Impact Groundwater Quality Research Articles

Potential use of a new nitrogen trading tool to assess nitrogen management practices to protect groundwater quality

The Nitrogen Loss and Environmental Assessment Package (NLEAP) with Geographic Information Systems (GIS), version 5.0, with a Nitrogen Trading Tool (NTT) is a model that can be used to integrate site-specific information about soils, weather, and management to conduct quick assessments of nitrogen (N) management practices to increase N use efficiencies while minimizing N losses. This tool is a valuable resource that can be used to conduct quick assessments of risky combinations of management practices and landscapes across several fields to identify hot spot areas that are susceptible to nitrogen losses. The NLEAP GIS 5.0 NTT can quickly assess the temporal and spatial N losses of a given scenario simulated across all the fields and subtract them from the baseline scenario. This allows the user to compare scenarios and use the tool as a nitrogen trading tool to assess the potential reductions in nitrate leaching or emissions of nitrous oxide that may be achieved with a given management practice. The tool can be used to quickly assess the potential to use management practices to reduce the potential losses of reactive nitrogen to groundwater and the atmosphere, as well as the potential to trade these reductions in reactive nitrogen in water or air quality markets. It can quickly calculate the potential savings (reductions in) direct and indirect N2O emissions (and the carbon sequestration equivalent) achieved due to improvements in N management practices. The carbon sequestration equivalent could also be traded in air quality markets. There is potential to use the tool to assess which areas are more sensitive to nitrate leaching, which can impact groundwater quality, and to assess what would be the best management practices to implement in these areas for protection of groundwater quality.

Analysis of Potential Risks Associated with Urban Stormwater Quality for Managed Aquifer Recharge.

Managed aquifer recharge (MAR) can be used to increase storage and availability of groundwater resources, but water resources available for recharge are constrained due to a surface water shortage. Alternative resources, like stormwater, are receiving increasing attention as sustainable resources for reuse in MAR. However, pollutants in stormwater can impact groundwater quality, and cause clogging of the infiltration system. Based on the stormwater data in the literature, the physicochemical stormwater properties of data were analyzed. The results showed that concentrations of pollutants from different underlying surfaces varied widely. The main pollutants of stormwater were as follows: Total suspended particles (TSSs), organic matter represented by the chemical oxygen demand (COD), nutrients (total nitrogen, TN; total phosphorus, TP; and NH3-N), and metals (Zn, Pb, Cu, Cd, Fe, and Mn). Based on the simulation of TOUGHREACT, the contamination risk of pollutants for each type of stormwater was assessed. The risk of contamination was divided into four categories due to the different migration times of ions through the sand column. The iron ion has the highest risk of contamination, followed by Zn and Mn, and the contamination risk of nutrients and other metals (Pb, Cu, and Cd) are relatively low. Besides, the physical, biological, and chemical clogging risk were evaluated. The physical clogging potential of all types of stormwater is very high because of the high concentration of TSS. According to the concentration of TN that can spur the growth of bacteria and algae, the relative risk of biological clogging for stormwater is greenbelt stormwater < road stormwater < roof stormwater. However, only road stormwater has high chemical clogging due to the existence of iron, which can generate precipitation that blocks the pore volume.

Effects of groundwater metal contaminant spatial distribution on overlaying kriged maps.

Groundwater is a major source of drinking water for many Canadians, and contamination by heavy metals poses a significant risk to people and the environment. In this study, three water quality indices are studied in the vicinity of an unlined landfill in a semiarid climate. The study investigates indices using geostatistical analysis and ordinary kriging. This study employs a novel coupling technique in order to compare the index-based maps to a groundwater quality map from overlapping heavy metal kriged maps. A total of 11 heavy metals were evaluated in preliminary analysis, but only four (Mn, As, Fe, and U) had higher concentrations than allowable limits in some or all of the monitoring wells at the site. Results from mean-based classification of indices suggest the aquifer in proximity to the landfill has been impacted by metal contaminants. Kriged maps show that the spatial variations of Mn and U are similar, while results of Fe and As are also similar. However, the two sets of maps have distinctly different patterns. Maps for indices show an elevated plateau extending from the unlined landfill to the southeast corner, implying that the landfill may have negatively impacted groundwater quality. A groundwater quality map is developed by overlaying the heavy metal maps. The resulting map shows that the north and west parts of the study have lower groundwater pollution with respect to metal contaminants. The groundwater quality map may be more applicable for practitioners who need comprehensive water quality measurement.

