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Nitrate Distribution, Fate and Transport in Helena Area WatersJames Swierc, PGLewis & Clark Water Quality Protection DistrictLewis & Clark County, MT

April 22, 2014

Lewis and Clark CountyWater Quality Protection District316 North Park, Room 220Helena, MT 59623(406) 447-8585 Fax: (406) 447-8398

BackgroundHelena Valley SW Montana Typical Western Montana ValleyAlluvial Aquifer in Valley bounded by Bedrock/Tertiary Basin FillRiver/Stream Aquifer connectionsLosing Streams at Upgradient Valley MarginsGaining Streams at Downgradient MarginsIrrigation CanalsLocal Water Issues Nitrate RelatedGround (Drinking) Water QualityPublic Water Supplies vs Private WellsWastewater treatment/managementSewered Areas vs Septic SystemsConcerns over Nitrate ContaminationUSGS Studies 1973, 1980, 1992, 2000County Septic Maintenance DistrictRecent Studies: TMDL 319, MBMGWater Quality Map (Major Ion Types)Isotopes (Nitrogen & Oxygen of Nitrate)Drain Assessment & Cl/Br Ratios

2LCWQPD Monitoring Well Data (2009-2012)Residential Areas with Reported Problems (limited data)BackgroundStreams Recharge Areas < 1 mg/LGround Water Undefined, < 2 mg/LSources?Agriculture vs SepticsDifferentiation MethodsNitrate IsotopesCl/Br RatiosNitrate in Ground Water

Helena Valley HydrogeologyAquifer - Unconsolidated AlluviumClay lenses towards central valleyVertical upward gradient Ground Water FlowShallow - Towards Lake HelenaUnconfined at valley marginsUpwelling in central valleyArtesian flowing wellsVertical Upward GradientGaining streams in central valleyRechargeStream loss at valley marginsprecipitation, irrigation lossBedrock Aquifer discharge in subsurface to Alluvial AquiferHelena Valley Irrigation CanalMissouri River Water into BasinDistribution Laterals/DrainsLake HelenaDischarge point for surface and ground waterWater Surface Map from Briar & Madison (1992)Conceptual System Model

Recharge to Aquifer from Stream Loss546Recharge to Aquifer from PrecipitationRecharge from Irrigation Waters

Nitrate IsotopesNitrate IsotopesNitrogenOxygenTracking Nitrate Recharge SourcesDenitrification PathwayLighter atoms denitrify firstMicrobially mediated

From Kendall (1998)All Helena Area Nitrate Isotope DataNitrate Isotope Sampling LocationsDatasetsUSGS, 2000 (Not Shown)Bedrock LocationsMBMG GWIP Studies (2011)LCWQPD Studies (2011, 2012)

Nitrate Isotope Sampling ResultsDatasetsLCWQPD Studies (2011, 2012)No long decay series

Nitrate Isotope Sampling Results

SourcesOld Problem near Helena; FairgroundsFertilizer in Central ValleyRemaining Data clusteredChloride/Bromide RatioCl/Br ratio premise, Cl from anthropogenic uses discharged to septic system drainfieldBromine stable/constant for backgroundIncrease in nitrates associated with increase in chlorideNitrate can degrade, leaving elevated chloride

Problem for Helena Valley different recharge sources/ hydrologic areasGround Water Cl/Br ResultsPoor Correlation at Valley ScaleInconclusive ResultsLook at Drains

Drain System Central ValleyIrrigation SystemMain HVID CanalDistribution LateralsDitches/Return Flow LateralsTile DrainsSamples Ground Water from top of water table

Drain Data West ValleyD2-4Drains Residential and Agricultural AreasNitrate decreases in summer, increase after irrigation seasonCl/Br Ratio varies, 164-500

Drain Data SouthwestD3-2Drains Residential and Agricultural AreasNitrate stableCl/Br Ratio varies, 205-517

Drain Data Northwest

D2.2-1Drains Residential and Agricultural AreasNitrate increases in summerCl/Br Ratio varies, 182-420D2.2-5Drains Agriculture AreaNitrate increases post-irrigationCl/Br Ratio varies, 111-535Drain Data North

D1-1Drains Residential and Agricultural AreasNitrate increases in summerCl/Br Ratio varies, 146-543D0-1Drains Agriculture AreaNitrate increases post-irrigationCl/Br Ratio varies, 170-792

Drain Data East Valley

D7-1Drains Primarily Agricultural AreasNitrate low, stableCl/Br Ratio varies, 145-375Drain Data Observations

NitratesSome Variability pre/post irrigation seasonChloride / Bromide Chloride generally stableBromide widely variableLow/Trace Levels Lab quantification issuesDifferent Sources for BrNeed to characterize recharge sources as baseline for comparisonChloride (& Bromide) Sources?From De-icing Solutions for Roads (MgCl, NaCl, etc.)Highest Chloride concentrations adjacent to roadsFrom Fertilizers?Saffigna & Keeney, 1977 Ground Water, V. 15, No. 2Wisconsin Agricultural Areas, NO3/CL Ratio constantNoted FERTILIZERs as source for Nitrate & ChloridePotassium Chloride used for Potassium sourceSee Nitrate-Chloride Linear Relationship at valley residential wells with Nitrate Problems, by agricultural fields

Fate & TransportVertical Upward GradientEast Helena area well cluster (trio)Well 1, TD 103Well 2, TD 128Well 3, TD 1694 feet vertical head upward over 60 feet

Horizontal vs Vertical flow ratesVertical gradient order of magnitude higher than horizontal gradientHydrograph shows similar response pattern so affected by same surficial recharge sourcesDeep water recharge source, vertical flow retarded by finer-grained layersResult keeps surface contaminants near surface, even if drawn down by well pumping

Gradients are real, aquifer hydraulic properties are estimated to illustrate conceptHigh KHigh KLower KAquitardflowpathflowpath

What does clustering ofIsotope data here mean?Mixing of different sources?Rapid Denitrification?Fate and Transport SummaryNitrates released to top of aquifer from surfaceFertilizer AND Septic System sourcesCentral Valley area near DrainsDenitrification occurs, low Nitrate and low dissolved oxygen levels in shallow wellsDrains flush top of water table into ditchesVertical upward gradientDilution of nitrate watersHigh Chloride, Low NO3Denitrification, dilutionAdded chloride Questions/Discussion?

Helena Valley from Divide (view East)Note work is ongoing, drain study continues through 2014James Swierc, PG jswierc@lccountymt.gov Project Report(s), Poster(s) and more information available at http://www.lccountymt.gov/health/water.html