Emerging Issues in Groundwater Resources

A better understanding of the relevant climate-change drivers for coastal areas has been realized in the past few years. A significant increase in atmospheric CO₂ concentration is predicted to virtually occur and as a result, more CO₂ is absorbed by surface waters, decreasing seawater pH and carbonate saturation. Sea surface temperatures are also essentially certain to rise significantly, although less than the global mean temperature rise. Globally, SLR derived from thermal expansion due to warming of oceans and the melting of ice caps, glaciers, and ice sheets (i.e., Greenland and Antarctica) act together as major factors contributing to RSLR. The rise will not be spatially uniform, with possible intensification of ENSO and time variability which suggests greater change in extremes with important implications for coral reefs. In most cases there will be significant regional variations in the changes, and any impacts will be the result of the interaction between climate change drivers (i.e., CO₂ concentrations, SST, SLR, storm intensity, frequency, and track, wave conditions and runoff) and other drivers of change, leading to diverse effects and vulnerabilities. The direct influences of sea level rise (SLR) on coastal water resources are associated with seawater encroachment into surface waters and coastal aquifers. Inundation as a result of increases in mean sea level will have devastating impacts on unprotected low-lying areas, especially as a result of storm events which are expected to intensify. Seawater intrusion caused by natural and human-derived factors will be exacerbated by SLR. However, some coastal areas, especially on some arid coasts, receiving more precipitation may be less impacted by seawater intrusion as a result of increased aquifer recharge. Climate change adverse impacts on freshwater supplies at a global scale are most likely to be more visible in developing countries with large extents of coastal lowland, small island states, semi-arid and arid coasts, and large coastal cities particularly in the Asia-Pacific region, reflecting both natural and socio-economic aspects that increase the risk levels. Thus, it is difficult to identify future coastal areas with stressed freshwater resources, particularly where there is a seasonal water demand stress and poor management. Assessments of RSLR-related coastal impacts, adaptation, and mitigation, require information related to climate-induced GMSLR, regional variations, and non-climate-related sea level changes and freshwater stressors.

Groundwater systems worldwide are facing increasing pressure from climate variability and human activities. The climate can affect the aquifer directly and/or indirectly through various pathways, such as groundwater recharge, the change in soil biogeochemical processes, and land use activities. To date, there has been relatively little research that specifically addressed the impacts of climate change on groundwater quality. To address the research gap, this paper highlights the mechanisms occurring at various hydrogeologic phases (e.g., soil, unsaturated zones and aquifers) of groundwater contamination that are susceptible to the effects of climate change. Relevant studies on groundwater pollution risk that have addressed or can potentially incorporate climate change impacts are summarized and synthesized in this article. It has been found that change in groundwater quality as a direct result of climate change is subject to various uncertainties affecting credible future projections. The change in land use activities, indirectly affected by climate change, may play more important roles in determining future patterns of groundwater pollution risks. Research and policy recommendations are provided to cope with the challenges to sustainable water quality management in a changing climate.

The High Plains aquifer shown in Fig. 3.1 underlies 453,248 km² in parts of eight states (Nebraska, Texas, Kansas, Colorado, New Mexico, Oklahoma, Wyoming, and South Dakota) making it the biggest aquifer in North America (Fig. 3.1). The predominant formation in the High Plains aquifer is the Ogallala Formation of the Miocene/Pliocene age (Sophocleous 2012), thus this aquifer is commonly referred to as the Ogallala aquifer. This predominantly unconfined aquifer comprises of silt, sand, gravel and clay, and varies in saturated thickness and permeability (Buchanan et al. 2009). For example, the predevelopment aquifer thickness and depth to water in Kansas varies from 15 m to over 90 m, and 8 m to over 105 respectively (High Plain Atlas). Most of the water from the aquifer is paleo or fossil water associated with the events of the last ice age when glaciers covered the Great Plains.

