SLOPES V Innovative Ways to Show Storm Water

SLOPES V
Innovative Ways to Show Storm
Water Quality Compliance
Robert J. Léger, P.E.
May 27th, 2015
EWRG Oregon http://oregonewrg.org/
Presentation Outline
1. Introduction
2. SLOPES V Triggers
3. SLOPES V Stormwater Regulations
4. Demonstrating Compliance for Local
Water Quality BMP's - Examples
5. Cost / Benefit Analysis
Endangered Species Act – Section 7 Programmatic Consultation
Conference and Biological Opinion
and
Magnuson-Steens Fishery Conservation and
Management Act
Essential Fish Habitat Consultation
for
Revised Standard Local Operating Procedures for Endangered Species to
Administer Maintenance or Improvement of Stormwater, Transportation,
and Utility Actions Authorized or Carried Out by the U.S. Army Corps of
Engineers in Oregon
(SLOPES for Stormwater, Transportation or Utilities)
NMFS Consultation No.: NWR-2013-10411
http://www.oracwa.org/documents/2014_03-14_SLOPESVTransportation_NWR-2013-10411.pdf
Action Agency: U.S. Army Corps of Engineers
Portland District, Operations and Regulatory Branches
SLOPES V Triggers
(That I am aware of):
Projects that require USACE Permits:
•Discharge into Waters of the State below the
Ordinary High Water mark
•Fills in wetlands/waters of the state
•Projects that receive Federal funding
(roadways, BLM projects, etc.)
DEQ 401 Certification will be triggered also…
SLOPES V Standards
Standards that stormwater engineers need to know about:
•Detention
•Operations and Maintenance
•Water Quality
Detention
Section 36.c.iii. - Water quantity treatment (retention or detention
facilities), unless the outfall discharges directly into a major water body
(e.g., mainstem Columbia River, Willamette River (downstream of
Eugene), large lakes, reservoir, ocean, or estuary). Retention or
detention facilities must limit discharge to match pre-developed
discharge rates (i.e., the discharge rate of the site based on its natural
groundcover and grade before any development occurred) using a
continuous simulation for flows between 50% of the 2-year event and
the 10-year flow event (annual series).
Detention
•No detention required if you discharge directly to major
water bodies
•Match pre-developed discharge rates (continuous
simulation)
•Events between the water quality event and the 10-year
event
Very similar to standard Portland metro area detention
requirements
Operations & Maintenance
This information is buried in the document, page 146
Listed in Incidental Take Statement, 2.8.1 Amount or Extent of Take:
1. Each part of the stormwater system, including the catch basin and flow-through
planter, must be inspected and maintained at least quarterly for the first three years,
at least twice a year thereafter, and within 48-hours of a major storm event, i.e., a
storm event with greater than or equal to 1.0 inch of rain during a 24-hour period
(City of Portland 2008a; Valentine 2012).
2. All stormwater must drain out of the catch basin within 24-hours after rainfall
ends, and out of the flow-through planter within 48-hours after rainfall ends.
3. All structural components, including inlets and outlets, must freely convey
stormwater.
4. Desirable vegetation in the flow-through planter must cover at least 90% of the
facility – excluding dead or stressed vegetation, dry grass or other plants, and weeds.
Very similar to standard Portland metro area O&M requirements
Water Quality
Section 36. e. All stormwater quality treatment practices and
facilities will be designed to accept and fully treat the volume of
water equal to 50% of the cumulative rainfall from the 2-year,
24-hour storm for that site, except as follows: climate zone 4 –
67%; climate zone 5 – 75%; and climate zone 9 – 67% (Figure 1).
(ESA-listed species considered in this opinion are unlikely to occur
in Zones 5 or 9.) A continuous rainfall/ runoff model may be
used instead of runoff depths to calculate water quality
treatment depth.
Water Quality
All stormwater quality treatment practices
and facilities will be designed to accept and
fully treat the volume of water equal to
50% of the cumulative rainfall from the 2-
year, 24-hour storm for that site
(Volume, not necessarily flow rates)
Water Quality
50% of the cumulative rainfall from the 2-year, 24-hour
storm for that site
Older engineers like me are conditioned to
accept this as our design starting point
(especially those of us still using SBUH
modeling techniques). However, it may not
be necessary to start here…
Water Quality
What is Demonstrating Compliance?
