title: Setback distances between small biological wastewater treatment systems and drinking water wells against virus contamination in alluvial aquifers.
abstract: Contamination of groundwater by pathogenic viruses from small biological wastewater treatment system discharges in remote areas is a major concern. To protect drinking water wells against virus contamination, safe setback distances are required between wastewater disposal fields and water supply wells. In this study, setback distances are calculated for alluvial sand and gravel aquifers for different vadose zone and aquifer thicknesses and horizontal groundwater gradients. This study applies to individual households and small settlements (1-20 persons) in decentralized locations without access to receiving surface waters but with the legal obligation of biological wastewater treatment. The calculations are based on Monte Carlo simulations using an analytical model that couples vertical unsaturated and horizontal saturated flow with virus transport. Hydraulic conductivities and water retention curves were selected from reported distribution functions depending on the type of subsurface media. The enteric virus concentration in effluent discharge was calculated based on reported ranges of enteric virus concentration in faeces, virus infectivity, suspension factor, and virus reduction by mechanical-biological wastewater treatment. To meet the risk target of <10-4infections/person/year, a 12 log10reduction was required, using a linear dose-response relationship for the total amount of enteric viruses, at very low exposure concentrations. The results of this study suggest that the horizontal setback distances vary widely ranging 39 to 144m in sand aquifers, 66-289m in gravel aquifers and 1-2.5km in coarse gravel aquifers. It also varies for the same aquifers, depending on the thickness of the vadose zones and the groundwater gradient. For vulnerable fast-flow alluvial aquifers like coarse gravels, the calculated setback distances were too large to achieve practically. Therefore, for this category of aquifer, a high level of treatment is recommended before the effluent is discharged to the ground surface.
authors: TU Wien, Institute of Hydraulic Engineering and Water Resources Management, E222/2, Karlsplatz 13, A-1040 Vienna, Austria; Interuniversity Cooperation Centre for Water and Health (ICC Water & Health), www.waterandhealth.at; Centre for Water Resource Systems, TU Wien, Vienna, Austria. Electronic address: blaschke@hydro.tuwien.ac.at.
authors: A P
authors: AP
authors: Blaschke
authors: TU Wien, Institute of Hydraulic Engineering and Water Resources Management, E222/2, Karlsplatz 13, A-1040 Vienna, Austria; Interuniversity Cooperation Centre for Water and Health (ICC Water & Health), www.waterandhealth.at; Centre for Water Resource Systems, TU Wien, Vienna, Austria. Electronic address: derx@hydro.tuwien.ac.at.
authors: J
authors: J
authors: Derx
authors: Centre for Water Resource Systems, TU Wien, Vienna, Austria; Institute of Water Quality, Resources and Waste Management, TU Wien, Vienna, Austria.
authors: M
authors: M
authors: Zessner
authors: Donauconsult Ltd., Vienna, Austria.
authors: R
authors: R
authors: Kirnbauer
authors: Austrian Federal Agency for Water Management, Petzenkirchen, Austria.
authors: G
authors: G
authors: Kavka
authors: TU Wien, Institute of Hydraulic Engineering and Water Resources Management, E222/2, Karlsplatz 13, A-1040 Vienna, Austria.
authors: H
authors: H
authors: Strelec
authors: Interuniversity Cooperation Centre for Water and Health (ICC Water & Health), www.waterandhealth.at; Centre for Water Resource Systems, TU Wien, Vienna, Austria; TU Wien, Institute of Chemical Engineering, Research Area Biochemical Technology, Research Group Environmental Microbiology and Microbial Diagnostics, Gumpendorferstraße 1a, 1060 Vienna, Austria.
authors: A H
authors: AH
authors: Farnleitner
authors: Institute of Environmental Science & Research Ltd., P.O. Box 29181, Christchurch, New Zealand.
authors: L
authors: L
authors: Pang
mesh_terms: D000074067:Conservation of Water Resources / Q000379:methods*; D060766:Drinking Water / Q000032:analysis / Q000592:standards / Q000821:virology*; D060587:Groundwater / Q000032:analysis / Q000592:standards / Q000821:virology*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D062065:Wastewater / Q000032:analysis / Q000821:virology*; D014871:Water Microbiology / Q000592:standards; D014876:Water Pollution / Q000517:prevention & control; D018508:Water Purification / Q000379:methods*; D060753:Water Quality; D060986:Water Wells
chemical_list: D060766:Drinking Water; D062065:Wastewater
keywords: Effluent land disposal; Enteric viruses; Setback distances; Small biological wastewater treatment systems; Vadose zone; Water quality