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Raingarden Handbook for Western Washington

This handbook will guide you
through the following stages:
plan, build, plant, and
maintain. The handbook is
written for conditions specific to
western Washington, including
appropriate plant selections
and sizing recommendations
based on regional soils and
rainfall patterns.

Rainwater Harvesting Brochure-Puyallup

This program offers a cost-share opportunity to City of Puyallup residents to
encourage the replacement of impervious surfaces with green stormwater
infrastructure (GSI) at their residential properties.
Green stormwater infrastructure refers to systems and practices that use or
mimic natural hydrological processes. These systems manage stormwater
where it falls, letting it soak into the ground instead of running off into our
waterways.
Approved participants cost share is based on the type of GSI they install,
which includes:
• Rain Gardens: participants pay for contractor labor, or perform labor
themselves, to build the rain garden and the City purchases all materials
up to $1,500.00
• Permeable Pavements: participants receive a reimbursement for 50% of
the total costs, up to $10,000.00
• Rain Barrels: Participants receive a reimbursement for the cost of the
rain barrel, up to $150.00
How it works:
1.) Application: Existing City of Puyallup residential properties are eligible.
2.) Preliminary Site Evaluation: Program staff will evaluate the site to
suggest possible GSI.
3.) Percolation Test: Soils will be tested for infiltration rate to ensure GSI is
feasible at proposed site.
4.) Cost-Share Agreement: Written and signed agreements will completed
between homeowner and City.
5.) Select pre-approved contractor, design and install: To ensure GSI is
installed correctly, homeowner will need to hire a pre-approved contractor
or follow a plan provided by the city.
For more information,
contact:
City of Puyallup Stormwater
Engineering

Compendium of MS4 Permitting Approaches

The U.S. Environmental Protection Agency (EPA) encourages the use of green infrastructure to manage stormwater discharges. While local codes, stormwater utilities, and other innovative financing mechanisms often create standards and incentives for green infrastructure, regulatory drivers such as permits can also provide an effective foundation for consistent implementation of green infrastructure at the local, state, or cross-jurisdictional level. This compendium presents a variety of existing permitting approaches that encourage or require green infrastructure in municipal separate storm sewer systems (MS4s); it also provides excerpts from current state and EPA MS4 permits and examples of how MS4 permittees implement green infrastructure permit requirements. These excerpts and examples can serve as a road map for permitting authorities and permittees that are interested in incorporating green infrastructure into permitting programs or identifying successful strategies to maintain compliance. To develop this compendium, EPA reviewed final individual and general National Pollutant Discharge Elimination System (NPDES) MS4 permits issued through August 2021.
This compendium is part of a series of compendia of MS4 permit excerpts and is intended to serve as a snapshot of permit provisions. As permits are reissued or revised, EPA may update this compendium to include more recent examples and new information. EPA also welcomes input on this compendium and expects to update it as appropriate based on the comments received. EPA notes that the inclusion of any particular permit example should not be read as an endorsement of the entire approach taken in that permit, nor should it be read as EPA’s independent determination that the permit terms meet the Phase I and/or Phase II MS4 requirements.
In addition, this document does not impose any legally binding requirements on EPA, states, or the regulated community and does not confer legal rights or impose legal obligations upon any member of the public. EPA made every attempt to ensure the accuracy of the examples included in this document. In the event of a conflict or inconsistency between this compendium and any statute, regulation, or permit, it is the statute, regulation, or permit that governs, not this compendium. For more information about the NDPES Stormwater Program, visit www.epa.gov/npdes/stormwater.

