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Diffuse pollution of groundwater in urban areas David Lerner, Nigel Tait and Brenda Chisala Catchment Science Centre University of Sheffield With thanks.

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Presentation on theme: "Diffuse pollution of groundwater in urban areas David Lerner, Nigel Tait and Brenda Chisala Catchment Science Centre University of Sheffield With thanks."— Presentation transcript:

1 Diffuse pollution of groundwater in urban areas David Lerner, Nigel Tait and Brenda Chisala Catchment Science Centre University of Sheffield With thanks to Mike Rivett, Yuesuo Yang, Mike Barrett and other colleagues …and thanks to our funders, NERC, EPSRC, EA

2 Outline The message: –Multiple urban sources ≡ diffuse pollution Outline: –Urban recharge –Urban groundwater pollution –Nitrate loads in Nottingham –Organic sources and risks –Summary

3 Urban pathways for precipitation Evapo- transpiration Precipitation Evaporation Surface runoff Storm sewers Direct recharge Sewer leakage Infiltration systems Roofs Roof soakaways Lerner, 2002, Hydrogeology Journal, 10, Urban recharge

4 Consumptive use Sewers Mains leakage Sewer leakage Septic tanks Irrigation excess Local groundwater Imported water supply Urban supply pathways Lerner, 2002, Hydrogeology Journal, 10, Urban recharge

5 Water supply and rainfall to selected cities CityRainfall (mm/y) Water supply (mm/y) Leakage (%) Nottingham  Lima, Peru (1979) <101650~50 Hong Kong (1980) <10 Urban recharge

6 Urban recharge, Nottingham Yang et al. 1999, Environmental Geology, 38, Urban recharge

7 Chlorinated solvents in urban groundwater Chlorinated hydrocarbon %age of pumped boreholes over 1  g/l CoventryBirmingham Trichloroethene7274 Tetrachloroethene40 Trichloroethane5222 Chloroform4317 Carbon Tetrachloride312 Rivett et al. 1990, Journal of Hydrology, 113, Burston et al. 1993, Journal of Hydrology, 149, Urban groundwater pollution

8 Sewage in groundwater, Meadows, Nottingham Barrett et al Water Research. 33(14), Urban groundwater pollution Meadows, like all UK urban areas, is fully sewered

9 Road salt in groundwater LocationRoads (10 3 km) Salt (10 3 t in 86-87) UK Germany40627 Howard & Haynes, 1993 Geoscience Canada, 20, 1-8 Howard & Beck, 1993 JCH, 12, Urban groundwater pollution Toronto Salt applied>100x10 3 t/year Cl in groundwater near Toronto highways2000 – mg/l Cl in springs on Toronto lakefront400 mg/l

10 N in Nottingham groundwater Location of sampled boreholes NO 3 -NNH 4 -N Detects % Mean mg/l Detects % Mean mg/l Deep rural Deep urban Shallow urban Urban groundwater pollution

11 Nottingham case study Sheffield Nottingham Meadows Nitrate loads in Nottingham

12 Hydrogeological map of Nottingham Km Alluvium Glacial drift L. Magnesian Lst. Mercia Mudstone Triassic Sandstone Groundwater level River Multi-level sampler Nitrate loads in Nottingham Nottingham Meadows

13 Recharge rates from solutes Rain Water Mains Sewers Cl:N:SO 4 Nitrate loads in Nottingham

14 Process for estimating recharge and loads Conceptual aquifer model Groundwater flow model Calibrated heads? Yes No Transport models for Cl, SO 4, N Change flow model? No Yes Calibrated concentrations? No Yes START TOTAL RECHARGE De- convolute RECHARGES LOADS Nitrate loads in Nottingham

15 Time and space division of 4 mass balance models 20 km N-S 16 km W-E standard spacing 500m 1 layer MODFLOW & MT3D in Visual MODFLOW River Leen River Trent Nitrate loads in Nottingham

16 N loads to Nottingham groundwater 1990s urban load 21 kg/ha/y Comparable to intensive arable load Where from? Nitrate loads in Nottingham

17 Urban fertilisers LocationLoading (kg N/ha/y) Perth, Australia100 USA1-55 Nitrate loads in Nottingham Wakida & Lerner, 2005, Water Research,

18 Leaking sewers Nitrate loads in Nottingham

19 Septic tank systems LocationN load from septic tanks (kg N/ha/y) Merida, Mexico100 New England48 Nitrate loads in Nottingham Wakida & Lerner, 2005, Water Research,

20 Housing and house building Nitrate loads in Nottingham

21 Industrial use and spillage Nitrate loads in Nottingham

22 Field Well Yard Well Factory Spoil Heap Ponds Farm Borehole N Former Colliery Pit Head T2 14 T3 T4 Lagoon Large Lagoon Drain Former Coking Plant Monitoring BH Abstraction BH Groundwater head Ammonium concentration Ammonium plume from Rexco mg/l Nitrate loads in Nottingham

23 Landfills NH 4 in leachate up to 1500 mg/l > closed landfills in UK, mostly unlined Loads up to 4000 kg N/ha/y Nitrate loads in Nottingham

24 N loads in Nottingham Wakida & Lerner, 2005, Water Research, Nitrate loads in Nottingham

25 Organic sources and risks Density of sources –National –Nottingham Risks from urban sources –Nottingham Loads Organic sources

