Stormwater management basins and road salt loading to groundwater in Baltimore County

Joel Moore Towson University Dept. of Physics, Astronomy, & Geosciences Urban Environmental Biogeochemistry Laboratory

2014 Maryland Groundwater Symposium

Towson University collaborators

Steve Lev Dept. of Physics, Astronomy, & Geosciences

Ryan Casey & David Ownby Dept. of Chemistry

Michael McGuire Dept. of Computer Science

Joel Snodgrass Dept. of Biology (now VT)

Rob Flora & Brandon Sandosky Environmental Science M.S. students

Allison Ricko, Gabby Shepherd, Greg Woodward Geology / Environmental Science B.S. students

Funding

The National Institute for Water Resources

Maryland Water Resources Research Center

US Geological Survey via

Jess & Mildred Fisher Endowed Chair of

Geological Sciences

Road salt usage

http://www.post-gazette.com

http://www.sciencedaily.com; http://www.usatoday.com/story/news/nation/2013/02/23/road-salt-substitute/1939793/

Salt pile, Chelsea, MA

• 10-17 million tons annually • Maryland application policy: 300-

500 Ib/lane mile/storm • US: Not classified contaminant • Canada: Is classified contaminant

Potential Impacts of Road Salt

Soils

Increased mobility of metals (e.g., Cu & Zn) and displacement of Ca, K, Mg

Inhibition of plant vigor and reproduction

Tree kill, Owings Mills, MD

Potential Impacts of Road Salt

Soils

Increased mobility of metals (e.g., Cu & Zn) and displacement of Ca, K, Mg

Inhibition of plant vigor and reproduction

Groundwater

NaCl intrusion into drinking water sources

Eventually gets into streams

Tree kill, Owings Mills, MD

Potential Impacts of Road Salt

Soils

Increased mobility of metals (e.g., Cu & Zn) and displacement of Ca, K, Mg

Inhibition of plant vigor and reproduction

Groundwater

NaCl intrusion into drinking water sources

Eventually gets into streams

Streams

NaCl addition to drinking water sources

Toxic effects on aquatic organisms & changes in N and P cycling

Tree kill, Owings Mills, MD

Research questions

In a watershed with modern storm water management practices:

1) By what pathways do Cl and Na move from impervious surface to stream?

Novel: whole system from road to stream

2) How does Na from road salt affect cation (Ca, Mg, K) concentrations & fluxes in soils, aquifers, and streams?

Novel: focus on Na & other cations

Increased road salt use over last 70 years

Jackson R. B., Jobbágy E. G. (2005) PNAS ; Kelly et al. (2010)

Began 1938 in NH

75% all US salt applied in IL, MI, NY, OH, PA, WI

Increased road salt use over last 70 years

Jackson R. B., Jobbágy E. G. (2005) PNAS ; Kelly et al. (2010)

Began 1938 in NH

Increased road salt use over last 70 years

Jackson R. B., Jobbágy E. G. (2005) PNAS ; Kelly et al. (2010)

Began 1938 in NH 10-17 million tons applied annually across US

Why increasing salt usage?

http://wikipedia.org; http://www.google.com/publicdata/explore?ds=gb66jodhlsaab_; http://biology.usgs.gov/luhna/chap5.html

US Population growth 1960 – 180 M 2010 – 309 M 72% growth More vehicles 1960 – 74 M 2010 – 242 M 227% growth

Urbanization in Baltimore-DC

Why increasing salt usage?

http://wikipedia.org; http://www.google.com/publicdata/explore?ds=gb66jodhlsaab_; http://biology.usgs.gov/luhna/chap5.html

Urbanization in Baltimore-DC

US Population growth 1960 – 180 M 2010 – 309 M 72% growth More vehicles 1960 – 74 M 2010 – 242 M 227% growth