Understanding the influence of industrial and agricultural land uses on groundwater quality in semiarid region of Solapur, India

A comprehensive groundwater quality investigation of 98 representative groundwater samples collected from Chincholi MIDC area has been carried out to identify the impact of different land uses on groundwater quality during pre- and post-monsoon seasons of 2014. Hydrochemical results confirm that groundwater is slightly alkaline and hard to very hard type. The contents of TDS, Na, Ca, NO3 and K exceeded the permissible limit prescribed by BIS in industrial land use in both the seasons. The ionic ratios suggest that silicate weathering is dominant hydro-geochemical process followed by carbonate weathering and ion exchange. The correlation and principal component analysis identifies the relation among different parameters and mixed sources of ionic constituents. The cluster analysis differentiates the samples affected due to anthropogenic activities through the classification of groundwater samples in different clusters, and principal component analysis identifies the EC, Ca, Mg, Cl, NO3, TH and TDS as major causative factors. The spatiotemporal maps depict the enrichment of specific ions mainly observed at industrial and agricultural sites. Samples located in industrial area vicinity are not suitable for drinking and irrigation. From an industrial perspective, groundwater is corrosive and incrusting in nature. Groundwater sample numbers 14 and 15 located in agricultural area and 29, 30, 41, 42, 43 and 47 in the vicinity of industrial area found problematic represent that the change in water quality is caused due to alteration in land use type. Therefore, it becomes immensely important to identify the negatively impacted groundwater quality and mitigate the cause.

Assessment of future groundwater quality using GIS for Bhimrad area of Surat City (India)

Declination of water quality has become a global issue of concern as with the growth of human population, industrial and agricultural activities expand. The Bhimrad area of Surat City (Gujarat) is highly affected by ground water pollution because of its location in the vicinity of the industrial zone. There exists a creek adjoining Arabian Sea, in which all the wastewater of the city, including that of the industrial area is discharged, thus polluting land and other sources of water in the surrounding areas. This research paper aims to analyse groundwater dilution used under the threat of pollution by identifying the prospects for improving the quality through artificial recharging that may impact groundwater quality. Calculation of percentage reduction in the groundwater quality parameters after recharging was carried out through which estimated improvement in GWQI using GIS, GWQI after recharging is analysed for the years 2015 to 2050.

Assessment of future groundwater quality using GIS for Bhimrad area of Surat City (India)

Declination of water quality has become a global issue of concern as with the growth of human population, industrial and agricultural activities expand. The Bhimrad area of Surat City (Gujarat) is highly affected by ground water pollution because of its location in the vicinity of the industrial zone. There exists a creek adjoining Arabian Sea, in which all the wastewater of the city, including that of the industrial area is discharged, thus polluting land and other sources of water in the surrounding areas. This research paper aims to analyse groundwater dilution used under the threat of pollution by identifying the prospects for improving the quality through artificial recharging that may impact groundwater quality. Calculation of percentage reduction in the groundwater quality parameters after recharging was carried out through which estimated improvement in GWQI using GIS, GWQI after recharging is analysed for the years 2015 to 2050.

