A Dry Injection System for the Emplacement of Filter Packs and Annular Seals in Ground Water Monitoring Wells

The reliability of filter pack and annular seal emplacements, and the degree of integrity of installed seals, are two of the most important factors to be considered when both installing and later utilizing ground water monitoring wells.
Numerous, and often costly, problems of using existing methods of installing filter packs and annular seals during the construction of ground water monitoring wells have led to the development of a technique of installing these monitoring well components using a dry injection system.
The dry injection system has been used to construct monitoring wells in extremely complex overburden/bedrock environments with a variety of drilling techniques. The system has shown that a high degree of reliability in the, construction of monitoring wells and greater confidence in obtaining representative ground water samples can be achieved over existing methods of filter pack and annular seal emplacement. The system has also been more cost effective than existing methods, especially for deep boreholes and multilevel monitoring system installations.     

A New Multilevel Ground Water Monitoring System Using Multichannel Tubing

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.     

A New System for Ground Water Monitoring

This paper describes a new system for ground water monitoring, "the BAT System," which includes the following functions: (a) sampling of ground water in most types of soils, (b) measurement of pore water pressure, and (c) in situ measurement of hydraulic conductivity. The system can also be used for tracer tests. The system utilizes a permanently installed filter tip attached to a steel or PVC pipe. Installation is normally performed by pushing the tip down to the desired depth. The filter tip can also be buried beneath a landfill. The primary feature of the new system is that the filter tip contains a self-sealing quick coupling unit, which makes it possible to temporarily connect the filter tip to adapters for various functions, e.g. water sampling and for measurement of pore pressure and hydraulic conductivity. The new technique makes sampling of both pressurized water and gas possible. Samples are obtained directly in hermetically sealed, pre-sterilized sample cylinders. Sampling of ground water and measurement of pore pressure can be repeated over a long period of time with undiminished accuracy. This technique is also well-adapted for taking water samples from different strata in a soil profile, in both the saturated and unsaturated zones. Actual installations range from 0.5 to 60m depth.     

A ground motion selection algorithm based on the generalized conditional intensity measure approach

An algorithm is presented for the selection of ground motions for use in seismic response analysis. The algorithm is based on the use of random realizations from the conditional multivariate distribution of ground motion intensity measures, IM|IM_j, obtained from the generalized conditional intensity measure (GCIM) approach. The algorithm can be applied to the selection of both as-recorded amplitude-scaled and synthetic/simulated ground motions. A key feature is that the generality of the GCIM methodology allows for ground motion selection based on only explicit measures of the ground motions themselves, as represented by the various IM’s considered, rather than implicit causal parameters (e.g., source magnitude, source-to-site distance) which are presently used in other contemporary ground motion selection procedures. Several examples are used to illustrate the salient features of the algorithm, including: the effect of intensity measures considered; and the properties of ground motions selected for multiple exceedance probabilities. The flexibility of the proposed algorithm coupled with the GCIM methodology allows for objective and consistent ground motion selection as a natural extension of seismic hazard analysis.     

Laboratory calibration of chemical volcanic gas sampling techniques using an artificial fumarole

We have constructed an artificial laboratory fumarole to calibrate the most common chemical volcanic gas sampling techniques and obtain a quantitative measure of their efficacy. We have also developed and tested a new rugged and portable venturi spray gas sampler. The venturi sampler reproduced the output gas composition most accurately, followed by the Giggenbach bottles, filter packs, and lastly alkaline traps. Passive alkaline traps, however, did better than filter packs when sampling more concentrated fumarole gases. Under ideal conditions, the accuracy of the Giggenbach bottles was identical to the venturi sampler, although there was slightly more scatter. The Giggenbach sampler was more susceptible to problems with condensation on the input train even in a laboratory setting, and this technique was only effective in relatively concentrated gas streams. Filter packs are also effective, but extreme care must be exercised to maintain strong undersaturation with respect to the acid gas. If strong undersaturation (high pH) is not maintained, the filter packs return erroneously low S/Cl and S/F ratios. Use of a pH indicator is an effective way of avoiding this problem. The passive alkaline traps also under-sample sulfur, resulting in low reported S/Cl and S/F ratios. It appears that the overall sampling efficiency of all techniques was not strongly affected by oxygen fugacity over the limited range tested. When detecting sulfate and sulfite simultaneously, we found no difference in total sulfur before and after oxidation. This suggests that all sulfur from the gas regardless of oxidation state was absorbed as sulfite or sulfate and/or was quickly oxidized in solution. This conclusion is supported by IC HS⁻ reference samples.     

