scholarly journals Vertical hydraulic conductivity of a clayey-silt aquitard: accelerated fluid flow in a centrifuge permeameter compared with in situ conditions

2014 ◽  
Vol 11 (3) ◽  
pp. 3155-3212 ◽  
Author(s):  
W. A. Timms ◽  
R. Crane ◽  
D. J. Anderson ◽  
S. Bouzalakos ◽  
M. Whelan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Centrifugal Force ◽  
Stress Conditions ◽  
K Value ◽  
Geotechnical Centrifuge ◽  
In Situ Conditions ◽  
Clayey Silt ◽  
Vertical Hydraulic Conductivity ◽  
Permeameter Tests

Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, extraction of fuels from strata such as coal beds, and confinement of waste within the earth. Characterizing low or negligible flow rates and transport of solutes can require impractically long periods of field or laboratory testing, but is necessary for evaluations over regional areas and over multi-decadal timescales. The current work reports a custom designed centrifuge permeameter (CP) system, which can provide relatively rapid and reliable hydraulic conductivity (K) measurement compared to column permeameter tests at standard gravity (1g). Linear fluid velocity through a low K porous sample is linearly related to g-level during a CP flight unless consolidation or geochemical reactions occur. The CP module is designed to fit within a standard 2 m diameter, geotechnical centrifuge with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length. At maximum RPM the resultant centrifugal force is equivalent to 550g at base of sample or a total stress of ~2 MPa. K is calculated by measuring influent and effluent volumes. A custom designed mounting system allows minimal disturbance of drill core samples and a centrifugal force that represents realistic in situ stress conditions is applied. Formation fluids were used as influent to limit any shrink-swell phenomena which may alter the resultant K value. Vertical hydraulic conductivity (Kv) results from CP testing of core from the sites in the same clayey silt formation varied (10−7 to 10−9 m s−1, n = 14) but higher than 1g column permeameter tests of adjacent core using deionized water (10−9 to 10−11 m s−1, n = 7). Results at one site were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses within a 30 m clayey sequence in a homogenous area of the formation. Kv sensitivity to sample heterogeneity was observed, and anomalous flow via preferential pathways could be readily identified. Results demonstrate the utility of centrifuge testing for measuring minimum K values that can contribute to assessments of geological formations at large scale. The importance of using realistic stress conditions and influent geochemistry during hydraulic testing is also demonstrated.

scholarly journals Accelerated gravity testing of aquitard core permeability and implications at formation and regional scale

2015 ◽  
Vol 12 (3) ◽  
pp. 2799-2841
Author(s):  
W. A. Timms ◽  
R. Crane ◽  
D. J. Anderson ◽  
S. Bouzalakos ◽  
M. Whelan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Preferential Flow ◽  
Fluid Velocity ◽  
Regional Scale ◽  
Geotechnical Centrifuge ◽  
Regional Flow ◽  
Clayey Silt ◽  
Vertical Hydraulic Conductivity ◽  
Core Permeability

Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, the extraction of fuels from strata such as coal beds, and the confinement of waste within the earth. The current work demonstrates that relatively rapid and reliable hydraulic conductivity (K) measurement of aquitard cores using accelerated gravity can inform and constrain larger scale assessments of hydraulic connectivity. Steady state fluid velocity through a low K porous sample is linearly related to accelerated gravity (g-level) in a centrifuge permeameter (CP) unless consolidation or geochemical reactions occur. The CP module was custom designed to fit a standard 2 m diameter geotechnical centrifuge (550 g maximum) with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length, and a maximum total stress of ~2 MPa at the base of the core. Formation fluids were used as influent to limit any shrink–swell phenomena which may alter the permeability. Vertical hydraulic conductivity (Kv) results from CP testing of cores from three sites within the same regional clayey silt formation varied (10−7 to 10−9 m s−1, n = 14). Results at one of these sites (1.1 × 10−10 to 3.5 × 10−9 m s−1, n = 5) that were obtained in < 24 h were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses over several weeks within a 30 m clayey sequence. Core scale and in situ Kv results were compared with vertical connectivity within a regional flow model, and considered in the context of heterogeneity and preferential flow paths at site and formation scale. More reliable assessments of leakage and solute transport though aquitards over multi-decadal timescales can be achieved by accelerated core testing together with advanced geostatistical and numerical methods.

scholarly journals Accelerated gravity testing of aquitard core permeability and implications at formation and regional scale

