Drill-Through Casing Driver Drilling Method for Construction of Monitoring Wells in Coarse, Unconsolidated Sediments

Hole stability problems occurring during construction of monitoring wells in coarse, unconsolidated alluvium can be overcome by using a drill-through casing driver mounted on a standard top-head drive rotary rig. Steel casing is driven contemporaneously with drilling, providing continuous hole stability. Samples of aquifer material and ground water can be taken at discrete depths as drilling proceeds. Monitoring well completion is accomplished by: (1) using the steel casing as an open-ended piezometer; (2) installing a telescoping well screen; (3) plugging the casing end and perforating desired intervals, (4) installing one or more smaller diameter wells, and then (5) pulling back the steel casing. Advantages of this drilling method include maintenance of hole stability during drilling and well completion, faster borehole construction time than traditional methods in coarse alluvial deposits and other poorly sorted formations, and collection of representative samples of the geologic formations and ground water; additionally, drilling fluids are not required.     

TABLE DES MATIÈRES DU BULLETIN DE 1956 A 1960 / CONTENTS OF THE BULLETIN 1956–1960

Abstract

Piezometers and wells installed for water quality monitoring are frequently used to assess the saturated hydraulic conductivity (K) in the surrounding formation. A series of recovery tests was conducted to evaluate how purging, required to obtain representative water quality samples, affected measured values of hydraulic conductivity in 15 newly installed and undeveloped piezometers placed to between 2 and 15 m depth (in oxidized and unoxidized material) in a loamy glacial till (K range from 10^?6 to 10^?9 m s^?1). Piezometers were purged between 9 and 11 times for sampling over a period of five months. The effect of the purgings on piezometer development was evaluated by changes in slope of the water level recovery curves which were used to calculate hydraulic conductivity. The first five purgings following piezometer installation increased K in the 15 piezometers by an average of 34%. The average increase in a value of K after 10 purgings was 44%. Values measured for hydraulic conductivity in a 75 mm diameter auger hole appeared stable after four purgings but piezometers installed in larger diameter boreholes (100 mm to 280 mm) snowed increases in K with up to 10 purgings. The hydraulic conductivity determined for piezometers installed at a 30° angle to the vertical showed greater variability than was observed in the adjacent vertically installed piezometers at the same depth.     

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.     

A Method for Installing Piezometers in Large Cobble Bed Rivers

An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies.     

Some Biases in Sampling Multilevel Piezometers for Volatile Organics

Multilevel piezometers are cost-effective monitoring devices for determining the three-dimensional distribution of solutes in ground water. Construction includes flexible tubing (plastic or Teflon®). Their sampling is subject to a number of'potential biases, particularly: (1) losses of volatile organic solutes via volatilization, (2) sorption onto the flexible tubing of the piezometers, (3) leaching of organics from this tubing, and (4) collection of unrepresentative samples due to inadequate piezometer flushing. It is shown that these biases are minimal or are easily controlled in most situations.
Another source of bias has been recognized. Organic solutes present in ground water above the screened level can penetrate the flexible plastic or Teflon tubing and contaminate the sampled water being drawn through this tubing. Laboratory tests and field results indicate this transmission causes low organic contaminant concentrations to be erroneously attributed to ground water which is free of such contaminants. The transmitted organics apparently desorb from the plastic tubing during flushing of even 40 piezometer volumes.
Recognition of this transmission problem provides for a better interpretation of existing organic contaminant distribution data. Caution is advised when considering the use of these monitoring devices in organic solute contaminant studies.     

Conducting Slug Tests in Mini‐Piezometers

Slug tests performed using mini‐piezometers with internal diameters as small as 0.43 cm can provide a cost effective tool for hydraulic characterization. We evaluated the hydraulic properties of the apparatus in a laboratory environment and compared those results with field tests of mini‐piezometers installed into locations with varying hydraulic properties. Based on our evaluation, slug tests conducted in mini‐piezometers using the fabrication and installation approach described here are effective within formations where the hydraulic conductivity is less than 1 × 10^?3 cm/s. While these constraints limit the potential application of this method, the benefits to this approach are that the installation, measurement, and analysis is cost effective, and the installation can be completed in areas where other (larger diameter) methods might not be possible. Additionally, this methodology could be applied to existing mini‐piezometers previously installed for other purposes. Such analysis of existing installations could be beneficial in interpreting previously collected data (e.g., water‐quality data or hydraulic head data).     