26 IndustrySectorSites Data Analysis Engineering Transport Mechanical Machine Tools Plant Machinery Precision Aerospace Defence 50,000 75,000 industries 60,000 manufacturing sites Postcodes give 100m resolution 1 Bartholomew digital map data 2 Geoplan digital postcode map 3 1 University of Essex, 2 University of Manchester, 3 University of Greenwich Electronics Electrical Eng. Electronic Eng. 12,000 Chemical Paints Varnishes Inks Pesticides Adhesives / Sealants Rubber 3,500 Metal Finishing 2,000 Textile Pretreatment Dry Cleaning 7,000 Chlorinated solvent industry database Tait et al. 2004

27 Density of chlorinated solvent users current sites London - 2,500 dry cleaning outlets Density scale: sites/km 2 Organic sources Tait et al. 2004, SOTTE 319, Sheffield London Nottingham

28 Nottingham: point or diffuse sources? Potential TCE sources in Nottingham –1991 –Unconfined aquifer How dense a pattern to become diffuse pollution? Potential TCE sources Organic sources

29 Risk analysis for urban groundwater Receptor Sources Pathways Organic sources

30 BOS: the model components GUI Catchment zone tool Landuse analysis Pollution risk model Groundwater flow model Databases Tait et al., 2004, Environmental Modelling and Software, 19, Organic sources

31 The catchment zone model Stochastic MODPATH 1 particle per node Monte Carlo simulations –E.g., recharge, permeability Frequency of arrival gives probability of node in capture zone Organic sources

32 Landuse GIS Organic sources

33 Specific industry databases Organic sources

34 New unconfined catchment Unconfined Confined Existing borehole New borehole Raw predicted catchment Probability contoured catchment with industries Industries Organic sources

35 The pollution risk component Organic sources Monte Carlo analysis

36 Predicted concentrations Organic sources

37 Validation Risk models are rarely validated Construct and believe Attempted validation against field data –2 wells14 (not independent) –7 contaminantsmeasurements Also national MTBE observations (not shown) Organic sources

38 Validation ParameterDrinking Water Std (  g/l) Borehole 1Borehole 2 Field (  g/l) Model (  g/l) Field (  g/l) Model (  g/l) TCE ,1,1 TCA PCE Benzene1 bql0.07bql0 Toluene<10 bql0.03bql0 Ethylbenzene<10 bql0.05bql0.1 Xylene<10 bql bql = below quantification limit 13/14 predictions within a factor of 2 Organic sources

39 Predicted PCE concentrations Study Area 50%ile log(C PCE ), 2005 Tait et al., submitted, Environmental Modelling and Software Organic sources Borehole Simulation Location

40 Risks from leaking sewers Nottingham sewer network Stochastic distribution of leaks –Related to sewer age Total leakage ≡ 10 mm/y Amended pollution risk model –Bacterial sorption and die-off Organic sources

41 Nottingham: Potential MTBE load Summing sources in Nottingham risk analysis Load ~10 kg/ha/yr Probably too high Potential MTBE sources Organic sources

42 Chlorinated solvent load in Birmingham aquifer Assume: –Steady state –Boreholes are pumping representative concentrations of TCE, PCE, etc Unconfined aquifer 0 4 km Confined aquifer Tame Valley Birmingham Fault Aquifer boundary Borehole and catchment Industrial area Year% recharge pumped Mass removed (kg/yr) 1 Load (kg/ha/ yr) ~1 1 from Rivett et al QJEGH 38, Organic sources

43 Reminder of the story Urban recharge –plenty in cities Urban groundwater pollution –N, organics, sewage, salt, etc Nitrate loads in Nottingham –21 kg/ha/yr from contaminated land, sewers, mains Organic sources and risks –Many sources, significant risks The message: –Multiple urban sources ≡ diffuse pollution Summary

44 Selected Nottingham references M.H. Barrett, K.M. Hiscock, S. Pedley, D.N. Lerner, J.H. Tellam and M.J. French, Marker species for identifying urban groundwater recharge sources – a review and case study in Nottingham UK. Water Research. 33(14), Y. Yang, D.N. Lerner, M.H. Barrett, and J.H. Tellam, Quantification of groundwater recharge in the city of Nottingham, UK. Environmental Geology, 38(3), D.N. Lerner, Identifying and quantifying urban recharge: a review. Hydrogeology Journal, 10(1), D.N. Lerner, Estimating urban loads of nitrogen to groundwater. Journal of the Chartered Institution of Water and Environmental Management. 17(4), N. G. Tait, R. M. Davison, J. J. Whittaker, S.A. Leharne and D. N. Lerner, Borehole Optimisation System (BOS) - A GIS based risk analysis tool for optimising the use of urban groundwater. Environmental Modelling and Software, 19, F.T. Wakida & D.N. Lerner, Non-agricultural sources of groundwater nitrates: a review and case study. Water Research, 39, F.T. Wakida & D.N. Lerner, Potential nitrate leaching to groundwater from house building. Hydrological Processes, 20(9): B.N. Chisala, N.G. Tait and D.N. Lerner,in press. Evaluating the risk of methyl tertiary- butyl ether (MTBE) to urban groundwater at city scale: Nottingham case study. Journal of Contaminant Hydrology, December N. G. Tait, R. M. Davison, S. A. Leharne and D. N. Lerner. Borehole Optimisation System (BOS) - Assessing the Potential Value of Urban Groundwater in Nottingham. Submitted, January Also papers led by R Taylor, K Powell and S Trowsdale. Summary

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