Urban Tree Canopy Assessment Toolkit

Within our cities and towns, the trees that line our streets, fill our parks and
shade our streams provide people and nature with a multitude of benefits—
seen and unseen. These trees help clean the water flowing into streams, rivers
and Puget Sound, help purify the air we breathe, cool our neighborhoods—and
so much more.
AS THE PUGET SOUND
REGION’S cities and towns
experience increasing growth,
identifying opportunities to
invest in high-impact tree
planting and preservation
based on local priorities is a
fundamental step to ensuring
people will continue to
receive the myriad benefits
trees provide.
Urban tree canopy
assessments are foundational
to understand the amount
and distribution of tree
canopy cover in a community
to set goals and targets
to strategically increase
canopy cover and prioritize
protection of existing tree
canopy. However, our cities
often lack the resources
to support urban tree
canopy assessments as
well as efforts to expand,
manage and protect urban
tree canopy based on the
priorities of their individual
communities.
With these challenges in mind,
a coalition was formed with the
following goals:
1. Create a regional highresolution urban tree canopy
assessment based on best
available science to prioritize
urban tree canopy projects
that achieve the highest
return on investment.
2. Pilot urban forest carbon
credit projects to tap new
sources of funding.
Funding from the USDA Forest
Service Urban and Community
Forestry Program, administered
through the State of Washington
Department of Natural Resources
supported collaboration across The
Nature Conservancy, Davey Tree
Expert Company, American Forests,
and City Forest Credits in developing
a suite of resources to deliver on
these goals.
The outcome is the Urban Tree
Canopy Model. The model provides
Central Puget Sound municipalities,
organizations and tree advocates
with the data and tools to prioritize
tree planting and preservation that
supports multiple benefits: reduced
stormwater pollution, improved air
quality, captured carbon, expanded
habitat, health and well-being, and
social equity. Carbon financing
resources supplement the model as
a new form of funding to support
implementation.
Now, practitioners in the region and
beyond can access these resources
and engage with the partners
behind the effort. The Urban Tree
Canopy Assessment Toolkit provides
guidance and resources to get
started.

Residential Swimming Pool and Hot Tub Maintenance

Stormwater Pollution Prevention Manual King County Stormwater Services 132 July 2021 R-7: Residential Swimming Pool and Hot Tub Maintenance Improper drainage or discharge of water from swimming pools, hot tubs, or spas to storm drains or ditches during maintenance activities can lead to pollution of streams, rivers, and lakes. Chemicals used in pool, spa, and hot tub maintenance can contaminate stormwater and surface water if they are not stored, used, and disposed of correctly. Potential pollutants can include but are not limited to fecal coliform bacteria, nutrients, oxygen demanding substances, pH, and sediment. Best Management Practices (BMPs) are required by King County Water Quality Code (KCC 9.12). If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required Operational BMPs • Clean the pool, spa, hot tub, or fountain regularly. • Maintain proper chlorine levels, water filtration, and circulation, which will limit the need to drain the facility. • Manage pH and water hardness to reduce copper pipe corrosion that can stain the facility and pollute receiving waters. • Before using copper algaecides, try less toxic alternatives. Only use copper algaecides if the other alternatives do not work. Ask a pool/spa/hot tub/fountain maintenance service or store for help resolving persistent algae problems without using copper algaecides. • Develop and regularly update a facility maintenance plan that follows all discharge requirements. • Dispose of unwanted chemicals properly. Many of them are hazardous wastes when discarded. • Store pool chemicals under cover and in enclosed containers. Required Water Disposal BMPs If the pool or spa does not have a permanent drain connection, then water must be pumped or drained to the sanitary sewer or meet the following BMPs. • Discharging pool and spa water if sanitary sewer is not available: o Non-saltwater and saltwater pool and spa water  Have it hauled off-site for disposal at an approved location; or  Infiltrate to ground if all 9 conditions below are met. Saltwater pool and spa water must not be allowed to flow off-site, nor may it enter stormwater drainage systems or surface waters. Saltwater discharges can elevate salt concentrations in your soil and damage vegetation. o Non-saltwater pools and spas only  Drain to the stormwater drainage system if all 9 conditions listed below are met Stormwater Pollution Prevention Manual King County Stormwater Services 133 July 2021 • Conditions for draining to ground (non-saltwater and saltwater pools and spas) or to a stormwater drainage system (non-saltwater pools and spas only): 1. No copper-based algaecides were used; 2. The water must be tested to determine chlorine levels and pH; 3. The water is dechlorinated to 0.10 ppm Chlorine or less, using neutralizing chemicals or by letting the pool or spa “sit” long enough to reduce the chlorine level to the allowable limit. The pool or spa must not be used during this period; 4. The pH is neutral (6-8); 5. Free of any coloration, dirt, suds, or algae; 6. Free of any filter media; 7. Free of acid cleaning wastes; 8. Released at a rate that does not cause erosion either onsite or in the drainage system; and 9. At ambient temperature. • Saltwater pool and spa water must not be discharged to the stormwater drainage system. Either infiltrate to ground if all 9 conditions above are met or hire a professional pool-draining service to collect all water for off-site disposal at an approved location. • Diatomaceous earth (commonly used as a filtering agent) and water from back flushing filter systems cannot be discharged to surface waters, storm drainage systems, septic systems, or the ground. Dispose of diatomaceous earth filter material as solid waste. • Do not discharge pool or spa water to a septic system, as it is prohibited and may cause the system to fail. • The discharge of pool and spa filter backwash or cleaning water to the ground, surface waters or the storm drainage system is not allowed. Tips • Hire a professional maintenance company to service your pool, hot tub, or spa. For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater.

