Assessment of groundwater exploitation and land subsidence development in the Toluca aquifer system, Mexico

EbookRegional land subsidence accompanying groundwater abstraction in the Toluca aquifer-system is a challenge for managing groundwater resources and mitigating associated hazards. In order to improve this situation, groundwater management scenarios for the Toluca Valley are examined with a three dimensional groundwater flow model coupled to a one dimensional compaction module. Subsequently, the land subsidence evolution was investigated by integrating SAR interferometry and geological and hydrogeological data to shed insight on the underlying processes governing subsidence. The results indicate that continuing at current rates of water consumption will lead to subsidence of more than 1.6 m over a 40 year period (2010–2050). Completely stopping exports to Mexico City is not the most important factor in controlling subsidence because the pumping system is mostly located in regions with low clay content, where subsidence is lower. However, decreasing exports by half and relocating the pumping centres to low-clay-content areas does have a positive effect on the overall water budget and subsidence. From 2003 to 2016, groundwater level declines of up to 1.6 m/yr, land subsidence up to 77 mm/yr, and major infrastructure damages are observed. Groundwater level data show highly variable seasonal responses according to their connectivity to recharge areas. However, the trend of groundwater levels consistently range from −0.5 to −1.5 m/yr regardless of the well location and depth. By analysing the horizontal gradients of vertical land subsidence, we provide a potential ground fracture map to assist in future urban development planning in the Toluca Valley. The approach taken in this study could be applied to their locations with similar problems in order to determine the most viable option for water supply.CONACyT, Institute for Groundwater Research, University of Guelph UAE

Prediction of sustainable management and associated land subsidence features in the Toluca aquifer system

EbookRegional land subsidence accompanying groundwater abstraction in the Toluca aquifer-system is a challenge for managing groundwater resources and mitigating associated hazards. In order to improve this situation, groundwater management scenarios for the Toluca Valley are examined with a three dimensional groundwater flow model coupled to a one dimensional compaction module. Subsequently, the land subsidence evolution was investigated by integrating SAR interferometry and geological and hydrogeological data to shed insight on the underlying processes governing subsidence. The results indicate that continuing at current rates of water consumption will lead to subsidence of more than 1.6 m over a 40 year period (2010–2050). Completely stopping exports to Mexico City is not the most important factor in controlling subsidence because the pumping system is mostly located in regions with low clay content, where subsidence is lower. However, decreasing exports by half and relocating the pumping centres to low-clay-content areas does have a positive effect on the overall water budget and subsidence. From 2003 to 2016, groundwater level declines of up to 1.6 m/yr, land subsidence up to 77 mm/yr, and major infrastructure damages are observed. Groundwater level data show highly variable seasonal responses according to their connectivity to recharge areas. However, the trend of groundwater levels consistently range from −0.5 to −1.5 m/yr regardless of the well location and depth. By analysing the horizontal gradients of vertical land subsidence, we provide a potential ground fracture map to assist in future urban development planning in the Toluca Valley. The approach taken in this study could be applied to their locations with similar problems in order to determine the most viable option for water supply.CONACyT UAEM Institute for Groundwater Research, University of Guelp

Glacial Melt in the Canadian Rockies and Potential Effects on Groundwater in the Plains Region

The prevailing concern in the Western Canadian Plains is that glaciers from the eastern Canadian Rocky Mountains (CRM) are losing mass, thus affecting groundwater recharge in the Plains. The generally accepted hypothesis is that those glaciers are the geological source of groundwater for aquifers located in the Plains. The aquifers located in this region, close to the eastern part of the Rockies, represent a major source of water for the local population. It is believed that aquifer recharge originates as infiltration from snowmelt and ice in the Front Ranges of the eastern Rockies. A growing concern relates to the significant glacier melt estimated from glacier mass balances, which indicate that glaciers and ice fields have experienced considerable mass losses over the last 15 years, between 1 and 5 km3 per year, thus reducing recharge. However, deep groundwater flow under melting glacier conditions in mountainous regions is poorly understood. In this study, three 2D numerical hydrogeological models are built in order to simulate the groundwater flow under the glaciers from the Main and Front Ranges of the CRM and the Plains in the province of Alberta, Canada. Numerical results and a sensitivity analysis indicate that up to three different regional groundwater-flow systems are present in the region. These systems reveal the time- and space-scales associated with the combination of a mountainous region, foothills, Plains, and deep geological conditions. Based on the current knowledge of the hydrogeology of the study area and numerical modelling results, it is highly unlikely that the melting of glaciers affects groundwater in the Plains in the immediate future. The contribution of glacier water in the eastern part of the Rockies is time-dependent with delayed groundwater flows of 1000s of years in the Front ranges, 1000s to 100,000s of years in the foothills and Foreland; and 100,000s to millions of years to the Plains, at the regional scale

Characterization and Quantification of Mining-Related “Naphthenic Acids” in Groundwater near a Major Oil Sands Tailings Pond

The high levels of acid extractable organics (AEOs) containing naphthenic acids (NAs) found in oil sands process-affected waters (OSPW) are a growing concern in monitoring studies of aquatic ecosystems in the Athabasca oil sands region. The complexity of these compounds has substantially hindered their accurate analysis and quantification. Using a recently developed technique which determines the intramolecular carbon isotope signature of AEOs generated by online pyrolysis (δ¹³C_pyr), natural abundance radiocarbon, and high resolution Orbitrap mass spectrometry analyses, we evaluated the sources of AEOs along a groundwater flow path from a major oil sands tailings pond to the Athabasca River. OSPW was characterized by a δ¹³C_pyr value of approximately −21‰ and relatively high proportions of O₂ and O₂S species classes. In contrast, AEO samples located furthest down-gradient from the tailings pond and from the Athabasca River were characterized by a δ¹³C_pyr value of around −29‰, a greater proportion of highly oxygenated and N-containing compound classes, and a significant component of nonfossil and, hence, non-bitumen-derived carbon. The groundwater concentrations of mining-related AEOs determined using a two end-member isotopic mass balance were between 1.6 and 9.3 mg/L lower than total AEO concentrations, implying that a less discriminating approach to quantification would have overestimated subsurface levels of OSPW. This research highlights the need for accurate characterization of “naphthenic acids” in order to quantify potential seepage from tailings ponds