This document provides an overview of new stormwater rules pending adoption in June. It discusses three main changes: 1) requiring a mandatory pre-application meeting, 2) updating the technical approach to use a 5.11 inch 24-hour 1% storm and infiltration of the first 1 inch of runoff, and 3) requiring infiltration of runoff unless soils are proven unsuitable. It provides examples of how green infrastructure can benefit development through lower construction and maintenance costs. Community benefits include reducing long-term costs and water quality impacts.
Green infrastructure policy for stormwater infiltration
1. An Overview of
NEW STORMWATER RULES
(PENDING June adoption)
Evan N. Pratt, P.E.
Water Resources Commissioner
2. 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
3. WHY ARE WE HERE?
THESE PEOPLE CAN’T CHANGE POLICY – BUT HAVE TO LIVE WITH IT
12. 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
14. 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
15. 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
16. 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
17. 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.
18. 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?
19. 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?
21. 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)
22. 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
24. HOW POROUS O/M IS MUCH LESS
WHAT IF PAVEMENT NEVER CRACKED?
25. HOW POROUS O/M IS MUCH LESS
…AND IS SUPPOSED TO HAVE WATER IN THE BASE
26. 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
27. 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
29. 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
30. 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.
31. 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
37. 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.