Applications of Dual-Wall Reverse-Circulation Drilling in Ground Water Exploration and Monitoring

Dual-wall reverse-circulation drilling uses flush-threaded double-wall drill pipe and high-pressure air to provide continuous return of formation and water samples. Cuttings and formation waters are not contaminated with drilling additives or mixed with other borehole material. Up-hole velocity of about 70 ft/sec provides reliable logging of water, mineral or contaminant-bearing strata. Water samples representative of specific strata may be airlifted or bailed to the surface.
In the percussion hammer system, dual-wall drill pipe is advanced through chiefly unconsolidated material by the percussion action of an above-ground pile hammer. The borehole is drilled and temporarily cased in one pass. Wells or monitoring devices are installed as the drill pipe is hydraulically retracted during construction. A rotary head may be adapted as an option to allow dual-wall rotary drilling into consolidated or crystalline formations through a percussion hammer drill string temporarily left in place as a conductor.
The complex geology and variety of geoenvironmental problems in southern California has provided a testing ground for dual-wall drilling on hazardous material site investigations. Several case histories have demonstrated the capabilities and versatility of this method, including: (1) the installation of 4-inch and 6-inch diameter gasoline monitoring and recovery wells through gravels and cobbles at a filling station where hollow-stem auger drilling failed; (2) the confirmation of a dry borehole initially drilled by direct rotary at a landfill; and (3) multiple installations of monitoring devices through municipal refuse at a city of Los Angeles landfill.     

Significance of ground motion time step in one dimensional site response analysis

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.     

Multiport Sock Samplers: A Low-Cost Technology for Effective Multilevel Ground Water Sampling

The importance of obtaining depth-specific ground water samples is now well recognized among practitioners and scientists alike. Many methods and technologies are available for level discrete or depth-specific ground water sampling in consolidated aquifers. All methods have their associated advantages and drawbacks, however. One common disadvantage is that they are expensive. A large number of point discrete ground water samples were required for a UK research project aimed at quantifying natural attenuation processes in ground water contaminated by a former coal carbonization plant. Based on experience from a previous project to develop novel level accurate sampling methodologies for use in existing boreholes, the Ground Water Protection and Restoration Research Unit (GWPRRU) produced and tested a low-cost design multiport sock sampler for ground water monitoring. The sock sampler design allowed the recovery of multiple depth-specific ground water samples from depths of 150 feel (45 m) from individual boreholes in the sandstone aquifer at the field site. Because of their use of inexpensive materials, simple design, installation and use that does not require gravel packs, packers, or grouting, sock samplers were found to be the most cost effective, convenient, and reliable method of obtaining multiple depth-specific ground water samples at the project field site.     

Extinguishing Petroleum Vapor Intrusion and Methane Risks for Slab-on-ground Buildings: A Simple Guide

The occurrence of aerobic biodegradation in the vadose zone between a subsurface source and a building foundation can all-but eliminate the risks from methane and petroleum vapor intrusion (PVI). Understanding oxygen availability and the factors that affect it (e.g., building sizes and their distribution) are therefore critical. Uncovered ground surfaces allow oxygen access to the subsurface to actively biodegrade hydrocarbons (inclusive of methane). Buildings can reduce the net flux of oxygen into the subsurface and so reduce degradation rates. Here we determine when PVI and methane risk is negligible and/or extinguished; defined by when oxygen is present across the entire sub-slab region of existing or planned slab-on-ground buildings. We consider all building slab sizes, all depths to vapor sources and the effect of spacings between buildings on the availability of oxygen in the subsurface. The latter becomes critical where buildings are in close proximity or when increased building density is planned. Conservative assumptions enable simple, rapid and confident screening should sites and building designs comply to model assumptions. We do not model the aboveground “building” processes (e.g., air exchange), and assume the slab-on-ground seals the ground surface so that biodegradation of hydrocarbons is minimized under the built structure (i.e., the assessment remains conservative). Two graphs represent the entirety of the outcomes that allow simple screening of hydrocarbon vapors based only on the depth to the source of vapors below ground, the concentration of vapors within the source, the width of the slab-on-ground building, and the gap between buildings; all independent of soil type. Rectangular, square, and circular buildings are considered. Comparison with field sites and example applications are provided, along with a simple 8-step screening guide set in the context of existing guidance on PVI assessment.     