Applicability of the dual isotopes δ15N and δ18O to identify nitrate in groundwater beneath irrigated cropland

Identification of the nitrate sources that adversely impact groundwater quality is a necessary first step in the control of this major worldwide pollutant. The impact of nitrate leachate from urea-ammonium nitrate (UAN) (50% urea-N, 25% ammonium-N, 25% nitrate-N) fertilizer, whose use has increased dramatically in the last three decades largely because it can be applied through sprinkler irrigation systems to corn in all growth stages, is investigated. The dual isotopes δ15NNO3 and δ18ONO3 were measured in groundwater samples from 39 irrigation wells in two intensively sprinkler-irrigated, corn-growing areas of Nebraska with nitrate-contaminated (N > 10 mg/L) groundwater and documented UAN use to ascertain whether nitrified ammonia and nitrate fertilizers can be distinguished in the High Plains aquifer. The areas, which are highly vulnerable to nitrate leaching and differ only in the composition and thickness of their unsaturated zones, are uniquely suited to provide scientific evidence of the feasibility of identifying nitrate fertilizer leachate in groundwater and thereby add significantly to the small body of existing and inconclusive data. The dual isotope method (DIM) results indicate that the nitrate contamination in 38 wells is mostly nitrified ammonium fertilizer. Most importantly, nitrate fertilizer from UAN was not identified isotopically in groundwater beneath almost all fields with documented heavy UAN use. This could be a potentially valuable finding for fertilizer management or it could convey limitations on the appropriateness of the DIM for nitrate fertilizer source identification in groundwater. Slightly enriched δ15NNO3 values in a few wells coincide with the practice of wintering cattle on corn stubble, which reportedly occurred more frequently in one focus area. The absence of natural soil-N leachates and denitrification in groundwater enabled an apparently reliable identification of manure leachates in both areas.

Integrated Deep Soil N and Groundwater Isotope Investigation of N Sources Captured by Municipal Wells

AbstractIdentification of major nitrate sources that adversely impact groundwater quality in municipal well capture zones in areas of emerging nitrate contamination is essential to minimize leaching and prevent exceedance of the nitrate drinking water standard. Vertical profiles of nitrate leachate in deep soils provide an estimate of the amount of nitrate in transit beneath irrigated, row‐cropped fields; depths of peak leachate; and the approximate rate of downward movement. Profiles of pore‐water soil‐nitrate concentrations in thick 60‐feet (~18 m), fine‐textured soils near Hastings, Nebraska clearly indicate that considerably more nitrate leached beneath furrow‐irrigated than center‐pivot irrigated fields. Peak leaching appeared to correlate with recorded periods of poor weather conditions during some growing seasons and may best be controlled by “spoon feeding” fertilizer to the crop through the sprinkler irrigation system at times of nutrient need. The presence of trace levels of atrazine and deethylatrazine to 60 feet (18 m) in core samples indicates that larger, more complex anthropogenic molecules also leach through the fine‐textured soils. The light δ15NNO3 values in the surficial groundwater beneath fertilized and irrigated cropland indicate that ammonium fertilizer is a major N source and suggest that the natural soil‐N contribution is negligible. δ15NNO3 values were most enriched in irrigation wells located within municipal well capture zones downgradient of a large feedlot. Dual isotope method (DIM) δ15NNO3 and δ18ONO3 values suggest that the Hastings’ municipal wells farther downgradient are contaminated with a mixture of nitrate from manure and commercial ammonium‐based fertilizer. DIM values indicate an absence of denitrification, which has implications for long‐term management of the water resources.

Impacts of a Rural Subdivision on Groundwater Quality: Results of Long-Term Monitoring.

A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78-acre (32 ha) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002 to 2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/L and some detections of the herbicide atrazine. Our 12-year study shows that the transition from agricultural to residential land use has changed groundwater quality in both negative and positive ways. Although groundwater elevations showed typical seasonal fluctuations each year, there were no measurable changes in groundwater levels or general flow directions during the 12-year study period. Chloride values increased in many wells, possibly as a result of road salting or water softener discharge. Nitrate concentrations varied spatially and temporally over the study period, with some initial concentrations substantially above the drinking water standard. In some wells, nitrate and atrazine levels have declined substantially since agriculture ceased. However, atrazine was still present at trace concentrations throughout the site in 2014. Wastewater tracers show there are small but detectable impacts from septic effluent on groundwater quality. Particle traces based on a groundwater flow model are consistent with the hypothesis that septic leachate has impacted groundwater quality.

