Yelm Field RMS Stormwater Memo - 2200807 Page 1 of 4
TO: City of Yelm Community Development
106 2nd Street
Yelm, WA 98597
DATE: March 19, 2021
FROM: Todd Sawin, PE
Tacoma - (253) 383-2422
PROJECT NO.: 2200807.10
PROJECT NAME: Ridgeline Middle School Field
Maintenance
SUBJECT: Stormwater Requirements Memo
The purpose of this memo is to discuss the Minimum Requirements required as part of the proposed maintenance
improvements at the existing Ridgeline Middle School track and field area. Ridgeline Middle School is located at
909 Mill Road SE, Yelm, WA 98597 on Tax Parcel 21725140100. The project parcel totals 29.99 acres and
houses both Ridgeline Middle School and Mill Pond Intermediate School; maintenance improvements are located
in the northwest corner of the site and will cover approximately 3.35 acres. The proposed Ridgeline Middle School
field maintenance project includes replacing the existing underdrained grass field with an underdrained artificial
turf field, replacing the existing track with a new rubberized track over asphalt, new field event facilities within the
track and field area, minor drainage improvements to the concrete pedestrian areas east of the existing track, and
hose connections to the onsite irrigation system. There are no proposed changes to the site’s existing domestic
water and fire service or sanitary service. The proposed improvements will discharge to the existing infiltration
pond in the northwest corner of the project parcel; this matches existing conditions. No pollution generating
surfaces are proposed as part of the track and field maintenance improvements. This memo demonstrates that
the stormwater design for this project complies with the requirements of the 2019 Department of Ecology (DOE)
Stormwater Management Manual for Western Washington (SWMMWW) (July 2019 Amended Edition), as
adopted by City of Yelm.
This project is subject to the 2019 SWMMWW. The project is a redevelopment that will add more than 5,000
square feet of new play replaced hard surfaces and the value of the proposed improvements does not exceed
50% of the assessed value of the existing project site. Therefore, all Minimum Requirements (MRs) apply to the
new hard surfaces and the converted vegetation areas (see the attached Flow Chart for Determining
Requirements for Redevelopment).
MR 1: Preparation of the Stormwater Site Plan
This Stormwater Requirements Memo has been prepared in accordance with III-3 Stormwater Site Plans
of the SWMMWW with all of the technical information and analysis necessary for the City of Yelm to
evaluate the proposed maintenance improvements for compliance with stormwater requirements.
MR 2: Construction Stormwater Pollution Prevention
A Construction Stormwater Pollution Prevention Plan (CSWPPP) complying with the 13 Elements
identified in the SWMMWW is included as part of this permit submittal package. This CSWPPP has been
prepared for both the Ridgeline Middle School and Yelm High School sites. A copy of this CSWPPP must
be kept at each project site.
MR 3: Source Control of Pollution
The proposed project is required to provide source control of pollution. The following are proposed
measures to be implemented as part of the civil plans:
· All pollutants, including waste materials and demolition debris created onsite during construction,
shall be handled and disposed of in a manner that does not cause contamination of surface
water.
Project Memo Page 2 of 4
Ridgeline Middle School Field Maintenance
2200807.10
March 19, 2021
· Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid
products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304
WAC for the definition of inert waste).
· Maintenance and repair of heavy construction equipment that may result in discharge or load of
pollutants into nearby surface waters shall be prevented utilizing proper spill prevention
measures.
· All Best Management Practices (BMPs) specified in the CSWPPP must be maintained throughout
the construction process.
The CSWPPP is included as part of this submittal package and provides details on the control of pollution
during construction.
MR 4: Preservation of Natural Drainage Systems and Outfalls
The existing Ridgeline Middle School track and field area discharges runoff north to an onsite infiltration
pond for 100% onsite infiltration. The proposed maintenance improvements will maintain this existing
discharge location of the existing track and field area. Underdrains are proposed within the artificial turf
field to collect runoff from the track and field area and discharge runoff north to the existing infiltration
trench. The proposed underdrainage discharges to a perforated pipe that runs along the perimeter of the
field improvements.
The proposed artificial turf fields will discharge runoff at a rate similar to the existing underdrained grass
fields therefore the proposed maintenance improvements will not increase flows discharging form the
proposed improvements. Existing discharge rates are expected to be maintained to the existing discharge
location.
