HomeMy WebLinkAbout19-18 - Ord. Affirming Ord. 04-18 and 12-18 Ensuring Water Adequacy ORDINANCE NUMBER
An Ordinance ensuring water adequacy for development through amendments to Mason
County Code Title 14 Buildings and Construction and Title 6 Sanitary Code and affirming
Ordinance#04-18-18.
An Ordinance of the Mason County Board of Commissioners adopting procedures for determining
water adequacy for building permits relying on individual water sources and establishing a public
hearing date within sixty(60)days of adoption, unless superseded prior to this date.
Whereas, RCW 36.7oA.070(1), requires that the land use element of a county comprehensive plan
"shall provide for protection of the quality and quantity of groundwater used for public water
supplies"; and,
Whereas, RCW 36.7oA.070(5)(c)(iv) requires that the rural element of a county comprehensive plan
"shall include measures that apply to rural development and protect the rural character of the
area, as established by the County, by: ... protecting critical areas...and surface water and
groundwater resources"; and,
Whereas, RCW 19.27.097(1) requires that applicants for building permits of buildings necessitating
potable water provide evidence of an adequate water supply for the intended use of the building;
and,
Whereas, RCW 58.17.110(2) requires that "A proposed subdivision and dedication shall not be
approved unless the ...county legislative body makes written findings that...appropriate provisions are
made for... potable water supplies..."; and,
Whereas, Mason County Code (MCC) Title 14.04 specifies information required for a complete
building permit application; and,
Whereas, MCC Title 20.97 provides definitions of terms used in the code; and
Whereas, MCC Titles 21.04 and 21.05 contain requirements for water supply in short subdivisions
and long subdivisions, respectively; and,
Whereas, MCC Title 6 contains requirements for potable water; and,
Whereas, Title 173-501 WAC Instream Resources Protection Program - Kennedy Water Resource
Inventory Area (WRIA) 14 identifies waterbodies in Mason County that are closed or partially
closed to further appropriation, by listing their status as "closure," "partial year closure," "low
flow," or"minimum flow,"; and,
Whereas, RCW 36.70.790 and RCW 36.70.795 allow for adoption of interim official controls as long
as a public hearing is held within sixty(60)days of adoption; and,
Whereas, on January 18,2018,the Washington State Legislature adopted ESSB 6091, ensuring that
water is available to support development and amending RCWs 19.27.097, 58.17.110, 90.03.247, and
90.03.290; adding a new section to chapter 36.7oA RCW; adding a new section to chapter 36.7o RCW;
Ordinance No.19-41 S'
adding a new chapter to Title go RCW;
Whereas, ESSB 6ogi requires the Department of Ecology to work with the initiating governments
and the planning unit in WRIA 14 to review existing watershed plans to identify the potential
impacts of exempt well use, identify evidence-based conservation measures, and identify projects
to improve watershed health. Until rules are adopted that specify otherwise, Section 202(5) of
ESSB 6ogi, which effectively reverses the Court's decision in Hirst, allows new domestic water
uses in WRIA 14 that rely on groundwater withdrawals exempt from permitting under RCW
90.44.050, provided that applicants pay a fee of five hundred dollars to the permitting authority
and limit their maximum annual average withdrawal of nine hundred fifty gallons per day, per
connection, and record this limitation on the property title; and,
Whereas, the amendments proposed by this ordinance are consistent with the aforementioned
requirements of ESSB 6ogi and are therefore consistent with the GMA, as specifically addressed in
Section 102 of ESSB 6ogi; and,
Whereas, ESSB 6ogi was signed by Governor Inslee on January 19, 2oi8, and, pursuant to the
emergency clause in Section 307 of Session Law, it became effective immediately as the
Legislature declared that it was "necessary for the immediate preservation of the public peace,
health, or safety, or support of the state government and its existing institutions ... "; and,
Whereas, pursuant to Title 15 of the Mason County Code and RCWs 36.70.390 and 36.70.795, an
emergency ordinance necessary for the immediate preservation of the public peace, health, or
safety or support of the County government and its existing institutions was passed by the County
Commission on February 1, 2o18 (Ordinance 04-18)and is effective immediately; and,
Whereas, it is necessary for Ordinance 04-18 to take effect immediately in order for property
owners to be allowed to proceed with their development plans forthwith and thus obtain relief
from the impacts of Hirst; and,
Whereas, the County Commission held a public hearing on Ordinanceo4-ti8 on February 20, 2oi8 and
subsequently issued findings that Ordinance 04-18 meets state and local requirements and
adopted Ordinance 12-18;
Whereas,the County Commission scheduled an additional hearing on March 20, 2o18;
NOW, THEREFORE, BE IT ORDAINED that the Mason County Commission adopts the above
"WHEREAS" recitals as findings of fact in support of its action as required by RCW 36.7oA.390.
