Drainage report.pdfDECC1O Engineering Inc.
17217 7th Avenue W.
Bothell, WA. 98012
(206)390-8374
Fax: (425) 741-8214
Keller 2-Lot Short Plat
City # PLN 20130053
Conceptual Drainage Design
Report, Operation and
Maintenance Manual & SWPP
Report
Property Location:
19325 80th Ave W.
Edmonds, WA 98020
March 6, 2014
Revised: July 22, 2014
Prepared for:
Mr. Joshua Keller
KELLER SHORT PLAT
STORMWATER REPORT
TABLE OF CONTENTS
Page
Introduction.......................................................................................................................................... 2
ProjectOverview..................................................................................................................................2
PreliminaryConditions Summary......................................................................................................2
Minimum Requirement #1: Stormwater Site Plan Narrative.....................................................2
Off -Site Analysis and Mitigation................................................................................................... 3
MinimumRequirement #2: SWPPP Narrative............................................................................9
Minimum Requirement #3: Water Pollution Source Control..................................................10
Minimum Requirement #4: Preservation of Natural Drainage Systems & Outfalls ..............11
Minimum Requirement #5: On -Site Stormwater Management...............................................11
Minimum Requirement #6: Runoff Treatment..........................................................................11
WaterQuality Analysis................................................................................................................11
MinimumRequirement #7: Flow Control..................................................................................11
InfiltrationAnalysis...................................................................................................................... 12
Conveyance.................................................................................................................................. 12
MinimumRequirement #8: Wetlands Protection......................................................................14
Minimum Requirement #9: Basin/Watershed Planning............................................................14
MinimumRequirement #10: Operations and Maintenance.......................................................14
List of Figures:
Figure 1.
Site Location & Vicinity Map
Figure 2.
Existing Site Conditions
Figure 3
Developed Site Conditions
Figure 4.
Downstream Analysis and Sub -Basin Map
Figure 5:
Soils logs
Introduction
This report has been prepared at the request of Mr. Joshua Keller in support of a 2-lot short plat, located
at 19325 80th Ave W, Edmonds, Snohomish County Washington in the southeast 1/4 of the southeast 1/4
of Section 18, Township 27 North, Range 4 East W.M. (Parcel #27041800403500) (Refer to Figure 1,
Site Location and Vicinity Map).
This report addresses the drainage report contents and organization per the City of Edmonds and the
2005 Storm Water Management Manual for Western Washington (S WMM Manual). We have prepared
this report using the required Drainage Outline as directed under Volume I, Chapter 2 of the manual.
Project Overview
The project consists of development of a 2-lot short plat located at 19325 80th Ave W, Edmonds,
Washington. The existing lot is 0.48 acres in size and contains an existing home, garage and driveway.
Once developed, the existing home will remain and a 2nd lot will be added to the north side of the
property. The site is accessed off of 80th Ave W.. The site improvements include 2 residential lots, and
use of the existing driveway to serve both lots. Infiltration is proposed for the site. The runoff from the
new roof and driveway will be infiltrated in individual on -site infiltration trenches. The proposed new
impervious area is under 5,000 sf and exempt from water quality and the site will use LID methods to
address runoff. See Figure 1 "Existing Site Conditions" & Figure 2 "Developed Site Conditions"
Conditions of Approval Summary
The City will issue the conditions of approval once the preliminary plans have been reviewed
VICINITY MAP
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Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 2
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Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 3
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Minimum Requirement #1
Stormwater Site Plan Narrative
Per Section 2.5, Conceptual stormwater site plans and SWPP Plans have been prepared for the site and
are included with this storm drainage report. No detention is proposed for the site since the runoff from
the new roof and driveway will be infiltrated on -site. The proposed drainage system will be required to
be designed and installed as part of the building permit issued once the plat has recorded.
OFF SITE ANALYSIS AND MITIGATION
An Off Site Analysis and Mitigation Study meeting requirements outlined in Section 3.2.6 was
performed on March 5, 2014. The weather was rainy at the time of the field inspection. See Figure 4:
"Downstream Analysis Map".
TASK I: PROJECT OVERVIEW & STUDY AREA DEFINITION
The proposed project is located 19325 801h Ave W, Edmonds, Edmonds and is a 2-lot short plat.
