attenuation of pollutants in the hyporheic zone: river tame, west midlands michael rivett...

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Attenuation of Pollutants in the Hyporheic Zone: River Tame, West Midlands Michael Rivett School of Geography, Earth & Environmental Sciences Groundwater modellers Forum: Groundwater Surface Water Interaction Modelling Workshop Birmingham, UK. 28 Mar 2007 Slide 2 Outline Pollutant natural attenuation in the hyporheic zone River Tame field studies Issues / questions relevant to modelling Summary discussion points Slide 3 Pollutant Natural Attenuation (NA) Natural Attenuation (NA) refers to the naturally occurring physical, chemical or biological processes that act within an aquifer to reduce contaminant mass, concentration, flux or toxicity (Environment Agency, 2000) m - Xylene CH 3 Data from: J.F. Barker (Univ. Waterloo, Canada) Slide 4 Attenuation Hyporeheic Zone (HZ) Infiltration of oxygenated SW High organic carbon, nutrients High microbiological activity Steep redox gradients Dynamic flows (USGS Circular 1139, 2001) River Hyporheic Zone Groundwater surface water mixing Last gasp remediation of groundwater contaminant plumes Slide 5 Attenuation Hyporeheic Zone (HZ) HZ natural attenuation (NA) capacity: Contaminant flux that can be treated by attenuation processes during transport through the HZ Treatment: Reduction in contaminant concentration and transformation to benign products. ( MNA strategies) Slide 6 HZ: the reality is complex Some issues: Defining an attenuation capacity that is Temporally and spatially predictable and sufficient Receptor definition: riverbed, benthic life, river Scales of measurement, regulation, modelling (Conant, 2000) Spatial variable Temporally dynamic Slide 7 River Tame field studies Slide 8 River Tame - Birmingham aquifer Rivett, M.O., Ellis, P.A., Greswell, R.B., Ward, R.S., Roche, R.S., Cleverly, M., Walker, C., Conran, D., Fitzgerald, P.J., Willcox, T., Dowle, J., in subm. Cost-effective mini drive- point piezometers and multilevel samplers for monitoring the hyporheic zone. In submittal to Quarterly Journal of Engineering Geology & Hydrogeology. Ellis, P.A., Mackay, R., Rivett, M.O., 2007. Quantifying urban riveraquifer fluid exchange processes: A multi-scale problem. Journal of Contaminant Hydrology 91, 51-80. Ellis, P.A., Rivett, M.O., 2007. Assessing the impact of VOC-contaminated groundwater on surface-water at the city scale. Journal of Contaminant Hydrology 91, 107-127. Rivett, M.O., Greswell, R.B., Mackay, R., Lydon, C., Conran, D.J., Ellis, P.A., 2007. Natural attenuation potential of the urban hyporheic zone: Foundational studies to the River Tame (Birmingham, UK) dipole field experiments. In: Proceedings of the First SWITCH Scientific Meeting, Birmingham, UK, 9-10 Jan 2007. Shepherd, K.A., Ellis, P.A., Rivett, M.O. 2006. Integrated understanding of urban land, groundwater, baseflow and surface-water quality The City of Birmingham, UK. The Science of the Total Environment 360, 180-195. Ellis, P.A., 2003. The impact of urban groundwater upon surface water quality: Birmingham River Tame study, UK. PhD thesis, School of Geography, Earth & Environmental Sciences, University of Birmingham, UK, 360 pp. Ellis, P.A., Rivett, M.O., Henstock, J, Dowle., Mackay, R., Ward, R. and Harris, R., 2002. Impacts of contaminated groundwater on urban river quality Birmingham, UK. In: Groundwater quality: Natural and enhanced restoration of groundwater pollution. IAHS publication No. 275, 71-77. Ellis, P.A., Rivett, M.O. and Mackay, R. 2004. Estimation of groundwater-contaminant fluxes to urban rivers. In: Hydrology: Science & Practice for the 21st Century, British Hydrological Society (Publ.) 272-279. Slide 9 Triassic Sandstone aquifer effluent to 7km reach of the River Tame Q min ~180 Ml/d Baseflow ~7% Q total Quality Class E/F K ~ 2 m/d n ~ 0.27 S y ~ 0.1 Chlorinated solvents, metals Slide 10 Methods: Drivepoint piezometers Drivepoint multilevel samplers (c) (d) (e)(f) (a) (b) Slide 11 Methods: MLS Transect #1 (g)(h) (i)(j) Slide 12 Issue 1: assessment scale(s) Field investigation City reach 7 km 400 m reach 50 m reach Single multilevel profile Attenuation process investigation Regulatory compliance Up-scaling issues ? Models developed at appropriate scale(s) Slide 13 Profile Number Bank 1 Bank 2 VOCs in groundwater baseflow (7 km reach) 7 km Reach Slide 14 400 m reach scale TCA is parent solvent DCE is abiotic degradation product DCA is biotic degradation product TCA DCE DCA Slide 15 Cross river transect: Evidence of negligible (if any) NA in HZ Slide 16 Modelling at various scales Based of River Tame studies: Ellis, P.A., Mackay, R., Rivett, M.O., 2007. Quantifying urban river aquifer fluid exchange processes: A multi-scale problem. Journal of Contaminant Hydrology 91, 51-80. Slide 17 Modelling Examine GW-SW interations / mixing zone 4 models at various scales (+ aquifer model) Slide 18 Model 2: 300 m transect Slide 19 Issue #2 How to i mprove our understanding of flow nuances Dominance of lateral flows into the river through the river sides, e.g. central 50% of the river bed contributes only 25 % of total baseflow River water entering the river bed during the passage of the flood wave occurs only for very short times (