Source reduction for urban stormwater

Biogeochemical Perspectives on Stormwater Management

Larry Baker

Water Resources Center and

WaterThink, LLC

Goals• Examine problems with best management

practices (BMPs)• Examine biogeochemical processes

– Process limitations– Sustainability

• Applications:– Soluble P– Nitrate removal– Road salt

• Human dimension

Limitations of end-of-pipe storm water treatment

1. Low and variable treatment performance 2. High cost:

$1000/Ton SS (Weiss et al. 2007)

$500/kg P3. Some constituents are not readily treated in BMPs

(chloride, soluble P, fecal coliforms)4. Poor cold weather performance5. Low sustainabilty (pollutant accumulation,

clogging, etc.)6. Unfair cost allocation – polluted pays

Type Phosphorus Sediment

Ave. %

Removal

CV, % Ave. % removal

CV, %

Dry extended ponds

53 ±28 25 ±15

Wet basins 65 ±32 53 ±23

Bioretention 85 ±23 72 ±11

Sand filters 85 ±14 46 ±31

Wetlands 68 ±25 42 ±26

Typical removal efficiencies for structural BMPsSource: Weiss et al., 2007

Pollution production

Gas loss: CO2 (decomposition) N2 (denitrification) VOCs

Sedimentation Plant debris Adsorption

Remaining pollutants-Soluble P, coliforms, salt, suspended solids

Sediment

Processes in a stormwater pond or wetland

Water

Plant uptakeN, P, metals

Algae growth

Recycled

Sediment accumulationP recyclingToxics?

Pollution production

Processes in infiltration BMPs

Gas loss: CO2, N2, VOCs

Aquifer

FiltrationAdsorptionPrecipitation

Soil

NitrateChloride

Clogging

Metal accumulationSaturation of adsorption sites

End-pipe-BMPsDetention basinsWet pondsInfiltrations basinsWetlands

Level 2: Sources from landscapes to streets

Level 1: Sources to watershed

Level 3: Source from streets to storm sewer

Pollutant mass balances:System boundaries

Streets are not a source of pollution but a conduit for pollution

Level 1 analysis: Effect of lawn P fertilizer restriction

Conditions: 5 km2 residential neighborhood, 0.5 ha lot size, 20% impervious area on lot; 80% pervious area fertilized; 1 dog/house; irrigation. Updated from Baker and Brezonik, 2007 using MN Ag 2006.

Source Input rate total,kg/yr

%

Fertilizer 7.5 kg/ha-yr 1,920 73

Dogs 1.2 kg/dog-yr 1,770 23

Irrigation 0.3 mg P/L; 0.2 m/yr 169 2

Deposition 0.25 kg/ha-yr 125 2

Total - 3,984 100

total, kg/yr

%

1,000 0

1,770 86

169 8

125 6

3,064 100

Before MN P fertilizer ban After MN P fertilizer ban

23% reduction

Maples (all species)

y = 0.0009x2.2188

R2 = 0.9959

0

10

20

30

40

50

0 50 100 150

Diameter at breast height, cm

Le

af f

all,

kg

P p

er

tre

e

Level 2 analysis: Inputs from boulevard trees to streets

Example: maple trees(based on UFORE model)

DBH measurement

Suspended solids

0

500

1000

1500

2000

2500

3000

M HN HF VHN VHF

SS

, m

g/L

0.0

0.5

1.0

1.5

2.0

2.5

M HN HF VHN VHF

P, m

g/L

Particulate P

Soluble PLevel 2 analysis (cont’d): Lawn runoff to street

Source: Barten (1994)

For comparison: Raw sewage P = 5 mg/L SS = 200 mg/L

Eutrophic lake:P = 0.05 mg/L

Soil P level vs. dissolved P in runoff from

turf (left) and bare soil (right)

Soldat et al., 2008 Water, Air, Soil Poll.

Trees

20%

Lawn

70%

Atm. Dep.

0%

Dogs

10%

Level 2 (lawns to street) total P input

Assumptions:- Medium fertility lawns- 1 tree per 20 m- 30 m lot width- 0.6 dogs/household

Percentage of total P entering street(total = 8 kg P/km street)

Baker et al., Chapter 7, in Assessment of Stormwater BMPs Manual(WRC web page)

Growing turf

Soil inorganic P Soil organic P

Fertilizer P

Runoff soluble P

Runoff particulate P

Exported clippings

Mowed grass

Leaching

Integrating biophysical and social aspects of lawns to reduce soluble P in runoff

Baker, Wilson, Fulton, and Horgan, Cities and the Environment, 2008.