Existing Site Conditions: The existing lot is 0.48 acres in size. The site currently contains a home,
driveway, grass, and shrubs and trees. The site and surrounding area is zoned RS-8 residential and is
fully developed with existing residential homes surrounding the site. The site itself slopes east to west
with slopes around 2 to 10%. There are no known sensitive areas contained on or near the site.
The soil logs identified soils type as Gravelly Sand according to soils logs dug on site.
TASK 2: REVIEW OF AVAILABLE INFORMATION ON STUDY AREA
Resource Review:
The following is a description of the resources that were reviewed for the preparation of this Level 1
Drainage Study:
A. Basin Recognizance Summary: Enclosed within are downstream and upstream basin area map
which clearly define the flow pass and the drainage basins related to this project. See (Figure
4: "Downstream Analysis Map" )
Evidence of Existing and Predicted Problems
Lack of capacity or constrictions in the existing drainage system.
0 On -site: No evidence of any problem.
0 Off -site: 18 inch storm pipes with catch basins
(no evidence of capacity or any other problems)
Overtopping. Scouring, Bank, Sloughing of Sedimentation
0 On -site: No evidence of any problem.
0 Off -site: ditches: none noted
18-inch pipes: none noted
Catch Basins None noted
Flooding etc.
0 None Noted
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 5
Significant Destruction of Aquatic Habitat or Organisms
0 None Noted
B. Floodplain/Floodway (FEMA Maps): Does not appear to be located within the flood plain of
the stream as determined by the FEMA maps.
C. Other Off -Site Analysis Issues: None Noted
TASK 3 & 4: FIELD INSPECTION AND DESCRIPTION OF DRAINAGE SYSTEM WITH
EXISTING AND PREDICTED PROBLEMS
A Level 1 drainage analysis was preformed for the site on March 5, 2014 to determine any pre-existing
drainage problems downstream. The weather was rainy. The total distance covered was over 3/4 mile
downstream. (Refer to: Figure 4: Downstream Analysis Map)
Level 1 Downstream Drainage Analysis:
Section 1: Upstream Drainage Analysis:
The 0.48 acre site is located the west side of 80th Ave W, Edmonds. This street picks up all offsite runoff
from the east and directs it around the site. The site itself slopes from east to west eliminating any off -
site runoff from the north and south sides. Therefore, there is little if any upstream drainage areas
draining onto the site and the off -site area flowing onto the 0.48 acre site is limited to the site itself.
A review of the upstream area indicated that there were no indications of capacity problems observed in
the roadway system conveying the runoff upstream of the site.
Section 2: On -site Drainage Considerations:
"flit 0.48 acre site generally slopes from the east to west with all runoff leaving the site along the west
property line, where it flows onto and adjacent lot before being intercepted by the storm drainage in 801h
Ave W.
Section 3: 801h Ave W. to 196th St SW to Puget Sound.
The runoff from the site discharges into the existing drainage system on 80th Ave W. This storm drain
system consists of 18" stonn pipe and CB's (flowing south) for 500 feet which then turns west in the
storm system in 196th St SW for a distance of over 3,100 ft
There appeared to be no issues with the existing storm system. No indications of capacity or over
topping of the street's drainage systems, storm pipes of catch basins. (See Figure 4: Downstream
Analysis Map)
With use of proposed LID measures including infiltration of the roof and driveway access runoff, the
proposed site improvements should have little if any impact on downstream conditions.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 6
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Figure 4: Downstream Analysis Map
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 7
TASK 5: LEVEL 1 MITIGATION OF EXISTING PROBLEMS
On -Site Infiltration:
The project proposes to infiltrate the runoff from the roof and driveway areas thereby mitigating the
proposed increase in runoff and the impacts from the development.
Water Quality Requirements:
The new PGIS area is well under the 5,000 sf threshold. Therefore, no water quality is required.
Conclusions:
Based on the existing mitigation and lack of problems noted downstream, the site development should
have little if any impact on downstream conditions.
Minimum Requirement #2
SWPPP Narrative
The topography of the 0.48 acres containing the proposed site improvements has slopes between 4 and
10-percent. The site soils have been identified as a Gravelly Sand.. With minimal disturbance and
standard erosion control measures such as silt fence, straw mulching and hydro -seeding, the risk of
erosion can be minimized. The limits of clearing will be restricted to the 2nd lot and driveway access.
