Environmental Hazards of an Unrecultivated Liquid Waste Disposal Site on Soil and Groundwater

Disposal sites without adequate engineering controls pose a significant risk to the environment. In the present study, the environmental hazards of an abandoned and unrecultivated liquid waste disposal are investigated with a special focus on soil and shallow groundwater contamination. After a period of operation from 1994 to 2010, when the wastewater collection of the municipality was regulated, the disposal site was subsequently decommissioned without further action. Eight monitoring wells have been established in the disposal basins and in the surrounding area to determine the contamination of the site. Sampling took place in the summers of 2020 and 2021. The results of the analysis of the soil and water samples collected showed a high level of contamination in the area. In the borehole profile of the infiltration basin, a well-developed leachate nitrate profile was observed, with a concentration above 3000 mg/kg NO3−. The soil phosphate content was also significant, with a value of over 1900 mg/kg in the upper 40 cm layer. Extremely high concentrations of ammonium (>45 mg/L) and organic matter (>90 mg/L) were detected in the groundwater of the basins, indicating that contaminated soil remains a major source of pollutants more than 10 years after closure. For all micro- and macroelements present in detectable concentrations, a significant increase was observed in the infiltration basin. Our results have revealed that the surroundings are also heavily contaminated. NO3− concentrations above the contamination limit were measured outside the basins. Recultivation of liquid waste disposal sites of similar characteristics is therefore strongly recommended.

Using Heat as a Tracer to Detect the Development of the Recharge Bulb in Managed Aquifer Recharge Schemes

Managed Aquifer Recharge (MAR), the intentional recharge of aquifers, has surged worldwide in the last 60 years as one of the options to preserve and increase water resources availability. However, estimating the extent of the area impacted by the recharge operations is not an obvious task. In this descriptive study, we monitored the spatiotemporal variation of the groundwater temperature in a phreatic aquifer before and during MAR operations, for 15 days, at the LIFE REWAT pilot infiltration basin using surface water as recharge source. The study was carried out in the winter season, taking advantage of the existing marked difference in temperature between the surface water (cold, between 8 and 13 °C, and in quasi-equilibrium with the air temperature) and the groundwater temperature, ranging between 10 and 18 °C. This difference in heat carried by groundwater was then used as a tracer. Results show that in the experiment the cold infiltrated surface water moved through the aquifer, allowing us to identify the development and extension in two dimensions of the recharge plume resulting from the MAR infiltration basin operations. Forced convection is the dominant heat transport mechanism. Further data, to be gathered at high frequency, and modeling analyses using the heat distribution at different depths are needed to identify the evolution of the recharge bulb in the three-dimensional space.

Water Distribution from Artificial Recharge via Infiltration Basin under Constant Head Conditions

The vadose zone plays a significant role during artificial recharge via the infiltration basin. Its thickness, lithology, heterogeneity, among others greatly affect the recharge efficiency. The main objective of this research is to establish the role of the vadose zone and the impacts of infiltration basin features and vadose zone factors on water distributions. In this work, an ideal conceptual model was considered, and mathematical models were built using HYDRUS (2D/3D) software package version 2.05. A total of 138 numerical experiments were implemented under seven types of experimental conditions. The experimental data were analyzed with the aid of correlation and regression analysis. The results showed that infiltration basin features and vadose zone factors had various impacts on water distribution, low permeability formation had various effects on evaporation depending on its depth, and there were consistent, similar, or different variation trends between infiltration and recharge. In conclusion, it is recommended that when the vadose zones are to be chosen as an infiltration basin site, the trade-off among the infiltration, recharge, storage, and evaporation should be seriously considered. This paper may contribute to a better understanding of the vadose zone as a buffer zone for artificial recharge.