An instrument system for the investigation of particle fluxes

We present the rationale, design, and use of an instrument system to measure the variability of vertical and horizontal particle fluxes. The system features a new sequentially sampling sediment trap which collects and seals 10 separate samples during a single deployment. Horizontal particle fluxes are simultaneously monitored with a beam transmissometer interfaced to a standard Aanderaa current meter. Results from a 10-week deployment of instruments at several depths in a deep fjord estuary indicate that the trapping rate increases from 0.5g m⁻² day⁻¹ at 20 m to 150g m⁻² day⁻¹ at 200 m (5 m above bottom) because of frequent erosion in the deep waters. Periodic flushing of the deep water by intrusions of marine water over the seaward sill markedly enhances erosion and causes an up-estuary particle transport comparable to the vertical particle flux originating at the surface.     

Review of the Different Sources of Uncertainty in Single Polarization Radar-Based Estimates of Rainfall

It is well acknowledged that there are large uncertainties associated with radar-based estimates of rainfall. Numerous sources of these errors are due to parameter estimation, the observational system and measurement principles, and not fully understood physical processes. Propagation of these uncertainties through all models for which radar-rainfall are used as input (e.g., hydrologic models) or as initial conditions (e.g., weather forecasting models) is necessary to enhance the understanding and interpretation of the obtained results. The aim of this paper is to provide an extensive literature review of the principal sources of error affecting single polarization radar-based rainfall estimates. These include radar miscalibration, attenuation, ground clutter and anomalous propagation, beam blockage, variability of the Z–R relation, range degradation, vertical variability of the precipitation system, vertical air motion and precipitation drift, and temporal sampling errors. Finally, the authors report some recent results from empirically-based modeling of the total radar-rainfall uncertainties. The bibliography comprises over 200 peer reviewed journal articles.     

Investigation of Possible Contamination of Shallow Ground Water by Deeply Injected Liquid Industrial Wastes

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.     

Tracer Test to Evaluate Dilution of Ground Water from Lost Circulation

Lost circulation, the inadvertent injection of drilling fluids into a highly permeable and/or fractured aquifer during rotary drilling, may result in collection of spurious information if the lost drilling fluids are not adequately purged before sampling the ground water. The purpose of this study was to determine whether removal of the volume of water lost during coring of a monitoring well in the carbonate Scotch Grove Formation (Silurian, east central Iowa) necessarily ensures collection of representative ground water samples. To monitor dilution of the ground water due to lost circulation, rhodamine dye was added to the drilling water and dye recovery was measured in samples collected during purging of five separate 5- to 10-foot intervals.
Circulation loss occurred in all five intervals, ranging from nearly 200 gallons in the upper permeable portion of the Scotch Grove to 25 gallons in the less permeable Buck Creek Member below. When the volume of water purged from the upper three intervals corresponded to the volume of water lost during coring, the purge water still contained 11 to 20 percent dyed drilling water. As purging continued, the proportion of drilling water in the samples decreased slowly. After purging more than 200 gallons of water, 86 to 98 percent of the dyed drilling water was recovered from the five test intervals. Four traditionally measured water quality parameters-pH, temperature, specific conductance, and dissolved oxygen — were less useful than the dye recovery for distinguishing drilling water from formation water in those zones in which the ground water quality was similar to the drilling water. These results indicate that the determination of the quantity of water to be purged prior to sampling must be based, at least in part, on aquifer lithology and hydraulic characteristics.     