BE IT FURTHER ORDAINED that Ordinance No. 8117, Mason County Code Section 6.68 Water
Adequacy only, is hereby repealed in its entirety and replaced upon the effective date of this
ordinance (Attachment A)and Mason County Code Section 14.48.15o is amended (Attachment B).
BEITFURTHER ORDAINEDthatif asection,subsection,paragraph,sentence,clause,or phrase of this
ordinance is declared unconstitutional or invalid for any reason by any court of competent
jurisdiction; such decision shall not affect the validity of the remaining portions of this ordinance,
and if the provisions of this ordinance are found to be inconsistent with other provisions of the
Mason County Code, this ordinance shall control.
Mason County Code Section 6.68 Water Adequacy and 14.48 Stormwater Adopted: 3/20/18
Page 2
Ordinance No.M- �w
DATED this 20th day of March 2oi8.
BOARD OF COUNTY COMMISSIONERS
MASON COUNTY,WASHINGTON
ATTEST:
Randy Neatherlin,Chair
Cle k AtWB6d
Y
APPR S TO FORM: Terri Drexler,Co missioner
Tim Whitehead,Chief DPA
Kevin Shu y, ommissioner
Mason County Code Section 6.68 Water Adequacy and 14.48 Stormwater Adopted: 3/20/18
Page 3
Chapter 6.68— MASON COUNTY WATER ADEQUACY REGULATIONS
Sections:
6.68.010- Purpose.
6.68.020-Scope of coverage.
6.68.030- Definitions.
6.68.040- Determination of adequacy for building permits.
6.68.050- Determination of adequacy for division of land.
6.68.060-Waiver of regulations.
6.68.070-Appeals.
6.68.010- Purpose.
(a) The purpose of these rules is to define basic water adequacy in accordance with the Growth
Management Act (RCW 36.70A) for new construction and to each lot in a proposed subdivision or a
short subdivision prior to approval.
(b) It is the express purpose of this chapter to provide for and promote the health, safety and welfare of
the general public, and not create or otherwise establish or designate any particular class or group of
persons who will or should be especially protected or benefitted by the terms of this chapter.
6.68.020-Scope of coverage.
(a) The provisions of this chapter shall apply to all territories contained within the jurisdictional
boundaries of the Mason County dDepartment of health Community ServicesSeN'Ge6. The
provisions of these rules and regulations shall apply to all new residences, places of business, or
other buildings or places where persons congregate, reside or are employed which requires potable
water and to land segregation regulated under Title 16 of this code.
(b) Any building necessitating potable water shall provide proof of potable water as delineated in this
code and approved by the health seFV*GesCommunity Services director or designee(s) prior to
issuance of the permit. Exemptions to this code are listed as follows:
(1) Buildings identified by the building official which do not require potable water facilities;
(2) Improvements, replacement structures, or additions to buildings which already contain potable
water and will not result in increased water usage;
6.68.030- Definitions.
The definitions of terms in WAC 246-290, WAC 246-291, RCW 90.03, RCW 90.44, and Title 16 of
this code are adopted and incorporated by reference.
03.13.18 Adopted 3/20/18 Attachment A Page 1
6.68.040-Determination of adequacy for building permits.
(a) Group B or Two-Party Public Water Systems.
(1) Prior to issuance of a building permit, the water system manager provides, in writing, verification
that the water system is able and willing to provide water to the new connection and that doing
so will not exceed limits imposed upon the system by any state and local regulation. Verification
in writing will be accomplished by signing a statement on an application form; and
(2) Upon receipt of the application, the Group B public water system file is reviewed for the
following:
(A) Quality.
(i) Public water sources must meet all the standards set forth by state regulation and be
current on monitoring requirements.
(ii) In areas of water quality concern, water quality may be required to be further
evaluated for any or all of the following:
A. Primary contaminates,
B. Secondary contaminates,
C. Volatile organic compounds (VOC), and/or
D. Synthetic organic compounds (SOC).
(B) Quantity. The minimum quantity of available water supply shall be eight hundred gallons
per connection per day and a pumping rate of one gallon per minute per connection.