Design, Installation, and Uses of Combination Ground Water and Gas Sampling Wells

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.     

Monitoring in the Vadose and Saturated Zones Utilizing Fluoroplastic

A ground water monitoring program should include an investigation of all possible areas of concern. To be completely effective, the program should include soil sampling, soil analysis and water-quality examination of both the saturated and unsaturated zones. A well-tooled drill rig can take all the proper soil samples, perform all necessary tests and install a functional monitoring well. With the introduction of the fluoropolymer (Teflon(r)) sleeve lysimeter, a single monitoring well can be constructed to monitor both the saturated and unsaturated zones in one installation. The monitoring well screen and casing may also be completely constructed of fluoropolymer.
The sleeve lysimeter is designed with a threaded hollow inner diameter, allowing it to be attached between the joints of a casing string. This hollow I.D. acts as an extension of the casing; the lysimeter surrounds the casing. This creates an isolated vessel for sampling the vadose zone. Access to the screened monitoring well below is unaffected. Tests have shown that when properly installed, these porous fluoropolymer filter units can collect samples with no interaction between the filter and collected fluids.     

The Transiometer: An Alternative Method of Soil Moisture Measurement in Slowly Permeable Soils

The union of a piezoresistive pressure transducer and a porous ceramic cup was termed "transiometer." The transiometer was constructed from economical and readily available materials. It could be used to measure soil water potentials in both saturated and unsaturated conditions, and was well suited to continuous monitoring with data acquisition equipment.
Transiometer testing was conducted at two sites, one of moderate permeability and the other of slow permeability. The slowly permeable site was instrumented with four replications of the following: (1) transiometers installed at four depths, (2) a transi-ometerwithout the ceramic cup, (3) apiezometer, and (4) access tubes for monitoring soil moisture with a neutron probe. The moderately permeable site was instrumented with a transiometer, two piezometers, and an access tube for monitoring with a neutron probe.
In saturated conditions the transiometer had a faster response time after installation than the piezometer. Faster response makes the transiometer more desirable for use in slowly permeable soils, especially when monitoring dynamic soil water.
Calculated random error of the transiometer measuring system, including a digital voltmeter and a scanner, was typically 0.09 feet (2.8cm), with a maximum calculated to be 0.38 feet (11.5cm). The two most significant components were imprecision of the scanner card and calibration shift. The transiometer was sensitive to atmospheric pressure fluctuations, with sensitivity to atmospheric pressure change increasing with installation depth.     

A Comparison of Office-Derived vs. Field-Derived Water Table Maps for a Sandy Unconfined Aquifer

This study compares the accuracy of two types of water table maps both of which were constructed with the object of optimizing future mapping efforts in similar environments. The. first type of map is based solely on office information, with no field verification. The second type of map is based on careful field mapping using numerous measurement points.
The office-derived maps were based on topography, surface water features, existing reports, maps and data in the files of the Wisconsin Geological and Natural History Survey; the data were not field-verified. The field-derived maps used a dense network of 236 piezometers at 176 sites in an area of approximately 170 square miles. The field project was much more expensive and labor-intensive than was the construction of office-derived maps for the same area.
The two methods produce water table maps which agree to an appreciable extent, the greatest agreement being in areas having ground water-fed streams. Differences in water table elevations indicated by the two methods range from negligible to approximately 5 feet. Thus, depending upon the availability of existing information, relatively accurate water table elevations can be delineated in similar sandy unconfined aquifers without time-consuming and expensive field work that drilling and piezometer installation entails.
Preliminary construction of office-derived water table maps enables researchers to use their resources efficiently. In some situations, expensive installation of wells and piezometers for a regional monitoring network may add little accuracy to the regional map. For localized problems, collection of additional field data will always be necessary, but can be guided by the office-derived maps. The authors caution that this technique may only be applicable to sandy, unconfined aquifers in humid climates.     