Greater source control measures would have to be taken during winter construction such as mulching or
plastic sheeting. Good construction practices will prevent any sediment from leaving the site.
The following are BMP measures to limit adverse impact upon the off -site drainage system:
• Filter fabric fences, as required
• Limited clearing area
• Rock construction entrance pad
Graveling of driveway immediately upon reaching final sub -grade.
• Catch Basin Protection as required
• Seeding and mulching of any slopes
• Limited months of construction
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 8
THE 12 ELEMENTS OF A CONSTRUCTION SWPPP
1. Preserve Vegetation/Mark Clearing Limits: The clearing limits are indicated on the plan sheet.
Furthermore, clearing and grading will be limited to only areas that need to be disturbed for
grading/construction of the road surface to preserve as much natural vegetation as possible. Field
marking the clearing limits shall be completed prior to clearing and grubbing activities.
BMP's: Preserve Natural Vegetation (VEG)
Field Marking Clearing Limits (CL)
2. Establish Construction Access: Access to the construction site shall be limited to the rock
construction entrance. The construction entrance shall be extended to provide access to the
construction vehicle/equipment staging and employee parking areas.
BMP's: Stabilized Construction Entrance (CE)
3. Control of Flow Rates: Storm water detention: No detention during the TESC process is proposed
for the site since the increase in volume is less than 0.27-precent.
4. Installation of Sediment Controls: Sediment control will be provided through a combination of
filtration through the surround on -site vegetation, filter fence, straw bails,
BMP's: Silt Fence (FF) Straw bails (SB) (as required)
5. Soils Stabilization: Temporary and permanent soil stabilization will be provided. Temporary
stabilization will be provided through the application of straw and/or plastic sheeting to exposed,
worked earth. From October 1 until April 30, no exposed soil may remain exposed and unworked
for more than two days; after May 1, no exposed soil may remain exposed and unworked for more
than seven days.
BMP's: Straw Covering, Plastic Sheeting, Hydroseeding
5. Slope Protection: Slopes shall be protected from erosion through cover and prevention of
concentrated surface runoff flows.
BMP's: Straw Covering Plastic Sheeting,
7. Protection of Permanent Drain Inlets: Inlet protection will pe provided for all catch basins and
yard drains.
BMP's: Inlet Protection (IP) as required.
9. Stabilization of Channels and Outlets: All channel slopes shall be constructed and protected
against erosion in accordance with City of Edmonds and the 2005 SWDM Manual
BMP's: Straw Bales (As required)
9. Pollutant Control: Pollutants shall be controlled as described in the Potential Pollutants section of
this SWPPP.
10. Dewatering Control: De -watering: Interception of the water table is not expected to occur, even if
there is an increase in precipitation. However, should ground water flows be encountered, the flows
can be directed to on site native vegetation for cleanup.
BMP's: Native vegetation (As Required)
11. BMP Maintenance: All BMP's and SWPPP elements shall be inspected daily and maintained as
required.
12. Project Management: The project shall be managed in a cooperative effort by the project manager,
contractor, engineer, and the county inspector. During the construction process, if unforeseen issues
arise that cannot be resolved on site, construction activity (other than SWPPP maintenance) shall be
halted and the county inspector and the project engineer are to be contacted and informed of the
situation. The Erosion Control Lead is Richard Deccio P.E.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 9
Minimum Requirement #3
Water Pollution Source Control
The proposed project will require only minimal erosion and sedimentation control measures during
construction. Clearing limits will be set in the field and basically limited to the new lot itself. Silt fences
will be installed on the down gradient side of the site. The existing driveway will serve as the rock
construction entrance pad, required to be installed off of the main road and temporary seeding of the site
will take place upon reaching the final sub -grade level. In addition, catch basin protection will be
installed. Any disturbed areas, slopes, ditches, etc. will be seeded and mulched to prevent erosion.
Disturbed buffers will be replanted per plans.
Pollution Source Control
Once site construction is complete, some small amounts of oils and grease will be present do to the daily
traffic. In addition, small amounts of silt and dirt will be present.
Any driveway pollutants generated during the permanent operation of the site will be directed to the
existing lawn areas for pollutant and sediment removal.