Coal-derived compounds and their potential impact on groundwater quality during coalbed methane production.

Coalbed methane (CBM) is an important unconventional energy source and accounts for a substantial portion of the overall natural gas production in the USA. The extraction of CBM generates significant amounts of produced water, where the withdrawal of groundwater may disturb the subsurface environment and aquifers. The release of toxic recalcitrant compounds from the coal seam is of great concern for those who use groundwater for irrigation and potable water sources. Experiments were conducted that determined a small fraction of coal carbon can be extracted and solubilized in water during the CBM formation and production. These soluble components included long-chain alkanes, aromatic hydrocarbons, and humic compounds. Biometer flask assays demonstrated that these compounds are bioamenable and can be potentially degraded by microorganisms to produce methane and carbon dioxide, where these biodegradation processes may further impact groundwater quality in the coal seam.

Using geographic distribution of well-screen depths and hydrogeologic conditions to identify areas of concern for contaminant migration through inactive supply wells

Contaminant migration through inactive supply wells can negatively affect groundwater quality and the combined effects from groups of such wells may cause greater impacts. Because the number of wells in many basins is often large and the geographic areas involved can be vast, approaches are needed to estimate potential impacts and focus limited resources for investigation and corrective measures on the most important areas. One possibility is to evaluate the geographic distribution of well-screen depths relative to hydrogeologic conditions and assess where contaminant migration through wells may be impacting groundwater quality. This approach is demonstrated for a geographically extensive area in the southern Central Valley of California, USA. The conditions that lead to wells acting as conduits for contaminant migration are evaluated and areas where the problem likely occurs are identified. Although only a small fraction of all wells appear to act as conduits, potential impacts may be significant considering needs to control nonpoint-source pollution and improve drinking water quality for rural residents. Addressing a limited number of areas where contaminant migration rates are expected to be high may cost-effectively accomplish the most beneficial groundwater quality protection and improvement. While this work focuses on a specific region, the results indicate that impacts from groups of wells may occur in other areas with similar conditions. Analyses similar to that demonstrated here may guide efficient investigation and corrective action in such areas with benefits occurring for groundwater quality. Potential benefits may justify expenditures to develop the necessary data for performing the analyses.

Hydraulic fracturing near domestic groundwater wells

Hydraulic fracturing operations are generating considerable discussion about their potential to contaminate aquifers tapped by domestic groundwater wells. Groundwater wells located closer to hydraulically fractured wells are more likely to be exposed to contaminants derived from on-site spills and well-bore failures, should they occur. Nevertheless, the proximity of hydraulic fracturing operations to domestic groundwater wells is unknown. Here, we analyze the distance between domestic groundwater wells (public and self-supply) constructed between 2000 and 2014 and hydraulically fractured wells stimulated in 2014 in 14 states. We show that 37% of all recorded hydraulically fractured wells stimulated during 2014 exist within 2 km of at least one recently constructed (2000-2014) domestic groundwater well. Furthermore, we identify 11 counties where most ([Formula: see text]50%) recorded domestic groundwater wells exist within 2 km of one or more hydraulically fractured wells stimulated during 2014. Our findings suggest that understanding how frequently hydraulic fracturing operations impact groundwater quality is of widespread importance to drinking water safety in many areas where hydraulic fracturing is common. We also identify 236 counties where most recorded domestic groundwater wells exist within 2 km of one or more recorded oil and gas wells producing during 2014. Our analysis identifies hotspots where both conventional and unconventional oil and gas wells frequently exist near recorded domestic groundwater wells that may be targeted for further water-quality monitoring.

Groundwater Quality: Analysis of Its Temporal and Spatial Variability in a Karst Aquifer.

