road salt accumulation and transport in urban watersheds · (1) retention / cl budget (2) timing of...

http://stormwater.safl.umn.edu/

Road Salt Accumulation and Transport in Urban Watersheds

Iowa Water Conference • March 12, 2019

Ben JankeResearch AssociateUniversity of [email protected]


Road Salt Use

1: Data -- Salt Institute; Graph -- Walt Kelly (illinois.edu/blog/view/789/62191)

U.S. Salt Sales since 19401

Road salt use has increased dramatically since 1960

2: Sander et al. 2007 (SAFL Report)

Salt Use in the Twin Cities, 2000-20052

Cities 33%

Counties20%

MnDOT23%

Commercial19%

Packaged 5%

~349,000 tons / year

Road salt is primarily Sodium Chloride (NaCl)Alternatives: other chloride salts, beet sugar by-products, cheese brine


Road Salt: Where does it go?77% Retention of Road Salt in the Twin Cities

Metro Area (TCMA) from 2000 – 2005*

Retention: Loss of chloride from runoff- Infiltration to soils and groundwater- Storage in bottom of lakes/ponds

109,000 tons/year Chloride

56% - 85% Road Salt Retention in 10 Sub-watersheds

*Novotny et al. 2008 WRR


Problems with Excess Chloride

Total Cost: ~$1,000 - $3,500 per ton of salt applied (salt, labor, damage) Fortin Consulting / Minnesota Pollution Control Agency, 2014


EPA Water Quality Standards for Chloride Aquatic Life• Chronic (4 days): 230 mg/L• Acute (1 day) : 860 mg/L

Drinking Water• 250 mg/L (taste)

1 tsp

5 gal


Chloride Impairment of Drinking Water

250 mg/LUrban

MunicipalWater

Northern US Drinking Water Wells,

1991-2004 (USGS/Mullaney et al., 2009)


Chloride Impairment of Drinking WaterMinnesota (MN Pollution Control Agnecy, 2013)

– 27% of shallow wells in TCMA > 250 mg/L Cl– Median Cl in TCMA wells 5X that in rural wells


Chloride Impairment of Surface WatersU.S. Streams

(Stets et al. 2017)

Mpls-St. Paul Metro Lakes

(Novotny 2009)


TCMA Chloride Assessment (MN Pollution Control Agency, 2014)

340 water bodies (lakes, wetlands, streams) in Mpls – St. Paul metro• 39 impaired• 38 high risk


Chloride TMDLs in the TCMAShingle Creek

– Listed 1998, TMDL approved 2007– Requires 71% road salt reduction

Nine Mile Creek – Listed 2004– TMDL approved 2010– Requires 62% road salt reduction

ninemilecreek.org


Study of de-icing salt accumulation and transport through a watershed

- Highway Ditch/Swale- Sewered (Curb-and-gutter) Roadway- Stormwater Detention Ponds

Goal: Understand chloride accumulation, residence time, and timing of export in an urban watershed (small scale, source areas)

Outcome: Inform where and when of potential chloride management and mitigation practices

Funding: MN Local Road Research Board


Study Approach• Continuous Monitoring (Flow, Sp. Cond.)

• Water sample analysis for Chloride– Chloride-Conductivity regressions

• Chloride load calculations(1) Retention / Cl Budget(2) Timing of export / residence time

• Periodic water column profiles in ponds

• Three Winter Field Seasons (2015 – 2017)

RETENTION: Of road salt applied in a winter, how much is NOT observed in surface runoff over the next year (presumably lost to soil / groundwater)


Chloride Load Calculations

Annual Chloride Export in Surface Runoff

Annual Road Salt AppliedRETENTION = 1 -

Specific ConductivityDischarge

(1) Monitoring Time Series

Chlo

ride,

mg/

L

Spec. Conductivity, uS/cm

(2) Conversion of Conductivity to Chloride Concentration Using Site-Specific Regressions

