Influence of the Missoula Floods on Willamette Valley Groundwater Roy Haggerty Geosciences, OSUOverviewGeneralized Geology of the Willamette ValleySlide 4Slide 5Slide 6Pleistocene River AlluviumBasin-fill—older and younger coarse-grained depositsSlide 9Slide 10… dry “falls”Slide 12Slide 14Missoula Flood DepositsSlide 16Hydrogeology FieldworkSlide 18Slide 19Measurements & AnalysesSlide 21Lab Test ResultsNumerical Model Purpose and ApproachNumerical Model Boundary and Initial ConditionsNumerical Model Optimized ParametersNumerical Model Wells with Good FitsNumerical Model: Wells with Poor FitsModel ResultsWS as a Chemical BufferWS Chemical Buffering CapacityDenitrificationSlide 32Influence of the Missoula Floods on Willamette Valley GroundwaterRoy HaggertyGeosciences, OSUOverview•Missoula Floods 12.5-15ka–catastrophic floods, huge impact on landscape•Left thick silt (up to 30 m) unit over most of Willamette Valley - “Willamette Silt”•Underlying unit is Willamette Aquifer•WS has two major effects on groundwater:–hydrologically buffers groundwater in WA from surface water and vice versa–protects groundwater from pollutants0 10 20 30 MILESGeneralized Geologyof the Willamette ValleyWillamette SiltColumbia River Basalt GroupMarine sedimentary rocks andCascade Range rocksAlluvium and basin-fill sedimentPSCEGannett &Caldwell, 1998Willamette SiltAlluvium and coarse-grained basin-fill depositsFine-grained basin-fill depositsColumbia RiverBasalt Group lavaMarine sediments andWestern Cascade rocksNORTH-SOUTH SECTION THROUGH THECENTRAL WILLAMETTE VALLEYSEA LEVEL500-5001,000-1000-1,400Mill CreekLake LabishWillamette R.French PrairieS NGannett &Caldwell, 1998Willamette SiltAlluvium and coarse-grained basin-fill depositsFine-grained basin-fill depositsColumbia RiverBasalt Group lavaMarine sediments andWestern Cascade rocksSEA LEVEL800-600McKenzie R.Willamette R.Long Tom R.McKenzie R.NORTHWEST-SOUTHEAST SECTION THROUGH THESOUTHERN WILLAMETTE VALLEYNWSEGannett &Caldwell, 1998100140220606020202030020100140180602010020140202060Thickness of theCoarse-GrainedBasin-Fill Deposits(contour interval 40 ft)SCEMarshall Gannett, 2003Pleistocene River AlluviumUp to 100 m thick.Includes lahars from Mt. Jefferson and a Middle Fk. Willamette(?) source.Locally older than 420 ka.Locally younger than 23 ka. Deposited in broad braidplains.Jim O’Connor, 2003Gravels, Walling PitTurner, ORGravels,Delta Pit,Eugene, ORGravels and Lahar (0.4 Ma),Delta Pit,Eugene, ORBasin-fill—older and younger coarse-grained depositsTerrence Conlon, 20032060804010020202010201010100120403020806020Thickness and Distributionof the Willamette Silt(contour interval 10 and 20 ft)SCEMarshall Gannett, 2003The Missoula Floods- 15-12ka- perhaps 100 floods- 500 mi3 of water, 40 hrs.