MR 5: Onsite Stormwater Management
The project site triggers MRs 1-9, is located inside the UGS, and the LID Performance Standard has not
been chosen as a way to meet the requirements of MR 5. Per the Flow Chart for Determining MR #5
Requirements, attached, for each surface, BMPs found in List #2 must be considered in the order listed
for each type of surface; the first BMP that is considered feasible must be used.
All stormwater runoff generated on the proposed project site will discharge to the existing infiltration pond
at rates similar to existing conditions. No roof surfaces, or lawn/landscape areas are proposed as part of
the proposed improvements therefore, no onsite stormwater management BMPs are applicable to the
proposed improvements for roof or lawn/landscape areas.
The existing track will be replaced as part of the proposed maintenance improvements as well as portions
of the existing concrete pedestrian access areas on the east side of the track to eliminate existing
drainage issues at these locations. These replaced hard surfaces trigger MR #5. Due to the location of
these replaced hard surfaces, full dispersion is not feasible because there are no vegetated paths long
enough to provide dispersion. Permeable pavements are not feasible because a permeable pavement
track does not meet the needs athletic requirements of a middle school track, and the concrete pedestrian
areas to be replaced are proposed to match the existing concrete pavement to create an aesthetically
pleasing and consistent look. Bioretention is infeasible due to the limited amount of space to provide a
bioretention facility in the vicinity of these replaced hard surfaces. Sheet flow dispersion and concentrated
flow dispersion are infeasible for the same reasons as full dispersion. No stormwater management BMPs
listed in List #2 are feasible therefore stormwater form these proposed surfaces will continue to discharge
directly to the existing infiltration trench.
MR 6: Runoff Treatment
Project Memo Page 3 of 4
Ridgeline Middle School Field Maintenance
2200807.10
March 19, 2021
Proposed improvements do not include any pollution generating surfaces and therefore no runoff
treatment is proposed.
MR 7: Flow Control
Proposed improvements do not include any pollution generating surfaces and therefore no runoff
treatment is proposed. The proposed artificial turf fields will discharge runoff at a rate similar to the
existing underdrained grass fields therefore the proposed maintenance improvements will not increase
flows discharging form the proposed improvements. Existing discharge rates are expected to be
maintained to the existing discharge location therefore the existing onsite infiltration pond will continue to
provide 100% onsite infiltration of runoff from the proposed maintenance improvements.
Minimum Requirement #8: Wetlands Protection
To our knowledge, there are no wetlands on or adjacent to the project site.
Minimum Requirement #9: Operation and Maintenance
Maintenance standards have been prepared for all proposed onsite drainage structures. It will be the
responsibility of the owner to keep a copy of these standards onsite and to perform routine maintenance
on all drainage facilities. These maintenance standards are attached to this Stormwater Requirements
Memo.
Soils Report
Landau Associates, Inc. prepared a Summary of Geotechnical Engineering Services, dated February 5, 2021,
which is included as part of this submittal package. The Ridgeline Middle School portion of the investigation, test
pits 1-4, found that subsurface conditions mainly consist of glacial outwash consisting of gravel with variable
sand, silt, and cobble content in a medium dense to very dense, moist to wet condition. Groundwater was
observed at depth ranging from 6.9 to 7.9 feet below existing ground surface.
Wells and Septic Systems
To our knowledge, there are no existing wells or septic systems within the proposed Ridgeline Middle School
maintenance project limits. No onsite domestic water service or sewer services will be affected as part of the
proposed improvements.
Fuel Tanks
To our knowledge, there are no existing fuel tanks within the proposed Ridgeline Middle School maintenance
project limits.
Analysis of the 100-Year Flood
According to the FEMA Map 53067C0365E the site is not located within the 100-year floodplain (see attached).
Covenants, Dedications, and Easements
To the best of our knowledge, no known covenants, dedications, or easements are associated with this project.
Conclusion
This analysis is based on data and records either supplied to or obtained by AHBL. These documents are
referenced within the text of the analysis. The analysis has been prepared utilizing procedures and practices
Project Memo Page 4 of 4
Ridgeline Middle School Field Maintenance
2200807.10
March 19, 2021
within the standard accepted practices of the industry. We conclude that this project, as schematically
represented, will not create any new problems within the downstream drainage system. This project will not
aggravate any existing downstream problems due to either water quality or quantity.
