Groundwater Drought Analysis under Data Scarcity: The Case of the Salento Aquifer (Italy)

Salento is a regional coastal karst aquifer located in Southern Italy with a highly complex geological, geomorphological, and hydrogeological structure. High and unruly exploitation of groundwater from licensed and unlicensed wells for irrigation and drinking purposes affects groundwater, with consequent degradation of its qualitative and quantitative status. The increased frequency of meteorological droughts and rising temperatures may only worsen the already compromised situation. The absence of complete and enduring monitoring of groundwater levels prevents the application of some methodologies, which require long time series. The analysis of climate indexes to describe the groundwater level variation is a possible approach under data scarcity. However, this approach may not be obvious for complex aquifers (in terms of scale, intrinsic properties, and boundary conditions) where the response of the groundwater to precipitation is not necessarily linear. Thus, the proposed research deals with the assessment of the response of the Salento aquifer to precipitation variability based on correlations between the Standardized Precipitation Index (SPI) and Standardized Precipitation and Evapotranspiration Index (SPEI) and groundwater levels for nine monitoring wells from July 2007 to December 2011. The study aims at evaluating the ability of the above indicators to explain the behavior of groundwater on complex aquifers. Moreover, it has the general aim to verify their more general reliable application. Results of three different correlation factors outline direct and statistically significant correlations between the time series. They describe the Salento aquifer as a slow filter, with a notable inertial behavior in response to meteorological events. The SPI 18-months demonstrates to be a viable candidate to predict the groundwater response to precipitation variability for the Salento aquifer.

Earthquake-induced hydrogeological changes in New Zealand

<p>Earthquakes redistribute fluids and change associated flow paths in the subsurface. Earthquake hydrology is an evolving discipline that studies such phenomena, providing novel information on crustal processes, natural hazards and water resources. This thesis uses the internationally significant New Zealand "hydroseismicity" dataset, in a regional-scale multi-site multi-earthquake study which includes the occurrence and the absence of responses, spanning a decade. Earthquake-induced groundwater level and tidal behaviour changes were examined in a range of aquifers, rock types and hydrogeological settings. Monitoring wells were within one (near-field) to several (intermediate- field) ruptured fault lengths of a variety of earthquakes that had a range of shaking intensities. This thesis presents three studies on the seismic and hydrogeological controls on earthquake-induced groundwater level changes. Water level changes were recorded New Zealand-wide within compositionally diverse, young shallow aquifers, in 433 monitoring wells at distances between 4 and 850 km from the 2016 Mw 7.8 Kaikoura earthquake epicentre. Water level changes are inconsistent with static stress changes, but do correlate with peak ground acceleration (PGA). At PGAs exceeding ~2 m/s2, water level changes predominantly increased persistently, which may have resulted from shear-induced consolidation. At lower PGAs there were approximately equal numbers of persistent water level increases and decreases, which are thought to have resulted from permeability enhancement. Water level changes also occurred more frequently north of the epicentre, due to the northward directivity of the Kaikoura earthquake rupture. Local hydrogeological conditions also contributed to the observed responses, with larger water level changes occurring in deeper wells and in well-consolidated rocks at equivalent PGA levels. Earthquakes have previously been inferred to induce hydrological changes in aquifers on the basis of changes to well tidal behaviour and water level, but the relationship between these changes have been unclear. Earthquake-induced changes to tidal behaviour and groundwater levels were quantified in 161 monitoring wells screened in gravel aquifers in Canterbury, New Zealand. In the near-field of the Canterbury earthquake sequence of 2010 and 2011, permeability reduction detected by tidal behaviour changes and increased water levels supports the hypothesis of shear-induced consolidation. Water level changes that occurred with no change in tidal behaviour re-equilibrated at a new post-seismic level within ~50 minutes possibly due to high permeability, good well-aquifer coupling, and/or small permeability changes in the local aquifer. Water level changes that occurred with tidal behaviour changes took from ~240 minutes to ~10 days to re-equilibrate, thought to represent permeability changes on a larger scale. Recent studies commonly utilise a general metric for earthquake-induced hydrological responses based on epicentral distance, earthquake magnitude and seismic energy density. A logistic regression model with random effects was applied to a dataset of binary responses of 495 monitoring well water levels to 11 Mw 5.4 or larger earthquakes. Within the model, earthquake shaking (represented by peak ground velocity), degree of confinement (depth) and rock strength (site average shear wave velocity in the shallow subsurface) were incorporated. For practical applications, the probabilistic framework was converted into the Modified Mercalli (MM) intensity scale. The model shows that water level changes are unlikely below MM intensity VI. At an MM intensity VII, water level changes are about as likely as not to very likely. At MM intensity VIII, the likelihood rises to very likely to virtually certain. This study was the first attempt we are aware of worldwide at incorporating both seismic and hydrogeological factors into a probabilistic framework for earthquake-induced groundwater level changes. The framework is a novel and more universal approach in quantifying responses than previous metrics using epicentral distance, magnitude and seismic energy density. It has potential to enable better comparison of international studies and inform practitioners making decisions around investment to mitigate risk to, and to increase the resilience of, water supply infrastructure.</p>