The following assessment has been prepared for the site:
Slope: The slope of the 2"d lot contains gentle slopes ranging 2.0 to 10.0 percent.
Critical areas: No critical areas were noted on or adjacent to the site.
Soils: The Soil has been mapped the site as a Gravelly Sand.
Source of water for erosion: Rainfall hydrology is the only source of runoff.
Measures proposed to prevent/minimize erosion: With summertime measures such as silt fence,
hydro -mulching and the use of straw bales as required, the risk of erosion can be minimized. Greater
source control measures shall be taken during winter construction such as seeding, mulching or plastic
sheeting. Good construction practices will prevent sediment from leaving the site.
Conclusion: Potential for significant erosion and pollution impacts on or offsite is considered low for
the following reasons:
• There will be minimal disturbance of established vegetation.
• Only the Lot, which is 0.24 acres in size, will be cleared.
• Graveling of the driveways and seeding of the site will take place immediately upon site reaching
final grade.
• No significant source of water is present on the site outside rainfall.
• Erosion control BMPs will be employed and adjusted seasonally.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 10
Minimum Requirement #4
Preservation of Natural Drainage Systems and Outfalls
All runoff currently leaves the site along the west side of the property, where it discharges into the 80th
Ave W.. The proposed storm water measures will infiltrate the runoff from the proposed improvements
with any overflow continuing to discharge at the same location maintaining the site's natural discharge
location and preserve the natural drainage system and outfall
Minimum Requirement #5
On -Site Stormwater Management
As discussed above, stormwater will be managed through the use of LID methods using infiltration
trenches designed under Chapter 12, BMP 12.3.3, in Volume III of the 2005 SWMM Drainage Manual.
To the extent possible, the existing detention system addresses the required stormwater management as
required under the Drainage Manual including:
• Runoff generated from the site improvements including roofs and driveways will be controlled
through the use of on -site infiltration trenches using the infiltration design contained in the
WWHM3 program.
• The use of applicable BMPs will be employed as outlined in Volume Il, of the Drainage Manual.
BMP T5.13 "Post Construction Soil Quality and Depth"
The top soils will be stockpile on -site and reused per `Implementation Options #3 per Volume V,
Chapter 5, BMP T5.13 "Post Construction Soil Quality and Depth" which requires "Stockpile existing
top soils during grading and replace it prior to planting... " The volume required will be calculated as
part of the residential building permit application.
Minimum Requirement#6
Runoff Treatment Requirements
ACCESS DRIVEWAY AND PARKING PGIS AREA
Pollution -generating impervious surface (PGIS) is well under the 5,000 sf threshold and is therefore
exempt from water quality required for the site.
Minimum Requirement #7
Flow Control
Under Volume III, Chapter 12, "Onsite Stormwater Management BMP's" "Flow Control", the City
requires any project to utilize LID methods to address flow control.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 11
For small sites and individual lots, infiltration trenches are proposed and will designed per City of
Edmonds Development Information Bulletin #E72B LID & B110's Simplified Sizing"
Soils logs were excavated at two locations on site. The site soils were found to be Gravelly Sand using
the Soils Classification based on the Textural Triangle (Figure C-1). Therefore, the design will use the
"Sand" sizing requirements of Table C-1 "Recommended Infiltration Rates" with a long-term infiltration
rate of 2 in/hr
The infiltration trench design was based on the total proposed impervious roof area of
approximately 2,200 sf and a design infiltration rate of 2 in/hr and a trench depth of 3.0 feet
NPGIS Infiltration Systems (Table 5)
INFILTRATION TRENCH RESIGN
• Required length: 1.8% x 2,200sf/100 = 39.5 ft @ 2-feet wide.
Table 5. Bioretention and Infiltration BMP Sizing Factors.
