction in the required number of annual routine ground water samples at LLNL. This has saved LLNL $390,000 annually in sampling, analysis, and data management costs.  相似文献   

13.
Micropurge sampling of ground water wells has been suggested as a possible replacement to traditional purge and sample methods. To compare methods, duplicate ground water samples were collected at two field sites using iraditional and micropurge methods. Samples were analyzed for selected organic and inorganic constituents, and the results were compared statistically. Analysis of the data using the nonparametric sign test indicates that within a 95 percent confidence interval, there was no significant difference between the two methods for the site contaminants and the majority of analytes. These analytical results were supported by visual observations with the colloidal borescope, which demonstrated impacts on the flow system in the well when using traditional sampling methods. Under selected circumstances, the results suggest replacing traditional sampling with micropurging based on reliability, cost, and waste minimization.  相似文献   

14.
Ground water at the Norman Landfill Research Site is contaminated by a leachate plume emanating from a closed, unlined landfill formerly operated by the city of Norman, Oklahoma, Ground water contaminated by the leachate plume is known to be elevated in the concentration of many, organic and inorganic constituents. Specific conductance, alkalinity, chloride, dissolved organic carbon, boron, sodium, strontium, and deuterium in ground water are considered to be indicators of the leachate plume at this site.
Leaf samples of broad-leafed cottonwood, Populus deltoides , were collected from 57 sites around the closed landfill. Cottonwood, a phreatophyte or "well plant," functions as a & surrogate well and serves as a ground water quality sampler. The leaf samples were combusted to ash and analyzed by instrumental neutron activation for 35 elements and by prompt-gamma instrumental neutron activation, for boron. A monitoring well was located within a few meters of a sampled cottonwood tree at 15 of the 57 sites, and ground water samples were collected from these monitoring wells simultaneously with a leaf sample. The chemical analyses of the ground water and leaf samples from these 15 sites indicated that boron, bromine, sodium, and strontium concentrations in leaves were significantly correlated with leachate indicator constituents in ground water. A point-plot map of selected percentiles indicated high concentrations of boron, bromine, and sodium in leaf ash from sites downgradient of the most recent landfill and from older landfills nearby.
Data from leaf analysis greatly extended the known areal extent of the leachate plume previously determined from a network of monitoring wells and geophysical surveys. This phytosgeochemical study provided a cost-effective method for assessing the extent of a leachate plume from an old landfill. Such a method may be useful as a preliminary sampling tool to guide the design of hydrogeochemical and geophysical studies.  相似文献   

15.
This article provides actual site data that confirm that turbid ground water samples collected from within the smear zone at petroleum release sites can be significantly biased high by the inclusion of a nondissolved component that is an artifact of the sampling process. Side-by-side comparisons show that reducing sample turbidity can result in significant reductions of reported concentrations for the ground water samples and that the lower turbidity results are more representative of the petroleum actually dissolved in the ground water. Depending on site-specific factors, ground water sample turbidity can be reduced by four field-based and two laboratory-based methods. These methods should be used routinely at sites where turbid samples with a nondissolved component are being collected.  相似文献   

16.
Waste disposal sites with volatile organic compounds (VOCs) frequently contain contaminants that are present in both the ground water and vadose zone. Vertical sampling is useful where transport of VOCs in the vadose zone may effect ground water and where steep vertical gradients in chemical concentrations are anticipated. Designs for combination ground water and gas sampling wells place the tubing inside the casing with the sample port penetrating the casing for sampling. This physically interferes with pump or sampler placement. This paper describes a well design that combines a ground water well with gas sampling ports by attaching the gas sampling tubing and ports to the exterior of the casing. Placement of the tubing on the exterior of the casing allows exact definition of gas port depth, reduces physical interference between the various monitoring equipment, and allows simultaneous remediation and monitoring in a single well. The usefulness and versatility of this design was demonstrated at the Idaho National Engineering and Environmental Laboratory (INEEL) with the installation of seven wells with 53 gas ports, in a geologic formation consisting of deep basalt with sedimentary interbeds at depths from 7.2 to 178 m below land surface. The INEEL combination well design is easy to construct, install, and operate.  相似文献   

