Delineation of wellhead protection zones: the analysis of main geological factors

Introduction. Analysis of the projects concerning wellhead protection (WHP) zones delineation shows the majority of the reports to use a simplified calculation. The applied analytical solutions do not refer to the actual geological conditions of the operating water intakes. The lack of distinct guidelines for geological data to be used in the research and the cost increase force the researchers to represent a simplified assessment. Materials and methods. The control of different WHP zone size geological parameters was studied by applying a series of theoretical calculations. Thus, software for analytical modelling of groundwater wells ANSDIMAT developed by the Institute of environmental geoscience, RAS, was used. Delineation of WHP zones is performed by the Particle-Tracking method. Results. Both size and geometry of WHP zones are controlled by several geological and hydrogeological parameters, which entail a synergetic effect. Within the parameters mentioned above, there are such as 1) pumping discharge; 2) aquifer thickness; 3) accessible porosity; 4) flow direction and the hydraulic gradient; 5) hydraulic conductivity; 6) the hydraulic connectivity of an aquitard. Our research shows all six factors perceptibly influence the results. To avoid significant errors each of the factors should be taken into account. Conclusion. Regulations actualization and the Guideline for delineation of wellhead protection zones, in particular, remain to be an area for improvement. Clear requirements for geological and hydrogeological parameter contamination, parameters uncertainty.

From point to field scale results: upscaling pointwise analysis of glyphosate vertical mobility through the spatial knowledge of the soil infiltration capacity

<p>In the two-year period 2018-2020 the Centre of Hydrology ‘Dino Tonini’ of the University of Padova developed the UNI-Impresa research project SWAT (Subsurface Water quality and Agricultural pracTices monitoring) to study the interactions between agricultural practices, mainly those involved in the production of Prosecco, and the wellhead protection areas in the province of Treviso (Italy). Specific experimental activities, integrated by a modelling analysis of the collected data, were developed to understand the processes affecting the vertical evolution of a glyphosate-based pesticide in the unsaturated soil up to a depth of 0.70 m BGL. The pesticide, along with a non-reactive tracer (potassium bromide), was applied in November 2018 in two experimental sites (Settolo-Valdobbiadene and Colnù-Conegliano) organized nearby well-fields supplying public water systems. Its evolution subjected only to the natural hydrological forcing compared to the infiltration dynamics of the tracer was locally monitored by collecting and analyzing soil and water samples along six months. Both the application and the monitoring activities were carried out in each experimental site on two 25 m<sup>2</sup> parcels located at reciprocal distances of 30 m (Settolo) and 115 m (Colnù), obtaining a detailed information about the glyphosate vertical evolution. Each point-wise analysis highlights a strong tendency of the pesticide and its principal metabolite (AMPA) to be adsorbed to the soil matrix rather than to be dissolved in the infiltrated rainwater and carried toward the deeper layers of the soil. However, high concentrations of the pesticide spotted at the depth of -0.70 m suggest that preferential pathways and more intense precipitation events enhance the downward movement of the glyphosate, either dissolved in water or adsorbed to microscopic particles. Differences in the pesticide spatio-temporal evolution were observed between parcels belonging to the same site.  Despite the decay analyzed during the experiments is related to both the chemical-physical properties of the soil, the potential movement is dominated by the heterogeneity of the hydraulic properties of soil. Hence, the evaluation of the infiltration capacity was considered a low-cost proper method to extend the analysis to the field scale (~10<sup>2</sup> m characteristic length). In the experimental site of Colnù, the spatial variability of the soil infiltration capacity (mm/min) and dynamics has been assessed developing a series of tests using the double ring infiltrometer in 17 different positions within an area of 1.75 ha. The investigated area extends over two contiguous vineyards inside the wellhead protection area. Two tests positions correspond to the site parcels while the remaining were spatially distributed maintaining reciprocal distances ranging between 15 and 50 meters. The measured soil infiltration capacity shows a large spatial variability, up to two orders of magnitude. The geostatistical interpolation (kriging) of the achieved data gives a quantitative estimation of the soil vulnerability at the field scale based on the potentially infiltrating pesticide.</p>

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of ~ 10−1–1 mm) fractures is coupled with that in pipe cavities (~ 0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10−4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically ~ 102 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from ~ 100 up to ~ 500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to ~ 9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.

Comparative Study of Methods for Delineating the Wellhead Protection Area in an Unconfined Coastal Aquifer

Various delineation methods, ranging from simple analytical solutions to complex numerical models, have been applied for wellhead protection area (WHPA) delineation. Numerical modeling is usually regarded as the most reliable method, but the uncertainty of input parameters has always been an obstacle. This study aims at examining the results from different WHPA delineation methods and addressing the delineation uncertainty of numerical modeling due to the uncertainty from input parameters. A comparison and uncertainty analysis were performed at two pumping sites—a single well and a wellfield consisting of eight wells in an unconfined coastal aquifer in Israel. By appointing numerical modeling as the reference method, a comparison between different methods showed that a semi-analytical method best fits the reference WHPA, and that analytical solutions produced overestimated WHPAs in unconfined aquifers as regional groundwater flow characteristics were neglected. The results from single well and wellfield indicated that interferences between wells are important for WHPA delineation, and thus, that only semi-analytical and numerical modelling are recommended for WHPA delineation at wellfields. Stochastic modeling was employed to analyze the uncertainty of numerical method, and the probabilistic distribution of WHPAs, rather a deterministic protection area, was generated with considering the uncertain input hydrogeological parameters.

PROBLEMS OF DESIGNING AND SANITARY-EPIDEMIOLOGIC EXPERTIZE OF PROJECTS OF SANITARY PROTECTION ZONES OF UNDERGROUND WATER SUPPLY SOURCES

Introduction. One of the main tasks in the area of public health in Russia is the adequate quality of drinking water supply, i.e. its sound chemical composition and epidemiological safety. The latter is provided among others, by proper wellhead protection activities which aim to ensure sanitary protection of water intakes, water supply and distribution facilities and sites of their location from anthropogenic influence. The aim of the study. The analysis of most common errors revealed during the expertize of wellhead protection (WHP) plans for groundwater intakes. Material and Methods. laws and regulations related to wellhead protection plan development, particular WHP plans, related technical papers. The study is methodologically based on common scientific approaches to investigate social interactions in the field of drinking and domestic water supply such as analytical, comparative, structured system analysis. Results. It is shown that a great deal of uncertainty exists in practical assessment of parameters necessary to estimate wellhead protection area that makes wellhead protection area delineation rather approximate. To enhance the reliability of estimates it is necessary to account for a minimal set of estimation indices and increase the requirements to the quality and scope of project documentation. Conclusion. Authors set forth a complex of additional investigations to refine parameter estimates for wellhead protection plan development, and several new requirements for the project design regarding both the textual part and graphics. Some recommendations to amend current regulations related to wellhead protection are also suggested.