Sizing Factor
(% of contributing
Native Soil Design
impervious area)
Category
Category
Infiltration Rate
BMP
Facility Overflow Depth
(inches/hour)
1 Sites a
2 Sites b
Sizing Equation
Bioretention
6 inch ponding depth
0.25
9.7%
9 7%
Bioretention Bottom Area (square
Cell `"
0.5
6.8%
6.8%
feet) = Impervious Area (square
feet) x Sizing Factor (%)/100
2.0
3.6%
3.9%n
12 inch pending depth
0.25
6.2%
6.2%
0.5
4.2%,
4.2%
2.0
2.2%
2.3%
Infiltration
1.5 foot depth
0.25
9.1 %
9.1 %
Infiltration Trench Length (feet) _
Trench e
0.5
6.2%
6.2%r
Impervious Area (square feet) x
Sizing Factor 00
2.0
2.3%
2.9%
3 foot depth
0.25
5.4%
5.4%r
0.5
4.0%
4.0%
2.0
1.8%n
2.0%
Gravelless
NA
0.25
3.7%
3.7%
Gravelless Chamber Length (feet)
Chamber'
= Impervious Area (square feet) x
0.5
2 .7%
2 %
.7'/n
Sizing Factor (%)/100
2.0
1.3%
1.4%
Drywell
4 foot depth
0.5
6.2%
6.2%o
Diywell Area (square feet) _
2.0
3.0%
3.1 %
Impervious Area (square feet) x
Sizing Factor (%)/100
6 foot depth
0.5
4.7%
4.8%
2.0
2.4%
1 2.5%
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 12
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Figure 5: Soils logs
CONVEYANCE SYSTEM ANALYSIS AND DESIGN
There is no proposed piping and conveyance system for the interception of the drainage since street
improvements are not required. Therefore, no conveyance analysis is required.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 13
Minimum Requirement #8
Wetlands Protection
The are no wetlands on or adjacent to the site.
Minimum Requirement#9
Basin/Watershed Planning
The subject property situated within the Puget Sound Drainage Basin. It is not known if a basin plan for
this area exists.
Minimum Requirement #10
Operations and Maintenance
Stormwater System Description
The stormwater system for the lot is fairly basic and contains the following elements:
• Gravel filled infiltration trenches and yard drains
The stormwater runoff from the access driveway and roof is intercepted where it is directed over to the
infiltration trenches for release.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 14
No. 2 — Wiltration Facilities
Maintenance
Detect
Conditions When Maintenance is Needed
Results Expected When
Component
Ivlainlenance is
Performed
General
Trash & Debris
Function of facility is impaired by or likely to
Trash and debris is
be impaired by trash and debris.
removed.
Vegetation
function of facility is impaired by vegetation.
Vegetation is removed or
managed to restore proper
function offacility.
Use ofherbicides shall be in
accordance with an
Integrated Pest
Management Plan,
Contaminants and
Any evidence ofoil, gasoline, contaminants or
Contaminants or pollutants
Pollution
other pollutants
are removed
Note: Coordinate removal/cleanup with local
and/or state water quality response agency.
Erosion
Eroded damage over 2 inches deep where cause
Slopes are stabilized using
of dnmagc is still present or where there is
appropriate erosion control
potential for conlinued erosion.
ntensure(s); e.g., rock
reinforcement, planting of
grass, compaction.
Storage Area
sediment
Water pending io infiltration pond after rainfall
Sediment is removed and/or
ceases and appropriate time allowed for
facility is cleaned so that
infiltration.
infiltration system works
(A percolation test pit or test of facility
according to design.
indicates facility is only working at 90% of its
designed capabilities. If two inches or more
sediment is present, remove).
Filler Hags (if
Sediment and Debris
Sediment and debt is rill bag more Than 1 /2 full
Filler bag is replaced or
applicable)
system is redesigned.
Rock filters
Sediment and Debris
By visual inspection, little or no water (lows
Gravel in rock filter is
through filter during heavy min storms.
replaced.
Side Slopes of Pond
Erosion
See "Deienion Ponds" (No. 1).
See "Detention Ponds" (No.
1).
Het ins
Settling
Any part of a berm which has settled at least 4
Berm is repaired and
inches lower than the design elevation.
restored to the design
If settlement is apparent, measure berm to
elevation.
determine amount orseulement.
Settling can be an indication of more severe
problems with the berm or outlet works. Note:
A licensed civil engineer may be needed to
determine the cause of the settlement.
Erosion
Any erosion observed on a compacled structural
Slopes should be stabilized
berm embankment.
using appropriate erosion
Note: A licensed civil engineer may be needed
control measure(s); e.g.,
rock reinforcement, planting
to inspect. evaluate and recommend a repair
of grass, compaction.
plan.