(C) Compliance.
(i) Water systems must be in compliance with state and local design and construction
requirements and with on-going requirements set forth by state regulation.
(ii) Source wells must be constructed according to the requirements set forth by WAC
173-160. Proper permitting and notification to state and local departments shall be
adhered to.
(iii) A water right permit or certificate of surface water right shall be obtained from the
Washington State Department of Ecology where required by RCW 90.03 and 90.44.
(b) Group A Public Water Systems.
(1) Prior to issuance of a building permit, the water system manager provides, in writing, verification
that the water system is able and willing to provide water to the new connection and that doing
so will not exceed limits imposed upon the system by any state and local regulation. Verification
in writing will be accomplished by signing a statement on an application form; and
(2) Upon receipt of the application form, the Washington State Department of Health is consulted
and the Washington State Department of Health determines that the water system is adequate.
(c) Individual Sources.
(1) Prior to issuance of the building permit, a copy of the water well report, a satisfactory
bacteriological report, and a capacity test is attached to the application; and
(2) Upon receipt of the application, documentation will be reviewed for the following:
(A) Quality.
(i) A satisfactory bacteriological analysis is required.
(ii) In areas of water quality concern, the same requirements apply as described in
subsection (a)(2)(A)(ii) of this section.
03.13.18 Adopted 3/20/18 Attachment A Page 2
(B) Quantity. The same requirements apply as described in subsection (a)(2)(B) with the
exception that appropriate conservation in conjunction with adequate storage measures
may be used to justify a daily volume of less than eight hundred gallons.
(C) Compliance. The same requirements apply as described in section (d),-subsections
(a)(2)(C)(i) and (ii) and assurance that the water source will not interfere with existing water
rights;
(d) New connections including individual sources . Accessory Dwelling
and additional bedrooms, will comply with the following:
(i)Any permit-exempt groundwater withdrawal associated with a water well constructed
before January 19, 2018 is deemed to have evidence of adequate water supply under this
section:
(ii)An applicant whose building location is in Water Resource Inventory Area (WRIA) 14,
15, and 22 shall pay a fee of five hundred dollars to Mason County and record relevant
water restrictions or limitations with the property title:
NO Except as provided in (iv) of this subsection, an applicant whose building location is
within WRIA 14 and 15 may obtain approval for a withdrawal exempt from permitting under
RCW 90.44.050 for domestic use only, with a maximum annual average withdrawal of nine
hundred fifty gallons per day per connection:
iv)An application whose building location is within WRIA 22 may obtain approval for a
withdrawal exempt from permitting_under RCW 9.44.050 for domestic use only, with a
maximum annual average withdrawal of three thousand gallons per day per connection:
(v) Upon the issuance of a drought emergency order under RCW 43.83B.405, Ecology
may curtail withdrawal of groundwater exempt from permitting under RCW 90.44.050 and
approved under this subsection (C), NO to no more than three hundred fifty gallons per day
per connection for indoor use only:
NO Notwithstanding the limitation to no more than three hundred fifty gallons per day per
connection for indoor use only, an applicant may use groundwater exempt from permitting
to maintain a fire control buffer during a drought emergency order.
NO Projects proposing to rely on well water have the opportunity to demonstrate that their
proposed withdrawal is not hydraulically connected to closed or regulated surface waters,
or that they can provide adequate mitigation to offset new consumptive use impacts. This
requires site specific analysis that is typically conducted by a licensed hydro-geologist and
is consistent with Mason County Stormwater Regulations (MCC 14.48).
(3) A surface water source will be determined to be adequate or issuance of a building permit upon
receipt of a copy of the certificate of surface water right and evidence of an appropriate
disinfection method is attached to the application.
6.68.050-Determination of adequacy for division of land.
(a) Group B or Two-Party Public Water Systems.
03.13.18 Adopted 3/20/18 Attachment A Page 3
(1) New Water System.
(A) The water system is completely installed and meets all state and local regulations; or
(B) Moneys, under the name of Mason County health services, totaling one hundred thirty-five
percent of a bid obtained from an appropriate contractor for the entire cost of drilling the
well, obtaining approvals, and installing the system, is placed either into an escrow account
or a bond to secure completion of the work after the well site location is passed.
(2) Existing Water System. The same requirements apply as described in subsection 6.68.040(a).
(b) Group A Public Water System. The same requirements apply as described in subsection
6.68.040(b).
