Mass Discharge - E2S2

Mass Discharge - E2S2

Two Emerging Concepts AboutGroundwater Plumes:Matrix Diffusion and Mass DischargeCharles Newell, Ph.D., P.E.GSI Environmental Inc.1

Groundwater Plume Contaminant TransportTest Tankwith Dye3

Groundwater Plume Contaminant TransportTest Tankwith Dye5

Groundwater Plume Contaminant TransportThreat to HumanHealth and theEnvironment:Drinking water well“captures” part ofthe plume socontaminants arebrought to thesurface and ingested6

Groundwater Plume Contaminant TransportKey Concepts:1. Contaminants ingroundwater flowthrough sand layerssurrounded byimpermeable clayand sitls2. We need to regulatethe concentrations ingroundwater (in unitsof micrograms perliter / parts perbillion)7

Two Emerging ConceptsMatrix Diffusion• Process where low permeability zones become sources• Difficult to get to the contaminant mass in low perm zone• Creates a long “concentration vs. time tail”Mass Discharge/Mass Flux• Based on “loading” to a groundwater aquifer• Different way to think about sites• Recent advances in techniques

Real World: Heterogeneity Rules,Even in “Sandy Aquifers”Image from Fred Payne /ARCADIS99

Matrix Diffusion ExplainedAfter NRC 20051010

Matrix Diffusion MovieDoner and Sale, Colorado State UniversityLoading Phase1111

Matrix Diffusion MovieDoner and Sale, Colorado State UniversityFlushing Phase1212

Key Point – Matrix Diffusion is aSmall Scale PhenomenaContaminant storage and release processes in lowpermeability zone is important, but it is governed byconcentrations gradients that occur at scales of centimetersto millimeters.AB84 cmD107 cmCTo Download Movie:www.gsi-net.comDay 2813

Connecticut SiteNSourceZoneGroundwaterFlowTransect 1Chapman and Parker WRR 2005Image Courtesy of B. Parker500 ft1414

Aquifer – Aquitard ContactStratigraphicColumn0UpperSandAquifer~3 mAquifer0510[cm]9 m15SiltyAquitardAquitard2030 mImage Courtesy of B. Parker251515

High-Resolution Data from Core43Distance (m from Interface)210-1-2AquiferContinuity atInterfaceAquitardr w = 1.95 g/cm 3f = 0.43R = 1.2UpperSandAquiferSiltyAquitard-30 20 40 60 80TCE (mg/L)Chapman and Parker 2005Image Courtesy of B. Parker1616

Connecticut SiteNTransect 1SourceZone3000 kg TCE presentin low-perm zone!GroundwaterFlow500 ft1717

Concentration vs. Time from Monitoring WellsWithTailingIf NoTailingSource: Chapman and Parker, 2005 Copyright 2005 American Geophysical Union.Reproduced/modified by permission of AGU.1818

Two Emerging ConceptsMatrix Diffusion• Process where low permeability zones become sources• Difficult to get to the contaminant mass in low perm zone• Creates a long “concentration vs. time tail”Mass Discharge/Mass Flux• Based on “loading” to a groundwater aquifer• Different way to think about sites• Recent advances in techniques• Key Reference: ITRC Mass Flux / Mass Discharge GuideGoogle “ITRC Mass Flux”

Consider Two Sites WithSame Maximum ConcentrationSite M: Mega SiteBig Source,Extreme Hi GW VelocitySite P: Small SiteSmall Source,Almost Stagnant“Well Snapper”“PASU”20

DefinitionsMASS DISCHARGE• The total mass of any solute conveyed by a plumeat a given location in units of mass per time.Symbol: M dUnits:grams per day orkilograms per year21

DefinitionsMass flux, JIntegrateMass discharge, M d“This plume ” has amass discharge of1.5 grams per day.”Sir IsaacNewton:“Method ofFluxions”22

Five Methods for Mass Discharge• Method 1: Transect Method• Method 2: Well Capture/Pumping Methods• Method 3: Passive Flux Meters• Method 4: Using Existing Data (Isocontours)• Method 5: Solute Transport ModelsAll methodsare“ready to go”SourceSourceStrengthPlumeStrength23

Method 1: Transect Method1. Characterize plume and flow(q and C)2. Select transect: with simpleapproach, build crosssectionalpolygons (“windowpanes”) for each well3. Determine area (W • b = A)4. Multiply terms and sum:M d = Mass dischargeC n = Concentration in polygon n= Area of segment nA nM d = Σ (C n • A n •q)< 0.5ug/LCROSS-SECTIONW 4 W 3 W 2 W 1b45ug/LWidthPolygon 1Nichols and Roth, 200474ug/LWidthPolygon 2< 0.5ug/L24

Methods 3 – Passive Flux Meter Permeable sorbent• Accumulatescontaminantbased on flowand concentration Soluble tracers• Loses tracer basedon groundwatervelocity and fluxconvergencecalculations1. Contaminantadsorbed ontopassive flux meterover time to getConcentrationPhoto: Dyeintercepted in a meterK 0K>>K 0t 1t 2t 32. Tracer desorbs from passive fluxmeter over time to get Flow (Q)Source: Hatfield and AnnableGroundwater Flowlines26

Passive Flux MeterInstallationSamplingVendor:

Method 5: REMChlor Model ofSource RemediationAuthor: Ron Falta, Clemson Univ.:Google: “REMChlor EPA”Remove 90% of mass in 2010.REMchlor shows mass discharge vs. distance in future yearsMass Discharge (Kg per year)2008 2014 2080Distance from Source (meters)28

Using Mass Discharge: Estimating Well ImpactsUse mass discharge of plume topredict constituent of concernconcentration in downgradientwater supply wellSourcezoneClean waterClean waterCapture zoneM d = 2grams/dayExtractionwellC well = M d ÷ Q Well Q w = 600gpmC well = Concentration in extraction wellQ well = Pumping rate for extraction wellClean water2 g/day11 gal 10x ÷ 1440 min x 6 ug=x g600 gpm3.79 L< 1 ug /LEinarson and Mackay, 200129

“Plume Magnitude Classification System”Mass DischargePlume(grams/day)Category< 0.001 “Mag 1 Plume”0.001 to 0.01 “Mag 2 Plume”0.01 to 0.1 “Mag 3 Plume”0.1 to 1 “Mag 4 Plume”1 to 10 “Mag 5 Plume”10 to 100 “Mag 6 Plume”100 to 1,000 “Mag 7 Plume”1,000 to 10,000 “Mag 8 Plume”10,000 to 100,000 “Mag 9 Plume”>100,000 “Mag 10 Plume”Newell et al., accepted Journal of Ground Water30

What Mag Plume Does It Take for Impact?For complete capture and MCL = 5 ug/L:MassDischarge(grams/day)PlumeClassification0.001 to 0.01 Mag 2 PlumeThis Mag PlumeCould Impact:Domestic wellpumpingat 150 gallons/day1 to 10 Mag 5 Plume1,000 to 10,000 Mag 8 PlumeMunicipal wellpumpingat 100 gallons per minuteStream with a mixing zoneand base flow of 100 cubicfeet per secondNewell et al., accepted Journal of Ground Water31

SummaryTwoEmergingConceptsWhy Now?Implications• Matrix Diffusion• Mass Discharge/Mass Flux• Groundwater sites very difficult to remediate• New thinking about processes andmanagement strategies• Matrix diffusion can result in persistent lowlevel concentrations even after remediation• Might consider tailoring site characterization/performance monitoring projects toinclude mass flux/mass discharge32

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