2016 ◽  
Vol 20 (1) ◽  
pp. 39-54 ◽  
Author(s):  
W. A. Timms ◽  
R. Crane ◽  
D. J. Anderson ◽  
S. Bouzalakos ◽  
M. Whelan ◽  
...  
Keyword(s):  
Preferential Flow ◽  
Fluid Velocity ◽  
Regional Scale ◽  
Geotechnical Centrifuge ◽  
Clayey Silt ◽  
Vertical Hydraulic Conductivity ◽  
Geochemical Reactions ◽  
Set Up ◽  
Core Permeability

Abstract. Evaluating the possibility of leakage through low-permeability geological strata is critically important for sustainable water supplies, the extraction of fuels from coal and other strata, and the confinement of waste within the earth. The current work demonstrates that relatively rapid and realistic vertical hydraulic conductivity (Kv) measurements of aquitard cores using accelerated gravity can constrain and compliment larger-scale assessments of hydraulic connectivity. Steady-state fluid velocity through a low-K porous sample is linearly related to accelerated gravity (g level) in a centrifuge permeameter (CP) unless consolidation or geochemical reactions occur. A CP module was custom designed to fit a standard 2 m diameter geotechnical centrifuge (550 g maximum) with a capacity for sample dimensions up to 100 mm diameter and 200 mm length, and a total stress of  ∼  2 MPa at the base of the core. Formation fluids were used as influent to limit any shrink–swell phenomena, which may alter the permeability. Kv results from CP testing of minimally disturbed cores from three sites within a clayey-silt formation varied from 10−10 to 10−7  m s−1 (number of samples, n = 18). Additional tests were focussed on the Cattle Lane (CL) site, where Kv within the 99 % confidence interval (n = 9) was 1.1 × 10−9 to 2.0 × 10−9 m s−1. These Kv results were very similar to an independent in situ Kv method based on pore pressure propagation though the sequence. However, there was less certainty at two other core sites due to limited and variable Kv data. Blind standard 1 g column tests underestimated Kv compared to CP and in situ Kv data, possibly due to deionised water interactions with clay, and were more time-consuming than CP tests. Our Kv results were compared with the set-up of a flow model for the region, and considered in the context of heterogeneity and preferential flow paths at site and formation scale. Reasonable assessments of leakage and solute transport through aquitards over multi-decadal timescales can be achieved by accelerated core testing together with complimentary hydrogeological monitoring, analysis, and modelling.

The heterogeneity of 3-D vertical hydraulic conductivity in a streambed

2015 ◽  
Vol 47 (1) ◽  
pp. 15-26 ◽  
Author(s):  
Guangdong Wu ◽  
Longcang Shu ◽  
Chengpeng Lu ◽  
Xunhong Chen
Keyword(s):  
Hydraulic Conductivity ◽  
Three Dimensional ◽  
Deposition Process ◽  
Near Surface ◽  
River Bank ◽  
Vertical Hydraulic Conductivity ◽  
Different Populations ◽  
Permeameter Tests ◽  
D Model

The heterogeneity of vertical hydraulic conductivity (Kv) is a key attribute of streambed for researchers investigating surface water–groundwater interaction. However, few three-dimensional (3-D) Kv models with high spatial resolutions have been achieved. In this study, in-situ permeameter tests were conducted to obtain Kv values. A 3-D model with 443 Kv values was built comprising 10 lines, 10 rows, and five layers. Statistical analysis was done to reveal the spatial characteristics of Kv. The influence of bedform on Kv values was restricted to the near-surface streambed. Kv increased with the increasing distance from the south river bank for the upmost layer, but it was not the case for other layers and the combined Kv values of five layers; the spatial pattern at transects across the channel did not differ significantly. The Kv values of each layer pertained to different populations; the sediments of individual layers were formed under different sedimentation environments. The coupling of erosion/deposition process and transport of fine materials primarily contributed to a reduction of the mean and median of Kv values and an increase of heterogeneity of Kv values with depth. Thus, a collection of Kv values obtained from different layers should be considered when characterizing the heterogeneity of streambed.