CHS/
c: Charles Stout, AHBL Inc.
Attachments:
Flow Chart for Determining Requirements for Redevelopment
Flow Chart for Determining MR #5 Requirements
FEMA Flood Insurance Rate Map Number 53067C0365E
SWMMWW BMP Maintenance Tables
Q:\2020\2200807\10_CIV\NON_CAD\REPORTS\RMS\20210318 RMS Memo (SSP) 2200807.10.docx
Figure 1-3.1: Flow Chart for Determining Requirements for New
Development
Start Here
See Redevelopment Project
Does the Site have 35% Yes
Thresholds and the Figure Flow
or more of existing hard 10 Chart for Determining
surface coverage? Requirements for Redevelopment".
No
Does the Project convert %
IF
acres or more of vegetation to
Does the Project result in
lawn or landscaped areas, or
5,000 square feet, or No
convert 2.5 acres or more of
greater, of new plus
native vegetation to pasture?
replaced hard surface
area?
I
\ No
Yes
Yes Does the Project result in 2,000
IF square feet, or greater, of new plus
All Minimum Requirements replaced hard surface area?
apply to the new and replaced
hard surfaces and converted
vegetation areas. Yes/ No
Does the Project have land
Minimum Requirements #1 disturbing activities of 7,000
through #5 apply to the new Yes square feet or greater?
and replaced hard surfaces
and the land disturbed. No
Minimum Requirement #2
applies.
Flow Chart for Determining Requirements for
New Development
DEPARTMENT OF Revised March 2019
ECOLOGYPlease see http.lAvww.ecy.wa.gov/copyright.html for copyright notice including permissions,
State of Washington limitation of liability, and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 1- Chapter 3 - Page 89
Figure 1-3.2: Flow Chart for Determining Requirements for
Redevelopment
2019 Stormwater Management Manual for Western Washington
Volume 1- Chapter 3 - Page 90
Does the Project result in 2,000 square feet, or more, of new plus replaced hard surface area?
OR
Does the land disturbing activity total 7,000 square feet or greater?
Ilr Yes No
IF
Minimum Requirements #1 through #5
apply to the new and replaced hard Minimum Requirement #2 applies.
surfaces and the land disturbed.
Next Question
Does the Project add 5,000 square feet or more of new hard surfaces?
OR
Convert %4 acres or more of vegetation to lawn or landscaped areas?
OR
Convert 2.5 acres or more of native vegetation to pasture?
Yes IF No
All Minimum Requirements apply Next Question Is this a road
to the new hard surfaces and the related project? NO
converted vegetation areas.
Yes
Does the Project add 5,000 square feet or more of new hard surfaces?
Yes No
Is the total of new plus replaced hard surfaces 5,000
square feet or more,
Do the new hard IF
AND
surfaces add 50% ordoes
No No
the value of the proposed improvements -
No additional
more to the existing
including interior improvements - exceed 50% of the
requirements.
hard surfaces within
assessed value (or replacement value) of the:
the Site?
• existing Project Site improvements (for
commercial or industrial projects) OR
• existing Site improvements (for all other projects)
Yes
All Minimum Requirements apply to the new and replaced
Yes
hard surfaces and converted vegetation areas.
Flow Chart for Determining Requirements for
Redevelopment
DEPARTMENT OF
Revised March 2019
ECOLOGYPlease
see http.lAvww.ecy.wa.gou/copyright.html for copyright notice including permissions,
State of Washington
limitation of liability, and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume 1- Chapter 3 - Page 90
Figure 1-3.3: Flow Chart for Determining MR #5 Requirements
Does the entire project qualify as Flow Control exempt (per MR #7)?
Yes
Did the project developer choose to meet
the LID Performance Standard?
No
Yes REQUIRED: For each
surface, consider the BMPs
in the order listed in List #3
for that type of surface. Use
the first BMP that is
considered feasible.
NOT REQUIRED:
Achievement of the LID
Performance Standard.
REQUIRED: For each
surface, consider the
BMPs in the order
listed in List #1 for that
type of surface. Use
the first BMP that is
considered feasible.
