Existing Monitoring Wells Research Articles

Push–pull tests evaluating in situ aerobic cometabolism of ethylene, propylene, and cis-1,2-dichloroethylene

In situ aerobic cometabolic transformations of ethylene, propylene, and cis-1,2-dichloroethylene (c-DCE), by microorganisms stimulated on propane, were examined in groundwater contaminated with c-DCE and trichloroethylene (TCE). In situ measurements were performed by conducting field push–pull tests, which consisted of injecting site groundwater amended with a bromide tracer and combinations of propane, dissolved oxygen (DO), nitrate, ethylene, propylene, c-DCE, and TCE into existing monitoring wells and sampling the same wells over time. Mass balance and transformation rate calculations were performed after adjusting for dilution losses using measured tracer concentrations. Initial rates of propane utilization were very low; rates increased substantially following sequential additions of propane and DO. Evidence that propane and DO additions had stimulated organisms expressing a propane monoxygenase enzyme system and that had the capability to transform chlorinated aliphatic hydrocarbons (CAHs) included: (1) the transformation of injected ethylene and propylene to the cometabolic byproducts ethylene oxide and propylene oxide, (2) the transformation of c-DCE, and (3) the inhibition of these transformations in the presence of coinjected acetylene, a known monoxygenase mechanism-based inactivator. These results suggest that a series of push–pull tests performed with nontoxic chemical probes can be useful for detecting and monitoring in situ aerobic cometabolism of CAHs.

観測井地下水の濁りに関する調査研究

The grain-size distribution of turbidity, water chemistry, and the size of fine particles associated with contaminants in turbid groundwater were investigated in existing monitoring wells. Groundwater monitoring wells are used in obtaining general information on groundwater quality and specific information on concentrations and specification of mobile contaminants in the vicinity of a monitoring well. This information is used in determining whether a given facility is currently in compliance with regulations. Turbidity (fine particles) are present in monitoring wells as a result of well installation in a stratum containing many fine particles (e.g., clay and silt) at a depth of less than GL-10m, well development, prior purging, sampling events, and natural colloidal transport and deposition over time. It is crucial that samples obtained from monitoring wells accurately reflect in situ mobile contaminant concentrations. The filtration of groundwater samples may remove both mobile fine particles/colloids and artifact particles. The most common groundwater purging method is to purge a monitoring well using bailers or pumps to remove 3 to 5 casing volumes to obtain formation water. In this paper, the concept and numerical formulas of a well-purging model are introduced and discussed. The calculation result shows that prepurging more than 3 casing volumes ensures a sampling of well water which is similar to formation water. The differences between filter pack and gravel pack (filter media #2 - #4) and the method of selecting the sizes of filter media were surveyed and discussed with the aim of installing a monitoring well in a stratum containing many fine particles.

Reducing Spatial Sampling in Long-Term Groundwater Monitoring Networks Using Ant Colony Optimization

Groundwater long-term monitoring (LTM) is required to assess human health and environmental risk of residual contaminants after active groundwater remediation activities are completed. However, LTM can be costly because of the large number of sampling locations that exist at a site from previous site characterization and remediation activities. The cost of LTM may be reduced by identifying redundant sampling locations. However, care must be taken so that the elimination of specific individual wells from the monitoring network does not result in unacceptable levels of data loss and errors. An ant colony optimization (ACO) algorithm is proposed to identify optimal sampling networks that minimize the number of monitoring locations while maintaining the overall data loss below a given threshold. ACO is inspired by the ability of an ant colony to identify the shortest route between its nest and a food source through indirect communication and positive feedback. Metrics for quantifying well redundancy and overall data loss after optimization are quantified and used in the ACO heuristics. To demonstrate its effectiveness, the ACO developed for LTM optimization is applied to a case study with 30 existing monitoring wells. The LTM optimization problem was solved using different data loss thresholds to identify solutions with 27 to 21 wells remaining in the LTM network. Contour mapping of the contaminant plume using the remaining wells show that the ACO solutions are effective and practical. These results demonstrated that ACO is a promising method for solving LTM optimization problems.

Geoelectrical and Hydrogeochemical Studies for Delineating Ground‐Water Contamination Due to Salt‐Water Intrusion in the Northern Part of the Nile Delta, Egypt

AbstractA resistivity survey was conducted in the Nile Delta area to delineate ground‐water contamination caused by an improper sewage and irrigation drainage system, leaching from old lagoonal deposits, and salt‐water intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity. Vertical electrical sounding (VES) data for sounding points located near monitoring wells, together with the water salinity data of these wells, were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used together with the constructed apparent resistivity depth and geoelectric longitudinal sections to identify three zones of water‐bearing formation (fresh‐, brackish‐, and salt‐water zones). Along the studied profile, depth to the fresh‐brackish interface exceeds 150 m at Tanta City and decreases northward to 40 m or less between Qutor and Kafr El‐Sheikh. Depth to the brackish‐saline interface exceeds 180 m south of Kafr‐El‐Sheikh and decreases northward to 70 m near Hadadi village.

