Tracer movements in a straight uniform flow: New equations for the advective part considering the distortion of flow lines around the well.

Methods for interpreting tracer tests often rely on equations assuming a natural regional flow which is straight and uniform. The main purpose of this project was to develop more realistic equations for the advective part of contaminant transport, by including the flow lines distortion occurring in the vicinity of the injection well. The complex potential of the flow during a tracer test was calculated by superimposing the complex potential of a natural, straight and uniform flow distorted by the presence of a passive well, and the complex potential of a radial flow corresponding to an isotropic injection alone. The equations were developed for a horizontal plan and the calculated complex potential yielded a groundwater velocity field, and after that a formula connecting the position of the advancing front of the tracer plume to the injection duration. These new equations were then tested with numerical simulations. A two-dimensional aquifer plan was modeled and set in order to numerically solve particle tracking and travel time computation of the moving front within a reasonable calculation time. This model provided a comparison of times needed to fully recover the tracer plume previously injected, the one calculated with the new equations and the one calculated with former equations neglecting the impact of the well presence on the groundwater flow field. The results showed that the new equations are significantly more precise, in particular when the injection rate is sufficiently low compared to the natural regional flow rate, with a relatively large well diameter and in the vicinity of the injection well. Three different plume shapes could be visualized numerically, and those shapes depend on the value of a parameter △ which compares the velocity component caused by the injection in the well and the component caused by the natural regional flow.

Lung bioaccessibility of As, Cu, Fe, Mn, Ni, Pb, and Zn in fine fraction (<20µm) from contaminated soils and mine tailings.

The present study aims (1) to characterize contaminated soils (n=6) and mine tailings samples (n=3) for As, Cu, Fe, Mn, Ni, Pb, and Zn content; and (2) to assess elemental lung bioaccessibility in fine fraction (d<20µm which might contribute to airborne particulate matter (PM) and thus be inhaled) by means of in vitro tests using Gamble's solution (GS) and an artificial lysosomal fluid (ALF). Elemental concentrations were high in the majority of samples, particularly for As (up to 2040mg·kg-1), Fe (up to 30.7%), Mn (up to 4360mg·kg-1), and Zn (up to 4060mg·kg-1); and elemental concentrations (As, Cu, and Ni) in the sieved fraction (d<20µm) obtained from contaminated soils were significantly higher than in the bulk fraction (<160µm). In vitro tests with ALF yielded much higher bioaccessibility than tests with GS, and the use of ALF in addition to GS is recommended to assess lung bioaccessibility. Bioaccessibility in ALF was high for all elements after 2weeks of testing both in terms of concentration (e.g. up to 1730mg·kg-1 for As) and percentages (e.g. up to 81% for Pb). The elemental solubilization rate generally declined rapidly and continuously with time. Similarly, bioaccessibility increased rapidly and tended to reach a plateau with time for most samples and metals. However, it is not possible to recommend a general testing duration as the solubilization behavior was highly element and sample-specific.

Lung bioaccessibility of contaminants in particulate matter of geological origin.

Human exposure to particulate matter (PM) has been associated with adverse health effects. While inhalation exposure to airborne PM is a prominent research subject, exposure to PM of geological origin (i.e., generated from soil/soil-like material) has received less attention. This review discusses the contaminants in PM of geological origin and their relevance for human exposure and then evaluates lung bioaccessibility assessment methods and their use. PM of geological origin can contain toxic elements as well as organic contaminants. Observed/predicted PM lung clearance times are long, which may lead to prolonged contact with lung environment. Thus, certain exposure scenarios warrant the use of in vitro bioaccessibility testing to predict lung bioavailability. Limited research is available on lung bioaccessibility test development and test application to PM of geological origin. For in vitro tests, test parameter variation between different studies and concerns about physiological relevance indicate a crucial need for test method standardization and comparison with relevant animal data. Research is recommended on (1) developing robust in vitro lung bioaccessibility methods, (2) assessing bioaccessibility of various contaminants (especially polycyclic aromatic hydrocarbons (PAHs)) in PM of diverse origin (surface soils, mine tailings, etc.), and (3) risk characterization to determine relative importance of exposure to PM of geological origin.

Interpreting a pumping test influenced by another well in an anisotropic aquifer.