NOT REQUIRED:
Achievement of the LID
Performance Standard.
No
Does the project trigger
only MRs #1 - #5? (Per
the Project Thresholds in
Applicability of the
Minimum Requirements
Section).
Yes
No
(the project triggers
MRs #1 - #9)
No
Did the project
developer choose to
meet the LID
Performance
Standard?
N/
Yes
REQUIRED: Meet the LID Performance
Standard through the use of any Flow Control
BMP(s) in this manual.
REQUIRED: Apply BMP T5.13 Post
Construction Soil Quality and Depth.
NOT REQUIRED: Applying the BMPs in Lists
#1, #2, or#3.
DEPARTMENT OF
ECOLOGY
State of Washington
REQUIRED: For each
surface, consider the BMPs
in the order listed in List #2
for that type of surface. Use
the first BMP that is
considered feasible.
NOT REQUIRED:
Achievement of the LID
Performance Standard.
Is the project outside
the UGA on a parcel
that is 5 acres or larger?
Did the project
developer choose to
meet the LID
Performance
Standard?
No
Yes
REQUIRED: Meet the LID
Performance Standard through
the use of any Flow Control
BMP(s) in this manual.
REQUIRED: Apply BMP T5.13
Post -Construction Soil Quality
and Depth.
NOT REQUIRED: Applying the
BMPs in Lists#1, #2, or#3.
Flow Chart for Determining MR #5
Requirements
Revised March 2019
Please see http.lAvww.ecy.wa.govlcopyright.html for copyright notice including permissions,
limitation of liability, and disclaimer.
2019 Stormwater Management Manual for Western Washington
Volume I - Chapter 3- Page 118
NOTES TO USERS LEGEND
CITY OF YELM
This map is for use in administering the National Flood Insurance Program. It does 1115000 FT 530310 SPECIAL FLOOD HAZARD AREAS (SFHAS) SUBJECT TO
not necessar ly tlentty all areas subject to flooding, particular from local dmina a 122° 37 30" 1120000 FT INUNDATION BY THE 1% ANNUAL CHANCE FLOOD
Sources of smallsm. The community map repository should be consulted 46°5615 JOINS PANEL 0353 The l% cal chs Eiv.d(1or Smedeot), alu—yes, knZvn a, M! Sixfltl Hoothlflood Mathes
NE.IL W JOINS PANEL 0354 a t%maitre of being egmled or exceeds In arty gNen Yeas The Slaetal Rpptl Nawk Area s
possible updated or additional flood hazard information. USE 7 N 122° 33' 45" the mm -jq m flooding by the 1%annual mance noxa Areas of Spetal Flood Hawn
K K Pea sky 46° 56' 15" lou , Zones A, AE, AH, A0, AR, A99, V, aM W. Tile Baas Flood Eleiatbn Is the water-sur%,
To obtain more detailed information in areas where Base Flood Elevations (BFES) aevauon ofthe 1%annual mance flood.
and/or floodwa have been determined, users are encouraged W consult the Flood ZONE A I _� e v m
g RSTEE r f ZONEA No ease Floyd E—tons deferml�ro].
Profles and Floodway, Data and/or Summary of Stillwater Elevations tables contained CARTE N ,` -NEAE ease hood Elevations dearmined.
within the Flood Insurance Study (FIS) Repot that accompanies this FIRM. Users sem
should be aware that BF
shown on the FIRM represent rounded whole-footf I re ZONE AH Flood depths of l to 3 fest(usuxwi
ly areas of pang); Base Flood Elevx—
elevations. These BFEs are intended for flood insurance rating purposes only and I 1 Pia a s'9800o"'N dete,minea.
should not be used as the Sole Source of flood elevation information. Accordingly, CITY OF YELM g•
flood elevation data presented in the FIS Report should be utilized in conjunction with 530310 J as �+ C ZONE AO Flood deptlss d 1 to 3 feet (usually sheet flow on Wong [main); average
the FIRM for purposes of construction and/or floodplain management. depths —1—For areas of fin, noodl�g, —Ins Alto determined.