Earthquake-induced hydrogeological changes in New Zealand

<p>Earthquakes redistribute fluids and change associated flow paths in the subsurface. Earthquake hydrology is an evolving discipline that studies such phenomena, providing novel information on crustal processes, natural hazards and water resources. This thesis uses the internationally significant New Zealand "hydroseismicity" dataset, in a regional-scale multi-site multi-earthquake study which includes the occurrence and the absence of responses, spanning a decade. Earthquake-induced groundwater level and tidal behaviour changes were examined in a range of aquifers, rock types and hydrogeological settings. Monitoring wells were within one (near-field) to several (intermediate- field) ruptured fault lengths of a variety of earthquakes that had a range of shaking intensities. This thesis presents three studies on the seismic and hydrogeological controls on earthquake-induced groundwater level changes. Water level changes were recorded New Zealand-wide within compositionally diverse, young shallow aquifers, in 433 monitoring wells at distances between 4 and 850 km from the 2016 Mw 7.8 Kaikoura earthquake epicentre. Water level changes are inconsistent with static stress changes, but do correlate with peak ground acceleration (PGA). At PGAs exceeding ~2 m/s2, water level changes predominantly increased persistently, which may have resulted from shear-induced consolidation. At lower PGAs there were approximately equal numbers of persistent water level increases and decreases, which are thought to have resulted from permeability enhancement. Water level changes also occurred more frequently north of the epicentre, due to the northward directivity of the Kaikoura earthquake rupture. Local hydrogeological conditions also contributed to the observed responses, with larger water level changes occurring in deeper wells and in well-consolidated rocks at equivalent PGA levels. Earthquakes have previously been inferred to induce hydrological changes in aquifers on the basis of changes to well tidal behaviour and water level, but the relationship between these changes have been unclear. Earthquake-induced changes to tidal behaviour and groundwater levels were quantified in 161 monitoring wells screened in gravel aquifers in Canterbury, New Zealand. In the near-field of the Canterbury earthquake sequence of 2010 and 2011, permeability reduction detected by tidal behaviour changes and increased water levels supports the hypothesis of shear-induced consolidation. Water level changes that occurred with no change in tidal behaviour re-equilibrated at a new post-seismic level within ~50 minutes possibly due to high permeability, good well-aquifer coupling, and/or small permeability changes in the local aquifer. Water level changes that occurred with tidal behaviour changes took from ~240 minutes to ~10 days to re-equilibrate, thought to represent permeability changes on a larger scale. Recent studies commonly utilise a general metric for earthquake-induced hydrological responses based on epicentral distance, earthquake magnitude and seismic energy density. A logistic regression model with random effects was applied to a dataset of binary responses of 495 monitoring well water levels to 11 Mw 5.4 or larger earthquakes. Within the model, earthquake shaking (represented by peak ground velocity), degree of confinement (depth) and rock strength (site average shear wave velocity in the shallow subsurface) were incorporated. For practical applications, the probabilistic framework was converted into the Modified Mercalli (MM) intensity scale. The model shows that water level changes are unlikely below MM intensity VI. At an MM intensity VII, water level changes are about as likely as not to very likely. At MM intensity VIII, the likelihood rises to very likely to virtually certain. This study was the first attempt we are aware of worldwide at incorporating both seismic and hydrogeological factors into a probabilistic framework for earthquake-induced groundwater level changes. The framework is a novel and more universal approach in quantifying responses than previous metrics using epicentral distance, magnitude and seismic energy density. It has potential to enable better comparison of international studies and inform practitioners making decisions around investment to mitigate risk to, and to increase the resilience of, water supply infrastructure.</p>

