Single borehole dilution tests are a method for characterizing groundwater monitoring wells or boreholes and can either be conducted as uniform injection throughout the entire saturated length or as point injection at one specific depth. By injecting a tracer into a borehole and measuring concentration profiles, flow horizons and possible vertical flow can be identified and quantified. Compared to conventional methods, such as flowmeters, SBDTs are cheaper and require less equipment, but allow important conclusions about wells and aquifers.

Uniform injections deliver information about the entire saturated length and can be conducted using different techniques. The most common one uses a hosepipe filled with tracer solution to obtain a uniform concentration over the entire water column. We present a simplified method using a permeable injection bag to achieve close-to-uniform tracer distribution in the well.

However, uniform injections are not ideally suitable for the investigation of vertical flow. For this purpose, point injections are more appropriate. We introduce a newly developed probe which can be filled with saline solution, lowered into the intended depth and then be opened by a falling weight. Numerous tests have been carried out in the laboratory and several groundwater monitoring wells, to evaluate the simplified method for uniform injections and the new probe for point injections. Results show that with the simplified method, significant and reproducible results can be obtained. The functionality of the new injection probe was also demonstrated. Both techniques represent useful tools for efficient hydraulic characterization of boreholes in karst and other aquifers.

Characterising subsurface hydraulic and geomechanical properties is a prerequisite for Earth resource management. Traditional approaches such as hydraulic testing are costly and require specific infrastructure as well as expertise which limits general testing capabilities. Passive Subsurface Characterisation (PSC) uses the groundwater response to natural forces, such as Earth tides and atmospheric pressure changes, to determine state of confinement and estimate hydro-geomechanical properties of the subsurface in-situ. This approach only requires standard measurements of groundwater hydraulic head and barometric pressure as well as theoretical Earth tides which can be calculated. This presentation gives an overview of the state of the science. Calculation of hydro-geomechanical subsurface properties from standard groundwater monitoring datasets can be done conveniently using the new python package HydroGeoSines (HGS). HGS contains key methods from the peer-reviewed literature and therefore allows anyone with python skills to apply PSC to their datasets. PSC offers cost-effective estimations and can be applied to existing datasets provided they meet minimum quality criteria. Further analysis applied to monitoring bores at different field sites around the world exemplifies that, apart from basic hydraulic properties (hydraulic conductivity, specific storage, barometric efficiency), the full poroelastic parameter space (porosity, shear, Young’s and bulk moduli, Skempton’s and Biot-Willis coefficients and undrained/drained Poisson’s ratios) can be determined. Since PSC is an underutilised tool, this presentation aims to raise awareness as well as for the need to update groundwater monitoring practice to maximise the benefits of PSC.

Facing a couple of dry and warm years which are consistent with climate change scenarios, there is now increasing need for advanced diagnostic tools for drought risk assessment at the scale of years or decades. Commonly models are used for that purpose. However, they often suffer from a lack of data at sufficient spatial resolution, resulting in substantial uncertainties when applied beyond the bounds of single case studies. On the other hand, recent experience showed that simple extrapolating of trends of observed behaviour would not be adequate due to substantial changes of boundary conditions.

A new method has been developed and tested at a regional scale (about 10⁵ km²). It has been shown recently that most of the variance of groundwater head dynamics at that scale can be ascribed to differing degrees of damping of very similar input signals, that is, groundwater recharge dynamics, depending on the thickness and the texture of the overlying vadose zone. The degree of damping can easily be determined by a principal component analysis of a set of groundwater head time series. The stronger the damping the more pronounced is the memory. It could be shown that for wells with pronounced memory groundwater heads have been decreased for about 40 years in Northeast Germany. Thus the backbone of landscape hydrology has been exhibiting continuous weakening, resulting in increasing drought risk in the mid-term, although intermittent recovery at other sites seems to suggest the opposite.

Irrigation agriculture in Los Arenales aquifer has resulted in staggering groundwater level declines in the last quarter of the XX century. The objective of this study is to assess the contribution of MAR to reverse such a problematic situation. To this end, we compare two neighbouring and analogous groundwater bodies within this aquifer, namely Los Arenales (LA) and Medina del Campo (MC). The primary difference between them is the presence of three large-scale MAR sites in LA. We employ the Mann-Kendall test and Theil-Sen estimator for slope analysis and an empirical approach to assess field significance. Additionally, we compute the average groundwater levels and explore agricultural and climatological information to complement the statistical analysis. The slope analysis reflects a dramatic drop in groundwater levels in LA and MC during 1985-2001 (~100% of trends are negative) with slope strengths in the order of -1.5 m/year. The subsequent analysis periods (2002-2011 and 2012-2020) show a substantial improvement of groundwater availability in LA (~75% of the trends are positive) and marginally in MC (~25% of the trends are positive). No field significance was detected in the area. The analysis of average groundwater levels against climatological and agricultural information depicts the socioeconomic similarities between both groundwater bodies and the pronounced recovery in LA (~10% higher than the lowest average level) when compared to MC (~4%). This study demonstrates that MAR very likely accounts for the difference in groundwater storage recovery between LA and MC and the suitability of this technique to counteract aquifer overexploitation.

The improvement of groundwater availability in arid areas by infiltration of treated wastewater will play an important role in the next few years. Small wastewater plant is a good alternative in places where central wastewater treatment is not available. Numerical models can be applied to examine the processes more closely and to examine a large number of scenarios analysing.

The study described deals with the numerical modeling of a hypothetical infiltration system at Sarden (Syria) which is supposed to infiltrate treated wastewater into the aquifer. The aim of this work was the evaluation of the infiltration of the treated wastewater and the combination of this with rainwater infiltration from small village, as well as to propose a practicable procedure a possible influence on the groundwater quality can be estimated and evaluated.

PCSiWaPro^® (a software for seepage water simulation) was used to create and to simulate their influence on the saturation ratios in the unsaturated zone. In addition, scenarios with different boundary conditions were created and implemented in the model variants.

Results of the simulations carried out indicate that the treated wastewater can infiltrate according to the geofactors at the Sarden site. The distance between the groundwater level and the top of the groundlevel shows a great influence on the saturation conditions of the soil zone under consideration.

A decrease in the substance concentration over depth, according to the degradation parameters used, show the results of the simulation. The concentrations at the measuring points increase with the simulation time.