Unconventional natural gas extraction from impermeable geologic formations is getting momentum in recent years due to advances in horizontal drilling and hydraulic fracturing. By 2040, shale resources are projected to account for 53 % of all natural gas production in the U.S. However, the development of unconventional oil/gas production from hydraulic fracturing has raised serious concerns about its potential impact on the quantity and quality of water resources and the environment due to the large volume of water needed and the use of toxic substances in hydraulic fracturing fluids. This paper gives an overview of the hydraulic fracturing used to extract shale gas, its potential impact on water resources, provides an overview of modeling studies and tools used to assess its potential impacts, and regulation issues related to it. The most significant risks resulting from hydraulic fracturing and shale gas development are (1) the excessive withdrawal of water, (2) gas migration and groundwater contamination due to faulty well construction, blowouts, (3) contamination by wastewater disposal, and (4) accidental leaks and spill of wastewater and chemicals used during drilling and hydraulic fracturing process.

Due to advances in analytical techniques and increasing concerns related to the potential impact on aquatic and terrestrial organisms, the reported occurrence of pharmaceutical compounds in groundwater has significantly increased during the past two decades. This chapter provides an overview of the detection of pharmaceutical, life-style, and endocrine disruptor compounds in groundwater from five geographical areas (Africa, Asia, Central and South America, Europe, and North America). The occurrence of these compounds has been linked to the four major sources of contamination: agricultural practices/wastes, landfill, septic tanks, and wastewater. The concentration of the detected compounds ranged between ng/L and μg/L. Pharmaceutical compounds, in particular antibiotic and analgesic/anti-inflammatory, represent the most common group detected in groundwater, regardless of the geographic location. Carbamazepine (anticonvulsant), sulfamethoxazole (antibiotic), and caffeine (life-style) represent the three most common compounds detected in groundwater. The occurrence of the detected compounds in groundwater is primarily related to wastewater and/or agricultural practices/wastes. None of the detected compounds has been linked to all four major sources of contamination. However, five compounds (ibuprofen, paracetamol, triclosan, caffeine and cotinine) have been linked to three sources of contamination such as wastewater, landfill, and septic tanks.

A reliable groundwater balance assessment is a fundamental tool for any effective resource exploitation plan. Nevertheless, some terms of the balance equation are, generally, very difficult to be estimated, even on average, especially when large and heterogeneous groundwater bodies are considered.

In this work, a methodology for mutually calibrating groundwater balances carried out by means of different methods is proposed, also capable of providing an average estimation of the specific yield of the considered aquifer, as by-product.

A long time series of groundwater balances has been calibrated by assessing the average value of the term “inflow/outflow”, which had not been previously considered. Furthermore, the average value of the specific yield of the considered aquifer has been assessed.

Globally, submarine groundwater discharge (SGD) is responsible for 3–4 times the water discharge delivered to the oceans by rivers. Moreover, nutrient concentrations in SGD are usually elevated in comparison to river fluxes. Here we review the major advances in the field of SGD studies and related nutrient fluxes to the coastal ocean. To demonstrate the significance of SGD as terrestrial nutrient pathway we compare stream and submarine groundwater discharge rates in a watershed on the windward side of Oahu, one of the major islands of the Hawaii archipelago. Our analysis of Kaneohe Bay, which hosts the largest coral reefs on the island revealed that SGD in the form of total (fresh+brackish) groundwater discharge was 2–4 times larger than surface inputs. Corresponding DIN and silicate fluxes were also dominated by SGD, while DIP was delivered mostly via streams. We quantified bulk nutrient uptake in coastal waters and also demonstrated that nutrients were quickly removed from the bay due to fast coastal flushing rates. This study demonstrates the need to understand SGD-derived nutrient fluxes in order to evaluate land-based coastal nutrient and pollution sources.