Effect of temperature on streambed vertical hydraulic conductivity

2013 ◽  
Vol 45 (1) ◽  
pp. 89-98 ◽  
Author(s):  
Weihong Dong ◽  
Gengxin Ou ◽  
Xunhong Chen ◽  
Zhaowei Wang
Keyword(s):  
Hydraulic Conductivity ◽  
Water Temperature ◽  
Sediment Cores ◽  
Effect Of Temperature ◽  
In Situ Tests ◽  
Effect Of Water ◽  
Vertical Hydraulic Conductivity ◽  
Increasing Trend ◽  
Streambed Vertical Hydraulic Conductivity

In this study, in situ and on-site permeameter tests were conducted in Clear Creek, Nebraska, USA to evaluate the effect of water temperature on streambed vertical hydraulic conductivity Kv. Fifty-two sediment cores were tested. Five of them were transferred to the laboratory for a series of experiments to evaluate the effect of water temperature on Kv. Compared with in situ tests, 42 out of the 52 tests have higher Kv values for on-site tests. The distribution of water temperature at the approximately 50 cm depth of streambed along the sand bar was investigated in the field. These temperatures had values in the range 14–19 °C with an average of 16 °C and had an increasing trend along the stream flow. On average, Kv values of the streambed sediments in the laboratory tests increase by 1.8% per 1 °C increase in water temperature. The coarser sandy sediments show a greater increase extent of the Kv value per 1 °C increase in water temperature. However, there is no distinct increasing trend of Kv value for sediment containing silt and clay layers.

Measuring in situ vertical hydraulic conductivity in tidal environments

2014 ◽  
Vol 70 ◽  
pp. 118-130 ◽  
Author(s):  
Xuejing Wang ◽  
Hailong Li ◽  
Jinzhi Yang ◽  
Li Wan ◽  
Xusheng Wang ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Vertical Hydraulic Conductivity

Methods of interpretation of borehole falling-head tests performed in compacted clay liners

2005 ◽  
Vol 42 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Paul Chiasson
Keyword(s):  
Hydraulic Conductivity ◽  
Time Lag ◽  
Past Research ◽  
Quality Assurance Program ◽  
Data Sets ◽  
Compacted Clay ◽  
Clay Liners ◽  
K Value ◽  
Considerable Uncertainty ◽  
Vertical Hydraulic Conductivity

The interpretation of falling-head tests in cased boreholes is discussed. These tests are commonly used to measure hydraulic conductivity of compacted clay liners and are often part of the construction quality assurance program. Three methods of interpretation are reviewed with data sets collected from real tests. Two of these methods have been the subject of past research by other authors: the Hvorslev, or time-lag, method and the velocity method. After the limitations of these two approaches have been underlined, a third method is proposed. It uses a best linear unbiased estimator to fit the theoretical head difference function in a plot of falling water column elevation as a function of time (Z–t method). The Hvorslev method is found unreliable and is not recommended. The velocity method is theoretically sound, but statistical uncertainty can become high when this method is used in testing materials with low hydraulic conductivity, such as clay liners. Materials with low hydraulic conductivity tend to produce scattered velocity plots, creating considerable uncertainty for the estimated k value. The proposed Z–t method is less sensitive to inaccuracies in measurements, yielding a more reproducible result. An interpretation method for stages I and II of two-stage borehole tests is also proposed. This method yields the anisotropy of the liner and the vertical hydraulic conductivity. As a result of inaccuracies in measurements and limited difference between the geometries of stages I and II, the computed anisotropy exhibits significant uncertainty.Key words: clay liners, clay covers, hydraulic conductivity, permeability, in situ test, anisotropy, interpretation.

scholarly journals CONDUCTIVITY TESTING AND EVALUATION / PAVIRŠINIŲ NUOTEKŲ FILTRO HIDRAULINIO LAIDUMO TYRIMAI IR VERTINIMAS

2015 ◽  
Vol 7 (4) ◽  
pp. 436-442
Author(s):  
Lygita Makaravičiūtė ◽  
Eglė Marčiulaitienė
Keyword(s):  
Hydraulic Conductivity ◽  
Poa Pratensis ◽  
Silica Sand ◽  
Sand Filter ◽  
Autoclaved Aerated Concrete ◽  
In Situ Conditions ◽  
Aerated Concrete ◽  
Constant Head ◽  
Hydrus 1D

