University of Minnesota

Paula Kalinosky, Lawrence Baker, Sarah Hobbie, Chris Buyarski, In Partnership with the City of Prior Lake, MN

Ross Bintner LID Symposium, August 20, 2013

Quantifying Nutrient Load Recovery through Targeted, Intensive Street Sweeping

Summary of Questions Addressed

Why Revisit Street Sweeping?

What’s Different About the Prior Lake Street Sweeping Study?

What was found in Prior Lake?

How is this information useful?

Statement of Problem

Nutrient management is a significant

concern in urban watersheds

Streets act as a conduit for pollution to the storm drainage

network

Meeting watershed management goals

(TMDL, permits) can be costly $$

Is Street Sweeping a Cost-effective Source Control BMP?

Study Design Nine Study Routes

LOW Canopy MEDIUM Canopy HIGH Canopy

1 X, 2X, 4X/month 1 X, 2X, 4X/month 1 X, 2X, 4X/month

Q: What is the relationship between overhead tree canopy and recovered solids, nutrients?

Distribution of Sweeping Routes

Focus on Recovered Material

Collection Protocol WEIGH

INSPECT

DUMP

INSPECT

SAMPLE

INSPECT

Material Removed From the Street is Not Available for Transport

Lab Methods: Unique Fractionation Scheme

Suited to Focus on Nutrients

Fines (<2mm)

Coarse Organics (≥2mm)

Rocks (≥2mm)*

TP, TN, TOC (Leached during separation process)

TS, TP, TN, TOC, % Organic TS, TP, TN, TOC, % Organic

* Dry mass only, nutrient contribution assumed negligible.

Sweeper Waste

Findings: Recovered Solids

Average Load Recovered per Month Dry Solids (lb/curb-mile)

Sweeping Frequency Low Canopy Med Canopy High Canopy

1X/mo 183 219 435

2X/mo 269 423 664

4X/mo 478 849 649

Big Picture – Loads increase as tree canopy cover increases.

Seasonal Trends

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Jan Feb Mar Apr May Jun Jul Aug Se[ Oct Nov Dec

Tota

l Dry

So

lids

(lb

)

Month

Year 1Year 2

Winter Weather Influence

Sep

Influence of month/season on load intensity is significant.

Role of Coarse Organics

0%

20%

40%

60%

80%

100%

Jun

-10

Jul-

10

Sep

-10

Oct

-10

No

v-1

0

Jan

-11

Feb

-11

Mar

-11

May

-11

Jun

-11

Jul-

11

Sep

-11

Oct

-11

No

v-1

1

Jan

-12

Feb

-12

Mar

-12

May

-12

Jun

-12

Jul-

12

Au

g-1

2

Pe

rce

nt

Load

as

Co

arse

Org

anic

s

Dry Solids Phosphorus Nitrogen

Coarse organics are a significant source of nutrients

Trends in Cost Effectiveness

$0

$100

$200

$300

$400

$500

$600

$700

2 4 6 8 10 12

Ave

rage

Co

st-e

ffe

ctiv

en

ess

, $/l

b

Rec

ove

red

Ph

osp

ho

rus

Month

L4

H2

Least cost effective

Most cost effective

In high canopy areas, phosphorus can be recovered for less than $100/lb

Correlation between Tree Canopy Cover and Recovered Phosphorus

R² = 0.84

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0% 5% 10% 15% 20%

Cu

mu

lati

ve P

Lo

ad, S

no

w-f

ree

sea

son

(l

b/c

urb

-mile

)

Percent Tree Canopy Cover Over the Street

Study Total P Load Intensity

1X/mo 2X/mo 4x/mo

General Model for Predicting Recoverable Loads

E(Load│m, f, c)=

o + 1(month) + 2(frequency) + 3(canopy)

Goal: Produce a tool for estimating nutrient recovery based on easily obtained inputs.

TIMING of sweeping event

FREQUENCY of sweeping events

CANOPY COVER for sweeping route

Model Validation

Predicted Study Load, Five Fold Cross-Validation

MEASURED MLR

Prediction RT Prediction

Fresh Solids 853855 756549 (-11%)

793020 (-7%)

Dry Solids 618622 547977 (-11%)

565047 (-9%)

Total Phosphorus 502 424 (-16%)

443 (-12%)

Total Nitrogen 1945 1645 (-15%)

1682 (-14%)

Spreadsheet Planning Tool: User Inputs

Users define sweeping routes for which nutrient recovery will be estimated.

Spreadsheet Planning Tool: User Inputs

Use supplies a default cost per curb-miles (Prior Lake Method available in Guidance Manual).

Spreadsheet Planning Tool: Estimate Nutrient Recovery

1. Choose Route

2. Define Sweepings

3. Check Estimates

4. Save Routine

Spreadsheet Planning Tool: Output, Annual Summary of Sweepings by Route

Spreadsheet Planning Tool: Output, Summary of Planned Sweepings by Month

Spreadsheet Planning Tool: Output, Monthly Subtotals for Planned Sweeping

Predicted vs. Measured, Prior Lake

Predicted vs. Measured, Prior Lake

Potential Application: Tracking Nutrient Recovery

Five –Fold Cross-Validation Exercise using Predicted P-concentrations, Regression Trees

P (lb)

Measured Recovered Phosphorus 505

Estimate based on:

Curb-miles Swept 457 (-9.4%)

Fresh Load (lb) 505 (-0%)

Dry Load (lb) 495 (-1.9%)

Next Steps

EXTRAPOLATE OPTIMIZE QUANTIFY