This study develops an approach based on hierarchical cluster analysis for investigating the spatial and temporal variation of water quality governing processes. The water quality data used in this study were collected in the karst aquifer of Yucatan, Mexico, the only source of drinking water for a population of nearly two million people. Hierarchical cluster analysis was applied to the quality data of all the sampling periods lumped together. This was motivated by the observation that, if water quality does not vary significantly in time, two samples from the same sampling site will belong to the same cluster. The resulting distribution maps of clusters and box-plots of the major chemical components reveal the spatial and temporal variability of groundwater quality. Principal component analysis was used to verify the results of cluster analysis and to derive the variables that explained most of the variation of the groundwater quality data. Results of this work increase the knowledge about how precipitation and human contamination impact groundwater quality in Yucatan. Spatial variability of groundwater quality in the study area is caused by: a) seawater intrusion and groundwater rich in sulfates at the west and in the coast, b) water rock interactions and the average annual precipitation at the middle and east zones respectively, and c) human contamination present in two localized zones. Changes in the amount and distribution of precipitation cause temporal variation by diluting groundwater in the aquifer. This approach allows to analyze the variation of groundwater quality controlling processes efficiently and simultaneously.

Mechanisms leading to potential impacts of shale gas development on groundwater quality

The development of shale gas resources was made possible by the combination of horizontal drilling and high‐volume hydraulic fracturing (fracking). Environmental concerns have been raised relative to shale gas production, especially potential impacts on groundwater. Fluids related to unconventional oil and gas (O&amp;G) operations contain chemical compounds that can impact groundwater quality. Such impacts can occur due to (1) the infiltration of surface contaminant releases, (2) failures of the integrity of O&amp;G wells, and (3) upward fluid migration from a shale/tight reservoir along preferential paths that can be natural (faults or fracture zone) or man‐made (O&amp;G wells). Surface releases represent the most probable mechanism leading to groundwater contamination. Improvements in O&amp;G drilling operations under stringent regulations can minimize this risk. Experts identify O&amp;G well integrity as the most challenging issue that may lead to groundwater contamination. Failure of casing and cement can lead to upward fluid flow within or outside O&amp;G wells, especially of methane. Integrity failures leading to fluid migration to shallow fresh water aquifers or to the surface are well understood and can be detected and repaired, but this can be complex and costly. A few regulators now impose groundwater monitoring to detect impacts from integrity failures. Occurrences of communication with existing O&amp;G wells from fracking operations have also led some regulators to impose rules aiming to avoid such potential fluid migration paths. There is an ongoing scientific debate regarding the potential for fluids to migrate upward from exploited shale gas units to aquifers through natural preferential paths. WIREs Water 2017, 4:e1188. doi: 10.1002/wat2.1188This article is categorized under: Engineering Water &gt; Sustainable Engineering of Water Science of Water &gt; Water Quality

Geochemical indicators of the origins and evolution of methane in groundwater: Gippsland Basin, Australia.