Last 30 years: 1984 to present

Sexton et al. (2013) Remote Sensing of the Environnment

Baltimore/DC Impervious surfaces 1984 881 km2 2010 1176 km2

4.9% of total area Growth rate 11 km2/year

Impervious surface area in Maryland

Source: Maryland Department of Natural Resources, Chesapeake & Coastal Watershed Service (2000)

Increased road salt use & Cl – in streams

Jackson R. B., Jobbágy E. G. (2005) PNAS; Kaushal & Belt (2012) Urban Ecosys

Rural rivers feeding Baltimore water supply reservoirs

3x increase [Cl–] since 1960

Road salt effects on streams

Kaushal et al. (2005) PNAS

[Cl–] correlates with impervious surfaces

Avg. [Cl–] in urban

streams >250 mg/L

Data from Baltimore (Long-Term Ecological Research site)

Urban streams and altered flow

Impervious surfaces

0-10% runoff

90-100% runoff

Urban streams and altered flow

Impervious surfaces Pre-1990s development: Water & associated chemicals move quickly & directly to streams

http://pages.vassar.edu/casperkill/road-salt-in-the-casperkill/

0-10% runoff

90-100% runoff

Stormwater management basins (SMBs)

http://sustainablestormwater.org/2009/05/28/stormwater-101-detention-and-retention-basins/

- Newer construction/regulation attempts to redirect runoff to groundwater

- Little study of effect of SMBs on road salt runoff

Baltimore

Red Run in Gwynns Falls watershed (Owings Mills, MD)

Owings Mills, MD – Development over last 30 years

0

20

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120

140

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1980 1990 2000 2010

Num

ber o

f Pon

ds

Year

Lev & Snodgrass (TU)

Gallagher et al. (2011) Urban Ecol.

Owings Mills, MD – Study site

Well

Well w/ Sensor 100 m

0.38 km2 Schist bedrock Acidic soil SMBs <48h RT

Figure by Brandon Sandosky

Stormwater ponds: Groundwater concentrations

EPA secondary limit for Cl– 7 mmol/L Seawater 535 mmol/L Ref. site ~15 km NE Cleaves et al. 1970

2013 2014

July

Stormwater ponds: Groundwater concentrations

EPA secondary limit for Cl– 7 mmol/L Seawater 535 mmol/L Ref. site ~15 km NE Cleaves et al. 1970 Versus ref. site [Ca2+] avg. 140x higher [Na+] & [Cl–] avg 2100x 2013 2014

July

Owings Mills, MD – Study site

Well

Well w/ Sensor 100 m

60 & 120 m

Figure by Brandon Sandosky

Floodplain aquifer concentrations

Close to pond

[Ca2+] avg. 20x higher than ref. site [Na+] & [Cl–] avg 180x

Farther from pond

2013 2014

July July

Owings Mills, MD – Study site

Well

Well w/ Sensor 100 m

<20% of basin

Figure by Brandon Sandosky

Effects of high Na water on soil/aquifer chemistry

Bkgd

Pond Flowpath

Increased soil pH 1.5 – 2.5

Effects of high Na water on soil/aquifer chemistry

Bkgd

Pond Flowpath

Bkgd

Pond

Flowpath

Increased soil pH 1.5 – 2.5 Na up to 40% of exchange pool

Impact of road salt on tree growth

Tree kill zone, Owings Mills, MD – January 2013

Impact of road salt on tree growth

Ownby & Snodgrass (TU)

0

0.05

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0.15

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0.25

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0.35

1995 2000 2005 2010

Gro

wth

(mm

/yea

r)

Pond construction complete in 2000

Stressed tree core showing most recent growth on the left. Tree rings are much thinner than those in the core below, indicating less growth

Unstressed tree core showing most recent growth on the left. Rings are wider, indicating healthy growth