2019 – 2024 Ecology WW Phase II Municipal Stormwater Permit

Summary: External link to Ecology Phase II permit site

We develop and administer Clean Water Act National Pollutant Discharge Elimination System (NPDES) municipal stormwater permits in Washington. The Western Washington Phase II permit requires local governments to manage and control stormwater runoff so that it does not pollute downstream waters.
The current permit is effective Aug. 1, 2024, and expires on July 31, 2029.
Overview of permit timelines
View
permit timelines
for continuing permittees. These timelines provide an overview of major deadlines for implementing permit requirements.
Annual reports for the calendar year are due by
March 31 the following year.
Municipal stormwater permit guidance
For guidance about applying, changing, or implementing and complying with your municipal stormwater permit see
municipal stormwater guidance
Stormwater manuals
provide stormwater permit implementation and management guidance. For more general stormwater permit guidance, see the
stormwater guidance
page.
Frequently asked questions
Have a question? Check out our
frequently asked questions page
Permit history
Keep in touch with us
Join our
municipal stormwater permit email list
to receive updates about this permit.

EJ League of Rhode Island, Urban Ponds and Stormwater

Summary: Urban ponds and stormwater, environmental justice, pollution in local pond, greening neighborhoods, managing stormwater in urban areas to handle pollution, heat islands, recreational opportunity access, green spaces

