The Tula Valley receives untreated wastewater from Mexico City for agricultural irrigation, half of which infiltrates to aquifers from where drinking water is extracted. Samples of wastewater and infiltrated water from three areas of the valley were analyzed for microorganisms, organic micropollutants, and some basic parameters. Concentrations of microorganisms in the infiltrated water were generally very low but the incidence of fecal coliforms (present in 68% of samples), somatic bacteriophages (36%), Giardia spp. (14%), and helminth eggs (8%) suggested a health risk. Organic micropollutants, often present at high concentrations in the wastewater, were generally absent from the infiltrated water except carbamazepine which was in 55% of samples (up to 193 ng/L). There was no correlation between carbamazepine concentrations and the presence of microorganisms but highest concentrations of carbamazepine and boron coincided. A treatment such as nanofiltration would be necessary for the infiltrated water to be a safe potable supply.

The dichlobenil metabolite BAM (2,6-dichlorobenzamide) is frequently detected in aquifers e.g. in Denmark despite the mother compound dichlobenil was banned here since 1997. BAM mineralization was investigated at environmentally relevant concentrations in sediment samples. Undisturbed sediment cores with known dichlobenil application were collected from topsoil to 8.5 m below surface resulting in 57 samples hereof 4 aquifer samples. Mineralization was only substantial (>10%) in the uppermost meter of the unsaturated zone. Microbial adaptation, observed as faster mineralization in pre-exposed than in pristine sediments from the same location, was only evident in sandy sediment where dichlobenil was still present, but not in clayey sediments. Higher initial concentrations (1–5000 μg/kg) did not stimulate mineralization in pristine clayey or sandy sediments, or in pre-exposed sand. However, in pre-exposed clay mineralization was stimulated at high concentrations. Furthermore BAM was for the first time mineralized in aerobic aquifer sediments from different BAM-contaminated groundwater locations.

Intensive land development as a result of the rapidly growing tourism industry in the “Riviera Maya” region of the Yucatan Peninsula, Mexico may result in contamination of groundwater resources that eventually discharge into Caribbean coastal ecosystems. We deployed two types of passive sampling devices into groundwater flowing through cave systems below two communities to evaluate concentrations of contaminants and to indicate the possible sources. Pharmaceuticals and personal care products accumulated in the samplers could only have originated from domestic sewage. PAHs indicated contamination by runoff from highways and other impermeable surfaces and chlorophenoxy herbicides accumulated in samplers deployed near a golf course indicated that pesticide applications to turf are a source of contamination. Prevention and mitigation measures are needed to ensure that expanding development does not impact the marine environment and human health, thus damaging the tourism-based economy of the region.

Arsenic and other trace element concentrations were determined for tube-well water collected in the Lao PDR provinces of Attapeu, Bolikhamxai, Champasak, Savannakhet, Saravane, and Vientiane. Water samples, especially from floodplain areas of central and southern Laos, were significantly contaminated not only with As, but with B, Ba, Mn, U, and Fe as well. Total As concentrations ranged from <0.5μgL⁻¹ to 278μgL⁻¹, with over half exceeding the WHO guideline of 10μgL⁻¹. 46% of samples, notably, were dominated by As(III). Samples from Vientiane, further north, were all acceptable except on pH, which was below drinking water limits. A principal component analysis found associations between general water characteristics, As, and other trace elements. Causes of elevated As concentrations in Lao tube wells were considered similar to those in other Mekong River countries, particularly Cambodia and Vietnam, where young alluvial aquifers give rise to reducing conditions.

Little is known about the importance of drainage/irrigation channels and biogeochemical processes in arsenic distribution of shallow groundwaters from the Hetao basin. This investigation shows that although As concentrations are primarily dependent on reducing conditions, evaporation increases As concentration in the centre of palaeo-lake sedimentation. Near drainage channels, groundwater As concentrations are the lowest in suboxic-weakly reducing conditions. Results demonstrate that both drainage and irrigation channels produce oxygen-rich water that recharges shallow groundwaters and therefore immobilize As. Groundwater As concentration increases with a progressive decrease in redox potential along the flow path in an alluvial fan. A negative correlation between SO₄ ²⁻ concentrations and δ³⁴S values indicates that bacterial reduction of SO₄ ²⁻ occurs in reducing aquifers. Due to high concentrations of Fe (>0.5mgL⁻¹), reductive dissolution of Fe oxides is believed to cause As release from aquifer sediments. Target aquifers for safe drinking water resources are available in alluvial fans and near irrigation channels.

Mining activities and industries have created nickel (Ni) contaminations in many parts of the world. The objective of this study is to increase our understanding of Ni adsorption and Nickel–Aluminium Layered Double Hydroxide (Ni–Al LDH) precipitation to reduce Ni mobility in a sandy soil aquifer. At pH ≥7.2 both adsorption and Ni–Al LDH precipitation occurred. In batch experiments with the sandy soil up to 70% of oxalate-extractable Al was taken up in LDH formation during 56 days. In a long term column experiment 99% of influent Ni was retained at pH 7.5 due to Ni adsorption (≈34%) and Ni–Al LDH precipitation (≈66%) based on mechanistic reactive transport modeling. The subsequent leaching at pH 6.5 could be largely attributed to desorption. Our results show that even in sandy aquifers with relatively low Al content, Ni–Al LDH precipitation is a promising mechanism to immobilize Ni.