(c) Individual Water Sources.
(1) Individual water sources will be adequate for land division when the lots meet the sizing criteria
in WAC 246-272-20501. The following disclaimer shall be placed on the face of the plat when
potable water is not available for each parcel at the time of subdivision approval:
"The lots, parcels or tracts contained within this land segregation have been created after
establishing a potable water supply meeting all state and local regulations."
(2) In areas where a water quantity or quality problem may exist, the following may be required:
(A) Well logs of adjacent properties;
(B) One or more well drilled;
(C) Water study by a qualified hydrogeologist.
6.68.070-Appeals.
Decisions of the Dclirector of health Community Sservices may be appealed to the Mason County
Bboard of Hhealth. Appeals must be made in writing within twenty working days of the decision which is
being disputed. A hearing date shall be scheduled with the board for their next regular meeting. All
appeals shall be sent to the board in writing via certified mail with return receipt requested.
03.13.18 Adopted 3/20/18 Attachment A Page 4
14.48.150- New development and redevelopment—Minimum requirements.
Development of individual, detached, single-family residences and duplexes exceeding two thousand
square feet of impermeable surfacing must have a small parcel erosion and sediment control plan, and a
residential site improvement plan (which includes a written description of the proposed work and
development) prepared and submitted for county review and approval.
Nonresidential development exceeding five thousand square feet of impermeable surfacing and/or
land disturbing activities of one acre or more must have the large parcel ESC plan (if required) and the
permanent stormwater quality control (PSQC) plan (if required) prepared and stamped by a licensed civil
engineer.
All applicants shall manage stormwater runoff on-site to the extent practicable by maximizing
infiltration, including using low-impact development techniques as defined in the most current version
of the Stormwater Manual for Western Washington produced by Washington State Department of
Ecology,or pursuant to stormwater management requirements adopted by Mason County,where more
stringent.
(1) New Development.
(A) All new nonresidential development that includes the creation or addition of five thousand
square feet, or greater, of new impervious surface area, and/or land disturbing activity of
one acre or greater, shall comply with minimum requirements #1 through #11 in
subsections(3)through (13)of this section.
Compliance shall be demonstrated through the implementation of an approved
stormwater site plan consisting of a large parcel ESC plan and a PSQC plan, as
appropriate.
(B) All new nonresidential development that includes the creation or addition of five thousand
square feet, or greater, of new impervious surface area, and land disturbing activity of less
than one acre, shall comply with minimum requirements#2 through#11 in subsections (4)
through (13) of this section and the small parcel minimum requirements found in Section
14.48.140 above. This category of development shall also prepare a stormwater site plan
that includes a small parcel erosion and sediment control plan.
Compliance shall be demonstrated through the implementation of an approved
stormwater site plan that includes a small parcel erosion and sediment control plan and a
PSQC plan.
(C) All new residential development and redevelopment (individual, detached, single family
residences and duplexes) that includes the creation or addition of two thousand square
feet, or greater of new impervious surface area, shall prepare a small parcel erosion and
sediment control plan which complies with minimum requirements #1 through #5 in
Sections 14.48.140(1) through 14.48.140(5), and shall prepare a residential site
improvement plan which includes a written description of the proposed work and
development. The small parcel erosion and sediment control plan along with the residential
site improvement plan should show and describe how development impacts are proposed
to be mitigated.
Compliance shall be demonstrated through the implementation of approved erosion
and sediment control plan, and a residential site improvement plan.
(2) Redevelopment.
(A) Where nonresidential redevelopment of greater than or equal to five thousand square feet
occurs:
The new development minimum requirements #1 through #11, subsections (3)
through (13), shall apply to that portion of the site that is being redeveloped, and source
Adopted 3/20/18 Attachment B
control BMPs shall be applied to the entire site, including adjoining parcels if they are part
of the project. A stormwater site plan shall be prepared.
(B) In addition to the above requirements, where one or more of the following conditions
apply, a stormwater site plan shall also be prepared that includes a schedule for
implementing the minimum requirements to the maximum extent practicable, for the entire
site, including adjoining parcels if they are part of the project. An adopted and implemented
basin plan (minimum requirement #9) may be used to develop redevelopment
requirements that are tailored to a specific basin.
(i) Existing sites greater than one acre in size with fifty percent or more impervious
surface.
