Preliminary Evaluation of the Possible Occurrence of Pesticides in Groundwater Contaminated with Nitrates—A Case Study from Southern Poland

This paper addresses groundwater pollution and the potential presence of pesticides within the catchment areas of two reservoirs that are sources of drinking water. The two reservoirs are Goczałkowice and Kozłowa Góra, both in Southern Poland. Agricultural and rural areas dominate both catchments. Archival data showed local groundwater contamination with nitrates. This indicated the possible presence of pesticides in shallow groundwater. In total, 13 groundwater samples from shallow sandy aquifers were collected. All the samples were tested for the presence of 35 organophosphate pesticides and 28 organochlorine pesticides. Additionally, in order to determine the current groundwater conditions, physicochemical parameters were measured in the field, and water samples were subjected to analysis of their chemical composition (incl. the determination of nitrates). The research outcomes showed that pesticides were not detected above the detection limits in any of the samples. Due to variations in the persistence and degradation rates of pesticides, the occurrence of these substances in the groundwater environment and the possibility of their migration to aquifers should not be completely excluded. Natural processes and factors (e.g., sorption, biodegradation, hydrolysis and redox conditions) may gradually reduce the pesticide concentrations in groundwater. The chemical analyses revealed high concentrations of nitrates in the groundwater. This suggests the possible influence of agriculture and fertilizer application on groundwater quality; however, a proportion of NO3- ions may be connected with improper sewage management within the two catchments. The absence of pesticides in groundwater impacted by agriculture may result from processes occurring in the aquifer and the rapid degradation of these compounds due to photolysis and prevailing weather conditions. In the vicinity of dwellings, nitrates also originate from domestic wastewater. Thus, the occurrence of pesticides in groundwater contaminated with NO3 cannot always be expected.

A transient backward erosion piping model based on laminar flow transport equations

<p>Backward erosion piping (BEP) has been proven to be one of the main failure mechanisms of water-retaining structures worldwide. Dikes, which are often built on sandy aquifers, are particularly vulnerable to this special type of internal erosion. In this research, we propose a numerical solution that combines a 2D Darcy groundwater solution with Exner’s 1D sediment transport mass conservation equation. The inclusion of criteria for incipient particle motion, as well as the linkage of the bedload transport rate to the pipe progression, enables us to build a stable time-dependent piping model. As an estimate of sediment transport, we tested four different empirical transport equations for laminar flow. The model performance was evaluated based on the results of a real-scale dike failure experiment. Through this, we were able to demonstrate the applicability of existing sediment transport equations to the description of particle motion during piping erosion. The proposed transient piping model not only predicts the pipe progression in time, it also allows for an identification of pore pressure transitions due to the erosion process. The main finding of the study is that from the four different modeling approaches for laminar flow, it is recommended to follow the approach of Yalin et al. (1963, 1979) to simulate backward erosion piping in dikes.</p>

The Applicability of an Inverse Schlumberger Array for Near-Surface Targets in Shallow Water Environments

We investigate the applicability of offshore geoelectrical profiling in the littoral zone, e.g., for archaeological prospection, sediment classification and investigations on coastal ground water upwelling. We performed field measurements with a 20 m long multi-electrode streamer in inverse Schlumberger configuration, which we used to statistically evaluate measurement uncertainty and the reproducibility of offshore electric resistivity tomography. We compared floating and submerged electrodes, as well as stationary and towed measurements. We found out that apparent resistivity values can be determined with an accuracy of 1% to 5% (1σ) depending on the measurement setup under field conditions. Based on these values and focusing on typical meter-scale targets, we used synthetic resistivity models to theoretically investigate the tomographic resolution and depth penetration achievable near-beach underneath a column of brackish water of about 1 m depth. From the analysis, we conclude that offshore geoelectric sounding allows the mapping of archaeological stone settings. The material differentiation of low-porosity rock masses < 15% is critical. Submerged wooden objects show a significant resistivity contrast to sand and rocks. Distinguishing brine-saturated sandy sediments from cohesive silty-clayey sediments is difficult due to their equal or reversed resistivity contrasts. Submarine freshwater discharges in sandy aquifers can be localized well, though difficulties may occur if the seafloor encounters massive low-porosity rock masses. As to the measurement setups, submerged and floating electrodes differ in their spatial resolution. Whereas stone settings of 0.5 to 1 m can still be located with submerged electrodes within the uppermost 4 m underneath the seafloor, they have to be >2 m if floating electrodes are used. Therefore, we recommend using submerged electrodes, especially in archaeological prospection. Littoral geological and hydrogeological mapping is also feasible with floating electrodes in a more time-saving way.

Testing the relation between pre-sample purge extent, parameter stabilization and dissolved contaminant concentration at a DNAPL site

&lt;p&gt;Groundwater contamination resulted from anthropogenic activity often proves to be a persistent feature of the affected groundwater regime. The contaminated groundwater body is a complex and dynamic entity commonly called the &amp;#8220;contaminant plume&amp;#8221;, it is characterized by spatially dependent concentration pattern that exhibits temporal changes. In order to assess the actual state of the plume contemporaneous sampling of all assigned monitoring wells is necessary. These contemporaneous samplings should provide compatible results, just like subsequent sampling campaigns. Differences between consecutive concentration patterns help to understand the temporal behavior of the plume.&lt;/p&gt;&lt;p&gt;A monitoring well provides direct contact between the water originating from of the screened aquifer and the atmosphere. The water within the well may undergo physicochemical changes, between sampling events, mainly when aquifer water movement at the screened section of the well is slow. Among diverse alterations the stagnant water within the well may be depleted in volatile components, enriched in dissolved oxygen therefore the chemistry of the stagnant water within the well is typically not representative of the aquifer water. These alterations would not confine to the water contained inside of the well casing, they will diffuse into the aquifer at the screened section. The extent of this altered zone is hard to calculate, as it depends on a number of factors. The sampling procedure should ensure that representative formation water is sampled instead of altered water.&lt;/p&gt;&lt;p&gt;It is well known for long that sampling procedure can affect sample integrity. Most standardized sampling procedures consist a pre-sampling purge phase to avoid the sampling of stagnant water instead of aquifer water. Most procedures aim to define the necessary extent of the purging in well volumes (from three-five to twenty volumes). The other approach is to purge the well until all or some of certain field parameters (such as pH, specific electric conductivity, temperature, dissolved oxygen, oxidation-reduction potential, turbidity) stabilize, however definitions for parameter stabilization criteria are not uniform. Parameter stabilization approach is used mostly, when low-flow sampling technique is applied. In addition to the stabilization of field parameters low-flow technique requires water level stabilization as well.&lt;/p&gt;&lt;p&gt;The test site is a chlorinated hydrocarbon contaminated site, the affected subsurface consists of layered sandy aquifers and silt-clay aquicludes. Three monitoring wells were repeatedly tested quarterly on five sampling occasions. Field parameters were measured in a flow through cell and recorded regulary. Three samples were taken during purging: at the beginning of the purging; after extraction of three well volumes; and when field parameters are stabilized. The samples were analysed for organic and inorganic components.&lt;/p&gt;&lt;p&gt;Results indicate that at wells with lower contaminant concentrations insufficient purging may result in overestimating the proportion of contaminant degradation products over primer contaminant components.&lt;/p&gt;

Modelling double diffusion in soils and materials

The double diffusivity model proposed earlier by Aifantis and co-workers was applied in this work for modelling the diffusion of metals in sandy aquifers, as well as chloride diffusion in concrete specimens. The theoretical predictions are in very good agreement with the measured concentrations in all cases, showing that the model is capable of dealing with a large variety of double diffusivity problems.