The objective of this study is to develop a method for using the single-well natural gradient drift test (SWNGDT) in the field to assess in situ aerobic cometabolism of trichloroethylene (TCE) and to analyze microbial community changes. The SWNGDT was performed in a monitoring well installed in a TCE-contaminated aquifer in Wonju, South Korea. The natural gradient drift biostimulation test (NGDBT) and surrogate test (NGDST) were performed by injecting dissolved solutes (bromide (a tracer), toluene (a growth substrate), ethylene (a nontoxic surrogate substrate to probe for TCE transformation activity), dissolved oxygen (DO, an electron acceptor), and nitrate (nutrient)) into the aquifer. Push–pull blocking tests (PPBT) were also performed to examine whether the monooxygenase of toluene oxidizers is involved in the degradation of toluene and the transformation of ethylene. Through the NGDBT, NGDST, and PPBT, we confirmed that the addition of toluene and oxygen in these field tests stimulated indigenous toluene utilizers to cometabolize aerobically TCE, with the following results: (1) the observed simultaneous utilization of toluene and DO; (2) the transformation of ethylene to ethylene oxide and propylene to propylene oxide; and (3) the transformation of TCE. Furthermore, the results of restriction fragment length polymorphism suggested that the microbial community shifts and the microbes capable of transforming TCE are stimulated by injecting the growth substrate, toluene.

This study focuses on spatial and temporal nutrient pollution of groundwater in the unconfined sandy aquifers of Kalpitiya peninsula, Sri Lanka, where agricultural activities are intense. The study covers two consecutive dry and rainy seasons during the period from 2008 to 2010. Nitrate is the dominant nutrient pollutant in groundwater. The values of Nitrate-N contents ranged from 0.60 to 212.40 mg/L in the dry seasons and 0.20–148.50 mg/L in rainy seasons. Phosphate in groundwater ranged from 0.20 to 5.70 mg/L in dry seasons and 0.04–10.35 mg/L with few exceptions in rainy seasons. About 50% of the studied water samples had Nitrate-N concentrations above WHO drinking water guideline values both in dry and rainy periods. These high concentrations were recorded from wells in agricultural lands. Although there is a slight decrease in the Nitrate-N concentrations at random in rainy seasons, an increasing trend of average concentrations became evident over the study period as a whole, probably indicating building up of Nitrate-N in groundwater in the vegetable growing areas. The spatial distribution of Nitrate-N too shows a good match of high Nitrate-N bearing zones with vegetable cultivated areas indicating intensive leaching from application of excessive chemical fertilizers. High Nitrate-N zones also showed fairly steady lateral distribution indicating slow lateral mobility of Nitrate-rich groundwater probably due to low hydraulic gradients. Low phosphate concentrations in both groundwater and surface soils either indicates their less use in the area or that the available phosphate is leached and removed from the aquifer water and (sandy) soil solutions and probably adsorbed in clayey deeper horizons. Low concentrations of major cations (especially K, Ca, and Na) indicate less impact on cation concentrations in groundwater by the fertilizer application or sea water intrusions/up-coning.

Poorly constructed wells (leaky or without a gravel pack) and abandoned wells can behave as conduits for the interconnection of aquifers at different depths and facilitate the transfer of contaminants between these aquifers. This is the case with Campo de Cartagena (SE Spain) where the primary land use is intensive irrigated agriculture, along with a high density of wells. The unconfined aquifer is heavily impacted by a high concentration of nitrate associated with agricultural activities. The present work provides a methodological approach to evaluate the impact of the unconfined aquifer on the water quality of the confined aquifer caused by leaky wells in high-density areas of production wells. The research approach included the use of geochemical and isotopic tools; specifically, nitrate was used as a tracer for evaluating the impact, and the code MIX_PROGRAM was used for mixing calculations. Results show an increase of the impact of the unconfined aquifer on the confined aquifer along the groundwater flow direction toward the coast, although this general pattern is controlled by local factors (pumping, intensity of agricultural practices, density of wells, and groundwater residence time).

Diffused petroleum and chlorinated hydrocarbon contamination was detected in a sandy aquifer below a chemical plant in Southern Italy. The contamination was due to underground leaking tanks and pipes. The site is located near the shore line and is bordered by canals which, in combination with pumping wells, control the groundwater flow direction toward the sea. In this study, a comprehensive three-dimensional flow model was developed and calibrated to simulate the general groundwater flow system and to individuate a flow line. On this latter, a detailed field investigation was performed in order to determine the fate of dissolved hydrocarbons. Depth profiles obtained from multi-level samplers located along the modelled flow line, including measurements of hydrocarbons, all major ions and dissolved gasses, were used to constrain the conceptual model. These data were then included into a two-dimensional transport model in order to verify the efficacy of the hydraulic barrier (HB) in preventing the hydrocarbon plume to reach the shore line. Two different approaches were used in the transport simulation, one accounting for density-dependent flow and the other not. The calibrated models show that the plume length and consequently, the submarine groundwater discharge of contaminants is slightly different for the two approaches. For the simulation not accounting for the density contrast between freshwater and saltwater, the mass of contaminant discharged downstream to the HB was underestimated and also the reconstructed plume geometry was different than the observed. Moreover, the reconstruction of the saltwater intrusion interface (SWII) with the two different approaches was substantially different. This study demonstrates that at field site, variable density processes should be carefully taken into account not only when the modelling is devoted to the reconstruction of the SWII but also when the modelling is targeting the fate of hydrocarbons at sites affected by SWII, in order to provide accurate data on which soundly environmental management of the coastal zone can be based.