(3) Chloride Load (Export) = Discharge Volume x Cl Concentration


Study Sites: Lake McCarronsWatershed

(2) Curb & Gutter Roadway

(1) Ditch(3) Pond / Residential Watershed

020406080

100120140

1970 1980 1990 2000 2010

Mea

n Ch

lorid

e, m

g/L


Curb & Gutter Roadway (Co. Rd B)28 ac, no BMPs, ~1 lane-mile

Highway Ditch (Hwy 36)12 ac, 1.5 lane-miles

Residential Watershed(Alameda Pond)285 ac, Some wetlands


0%

20%

40%

60%

80%

100%

Results: Road Salt Retention

42% 38% 52% 94%Mean:

Field Season 2(Nov 2015 – Nov 2016)

Field Season 3 (Dec 2016 – July 2017)

Minn. R & Miss. R. tributaries*

*Novotny et al. 2008

Residential(Pond Inlet)

PondOutlet

Curb &Gutter

Ditch

Chlo

ride

Rete

ntio

n


Why such high retention of road salt?

Residential Watershed 42%

Curb & Gutter 52%Ditch 94%


0

200

400

600

0

50

100

150

200

Chlo

ride

Load

, lbs

/yr

DITCH

CURB & GUTTERSeasonality ofChloride Export

Mean Monthly Chloride Loading,Roadway Sites

Aug 2015 – July 2017


Fall Export of ChlorideBaseflow in Large Storm Drains

Capitol Region Watershed DistrictSt. Paul, MN

Study Watershed

230 mg/L

Chloride will be a “legacy” pollutant in groundwater


BattleCreek

Nine MileCreek

Fall Export of ChlorideBaseflow in Impaired TCMA Streams

0

200

400

600

800

1000

1 2 3 4 5 6 7 8 9 10 11 12

Mon

thly

Mea

n Ch

lorid

e, m

g/L

Battle Creek1999-2011

050

100150200250300350

1 2 3 4 5 6 7 8 9 10 11 12

Mon

thly

Mea

n Ch

lorid

e, m

g/L

Nine Mile Creek1999-2011


Seasonality ofChloride Export:

Mean Monthly Chloride Loading,Pond Site in aResidential watershed

Aug 2015 – July 2017

01,0002,0003,0004,0005,0006,000

Dec Jan

Feb

Mar Ap

rM

ay Jun

Jul

Aug

Sep

Oct

Nov

01,0002,0003,0004,0005,0006,000

Dec Jan

Feb

Mar Ap

rM

ay Jun

Jul

Aug

Sep

Oct

Nov

POND OUTLET

POND INLET

Chlo

ride

Load

, lbs

/yr

**Retention Within Pond (Inflow vs. Outflow):

+/- 10%


Daily Precip

Chloride Load (lbs) in Outflow

200

120

50

Approx. Outflow Chloride Conc., mg/L(daily mean)

Chloride Exportfrom Alameda

Pond (2016-17)

DEC JAN FEB MAY JUN JUL AUGMAR APR


Seasonal patterns of salt accumulation and flushingSpecific conductivity (µS/cm

)

Pond

Dep

th (m

)

Winter Spring Summer Fall Winter Spring Summer Fall 0

0.5

1.0

1.5

2.0January March May July Sept Nov January March May July Sept

Water surface

2017 2018

Chloride ~230mg/L

Alameda Pond


Mid May, 2018High road salt areas

6 “deep” pondsMax Cl 18 grams/L

Specific conductivity (S)0 10000 20000 30000 40000 50000 60000

Dep

th (c

m)

-250

-200

-150

-100

-50

0

230 mg/L Cl

Water surface

Chloride Accumulation and Persistence in Ponds

Seawater


Salt entering ponds in winter snowmelt…

sinks

accumulates

persists into summer

Water Quality ImpactsChloride toxicity +

Heavy metal concentrations +Mixing & Dissolved Oxygen -

Release of Phosphorus to Downstream


• High chloride retention (50%+) – what is its fate below ground?– Shallow groundwater, deeper aquifer, soil storage (current work at SAFL) – What is the role of Infiltration BMPs?