(ii) Sites that discharge to a receiving water that has a documented water quality
problem. Subject to local priorities, a documented water quality problem includes, but
is not limited to water bodies:
a. Listed in reports required under Section 305(b) of the Clean Water Act, and
designated as not supporting beneficial uses;
b. Listed under Section 303(d) of the Clean Water Act as not expected to meet
water quality standards or water quality goals;
C. Listed in Washington State's Non-point Source Assessment required under
Section 319(a) of the Clean Water Act that, without additional action to control
non-point sources of pollution cannot reasonably be expected to attain or
maintain water quality standards.
(iii) Sites where the need for additional stormwater control measures has been identified
through a basin plan, the watershed ranking process under Ch. 400-12 WAC, or
through Growth Management Act planning.
(3) Minimum Requirement #1: Erosion and Sediment Control. All new development and
redevelopment that includes land disturbing activities of one acre or greater shall comply with
erosion and sediment control requirements 1 through 14, below. Compliance with the erosion
and sediment control requirements shall be demonstrated through implementation of a large
parcel erosion and sediment control plan.
All new development and redevelopment that includes land disturbing activities of less than
one acre shall comply with the small parcel minimum requirements found in Section 14.48.130,
above. Compliance with the small parcel requirements shall be demonstrated through
implementation of a small parcel erosion and sediment control plan.
The following erosion and sediment control requirements shall be met:
(A) Erosion and Sediment Control Requirement#1: Stabilization and Sediment Trapping. All
exposed and unworked soils shall be stabilized by suitable application of BMPs. From
October 1 to April 30, no exposed and unworked soils shall remain unstabilized for more
than two days. From May 1 to September 30, no exposed and unworked soils shall remain
unstabilized for more than seven days. Prior to leaving the site, stormwater runoff shall
pass through a sediment pond or sediment trap, or other appropriate BMPs.
(B) Erosion and Sediment Control Requirement#2: Delineate Clearing and Easement Limits.
In the field, mark clearing limits and/or any easements, setbacks, sensitive/critical areas
and their buffers, trees, and drainage courses.
(C) Erosion and Sediment Control Requirement #3: Protection of Adjacent Properties.
Properties adjacent to the project site shall be protected from damage by sediment
deposition.
(D) Erosion and Sediment Control Requirement #4: Timing and Stabilization of Sediment
Trapping Measures. Sediment ponds and traps, perimeter dikes, sediment barriers, and
other BMPs intended to trap sediment on-site shall be constructed as a first step in
Adopted 3/20/18 Attachment B
grading. These BMPs shall be functional before land disturbing activities take place.
Earthen structures such as dams, dikes, and diversions shall be seeded and mulched
according to the timing indicated in erosion and sediment control requirement#1.
(E) Erosion and Sediment Control Requirement #5: Cut and Fill Slopes. Cut and fill slopes
shall be designed and constructed in a manner that will minimize erosion. In addition,
slopes shall be stabilized in accordance with erosion and sediment control requirement#1.
Supplemental Guidelines: Consideration should be given to the length and steepness
of the slope, the soil type, upslope drainage area, ground water conditions, and other
applicable factors. Slopes which are found to be eroding excessively within two years of
construction must be provided with additional slope stabilizing measures until the problem
is corrected.
(i) Roughened soil surfaces are preferred to smooth surfaces on slopes (see BMP E2.35
in Chapter II-5).
(ii) Interceptors (see BMP E2.55 in Chapter II-5) should be constructed at the top of long
steep slopes, which have significant drainage areas above the slope. Diversions or
terraces may also be used to reduce slope length.
(iii) Concentrated stormwater should not be allowed to flow down cut or fill slopes unless
contained within an adequate temporary or permanent channel, or pipe slope drain
(see BMP E2.25 in Chapter II-5).
(iv) Wherever a slope face crosses a water seepage plane which endangers the stability
of the slope, adequate drainage or other protection should be provided (BMPs E2.30
and E2.75 in Chapter II-5).
(F) Erosion and Sediment Control Requirement #6: Controlling Off-site Erosion. Properties
and waterways downstream from development sites shall be protected from damage by
erosion due to increases in the volume, velocity, or peak flow rate of stormwater runoff
from the project site.
(G) Erosion and Sediment Control Requirement #7: Stabilization of Temporary Conveyance
Channels and Outlets. All temporary on-site conveyance channels shall be designed,
constructed and stabilized to prevent erosion from the expected velocity of the peak flow
from a two-year, twenty-four hour frequency storm for the developed condition.