Recent expansion of shale and coal seam gas production worldwide has increased the need for geochemical studies in aquifers near gas deposits, to determine processes impacting groundwater quality and better understand the origins and behavior of dissolved hydrocarbons. We determined dissolved methane concentrations (n=36) and δ13C and δ2H values (n=31) in methane and groundwater from the 46,000-km2 Gippsland Basin in southeast Australia. The basin contains important water supply aquifers and is a potential target for future unconventional gas development. Dissolved methane concentrations ranged from 0.0035 to 30mg/L (median=8.3mg/L) and were significantly higher in the deep Lower Tertiary Aquifer (median=19mg/L) than the shallower Upper Tertiary Aquifer (median=3.45mg/L). Groundwater δ13CDIC values ranged from -26.4 to -0.4‰ and were generally higher in groundwater with high methane concentrations (mean δ13CDIC=-9.5‰ for samples with >3mg/L CH4 vs. -16.2‰ in all others), which is consistent with bacterial methanogenesis. Methane had δ13CCH4 values of -97.5 to -31.8‰ and δ2HCH4 values of -391 to -204‰ that were also consistent with bacterial methane, excluding one site with δ13CCH4 values of -31.8 to -37.9‰, where methane may have been thermogenic. Methane from different regions and aquifers had distinctive stable isotope values, indicating differences in the substrate and/or methanogenesis mechanism. Methane in the Upper Tertiary Aquifer in Central Gippsland had lower δ13CCH4 (-83.7 to -97.5‰) and δ2HCH4 (-236 to -391‰) values than in the deeper Lower Tertiary Aquifer (δ13CCH4=-45.8 to -66.2‰ and δ2HCH4=-204 to -311‰). The particularly low δ13CCH4 values in the former group may indicate methanogenesis at least partly through carbonate reduction. In deeper groundwater, isotopic values were more consistent with acetate fermentation. Not all methane at a given depth and location is interpreted as being necessarily produced in situ. We propose that high dissolved sulphate concentrations in combination with high methane concentrations can indicate gas resulting from contamination and/or rapid migration as opposed to in situ bacterial production or long-term migration. Isotopes of methane and dissolved inorganic carbon (DIC) serve as further lines of evidence to distinguish methane sources. The study demonstrates the value of isotopic characterisation of groundwater including dissolved gases in basins containing hydrocarbons.

Hydrochemical characterization and pollution sources identification of groundwater in Salawusu aquifer system of Ordos Basin, China

Ordos Basin is located in an arid and semi-arid region of northwestern China, which is the most important energy source bases in China. Salawusu Formation (Q3 s) is one of the most important aquifer systems of Ordos Basin, which is adjacent to Jurassic coalfield areas. A large-scale exploitation of Jurassic coal resources over ten years results in series of influences to the coal minerals, such as exposed to the oxidation process and dissolution into the groundwater due to the precipitation infiltration. Therefore, how these processes impact groundwater quality is of great concerns. In this paper, the descriptive statistical method, Piper trilinear diagram, ratios of major ions and canonical correspondence analysis are employed to investigate the hydrochemical evolution, determine the possible sources of pollution processes, and assess the controls on groundwater compositions using the monitored data in 2004 and 2014 (before and after large-scale coal mining). Results showed that long-term exploration of coal resources do not result in serious groundwater pollution. The hydrochemical types changed from HCO3−-CO32− facies to SO42−-Cl facies during 10 years. Groundwater hardness, nitrate and sulfate pollution were identified in 2014, which was most likely caused by agricultural activities.

Little Potential of Spring Wheat Genotypes as a Strategy to Reduce Nitrogen Leaching in Central Europe

Nitrogen (N) losses negatively impact groundwater quality. Spring wheat genotypes varying in N-fertilizer recovery were studied (by using lysimeters) for their potential to minimize NO3-N leaching during spring and summer, over a three-year period. Additionally, we examined to what extent root growth and NO3-N leaching explain the well-known difference found between apparent and isotopic N recovery. The genotypes were grown under low (2 g m−2) and high (27 g m−2) N fertilizer supply. On average, the apparent and isotopic recoveries of N fertilizer by wheat were 43% and 51%, respectively. The three genotypes varied in fertilizer N recovery but not in NO3-N leaching, which only accounted for 15% of the applied N fertilizer. The differences in N uptake, fertilizer N recovery and root growth among the genotypes were not associated with the leached NO3-N because root growth and N uptake were not well synchronized with NO3-N leaching. Already at stem elongation 70% to 98% of the season-long NO3-N leaching had already taken place. Thus, the ability to minimize in-season NO3-N leaching by using spring wheat genotypes with higher fertilizer N recovery was limited because maximum N leaching occurred in the early crop season.