Climatic and anthropogenic factors can have a significant influence on groundwater resources, calling into question the future quality and quantity of the commodity. In this chapter, we discuss current and emerging issues concerning groundwater scarcity. These concepts are demonstrated using a case study from an urban reservoir that serves as a stormwater conduit to the nearshore ocean. Quantitative estimates of groundwater interaction with the reservoir were determined via direct tracer techniques which are rarely, if ever, used by urban hydrologists. Continuous time-series records of dissolved ²²²Rn were collected to evaluate the volumetric percentage of groundwater within the reservoir from 2012 through 2013. Using high-resolution sampling, we are able to characterize groundwater and reservoir response on event and seasonal time scales, while also offering general assessments of the hydrologic conditions during the study. When rainfall was not occurring, evapotranspiration served as the primary driver of overall hydrologic characteristics, directly influencing the water table and subsequent groundwater discharged from the reservoir. However, during storm events, hydrologic factors influencing the amount of groundwater within the reservoir were found to be more complex, including event duration, magnitude, and antecedent conditions. Seasonally, rainfall patterns were largely responsible for the magnitude of groundwater present within the reservoir and quasi-related to peak export to the coastal ocean. Most notably, we observed a decline in the volumetric percentage of groundwater within the reservoir as a result of increased groundwater residence time within the aquifer—a likely function of reduced aquifer recharge that would result from more efficient stormwater management.

We investigated the spatial distribution and severity of groundwater arsenic contamination in three previously un-studied villages located near the confluence of the Rivers Ganges and Sone, within the Maner block of Patna district in the Bihar State, India. We also gathered information on the demographic, socioeconomic and health issues of local residents in order to identify at-risk populations due to the exposure to elevated concentrations of arsenic. Arsenic concentrations were measured in 157 drinking water sources, which were tested using field-tests kits. Spatial patterns in arsenic distribution were compared with local physiographic and hydrogeologic parameters. Arsenic levels exceeding the WHO and the BIS standards (10 μg/L and 50 μg/L respectively) were found in all three villages, with a maximum of 300 μg/L. The shallow aquifers (≤50 m below ground surface) and older hand pumps were found to be arsenic contaminated. The deeper aquifers (>50 m) exhibited arsenic levels within permissible limits. Elevated arsenic levels are observed close to the River Ganges. However, a moderate (r = 0.240, p = 0.031) positive correlation with the surface water flow direction indicates that arsenic migrates from south to north and from west to east in the study area. This suggests that River Sone alluvium is a potential source of arsenic contamination in Bihar.

Groundwater and surface water interaction is an essential component of the hydrological cycle. The hydraulic connectivity and exchange of water between surface water (e.g. rivers, lakes, wetlands) and underlying aquifers provide many ecosystem services that sustain human and ecological well-being. Climate change, increased population, and industrial growth have resulted in substantial environmental (e.g. land use and land cover, climate, groundwater) changes across the globe. As a result, decline in groundwater levels, drying of streams, shrinking lakes, wetlands, and estuaries have been observed across the world. This generates concerns about the effects of such environmental changes on groundwater and surface water interactions, and on the quality and quantity of water resources. This chapter presents an overview of groundwater and surface water interactions, pressing environmental change issues centered on natural and anthropogenic environmental changes, and available management tools that quantify the integrated groundwater and surface water flow processes. This chapter also briefly discusses exciting research opportunities enabled by satellite remote sensing. We close in with a discussion of future management challenges and strategies for sustainable use of groundwater and surface water resources. One outcome of this chapter is to provide resource managers, researchers, consultant groups, and government agencies basic understanding of the types, mechanism, and effects of natural and anthropogenic landuse changes on groundwater and surface water interactions, and available management tools for studying groundwater and surface water interactions.