Groundwater Mapping of Total Coliform Contamination in Sleman, Yogyakarta, Indonesia

Groundwater is a pivotal resource to supply clean and drinking water besides surface water. In Indonesia, there are various issues regarding groundwater quality and quantity. By increasing population growth has an impact on groundwater quality, such as generated pathogen contamination. To prevent groundwater pollution was used sanitation facilities were called communal WWTPs. Unfortunately, most WWTPs were not performing optimal, and some had already stopped operating. This study aimed to display groundwater quality using the Inverse Distance Weighting (IDW) for 2018 to 2019 in the Sleman Region of Yogyakarta Province. The spatial analysis was completed by observation and interview methods. The total coliform number was measured from 29 monitoring wells. The results explained that compared to 2018, groundwater quality in 2019 showed a decrease in contamination by pathogenic bacteria. Groundwater flows also shown the spread of contamination from north to the south area. The distance between monitoring well and septic tank or WWTPs outlet, depth, and the physical condition were substantial factors for spreading the contamination.

A Closer Look at Hydraulic Fractures: Case Studies of Microseismic Results from Horizontal Monitoring Wells

Amongst different options of hydraulic fracture geometry detection or measurement, microseismic monitoring is a commonly used method to reveal the hydraulic fracture geometry in three-dimensional space. Microseismic monitoring typically requires one or several monitoring wells within an effective range from the treatment well, in which the geophones are set to detect the microseismic events occurring during or after the treatment. In the past, most of the monitoring wells have been vertical wells. We present several recent case studies in which both the treatment and monitoring wells were horizontal wells, which produced some unique and interesting observations beyond the initial expectations. One of the prerequisites of a proper microseismic monitoring of hydraulic fracturing treatment is to place the geophone in the proper position because a long distance between the actual fracturing events and the geophone may result in signal deterioration, which influences the processing and increases the uncertainty. This problem is more severe if the treatment well is a horizontal well because the distance from the geophone to the microseismic events varies between stages. One of the methods to solve this issue is to monitor the microseismic events in a horizontal offset well. As horizontal wells are often batched drilled in clusters for tight or unconventional resource nowadays, the availability of the monitoring well is less of a problem, and the constant distance from the monitoring well to the treatment well may help to generate better data quality and more accurate interpretation result. We implemented horizontal well monitoring in two difference cases between 2018 and 2019. For case A, one horizontal monitoring well was used to monitor 54 fracturing stages in three offset wells, and for case B, we monitored 24 fracturing stages in one offset well. In both cases, the geophone arrays were shifted in multiple positions to fit the distance requirements, and both cases generate satisfying interpretation results. The microseismic results from the two cases showed less uncertainty and better precision of microseismic events after processing, as we expected. What is surprising is this type of monitoring showed a unique physical phenomenon a couple of times, which is a casing background noise indicating excessive fracturing extension over a long distance. This phenomenon was captured in both cases, even with small injection rate and fluid volumes, which can be important information for us to better understand the dynamics of fracture propagation in such geomechanical environment and help to set a new guideline and design reference in the same region.

A Hotspot of Arid Zone Subterranean Biodiversity: The Robe Valley in Western Australia

Knowledge of subterranean fauna has mostly been derived from caves and streambeds, which are relatively easily accessed. In contrast, subterranean fauna inhabiting regional groundwater aquifers or the vadose zone (between surface soil layers and the watertable) is difficult to sample. Here we provide species lists for a globally significant subterranean fauna hotspot in the Robe Valley of the Pilbara region, Western Australia. This fauna was collected from up to 50 m below ground level using mining exploration drill holes and monitoring wells. Altogether, 123 subterranean species were collected over a distance of 17 km, comprising 65 troglofauna and 58 stygofauna species. Of these, 61 species were troglobionts and 48 stygobionts. The troglofauna occurs in small voids and fissures in mesas comprised mostly of an iron ore formation, while the stygofauna occurs in the alluvium of a river floodplain. The richness of the Robe Valley is not a localized aberration, but rather reflects the richness of the arid Pilbara region. While legislation in Western Australia has recognized the importance of subterranean fauna, mining is occurring in the Robe Valley hotspot with conditions of environmental approval that are designed to ensure species persistence.

