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

WHY CHANGE?

WHY CHANGE?

WHY CHANGE?

IT ALL
ADDS UP

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

OVERVIEW OF CHANGES

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

Comparison of Unit Costs

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

HOW POROUS O/M IS MUCH LESS
…AND IS SUPPOSED TO HAVE WATER IN THE BASE

HOW POROUS O/M IS MUCH LESS
$-
$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

EMU Student Housing

After planting – still standing water

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

InSite Design Studio, Inc.

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.

QUESTIONS?