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PRELIMINARY STO~ATER SITE PLAN
., FOR
MOUNTAIN SHADOW
r JANUARY 7, 2005
A
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Engineering
f
PRELIMINARY STORMWATER SITE PLAir
FOR
MOUNTAIN SHADOW
Prepared for:
Mr. Bob Benum
P.O. Box 73130
Puyallup, Washington 98373
(253) 845-5555
Project
Prepared by:
Apex Engineering PLLC
2601 South 35th, Suite 200
Tacoma, Washington 98409
(253) 473-4494
File #29177/0
January 7, 2005
P.,~~x
TABLE OF CONTENTS
Section I -Project Overview ............................................................................................
Section II -Existing Condition Summary .........................................................................
Section III -Off-Site Analysis Report ..................................................................................
Section IV -Permanent Stormwater Control Flow ...............................................................
Section V -Special Reports and Studies ........................................................................
Section VI -Other Permits ..............................................................................................
Section VII -Maintenance and Operations Manual .........................................................
Section VIII -Bond Quantities, Retention/Detention Summary Sheet
And Declaration of Covenant ........................................................................
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SECTION I -PROJECT OVERVIEW
This preliminary report format is to follow the Stormwater Site Plan Requirements, per
Page 3-7 of the Stormwater Management Manual for the Puget Sound Basin, Washington
State Department of Ecology (DOE).
Cite T nratinn
• Portions of the Southeast quarter of Section 18, Township 17 North, Range 2 East,
Willamette Meridian, City of Yelm.
• Triangular-shaped parcel between Wilkenson Road S.E. to the east, the Centralia
power canal to the north and Canal Rd. S.E. to the southwest.
See Figure 1 for Vicinity Map.
Site Area = 20+ acres.
The proposed project is to improve the site into 80 lots for single-family dwellings.
Included are roadways and utilities to serve the individual lots. Lot sizes average per
preliminary plat. See the preliminary plat map for site layout.
Our understanding is that the storm drainage system is to conform to the requirements of
the Stormwater Management Manual for Western Washington, prepared by the
Washington State Department of Ecology (DOE). This preliminary report is to provide
preliminary sizes of runoff control and water quality facilities, and show that the area
available is adequate.
Ppe~x
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Engineering;
2601 South 35th, Suite 200
Tacoma,Washington 98409
(253) 473-4494
Fax: (253) 473-0599
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SECTION II -EXISTING CONDITION SUMMARY
Per Map 0355 C, FIRM, the site is located within Zone C, minimal flooding area.
Per Soils Survey of the Thurston County Area, the site situates within the Spanaway
soils series of various slopes. See Figure 3 for soils mapping and Figure 4 for soils table.
Per DOE Manual Isopluvials the precipitation is as follows:
P2-year/24-hour = 3 inches
P 10-year/24-hour = 4 inches
P 100-year/24-hour = 6 inches
P 100-year/7-day = 12 inches
P~,('.~X
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SECTION III -OFF-SITE ANALYSIS REPORT
Per Optional Guidance #2, Section 2.6.2 D.O.E., projects that discharge stormwater off-
site are to provide an off-site analysis. The intent is to infiltrate stormwater runoff on-
site. Therefore, an off-site analysis is not required. However, an analysis can be
provided at final design if required by the City of Yelm.
P,P~„x
SECTION IV -PERMANENT STORMWATER CONTROL PLAN
This section will be divided into the following:
• Part A -Existing Conditions
• Part B -Developed Conditions
• Part C -Infiltration Analysis
• Part D -Water Quality
This analysis is based upon the following:
• Our understanding is the City of Yelm allows the use of the SCS/SBUH
methodology.
• SBUH Methodology for the 100-year/24-hour and 100-year/7-day storm events,
using the Thurston County Hyetograph.
• Pervious Area CN = 80, for lawns under hydrologic soils Group B. The higher
value was preliminarily used assuming topsoil will be placed over the lots.
• Time of concentration was assumed to be 5 min.
• StormShed software.
• 20 in./hr. infiltration rate, per previous experience at adjacent site.
Part A -Existing Conditions
The existing site is grasses and shrubs. Land slopes from 0.5% to 5%±, generally in the
northern direction. Because infiltration is proposed, existing condition calculations are
unnecessary.
Part B -Developed Conditions
For the developed site the following was assumed:
• Individual on-site roof drain infiltration systems would be used for roof runoff
disposal. The area was excluded from the infiltration analysis.
• Right-of--way to be 22 feet paved, 3 feet curb and gutter, 5 feet sidewalk, and a 9'
parking lane; total width = 39 feet of impervious area. The remaining areas is lawn.
This area will enter the stormwater facility. .
• 25-foot long x 20-foot driveways; 500 ft2, will enter the stormwater facility.
• 1/2 Street off-site road improvements.
Total impervious area = 5.6 Ac. t
Total pervious area = 9.8 Ac. f
• The remaining lot was assumed to be lawn. This area would enter the stormwater
facility.
P~,P~x
The outlets should be protected from erosion. As a minimum rip-rapping is required.