The EJ League, Urban Pond Procession, and Groundwork Providence are working together on a new campaign to address stormwater pollution in Mashapaug Pond, Providence’s only remaining natural pond, located in South Providence.
See below for all the great successes we’ve already had in Reservoir Triangle around the pond! Addressing stormwater pollution has a ton of positive impacts you might not even be aware of — things like:
beautifying and adding green space to urban neighborhoods
improving air quality with more trees and plants
reducing flooding on our streets
creating jobs and training opportunities for Providence residents
helping our neighborhoods be more resilient in the face of climate change impacts like heat waves, storms, and major flooding events
improving the quality of Rhode Island’s water bodies and beaches — from our urban ponds and rivers to Narraganset Bay — they’re all connected!
Solving our stormwater problem is central to achieving environmental justice in Providence and Rhode Island’s other urban centers. Our urban communities have higher poverty and unemployment rates, its where the majority of people of color in the state live, and these are the same places with poorer air and water quality and less access to good things like green space, recreational opportunities, and the beauty of the natural environment. Cleaner water means more recreational opportunities like fishing and boating can happen right in our cities and we’ll be safer when we go to beaches on the coast. Protecting our waterways, adding more green space, and improving the public spaces we already have means we’ll benefit by being more connected to the natural environment too. Investing in
green infrastructure
means more jobs can be created for residents in Providence and other cities to install and maintain rain gardens and permeable pavement, de-pave driveways and right-of-ways, cut curbs and plant trees.
Check out our resident handbook on stormwater and green infrastructure
below, created specifically for Reservoir Triangle, but can definitely be used for other neighborhoods across the state!
Resident Handbook – Stormwater and Green Infrastructure
(pdf)
“Toxic Legacy” — A short film about Gorham and Alvarez High School
Alvarez’s 2013 AP Environmental Science Class and Artist David Stephens
Toxic Legacy…
from
Urban Pond Procession
Vimeo
This project is funded by the
EPA Urban Waters Small Grants Program
View of Mashapaug Pond — a Providence gem!
Past Urban Waters Project Events and Workshops:
We’ll be hosting more of these types of events and workshops in the future, so keep checking in to see how you can get involved!
September 15th, 2012 – Kick-Off – Mashapaug Pond Party:
We want to make sure people see Mashapaug Pond as a
real asset and natural resource in our city
. Duck Truck Tours are a good first step! We took about 75 people out on the water at our kick-off event in September and had a great time with food, music, and games for kids.
Principal Socorro Gomez-Potter from the Reservoir Avenue Elementary School enjoys her first time on Mashapaug Pond
October 20th, 2012 – Stormwater Walk
led by George Harvey, Landscape Designer and project partner from
Groundwork Providence
: 20 people from the neighborhood and allies from partner organizations participated in a walk around Mashapaug Pond, focusing mostly on JT Owens ballfield and the Huntington Industrial Park.
George talked with us about various ways stormwater could be better managed to prevent runoff from the fields and businesses
there including:
raising grated storm drains located near baseball fields to slow down water rushing into pond
planting native plants to prevent soil erosion and slow water down, help it be absorbed
identifying specific pollution sources and stopping them at the source (see photo below)
raising the top of a building’s downspout just a couple inches so that rainwater can collect on the roof of the building and naturally evaporate rather then run down the downspout into the street
directing downspouts into plants, grass, or other vegetated areas
Check out this presentation created by Ana Mendiburu, a Reservoir Triangle resident, that summarizes what we learned on the stormwater walk:
Stormwater Walk Overview
(pdf)