Submarine Groundwater Discharge (SGD), which represents subsurface exchange of water between land and ocean, is a major component of the hydrological cycle. Until the mid-1990s, it was generally believed that SGD rates were not large enough to influence ocean water budgets. This thought might be due to the difficulty in quantifying rates of SGD, because most SGD occurs as diffusive flow, rather than discrete spring flow. However, there is a growing recognition that the submarine discharge of fresh groundwater into coastal oceans is just as important as river discharge in some areas of the coastal ocean. Due to growing ecological concerns about SGD, there is considerable progress on research about SGD with particular emphasis on how to quantify and trace the SGD, and to develop some forecasting or predictive capability of SGD rates based on climatic and seasonal effects. This chapter presents a comprehensive overview of the methods used to quantify SGD to coastal areas and summarizes the previous studies on SGD. In addition, this chapter also discusses driving forces of groundwater flow through coastal aquifers, mechanism of groundwater seawater interaction and some other important issues that are necessary to understand the methods for quantifying SGD in coastal areas. The main goal of this chapter is to provide an overview of the applied methodologies to quantify SGD in coastal areas, which in turn will allow researchers, coastal zone managers, and others to choose appropriate methods that meet their specific project requirements.

Recent decades have witnessed the expansion of irrigated agriculture in some of the most productive semi-arid economies in the world, such as the Texas High Plains. Interest in groundwater management continues to increase due to the excessive depletion of groundwater, which is the primary source of fresh water supply in these economies that critically depend on irrigated agriculture. In addition, the uncertainties posed through extreme climatic events such as drought exacerbate the challenge of managing this scarce yet vital resource. This chapter describes the problem of declining groundwater resources in a semi-arid economy exemplified by the Texas High Plains, discusses the management approach of water use restriction to handle the ever increasing demand for agricultural production with a limited supply in hand, and outlines the role of policy planning in groundwater management. For a semi-arid economy such as the Texas High Plains that is largely dependent on groundwater resources, an effective partnership between groundwater management bodies and local producers is an important step in planning towards the long term objective of ensuring adequate groundwater availability in the future.

Recently, in Italy, the interest for very low enthalpy geothermal resources (T < 20 °C) is growing. This is mainly because, these resources are widely available throughout the country and also unlike the other green energy sources (eg. solar and wind energy), and they do not need to be stored. Among the direct-use of geothermal resources, the open-loop groundwater heat pump (GWHP) system needs particular attention in terms of potential environmental impact. In coastal areas, that are generally densely populated, the installation of GWHP system is particularly appealing because the presence of shallow aquifers. This means significant savings of economic resources in terms of pumping energy and drilling costs. Nevertheless, vast areas of the Italian coastlines, as well as those of other Mediterranean countries, are often affected by seawater intrusion and hence are ruled by restrictive laws aimed to protect the groundwater quality and quantity.

In this chapter the environmental impacts, associated with the exploitation of low enthalpy geothermal resources, were assessed. For the purpose, a costal karst area in Southern Italy affected by seawater intrusion was investigated. A detailed characterization of the area was achieved in terms of geological, hydrogeological, geochemical and meteorological parameters. Moreover, the influence of an open-loop geothermal systems on the sea water intrusion was also studied by means of a long-term pumping test.

The investigated portion of aquifer was found to have a high hydraulic conductivity, as well as high and fast recharge rates, highlighting a good productivity of aquifer. The temperature of groundwater, reaching over 20 °C near the coast, was particularly useful for direct use especially for the space heating and cooling.

The long pumping test, lasted for 16 days, not affected the lowering of the water table that naturally occurs in the dry period. On the contrary, the reinjection of the extracted groundwater into the surface water drainage network partially restored the water table. The test also not detected any quality degradation of groundwater induced by pumping.

The quality of groundwater showed that the level of contamination in the investigated area was generally high both because of the presence of urban and industrial pollution and because of the presence of the seawater intrusion. The absence of a strong competition for use of groundwater makes them available for geothermal use. An extensive utilization of natural heat for the space cooling is also justified considering the local climate characteristics of the area that cause a peak of thermal energy demand in summer.