FACT SHEET
for the
PHASE I, WESTERN WASHINGTON PHASE II, AND
EASTERN WASHINGTON PHASE II
MUNICIPAL STORMWATER PERMITS
National Pollutant Discharge Elimination System and
State Waste Discharge General Permit
For discharges from
Small, Medium, and Large Municipal Separate Storm Sewer Systems
In Washington State
August 15, 2018
State of Washington
Department Of Ecology
Olympia, Washington 98504-7600
Extract of Sections 3 and 6 as referenced on
page 1 of the SMAP Guidance document
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In addition, Ecology also accepted comments on proposed preliminary changes to the
Stormwater Management Manual for Western Washington (SWMMWW). The preliminary draft
package of the 2019 SWMMWW included:
Full table of contents
All of Volume II
Select source control BMPs from Volume IV
The preliminary draft Permit language included explanatory notes documenting Ecology’s
rationale for the proposed draft requirements.
The preliminary draft documents generated a broad response. Ecology received comments from
over 30 individuals or entities via email, letters, and an online comment form. This extra step in
the public process provided valuable input from a wide range of interested parties. Ecology
considered those comments as it developed these proposed draft Permit requirements. The
preliminary draft language, explanatory notes, associated documents, and all the comments are
available on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Permits-
certifications/Stormwater-general-permits/Municipal-stormwater-general-permits/Municipal-
stormwater-permit-reissuance
3.0 Background
3.1 The Stormwater Problem
Stormwater runoff is a leading pollution threat to lakes, rivers, streams and marine water bodies
in urbanized areas of Washington State. The stormwater problem was well defined decades ago,
and we continue to learn about both the impacts of stormwater on receiving waters and biota
across the State, as well as the effectiveness of stormwater management approaches to prevent,
reduce, and correct these impacts.
Impacts from stormwater vary geographically due to differences in local land use conditions,
hydrologic conditions, the type and condition of the stormwater infrastructure, and the type of
receiving water. In typical undeveloped conditions, less than about ten percent of precipitation
runs off the land as surface flow. In urban areas, the large amount of impervious surfaces
interrupts infiltration and groundwater recharge, concentrates surface flows, and increases the
frequency and quantity of runoff sent to receiving waters. As a result, more than 40% of
precipitation exits urban areas rapidly through stormwater sewer systems1. This causes
hydrologic impacts such as scoured streambed channels, excessive sediment transport, loss of
habitat, and increased flooding.
Many pollution sources from common land use activities contaminate urban stormwater. Streams
and storm outfalls monitoring studies have shown elevated concentrations of metals, nutrients,
pesticides and organic compounds in relation to urban development. Contaminants in building
materials, in illicit discharges and spills, from vehicular traffic, and atmospheric deposition are
picked up by stormwater runoff and make their way to receiving waters if left untreated. Most of
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these pollution sources are not under the direct control of the Permittees that own or operate
municipal storm sewer systems.
The following is a list of typical and potential impacts caused by stormwater discharges:
• Human Health: Untreated stormwater contains bacteria, trash, excessive nutrients, toxic
metals, and harmful organic compounds. Untreated stormwater is not safe for people to
drink and is not recommended for swimming or contact recreation.
• Drinking Water: In some areas of Washington, notably Spokane County and parts of
Pierce and Clark Counties, gravelly soils allow rapid infiltration of stormwater. Untreated
stormwater discharging to the ground could contaminate aquifers that are used for
drinking water.
• Shellfish: Washington State’s multimillion dollar shellfish industry is increasingly
threatened by closures due to stormwater contamination.
• Degraded Water Bodies: In urban and urbanizing areas across Washington State,
residential, commercial, and industrial land development continues to change land cover
and drastically alter stream channels. Unmanaged stormwater from urban areas has
severely degraded beneficial uses of Washington’s waters.
o A recent study described the “urban stream syndrome”2 where development
predictably and consistently results in degraded conditions of instream water
quality and biota.
o Other recent studies suggest that road density and traffic volumes are main
stressors to benthos community health in urban streams indicating traffic
associated pollutants in stormwater degraded receiving water bodies3.
o Studies in the 1990s found degraded stream benthos communities in watersheds
with as little as 10% impervious surface4. Studies since then have found a
continuum, with impacts detectable at lower levels of impervious surfaces.