Drainage Manual Volume V - Runoff Treatment BMPs
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 15
No. 2 — Infiltration Facilities
Maintenance
Defect
Conditions When Maintenance Is Needed
Results Expected When
Component
Maintenance 1s
Performed
Piping
Discernable water flow through acompacted
Piping eliminated. Erosion
structural berm. Ongoing erosion with potential
potential resolved.
for erosion to continue.
Tree growth on a compacted structural berm
over 4 feet in height may lend to piping through
the berm which could lead to failure of the
berm.
Evidence of rodent holes in berm, and/or water
piping through berm via rodent holes
Note: A geolechnical engineer may be needed
to inspect and evaluate condition and
recommend repair of condition.
Emergency
Tree Growth
Tree growth on emergency spillways creates
Trees should be removed.
Overflow Spillway
blockage problems and may "use failure of the
If root system is small (base
berm due to uncontrolled overtopping.
less than 4 inches) the root
system may be [ell in place.
Otherwise the roots should
be removed and the berm
restored.
Note: A licensed civil
engineer may be needed to
detemtine proper
berm/spillway restoration.
Rock Armoring
Rock layer on subgrade is less than 1.0 feet
Rock and pad depth are
deep and/or subgrade is exposed
restored to a minimum
depth of 1.0 feet.
Erosion
Eroded damage over 2 inches deep where cause
Slopes are stabilized using
of damage is still present or where there is
appropriate erosion control
potential for continued erosion.
measure(s): e.g., rock
reinlbrcernenl, planting of
grass, compaction.
Pre -settling Ponds
Facility or surnp
he settling area or sump contains
Sediment/debris is removed.
and Vaults
filled with Sediment
sediment/debris up to a depth or either 6 inches
and/or debris
or the sedimentation design depth.
County Drainage Manual Volume V - Runoff Treatment BMPs
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 16
Access Roads/Easement
Maintenance Defect Conditions When Maintenance is Results Expected When
Component Needed Maintenance is Performed
General Trash and Debris Trash and debris exceeds 1 cubic foot per Trash and debris cleared from
1,000 square feet, i.e., trash and debris site.
would fill up one standard size garbage
can.
Blocked Roadway Debris, which could damage vehicle tires Roadway free of debris which
(glass or metal). could damage tires.
Any obstructions which reduce clearance Roadway overhead clear to 14
above road surface to less than 14 feet. feet high.
Any obstructions- restricting the access to a Obstruction removed to allow at
10- to 12-foot width for a distance of more least a 12-foot access.
than 12 feet or any point restricting access
to less than a 10-foot width.
Road Surface Settlement, When any surface defect exceeds 6 inches Road surface uniformly smooth
Potholes, Mush in depth and 6 square feet in area. In with no evidence of settlement,
Spots, Ruts general, any surface defect which hinders potholes, mush spots, or ruts.
or prevents maintenance access.
Vegetation in Road Weeds growing in the road surface that are Road surface free of weeds taller
Surface more than 6 inches tall and less than 6 than 2 inches.
inches apart within a 400-square foot area,
Shoulders and Erosion Damage
Ditches
Weeds and Brush
Keller Short Plat
Revised: July 22, 2014
Erosion within 1 foot of the roadway more Shoulder free of erosion and
than 8 inches wide and 6 inches deep. matching the surrounding road.
Weeds and brush exceed 18 inches in Weeds and brush cut to 2 inches
height or hinder maintenance access. in height or cleared in such a way
as to allow maintenance access.
Drainage Report
Page 17
Conveyance Systems (Pipes & Ditches)
Maintenance Defect Conditions When Maintenance is Results Expected When
Component Needed Maintenance is Performed
Pipes Sediment and
Accumulated sediment that exceeds 20%
Pipe cleaned of all sediment
Debris
of the diameter of the pipe.
and debris.
Vegetation
Vegetation that reduces free movement of
All vegetation removed so
water through pipes.
water flows freely through
pipes.
Damaged
Protective coating is damaged; rust is
Pipe repaired or replaced.
causing more than 50% deterioration to
any part of pipe.
Any dent that decreases the cross-section
Pipe repaired or replaced.
area of pipe by more than 20%.