Lawn P cycle

3 or more fertilizer applications,+ mulching

Steep slope, low infiltration soil

Nowak disproportionality concept applied to lawnsNowak et al., 2006 Society and Natural Resources

High nutrient export

Site design

Site management

0

5

10

15

20

25

Sand Fine-sand Clay-fine Clay

Soil type

% r

un

off

Low slope

Steep slope

Target these

1.Target vulnerable lawns (biophysical dimension)

Modeled runoff for 1” storm

0

20

40

60

80

100

0 1 or 2 3 or 4 > 5

# of fertilization times

% o

f h

om

eow

ner

s

2. Tailor messages to homeowner types(social dimension)

“Casual” “Perfectionist”

Adaptive management for road salt

MNDOT Salt use, tons/yr

0

50,000

100,000

150,000

200,000

250,000

300,000

y = 31.352e0.0437x

R2 = 0.85

0

50

100

150

200

0 10 20 30 40

% impervious

Str

eam

chl

orid

e, m

g/L

Relationship between % impervious surface and average stream chloride Sander, Novotny, Mohseni, and Stefan, 2008

Event analyzed by team - Weather - Pavement conditions - Stream chloride

Road crews add salt for snow/ice event.Salt quantities recorded

Sensor network recordsspecific conductance; temperature

Recommendations summarized; transmitted to road crews

Adaptive management schematic

dialogue

• “Salt” easy to measure – conductivity• There are many alternatives

- Alternative salts (calcium acetate, etc.)- Alternative methods – pre-wetting; brine

• Public works crews are small, dedicated• Communication would be fairly easy• Many learning opportunities• Could save money and improve safety• Nothing else will work – chloride is conservative

Why adaptive management should work

Mississippi + M

innesota Rivers

Inflow16.86

Outflow17.99

Wastewater 0.41

Withdrawal0.18

Groundwater pumping0.46

Recharge0.46 (assumed)

Evaporation1.37

Precipitation2.42

Runoff0.82

Will stormwater management alter the Twin Cites hydrologic balance?

Summary

• Structural BMPs are necessary but not sufficient to meet water quality goals

• We need to move toward a multiple barrier strategy

LID design source reduction structural BMPs

• Understanding biogeochemical processes – and limitations – tends to move point of control upstream

• Urban biogeochemistry involves human choice and the biophysical system

• Stormwater management is part of broader urban water management – hydrologic balance, etc.

References• Baker, L.A. 1998. Design considerations and applications for wetland treatment of high-nitrate

waters. Water Science Technology 38: 389-395.• Baker, L. 2007a. Instant runoff [on source reduction for stormwater]. Star and Tribune,

Minneapolis.• Baker, L. A. 2007b. Urban stormwater: getting to the source. Storm water 8:8.• Baker, L. A., R. Holzalksi, and J. Gulliver. 2008a. Source reduction. in J. a. J. A. Gulliver, editor.

Minnesota stormwater assessment manual. Minnesota Water Resources Center, St. Paul.• Baker, L. A., P. Westerhoff, and S. M. 2006. An adaptive management strategy using multiple

barriers to control tastes and odors. Journal of the American Water Works Association 98:113-126.

• Baker, L. A., B. Wilson, and D. D. Fulton. 2008b. Disproportionality as a framework to target nutrient reduction from urban landscapes (invited paper). Cities and the Environment. 1:Artilce 7.

• Baker, L. A., B. Wilson, J. Gulliver, O. Moshir, A. J. Erickson, and R. M. Hozalski. 2008c. Process assessment framework.in J. Gulliver, and J. Anderson, editor. Assessment of Stormwater Best Management Practices. Minnesota Water Resources Center St. Paul.

• Ingersoll, T. and L. A. Baker. 1998. Nitrate removal in wetland microcosms. Water Research . 32:766-684.

• Nowak, P., S. Bowen, and P. Cabot. 2006. Disproportionality as a framework for linking social and biophysical systems. Society and Natural Resources 19:153-173.

• Soldat, D. J., A. M. Petrovic, and Q. M. Ketterings. 2008. Effect of soil phosphorus levels on phosphorus runoff concentrations from turfgrass. Water, Air, Soil Poll. online.

• Weiss, P. T., J. S. Gulliver, and A. J. Erickson. 2007. Cost and pollutant removal of storm-water treatment practices. J. Water Resources Planning and Management 133:218-229.

Most of my articles can be downloaded from my WRC web site:http://wrc.umn.edu/aboutwrc/staff/baker/index.html (click on “vita”)Non-technical articles can also be downloaded from WaterThink.com