Owings Mills, MD – Study site

Well

Well w/ Sensor 100 m

Figure by Brandon Sandosky

Stream concentrations: like streams draining evaporites

Downstream Upstream

[Ca2+] avg. 25x higher than ref. site [Na+] & [Cl–] avg 125x

2013 2014

Stream export

Downstream Upstream

2013 2014

Ref [Na+] & [Cl–] ~25 mol/d Avg. Cl export 2100x higher; Ca 145x higher

Stormwater ponds seem to increase salt loading

10

100

1000

Chl

orid

e (m

g/L)

combined

managed

unmanaged

Lev & Snodgrass (TU)

Future work

A B C D E F G

A B C D E F G

SP5 NP5

CCEEECCEEE EEECCEEECC

A B C D E F G

A B C D E F G

SP5 NP5

Calculate Lag Time

• Sensor network & spatio-temporal data mining

• Scale up to more

subcatchments

Conclusions

• Addition of rock salt results in o Groundwater Na+ and Cl– concentrations that approach

seawater o Increased soil/aquifer pH & Na+ in cation exchange pool Affected soils/aquifers will then alter stream chemistry

for years to come o Na, Ca, and Cl concentrations in streams increased by 25–

125 over reference site o Stream export of Na, Ca, and Cl increased by >102 – 103

• Though Na, Ca, and Cl export is highest in winter months,

loading to groundwater through stormwater management basins produces high export year round Questions?

Owings Mills, MD – Study site

• Soil/aquifer formed on schist – acidic & relatively low cation exchange capacity (CEC)

• SMBs <48 hour residence time

• Shallow groundwater flows into 1st & 2nd order streams

• 42 wells in floodplain aquifer

• Wells sampled quarterly for water chemistry

Cl– from stormwater ponds

mmol/L <10 mmol/L <20 mmol/L <40 mmol/L white >50 mmol/L Data from Flora, 2011

ppm <355 <710 <1420 white >1775

seawater 10,000 EPA - 250

Soil/aquifer chemistry changes forced by high NaCl

Aqueous chemistry

CEC chemistry

Aqueous chemistry Measured

CEC chemistry Modeled

Modeled using PHREEQC

- Equilibrium - 1D transport

Soil/aquifer chemistry changes forced by high NaCl

Aqueous chemistry

CEC chemistry

Increase axis by > 102

Soil/aquifer chemistry changes forced by high NaCl

Aqueous chemistry

CEC chemistry

Soil/aquifer chemistry changes forced by high NaCl

Aqueous chemistry

CEC chemistry

Soil/aquifer chemistry changes forced by high NaCl

Aqueous chemistry

CEC chemistry

PHREEQC 1D transport at 0.6 m / day High concentration 20 days Low concentration 345 days

Cl– (chloride) vs Na+ transects thru plumes

Preceded by low snow/salt winter

Cl– (chloride) vs Na+ transects thru plumes

Preceded by low snow/salt winter

Cl– (chloride) vs Na+ transects thru plumes

Preceded by low snow/salt winter

Modeled groundwater chemistry entering stream

[Na+], [Ca2+], & [Cl–] higher after addition of road salt

Ca declines as Na ‘clears’

out CEC Absolute [Ca2+] to stream

increases but elemental ratios significantly different with implications for biota

Systems with stormwater management best practices

Uplands

Storm water Pond

Stream

Riparian Forest

TRANSPORT

Groundwater

Groundwater export of Cl– to stream

y = 0.0831x - 2.3095 R² = 0.5968

y = 0.2619x - 27.436 R² = 0.9812

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0 500 1000 1500 2000

Cl (

mg/

L)

Conductivity (uS/cm)

Upstream

Downstream

Lev & Snodgrass (TU)

Continuous record of Cl– export to stream

Lev & Snodgrass (TU)

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200

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1200

27-Apr 2-May 7-May 12-May 17-May 22-May 27-May 1-Jun

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duct

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(uS/

cm)

Upstream

Downstream

~135 ppm

~260 ppm

~203 ppm

~5 ppm

~52 ppm ~35 ppm