1 / 22

Nitrate Distribution, Fate and Transport in Helena Area Waters

Lewis and Clark County Water Quality Protection District. 316 North Park, Room 220 Helena, MT 59623 (406) 447-8585 Fax: (406) 447-8398. Nitrate Distribution, Fate and Transport in Helena Area Waters. James Swierc, PG Lewis & Clark Water Quality Protection District

chi
Download Presentation

Nitrate Distribution, Fate and Transport in Helena Area Waters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lewis and Clark County Water Quality Protection District 316 North Park, Room 220 Helena, MT 59623 (406) 447-8585 Fax: (406) 447-8398 Nitrate Distribution, Fate and Transport in Helena Area Waters James Swierc, PG Lewis & Clark Water Quality Protection District Lewis & Clark County, MT April 22, 2014

  2. Background • Helena Valley – SW Montana • “Typical” Western Montana Valley • Alluvial Aquifer in Valley bounded by Bedrock/Tertiary Basin Fill • River/Stream – Aquifer connections • Losing Streams at Upgradient Valley Margins • Gaining Streams at Downgradient Margins • Irrigation Canals • Local Water Issues – Nitrate Related • Ground (Drinking) Water Quality • Public Water Supplies vs Private Wells • Wastewater treatment/management • Sewered Areas vs Septic Systems • Concerns over Nitrate Contamination • USGS Studies 1973, 1980, 1992, 2000 • County – Septic Maintenance District • Recent Studies: TMDL 319, MBMG • Water Quality Map (Major Ion Types) • Isotopes (Nitrogen & Oxygen of Nitrate) • Drain Assessment & Cl/Br Ratios

  3. Nitrate in Ground Water • LCWQPD Monitoring Well Data (2009-2012) • Residential Areas with Reported Problems (limited data) • “Background” • Streams • Recharge Areas < 1 mg/L • Ground Water • Undefined, < 2 mg/L • Sources? • Agriculture vsSeptics • Differentiation Methods • Nitrate Isotopes • Cl/Br Ratios

  4. Conceptual System Model Helena Valley Hydrogeology Recharge to Aquifer from Precipitation • Aquifer - Unconsolidated Alluvium • Clay lenses towards central valley • Vertical upward gradient • Ground Water Flow • Shallow - Towards Lake Helena • Unconfined at valley margins • Upwelling in central valley • Artesian flowing wells • Vertical Upward Gradient • Gaining streams in central valley • Recharge • Stream loss at valley margins • precipitation, irrigation loss • Bedrock Aquifer discharge in subsurface to Alluvial Aquifer • Helena Valley Irrigation Canal • Missouri River Water into Basin • Distribution Laterals/Drains • Lake Helena • Discharge point for surface and ground water Recharge to Aquifer from Stream Loss Recharge from Irrigation Waters 546 Water Surface Map from Briar & Madison (1992)

  5. Nitrate Isotopes • Nitrate Isotopes • Nitrogen • Oxygen • Tracking Nitrate Recharge Sources • Denitrification Pathway • “Lighter” atoms denitrify first • Microbially mediated From Kendall (1998) All Helena Area Nitrate Isotope Data

  6. Nitrate Isotope Sampling Locations • Datasets • USGS, 2000 (Not Shown) • Bedrock Locations • MBMG GWIP Studies (2011) • LCWQPD Studies (2011, 2012)

  7. Nitrate Isotope Sampling Results • Datasets • LCWQPD Studies (2011, 2012) • No long decay series…

  8. Nitrate Isotope Sampling Results • Sources • “Old” Problem near Helena; Fairgrounds • Fertilizer in Central Valley • Remaining Data “clustered”

  9. Chloride/Bromide Ratio • Cl/Br ratio – premise, Cl from anthropogenic uses discharged to septic system drainfield • Bromine stable/constant for “background” • Increase in nitrates associated with increase in chloride • Nitrate can degrade, leaving elevated chloride • Problem for Helena Valley – different recharge sources/ hydrologic areas

  10. Ground Water Cl/Br Results • Poor Correlation at Valley Scale • Inconclusive Results • Look at Drains

  11. Drain System – Central Valley • Irrigation System • Main HVID Canal • Distribution Laterals • Ditches/Return Flow Laterals • Tile Drains • Samples Ground Water from top of water table

  12. Drain Data – West Valley • D2-4 • Drains Residential and Agricultural Areas • Nitrate decreases in summer, increase after irrigation season • Cl/Br Ratio varies, 164-500

  13. Drain Data – Southwest • D3-2 • Drains Residential and Agricultural Areas • Nitrate “stable” • Cl/Br Ratio varies, 205-517

  14. Drain Data – Northwest • D2.2-1 • Drains Residential and Agricultural Areas • Nitrate increases in summer • Cl/Br Ratio varies, 182-420 • D2.2-5 • Drains Agriculture Area • Nitrate increases post-irrigation • Cl/Br Ratio varies, 111-535

  15. Drain Data – North • D1-1 • Drains Residential and Agricultural Areas • Nitrate increases in summer • Cl/Br Ratio varies, 146-543 • D0-1 • Drains Agriculture Area • Nitrate increases post-irrigation • Cl/Br Ratio varies, 170-792

  16. Drain Data – East Valley • D7-1 • Drains Primarily Agricultural Areas • Nitrate low, “stable” • Cl/Br Ratio varies, 145-375

  17. Drain Data – Observations • Nitrates • Some Variability pre/post irrigation season • Chloride / Bromide • Chloride – generally stable • Bromide – widely variable • Low/Trace Levels – Lab quantification issues • Different Sources for Br • Need to characterize recharge sources as baseline for comparison

  18. Chloride (& Bromide) Sources? • From De-icing Solutions for Roads (MgCl, NaCl, etc.) • Highest Chloride concentrations adjacent to roads • From Fertilizers? • Saffigna & Keeney, 1977 Ground Water, V. 15, No. 2 • Wisconsin Agricultural Areas, NO3/CL Ratio constant • Noted FERTILIZERs as source for Nitrate & Chloride • Potassium Chloride used for Potassium source • See Nitrate-Chloride Linear Relationship at valley residential wells with Nitrate Problems, by agricultural fields

  19. Fate & TransportVertical Upward Gradient • East Helena area well cluster (trio) • Well 1, TD 103’ • Well 2, TD 128’ • Well 3, TD 169’ • 4 feet vertical head upward over 60 feet

  20. Horizontal vs Vertical flow rates • Vertical gradient order of magnitude higher than horizontal gradient • Hydrograph shows similar response pattern so affected by same surficial recharge sources • Deep water recharge source, vertical flow retarded by finer-grained layers • Result – keeps surface contaminants near surface, even if drawn down by well pumping High K flowpath Lower K Aquitard High K flowpath Gradients are real, aquifer hydraulic properties are estimated to illustrate concept

  21. Fate and Transport Summary • Nitrates released to top of aquifer from surface • Fertilizer AND Septic System sources • Central Valley – area near Drains • Denitrification occurs, low Nitrate and low dissolved oxygen levels in shallow wells • Drains flush top of water table into ditches • Vertical upward gradient • Dilution of nitrate waters • High Chloride, Low NO3 • Denitrification, dilution • Added chloride What does clustering of Isotope data here mean? Mixing of different sources? Rapid Denitrification?

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

More Related