Urban Subwatershed Stormwater Retrofit Analysis (SRA)

Shawn TracyRestoration SpecialistMetro Conservation Districts (MCD)

MCD SWCD’sAnoka – Carver – Chisago – Hennepin – Isanti – Ramsey – Scott – Sherburne – Washington - Wright

MCD

Anoka

Carver

Chisago

Hennepin

Isanti

Ramsey

Scott

Sherburne

Washington

Wright

MCDLRP

Ecological Restoration

Stormwater BMP Design

Education

Subwatershed Stormwater Assessment

Conservation District

WMO/WD

Cities &

Residents

Sub-WSRestoration

Urban

Rural/Ag

Dan Anderson: http://www.flickr.com/photos/stonebridgedapper/

Google Earth

Defining our task

What it isUrban stormwater retrofittingIdentification of the highest value stormwater BMP retrofit practices by location (e.g., $/LB-TP/YR)A Water Quality planning toolSupplement to existing analysesOne (major) consideration in Capitol Improvement planningA Precise and relative modelLabor investment and quantity/quality of geospatial and W.Q. data affects accuracy

It is not…a hydraulic or storm sewer analysis/planning tool…primarily used for street-scaping or park development (secondary benefit)…an elaborate excuse just to get in more raingardens

Defining our task

Why an SRA?Massive effort needed to affect change in WQDisproportionate (insufficient) funding resourcesDisproportionate (insufficient) labor resourcesTMDL implementation guidanceAssurance of “bang-for-buck”

ChallengesLittle-to-no outfall and source-area field dataLimited time and budgets

25 SRA’s completed in 2.5 years by SWCD’s withat least 5 more currently being worked on

Defining our task

The Plus Side>30 years of pollutant accumulation, behavior and washoff data available>20 years of BMP performance data with more recent, state-of-science research (bench and field)Midwest city data (loading)Several water quality models based on this researchIf outfall data exists, can be calibrated to improve accuracyCan easily be modified (build-scenarios)Repeatable (precise)Multiple-year to-do-list based on value (lbs/$/yr)

25 SRA’s completed in 2.5 years by SWCD’s withat least 5 more currently being worked on

Scope

3-Analysis of BMP’s by site

2-Ananlysis of SW’s Catchments

1-Selection of Subwatershed

Process Overview

Scoping and Remote Data collectionDesktop AnalysisField ReconnaissanceTreatment modeling and cost analysisReport

Process Overview

ScopingWater body needsLGU needsExisting data review (quality and needs)Budgets and timeframesStakeholder consensus

Desktop AnalysisField ReconnaissanceTreatment modeling and cost analysisReport

Process Overview

Scoping and Remote Data collectionDesktop Analysis

Catchment and/or pipeshed delineationDelineate and classify land usesDelineate and classify permeable surface soilsAnalyze existing WQ treatment / base load modelFirst-tier elimination of catchments for retrofittingFirst-tier determination of WQ potential treatments

Field ReconnaissanceTreatment modeling and cost analysisReport

Process Overview

Scoping and Remote Data collectionDesktop AnalysisField Reconnaissance

Visit existing BMPsConfirm/modify land-use and storm sewer dataConfirm/modify initial BMP-family selectionSelection of 1° and 2° BMP sites (parcels)Site-specific data collection

Treatment modeling and cost analysisReport

Process Overview

Scoping and Remote Data collectionDesktop AnalysisField ReconnaissanceTreatment modeling and cost analysis

Development and optimization of BMP designIterations of “train” and/or level of treatment by BMP quantity – load reduction estimatesEstimates of installation and life-cycle costsLife-Cycle Cost analysis

Report

Process Overview

Scoping and Remote Data collectionDesktop AnalysisField ReconnaissanceTreatment modeling and cost analysisReport

Summary table – catchments ranked based on performance ($/lb/LCyr)Catchment profilesAnalysis methods and dataReferences

