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1.
The detection of microbiological contamination in drinking water from groundwater wells is often made with a limited number of samples that are collected using traditional geochemical sampling protocols. The objective of this study is to examine the variability of fecal indicator bacteria, as observed using discrete samples, due to pumping. Two wells were instrumented as multilevel piezometers in a bedrock aquifer, and bacterial enumeration was conducted on a total of 166 samples (for total coliform, fecal coliform, Escherichia coli, and fecal streptococci) using standard membrane filtration methods. Five tests were conducted using pumping rates ranging from 0.3 to 17 L/min in a variety of purging scenarios, which included constant and variable (incremental increase and decrease) flow. The results clearly show a rapid and reproducible, 1 to 2 log‐unit decrease in fecal indicator bacteria at the onset of pumping to stabilized, low‐level concentrations prior to the removal of three to five well volumes. The pumping rate was not found to be correlated with the magnitude of observed bacterial counts. Based on the results, we suggest sampling protocols for fecal indicator bacteria that include multiple collections during the course of pumping, including early‐time samples, and consider other techniques such as microscopic enumeration when assessing the source of bacteria from the well‐aquifer system.  相似文献   

2.
A simple, inexpensive sampling pump has lately come into use in ground water monitoring. The pump is referred to as an inertial pump; its only downhole components are a foot valve connected to a length of tubing or pipe. The operating principle of the pump is based on the inertia of a column of water within the riser tubing. Ground water is drawn through the foot valve and up the riser tubing by rapid up and down movements of the tubing. This pumping method is not new, but has only recently been applied to monitoring wells. Foot valves are available in a variety of materials and sizes and can be used in monitoring wells as small as 19mm (3/4 inch) I.D. Flexible polyethylene or Teflon® tubing, and in some cases stainless steel tubing or rigid PVC pipe, is used as the riser. The inertial pump satisfies most of the criteria normally cited for an "ideal" sampling device. The pump is easy to operate, reliable, durable, portable, and virtually maintenance-free. It can be operated manually from as deep as 40m or from as deep as 60m using a motor drive. The pump is inexpensive, and therefore suitable for use as a dedicated sampling pump. Recent tests have shown the pump to be suitable for sampling volatile organics. The inertial pump has a high flow capacity and performs well in silty/sandy environments, which makes it useful for developing and purging monitoring wells. It may also be used to perform field hydraulic conductivity tests.  相似文献   

3.
Cone penetrometer tests and HydroPunch® sampling were used to define the extent of volatile organic compounds in ground water. The investigation indicated that the combination of these techniques is effective for obtaining ground water samples for preliminary plume definition. HydroPunch samples can be collected in unconsolidated sediments and the analytical results obtained from these samples are comparable to those obtained from adjacent monitoring wells. This sampling method is a rapid and cost-effective screening technique for characterizing the extent of contaminant plumes in soft sediment environments. Use of this screening technique allowed monitoring wells to be located at the plume boundary, thereby reducing the number of wells installed and the overall cost of the plume definition program.  相似文献   

4.
Kim K 《Ground water》2003,41(6):780-789
Ground water samples collected from a multilevel sampler shortly after its construction showed significantly higher alkalinity and concentrations of calcium and magnesium than those from nearby wells installed 10 years earlier. The sampler was drilled using a conventional hollow-stem power auger in a sandy, silicate aquifer lying beneath an isthmus between two lakes in northern Wisconsin. Ground water in the study area is of low ionic strength and its chemistry is dominated by silicate mineral weathering. Periodic sampling over two years following installation of the sampler showed that the higher solute concentrations had subsequently decreased. Oxygen isotope signature and other solute species, such as sulfate and chloride, were comparable to those of older wells and did not show any notable trends over time. Independent variation of other chemical species that cannot be derived from aquifer minerals, and the similarly high concentrations in older wells shortly after their installation, suggest that rapid dissolution of fresh mineral surfaces and hyperfine particles generated during drilling has induced the enhanced concentrations. This observation is consistent with the field equivalent of laboratory mineral dissolution experiments that show initially increased dissolution rates that decay over time. Well installations for geochemical sampling in dominantly silicate material may require longer times to reach an equilibrium state than has been previously thought.  相似文献   