Open Ditches Trash and Debris
Trash and debris exceeds 1 cubic foot per
Trash and debris cleared
1,000 square feet of ditch and slopes.
from ditches.
Sediment
Accumulated sediment that exceeds 20%
Ditch cleaned/flushed of all
of the design depth.
sediment and debris so that
matches design.
Vegetation
Vegetation that reduces free movement of
Water flows freely through
water through ditches.
ditches.
Side Slopes Erosion Eroded damage over 2 inches deep where Slopes should be stabilized
cause of damage is still present or where by using appropriate erosion
there is potential for continued erosion. control measure(s): e.g., rock
reinforcement, planting of
grass, compaction.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 18
Grounds (Landscaping)
Maintenance Defect
Component
Conditions When Maintenance is
Needed
Results Expected When
Maintenance is Performed
General Weeds (Non-
Weeds growing in more than 20% of the
Weeds present in less than
poisonous)
landscaped area (trees and shrubs only).
5% of the landscaped area.
Safety Hazard
Any presence of poison ivy or other
No poisonous vegetation
poisonous vegetation.
present in a landscaped area.
Trash or Litter
Paper, can, bottles, totaling more than 1
Area clear of litter.
cubic foot within a landscaped area (trees
and shrubs only) of 1,000 square feet.
Trees and Damage
Limbs or parts of trees or shrubs that are
Trees and shrubs with less
Shrubs
split or broken which affect more than
than 5% of the total foliage
25% of the total foliage of the tree or
with split or broken limbs.
shrub.
Trees or shrubs that have been blown
Trees or shrub in place free
down or knocked over.
of injury.
Trees or shrubs which are not adequately
Tree or shrub in place and
supported or are leaning over, causing
adequately supported;
exposure of the roots.
remove any dead or diseased
trees.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 19
CATCH BASINS
Maintenance
Conditions When Maintenance is
Results Expected When
Component Defect
Needed
Maintenance is Performed
General Trash and Debris
Trash or debris of more than 2 cubic
No trash or debris located
(Includes Sediment)
foot which is located immediately in
immediately in front of catch basin
front of the catch basin opening or is
blocking capacity of basin by more
opening.
than 10%.
Trash or debris (in the basin) that
No trash or debris in the catch basin,
exceeds 1/3 the depth from the bottom
of basin to invert of the lowest pipe
into or out of the basin.
Trash or debris in any inlet or outlet
Inlet and outlet pipes free of trash or
pipe blocking more than 1/3 of its
debris.
height.
Dead animals or vegetation that could
No dead animals or vegetation
generate odors that would cause
present within the catch basin.
complaints or dangerous gases (e.g.
methane)
Deposits of garbage exceeding 1 cubic
No condition present which would
foot in volume.
attract or support the breeding of
insects or rodents.
Structural Damage to
Corner of frame extends more than :
Frame is even with curb.
Frame and/or Top Slab
inch past curb face into the street (if
applicable)
Top slab has holes larger than 2 square
Top slab is free of holes and cracks.
inches or cracks wider than 3 inch
(intent is to make sure all material is
running into the basin).
Frame not sitting flush on top slab, i.e.
Frame is sitting flush on top slab.
separation of more than : inch of the
frame from the top slab.
Cracks in Basin
Cracks wider than 2 inch and longer
Basin replaced or repaired to design
Walls/Bottom
than 3 feet, any evidence of soil
standards.
particles entering catch basin through
cracks, or maintenance person judges
that structure is unsound.
Cracks wider than 2 inch and longer
No cracks more than 3 inch wide at
than 1 foot at the joint of any
the joint of inlet/outlet pipe.
inlet/outlet pipe or any evidence of soil
particles entering catch basin through
cracks.
Settlement/Misalignmen
Basin has settled more than 1 inch or
Basin replaced or repaired to design
t
has rotated more than 2 inches out of
standards.
alignment.
Fire Hazard
Presence of chemicals such as natural
No flammable chemicals present.
gas, oil, and gasoline.
Vegetation
Vegetation growing across and
No vegetation blocking opening to
blocking more than 10% of the basin
basin.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 20
CATCH BASINS
Maintenance
Conditions When Maintenance is
Results Expected When
Component
Defect
Needed
Maintenance is Performed
opening.