o Unmanaged stormwater has likely permanently destroyed stream habitat in some
urban areas of Puget Sound. There are no known instances of recovering “poor”
to “fair” or even “fair” to “poor” condition of stream benthos.
o Recent modeling exercises have demonstrated that current site-by-site approaches
to stormwater management approaches are insufficient to prevent continued
degradation of receiving water quality (see section 3.2.1 below on “Phase I
Counties’ Watershed Modeling and Planning”).
o Elevated concentrations of pollutants in small Puget lowland streams in 2015
were significantly correlated with indicators of urbanization including impervious
surfaces and watershed canopy5. This same study found significant differences
between conditions of water quality and biota in streams inside and outside Urban
Growth Areas (UGAs).
o Bacteria is the most common cause of stormwater-related water quality
impairment listings. Puget Sound nearshore monitoring programs that focus on
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monitoring storm events or source identification tend to have higher bacteria
levels than ambient programs6.
There are significantly more contaminants Puget Sound nearshore sediments in
the incorporated UGAs than the unincorporated UGAs, and sites identified as
depositional areas contained more chemicals than the high-energy drift cells (left,
right, or divergent)7 .
Contaminant levels in mussels along Puget Sound UGA shorelines were
correlated with impervious surfaces in the small watersheds adjacent to the
shoreline8.
The common urban use pesticide bifenthrin was found in sediment samples from
about ten percent of Puget lowland stream sites monitored in 20159.
Numerous 303(d) listed water bodies across the State have been assigned
stormwater waste load allocations.
Salmon Habitat: Urban stormwater degrades salmon habitat in streams through effects
on hydrologic flows and toxicity. Paved surfaces cause greater and more frequent winter
stormwater flows that erode stream channels and damage spawning beds. Toxic
chemicals in stormwater harm benthic insects, salmon embryos, immature fish, and adults
returning to spawn. Several studies have identified concerns. Two important examples:
Surveys of spawning adult Coho salmon in Seattle in the early 2000s found that
very high percentages of adult females (60-100 percent) were dying before they
could spawn10. Scientists soon found that stormwater pollution is likely
involved11 and the problem is widespread throughout urban streams in Puget
Sound. Untreated highway runoff is lethal, leading to 100% toxic response or
death of adult salmon within 24 hours12. Active scientific investigation continues,
and has made progress toward identifying the precise causes of these acute die-
offs. Scientists are most recently honing in on chemicals associated with some
tires13.
Ecology and Pierce County conducted in situ trout toxicity testing studies in four
urban streams in 2008. Pierce County found no significant toxicity14. However,
Ecology identified the following chemical stressors that were capable of causing
adverse effects that were detected on the native trout embryos and pre-swim-up
fry: copper, lead, nickel, zinc, polycyclic aromatic hydrocarbons, and the
agricultural fungicide Captan15.
Pollution: Urban stormwater is known to contain a fairly consistent suite of pollutants
from common land use activities.
An evaluation of stormwater monitoring data from the National Stormwater Quality Database
(NSQD)16 compared the results for a range of pollutants in urban runoff from areas of different
land uses. The NSQD contains a large data set from a representative number of Municipal
Stormwater Permit holders. Much of the data may be used to characterize stormwater produced
from specific land uses, such as industrial, commercial, low density residential, high density
residential, and undeveloped open space. Preliminary statistical analysis of the NSQD found
significant differences among land use categories for all pollutants, as shown in Table 2.
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In the 2007 Permit, Phase I cities and counties and the ports of Tacoma and Seattle were required
to conduct stormwater discharge characterization monitoring to improve our understanding of
the amounts of a wider range of pollutants found in stormwater from various land uses. That
monitoring and the findings are presented in section 3.2.8 below on “Phase I Permittees’
Stormwater Discharge Characterization Monitoring.”