Stabilization adequate to prevent erosion of outlets, adjacent streambanks, slopes and
downstream reaches shall be provided at the outlets of all conveyance systems.
(H) Erosion and Sediment Control Requirement #8: Storm Drain Inlet Protection. All storm
drain inlets made operable during construction shall be protected so that stormwater runoff
shall not be discharged offsite or be introduced into any fill area without first being filtered
or otherwise treated to remove sediment.
(1) Erosion and Sediment Control Requirement #9: Underground Utility Construction. The
construction of underground utility lines shall be subject to the following criteria:
(i) No more than five hundred feet of trench shall be opened at one time, unless
provisions are made to protect against adverse stormwater impacts.
(ii) Where consistent with safety and space considerations, excavated material shall be
placed on the uphill side of trenches.
(iii) Trench dewatering devices shall discharge into a sediment trap or sediment pond.
(J) Erosion and Sediment Control Requirement #10: Construction Access Routes.
Construction vehicle access shall be, whenever possible, limited to one route. Access
points shall be stabilized to minimize the tracking of sediment onto public roads.
Wherever construction vehicle access routes intersect paved roads, provisions must
be made to minimize the transport of sediment (mud) onto the paved road. If sediment is
Adopted 3/20/18 Attachment B
transported onto a road surface creating a hazard, the roads shall be cleaned immediately,
and thoroughly cleaned at the end of each day. Sediment shall be removed from roads by
shoveling or sweeping and be transported to a controlled sediment disposal area. Street
washing shall be allowed only after sediment is removed in this manner.
(K) Erosion and Sediment Control Requirement #11: Removal of Temporary BMPs. All
temporary erosion and sediment control BMPs shall be removed within thirty days after
final site stabilization is achieved or after the temporary BMPs are no longer needed.
Trapped sediment shall be removed or stabilized on site. Disturbed soil areas resulting
from removal shall be permanently stabilized.
(L) Erosion and Sediment Control Requirement#12: Dewatering Construction Sites. Trench
dewatering devices shall be discharged in a manner that will not adversely affect flowing
streams, drainage systems, or offsite property. Water discharged from dewatering pumps
shall be routed through a sediment pond or trap unless it is clear.
(M) Erosion and Sediment Control Requirement #13: Control of Pollutants Other Than
Sediment on Construction Sites. All pollutants other than sediment that occur on-site
during construction shall be handled and disposed of in a manner that does not cause
contamination of stormwater.
(N) Erosion and Sediment Control Requirement #14: Maintenance. All temporary and
permanent erosion and sediment control BMPs shall be maintained and repaired as
needed and in a timely manner to assure continued performance of there intended
function. All maintenance and repair shall be conducted in accordance with an approved
manual.
(0) Erosion and Sediment Control Requirement #15: Financial Liability. Performance
bonding, or other appropriate instruments, may be required to ensure compliance with the
approved erosion and sediment control plan.
(4) Minimum Requirement #2: Preservation of Natural Drainage Systems. Natural drainage
patterns shall be maintained, and discharges from the site shall occur at the natural location to
the maximum extent practicable.
(5) Minimum Requirement#3: Source Control of Pollution. Source control BMPs shall be applied
to all projects to the maximum extent practicable. Source control BMPs shall be selected,
designed, and maintained according to an approved manual. An adopted and implemented
basin plan (minimum requirement#9) may be used to develop source control requirements that
are tailored to a specific basin, however, in all circumstances, source control BMPs shall be
required for all sites.
(6) Minimum Requirement #4: Runoff Treatment BMPS. All projects shall provide treatment of
stormwater. Treatment BMPs shall be sized to capture and treat the water quality storm, defined
as the six month, twenty-four hour storm. The first priority for treatment of stormwater shall be to
infiltrate as much as possible of the water quality design storm into the ground. (Infiltration
BMPs practices shall be in accordance with Chapter III-3 of the PSWQA Manual) Pretreatment
of stormwater prior to infiltration into the ground may be required in cases where:
(A) The stormwater contains high concentrations of undesirable dissolved chemicals that can
move through soil.
(B) The stormwater contains large amounts of sediment that might clog the infiltrative
surfaces in the basin.
(C) The soils are extremely pervious and will not properly filter the stormwater as in the case
for some gravelly(type one)soils.
Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except
for necessary conveyance systems as approved by the director.
Adopted 3/20/18 Attachment B
An adopted and implemented basin plan (minimum requirement #9) may be used to
develop runoff treatment requirements that are tailored to a specific basin.