SiteCatchmentSubwatershed

SW #1C1

S1

S2

S3

S4

S5

S…

C2

C3

C…

STORMWATER BMP LOCATION

ANALYSIS

Existing Stormwater

Ponds

Storage Above Roadway Culverts

Storage Below Outfalls

Within Conveyance

SystemStorage in ROW

Large Parking Lots

Public Land

Catchments

BMPS

Extended Detention

Wet Ponds

Wetlands

Bioretention

FiltrationInfiltration

Swales

Other

Existing Pond Modification

Sites

Pleasant Lake Stormwater Retrofit Assessment, 2011

Laek McKusick existing stormwater routing diagram, MSCWMO

Lily Lake Stormwater Retrofit Assessment, 2009, Middle St. Croix WMO

Pleasant Lake Stormwater Retrofit Assessment, 2011

Pleasant Lake Stormwater Retrofit Assessment, 2011

Pleasant Lake Stormwater Retrofit Assessment, 2011

Pleasant Lake Stormwater Retrofit Assessment, 2011

Howard Lake Stormwater Retrofit Assessment

34-Acre Medium Density Residential Area

Pollutant Amt/year

Water Runoff 963,715 ft3

TSS 12,900 lbs

TP 35 lbs

TKN 128 lbs

Copper 0.73 lbs

Lead 1.34 lbs

Zinc 5.80 lbs

First Tier possible BMP locations

Lindstrom Retrofit Assessment, 2009,

Chisago SWCD

Catchment-based Cost/Benefit Analysis

EXISTING CONDITIONS RETROFIT OPTIONS

Base Loading Treatment

Marginal Network Treatment By BMP

Level 1 Level 2 Level 3

Treatmen

t

Existing BMP performance (%TP) 54% New Net % New Net % New Net %TP (lb/yr) 25.2 13.7 1.0 58% 1.9 62%TSS (lb/yr) 7887 6698 261 88% 357 89%Volume (acre-feet/yr) 21.90 0.00 0.00 0% 2.40 11%

Square feet of practice (or, CU FT of storage for WP, ED, SW) Exc. 3 ft below

outlet 1500

Marginal Cost

s

BMP Type Wet Pond Extended Detention

Moderately Complex

BioretentionNot yet advised

Materials/Labor/Design $30,000 $51,000

Unit Promotion & Admin Costs* $250 $254

Total Project Cost** $30,250 $54,803Annual O&M $0 $1,125Term Cost/lb/yr (30 yr) $1,008 $1,554

Retrofit Scenario: exc 3 ft on P27add 6 RG in

19

Catchment or Pond ID

Retro Type Qty of 100 ft3 BMPs

TP Reduction

(%)

TP Reduction

(lb/yr)

Volume Reduction (ac-ft/yr)

Overall Est. Cost1

O&M Term

(years)

Total Est. Term Cost/lb-

TP/yr

LILY-03 B 12 10 5 4 $19,900 30 $313

LILY-04 B, PS, VS 8 10 3.3 2.9 $14,150 30 $313

LILY-01 B 11 10 4.4 3.6 $17,650 30 $315

LILY-02 B 11 10 4.5 3.7 $18,000 30 $315

LILY-12 B 18 10 3.2 2.5 $12,000 30 $316

LILY-07 B, VS 20 20 7 5.8 $24,000 30 $318

LILY-09 B 11 20 4.3 3.6 $18,450 30 $337

LILY-22 B 14 20 2.5 4.2 $22,320 30 $352

LILY-10 B, PS, F 7 10 2.9 2.4 $15,225 30 $353

LILY-21 B 12 20 2.2 3.6 $19,325 30 $353 2P13-W PM n/a 50 20 0 $130,000 15 $433 2P18-W PM n/a 50 30 0 $265,000 15 $589

Lily Lake Stormwater Retrofit Assessment, 2009, Middle St. Croix WMO

Report

http://www.metrocd.org/

Questions