Table 2: Event Mean Concentrations of Pollutants Discharged via Stormwater Compiled from the
National Stormwater Quality Database, Version 1.0
Pollutant
Units
Land Use
Overall
Resident
-ial
Commer-
cial
Industrial
Freeways
Open
Space
Ammonia
mg/L
0.31
0.5
1.07
0.3
0.44
Biochemical Oxygen
Demand
mg/L
11.9
4.2
8.6
Cadmium, Total
ug/L
0.5
0.9
0.5
Cadmium, Filtered
ug/L
0.3
0.6
0.68
0.5
Chemical Oxygen
Demand
mg/L
100
Copper, Total
ug/L
5.3
Copper, Filtered
ug/L
7.6
10.9
Fecal Coliform
MPN/100
7,750
4,500
2,500
1,700
3,100
5,081
Lead, Total
ug/L
Lead, Filtered
ug/L
1.8
Nickel, Total
ug/L
5.4
Nickel, Filtered
ug/L
Nitrogen, NO2+NO3
mg/L
0.6
0.7
0.3
0.6
Nitrogen , Total
Kjeldahl
mg/L
1.4
1.6
1.4
0.6
1.4
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Pollutant
Units
Land Use
Overall
Resident
-ial
Commer-
cial
Industrial
Freeways
Open
Space
Phosphorus, Total
mg/L
0.3
0.22
0.26
0.25
0.27
Phosphorus, Filtered
mg/L
0.17
0.11
0.2
0.08
0.12
Suspended Solids,
Total
mg/L
Zinc, Total
ug/L
150
210
200
116
Zinc, Filtered
ug/L
112
ND = Not detected, or insufficient data to determine a value
mg/L = Milligrams per liter
ug/L = Micrograms per liter
MPN = Most probable number
3.2 Previous and Ongoing Regional Efforts
Ecology and Permittees are investing in efforts to inform and improve our collective
understanding of stormwater impacts and Permittees’ implementation of the stormwater
management programs and practices required in the Permits. The goals are to better understand
the sources and pathways of pollutants, to measure our progress over time, and to continue to
identify and target effective management approaches. In recent years, several regional efforts
have significantly contributed to an understanding of stormwater impacts and management
practices on the beneficial uses of Washington waters.
3.2.1 Phase I Counties’ Watershed Modeling and Planning
The 2013 Permit required detailed modeling and planning by the four Phase I counties in western
Washington. The purpose of the Permit requirement was to determine what stormwater
management and other actions are necessary to meet water quality standards in developing areas.
The counties invested considerable staff time and resources into this effort and learned some
lessons that can be broadly applied.17,18,19,20
Each of the counties selected a medium sized (10-50 square miles) watershed located in an
Urban Growth Area (UGA) designated pursuant to the State’s Growth Management Act (GMA)
and therefore known to be under pressure for development in the near future. The watersheds
have unique characteristics, but all are already partially urbanized.
The counties created models to test a suite of supplemental strategies in various scenarios to see
if water quality standards were, or could be, met. The modeling showed that current and future
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conditions in these watersheds are impacted in various ways, and that actions beyond site-by-site
stormwater management will be needed to prevent degradation of the receiving waters and meet
water quality standards. The models in all of the watersheds projected that riparian restoration
and large amounts of additional stormwater detention are needed to improve conditions.
The anticipated costs to recover from these impairments is hundreds of thousands of dollars per
acre of watershed. The costs per acre for these basins are somewhat lower for less developed
basins, but they are still well beyond what might be affordable with current funding programs
and approaches.
An important strategy that one of the four counties highlighted in their scenarios was changing
the land use designation or zoning established as part of the growth management process. King
County demonstrated that such changes will help protect water quality while substantially
lowering the high capital project costs identified by the models. Ecology encourages stormwater
managers to seriously consider pursuing this type of strategy in future planning to accommodate
projected population increases.
3.2.2 Puget Sound Ecosystem Monitoring Program Stormwater Work Group (SWG)
The SWG developed recommendations for a comprehensive stormwater monitoring strategy
focused on Puget Sound21. To develop the strategy, the SWG convened many of the region’s
stormwater experts to review previous work and evaluate the direct and indirect effects of
stormwater on the Puget Sound ecosystem. The SWG also evaluated the various pathways by
which those effects are transmitted and to develop the monitoring approach ultimately included
in the 2013 Phase I and Western Washington Phase II Permits. In the process of reaching
consensus from a broad range of expertise and technical backgrounds, the work group members
formulated a conceptual model of the factors driving the stormwater-related impairment of water
quality and habitat in the region. Figure 1 shows the types of stressors that should be considered,
the pathways by which those stressors are transmitted, and how the outcomes of our management
efforts should be assessed, using a Driver-Pressure-State Impact-Response (DPSIR) conceptual
model…