ZONEAR Specialmood Hawk Areas SHyprxeoSti rota Mel%annualdertm
Coastal Base Flood Elevations Shown on this map apply only landward of 0.0' 590000 FT } I '"$ = } f flood bye n-Onn.system that vas subsequently decaenm. Zone
North Amencen Vertical Datum of 1988(NAVD 88). Users of this FIRM should be 25oolw s _ 1 I AR lndireres that the former Hood control systan is beiy reawNmpmvide
aware that coastal flood elevations are also provided m the Summary of Stillwater J Protection fon Me 1%annual manor greener flood.
Elevations table in the Flood Insurance Study Report for this jurisdiction. Elevations L_ 30ZONE A99 Pr ea w be prdecMd from
1% nn Chan flood by a FA I flood
shown in the Summary of Stillwater Elevations table should be used for construction o Drotxtion system under --n; m Base Food E—dom datmor..
and/or fbodplain management purposes when they are higher than the elevations L
ZONE V One- flood!cone with wimby hawk (wave action); noBase Flood Eln,mons
shown on this FIRM. '� dekrmined.
20NE VE Uastal flood Sone win veladry hawk (wavy amen); Base Flood Elea[bns
Boundaries of the floodways were computed at cross sections and interpolated fl —"I-
between cross sections. The floodways were based on hydraulic considerations with FLOODWAY AREAS IN ZONE AE
regard to requirements of the National Flood Insurance Program. Floodway widths
and other pertinent floodway data are provided in the Flood Insurance Study Report
for this Jurisdiction. g dootlway is Me d,annel d a —. Dlm any adjacent floodplain areas Mat mus[ he kept free of
m Ma[Me 1%annual man floc[ Son bemmm wRM1out substantialimrmses in
Certain areas not in Special Flood Hazard Areas may be protected by flood control snood helgnrs.t
structures. Refer to Section 2.4 "Flood Promotion Measures" of the Flood InsumnceOTHER FLOOD AREAS
O
Study Report or information on flood control structures for this jurisdiction. 9700"N
The projection used in the preparation of this map was Washington State Plane zoxE x nese o.2%annual mann Soot; areas d 1% annual dunce flood Sore
average depths of Sat c Man t foot or Soo d—ge%army areas less Man 1 square
South Zone (FIPS zone n datum,
The herlzomN datum was NAD 83, s used
1980 mik; and areas Ixdeoed by kvea fon t%annual Chan none.
spheroid. Differences it datum, spheroiQ projection a UTM zones used in the
protluction of FIRMS for adjacent jurisdictions may result in slight positional OTHER AREAS
differences in map features across jurisdiction boundaries. These differences do not 3 20NEx Aims aetwmlneato be mmlae Me o.z%annual man nooepaln.
affect the accuracy of this FIRM.
20NE D Ams in whim flpotl hawks are undetermined, but possible.
Flood elevations on this map are referenced to the North American Vertical Datum of THIS AREA SHOWN ATA
1988. These flood elevations must be compared o structure and ground elevations j' COASTAL BARRIER RESOURCES SYSTEM (Celts) AREAS
mfem cad to the same vertical datum. For information regarding conversion SCALE OF 1" - 500'
between the National Geodetic Verfical Datum of 1929 and the North American OTHERWISE PROTECTED AREAS (OPAS)
Vertical Datum of 1988, visit the National Geodetic Survey webefte at ON MAP NUMBER
htto://rev or contact the National Geodetic Survey at the following www.nas. m q > CSR meta arcaPAs are Onormally looted or within Jtnant to Specht Food Area
Haww s.
adtlress: 585000 FT + } 111nnual Qanm Floodplain souMary
NGS In ornation Services 53067CO362
NOAA, N/NGS12 36 nam 31 Footway bp-sy FbodlNaln BouMary
NE a TJ NE sE "96"'N— — — Zone O bouMary
National Geodetic Survey yE u
SSMC-3,1{9202 wAr ............. ®RS and OPA
1315 Eprang Mt Highway
Silver Spring. Maryland 20910-3282 bouMary
(301) 713-3242 - BOtliviting Special Roos Hawn Area cones and bouMary
tlividog iding S Specht Flmtl Hawk Areas of tlimerem Base Flood! Elewtons,
To obtain current elevation, description, and/or location information for bench marks flood depths, I'— velottles.
shown on this map, please concoct the Information Services Branch of the National
^^�� 5f3's^e� M, FIooE Elemtlm linearca value; dentin. in ket"
Geodetic Survey at (301) 713-3242, or visit its website at htto://won,rigs.
