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Nitrate Distribution, Fate and Transport in Helena Area Waters James Swierc, PG Lewis & Clark Water Quality Protection District Lewis & Clark County, MT.

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Presentation on theme: "Nitrate Distribution, Fate and Transport in Helena Area Waters James Swierc, PG Lewis & Clark Water Quality Protection District Lewis & Clark County, MT."— Presentation transcript:

1 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 LCWQPD Monitoring Well Data ( ) Residential Areas with Reported Problems (limited data) “Background” – Streams Recharge Areas < 1 mg/L – Ground Water Undefined, < 2 mg/L Sources? – Agriculture vs Septics – Differentiation Methods Nitrate Isotopes Cl/Br Ratios Nitrate in Ground Water

4 Helena Valley Hydrogeology 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 Water Surface Map from Briar & Madison (1992) Conceptual System Model Recharge to Aquifer from Stream Loss 546 Recharge to Aquifer from Precipitation Recharge from Irrigation Waters

5 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,

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

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

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

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

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, NO 3 /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 & Transport Vertical 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 Gradients are real, aquifer hydraulic properties are estimated to illustrate concept High K Lower KAquitard flowpath

21 What does clustering of Isotope data here mean? Mixing of different sources? Rapid Denitrification? 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 NO 3 – Denitrification, dilution – Added chloride

22 Questions/Discussion? Helena Valley from Divide (view East) Note – work is ongoing, drain study continues through 2014 James Swierc, PG Project Report(s), Poster(s) and more information available at


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