In confined aquifers the influence of neighboring active wells is often neglected when interpreting a pumping test. This can, however, lead to an erroneous interpretation of the pumping test data. This article presents simple methods to evaluate the transmissivity tensor and storativity of an anisotropic confined aquifer when there is an interfering well in the neighborhood of the tested well. Two methods have been developed depending on whether the tested well or the interfering well is the first in operation. These new methods yield better estimates of the hydraulic parameters than when the influence of the interfering well is neglected. These methods have then been used on data obtained from numerical models with an interfering well and the results have been compared to an analytical method that neglects the influence of the interfering well. The methods require knowledge of the pumping rate of the interfering well and the time elapsed since the pumping started in each well. If the interfering well started pumping before the tested well, the method does not require knowledge of the aquifer piezometric level at the beginning of the test, which is often unknown in this case. As for the method without interference, at least three monitoring wells (MWs) are needed, the position of which influences the accuracy of the estimated parameters. Some recommendations concerning MWs position have been given to get more accurate results according to the sought parameter.

A leaky aquifer below Champlain Sea clay: closed-form solutions for natural seepage.

Closed-form solutions are proposed for natural seepage in semiconfined (leaky) aquifers such as those existing below the massive Champlain Sea clay layers in the Saint-Lawrence River Valley. The solutions are for an ideal horizontal leaky aquifer below an ideal aquitard that may have either a constant thickness and a constant hydraulic head at its surface, or a variable thickness and a variable hydraulic head at its surface. A few simplifying assumptions were needed to obtain the closed-form solutions. These have been verified using a finite element method, which did not make any of the assumptions but gave an excellent agreement for hydraulic heads and groundwater velocities. For example, the difference between the two solutions was smaller than 1 mm for variations in the 5 to 8 m range for the hydraulic head in the semiconfined aquifer. Note that fitting the hydraulic head data of monitoring wells to the theoretical solutions gives only the ratio of the aquifer and aquitard hydraulic conductivities, a clear case of multiple solutions for an inverse problem. Consequently, field permeability tests in the aquitard and the aquifer, and pumping tests in the aquifer, are still needed to determine the hydraulic conductivity values.

Interpretation of a pumping test with interference from a neighboring well.

In confined aquifers, the influence of neighboring active wells is often neglected when interpreting a pumping test. This can, however, lead to an erroneous interpretation of the pumping test data. This paper presents simple methods to evaluate the transmissivity (T) and storativity (S) of a confined aquifer under Theis conditions, when an interfering well starts pumping in the neighborhood of the tested well before the beginning of the test. These new methods yield better estimates of the T and especially S values than when the interfering well influence is neglected. They also permit to distinguish between interfering wells and other deviations from the Cooper-Jacob straight line, such as impermeable boundaries. The new methods were then applied on data obtained from a numerical model. The new methods require knowing the pumping rate of the interfering well and the time elapsed since the pumping started in each well, but contrary to previous methods, they do not require the aquifer natural level at the beginning of the test, which is often unknown if the interfering well has started pumping before the tested well.

Seepage face height, water table position, and well efficiency at steady state.

When a fully penetrating well pumps an ideal unconfined aquifer at steady state, the water table usually does not join the water level in the well. There is a seepage face inside the well, which is a key element in evaluating the well performance. This problem is analyzed using the finite-element method, solving the complete equations for saturated and unsaturated flow. The seepage face position is found to be almost independent of the unsaturated zone properties. The numerical results are used to test the validity of several analytic approximations. Equations are proposed to predict the seepage face position at the pumping well for any well drawdown, and the water table position at any distance from the pumping well for any in-well drawdown. Practical hints are provided for installing monitoring wells and evaluating well efficiency.

Travel time to a well pumping an unconfined aquifer without recharge.

A solution is given for the travel time to a well pumping an ideal, horizontal unconfined aquifer, under steady-state conditions, when recharge from infiltration is negligible. Three forms of the solution are provided: a closed-form solution, an integral to be calculated in a worksheet, and a simple equation. The three forms of the solution give travel times nearly identical to those obtained using a finite-element code for saturated and unsaturated flow and particle tracking.

Pumping test in a confined aquifer under tidal influence.

In a coastal environment, tide-induced head fluctuations can complicate the interpretation of drawdown data from pumping tests. For confined aquifers and sinusoidal tides, the superposition principle can be used to obtain a closed-form solution. After subtracting the net tidal effects, the drawdown data become amenable to the standard analyses. Numerical simulations have shown that the method is reliable when the distance of the monitoring well to the well does not exceed 10% of the distance between the well and the tidal boundary.

Phosphorus removal by electric arc furnace steel slag and serpentinite.

