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In the arid to semi-arid district of Chengcheng, Weinan City, in central Shaanxi Province, diminishing groundwater reserves in the shallow Quaternary (QLB) aquifer and elevated fluoride in the similarly shallow Permo-Triassic (PTF) aquifer, have promoted interest in the development of groundwater resources in the deep but poorly understood Cambrian-Ordovician carbonate aquifer system (COC). To investigate the origin of the COC groundwaters and the relationship between the deep and shallower systems, a hydrochemical study was undertaken involving 179 major and minor ion analyses, 39 stable isotope analyses (δD and δ18 O), and 14 carbon isotope analyses (14 C and δ13 C). PHREEQC 3.0 was used to investigate mixing. Hydrochemical data support the presence of a well-connected regional flow system extending southwards from the more mountainous north. Stable isotope data indicate that the COC groundwaters originate as soil zone infiltration, under a much cooler regime than is found locally today. This is confirmed by 14 C, which indicates the groundwater to be palaeowater recharged during the late Pleistocene (∼10-12 ka B.P.). The presence of nitrate in the COC groundwaters suggests leakage from overlying shallow aquifers currently provides an additional source of COC recharge, with major faults possibly providing the primary pathways for downward vertical flow.

The Great Lakes Basin (GLB) holds vast reserves of groundwater, the great majority of which eventually drains to the lakes. Urban growth significantly affects both the quality and quantity of this groundwater and thereby represents a potential threat to the long-term viability of the Great Lakes hydrologic system. Urban areas import, manufacture, store, transport, and utilise large volumes of chemicals, a proportion of which inevitably finds its way to the shallow sub-surface. In many cases, potentially polluting chemicals are applied directly to urban surfaces (e.g. as road salts, fertilizers and pesticides), are stored in the subsurface (e.g. gasoline tanks) or are released to the subsurface (e.g. septic systems). Because most of the basin's larger urban areas rely almost exclusively on lake-based supplies, very little attention is given to the accumulation of contaminants in shallow urban groundwaters and the serious risks they pose. Assessment of the problem is complicated by the widespread use of urban fill and a complex network of drains, pipes and tunnels that create “urban karst”, a shallow artificial aquifer, unique to urban settings, that exerts a major, yet often unpredictable influence on groundwater flow and contaminant transport. Management of ground water pollution, and its impact on the receiving Great Lakes, will require rigorous audits of all urban sources of contamination together with the development and calibration of groundwater flow and transport models that will enable the fate of urban pollutants to be reliably predicted even when groundwater is not used for supply.

Because of land subsidence in Nantong City caused by aquifer pumping, studies have been undertaken using a 3D groundwater flow model linked to a 1D land subsidence model to optimize the rates and distribution of abstraction. Model results to the end of 2022 show that the current pumping regime will cause subsidence rates to exceed established control targets by over 40% locally. However, a radical redistribution of pumping wells including the greater use of shallower aquifers will potentially allow annual yields to be increased threefold to around 128 × 106 m3 without exceeding those targets. The results of this work have important implications for the sustainable development of groundwater resources in Nantong City and demonstrate the considerable benefits of modelling for proactive aquifer management and protection against subsidence.

Groundwater is one of the main sources of drinking and agricultural water in arid and semi-arid regions but is becoming increasingly threatened by contamination. Vulnerability mapping has been used for many years as an effective tool for assessing the potential for aquifer pollution and the most common method of intrinsic vulnerability assessment is DRASTIC ( D epth to water table, net R echarge, A quifer media, S oil media, T opography, I mpact of vadose zone and hydraulic C onductivity). An underlying problem with the DRASTIC approach relates to the subjectivity involved in selecting relative weightings for each of the DRASTIC factors and assigning rating values to ranges or media types within each factor. In this study, a clustering technique is introduced that removes some of the subjectivity associated with the indexing method. It creates a vulnerability map that does not rely on fixed weights and ratings and, thereby provides a more objective representation of the system’s physical characteristics. This methodology was applied to an aquifer in Iran and compared with the standard DRASTIC approach using the water quality parameters nitrate, chloride and total dissolved solids (TDS) as surrogate indicators of aquifer vulnerability. The proposed method required only four of DRASTIC’s seven factors – depth to groundwater, hydraulic conductivity, recharge value and the nature of the vadose zone, to produce a superior result. For nitrate, chloride, and TDS, respectively, the clustering approach delivered Pearson correlation coefficients that were 15, 22 and 5 percentage points higher than those obtained for the DRASTIC method.

Throughout China, both coal and water are very important resources; however, serious conflict can arise between mining of deep coal reserves and essential aquifer resources. The problem is particularly severe in eastern China where a deep, thick, and productive Ordovician limestone aquifer immediately underlies Permo-Carboniferous coal-bearing sediments and poses a serious threat to the safety of coal exploitation. The problems are caused by high water pressures in the Ordovician aquifer and the risk of catastrophic flooding at the coalface caused by strong upward flow across a relatively thin aquitard. The problem can be alleviated by mine dewatering, but this generates large volumes of contaminated wastewater that require safe disposal. In a feasibility study carried out at Yanzhou coalfield, eastern China, hydrogeological studies have been undertaken to explore options for utilizing water pumped during mining operations, thus making more efficient use of the Ordovician groundwater reserves. The groundwaters are recharged at outcrops but readily become SO4·Cl–Ca·Mg in character with TDS increasing considerably with depth. Focusing on the Xinglongzhuang coal mine, test pumping and development of a transient groundwater flow model of the system have allowed alternative strategies for pressure management to be investigated. The study shows that coal-mining operations can proceed safely with as few as six underground dewatering boreholes removing 1800 m3/h. Moreover, the extracted water could be utilized after treatment to reduce sulfate concentrations. The coordinated exploitation approach demonstrated in this study provides a good example of wise environmental stewardship that other extractive industries would do well to consider.