Distribution of a Sulfolane-Metabolizing Rhodoferax sp. Throughout a Contaminated Subarctic Aquifer and Two Groundwater Treatment Systems

An extensive plume of the emerging contaminant sulfolane has been found emanating from a refinery in Interior Alaska, raising questions about the microbial potential for natural attenuation and bioremediation in this subarctic aquifer. Previously, an aerobic sulfolane-assimilating Rhodoferax sp. was identified from the aquifer using stable isotope probing. Here, we assessed the distribution of known sulfolane-assimilating bacteria throughout the contaminated subarctic aquifer using 16S-rRNA-amplicon analyses of ~100 samples collected from groundwater monitoring wells and two groundwater treatment systems. One treatment system was an in situ air sparging system where air was injected directly into the aquifer. The other was an ex situ granular activated carbon (GAC) filtration system for the treatment of private well water. We found that the sulfolane-assimilating Rhodoferax sp. was present throughout the aquifer but was significantly more abundant in groundwater associated with the air sparge system. The reduction of sulfolane concentrations combined with the apparent enrichment of sulfolane degraders in the air sparging zone suggests that the addition of oxygen facilitated sulfolane biodegradation. To investigate other environmental controls on Rhodoferax populations, we also examined correlations between groundwater geochemical parameters and the relative abundance of the Rhodoferax sp. and found only manganese to be significantly positively correlated. The sulfolane-assimilating Rhodoferax sp. was not a major component of the GAC filtration system, suggesting that biodegradation is not an important contributor to sulfolane removal in these systems. We conclude that air sparging is a promising approach for enhancing the abundance and activity of aerobic sulfolane-degraders like Rhodoferax to locally stimulate sulfolane biodegradation in situ.

Wildfire Impacts on Groundwater Aquifers: A Case Study of the 1996 Honey Boy Fire in Beaver County, Utah, USA

It is well known that wildfires destroy vegetation and form soil crusts, both of which increase stormwater runoff that accelerates erosion, but less attention has been given to wildfire impacts on groundwater aquifers. Here, we present a systematic study across the contiguous United States to test the hypothesis that wildfires reduce infiltration, indicated by temporary reductions in groundwater levels. Geographic information systems (GIS) analysis performed using structured queried language (SQL) categorized wildfires by their proximity to wells with publicly available monitoring data. Although numerous wildfires were identified with nearby monitoring wells, most of these data were confounded by unknown processes, preventing a clear acceptance or rejection of the hypothesis. However, this analysis did identify a particular case study, the 1996 Honey Boy Fire in Beaver County, Utah, USA that supports the hypothesis. At this site, daily groundwater data from a well located 790 m from the centroid of the wildfire were used to assess the groundwater level before and after the wildfire. A sinusoidal time series adjusted for annual precipitation matches groundwater level fluctuations before the wildfire but cannot explain the approximately two-year groundwater level reduction after the wildfire. Thus, for this case study, there is a correlation, which may be causal, between the wildfire and temporary reduction in groundwater levels. Generalizing this result will require further research.

Distribution of ETBE-degrading microorganisms and functional capability in groundwater, and implications for characterising aquifer ETBE biodegradation potential

Microbes in aquifers are present suspended in groundwater or attached to the aquifer sediment. Groundwater is often sampled at gasoline ether oxygenate (GEO)-impacted sites to assess the potential biodegradation of organic constituents. However, the distribution of GEO-degrading microorganisms between the groundwater and aquifer sediment must be understood to interpret this potential. In this study, the distribution of ethyl tert-butyl ether (ETBE)-degrading organisms and ETBE biodegradation potential was investigated in laboratory microcosm studies and mixed groundwater-aquifer sediment samples obtained from pumped monitoring wells at ETBE-impacted sites. ETBE biodegradation potential (as determined by quantification of the ethB gene) was detected predominantly in the attached microbial communities and was below detection limit in the groundwater communities. The copy number of ethB genes varied with borehole purge volume at the field sites. Members of the Comamonadaceae and Gammaproteobacteria families were identified as responders for ETBE biodegradation. However, the detection of the ethB gene is a more appropriate function-based indicator of ETBE biodegradation potential than taxonomic analysis of the microbial community. The study shows that a mixed groundwater-aquifer sediment (slurry) sample collected from monitoring wells after minimal purging can be used to assess the aquifer ETBE biodegradation potential at ETBE-release sites using this function-based concept.