TEL 90]) eau Food Ekvdtlon Solus where unlorm within cone; elevation in
kat•
Base map information shown on this FIRM was derived from multiple Sources.-Rderenced to the No. Amerlmn.—I... of tells
Base map files were provided in digital format by Thurston County Geodata
Center, WA DNR and USGS. This information was compiled at scales of A A cou Evzonllne
1:2400 to 1:24000 during the time Period of 19% to 2007.
5
This map reflects more detailed and up-[crista stream channel configuration"
O - - - - - 20 Tmnurt Ilne
than those shown on the previous FIRM for this jurisdiction. The flootlplains and T77 /5.02'00'.93.02'12' Oeographlc cpokinates mreenmd to the Neon Datum of
floodways that were transferred from the previous FIRM may have been adjusted T. 16 N. T. 17 N. 1983 (NAD 03) Western Hanlsphere
to con(Oml ro these new stream channel configurations. As aresult, the T 1 6 N. 3100000 FT 5000-foot tkks: Waahr,tm Scte Plane South Zone
Flood Profiles and Floodway Data tables or multiple streams in the Flood aviRoAD (FlPS--Z), lambert Conformal Conlc pod-on
Insumnce Study Report (which contains authoritative hydraulic data) may reflectul 1°89°'°" N 1000-meter universal Twnmrae vo—grit values, mm 1%
astream channel distances that differ from what is shown on this map. 9 Bend, mark see anatlon In Nates m Users —.n of this FlRM g4' o'9500Ai�N oxsslo x ( esW
Corporate limits shown on this map are based on the best data available at the time to $ Wneq
of publication. Because changes due to annexations or de-annexations may have 3 'M1.s alver rine
ocourred after this map was published, map users should contact appropriate O' MAP REPOSITORIES
COmmumky officials to verify current corporateNNIie limit locations. D NUS RMI S, Z Rder w Mep Reposibdea llaton Map Index
580DOO FT + + + d EFFECTIVE DATE OF COUNTYWIDE
Please refer to the separately printed Map Index for anOV map of the O FLOODINSIIRANCE RATEMAP
county showing the layout of map panels; community map repository addresses;
October 16. M12
and a Listing of Communities table containing National Flood Insurance Program N/ EFFECTIVE DATE(S) OF REVISION(S) TO THIS PANEL
dates or each community as well as a listing of the panels on which each community v
is located. .1
For information on available products associated with this FIRM visit the Map I 6
Service Center (MSC) website at ho://On-fema.cov. Available products may 5 4
include previously issued Letters of Map Change, a Flood Insurance Study Report, THURSTON COUNTY
and/or digital versions of this map. Many of these products can be ordered o ZONE A
obtained directly from the MSC webshe. UNINCORPORATED AREAS Formmmumymaprevislonhlswrpdormmun"dA mappog,rekrmms Commuelly
530188 Mist,Hhwr tads — in the F.d Inaurenm study d to, tris prisdieeon.
If you have questions about this map, how to order products, or the National To anarmina unooa insumnm is availaCla in this community, contact your insumnm agent
Flood Insurance Program in general, please call the FEMA Map Information Palm Creek wmIlMe Nattonal Flmdlnsurenm Pmqmm a[1AODG00-Efi20.
eXc ngenfe at (o 11w at aoov/I EMA MAP (1-877-336-2627) or vis[ the FEMA s,94o N
website at htto //www (ems cov/bus ness/nf o. Goodwin Lake
MAP SCALE 1"= 1000-
500 0 1000 2000
t00RO LANE SE FEET
METERS
AvENUE E.
me 0 300 800
Ll �
C-;7 a
PANEL 0365E
575000 FT + ° + + FIRM
a` n FLOOD INSURANCE RATE MAP
e 5'9300 N THURSTON COUNTY,
12 ® WASHINGTON
AND INCORPORATED AREAS
7 IINUI SE9 °
8 PANEL 365 OF 625
¢ t—as _ (SEE MAP INDEX FOR FIRM PANEL LAYOUT)
g ' 44NSALNS:
E COMMDN NUMBER PANEL 5577
IlLM, c11 or snol. oxs E
5
Creek
Yelm
11310 AVENUE ES g 1192—N
Noticeto User: The Map Number shown below
570000 FT �3 1$ + 176 + �sChould bery sNumbeed ers; the
en phowngabove map ohould be
used onninsumnce applications for the subject
48.52' 30" rc community.