Starting in November, members of our team reached out to businesses in the industrial park, many of which have been very receptive to our ideas about better managing stormwater runoff from their properties. We’re looking forward to working with them to improve their stormwater management practices, including a springtime tree planting among other projects. Stay tuned for more updates on this!
An example of an avoidable pollution source going into Mashapaug Pond
January 19th, 2013 – Residential Stormwater Workshop:
Neighborhood residents, City staff from the Parks Department and Office of Sustainability, among others, participated in a workshop to look at how individual residents could improve stormwater management at their homes and in the neighborhood as a whole.
Residents will begin meeting together to plan out springtime activities and outreach in the neighborhood to get more of their neighbors involved.
George Harvey co-led this workshop and prepared incredibly useful documents (see below) to help residents see tangible ways they could
prevent stormwater runoff from their homes, roofs, and lawns
. While a significant portion of the Reservoir Triangle neighborhood’s stormwater flows into the pond, especially from the homes right on the edge of the pond, much of the neighborhood’s stormwater goes into Combined Sewers (pipes where wastewater and stormwater combine) that are directed to Fields Point, the wastewater treatment facility off Allens Avenue. Ultimately all this treated water goes into Narragansett Bay. This still means stormwater can overburden the system and cost taxpayers and the City money — so figuring out ways to absorb more stormwater in the neighborhood will help a great deal.
Here are some photos of typical downspouts in Providence
– almost always letting out water from the roof onto concrete or some other non-absorbing material. Changing this can be easy though. We’ll be piloting some ideas in Reservoir Triangle this spring!
Examples of Downspouts in Reservoir Triangle
(pdf)
Here are some of the ways residents can help absorb more water coming off their roofs, lawns, and driveways.
The photos on the left are what it looks like in real life, and on the right each photo has been “doctored up” to show an example of a “BMP” – or a “best management practice” to better manage the stormwater. All renderings were prepared by George Harvey from Groundwork Providence:
Driveway Swale – Residential BMP
(pdf)
Right of Way Buffer Strip – Residential BMP
(pdf)
Stormwater Planter – Residential BMP
(pdf)
May 4th, 2013 – De-paving Demonstration Project at 46 Crescent St.:
Reservoir Triangle resident, Laura Maxwell, volunteered her driveway to our project, allowing the Groundwork Providence green job training program to remove a layer of asphalt and about 6 inches of concrete from her driveway, replacing it with geoblock material and grass that will still allow her to drive across it to get to her garage but will absorb rain water coming off the roof of her house — helping reduce the stormwater load on Mashapaug Pond. Thanks Laura!
Check out these photos of the process:
The original asphalt driveway.
The end result: A grassy area that can absorb roof runoff and stormwater!
October 2013 – Right-of-Way Depaving and Planting:
Nellie Richardson and her family gave the EJ League the go-ahead to cut the concrete in front of their home on Algonquin St and create a planted buffer in its place. This was done with permission from the Providence Department of Public Works, with some materials donated by the Parks Department. The work was conducted by Groundwork Providence’s job training crew. Thanks everyone!
Check out the before and after photos:
The planted buffer captures roof runoff, filters pollutants, and prevents flooding on this street corner!
The EJ League is also working with businesses on the other side of Mashapaug Pond in the Huntington Business Park to implement stormwater solutions.
Ximedica, RI PBS, and Brown University’s Library Collections Annex all participated in a spring tree planting in 2013:
And we’ll be continuing this outreach in 2014!