5.
The presence of a wellbore skin layer, formed during the drilling process, is a major impediment for the energy‐efficient use of water wells. Many models exist that predict its potential impacts on well hydraulics, but so far its relevant hydraulic parameters were only estimates or, at best, model results. Here, we present data on the typology, thickness, composition, and hydraulic properties obtained from the sampling of excavated dewatering wells in lignite surface mines and from inclined core drilling into the annulus of an abandoned water well. Despite the limited number of samples, several types of skin were identified. Both surface cake filtration and particle straining in the aquifer occur. The presence of microcracks may be a determining feature for the hydraulic conductivity of skin layers. In the case of the well‐developed water supply well, no skin layer was detected. The observed types and properties of wellbore skin samples can be used to test the many mathematical skin models.  相似文献   

6.
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7.
A six year field experiment has shown that a sand-bentonite mixture used to seal monitoring wells in aquitards contributes solutes to the ground water sampled from these wells. Monitoring wells were installed at field sites with hydraulic conductivity (K) ranging from 5 × 10 -9 m/s to 3 × 1011 m/s. In most cases the boreholes remained dry during installation which allowed the placement of a dry powdered bentonite/sand mixture tagged with potassium bromide (KBr) to seal and separate sampling points. Over six years, wells were sampled periodically and ground-water samples were analyzed for Br and Cl and other major ions. Typical Br results ranged from 10 mg/1 to 35 mg/1 in the first 700 days, as compared to an estimated initial concentration in the seal material of about 75 mg/1. After six years the bromide concentrations had decreased to between 3 mg/1 and 5 mg/1. The total mass of Br removed in six years is less than 50% of that placed; therefore the contamination effects, although considerably diminished, persist. The trends of Br, Cl, Na, and SO4 indicate that varying degrees of contamination occur. These data show that the materials used to seal monitoring wells in aquitards can have a significant and long-lasting impact on the chemistry of the water in the wells.  相似文献   

8.
The objective of most ground water quality monitoring programs is to obtain samples that are "representative" or that retain the physical and chemical properties of the ground water in an aquifer. Many factors can influence whether or not a particular sample is representative, but perhaps the most critical factor is the method or type of sampling device used to retrieve the sample.
The sampling equipment available today ranges from simple to highly sophisticated, and includes bailers, syringe devices, suction-lift pumps, gas-drive devices, bladder (Middelburg-type) pumps, gear-drive and helical rotor electric submersible pumps and gas-driven piston pumps. New devices are continually being developed for use in small-diameter wells in order to meet the needs of professionals engaged in implementing elaborate ground water monitoring programs.
In selecting a sampling device for a monitoring program, the professional must consider a number of details. Among the considerations are: the outside diameter of the device, the overall impact of the device on ground water sample integrity (including the materials from which the sampling device and associated equipment are made and the method by which the device delivers the sample), the capability of the device to purge the well of stagnant water, the rate and the ability to control the rate at which the sample is delivered, the depth limitations of the device, the ease of operating, cleaning and maintaining the device, the portability of the device and required accessory equipment, the reliability and durability of the device, and the initial and operational cost of the device and accessory equipment. Based on these considerations, each of the devices available for sampling ground water from small-diameter wells has its own unique set of advantages and disadvantages that make it suitable for sampling under specific sets of conditions. No one sampling device is applicable to all sampling situations.  相似文献   

9.
The results of a series of investigations are presented, performed by the governmental chemical laboratory Karlsruhe (CLUA) in order to determine pesticides in drinking water for purposes of food monitoring. 231 samples of 8 municipal water supplies (groundwater wells/no bank filtrate) and 34 private water supplies close to the bank of the river Rhine (groundwater wells/partly bank filtrate) were analysed. The sampling sites were located between Mannheim and Greffern, Germany. In 1986 high amounts of atrazine and simazine were determined in the drinking water wells of several private water supplies, especially at the sampling sites in the south. The likewise high chloride content of the samples was taken as a proof of bank filtrate contributing to the water. The decrease of atrazine load in the river water of the Rhine since 1987 has its parallel in the analytical results for the concerned drinking water wells. Obviously the pesticide contamination of water from bank filtrate pumping wells is mainly depending on the pesticide load of the river water. The application of fertilizers and pesticides in the fields seems not to be a significant source of the pesticide contamination of dringing waters derived from bank filtrate water. For reasons of public health a monitoring of pesticide content in bank filtrate pumping wells of private water supplies is recommended.  相似文献   