Electronic acquisition of hydrologic data from intensively instrumented hillslopes

A new concept in recording data from a large network of transducers in the field is described. Each transducer is equipped with an addressable switching unit enabling parallel connection by a single four wire cable and sequential interrogation from a micro-computer controlled data logger. A simple water level transducer suitable for both large stilling wells and piezometers, which returns an audio frequency signal with pulse width proportional to water level, is described. The use of audio frequency signals enables telephone grade circuits to be used and avoids many of the problems associated with direct current signals, whether current or voltage, commonly used at present. A field installation of 30 piezometers, a tipping bucket raingauge, a weir-stage recorder and logger controlled water sampler is described and examples given of the data collected from a single piezometer transect during a major storm event.     

Impact of grout curtains on karst groundwater behaviour: an example from the Dinaric karst

Grout curtains are vertical grout walls installed in the ground. In karst terrains, their construction is primarily connected with dams and reservoirs. Their main role is to increase water tightness and to prevent progressive erosion, blocking possible seepage paths along karst fissures and conduits. In this article, changes in the behaviour of the groundwater level (GWL) and the water temperature in nine deep piezometers, which were caused by the construction of a grout curtain at the ?ale Reservoir on the Cetina River (Croatia), were analysed. The total length of the grout curtain is 3966 m. It spreads 120 m below the dam. The most analysed data are from the period after the dam had been built. Only few data and figures concern the comparison between pre‐ and post‐dam periods. The hourly data of the GWL and the water temperature were analysed for the period between 1 September 2008 at 02:00 h to 31 December 2009 at 23:00 h (11 687 h total) in six deep piezometers (marked in the text and figures as 1, 2, 3, 4, 5 and 6). For three piezometers (marked in the text and figures as A, B and C), some discontinuous measurements of the GWL and the water temperature were available for analysis. The construction of the grout curtain made strong, sudden and possibly dangerous changes to the characteristics of the aquifer and the circulation of groundwater in the local area. Special attention is paid to analyses of the behaviour of the hourly GWL data measured in the piezometers pairs (two neighbouring piezometers, one inside and the other outside of the grout curtain). During more than 80% of the analysed period, the GWL was higher in the piezometer inside the grout curtain than the one outside of it. The intensity and range of the dynamics of GWL was higher in piezometer outside the grout curtain than the inside ones. After the construction of the grout curtain, the maximum measured hydrostatic pressure on some parts of the grout curtain was approximately 40 m. It changes quickly in both time and direction. The water temperature was found to be similar in all of the measured piezometers, and it varies between 10.2 and 15.7 °C with an average value of 12.7 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

A Multilevel Ground Water Monitoring System for Casing Advance and Bedrock Drilling Methods

A single-hole multilevel sampling piezometer system (MLSPS) has been designed by the Geological Survey of Canada (GSC) to be installed using drilling systems that continuously core (e.g., Rotosonic) or continuously sample (e.g., hollow-stem auger, Becker hammer) overburden and that have the flexibility of allowing additional coring (diamond drilling) or sampling (hammer drilling) of bedrock. The GSC-MLSPS (under license to Solinst Canada Ltd.) uses a patented GSC dry injection system for accurate emplacement of filter packs and seals. This system permits (a) the use of variable screen lengths; (b) the complete evacuation of piezometers before introduction of new ground water (no bailing); (c) the use of a number of types of hydraulic tests (e.g., slug, withdrawal/recovery, vacuum, pressure-pulse); (d) ground water sampling under a nitrogen atmosphere; (e) dissolved gas sampling; (f) a great deal of flexibility in the use of design materials; and (g) the elimination of bridging and collapse of filter packs and seals.     

Macro- and Micro-Purge Soil-Gas Sampling Methods for the Collection of Contaminant Vapors

Purging influence on soil‐gas concentrations for volatile organic compounds (VOCs), as affected by sampling tube inner diameter and sampling depth (i.e., system volume) for temporary probes in fine‐grained soils, was evaluated at three different field sites. A macro‐purge sampling system consisted of a standard, hollow, 3.2‐cm outer diameter (OD) drive probe with a retractable sampling point attached to an appropriate length of 0.48‐cm inner diameter (ID) Teflon^® tubing. The macro‐purge sampling system had a purge system volume of 24.5 mL at a 1‐m depth. In contrast, the micro‐purge sampling systems were slightly different between the field sites and consisted of a 1.27‐cm OD drive rod with a 0.10‐cm ID stainless steel tube or a 3.2‐cm OD drive rod with a 0.0254‐cm inner diameter stainless steel tubing resulting in purge system volumes of 1.2 and 7.05 mL at 1‐m depths, respectively. At each site and location within the site, with a few exceptions, the same contaminants were identified in the same relative order of abundances indicating the sampling of the same general soil atmosphere. However, marked differences in VOC concentrations were identified between the sampling systems, with micro‐purge samples having up to 27 times greater concentrations than their corresponding macro‐purge samples. The higher concentrations are the result of a minimal disturbance of the ambient soil atmosphere during purging. The minimal soil‐gas atmospheric disturbance of the micro‐purge sampling system allowed for the collection of a sample that is more representative of the soil atmosphere surrounding the sampling point. That is, a sample that does not contain an atmosphere that has migrated from distance through the geologic material or from the surface in response to the vacuum induced during purging soil‐gas concentrations. It is thus recommended that when soil‐gas sampling is conducted using temporary probes in fine‐grained soils, the sampling system use the smallest practical ID soil‐gas tubing and minimize purge volume to obtain the soil‐gas sample with minimal risk of leakage so that proper decisions, based on more representative soil‐gas concentrations, about the site can be made.     

Inferring Heterogeneity in Aquitards Using High-Resolution δD and δ18O Profiles

Vertical depth profiles of pore water isotopes (δD and δ¹⁸O) in clay-rich aquitards have been used to show that solute transport is dominated by molecular diffusion, to define the timing of geologic events, and to estimate vertical hydraulic conductivity. The interpretation of the isotopic profiles in these studies was based on pore water samples collected from piezometers installed in nests (typically 4 to 15 piezometers) over depths of 10 to 80 m. Data from piezometer nests generally have poor vertical resolution (meters), raising questions about their capacity to reveal the impact of finer scale heterogeneities such as permeable sand bodies or fractured till zones on solute transport. Here, we used high-resolution (30-cm) depth profiles of δD and δ¹⁸O from two continuously cored boreholes in a till aquitard to provide new insights into the effects of sand bodies on solute transport. High-resolution core-derived profiles indicate that such heterogeneities can cause major deviations from one-dimensional diffusion profiles. Further, comparison of piezometer-measured values with best-fit diffusion trends shows subtle deviations, suggesting the presence of heterogeneities that should not be ignored. High-resolution profiles also more clearly defined the contact between the highly fractured oxidized zone and the underlying unoxidized zone than the piezometers.     

Application of harmonic analysis of water levels to determine vertical hydraulic conductivities in clay-rich aquitards

A harmonic analysis method was used to determine vertical hydraulic conductivities (Kv) in geologic media between vertically separated piezometers using water level measurements. In this method, each water level time series was filtered and then decomposed using harmonic analysis into a sum of trigonometric components. The phase and amplitude of each harmonic function were calculated. These data were used to estimate Kv values between vertically separated data sets assuming one-dimensional transient flow. The method was applied to water level data collected from nested piezometers at two thick clay-rich till aquitards in Saskatchewan, Canada. At one site, routine water levels were measured in 12 piezometers (installed between 1 and 29 m below ground surface) since installation (1995). At the other site, water levels were measured in seven piezometers (installed between 4 and 53 m below ground surface) since installation (1998-1999). The Kv calculated using harmonic analysis decreased with depth below the water table at both sites, approaching matrix estimates of hydraulic conductivity between 10 and 11 m and between 21 and 43 m below ground surface. These depths reflected the depth of extensive vertical fracturing at the sites and showed that the depth of fracturing may be site specific.     

A simple constant-head injection test for streambed hydraulic conductivity estimation

A fast, efficient constant-head injection test (CHIT) for in situ estimation of hydraulic conductivity (K) of sandy streambeds is presented. This test uses constant-head hydraulic injection through a manually driven piezometer. Results from CHIT compare favorably to estimates from slug testing and grain-size analysis. The CHIT combines simplicity of field performance, data interpretation, and accuracy of K estimation in flowing streams.     

Optimizing Ground Water Observation Networks in Irrigation Areas Using Principal Component Analysis

Ground water monitoring networks can provide vital information for sustainable water resources management. This involves the measurement of ground water level, solute concentration, or both. This article deals with the former. It optimizes network distribution of piezometer or data sampling wells to effectively monitor ground water levels under an irrigation region while retaining adequate overall measurement accuracy. This article presents a structured process for applying principal component analysis (PCA) in optimizing a ground water monitoring network in an irrigation area of Australia. The PCA functions, distributed with the MATLAB package, were used to determine relative contributions of individual piezometers in capturing the spatiotemporal variation of ground water levels. Kriging gridding interpolation algorithm was used to render the data surface presentations and determine spatial differences in piezometeric surfaces using different number of data sets. The results show that the overall difference of ground water level between the original piezometer network and the optimized networks after the PCA process was applied is less than 20%, while the total number of piezometers in the optimized network is reduced by 63%, which will save the time and cost to monitor ground water levels in the irrigation area.     

Monitoring Hydrogeologlcal Conditions in Fractured Rock at the Site of Canada's Underground Research Laboratory

Atomic Energy of Canada Limited is constructing an Underground Research Laboratory (URL) at a depth of 250m in a plutonic rock body near Lac du Bonnet, Manitoba. The facility is being constructed to carry out a variety of in situ geotechnical experiments as part of the Canadian Nuclear Fuel Waste Management Program. A unique feature of the URL, in comparison to other similar facilities such as the Stripa Mine in Sweden, is that it is to be constructed below the ground water table in a previously undisturbed plutonic rock body. One of the main research objectives of the project is to develop and validate comprehensive three-dimensional models of the hydrogeology of the rock mass encompassing the URL site. These models will be used, before excavation of the URL shaft begins, to predict the hydrogeological perturbation that will be created by the excavation of the shaft and the horizontal working levels below the ground water table. As a model-validation exercise, these drawdown predictions will be compared with actual hydrogeological perturbations that will be monitored at the study area over the next several years by an extensive network of instrumented boreholes. Measurements made in an array of boreholes extending to depths of 1,000m on the 4.8 km² study area have established that the permeability distribution in three major extensive subhorizontal fracture zones controls the movement of ground water within the rock mass. Several types of multiple-interval completion systems have been installed in the boreholes to monitor the three-dimensional, physico-chemical hydrogeological conditions within the fractured rock mass. These include conventional piezometer nests and water-table wells that have been installed in shallow holes (less than 30m deep), and multiple-packer/ multiple-standpipe piezometers and multiple-interval casing systems installed in deeper holes (30 to 1,000m deep). An automated, electronic, piezometric pressure-monitoring system has been designed to collect continuous measurements from 75 isolated hydrogeological monitoring positions within the rock mass. Another 200 positions are being monitored frequently using a variety of techniques. Piezometric data have been collected from this monitoring network to establish baseline conditions prior to any excavation into the rock mass. These data have also been used to determine the steady-state, three-dimensional ground water flow regimes that exist at the URL site under natural conditions.