Electric arc furnace (EAF) steel slag and serpentinite were tested in columns either alone or mixed with limestone to determine their capacity to remove phosphorus (P) from a solution containing initially 20mg P/L (for 114 days) than 400mg P/L (for 21 days). EAF steel slag was nearly 100% efficient due to specific P adsorption onto metal hydroxides and precipitation of hydroxyapatite. Serpentinite also showed a good performance that decreased with time, adsorption appearing to be the dominant mechanism for P removal. Mixing limestone with these two materials did not improve their performance and in the case of serpentinite, it actually even decreased it. In 114 days of experimentation, serpentinite alone and the mixture of serpentinite and limestone removed 1.0mg P/g while in 180 days of experimentation, EAF steel slag and the mixture of slag and limestone removed an average of 2.2mg P/g, without attaining their maximum P removal potential. The void hydraulic retention time (HRTv) was a key factor for growing hydroxyapatite crystals and had a significant effect on P removal efficiency by EAF steel slag. A temporary increase in HRTv caused by clogging resulted in an increase in EAF steel slag efficiency (from 80% to almost 100%) towards the end of investigation. Results from this study indicate that the use of EAF steel slag in constructed wetlands or filter beds is a promising solution for P removal via adsorption and precipitation mechanisms.

Long-term persistence of a nutrient-starved biofilm in a limestone fracture.

The persistence of biofilms is a key element of the biobarrier concept applied to fractured rock. After a 43-day biostimulation with molasses for the biofilm growth (phase I), the effects of a 179-day starvation on the persistence of the biofilm (phase II) were investigated in a single-fractured limestone apparatus equipped to detect small changes in hydraulic conductivity (K) (cm min(-1)). The K in the central fracture section (Kf) decreased by 4.6 logs between days 0 and 167 and increased by 1.3 logs between days 167 and 222, leading to an overall 3.3-logs reduction for the 222-day experiment. Accumulation of rod- and filamentous-shaped bacteria and deposition of minerals were thought to account for the decrease in Kf. Even though the filamentous bacterial cells possibly enhanced the stability of the developing biofilm, increases in Kf became more frequent after 100 days of operation. This decrease in stability was presumably related to sloughing events, which were in turn attributed to a combination of processes, including nutrient deprivation, the release of deposited minerals, decreasing fluid flowrate, and endogenous decay as part of biofilm ageing. This study indicates that biofilms developed in fractures can persist for extended periods at reduced K when exposed to a long-term starvation.

Phosphorus saturation potential: a parameter for estimating the longevity of constructed wetland systems.

Phosphorus (P) adsorption capacities of materials derived from batch experiments can vary by several orders of magnitude depending on the method used, leading to potential misinterpretation of the P retention capacity on a long-term basis and unrealistic estimations of constructed wetland systems (CWS) longevity. The objective of this study was to determine if the P saturation of the material in a column could be used for this purpose with an improved accuracy. A 278-d column experiment with a synthetic P solution was conducted to investigate the long-term P retention capacity of electric arc furnace (EAF) steel slag up to its P saturation point. EAF slag showed a high affinity for P, reaching a saturation value of 1.35 g of P kg(-1). Investigations of the regeneration of the P adsorbing capacity by this material showed that, after 4 weeks of water desaturated resting, EAF steel slag was able to increase its initial P adsorptive capacity to 2.35 g of P kg(-1). A sequential P fractionation experiment was performed to quantify the proportion of P bound to mineral compounds in EAF. From the most loosely bound to the most strongly bound P fraction, P was associated with resin extractable (14%), Fe extractable (0.5 M Na2CO3, 47%), Al extractable (0.1 M NaOH, 1%), Ca extractable (1 M HCl, 12%), and Ca in a stable residual pool (concentrated hot HCl, 26.5%). X-ray fluorescence analyses of EAF steel slag chemical composition revealed that the continuous application of a P solution resulted in 75% and 59% increases in K2O and P2O5 respectively; Al2O3 and FeO increased by 8%, while the portion of CaO remained unchanged. The investigated properties (P retention potential, regeneration of P adsorption, P fractionation) provide useful data about the suitability of slag material as a media for long-term P removal and should enable an improved prediction of the longevity of full-scale CWS.

Methods to determine storativity of infinite confined aquifers from a recovery test.

Starting from the equations of Theis and Cooper-Jacob, two new mathematical methods are proposed for interpreting the residual drawdown data for an infinite confined aquifer. Under Theis' assumptions and using the Cooper-Jacob approximation, the principal aquifer characteristics of transmissivity, pumping storativity, and recovery storativity are expressed without any correction or additional assumption. An actual case is used for illustration and confirms the validity of proposed equations and methods.