10.
Volatile organic compounds (VOCs) are present in multiple water-bearing zones beneath and downgradient of Lawrence Livermore National Laboratory. This area is composed of interfingering unconsolidated alluvial sediments with hydraulic conductivities ranging over four orders of magnitude. The more permeable sediments exhibit moderate hydraulic interconnection horizontally and less interconnection vertically, and appear to consist largely of interconnected stream channel deposits. To optimize selection of monitoring well screened intervals in this complex environment, a technique that enables collection of saturated formation samples from each water-bearing zone without contamination from other VOC-containing zones was developed, tested, and implemented. The technique utilizes a wireline punch-coring system that allows the drill bit to be replaced with a core barrel without removing the drill rod from the borehole. To help ensure that a sample from one water-bearing zone is not contaminated by VOCs from another zone, the drilling fluid is replaced with new fluid before each sampling run. Overnight chemical analysis by gas chromatography enables field personnel to know the vertical distribution of VOCs as drilling proceeds. Since its first use in 1985, the technique has successfully characterized the presence or absence of VOCs in ground water in 123 of 140 wells, many with concentrations in ground water in the low parts-per-billion range. Our sampling technique is a cost-effective and rapid method of evaluating the vertical distribution of VOCs in ground water in a complex hydrogeologic environment.  相似文献   

11.
In compliance with the New Jersey Private Well Testing Act, 78,546 wells (93,787 samples, including samples from 13,290 wells that were analyzed more than once) were analyzed for total coliform (TC) bacteria by one or more of 39 laboratories over a 10‐year period. Samples containing TC bacteria were further analyzed for the presence of either fecal coliform or E. coli (FC/EC) bacteria. The large population of wells sampled multiple times permitted a systematic study of the effect of repeat sampling on coliform bacteria detection rates. The detection rate increased with the number of times wells were sampled. In bedrock, TC bacteria were detected in 21% of the population of wells analyzed only once, 33% in the population sampled twice, and 43% in the population sampled three times. It was estimated that TC bacteria would be detected in 90% of all wells if each well was analyzed 10 times. For FC/EC bacteria, it was estimated that 21 and 68 samples, respectively, would be required to reach the 50% and 90% population detection rates. In the Coastal Plain (CP), many more samples would be required to achieve the same estimated population detection rates. The population detection rate estimates were also dependent on the type of method used, the pH of the well water, and the geologic formation in which wells were located. A single sample was not sufficient to detect coliform bacteria when present in well water.  相似文献   

12.
Private wells in Cayuga and Orange counties in New York were sampled to determine the occurrence of pesticide contamination of groundwater in areas where significant pesticide use coincides with shallow or otherwise vulnerable groundwater. Well selection was based on local groundwater knowledge, risk modeling, aerial photo assessments, and pesticide application database mapping. Single timepoint samples from 40 wells in each county were subjected to 93‐compound chromatographic scans. All samples were nondetects (reporting limits ≤1 μg/L), thus no wells from either county exceeded any of 15 state groundwater standards or guidance values. More sensitive enzyme‐linked immunosorbent assays (ELISA) found two wells with quantifiable atrazine in each county (0.1–0.3 μg/L), one well with quantifiable diazinon (0.1 μg/L) in Orange County, and one well with quantifiable alachlor (0.2 μg/L) in Cayuga County. Trace detections (<0.1 μg/L) in Cayuga County included atrazine (five wells), metolachlor (six wells), and alachlor (one well), including three wells with multiple detections. All 12 Cayuga County wells with ELISA detections had either corn/grain or corn/forage rotations as primary surrounding land uses (although 20 other wells with the same land uses had no detections) and all quantified detections and most trace detections occurred in wells up to 9‐m deep. Orange County trace (<0.1 μg/L) ELISA detections (atrazine three wells, diazinon one well, and metolachlor five wells) and quantified detections were only generally associated with agricultural land uses. Finding acceptable drinking water quality in areas of vulnerable groundwater suggests that water quality in less vulnerable areas will also be good.  相似文献   

13.
The objective of this study was to assess the possible impact of deep well disposal operations, conducted between 1958 and 1974, on the ground water quality in a shallow fresh water aquifer beneath Sarnia, Ontario, Canada. Because of the breakout of formation fluids in Sarnia and Port Huron, Michigan, in the early 1970s, it had been hypothesized that liquid waste from the disposal zone in bedrock had leaked through numerous abandoned oil, gas, and salt wells in the area up to the shallow fresh water aquifer and from there to the surface.
A monitoring well network of 29 5cm (2 inch) diameter piezometers was established in the thin sand and shale aquifer system, which exists between 30 and 70m (100 and 230 feet) below ground surface. In addition, a 300m (1000 foot) deep borehole was drilled and instrumented with a Westbay multilevel casing, which permitted sampling of the disposal zone.
Ground water samples from the shallow monitoring wells and the Westbay multilevel casing were analyzed for volatiles by GC/MS. Those volatile aromatics that were conspicuously present in the deep disposal zone, e.g., ethyl toluenes and trimethyl benzene, were not detected in the shallow monitoring wells. Thus, if contaminants from the disposal zone did indeed migrate to the shallow aquifer, contamination was not widespread and probably consisted mostly of displaced chloride-rich formation waters.  相似文献   