The objectives of providing stormwater treatment BMPs are, for both surface and
ground waters, to protect the quality and quantity, to allow attainment of the designated
uses, and to meet state standards promulgated under Chapter 173 of the Washington
Administrative Code.
(7) Minimum Requirement#5: Streambank Erosion Control. The requirement below applies only to
situations where stormwater runoff is discharged directly or indirectly to a stream, and must be
met in addition to meeting the requirements in Minimum Requirement #4, Runoff Treatment
BMPs:
Stormwater discharges to streams shall control streambank erosion by limiting the peak
rate of runoff from individual development sites to fifty percent of the existing condition two-year,
twenty-four hour design storm while maintaining the existing condition peak runoff rate for the
ten-year, twenty-four hour and one hundred-year, twenty-four hour design storms. As the first
priority, streambank erosion control BMPs shall utilize infiltration to the fullest extent practicable,
only if site conditions are appropriate and ground water quality is protected. Streambank erosion
control BMPs shall be selected, designed, and maintained according to an approved manual.
Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except for
necessary conveyance systems as approved by the director, and maintained according to the
1992 manual
An adopted and implemented basin plan (minimum requirement #9) may be used to
develop streambank erosion control requirements that are tailored to a specific basin.
(8) Minimum Requirement #6: Wetlands. Stormwater discharges to wetlands shall maintain the
wetland's natural hydroperiod and flows to the extent needed to preserve or enhance its existing
functions and values. Prior to proposing discharge of higher volumes of stormwater to a
wetland, alternative discharge, detention, and infiltration practices located in areas outside the
wetland shall be evaluated and employed by the project engineer where feasible and
practicable.
These requirements apply to existing natural wetlands and wetlands created as mitigation
for loss of wetland acreage Wetlands constructed and operated solely for use as stormwater
treatmenUstorage areas are exempt from these and most other restrictions that apply to natural
wetlands. Constructed wetlands may lose this exemption if not operated and maintained as
stormwater areas for three or more years. Other local, state, or federal wetland protection
requirements may also apply.
(9) Minimum Requirement #7: Water Quality Sensitive Areas. Where the Mason County
commissioners or their desighee determine that the minimum requirements do not provide
adequate protection of water quality sensitive areas, either on-site or within the basin, more
stringent controls shall be required to protect water quality. An adopted and implemented basin
plan (minimum requirement#9) may be used to develop requirements for water quality sensitive
areas that are tailored to a specific basin.
(10) Minimum Requirement#8Off-site Analysis and Mitigation.
Downstream Analysis May Trigger Additional Requirements. The project engineer shall
provide a detailed qualitative analysis of the flow path of the discharge from the project site to
the receiving water. This requirement shall apply to all projects where a drainage and erosion
control plan is prepared, including those proposing retention facilities. This analysis shall include
flow routing, and provide existing pipe and channel sizes and estimated capacities. In addition,
the project engineer shall discuss any known or expected downstream erosion, flooding, or
water quality problems, including those that may be caused by interflow from the proposed
retention facility. The director or designee shall have the discretion to specify the distance and
level of detail to be provided by the project engineer. In making this determination, the director
or designee shall consider such factors as the relative size of the new development, availability
Adopted 3/20/18 Attachment B
of other hydrologic work for the drainage area, and the extent to which stormwater generated on
the project site is to be infiltrated.
Based upon this analysis, the project engineer may determine or the director or designee
may require that a quantitative analysis of the conveyance system be performed both upstream
and downstream of the project site. A quantitative analysis will not be required for most projects
that propose to infiltrate most or all stormwater. This analysis shall determine conveyance
system performance for the appropriate design event(s) both with and without the proposed
development. The director or designee shall have the discretion to specify the distance and
level of detail to be provided by the project engineer. The director or designee shall consider
factors such as the relative size of the new development, availability of other hydrologic work for
the drainage area, and the results of the qualitative analysis, in making this determination.
The quantitative downstream analysis will include modeling the hydraulics of the proposed
project and all other sources of runoff tributary to the receiving water body for the appropriate
design event. The project engineer shall include an analysis of the impact of the twenty-four
hour, one hundred-year event (in addition to "Design Event" analysis) for each component of
the system including pond spillway.
