Nitrate Challenges: The Lost Creek Alluvial Fan

Laura AlveyGroundwater Remediation Program

April 23, 2014

Stillwater River

Lost Creek

Stillwater River

Lost Creek

Lost Creek Fan Shallow (<150 ft) Potentiometric Surface Map (August 2008)

Lost Creek Fan Subsurface:• Cobbles and boulders• Sand lenses• Highly permeable

What’s the Problem?

Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 May-05 Oct-06 Feb-080

10

20

30

40

50

60

Nitrate Trends in Selected Wells

84527

137876

84486

84528

LaChapSh

Time

Nit

rate

(m

g/L

-N) Homeowner sample

DEQ InvestigationMBMG Study

What’s the Problem?

Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 May-05 Oct-06 Feb-080

10

20

30

40

50

60

Nitrate Trends in Selected Wells

84527

137876

84486

84528

LaChapSh

Time

Nit

rate

(m

g/L

-N) ?

Nitrate Source Identification (Where is it coming from?)

• Enforcement under MT Water Quality Act: responsibility based on causation

• Important for fate and transport analysis: – Where did nitrate enter the environment?– Who/what is being affected?– Where is it going?– What can we learn to better manage nitrate in

future?

Challenge: Many Nitrate Sources

Center Pivots

Septic Systems

Tools for Nitrate Source Identification

• Stable isotope analysis of NO3 nitrogen and oxygen

• Analysis of co-contaminants– Pharmaceuticals, residential wastes (caffeine, artificial

sweeteners)– Agricultural chemicals (herbicides, pesticides, other

fertilizers)– Metals (boron)– Chloride, other major ions– Bacteria

General Findings

• Nitrate highest in shallow (<150 ft) wells• Deeper wells have less nitrate (why?)• Stabile nitrate levels between 2002-2011• Isotope results: no clear single source, but

suggest fertilizer as a dominant source where nitrate is highest

• Co-contaminants: nitrate and chlorides trend together, other results inconclusive/mixed

Effective Nitrate Management: • Permitting programs need to recognize susceptible resources• Increased inspections of sensitive sites to ensure compliance

Effective Nitrate Management: • Permitting programs need to recognize susceptible resources• Increased inspections of sensitive sites to ensure compliance

Effective Nitrate Management Encourage Best Management Practices • Soil moisture sensors• Soil testing• Crop selection

• Use of shallow versus deep aquifer

Effective Nitrate Management:• Property owner education: fertilizers use, well testing, septic upkeep• Require engineered septic systems in sensitive areas• Require domestic wells completed in deep aquifer• Require well completion to minimize cross-contamination

Effective Management

• Baseline monitoring important (MBMG, Ag, USGS)

• Track impacted groundwater (statewide?)

Questions/Comments?