Surface wastewater is consideredas effluents, which are formed on the surface of urbanized areas. Stormwater treatment is performed out using a variety of filters: sand, grass. Wastewater penetration into the deeper layers is called hydraulic conductivity. After evaluation of the hydraulic conductivity, it is possible to determine the ability of the investigated fillers to entrap the stormwater flow. The hydraulic conductivity tests can indicate which fillers of stormwater filters may influence the more effective stormwater cleaning. Four stormwater filters were tested: crushed autoclaved aerated concrete filter; crushed autoclaved aerated concrete with Meadow grass (Poa pratensis) layer; silica sand filter with Meadow grass (Poa pratensis) layer; silica sand filter. Under in-situ conditions hydraulic conductivity in filters is investigated using Constant-head method. Mathematical modeling program Hydrus-1D presentsthe changes of hydraulic conductivity in each filler layer of the filter. Assessed hydraulic conductivity in filters under in-situ conditions hasn‘t changed only in crushed autoclaved aerated concrete filter (30 000 mm/d). The smallest hydraulic conductivity in filters under in-situ conditions was estimated in silica sand filter with Meadow grass (Poa pratensis) layer, here it was equal to 209.3 mm/d.With mathematical modeling program Hydrus-1D it was found that the hydraulic conductivity in each filter decreases, depending on the depth of filler in the filter. Paviršinėmis nuotekomis laikomos tokios, kurios susidaro ant urbanizuotos teritorijos paviršiaus. Paviršinių nuotekų valymas atliekamas taikant įvairius filtrus – smėlio, augalinius. Nuotekų skverbimasis į gilesnius sluoksnius vadinamas hidrauliniu laidumu. Įvertinus hidraulinį laidumą galima nustatyti tiriamų filtro užpildų gebėjimą sulaikyti atitekėjusių paviršinių nuotekų srautą filtro užpilduose. Atlikus hidraulinio laidumo tyrimus, galima nustatyti, kurie paviršinių nuotekų filtro užpildai gali lemti efektyvesnį paviršinių nuotekų išvalymą. Tiriami keturi paviršinių nuotekų filtrai: smulkinto autoklavinio akytojo betono filtras; smulkinto autoklavinio akytojo betono ir pievinės miglės dangos filtras; kvarcinio smėlio filtras su pievinės miglės danga; kvarcinio smėlio filtras. Natūrinėmis sąlygomis hidraulinio laidumo tyrimas atliekamas, taikant Constant-Head metodą. Matematinio modeliavimo programa Hydrus-1D pateikiama, kaip kinta hidraulinis laidumas kiekviename filtro užpildo sluoksnyje. Nustatytas hidraulinis laidumas filtruose natūrinėmis sąlygomis nekito smulkinto autoklavinio akytojo betono filtre (30 000 mm/d). Mažiausias hidraulinis laidumas natūrinėmis sąlygomis nustatytas kvarcinio smėlio filtre su pievinės miglės (Poa pratensis) augalinės dangos sluoksniu, čia jis nustatytas 209,3 mm/d. Matematinio modeliavimo programa Hydrus-1D nustatyta, kad hidraulinis laidumas filtruose mažėja priklausomai nuo filtro užpildo gylio.

Hydraulic conductivity and diffusion monitoring of the Keele Valley Landfill liner, Maple, Ontario

1993 ◽  
Vol 30 (1) ◽  
pp. 124-134 ◽  
Author(s):  
K. S. King ◽  
R. M. Quigley ◽  
F. Fernandez ◽  
D. W. Reades ◽  
A. Bacopoulos
Keyword(s):  
Hydraulic Conductivity ◽  
Major Ions ◽  
Geometric Mean ◽  
Actual Performance ◽  
Landfill Liner ◽  
Monitoring Programs ◽  
Field Diffusion ◽  
Clayey Silt ◽  
Sand And Gravel

The 99-ha Keele Valley Landfill is located in a former sand and gravel pit at Maple, Ontario. The base and sides of the pit are lined with a minimum of 1.2 m of excavated clayey silt till recompacted to achieve a design hydraulic conductivity of 1 × 10−8 cm/s or less. Extensive construction controls and monitoring programs have been implemented to determine the hydraulic conductivity and advective performance of the liner. A total of 267 postcompaction laboratory hydraulic conductivity (k) tests indicated that the first two stages of the liner had a geometric mean k of 7.7 × 10−9 cm/s. Calculations of in situ hydraulic conductivity based on lysimeter effluent collection rates show decreases in k to field values close to the laboratory values. In situ electrical conductivity sensors and lysimeter effluent chemistry measurements have monitored the advance of leachate-derived chemicals into the liner. Concurrent field verification by liner exhumation and chemical analysis has confirmed the importance of diffusion as the dominant migration mechanism through this low-k liner. Similar concentration trends for major ions have been observed in the field lysimeter effluents, effluents from laboratory liner–leachate compatibility tests, and pore water extracted from core samples of sections of exhumed liner exposed to leachate. The multicomponent field and laboratory testing and monitoring programs have shown good cross-agreement, and the actual performance of the liner has been close to preconstruction predictions. Key words : landfill, clayey liner, field hydraulic conductivity, field diffusion, municipal solid waste leachate, field lysimeter test, laboratory hydraulic conductivity, liner–leachate compatibility.

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