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 100 m
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.
Contaminants discharging from on-site wastewater treatment systems (OSWTSs) can impact groundwaterquality, threatening human health and surface water ecosystems. Risk of negative impacts becomes elevated inareas 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 poorlyproductive 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 areaof gross groundwater contamination close to the percolation area and, when combined with seismic refractionand water quality data, indicated that infiltrating effluent reaching the water table discharged to a deepermore permeable zone of weathered shale resting on more competent bedrock. Subsurface structure, definedby geophysics, indicated that elevated chemical and microbiological contaminant levels encountered in groundwatersamples 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/competentrock interface; those immediately up-gradient were too shallow to intercept this interval, and thus the more impactedzone of the contaminant plume. Intermittent occurrence of faecal indicator bacteria more than 100 mdown gradient of the percolation area suggested relatively short travel times. Study findings highlight the utilityof geophysics as part of multidisciplinary investigations for OSWTS contaminant plume characterisation, whilealso demonstrating the capacity of effluent discharging to PPAs to impact groundwater quality at distance. Comparablegeophysical responses observed in similar settings across Ireland suggest the phenomena observed inthis study are more widespread than previously suspected.
การแปล กรุณารอสักครู่..
