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]
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
Chloride Impairment of Drinking Water
250 mg/LUrban
MunicipalWater
Northern US Drinking Water Wells,
1991-2004 (USGS/Mullaney et al., 2009)
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
Chloride Impairment of Surface WatersU.S. Streams
(Stets et al. 2017)
Mpls-St. Paul Metro Lakes
(Novotny 2009)
http://stormwater.safl.umn.edu/
TCMA Chloride Assessment (MN Pollution Control Agency, 2014)
340 water bodies (lakes, wetlands, streams) in Mpls – St. Paul metro• 39 impaired• 38 high risk
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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)
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
Why such high retention of road salt?
Residential Watershed 42%
Curb & Gutter 52%Ditch 94%
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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%
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
• 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
http://stormwater.safl.umn.edu/
• 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?
http://stormwater.safl.umn.edu/
• 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”
http://stormwater.safl.umn.edu/
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
http://stormwater.safl.umn.edu/
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