Green infrastructure policy for stormwater infiltration

An Overview of
NEW STORMWATER RULES
(PENDING June adoption)
Evan N. Pratt, P.E.
Water Resources Commissioner

OUTLINE
A. Why Change?
B. Value of Infiltration
C. 3 Main Changes
D. Development Benefits and Concerns
E. Community Benefits and Concerns
F. Case/Cost Studies and Examples
G. Summary Talking Points – Let’s be consistent

WHY ARE WE HERE?
THESE PEOPLE CAN’T CHANGE POLICY – BUT HAVE TO LIVE WITH IT

Q: Why Infiltration?
A: TSS Removal Efficiencies
SOURCE: 2005 DATA REPORT, UNH STORMWATER CENTER

Top 5 TSS Removal Efficiencies
 POROUS PAVEMENT– 100%
 GRAVEL WETLAND – 100%
 STORAGE BASIN INFILTRATION– 100%
 TREE FILTER – 93%
 BIORETENTION – 92%
 RETENTION POND – 65%
 SWALE – 55+%

WCWRC RULES:
WHAT IS CHANGING?
3 KEY CHANGES
1. PROCESS: MANDATORY PRE-APPLICATION MEETING
2. TECHNICAL APPROACH
a. METHOD OF CALCULATING RUNOFF: NO IMPACT
b. STORMS HAVE GOTTEN BIGGER
3. INFILTRATION REQUIREMENT
a. First 1”, OR
b. Must prove that soils are unsuitable for infiltration

1. PROCESS:
PRE-APPLICATION MEETING
GENERAL EVALUATION
Purpose: Engage Owner, clarify changes and benefits
Soil types
Information on geology and hydrology including estimate
of groundwater table elevation
Topography
Land cover
Other pertinent natural or man-made features
Potential locations for infiltration BMPs

2. TECHNICAL: 1% STORM
 Current MDEQ 24 hour 1% storm = 4.36 inches
 NOAA Atlas 14, Volume 8
 Published 2013
 Provides data for discreet locations
 Ann Arbor, Milan & Ypsilanti Stations
 Range for the 24 hour 1% storm at these stations varies minimally
 All indicate the 24 hour 1% storm = 5.11 inches
 Chelsea Station
 24 hour 1 % storm = 5.21
 New WCWRC Rules 24 hour 1 % storm = 5.11 inches

2. TECHNICAL: Method of Calculation
SUMMARY: Method yields about the same results for
detention on several sites.
 “The Oakland County Method” vs. “NRCS Curve Number”
 Peer Review Comparisons
 WCWRC Deputy WRC -- Dennis Wojcik, P.E. verifications
 705 N. Zeeb Road
 Two Other Site Developments

3. INFILTRATION
 MDEQ NPDES Permit Application
 Require that post-construction runoff rate and volume of
discharges not exceed the pre-development rate and
volume for all storms up to the two-year, 24 hour storm at
the site. At a minimum, pre-development is the last land
use prior to the planned new development or
redevelopment.
 WCWRC Rules will require infiltration of the greater of the
first flush volume or difference between pre-settlement
and post-development 24 hour 50% storm.

HOW DOES DEVELOPMENT BENEFIT?
Many developers are finding lower cost for GI when used in
greenfields. Case studies at http://tinyurl.com/streetrunoff
 Less concrete infrastructure needed.
 Less surface area of storage needed if doing infiltration
 Less impact to developable area with co-location
 It will always be more costly to develop unsuitable land
 This is why poorly suited land (soils, etc) is cheaper
 Public cost of developing poorly suited land
 Whose job is it to look at total cost of a site?

COMMUNITY BENEFITS and CONCERNS
 Reduction in community costs related to development
 Soils have always been integral to land use decisions.
Now on County GIS – NRCS Soils layer under “Soils”
 Collaboration during pre-application process
 HOW WILL YOUR COMMUNITY FUND LEGACY COSTS OF
DEVELOPMENT? 35% GENERAL FUND (OLD WAY) OR
MORE LIKE WCRC?

DEVELOPER CASE STUDY:
GI COST SAVINGS

Case Study: Boulder Hills
Pelham, NH
 2009 -- 900’ OF PRIVATE RESIDENTIAL PAVING IN NE
 SITE GOAL OF ZERO DISCHARGE
 55+ ACTIVE ADULT COMMUNITY
 SANDY SOILS (NOT A MUST)

COST AVOIDANCE
 1616’ CONCRETE CURB
 785’ PIPE
 8 CATCHBASINS
 2 DETENTION BASINS & 2 OUTLET STRUCTURES
 SAVED 1.3 ACRES IN LAND CLEARING/CONSUMPTION
 CONVENTIONAL = $789,500 vs. LID SWM= $740,300
 INFILTRATION COST SAVINGS = $49,000 = (6.2%)
 O/M DISCUSSION LATER – ALSO LESS

HOW POROUS O/M IS MUCH LESS
WHAT IF PAVEMENT NEVER CRACKED?

…AND IS SUPPOSED TO HAVE WATER IN THE BASE

$-
$10,000
$20,000
$30,000
$40,000
$50,000
$60,000
$70,000
$80,000
$90,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
HMA Maintenance With Sweeping
Cumulative Porous Sweeping Costs

WHY CHANGE:
LET’S ALL GIVE THE SAME ANSWERS
SOAKING WATER INTO THE GROUND IS SIMPLER AND
CAN COST LESS
WCWRC WILL WORK WITH OWNERS BEFORE A
PURCHASE DECISION. OWNER’S RESPONSIBILITY TO
EVALUATE DEVELOPMENT COSTS OF CHEAPER PROPERTY.
GOVERNMENT AGENCIES ARE ALREADY INVESTING

GOVERNMENT AGENCIES ALREADY
INVEST IN GREEN INFRASTRUCTURE

WCWRC OFFICE – 705 N. ZEEB
 13 years old
 42,000+ sft.
 Detention (2)
 Bioswales
 Level Spreader
 Infiltration Bed
 Solar Panels
 Native Veg.
BUT
 No Credit

WASHTENAW COUNTY BUILDING
 Current method detention volume = 45,000 c.f.
 Revised method detention volume = 60,000 c.f.
 Reduction in volume utilizing BMPs installed = 11,000 c.f.
 Revised method required detention volume = 49,000 c.f.

705 ZEEB ROAD
REDUCED CONSTRUCTION COST
 8 structures @ $2,000 ea. = $16,000
 425 ft.-12in. RCP @ $40/ft. = $17,000
 265 ft.-15 in. RCP @ $50/ft. = $13,250
 Savings = $46,250 (FIRST FLUSH ONLY)
 BUT SOILS ARE SUITABLE FOR 100% INFILTRATION
 Extra Savings: 1,950 cyd earthwork @ $10/cyd = $19,500
 NET SAVINGS = at least $65,750
(plus additional pipe savings, offset by need to add bioswale)
-Will be estimating porous asphalt option in future version

After planting – still standing water

Eastern Michigan University, InSite Design Studio
Plants mature – no standing water

IT’S SIMPLE:
WHICH IS
BETTER??

http://tinyurl.com/streetrunoff
TAKE AWAY MESSAGES
1. Human activity is the #1 cause of many problems. The
purpose of the New Rules is to:
A. Reduce long term cost impacts to communities and taxpayers
B. Reduce water quality and flooding impacts of development
2. Good sites with good soils will result in less costly projects –
Owners’ responsibility during site selection & due diligence.
3. WCWRC is available to work with communities and the
Owner on challenging sites.

Green infrastructure policy for stormwater infiltration

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Green infrastructure policy for stormwater infiltration