The director or designee may impose stricter discharge and/or detention standards if the
discharge from the project, evaluated in the context of other existing conditions in the drainage
area, is reasonably expected to result in any of the following:
(A) Flooding;
(B) Loss of aquatic habitat due either to high or low flows;
(C) Property damage;
(D) Water quality problems;
(E) Erosion;
(F) Or an unacceptable interruption of vital services.
If the project engineer (or director or designee) determines that greater treatment,
infiltration and/or storage volumes, lower release rates, or downstream improvements are
needed, he/she shall specify project design criteria or other means to relieve the downstream
problems (providing that such solution will not violate minimum standards established in the
1992 manual). Other means might include increases in downstream flow capacity and/or offsite
detention and infiltration facilities, plans and financing for which will be subject to the approval of
the director or designee.
(11) Minimum Requirement #9: Basin Planning. Basin Plan Supersedes 1992 Manual. If a
proposed project is located in a basin or sub basin for which the county has an adopted basin
plan, stormwater requirements specifically identified in the basin plan shall take precedence
over those provided in this chapter. However, all other elements detailed in this chapter shall
continue to apply to such projects. Basin plans are required to be developed according to an
approved manual.
(12) Minimum Requirement #10: Operation and Maintenance. An operation and maintenance
schedule shall be provided for all proposed stormwater facilities and BMPs, and the party (or
parties) responsible for maintenance and operation shall be identified. An operation and
maintenance (O&M) Covenant will be required to cover all privately owned and maintained
stormwater facilities approved by the director. O&M covenant forms are available at the Mason
County public works office. A copy of the completed instrument, shall be recorded with the
county auditors'office by the proponent, and a copy of the recorded instrument is required to be
submitted to the public works department prior to final approval of the completed permanent
stormwater facilities.
(13) Minimum Requirement #11: Financial Liability. Performance bonding, or other appropriate
instruments shall be required for all projects to ensure compliance with these standards.
Adopted 3/20/18 Attachment B
(14) Variances from These Standards. Variances from these standards may be allowed at the
discretion of the director or designee provided that the proponent will substantially meet flow
control and water quality goals established by or implicit in these standards. Compliance with
ordinance requirements shall normally occur within the project area, but may be performed as
offsite mitigation in certain situations. Examples of cases when variances may be approved
includes, but are not limited to, the following:
(A) That the special conditions and circumstances exist which are peculiar to the land, such
as size, shape, topography, or location, and that literal interpretation of these standards
would deprive the property owner of rights commonly enjoyed by other properties similarly
situated, or
(B) That the site is being remodeled and certain site investigations would be destructive to
existing structures; or
(C) That remodels of existing projects which are either too small or so configured that in the
director's or designee's opinion some requirements of the manual cannot practically be
met: or
(D) That public works or private sector projects are in an existing road right-of-way, which is
not of adequate size to install preferred BMPs and for which right-of-way cannot be
expanded because of encroaching structures or setbacks for existing structures.
All requests for variances must be submitted in writing to the director or designee, and
must clearly state the specific section(s) of the ordinance from which a variance is requested
and why.
(15) Experimental BMPs. Experimental best management practices are defined as BMPs, which
have not been tested and evaluated by the Department of Ecology in collaboration with local
governments and technical experts. Some so-called experimental BMPs will likely be minor
variations on an existing theme. In that case, Ecology would review and approve or disapprove
the BMP in as timely a manner as possible. Where new designs are developed (examples of
experimental BMPs may be found in Section 1-2.17.2 of the PSWQA Manual), the review will be
extended through the use of a standing committee of technical experts. These persons will
review and comment on the practice. and Ecology will then determine whether or not these
BMPs should be approved and/or added to the manual.
(A) Approval of Experimental BMPs. Approval to use an experimental BMP may be granted
subject to initial approval by the Department of Ecology and the local government. If such
experimental BMPs prove useful they may be incorporated into later editions of the manual
following appraisal of the results and appropriate technical review conducted by Ecology in
collaboration with local governments and other interested parties. Approval to use an
experimental BMP will only be granted when a suitable contingency plan using approved
BMPs has been provided by the applicant to be used in the event that the experimental
BMP does not perform adequately.
In addition, several experimental BMPs have been included in the 1992 manual.
People may wish to use these BMPs on a trial basis, subject to approval by the local
government and provision of a contingency plan. In any event, use of experimental BMPs
is encouraged whenever applied research is being undertaken so that more information is
made available to facilitate judgement on their applicability and possible adoption as an
approved BMP.
(Ord. 81-08 (part), 2008).
Adopted 3/20/18 Attachment B