14.
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   

15.
Groundwater monitoring wells are present at most hydrocarbon release sites that are being assessed for cleanup. If screened across the vadose zone, these wells provide an opportunity to collect vapor samples that can be used in the evaluation of vapor movement and biodegradation processes occurring at such sites. This paper presents a low purge volume method (modified after that developed by the U.S. EPA) for sampling vapor from monitoring wells that is easy to implement and can provide an assessment of the soil gas total petroleum hydrocarbon (TPH) and O2 concentrations at the base of the vadose zone. As a result, the small purge method allows for sampling of vapor from monitoring wells to support petroleum vapor intrusion (PVI) risk assessment. The small purge volume method was field tested at the Hal's service station site in Green River, Utah. This site is well‐known for numerous soil gas measurements containing high O2 and high TPH vapor concentrations in the same samples which is inconsistent with well‐accepted biodegradation models for the vapor pathway. Using the low purge volume method, monitoring wells were sampled over, upgradient, and downgradient of the light nonaqueous phase liquid (LNAPL) footprint. Results from our testing at Hal's show that vapor from monitoring wells over LNAPL contained very low O2 and high TPH concentrations. In contrast, vapor from monitoring wells not over LNAPL contained high O2 and low TPH concentrations. The results of this study show that a low purge volume method is consistent with biodegradation models especially for sampling at sites where low permeability soils exist in and around a LNAPL source zone.  相似文献   

16.
In the BAT ground water sampling system, a stainless steel probe with a porous filter element is pushed vertically to the desired sampling depth. An evacuated glass sampling tube is then lowered down the penetration rods where it makes contact with the filter via a hypodermic needle and draws a pore fluid sample.
An investigation of the system was carried out at a number of sites contaminated by leaking underground gasoline storage tanks. Ground water samples obtained using the BAT system and adjacent monitoring wells were analyzed for volatile organic compounds (VOCs).
Because the BAT system is an in situ penetration device with a small filter length, it is possible to determine variations in contaminant concentration with depth. BAT samples in general exhibited higher recovery of VOCs than did bailer samples from adjacent monitoring wells screened over large intervals.
Much higher levels of VOCs were recovered when the probe was used with its 316 stainless steel filter than when using the high-density polyethylene (HDPE) filter. Significant sorption apparently occurred on the latter filter.
Because the BAT sample tubes are sealed and remain a closed system, the in situ water pressure is maintained. No significant loss of VOCs was found in sampling tubes containing headspace. Samples from the upper tube in the cascaded setup with headspace recovered levels of VOCs as high, or in a few cases higher, than the lower, no-headspace tubes.  相似文献   

17.
Clusters of elevated methane concentrations in aquifers overlying the Barnett Shale play have been the focus of recent national attention as they relate to impacts of hydraulic fracturing. The objective of this study was to assess the spatial extent of high dissolved methane previously observed on the western edge of the play (Parker County) and to evaluate its most likely source. A total of 509 well water samples from 12 counties (14,500 km2) were analyzed for methane, major ions, and carbon isotopes. Most samples were collected from the regional Trinity Aquifer and show only low levels of dissolved methane (85% of 457 unique locations <0.1 mg/L). Methane, when present is primarily thermogenic (δ13C 10th and 90th percentiles of ?57.54 and ?39.00‰ and C1/C2+C3 ratio 10th, 50th, and 90th percentiles of 5, 15, and 42). High methane concentrations (>20 mg/L) are limited to a few spatial clusters. The Parker County cluster area includes historical vertical oil and gas wells producing from relatively shallow formations and recent horizontal wells producing from the Barnett Shale (depth of ～1500 m). Lack of correlation with distance to Barnett Shale horizontal wells, with distance to conventional wells, and with well density suggests a natural origin of the dissolved methane. Known commercial very shallow gas accumulations (<200 m in places) and historical instances of water wells reaching gas pockets point to the underlying Strawn Group of Paleozoic age as the main natural source of the dissolved gas.  相似文献   