Vegetation growing in inlet/outlet pipe
No vegetation or root growth
joints that is more than six inches tall
present.
and less than six inches apart.
Pollution
Non-flammable chemicals of more
No pollution present other than
than 2 cubic foot per three feet of
surface film.
basin length.
Catch Basin Cover
Cover Not In Place
Cover is missing or only partially in
Catch basin cover is closed.
place. Any open catch basin requires
maintenance.
Locking Mechanism
Mechanism cannot be opened by one
Mechanism opens with proper tools.
Not Working
maintenance person with proper tools.
Bolts into frame have less than 2 inch
of thread.
Cover Difficult to
One maintenance person cannot
Cover can be removed by one
Remove
remove lid after applying 80 lbs. of
maintenance person.
lift; intent is keep cover from sealing
off access to maintenance.
Ladder
Ladder Rungs Unsafe
Ladder is unsafe due to missing rungs,
Ladder meets design standards and
misalignment, rust, cracks, or sharp
allows maintenance person safe
edges.
access.
Metal Grates
Grate with opening wider than 7/8
Grate openings meet design
(if applicable)
inch.
standards.
Trash and Debris
Trash and debris that is blocking more
Grate free of trash and debris.
than 20% of grate surface.
Damaged or Missing
Grate missing or broken member(s) of
Grate is in place and meets design
the grate.
standards.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 21
Maintenance
Component Defect
Conditions When Maintenance is Needed
Results Expected When
Maintenance is Performed
General Trash &
Any trash and debris which exceed 1 cubic
Trash and debris cleared from
Debris
foot per 1000 square feet (this is about equal to
site.
the amount of trash it would take to fill up one
standard size office garbage can). In general,
there should be no visual evidence of dumping.
Poisonous
Any poisonous vegetation which may
No danger of poisonous
Vegetation
constitute a hazard to County personnel of the
vegetation where County
public. Examples of poisonous vegetation
personnel or the public might
include: tansy ragwort, poison oak, stinging
normally be. (Coordination
nettles, devils club.
with Seattle/King County
Health Department).
Pollution
Oil, gasoline, or other contaminants of one
No contaminants present other
gallon or more or any amount found that
than a surface film.
could: 1) cause damage to plant, animal, or
(Coordination with
marine life; 2) constitute a fire hazard; or 3) be
Seattle/King County Health
flushed downstream during rain storms.
Department).
Unmowed If facility is located in private residential area, When mowing is needed,
Grass/
mowing is needed when grass exceeds 18
grass/ground cover should be
Ground Cover
inches in height. In other areas, the general
mowed to 2 inches in height.
policy is to make the pond site match adjacent
ground cover and terrain as long as there is no
interference with the function of the facility.
Rodent Holes
Any evidence of rodent holes if facility is
Rodents destroyed and dam or
acting as a dam of berm, or any evidence of
berm repaired. (Coordination
water piping through dam or berm via rodent
with Seattle/King County
holes.
Health Department),
Insects
When insects such as wasps and hornets
Insects destroyed or removed
interfere with maintenance activities.
from site.
Tree Growth
Tree growth does not allow maintenance
Trees do not hinder
access or interferes with maintenance activity.
maintenance activities.
(i.e., slope mowing, silt removal, vactoring or
Selectively cultivate trees
equipment movements). If trees are not
such as alders for firewood.
interfering with access, leave trees alone.
Side Slopes of Pond Erosion
Eroded damage over 2 inches deep where
Slopes should be stabilized by
cause of damage is still present or where there
using appropriate erosion
is potential for continued erosion.
control measure(s): e.g. rock
reinforcement, planting of
grass, compaction.
Storage Area Sediment
Accumulated sediment that exceeds 10% of
Sediment cleaned out to
the designed pond depth.
designed pond shape and
depth; pond reseeded if
necessary to control erosion.
Pond Dikes Settlements
Any part of dike which has settled 4 inches
Dike should be built back to
lower than the design elevation.
the design elevation.
Emergency Rock Missing
Only one layer of rock exists above native soil
Replace rocks to design
Overflow/Spill-way
in area five square feet or larger, or any
standards.
exposure of native soil.
Keller Short Plat Drainage Report
Revised: July 22, 2014 Page 22