Characterization of earthworms in an infiltration basin for maintaining water infiltration

<p>Infiltration basins are among the most spread techniques for managing stormwater. Infiltration basins allow the infiltration of stormwater, which prevents their piping towards treatment systems. However, stormwater contains loads of pollutants and suspended solids that accumulate at the surface of the basin and form a sedimentary layer. That sedimentary lay may clog the infiltration basin partially, thus reducing its bulk infiltration capability. Fortunately, plants and fauna colonize spontaneously this sedimentary layer, thus preventing complete clogging and restoring soils' infiltration functions. The knowledge of the effect on restoring the infiltration function requires properly characterize fauna, notably earthworms, with the aim to predict their impact on infiltration. Besides, earthworms, considered as ecosystem engineers, are known to be good candidates for integrating soil chemical pollution.</p><p>If earthworms have been intensively studied in natural and agricultural soil, very few studies have focused on the characterization of earthworms' communities in urban soils and, in particular, in infiltration basins. This study presents the description of earthworms sampled at several places over one infiltration basins. This basin receives the stormwater collected over an industrial peri-urban catchment. The infiltration basin has been functioning for more than two decades, thus, plants and fauna have colonized the surface related to water ponding at surface and water infiltration. The sampled places were selected to follow three specific water pathways at the surface. High population variability was measured with densities ranging from 0 to 300 earthworms per square meter with the presence of adults but also juveniles. But, only endogenic and epigeic functional groups were found. The characterization of abundance, age, and species over the sampled places was correlated to water content and sediment thickness, in addition to pollutant loads.</p><p>The results show that earthworms require given edaphic conditions (including thick enough sedimentary layer) to settle. We then expect most earthworms to colonize those specific places, increasing water infiltration punctually at these places. Put all together, our findings participate in the understanding of colonization of basin infiltration by organisms and their contribution to their primary function: infiltrating water.</p>

Water quality changes during the first meter of managed aquifer recharge

The direct sampling method revealed the high treatment capacity of the unsaturated zone and the significant impact of infiltration basin management on microbial communities in managed aquifer recharge (MAR).

Clogging of Infiltration Basin and Its Impact on Suspended Particles Transport in Unconfined Sand Aquifer: Insights from a Laboratory Study

A laboratory study was undertaken to investigate the physical clogging of a sand medium by injecting suspended particles (SP), with diameters ranging from 0.03 to 63.41 μm, into an infiltration basin, which was installed in a sand tank under the condition of constant head. The hydraulic conductivity (K) of the saturated porous medium was found to have decreased by 27% because of re-arrangement over the seven days of self-filtration. A clogging layer was observed on the infiltration basin bottom, probably due to straining over the stormwater infiltration stage. Particle-size analyses also indicate that retention of bigger SP led to faster straining of smaller SP, despite the small fraction of bigger SP. The clogging layer weakened the hydraulic connection between the water level in the basin and the water table of the unconfined aquifer until nearly no water could infiltrate into the aquifer. The deposition of finer SP that entered into the aquifer are governed by the hydrodynamic forces. These finer SP caused non-uniform permeability reduction of the porous medium, with an estimated 35% of permeability reduction occurring beneath the infiltration basin. However, the reduction appears to be reversible, as the fine SP deposited on the pore surfaces of the porous medium can be released or detached by the continuous horizontal hydraulic gradient. Extended tailing of the outlet breakthrough curve (BTC) also strongly supported the detachment of SP. This study focused on the effects of particles’ polydispersity and hydrodynamic forces on the hydraulic characteristics of the porous medium.

Estimation of saturated hydraulic conductivity from ring infiltrometer test taking into account the surface moisture stain extension

A large single-ring infiltrometer test was performed in order to characterize the saturated hydraulic conductivity below an infiltration basin in the well field of Lyon (France). Two kinds of data are recorded during the experiment: the volume of water infiltrated over time and the extension of the moisture stain around the ring. Then numerical analysis was performed to determine the saturated hydraulic conductivity of the soil by calibration.Considering an isotropic hydraulic conductivity, the saturated hydraulic conductivity of the alluvial deposits is estimated at 3.8 10−6m s−1. However, with this assumption, we are not able to represent accurately the extension of the moisture stain around the ring. When anisotropy of hydraulic conductivity is introduced, experimental data and simulation results are in good agreement, both for the volume of water infiltrated over time and the extension of the moisture stain. The vertical saturated hydraulic conductivity in the anisotropic configuration is 4.75 times smaller than in the isotropic configuration (8.0 10−7m s−1), and the horizontal saturated hydraulic conductivity is 125 times higher than the vertical saturated hydraulic conductivity (1.0 10−4m s−1).