122°37'30" a ® rya., MAPNUMBER
JOINS PANEL 0530 46° 52.30" 53067CO365E
°29°0°mE s�000mE
a31—E a32—E 122°33'45" x �'
F ,. EFFECTIVE DATE
33000mE uwa aE' OCTOBER 16, 2012
Federal Emergency Management Agency,
Appendix V-A: BMP Maintenance Tables
Ecology intends the facility -specific maintenance standards contained in this section to be conditions for determining if maintenance actions are required as identified through inspection. Recognizing that Permittees have limited main-
tenance funds and time, Ecology does not require that a Permittee perform all these maintenance activities on all their stormwater BMPs. We leave the determination of importance of each maintenance activity and its priority within
the stormwater program to the Permittee. We do expect, however, that sufficient maintenance will occur to ensure that the BMPs continue to operate as designed to protect ground and surface waters.
Ecology doesn't intend that these measures identify the facility's required condition at all times between inspections. In other words, exceedance of these conditions at any time between inspections and/or maintenance does not auto-
matically constitute a violation of these standards. However, based upon inspection observations, the Permittee shall adjust inspection and maintenance schedules to minimize the length of time that a facility is in a condition that
requires a maintenance action.
2019 Stormwater Management Manual for Western Washington
Volume V - AppendixA - Page 1005
Table V -A.6: Maintenance Standards - Debris Barriers (e.g., Trash Racks)
Maintenance Components
Defect
Condition When Maintenance is Needed
Results Expected When Maintenance is Performed
General
Trash and Debris
Trash or debris that is plugging more than 20% of the openings in the barrier.
Barrier cleared to design flow capacity.
External:
Rock Pad
Bars are bent out of shape more than 3 inches.
Bars in place with no bends more than 3/4 inch.
Rock pad replaced to design standards.
Damaged/ Missing Bars.
Bars are missing or entire barrier missing.
Bars in place according to design.
Metal
Bars are loose and rust is causing 50% deterioration to any part of barrier.
Barrier replaced or repaired to design standards.
Inlet/Outlet Pipe
Debris barrier missing or not attached to pipe
Barrier firmly attached to pipe
Accumulated sediment that exceeds 20% of the design depth.
Table V -A.7: Maintenance Standards - Energy Dissipators
Maintenance Com-
Defect
Conditions When Maintenance is Needed
Results Expected When Maintenance is
ponents
Performed
External:
Rock Pad
Missing or Moved Rock
Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil.
Rock pad replaced to design standards.
Erosion
Soil erosion in or adjacent to rock pad.
Rock pad replaced to design standards.
Pipe Plugged with Sediment
Accumulated sediment that exceeds 20% of the design depth.
Pipe cleaned/flushed so that it matches
design.
Not Discharging Water Properly
Visual evidence of water discharging at concentrated points along trench (normal condition is a "sheet flow" of water along trench).
Trench redesigned or rebuilt to standards.
Intent is to prevent erosion damage.
Dispersion Trench
Perforations Plugged.
Over 1/2 of perforations in pipe are plugged with debris and sediment.
Perforated pipe cleaned or replaced.
Water Flows Out Top of "Distributor"
Maintenance person observes or receives credible report of water flowing out during any storm less than the design storm or its causing
Facility rebuilt or redesigned to standards.
Catch Basin.
or appears likely to cause damage.
Receiving Area Over -Saturated
Water in receiving area is causing or has potential of causing landslide problems.
No danger of landslides.
I nternal:
Worn or Damaged Post, Baffles, Side
Structure dissipating flow deteriorates to 1/2 of original size or any concentrated worn spot exceeding one square foot which would
Structure replaced to design standards.
Manhole/Chamber
of Chamber
make structure unsound.
Other Defects
See Table V -A.5: Maintenance Standards - Catch Basins
See Table V -A.5: Maintenance Standards -
Catch Basins
2019 Stormwater Management Manual for Western Washington
Volume V - Appendix - Page 1010