A study on the characteristics of groundwater contamination of the Nanji landfill and its surrounding hydrogeologic system

Abstract The Nanji landfill causes a serious adverse affect to nearby groundwater and surface water systems due to that it has been constructed on the very permeable and valnerable sand and gravel deposit without installing any pollution control systems such as top cap, bottom liner, and leachate collection system. A comprehensive rededial investigation including exploratory boring, plume detection, and site‐characterization was performed to provide the basic data for the design of the remeadial measures. As a part of the investigation, this study was conducted using 10 numbers of existing monitoring wells and a bundle type well to determine the contaminant indicators for the plume detection and to define the vertical and horizontal variations of specific contaminants via distances from the landfill. The results clearly show that EC and temperature were a good pollution indicators and the vertical variation of specific contaminants measured in the fully screened well were 20 to 90% more than those measured at same depth in bundle type well located just 2m apart. This paper present a cost‐effective monitoring and sampling method to define the contaminant plume and provide a basic data for remedial actions.

Casing Leakage in Monitoring Wells: Detection, Confirmation, and Prevention

AbstractA small but significant proportion of all existing monitoring wells may be affected by leakage through the casing, usually at joints. Casing leakage can render data obtained from a monitoring well unreliable. Anomalous water level, water quality, or isotope data from a particular well are an indication of possible leakage. The occurrence of a casing leak can be confirmed by means of a pressure test using water. The magnitude of the leakage flow can be estimated from the pressure test or from the observed head anomaly. Casing leaks can be largely prevented with adequate care during monitoring well installation, but the possibility that data may be affected by casing leaks should always be taken into account during hydrogeological investigations.

Ground-water-quality assessment of the West Bountiful municipal landfill : Shank, D L Proc Symposium on Geology and Hydrology of Hazardous-Waste, Mining-Waste, Waste-Water and Repositories Sites in Utah, Salt Lake City, 1989P183–189. Publ Salt Lake City: Symposium and Field Conference, 1989 (Utah Geological Association Publication 17)

Abstract The West Bountiful Landfill occupies approximately 150 acres on the eastern shore of the Great Salt Lake in Davis County, Utah. The landfill has received municipal waste since about 1962 from 6 nearby municipalities and Davis County. Since about July 1987, the landfill has been operated solely by the City of Bountiful. To provide site-specific information regarding the potential for off-site movement of contaminated ground water, James M. Montgomery, Consulting Engineers, Inc. performed a Ground-Water-Quality Assessment study. To generate data necessary for this study, an extensive field investigation program was developed which consisted of drilling and sampling 7 perimeter soil borings to depths from 35 to 45 feet, constructing piezometers in each of these borings, and installing 8 new shallow monitoring wells. In addition, ground-water samples were collected from both the 8 new and 4 previously existing monitoring wells. The geologic conditions which underlie the West Bountiful Landfill are similar to those found in many locations along the shores of the Great Salt Lake. The landfill is underlain by interbedded layers of fine-grained soil such as clay and silt with occasional fine-grained sand and silty sand layers which range from thin laminae to 3.5 feet thick. Evidence suggesting lateral continuity of at least some of the individual layers was found in an areally extensive clay marker bed which was identified beneath the landfill in all of the 8 borings drilled at the site. Ground water beneath the West Bountiful Landfill occurs in fine sand and silty sand layers at various depths and in the refuse. The pattern of ground-water flow is generally from east to west in both the shallow zones, 8 to 12 feet below ground, and in deeper sand layers at depths of up to 40 feet below ground. Ground-water levels within the landfill refuse are elevated above the surrounding areas and create a ground-water mound. The difference between water levels in the ground-water mound and surrounding areas cause gradients to induce ground water to flow radially from the center of the landfill. Ground-water levels measured in piezometers indicate that the hydraulic head increases with depth which indicates that an upward vertical gradient underlies the landfill. The findings of this Ground-Water-Quality Assessment indicate that subsurface conditions beneath the site make it generally suitable for a municipal waste landfill. The low permeability clay layers which underlie the site appear to isolate the refuse and leachate from deeper aquifers. In addition, upward hydraulic gradients also tend to prevent a downward migration of leachate. However, leachate appears to migrate from the refuse into the Great Salt Lake through shallow, water-bearing zones.

Potential for Solute Retardation on Monitoring Well Sand Packs and Its Effect on Purging Requirements for Ground Water Sampling

AbstractMonitoring 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.

Use of a Geo Flowmeter for the Determination of Ground Water Flow Direction

AbstractThe Geo Flowmeter is manufactured by K.V. Associates of Falmouth, Massachusetts, and is used to determine ground water flow direction and velocity in monitoring wells or open boreholes. It operates by emitting heat pulses and measuring subsequent temperature increases carried by the ground water movement. The meter can be used in wells as small as 2 inches in diameter and only a single well is required for determination of ground water flow direction and rate.This paper is a case history of the use of the Geo Flowmeter in a complex hydrogeologic setting consisting of a partially above grade landfill located between a navigable waterway and a large storm water impoundment basin. Mounding effects of the landfill, tidal changes in the channel, varying water levels in the impoundment basin and a complex substrate (alternating layers of sand, silt and clay) presented a challenge for ground water interpretation and analysis. The Geo Flowmeter was lowered into existing monitoring wells surrounding the landfill to determine ground water flow direction and rate. Sensitivity of the meter was sufficient to distinguish two separate flow directions in a single well screen. Later investigation involving installation of piezometers, long‐term ground water level monitoring and plotting of ground water contours verified initial findings of the meter.This article presents numerous graphs and pictures to illustrate field use of the instrument and discusses advantages and disadvantages of its use. Actual field data collected is included to provide a basis for evaluating the accuracy of the instrument and identifying situations where it may be used.

Long‐Term Confidence in Ground Water Monitoring Systems

AbstractState‐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.