Assessment of groundwater suitability for irrigation in Madinah City, Saudi Arabia

In this study, the suitability of groundwater for irrigation purposes in Madinah city, Saudi Arabia was assessed. Of the 23 wells that were drilled in different locations of the city, 20 wells were sampled for water quality analyses. The United States Department of Agriculture (USDA) classification of irrigation water that is based on sodium hazard (SAR) and salinity hazard was used for irrigation suitability assessment. In addition, the residual sodium carbonate (RSC) and soluble sodium percentage (%Na) were calculated for all samples and also used for irrigation suitability assessment. Results showed that all groundwater samples are in the acceptable quality range for irrigation based on RSC values, and the majority of the samples had %Na in the acceptable range for irrigation. When SAR and salinity hazard were assessed, results showed that while almost all groundwater samples fell in the acceptable range of SAR, they were either in the high or very high salinity zones, indicating that the water can be used for irrigation after adopting some management practices. Comparing total dissolved solids (TDS) concentration obtained 35 years ago for the study area with the current TDS values indicates that the recent accelerated urban development in the study area did not significantly impact groundwater quality with regard to irrigation suitability.

Does Disposing of Construction and Demolition Debris in Unlined Landfills Impact Groundwater Quality? Evidence from 91 Landfill Sites in Florida.

More than 1,500 construction and demolition debris (CDD) landfills operate in the United States (U.S.), and U.S. federal regulations do not require containment features such as low-permeability liners and leachate collection systems for these facilities. Here we evaluate groundwater quality from samples collected in groundwater monitoring networks at 91 unlined, permitted CDD landfills in Florida, U.S. A total of 460,504 groundwater sample results were analyzed, with a median of 10 years of quarterly or semiannual monitoring data per site including more than 400 different chemical constituents. Downgradient concentrations of total dissolved solids, sulfate, chloride, iron, ammonia-nitrogen, and aluminum were greater than upgradient concentrations (p < 0.05). At downgradient wells where sulfate concentrations were greater than 150 mg/L (approximately 10% of the maximum dissolved sulfate concentration in water, which suggests the presence of leachate from the landfill), iron and arsenic were detected in 91% and 43% of samples, with median concentrations of 1,900 μg/L and 11 μg/L, respectively. These results show that although health-based standards can be exceeded at unlined CDD landfills, the magnitude of detected chemical concentrations is generally small and reflective of leached minerals from components (wood, concrete, and gypsum drywall) that comprise the bulk of discarded CDD by mass.

Geophysical and hydrogeological characterisation of the impacts of on-site wastewater treatment discharge to groundwater in a poorly productive bedrock aquifer

Contaminants discharging from on-site wastewater treatment systems (OSWTSs) can impact groundwater quality, threatening human health and surface water ecosystems. Risk of negative impacts becomes elevated in areas of extreme vulnerability with high water tables, where thin unsaturated intervals limit vadose zone attenuation. A combined geophysical/hydrogeological investigation into the effects of an OSWTS, located over a poorly productive aquifer (PPA) with thin subsoil cover, aimed to characterise effluent impacts on groundwater. Groundwater, sampled from piezometers down-gradient of the OSWTS percolation area displayed spatially erratic, yet temporally consistent, contaminant distributions. Electrical resistivity tomography identified an area of gross groundwater contamination close to the percolation area and, when combined with seismic refraction and water quality data, indicated that infiltrating effluent reaching the water table discharged to a deeper more permeable zone of weathered shale resting on more competent bedrock. Subsurface structure, defined by geophysics, indicated that elevated chemical and microbiological contaminant levels encountered in groundwater samples collected from piezometers, down-gradient of sampling points with lower contaminant levels, corresponded to those locations where piezometers were screened close to the weathered shale/competent rock interface; those immediately up-gradient were too shallow to intercept this interval, and thus the more impacted zone of the contaminant plume. Intermittent occurrence of faecal indicator bacteria more than 100m down gradient of the percolation area suggested relatively short travel times. Study findings highlight the utility of geophysics as part of multidisciplinary investigations for OSWTS contaminant plume characterisation, while also demonstrating the capacity of effluent discharging to PPAs to impact groundwater quality at distance. Comparable geophysical responses observed in similar settings across Ireland suggest the phenomena observed in this study are more widespread than previously suspected.