- 50 million cfs (3500 CR)Jim O’Connor, 2003… dry “falls”Ridges 15 ft highJim O’Connor, 2003Willamette ValleyMissoula Flood DepositsUp to 30 m thick in the northern valley.Deposited in as many as 40 beds up to 2 m thick.Deposited between 15-12 ka.Contains ice-rafted erratics.Jim O’Connor, 2003Missoula Flood DepositsUp to 30 m thick in the northern valley.Deposited in as many as 40 beds up to 2 m thick.Deposited between 15-12 ka.Contains ice-rafted erratics.Jim O’Connor, 2003HydrogeologyFieldworkField Area1. What is impactof pumping from WA on surface water?2. Transport of ag. chemicals across WS?Gannett &Caldwell, 1998Field Site Cross Sectionwith August 2001(near min.) Water TablePudding RiverSite 1Site 2Site 3WSWAEasting (ft)Elevation (ft amsl)Measurements & Analyses•Water level monitoring•Pump test•Slug tests at all site piezometers•Permeameter tests•Grain-size & porosity measurements•Numerical model•Measurement of major cations, anionsField Site Cross SectionPudding RiverSite 1Site 2Site 3WSWAEasting (ft)Elevation (ft amsl)K 7x10-5 m/s, 20 ft/daySs 1x10-6/m, 4x10-6 /ftPump Test ResultsSlug Test Results1.54 x 10-9 to 1.95 x 10-5 m/s0.0004 to 5.53 ft/day6.43 x 10-9 to 2.93 x 10-8 m/s0.0018 to 0.0083 ft/daySlug Test ResultsLab Test Results•Permeameter Test–WS average Kv ~ 3 x 10-7 m/s (0.008 ft/day)–3.03 x 10-7m/s–0.09 ft/day•Grain-size analysis–WS average porosity = 0.40Numerical Model Purposeand Approach•Determine the interaction between WA, WS, and Pudding River under the influence of pumping.•Model three day pump test and use volumetric balance analysis to determine percent removed water from boundaries, storage, and Pudding River leakage.Numerical Model Boundary and Initial Conditions •Initial Conditions based on Gannett and Caldwell, 1998 data•Few physical boundaries–Mt. Angel Fault–otherwise boundaries are beyond zone of influence for 3-day pump testNumerical ModelOptimized Parameters•Willamette Silt–Kh 1 x 10-7 m/s–Kv 1.8 x 10-9 m/s–Ss 8.7 x 10-4/m•Willamette Aquifer–Kh 2.4 x 10-5 m/s–Kv 2.4 x 10-5 m/s –Ss 3.2 x 10-6/m46.446.646.84747.247.447.60 100000 200000 300000 "EB-IR (observed)" "EB-IR (computedfrom "final10_Heads")"4747.147.247.347.447.547.60 100000 200000 300000 "EL-IR (observed)" "EL-IR (computedfrom "final10_Heads")"Numerical ModelWells with Good Fits4747.147.247.347.447.547.60 100000 200000 300000 "EL-IR (observed)" "EL-IR (computedfrom "final10_Heads")"46.446.646.84747.247.447.60 100000 200000 300000 "EB-IR (observed)" "EB-IR (computedfrom "final10_Heads")"48.1548.248.2548.348.3548.448.450 100000 200000 300000 "EU-IR (observed)" "EU-IR (computedfrom "final10_Heads")"44.644.744.844.94545.145.245.30 100000 200000 300000 "SE-IR (observed)" "SE-IR (computedfrom "final10_Heads")"Numerical Model:Wells with Poor Fits4646.146.246.346.446.546.646.746.846.94747.10 100000 200000 300000 "EG-IR (observed)" "EG-IR (computedfrom "final10_Heads")"44.144.244.344.444.544.644.70 100000 200000 300000 "PZ-2S (observed)" "PZ-2S (computedfrom "final10_Heads")"46.5446.5546.5646.5746.5846.5946.646.6146.620 100000 200000 300000 "PZ-3S (observed)" "PZ-3S (computedfrom "final10_Heads")"Model Results•Optimized parameters: Less than 1% of water pumped from the WA is recharged from the Pudding River.•Lab-based parameters: 17% of water pumped from the WA is recharged from the Pudding River.–near maximum-value due to the proximity of the well to the Pudding River.WS as a Chemical Buffer•Nitrate penetration front ~ 25 ft.•Water table ~15 ft to surface•Oxidized to ~ 25 ft with sharp “redoxcline”WS Chemical Buffering CapacitySite 3Site 2Denitrification•Conversion of