The RI Department of Environmental Management, in collaboration with our project, was awarded $50,000 through a legal settlement against Southern Union (an oil/gas company that was found guilty of illegally storing mercury in an unlocked shack in Pawtucket). This money will go directly to support green infrastructure projects in the Huntington Business Park — and give Groundwork Providence’s job training graduates — GroundCorp — an opportunity for paid, on-the-job professional development. More details to come on this exciting development!
In the meantime, check out these upcoming events in May 2014:
Overview of our project:
While continuing to monitor and advance progress on
the cleanup of the former site of the Gorham Manufacturing Company
, which sits on Mashapaug Pond, the EJ League,
Groundwork Providence
, and
Urban Pond Procession
are launching a new project that focuses on reducing stormwater runoff — the second major source of pollution for this almost 70-acre body of water.
Check out this presentation created by Will York, director of
smallFeat for Schools
and a project volunteer who lives in the watershed, about what stormwater is in the first place:
What is stormwater?
(pdf)
And this fantastic animated video about the need for green infrastructure in Providence, created by project volunteer, Stephanie Yin:
(HD) Lessons in Water Cycling: Green Infrastructure in Providence, RI
from
Steph Y
Vimeo
The main goals of our Mashapaug stormwater project are to:
Develop a core group of resident leaders to design and lead this project
Educate and engage residents and schoolchildren in the Reservoir Triangle neighborhood on ways they can contribute to the pond’s restoration through outreach, workshops, as well as hands-on trainings in basic stormwater management techniques led by
Groundwork Providence
Engage businesses in the Huntington Industrial Park located between Niantic Avenue and the pond, get commitments from them to reduce runoff from the business’s properties, and help them achieve these goals
Explore the potential to create jobs for Providence residents in the area of stormwater management and adding more green space to our city through innovative funding strategies
Urban stormwater runoff is a major source of pollution for all of our city’s waterways, including Mashapaug Pond, which creates unsafe conditions for people and ecosystems. Too much phosphorus from pet waste, fertilizers from people’s lawns, oil from the road, road salt, etc. wash into our waterways when it rains and contaminate them. In Mashapaug Pond, this process helps toxic bacterias develop that are a hazard to people and pets and reduce oxygen levels in the water, making it difficult for healthy plant and animal life to survive.
The solutions to this problem lie in eliminating these pollutants from runoff in the first place (picking up pet waste, not feeding geese or other birds, not using lawn fertilizers, ensuring motor oil is securely disposed of, etc) and increasing the amount of absorptive surfaces in our city — meaning increasing the amount of grass, plants, and trees, and reducing the amount of asphalt, concrete, and other surfaces that don’t absorb rain water.
Check out these
maps of Reservoir Triangle
created by George Harvey/Groundwork Providence that show
how much of the land us taken up by impervious surface
(meaning surfaces that don’t absorb water). Unfortunately this is all-too common all across Providence and is the biggest reason for polluted water quality in our city and state:
Streets in Reservoir Triangle
Streets and Sidewalks
Streets, Sidewalks, and Roofs
Streets, Sidewalks, Roofs, and Driveways
All Impervious Surfaces
Contact [email protected] to get involved.
More on the Urban Pond Procession (project partner):
Read up-to-date info on the Urban Pond Procession at
www.urbanpondprocession.org
History of the UPP:
Artist Holly Ewald started the Mashapaug Pond Procession as a culminating public event in June 2008 after a several-month residency in local schools and community centers educating young people about the pond and creating silkscreen posters and fish costumes. The posters were then the inspiration for 4 new more pictoral signs with text translated in 3 languages warning pond visitors of the health hazards of the pond site. Eight new signs fabricated by the Department of Transportation are permanently in place around the pond.
The new signs placed around Mashapaug Pond.