• Can you show that your BMP designed to
local water quality standards will accept
and fully treat the volume of water equal
to 50% of the cumulative rainfall from
the 2-year, 24-hour storm for that site?
Water Quality
Why Demonstrate Compliance?
•
•
•
•
•
Existing facility triggers SLOPES V
Existing design triggers SLOPES V
Site using proprietary treatment devices
Site maxed out / no room to expand facility
Reduce ROW acquisition requirements
Water Quality – Portland
City of Portland Water Quality Standards:
Seventy percent removal of total suspended
solids (TSS) is required from 90% of the
average annual runoff
This started me thinking about this demonstrating
compliance. This 90% standard is considerable. Do
COP standard BMPs meet SLOPES requirements?
Water Quality – Portland
City of Portland Water Quality Standards:
Facilities sized by routing a hydrograph through the facility (rate-based facilities with a storage volume
component) may use a continuous simulation program (with a minimum of 20 years of Portland
rainfall data) or a single-storm hydrograph-based analysis method, such as the Santa Barbara Urban
Hydrograph (with 0.83 inches of rainfall over 24 hours and NRCS Type 1A rainfall distribution), to
demonstrate treatment of 90 percent of the average annual runoff volume.
OR:
Water Quality with SLOPES V
SLOPES V Water Quality Standards:
Accept and fully treat the volume of water equal to 50% of the
cumulative rainfall from the 2-year, 24-hour storm for that site
•Using NOAA Isopluvial maps or the online tool, you can find the
NOAA 2-year, 24-hour event depth at your site.
•The value varies with location, but is roughly 2.4” – 2.5”.
•50% of the 2-year event is equivalent to a 1.2” or 1.25” storm
event.
Water Quality – Portland vs. SLOPES V
There appears to be a discrepancy between
the size of the storm events being used as
the Water Quality/Pollution Reduction
benchmark.
How can Portland treat 90% of annual runoff
using such small PR events?
Hydrographs – Type 1A vs. Type 2
TYPE 2
BOTH HYDROGRAPHS:
-SAME EVENT DEPTH
-SAME VOLUME OF RUNOFF
-DRAMATIC DIFFERENCE IN
DISTRIBUTION & PEAK RATE
TYPE 1A
TYPE 1A - FREQUENT, LOW INTENSITY STORM EVENTS
ALLOW FOR MORE CONTINUOUS TREATMENT
Water Quality – Example 1 (COP)
Water Quality swales with high-flow bypass manholes
•Larger events max out the diversion pipe, sending more
runoff toward the swales.
•Is more than 50% of the 2-year event diverted to the
swale?
•Will the diverted flow meet water quality design
requirements such as residence time, flow depth, velocity,
and vegetation zones?
Water Quality – Example 1 (COP)
Water Quality swale with high-flow bypass manhole:
Water Quality – Example 1 (COP)
The swales were designed using the City of
Portland Presumptive Approach Calculator
(PAC). The PAC uses a SBUH engine to calculate
and route events through facilities using the
0.83” event for Pollution Reduction / water
quality. Storm event data and hydrographs are
available to access in the ‘Chart Data’ tab.
Water Quality – Example 1 (COP)
Create a spreadsheet where you can copy and
paste the PAC hydrograph for the 2-year
event. Calculate the volume in each time step
up to the design PR rate and sum the volume
diverted to the swale. Calculate the amount
of diverted runoff of the 2-year event.
Water Quality – Example 1 (COP)
SLOPES V Water Quality Standards:
Accept and fully treat the volume of water
equal to 50% of the cumulative rainfall from
the 2-year, 24-hour storm for that site
Yes, >50% of the event accepted into swale
Water Quality – Example 1 (COP)
SLOPES V Water Quality Standards:
Accept and fully treat the volume of water
equal to 50% of the cumulative rainfall from
the 2-year, 24-hour storm for that site
Look at your facility Design Requirements to
determine this (Residence Time, flow depth,
velocity, vegetation zones, etc.)
Water Quality – Example 1 (COP)
NOTE – This method has not been reviewed and approved, but this is the method
I would use to demonstrate compliance:
If you are using a COP filter basin with an overflow,
analyze and account for the volume infiltrated
through the topsoil mix using your design infiltration
rate. Account for any overflow within the basin.
Can you demonstrate 50% of your 2-year event was
filtered through the topsoil mix prior to discharge?
Water Quality – Example 2
(CWS StormFilters)
Clean Water Services - StormFilters
•CWS Water Quality Standard – Section 4.05.4.d:
The stormwater quality facilities shall be designed for a dry
weather storm event totaling 0.36” of precipitation falling
in 4 hours with an average storm return period of 96 hours.
Vwq = 0.36” * Impervious Area / 12”/ft.
Qwq = Vwq / 4 hours
Water Quality – Example 2
(CWS StormFilters)
•Once the internal float activates, StormFilters continuously
treat runoff up to the capacity of the cartridge
•We design StormFilters to treat the peak of the CWS event,
assuming 4 hours of peak flow rates
•Analyze the 2-year hydrograph through your filter system
considering their continuous treatment capacity
•Disregard the 2-year peak rate for now
•Does it treat 50% of the 2-year event volume?
Water Quality – Example 2
(CWS StormFilters)
C – 2-year hydrograph
D – Available treatment capacity
E – Volume Treated
F – Total Volume Treated
G – Percent of Total event volume
treated
Does your facility treat 50% of the 2-year event?
I found at least 73% treatment of 2-year event
using StormFilters designed to CWS 0.36” event.
Water Quality – Example 3
(CWS Extended Dry Detention Pond)
Clean Water Services – Extended Dry Detention Pond
•Detention and Water Quality in the same pond
•Same water quality standard, but detention based systems
release Vwq over 48 hours (drawdown time):
Vwq = 0.36” * Impervious Area / 12”/ft.
Qwq = Vwq / 48 hours
Water Quality – Example 3
(CWS Extended Dry Detention Pond)
Detention and Water Quality in the same pond
Water Quality – Example 3
(CWS Extended Dry Detention Pond)
If you look at the outflow hydrographs of detained storm events, you
will often see that they take more than 3 days to pass through the
pond… WHY?
Water Quality – Example 3
(CWS Extended Dry Detention Pond)
WHY?
Due to the inclusion of the water quality volume and its
drawdown orifice in the detention pond, a portion of all
detained storm events will be restricted by the smaller
water quality drawdown orifice when their remaining
volume is equal to the water quality volume.
Water Quality – Example 3
(CWS Extended Dry Detention Pond)
Demonstrate Compliance:
•Create hydrograph equal to 50% of the 2-year event
•Route hydrograph through facility model used for
detention calcs
•Does outflow hydrograph show compliance with CWS
standard? Does it release Vwq over 48 hours or more?
•Verify Water Quality vegetation extends to peak WSE
Detaining all events larger than
the CWS WQ event for more than
48 hours for treatment is inherent
to EDDP design.
Water Quality – Example 4
(CWS Wet Pond)
Clean Water Services – Wet Pond
•Wet pond constructed in 2005
•2014 redevelopment triggered review of entire site
•All runoff conveyed through wet pond (no high-flow bypass)
•Larger events overflow at spillway
•6” of ‘live storage’ above 3’ wet pool
Water Quality – Example 4
(CWS Wet Pond)
Demonstrate Compliance:
•Create hydrograph equal to 50% of the 2-year event
•Route hydrograph through facility model
•Does outflow hydrograph show compliance with CWS
standard? Does it release Vwq over 48 hours or more?
•Verify Water Quality vegetation extends to peak WSE
Cost / Benefit Analysis
•Costs to client:
Analysis – 4 to 16 hours
Coordination /Submittal – 4 to 8 hours
•Benefits for new and existing sites:
Facility retrofit costs
Materials and installation costs reduced
Reduced maintenance costs
More buildable land / less ROW acquisition
Cost / Benefit Analysis
Calculating the SLOPES V Qwq using SBUH or
CWS method yields similar peak flow results
SLOPES V
Innovative Ways to Show Storm
Water Quality Compliance
Summary:
•Review your design (proposed or existing)
•Determine how to analyze “50% of the 2-year storm
event”
•Run event through the facility model
•Does it comply with Volume and Quality standards?
•Include clear calculations / exhibits in stormwater
report for review by NOAA
SLOPES V
Innovative Ways to Show Storm
Water Quality Compliance
Questions?
Robert J. Léger, P.E.
robertl@vlmk.com 971-254-8292
May 27th, 2015
EWRG Oregon http://oregonewrg.org/