18.
Transfer of zoonotic bacterial pathogens through intact soil columns was monitored in an outdoor lysimeter over 36 d. Manure spiked with Salmonella enterica serovar Senftenberg was applied to either the soil surface or injected 0.08 m into the soil to compare leaching associated with the two manure application methods. The highest concentrations of S. enterica (up to 60,000 S. enterica CFU/mL) were detected on Day 1 in the first drainage samples, with measurable but declining concentrations persisting for 10 to 36 d depending on replicate columns. The total recovery of leached S. enterica in drainage samples ranged from 0.08% to 13.8%. When comparing the two application methods, there was no statistically significant difference in the leaching concentration of S. enterica at each sampling time during the study period. In addition, comparison of enumerations by selective plating and real-time polymerase chain reaction yielded similar concentrations of S. enterica, indicating that mainly viable and culturable cells were leached from the columns. When the experiment was terminated, the fluorescent dye Acid Yellow was applied to four selected columns and the distribution of dye and size of active (dye-stained) pores were measured with a digital camera and visualization software. The profiles showed that the area covered by active pores ranged from 0.1% to 3.6%. The relatively small fraction of active pores in the soil profile was consistent with the evidence of rapid transport of S. enterica and chloride in the columns.  相似文献   

19.
The Effect of Three Drilling Fluids on Ground Water Sample Chemistry   总被引：1，自引：0，他引：1  
Three monitoring wells were installed in borings that were constructed using water-based drilling fluids containing either (1) guar bean, (2) guar bean with breakdown additive, or (3) bentonite. These fluids were selected to observe their effect on the chemistry of subsequent water samples collected from the wells. The wells were installed to depths of 66 feet, 100.5 feet and 103 feet, respectively, in fine-to-medium sand and gravel outwash deposits near Antigo, Wisconsin. Drilling fluids were necessary to maintain an open borehole during well construction through strata containing cobbles and boulders.
The bentonite and guar drilling fluids caused temporarily elevated concentrations of chemical oxygen demand (COD) in ground water samples collected from the monitoring wells. Using standard development, purging and sampling procedures, elevated COD concentrations persisted for about 50 days for the well bored with the guar-with-additive fluid, 140 days for the bentonite well and 320 days for the guar well. Unfiltered ground water samples for all wells had greater concentrations of COD than samples filtered through a 0.45 micron filter. Sulfate concentrations also decreased with time in the guar-with-additive well and bentonite well, but not in the guar well.
The elevated COD concentrations are attributed to the large concentrations of oxidizable carbon present in the guar bean drilling fluid and in the organic polymers present in the bentonite drilling fluid. Well development and purging procedures, including borehole flushing, surging, bailing and/or chemically induced viscosity breakdown of the guar mud decreased the time before background conditions were achieved. Future research should evaluate the physical and geochemical interaction of different drilling fluid compositions with a variety of geologic matrices and drilling, well development and well purging techniques.  相似文献   

20.
Seawater and sediment were collected on a monthly basis from a shallow (10.5 m depth) coastal site in the Ligurian Sea (NW Mediterranean) from November 1993 to December 1994 to determine the main environmental forces that influenced the biogeochemical processes and to study the relationships between the availability and lability of the organic matter (OM) and hydrolytic enzymatic activity. The current direction throughout the sampling year was influenced by the climatic conditions, which showed significant correlations with north atlantic oscillation (NAO) index values. The current generally flowed northwards in spring. This could cause significantly lower transparency values than in the summer, when an eastward current probably reduced the allochthonous input of material from the main local watercourse and contributed to turning the conditions from mesotrophic to oligotrophic. Spring and summer were separated by transitional periods more than by the canonical autumn and winter seasons. These transitions were characterised by a reduction in salinity values and by resuspension caused by water column mixing and a current flowing towards the southwest. The significant inverse correlations of the chlorophyll-a and protein concentrations, bacterial abundance and proteolysis of the bottom seawater and transparency showed the direct influence of resuspension on the organic matter dynamics. Moreover, OM trophic quality influenced the bacterial parameters and the enzymatic activities. The glycolytic β glucosidase and chitinase activities and their bacterial cell-specific hydrolytic rates were higher when substrates such as hydrolysable proteins were available, while they decreased when refractory compounds were abundant. The low leucine aminopeptidase: β glucosidase ratio values observed in the water column were presumably related to the potential ease with which microbes obtained protein-derived materials and energy, the protein hydrolysable fraction being estimated at ca. 90%. The significant correlations of protein with the chlorophyll-a concentrations suggested an autotrophic-derived origin, although the higher chlorophyll-a values corresponded to lower hydrolysable protein concentrations and an increase in the autotrophic biomass at the surface was correlated with a reduction in the proteolytic affinity for substrates, suggesting that a recent origin did not necessarily mean higher trophic availability.  相似文献   

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