Application of Direct Push Methods to Investigate Uranium Distribution in an Alluvial Aquifer

The U.S. EPA 2000 Radionuclide Rule established a maximum contaminant level (MCL) for uranium of 30 µg/L. Many small community water supplies are struggling to comply with this new regulation. At one such community, direct push (DP) methods were applied to obtain hydraulic profiling tool (HPT) logs and install small diameter wells in a section of alluvial deposits located along the Platte River. This work was conducted to evaluate potential sources of elevated uranium in the Clarks, Nebraska drinking water supply. HPT logs were used to understand the hydrostratigraphy of a portion of the aquifer and guide placement of small diameter wells at selected depth intervals. Low-flow sampling of the wells provided water quality parameters and samples for analysis to study the distribution of uranium and variations in aquifer chemistry. Contrary to expectations, the aquifer chemistry revealed that uranium was being mobilized under anoxic and reducing conditions. Review of the test well and new public water supply well construction details revealed that filter packs extended significantly above the screened intervals of the wells. These filter packs were providing a conduit for the movement of groundwater with elevated concentrations of uranium into the supply wells and the community drinking water supply. The methods applied and lessons learned here may be useful for the assessment of unconsolidated aquifers for uranium, arsenic, and many other drinking water supply contaminants.     

Field Evaluation of the Effectiveness of Surfactant Modified Zeolite and Iron-Oxide-Coated Sand for Removing Viruses and Bacteria from Ground Water

Field experiments were conducted to evaluate the efficiency of iron-oxide-coated sand (ICS) and surfactant modified zeolite (SMZ) to remove viruses and bacteria from ground water. The reactive media were employed as filter packs of a pumping well that withdrew sewage effluent from a constructed wetland at a rate of 0.72 L/min. The contact time of the pumped water with the filter pack (10 cm thick) was about two minutes. Upgradient of the pumping well, the sewage effluent was spiked with MS-2 bacteriophage and E. coli. While the employed ICS filter pack failed to remove viruses and bacteria to a significant degree, the SMZ filter pack removed more than 99% of the viruses and 100% of E. coli from the ground water while fresh. In an additional field experiment using the same configuration but leaving the filter pack in place for more than five months, the SMZ filter pack was still removing 100% of E. coli , but failed to reduce virus numbers to a significant degree.     

A Syringe and Cartridge Method for Down-Hole Sampling for Trace Organics in Ground Water

A newly developed technique which allows the down-hole sampling and subsequent analysis of ground water for trace organic contaminants was tested during an investigation of contaminant migration at an inactive landfill site in Burlington, Ontario, Canada. The sampling device, which is lowered down piezometers with a tube, consists of a small cylindrical cartridge of sorbent material attached to a syringe. Vacuum or pressure applied at the surface controls the movement of the plunger in the syringe. The volume of the syringe determines the volume of sample water that passes through the cartridge. The cartridge is removed from the syringe at the surface. One cartridge is used for each sampling; the syringe is reusable. The residual water in the cartridge is removed in the laboratory, and the cartridge is desorbed to a fused silica capillary column for analysis by gas chromatography (GC). The analyses discussed here were performed on a GC/mass spectrometer/data system (GC/MS/DS). Of the many organic compounds that were identified in the samples, three compounds were clearly landfill-related: 1,1,1-trichloroethane, chlorobenzene, and para-dichlorobenzene. The three compounds were found at levels substantially above blank levels in 9, 5, and 5 piezometers, respectively. The average concentrations were 14., 5.3, and 0.88μg/1 (ppb), respectively. The pooled coefficients of variation for the analyses for the three compounds were 27., 6.9, and 6.4%, respectively. The volatility of 1,1,1-trichloroethane was probably the cause of the greater variability in its analytical data. The main advantages of the technique over most conventional sampling methods include: (1) down-hole sampling in a manner which minimizes the potential for volatilization losses; (2) avoidance of passage of the sample through long sections of tubing that may contaminate the sample or cause adsorptive losses; (3) convenience of sample handling, storage, and shipping; and (4) high sensitivity.     

The Effect of Three Drilling Fluids on Ground Water Sample Chemistry

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.     

An Integrated Ground Water Monitoring Program Using Multilevel Gas-Driven Samplers and Conventional Monitoring Wells

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.     

Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills

Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill? fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill? requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains.