Installation Of Piezometers Research Articles

Issues of Sustainability of Coastal Groundwater Resources: Benin, West Africa

The largest city in Benin, West Africa (Cotonou), is reliant upon groundwater for its public water supply. This groundwater is derived from the Godomey well field which is located approximately 5 Km north of the coast of the Atlantic Ocean and in close proximity to Lake Nokoue—a shallow lake containing water with elevated concentration of chloride and other elements. Historical data indicate increased chloride concentration in a number of wells nearest to the lake, with unknown contribution from groundwater encroachment from the coastal area. Hence, there is substantial interest in better characterizing this groundwater system for the purpose of determining appropriate management practices and degree of sustainability. Among the efforts attempted to date are a series of numerical models ranging from assessment of flow to a recent effort to include density-dependent transport from the lake. In addition, substantial field characterization has been pursued including assessment of shallow water chemistry along the region of the coastal lagoon and border of the lake, characterization of hydraulic response to pumpage in the aquifer system, estimation of the distribution of electrical resistivity with depth along the coastal lagoons, and installation of multi-level piezometers at seven locations in the lake. When integrated across methods, these numerical and field results indicate that the lake remains a primary concern in terms of a source of salinity in the aquifer. Further, the coastal region appears to be more complex than previously suggested and may represent a future source of salt-water encroachment as suggested by current presence of saline waters at relatively shallow depths along the coast. Finally, hydraulic testing suggests that both natural and pumping-based fluctuations in water levels are present in this system. Substantial additional characterization and modeling efforts may provide a significantly greater understanding of the behavior of this complex groundwater system and, thereby, an improved ability to manage the potential for negative impacts from salt-water and anthropogenic contaminants entering this sole source of fresh water for southern Benin.

Water table monitoring in a mined riparian zone

The objective of this study was to test an easily fabricated tool that assist in the manual installation of piezometers, as well as water table monitor in the research site, located at the Gualaxo do Norte River Watershed, state of Minas Gerais, Brazil. The tool is made of iron pipes and is a low-cost alternative for shallow groundwater observation wells. The measurements were done in a riparian zone after being gold mined, when vegetation and upper soil layers were removed. The wells were installed in three areas following a transect from the river bank. The method was viable for digging up to its maximum depth of 3 meters in a low resistance soil and can be improved to achieve a better resistance over impact and its maximum depth of perforation. Water table levels varied distinctly according to its depth in each point. It varies most in the more shallow wells in different areas, while it was more stable in the deeper ones. The water table profile reflected the probably profile f the terrain and can be a reference for its leveling in reconstitution of degraded banks where upper layers of the soil were removed. Groundwater monitoring can be also an indicator of the suitability of the substrate for soil reconstitution in terms of the maintenance of an infiltration capacity similar to the original material.

Assessment of London underground tube tunnels - investigation, monitoring and analysis

Tube Lines has carried out a "knowledge and investigation programme" on the deep tube tunnels comprising the Jubilee, Northern and Piccadilly lines, as required by the PPP contract with London Underground. Many of the tunnels have been in use for over 100 years, so this assessment was considered essential to the future safe functioning of the system. This programme has involved a number of generic investigations which guide the assessment methodology and the analysis of some 5,000 individual structures. A significant amount of investigation has been carried out, including ultrasonic thickness measurement, detection of brickwork laminations using radar, stress measurement using magnetic techniques, determination of soil parameters using CPT, pressuremeter and laboratory testing, installation of piezometers, material and tunnel segment testing, and trialling of remote photographic techniques for inspection of large tunnels and shafts. Vibrating wire, potentiometer, electro level, optical and fibre-optic monitoring has been used, and laser measurement and laser scanning has been employed to measure tunnel circularity. It is considered that there is scope for considerable improvements in non-destructive testing technology for structural assessment in particular, and some ideas are offered as a "wish-list". Assessment reports have now been produced for all assets forming Tube Lines' deep tube tunnel network. For assets which are non-compliant with London Underground standards, the risk to the operating railway has to be maintained as low as reasonably practicable (ALARP) using enhanced inspection and monitoring, or repair where required. Monitoring techniques have developed greatly during recent years and further advances will continue to support the economic whole life asset management of infrastructure networks.

Field variable-head test in low-permeability materials: Assessing the effects of trapped gas pocket and cavity expansion

Trapped gas and cavity expansion may affect the data of a variable-head test in a monitoring well. In a low-permeability material, some gas may be trapped in the top of the filter pack. Presence of a gas pocket may be alleged when the initial change in water level in the pipe is less than the theoretical value due to the slug volume. A variable-head test with trapped gas is described by three equations to be solved simultaneously. The gas pocket contraction leads to an underestimation of the hydraulic conductivity, k, especially for small pipes used to test natural or compacted clay. It must be considered, however, that the difference between the theoretical and measured changes in initial water level is due to the sum of trapped gas contraction plus cavity expansion (falling-head) or trapped gas expansion plus cavity contraction (rising head). This difference cannot be used to assess the volume of trapped gas unless an independent mechanical test has established the material deformability. For example, pressuremeter tests can be done in cavities that are prepared with the same care as those used for the installation of piezometers. A simple test that consists of adding or removing known volumes of water in the pipe of the piezometer is described. Field data are provided along with the method to handle them and extract the correct k value. To avoid gas entrapment in the filter pack, a small diameter plastic tube can be installed and used as a gas vent.

Evaluation and field-scale application of an analytical method to quantify groundwater discharge using mapped streambed temperatures

A method for calculating groundwater discharge through a streambed on a sub-reach to a reach scale has been developed using data from plan-view mapping of streambed temperatures at a uniform depth along a reach of a river or stream. An analytical solution of the one-dimensional steady-state heat-diffusion–advection equation was used to determine fluxes from observed temperature data. The method was applied to point measurements of streambed temperatures used to map a 60 m long reach of a river by Conant Jr. [Conant Jr. B., 2004. Delineating and quantifying ground water discharge zones using streambed temperatures. Ground Water 42(2), 243–257] and relies on the underlying assumption that streambed temperatures are in a quasi-steady-state during the period of mapping. The analytical method was able to match the values and pattern of flux previously obtained using an empirical relationship that related streambed temperatures to fluxes obtained from piezometers and using Darcy’s law. A second independent test of the analytical method using temperature mapping and seepage meter fluxes along a first-order stream confirmed the validity of the approach. The USGS numerical heat transport model VS2DH was also used to evaluate the thermal response of the streambed sediments to transient variations in surface water temperatures and showed that quasi-steady-state conditions occurred for most, but not all, conditions. During mapping events in the winter, quasi-steady-state conditions were typically observed for both high and low groundwater discharge conditions, but during summer mapping events quasi-steady-state conditions were typically not achieved at low flux areas or where measurements were made at shallow depths. Major advantages of using this analytical method include: it can be implemented using a spreadsheet; it does not require the installation or testing of piezometers or seepage meters (although they would help to confirm the results); and it needs only a minimal amount of input data related to water temperatures and the thermal properties of water and the sediments. The field results showed the analytical solution tends to underestimate high fluxes. However, a sensitivity analysis of possible model inputs shows the solution is relatively robust and not particularly sensitive to small uncertainties in input data and can produce reasonable flux estimates without the need for calibration.

Investigation of the thermal properties and apparent molar volumes of ZnBr 2 (aq) in the temperature range from 298.15 to 398.15 K and at pressures up to p = 60 MPa using a piezometer of constant volume

The ( p, ρ, T) and ( p s, ρ s, T s) properties and apparent molar volumes V ϕ of ZnBr 2 (aq) at T = (298.15 to 398.15) K, pressures up to p = 60 MPa were reported, and apparent molar volumes of ZnBr 2 at infinite dilution V ϕ 0 have been evaluated. The experiments were carried out by the constant volume piezometer installation, ( p, ρ, T) and ( p s, ρ s, T s) values were described by an equation of state. The isothermal compressibilities k and thermal expansivities α were calculated from the equation of state. An empirical correlation for density of zinc bromide (aq) with pressure, temperature and molality has been derived. The experiments were carried out at molalities m = (0.06220, 0.17341, 0.38183, 0.84419, 1.43444, and 4.18418) mol kg − 1 of zinc bromide.

POST CONSTRUCTION REMEDIAL MEASURES AGAINST SUSPECTED HIGH SEEPAGE IN AN EARTH DAM

ABSTRACT Presence of pervious strata in the foundation of an earthen dam would pose a serious problem of seepage. Maskinala earthen dam in Raichur District of Karnataka was constructed on pervious foundation by providing partial cut-off and upstream blanket. Post construction detailed foundation investigation indicated presence of 2.0 to 8.0 m sand stratum underlain by 2.0 m thick highly pervious sand-gravel followed by impervious rock. Finite element steady seepage analysis for the dam and foundation indicated that the value of the exit gradient would be within the permissible limits. However, the quantity of seepage would be excessive after impoundment. This warranted additional defensive measures against seepage in the form of cut-off wall/diaphragm wall/slurry trench/geomembrane at the upstream toe and it should be embedded at least 1.0 m in impermeable bedrock. This would act as a positive cutoff. Since seepage quantity with this provision was found to be acceptable, suggestion for construction of a positive cut-off at upstream toe was recommended. Installation of piezometers in foundation and in the body of the dam was suggested to monitor performance of the earth dam after impoundment.

P–ρ–T and Ps–ρs–Ts properties of methanol + water and n-propanol + water solutions in wide range of state parametersElectronic supplementary information (ESI) available: Tables of values of the coefficients in eqn. (1), eqn. (7), eqn. (8) and eqn. (9). See http://www.rsc.org/suppdata/cp/b1/b109077c/

The P–ρ–T and Ps–ρs–Ts properties of methanol + water and n-propanol + water solutions in a wide range of state parameters have been investigated in a constant volume piezometer installation. The experiments were carried out for the methanol + water solutions in the temperature range 298.15 to 523.15 K, at mole fractions of methanol of x = 0.25, x = 0.50, x = 0.75, from the bubble point pressure up to 60 MPa and also for n-propanol + water solutions in the temperature range 373.15 to 573.15 K, at the x = 0.25, x = 0.50, x = 0.75 mole fractions of n-propanol, in the pressures range 0.1 to 5.25 MPa, in the 0.6628–118.6103 kg m−3 density interval. The experimental uncertainties are ΔT = ± 3 mK for temperature, ΔP = ± 5×10−2×P for pressure, Δρ = ± 3×10−2×ρ for density in liquid phases, and Δρ = ± 9×10−2×ρ in the vapor phase. A new equation of state was derived for correlation of the experimental data of methanol + water solutions. The experiments could be reproduced with deviations not exceeding experimental uncertainty. The data obtained for the n-propanol + water solution allowed us to establish the equation of state in virial form and thus the second and the third virial coefficients are calculated. The virial coefficients were obtained by two independent methods, namely, graphical and analytical. The temperature and mole fraction dependence of the coefficients of the equations of state are described.

Numerical modeling of saline water transport in the lower Nam Kam Basin, Amphoe That Phanom, Changwat Nakhon Phanom, Thailand

The objective of the project is to establish a conceptual groundwater model over the lower Nam Kam Basin in order to apply a numerical technique for the prediction of the impact of saline water transport due to the proposed weir across the Nam Kam River. Hydrogeological investigations including mapping, drilling, piezometer installations and monitoring were systematically conducted during 1997 to 1998. Brackish groundwater is saturated under the area with a depth of 30-60 m. Groundwater regionally flows from the south (the Phu Phan Range) to the north and discharges to the Nam Kam River. Another direction is from the northern region to the southern region, discharging to the central region. A two-dimensional model was constructed along the principal gradient in the NW-SE direction. There are several local recharge and discharge areas across the Nam Kam floodplain. A local groundwater flow is active within the depth of 2 m to 30 m below the ground surface within the sand and gravel unit. Simulations were calibrated with hydraulic heads and salinity of groundwater in the piezometers. It is found that the recharge and evapotranspiration rates are 1% to 40% of the rainfall and 10% to 15% of a pan evaporation, respectively. The ranges of horizontal hydraulic conductivity to vertical hydraulic conductivity are 0.1 to 0.01. The possible longitudinal dispersivity values of the hydrostratigraphic units are 20 m to 500 m, but the transverse dispersivity is less than the longitude by one order of magnitude. The comparison of calculated heads and measured heads give a root mean square error of less than 1 m. The different salinity concentrations are still in a range of 2000-5000 mg/l. Ten year simulation of saline water transport indicates that the reservoir ponding with water level at +140.5 m above mean sea level may divert groundwater flow and discharging to the northern boundary of the reservoir at Ban Don Kao.

Factors affecting the distribution of hydrocarbon contaminants and hydrogeochemical parameters in a shallow sand aquifer

The distributions of hydrocarbon contaminants and hydrogeochemical parameters were investigated in a shallow sand aquifer highly contaminated with petroleum hydrocarbons leaked from solvent storage tanks. For these purposes, a variety of field investigations and studies were performed, which included installation of over 100 groundwater monitoring wells and piezometers at various depths, soil logging and analyses during well and piezometer installation, chemical analysis of groundwater, pump tests, and slug tests. Continuous water level monitoring at three selected wells using automatic data-logger and manual measuring at other wells were also conducted. Based on analyses of the various investigations and tests, a number of factors were identified to explain the distribution of the hydrocarbon contaminants and hydrogeochemical parameters. These factors include indigenous biodegradation, hydrostratigraphy, preliminary pump-and-treat remedy, recharge by rainfall, and subsequent water level fluctuation. The permeable sandy layer, in which the mean water table elevation is maintained, provided a dominant pathway for contaminant transport. The preliminary pump-and-treat action accelerated the movement of the hydrocarbon contaminants and affected the redox evolution pattern. Seasonal recharge by rain, together with indigenous biodegradation, played an important role in the natural attenuation of the petroleum hydrocarbons via mixing/dilution and biodegradation. The water level fluctuations redistributed the hydrocarbon contaminants by partitioning them into the soil and groundwater. The identified factors are not independent but closely inter-correlated.

Improved Piezometer Construction and Sampling Techniques to Determine Pore Water Chemistry in Aquitards

AbstractDue to extremely slow water recovery rates in aquitards and high contamination potential from sealing materials, installation of piezometers in aquitards for geochemical studies requires specialized construction and careful sampling techniques. Few methods have been demonstrated for obtaining representative ground water samples for geochemical parameters from piezometers in aquitards. Here we implement and evaluate an aquitard piezometer installation and ground water chemistry sampling strategy and show that the use of an inert gas pocket in piezometer construction can be used to delay seal contamination for at least three years and avoid oxygenation and disturbance of downhole redox conditions. Major ion analyses did not change appreciably through the standing water columns in the aquitard piezometers over time; however, reliable measurements of typically unstable geochemical parameters (dissolved oxygen, pH, and oxidation‐reduction potential) were best obtained using downhole, in situ instrumentation, provided there was at least 2 to 10 m of standing water in the piezometer.

Locating groundwater discharge in large lakes using bottom sediment electrical conductivity mapping

Groundwater‐surface water studies that use conventional near‐shore piezometers and /or seepage meters are impractical in larger, areal extensive lakes, as they require exorbitant numbers of instruments to quantify groundwater discharge zones. In smaller lakes an electrical conductivity mapping method has proven useful in mapping groundwater discharge zones. The technique identifies groundwater discharge by measuring variations in sediment pore water electrical conductivity and reduces the number of instruments necessary to quantify inflow, thereby lowering instrumentation costs and increasing a study's efficiency. This study sought to determine the technique's applicability in larger lakes. Thus the method was tested within the Hamilton Harbour, at the western end of Lake Ontario. This study found systematic variations between nearshore and offshore sediments and identified three anomalous zones that were thought to represent groundwater inflow. Onshore and offshore piezometers were used to verify the presence of upward gradients and elevated electrical conductivities. The sediment probe survey provided qualitative maps of areas of elevated electrical conductivity indicative of groundwater discharge and allowed a fairly extensive shoreline to be mapped quickly and economically. Survey results guided the installation of nearshore piezometers to discharge zones, eliminating the inefficiency of more conventional “hit or miss” point source installation approaches. This research demonstrated that the sediment probe was a valuable tool for studying groundwater inputs into large lakes.

Grouted-in installation of piezometers in boreholes: G. T. McKenna, Canadian Geotechnical Journal, 32(2), 1995, pp 355–363

Grouted-in installation of piezometers in boreholes: G. T. McKenna, Canadian Geotechnical Journal, 32(2), 1995, pp 355–363

Grouted-in installation of piezometers in boreholes

Because a modern diaphragm-type piezometer tip only requires a small change in fluid volume for pressure equalization, the conventional, large sand intake zone around the piezometer tip can be omitted, and the tip can be grouted in a borehole with cement–bentonite grout. This grouted-in installation method allows simpler and easier installation, accurate readings, fast response to changing formation pore-water pressures, installation in boreholes shared with other geotechnical instruments, and can save 10–75% on the installation cost of a piezometer. The grouted-in installation method can be used for most soil conditions provided that the grout is less permeable than the formation. A theoretical basis for the grouted-in installation method is presented with supporting laboratory and field data from the Syncrude Canada Ltd. oil sands mine. Key words : piezometer, grout, instrumentation, hydraulic conductivity, hydrodynamic time lag, oil sands.

Distribution, origin, and hydraulic influence of fractures in a clay-rich glacial deposit

In the unconsolidated clay-rich glacial deposits underlying a site in southwestern Ontario, fractures and root casts greatly influence hydraulic conductivity and groundwater flow. The fractures are predominantly vertical and have visible oxidation staining from surface to a depth of 6 m. Root casts commonly occur along fracture surfaces in the upper 3 m, but can also occur as holes in apparently unfractured blocks. The fractures are believed caused mainly by dessication during past periods of low water table. This hypothesis is supported by a decrease in fracture density with depth and the presence of a stiff crust, presumably caused by desiccation-induced consolidation. The random pebble fabric and faint layering indicate deposition in a calm lacustrine environment, which precludes the possibility of the fractures having been caused by overriding ice. Fractures were found below the depth of oxidation staining (6 m) but most of these appear to have been caused by stress-relief due to the excavation and subsequent drying. In the upper 3 m the fractures and root casts are responsible for field-measured hydraulic conductivity values that are up to 3 orders of magnitude greater than measured in the laboratory for samples of the unfractured matrix. High values of field-measured hydraulic conductivity, seasonal head variations greater than 0.5 m, and high tritium content all persist below the depth of root casts, indicating that hydraulically conductive fractures do exist to depths of at least 6 m and possibly as great as 12–15 m, which is well below the depth of oxidation staining. However, there is some uncertainty in this assessment of the extent of hydraulically conductive fractures because of the sensitivity to small leaks in the piezometer installations. Key words : clay, glacial, fractures, desiccation, hydraulic conductivity.

Groundwater sampling methodology for mineral exploration in glaciated terrain using reverse circulation overburden drilling

Abstract A technique to sample groundwaters in the basal sediment aquifers of regions characterized by thick glacial sediments using reverse circulation drilling has been developed together with a methodology for carrying out detailed groundwater hydrogeochemical surveys aimed at discovery of sub-outcropping and deep-seated ore deposits. The method consists essentially of five steps, namely: (1) overburden drilling using a stable tracer dye to monitor the effects of drill water input into the basal aquifer, (2) removal of the tricones from the drill bit to allow emplacement of the piezometer unit and injection of filter sand packs and bentonite seals, (3) development of groundwater in the basal aquifer to remove drill water inputs, (4) emplacement of the piezometer unit and injection of the filter sand pack and bentonite seal, and (5) further development of the piezometer installation followed by sampling of basal aquifer groundwater and measurement of piezometric heads. The piezometer installation and sampling procedures can be performed with a minimal amount of training by geological technicians either employed by mining companies or more generally by overburden drilling management companies as part of their contractual agreement with a mining company.

Investigations of high uplift pressures beneath a concrete dam

Deficiency investigations were undertaken at Hugh Keenleyside Dam, near Castlegar, British Columbia, to identify the nature and sources of foundation defects responsible for high uplift pressures under a section of the concrete dam. Several techniques employed in the investigations proved particularly useful in delineating the defects. These were temperature surveys and chemical analysis of flows from pressure instruments and foundation drains, air-injection tests, foundation coring and installation of additional piezometers. A comprehensive program of pressure response testing of cells, piezometers, and drains was also carried out to establish the interconnections within the rock foundation. Detailed assessments of construction records to assemble relevant geological and foundation conditions, foundation excavation, preparation, and treatment aspects, and particular structural foundations were vital in discerning the cause for the high uplift pressures. Piping of a relatively thin, upstream, impervious till blanket (required for the earthfill dam) on blast-induced, highly fractured rock extending under the structure was found to be the defect responsible for reservoir leakage and high uplift pressures. Key words : uplift pressures, concrete dam, foundation drains, piezometers, uplift cells, temperature survey.

Effect of purging on hydraulic conductivity measured in piezometers installed in an aquitard

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...

Effects of installation of piezometers and wells on groundwater characteristics and measurements : Chapuis, R P; Sabourin, L Can Geotech JV26, N4, Nov 1989, P604–613

Effects of installation of piezometers and wells on groundwater characteristics and measurements : Chapuis, R P; Sabourin, L Can Geotech JV26, N4, Nov 1989, P604–613

Reconnaissance geophysical methods in landslide investigations

Landslides are a natural hazard in many countries and often affect civil engineering structures and projects. Three aspects in particular require examination in a geotechnical appraisal of a landslide's stability in engineering terms: (1) the definition of its three-dimensional shape with particular reference to shear surfaces and failure planes; (2) the definition of the hydrogeological regime with regard to water input to the landslide and its distribution within the slip mass; (3) the detection of movement by or within the slip mass and the characterisation of such movements. The site investigation costs may be very high since landslides may be extremely large, structurally complex and topographically severe. It is therefore advantageous in suitable circumstances to carry out reconnaissance geophysical surveys to define the structure and to guide optimum siting of boreholes and pits, and ultimately the installation of piezometers, inclinometers etc. Standard surface geophysical techniques including the seismic, electrical resistivity, acoustic emission and borehole methods have all been applied with varying success to look at a landslide before a major site investigation commences. In recent years electromagnetic methods have been the subject of considerable research in this field and significant advances have been made. In this paper, the application of the above geophysical methods at the reconnaissance stage in a landslide investigation has been reviewed and illustrated with several case histories taken from different geological settings.