17.
Oil field brine was applied to a gravel roadbed at an instrumented study site in Newark, Ohio, to simulate the use of brine as a deicer on roads in certain areas of Ohio. Brine was applied on a weekly basis eight times during the winter of 1988 as part of the deicing simulation. Eleven wells were installed at the site prior to brine application to permit collection of ground water quality samples. Surface geophysical methods — electrical resistivity and electromagnetic conductivity — were used to map the resulting brine plume. The accuracy of the methods was evaluated by comparing geophysical and ground water quality data. The presence of brine in ground water resulted in a decrease in resistivity and an increase in conductivity. Specific conductance measured in the field was used as a general indicator of the presence of the brine plume in ground water. Chloride concentration was an indicator of brine in the ground water. Results of the surface geophysical surveys correlated best with chloride and dissolved solids concentrations, and with specific conductance in ground water. The surface geophysical methods were found to be useful for qualitative interpretations of ground water quality changes resulting from the application of brine on roads.  相似文献   

18.
Woessner WW 《Ground water》2007,45(6):795-797
Hydrogeologic research often involves obtaining water quality samples in field settings without vehicle access. Such conditions often require the use of a sampling pump. Researchers at The University of Montana have been using a handheld peristaltic pump powered by a rechargeable variable-speed drill. This Montana Drill Pump (MDP) is highly portable and can be inexpensively built for about $225 to $295 (US). Over the last two decades, the pump has been used to sample and filter (as appropriate) surface water and ground water for analyses of general inorganic and organic chemistry, stable and radioactive isotopes, pathogens, and trace pharmaceuticals and to develop small-diameter wells and sample suction lysimeters. The MDP provides researchers and educators with an economical tool to pump water in classrooms, laboratories, and field settings.  相似文献   

19.
The discrete nature of the numerical methods utilized in 1D site response analysis and calculation of the response spectra (e.g., frequency domain, Duhamel integral, and Newmark β methods) introduces time-step dependence in the resulting solution. Using an input ground motion with too large of a time-step leads to under-prediction of high-frequency characteristics of the system response due to limitations in the numerical solution of single and multiple degree of freedom systems. In order to reduce potential errors, using a sampling rate at least ten times greater than the maximum considered frequency is recommended. The preferred alternative is selection of input ground motions with a sufficiently small time step to avoid introducing numerical errors. However, where such motions are not available, then the time step of the ground motion can be reduced through interpolation. This paper demonstrates that the use of Fourier transform zero-padded interpolation is the preferred approach to obtain a ground motion with an adequate time step for the calculation of the elastic acceleration response spectra, and to analyze site response using either frequency or time domain methods.  相似文献   

20.
A New Multilevel Ground Water Monitoring System Using Multichannel Tubing   总被引：5，自引：0，他引：5  
A new multilevel ground water monitoring system has been developed that uses custom-extruded flexible 1.6-inch (4.1 cm) outside-diameter (O.D.) multichannel HOPE tubing (referred to as Continuous Multichannel Tubing or CMT) to monitor as many as seven discrete zones within a single borehole in either unconsolidated sediments or bedrock. Prior to inserting the tubing in the borehole, ports are created that allow ground water to enter six outer pie-shaped channels (nominal diameter = 0.5 inch [1.3 cm]) and a central hexagonal center channel (nominal diameter = 0.4 inch [1 cm]) at different depths, facilitating the measurement of depth-discrete piezometric heads and the collection of depth-discrete ground water samples. Sand packs and annular seals between the various monitored zones can be installed using conventional tremie methods. Alternatively, bentonite packers and prepacked sand packs have been developed that are attached to the tubing at the ground surface, facilitating precise positioning of annular seals and sand packs. Inflatable rubber packers for permanent or temporary installations in bedrock aquifers are currently undergoing site trials. Hydraulic heads are measured with conventional water-level meters or electronic pressure transducers to generate vertical profiles of hydraulic head. Ground water samples are collected using peristaltic pumps, small-diameter bailers, inertial lift pumps, or small-diameter canister samplers. For monitoring hydrophobic organic compounds, the CMT tubing is susceptible to both positive and negative biases caused by sorption, desorption, and diffusion. These biases can be minimized by: (1) purging the channels prior to sampling, (2) collecting samples from separate 0.25-inch (0.64 cm) O.D. Teflon sampling tubing inserted to the bottom of each sampling channel, or (3) collecting the samples downhole using sampling devices positioned next to the intake ports. More than 1000 CMT multilevel wells have been installed in North America and Europe to depths up to 260 feet (79 m) below ground surface. These wells have been installed in boreholes created in unconsolidated sediments and bedrock using a wide range of drilling equipment, including sonic, air rotary, diamond-bit coring, hollow-stem auger, and direct push. This paper presents a discussion of three field trials of the system, demonstrating its versatility and illustrating the type of depth-discrete data that can be collected with the system.  相似文献   

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