2023 Fact sheet for Non-vegetated Filtration Swale Effectiveness Study

Summary: Fact sheet, non-vegetated filter strip, eastern washington, study results non-vegetated filtration strip, BMP efficacy study results, West Richland study fact sheet

NON-VEGETATED FILTRATION SWALE EFFECTIVENESS STUDY
Non-Vegetated Filtration Swale Effectiveness Study | Fact Sheet
Study Goal and Background
The goal of this study was to evaluate the
effectiveness of a non-vegetated filtration swale
BMP. Effectiveness was based upon whether the
BMP could provide basic treatment (80% reduction
of total suspended solids) in accordance with
Ecology treatment performance goals.
Constructing a non-vegetated filtration swale is
highly desirable for locations with hot and dry
summers or in areas where dry periods cause
grass to become dormant or where supplemental
water is needed to establish vegetation. A non-
vegetated BMP will benefit multiple Washington
State Permittees by providing a BMP option that
does not require irrigation. This fact sheet is a
summary of the information found in the Non-
Vegetated Filtration Swale Effectiveness Study
Technical Evaluation Report.
Study Description
The study goal was accomplished through controlled tests conducted at a test site in West
Richland. Four swale design alternatives (alternatives) were tested in 200-foot-long swales at
the site followed by one final swale design alternative (final alternative) as shown in Figure 1.
The final alternative was selected based on the treatment performance of the four alternatives.
A cross-section of the final alternative swale design is shown in Figure 2.
Figure 2: Final Swale Alternative Cross Section
Figure 1: TEST SWALE AND SAMPLE LOCATIONS
NON-VEGETATED FILTRATION SWALE EFFECTIVENESS STUDY
Non-Vegetated Filtration Swale Effectiveness Study | Fact Sheet
Treatment performance was measured from
samples collected from each alternative, which
were analyzed for total suspended solids (TSS). An
influent distribution system mixed and pumped
synthetic stormwater to the swale at the design
flow rate to simulate a storm event (as shown in
Figure 3).
As the synthetic stormwater flowed through the
swale, grab samples (shown in Figure 4) were
collected in eight sample locations that were
spaced at 25-foot increments along the swale.
After each simulated storm event, an amount of
TSS equivalent to one year of loading was
distributed to the swale to stress-test the swale
and determine when the swale would require
maintenance.
The travel time for stormwater to flow through the
swale was recorded at each sample location. The
measured travel time was then used to estimate the velocity of flow through the treatment
layer. This information was used to inform the velocity limits for the swale design guidance.
FIGURE 3: INFLUENT DISTRIBUTION SYSTEM AT TEST SWALE
Figure 4: GRAB SAMPLE FROM TEST SWALE
NON-VEGETATED FILTRATION SWALE EFFECTIVENESS STUDY
Non-Vegetated Filtration Swale Effectiveness Study | Fact Sheet
Study Location
The test site location was south of the City of West Richland Public Works Building and adjacent
to a gravel parking lot (as seen in Figure 5). An existing 430-foot-long swale at the test site was
retrofitted into the two 200-foot-long test swales. The controlled tests were conducted during
the dry season; therefore, no runoff from the gravel parking lot contributed to the test swales.
Results
The initial percent removals for the final alternative indicated that 84.5–87.8% removal of TSS
was achieved for the first simulated year, at the sample location at 200 feet from the start of
the swale. However, percent removal decreased for the following two simulated years, which
was likely due to modifications to the swale needed near the last sample port, due to observed
erosion from a grade break immediately downstream of the swale. As a result, the samples
collected at the last sample port (200 feet) were discarded and statistical trendline analysis
was used to determine how the swale would have performed if the swale modifications had
not occurred. This analysis is shown in Table 1 and indicates that the swale met performance
goals for the first two years. Since the treatment performance dropped below 80% for the third
year, it is likely that maintenance would need to be performed sometime around the third year
to restore treatment performance. Further testing needs to be done to confirm the
maintenance procedures and schedule.
Figure 5: Test Swale Location
NON-VEGETATED FILTRATION SWALE EFFECTIVENESS STUDY
Non-Vegetated Filtration Swale Effectiveness Study | Fact Sheet
Table 1: Final Alternative Water Quality Results from Trendline Analysis1
Location in Swale
Year 1
Year 2
Year 3
25 FEET
58.5%
-13.2%
11.9%
50 FEET
62.8%
1.00%
21.4%
75 FEET
67.0%
15.3%
30.9%
100 FEET
71.3%
29.5%
40.4%
125 FEET
75.5%
43.8%
49.9%
150 FEET
79.8%
58.0%
59.4%
175 FEET
84.0%
72.3%
68.9%
200 FEET
88.3%
86.5%
78.4%
1. Results shown are concentrations developed using trendlines.
The percent removal results in Table 1 were compared to the TAPE treatment performance
goals for TSS using the bootstrap statistical analysis to predict the treatment performance of
the swale. Years 1 and 2 represent the performance of the swale before maintenance is needed.
However, only two data points were available, causing the result of the bootstrap analysis to
be equivalent to the lower of the two removal efficiencies. The evaluation of removal
efficiencies calculated for years 1–3 added one data point and indicated the swale would meet
the TAPE treatment performance goal for all three simulated years.
The measured travel time for flow to travel through the
swale was 50 minutes, from which a design velocity of
0.066 ft/sec was calculated. It is anticipated that
treatment will be provided by a swale 200 feet long if the
velocity and residence time are less than or equal to the
values measured during the study.
Future Action Recommendations
Submit the swale for Conditional Level Use
Designation, so the performance of the swale can be
further evaluated in the field for actual storm events.
Perform additional field testing to understand
effective maintenance activities to restore the swale
treatment performance every two to three years and
the frequency at which more minor action items
such as removal of sediment and debris from inlets,
weed control, etc., should be performed.
Perform additional field testing to understand the impact that a catch basin or forebay
at the inlet would have on treatment performance and maintenance cycle of the swale.
Lead Entity:
City of West Richland
Contributing Entity:
City of Richland
City of Kennewick
City of Pasco
City of Walla Walla
Walla Walla County
City of Moses Lake
City of Pullman
Idaho Dept. of Environmental
Quality
Washington Dept. of Ecology
This
study
was
conducted
support the lead and participating
entities in meeting NPDES MS4
Phase II Permit Requirements for S8
Monitoring and Assessment.