• Persistent warm season chloride stratification and export from ponds

– Low dissolved oxygen reduced P removal?– Attenuate Cl export to downstream waters?

• Fall export of chloride – Long residence times (1+ year) – legacy pollutant– Groundwater contamination

Summary / Implications


• Management by runoff capture/diversion?At curb-and-gutter study site: 90% of chloride loading occurs in smallest 20% of flow events

– First-flush diversion into cisterns or ponds? – Ponds: an opportunity for chloride mitigation?

• Disconnect infiltration BMPs during winter?

Drawbacks• Expensive; Disposal difficult • Surface runoff only• High chloride loss in roadside areas

limits options & effectiveness

Chloride Management

www.willowcreekpavingstones.com

• Alternative Road Treatment (current research topics at SAFL, other MN universities)

– Non-halite de-icers?– Permeable pavements?


• Brine vs. Dry Application, Pre-wetting, Calibrating Spreaders, etc. [Public Works]– 30% - 70% reduction in Road De-Icer Use*

• Education of commercial and private applicators [Liability-driven Over-salting]

• Training and Certification: Minnesota Pollution Control Agency / Fortin Consulting*www.pca.state.mn.us/water/salt-applicators; fortinconsulting.com/winter-maintenance-certification-training/

• Limited Liability for those with Smart Salting Certification? (NH, IL)

Reducing road salt usage is necessary to protect water resourcesWater Quality vs. Public Safety

Chloride Reduction: “Smart Salting”


Road Salt Pjt PIs: Bill Herb, Heinz Stefan (Prof. Emeritus)Pond Project PIs: Profs. John Gulliver and Jacques FinlayFunding: MN Local Roads Research Board, MN Stormwater Research Council,

MN Pollution Control AgencyTechnical Advisory Panel

Elizabeth Klemann, Wayne Sandberg, Barb Loida, Nick Tiedeken, Tara Carson, Ryan Peterson, Nick Olson, Dan Sullivan, Al Rindels

MN Department of TransportationRamsey CountyCity of Roseville

Ryan JohnsonRoseville Covenant Church

Austin KaufmannCapitol Region Watershed District

Forrest Kelley, Britta BeldenField and Lab Assistance

Ben Erickson, Shelly Rorer, Katie Kemmitt, Evelyn Boardman, Tessa Belo, Sally Donovan, Vini Taguchi, Walt Atkins, Claire Jaeger Mountain, Krysta Garayt

Ben Janke [email protected]

Acknowledgements


Resources and ReferencesReports and Papers

• Herb, W.H., Janke, B.D. and Stefan, H.S. (2017) “Study of De-Icing Salt Accumulation and Transport Through an Urban Watershed”http://www.dot.state.mn.us/research/reports/2017/201750.pdf

• Novotny, E.V. and Stefan, H.S. (2010) “Projections of Chloride Concentrations in Urban Lakes Receiving Road De-Icing Salt”. Water, Air and Soil Pollution, 211(1-4). doi:10.1007/s11270-009-0297-0

• Novotny, E.V., Sander, A., Mohseni, O. and Stefan, H.S. (2009) “Chloride Ion Transport and Mass Balance in a Metropolitan Area Using Road Salt”. Water Resources Research, 45. doi:10.1029/2009WR008141

• Stefan, H.S., Novotny, E.V., Sander, A., and Mohseni, O. (2008) “Study of Environmental Effects of De-Icing Salt on Water Quality in the Twin Cities Metropolitan Area, Minnesota”https://conservancy.umn.edu/bitstream/handle/11299/151669/MN_RC2008-42.pdf

Minnesota Pollution Control Agency Resources

• Chloride Reports and Guidance Documents (Reports, Monitoring, TMDLs):https://www.pca.state.mn.us/water/chloride-reports-and-guidance-documents

• Salt and Water Quality Outreach (Winter Maintenance Assessment Tool, Training): https://www.pca.state.mn.us/water/salt-and-water-quality