Stilling basins or gabion outfalls protection may be required.
Poe~x
Part C -Infiltration Analysis
See Figure 4 for preliminary pond plan.
General Methodology
The developed conditions basins were routed through preliminary infiltration pond using
the StormShed Software and the level pool routing technique. The preliminary pond is
larger than required to anticipate access roads and grading setbacks.
Assumptions
No bypass areas were included. Final designs are yet to be prepared. Bypass areas
may require separate stormwater facilities.
• Curve Numbers were adjusted for the 7-day flow calculation.
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Engineeringa
2601 South 35th, Suite 200
Tacoma, Washington 98409
(253) 413-4494
Fax: (253) 413-0599
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ADJUSTED CN VALUES FOR 7-day STORMS
CN 7-day = 0.1549CN+.8451((CN"2.365/631.8)+15)
CN CN 7day
80 67.4 '
81 68.9
82 70.3 - - -
83 71.8 _ _ __
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84 73.2
85 74.8
_,
86 76.3
- - --
87 77.8
88 79.4
89 81.0
90 82.6
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91 84.2 I
92 85.9 _ _ -
- .- _: _ --
93 87.6
94 89.3
- - -__ --
95 91.0
___ __
96 92.8
__ _ - ---
97 94.5
98 96.3
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FILE: N:\JOEB\CN7DAY
DV1-24hr Event Summary:
BasinlD Peak O Peak T Peak Vol Area
------- (cfs) (hrs) (ac-ft) ac
DV1-24hr 24.22 8.00 5.7767 15.40
Drainage Area: DV1-24hr
Hyd Method: SBUH Hyd
Peak Factor: 484.00
Storm Dur 24.00 hrs
Area
Pervious 9.8000 ac
Impervious 5.6000 ac
Total 15.4000 ac
Supporting Data:
Pervious CN Data:
PERVIOUS AREA
Impervious CN Data:
IMPERVIOUS AREAS
Pervious TC Data:
Flow type: Description:
Fixed ASSUME
Impervious TC Data:
Flow type: Description:
Fixed ASSUME
Method Raintype Event
/Loss
SBUH/SCS THUR100Y 100 yr
Loss Method: SCS CN Number
SCS Abs: 0.20
CN TC
80.00 0.08 hrs
98.00 0.08 hrs
80.00 9.8000 ac
98.00 5.6000 ac
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
DV1-7day Event Summary:
BasinlD Peak Q Peak T Peak Vol Area
------- (cfs) (hrs) (ac-ft) ac
DV1-7day 12.56 77.00 11.7088 15.40
Drainage Area: DV1-7day
Hyd Method: SBUH Hyd
Peak Factor: 484.00
Storm Dur 168.00 hrs
Area
Pervious 9.8000 ac
Impervious 5.6000 ac
Total 15.4000 ac
Supporting Data:
Pervious CN Data:
PERVIOUS
Impervious CN Data:
IMPERVIOUS AREAS
Pervious TC Data:
Flow type: Description:
Fixed ASSUME
Impervious TC Data:
Flow type: Description:
Fixed ASSUME
Method Raintype Event
/Loss
SBUH/SCS Thur7day 7 DAY
Loss Method: SCS CN Number
SCS Abs: 0.20
CN TC
68.00 0.08 hrs
96.00 0.08 hrs
68.00 9.8000 ac
96.00 5.6000 ac
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
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2601 South 35th, Suite 200
Tacoma, Washington 98409
(253) 473-4494
Fax: (253) 413-0599
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RLPCOMPUTE [RLP INFIL] SUMMARY
100 yr Match Q: 5.1544 cfs Peak Out Q: 5.0000 cfs -Peak Stg: 18.37 ft -Active Vol: 0.77 acft
7 DAY Match O: 4.7658 cfs Peak Out O: 5.0000 cfs -Peak Stg: 18.86 ft -Active Vol: 0.93 acft
Summary Report of RLPooI Data
Project Precips
[WO] 1.90 in
[100 yr] 6.00 in
[7 DAY] 12.00 in
HYDLIST SUMMARY
[100yr/24hr] [100yr/7day]
LSTEND
HydID Peak O Peak T Peak Vol Cont Area
------- (cfs) (hrs) (ac-ft) (ac)
100yr/24hr 5.00 7.67 5.7765 15.4000
100yr/7day 5.00 72.00 11.7265 15.4000
Node ID: INFIL POND
Desc: PRELIMINARY INFILTRATION POND
Start EI: 16.0000 ft Max EI: 20.0000 ft
Contrib Basin: Contrib Hyd:
Stage Area Volume Volume
16.00 11000.00 0.00 cf 0.0000 acft
20.00 17250.00 56500.00 cf 1.2971 acft
Control Structure ID: INFIL -Stage Discharge rating curve
Descrip: PRELIMINARY INFILTRATION POND
Start EI Max EI Increment
16.0000 ft 20.0000 ft 0.10
Stage Discharge
16.0000 ft 0.0000 cfs
16.1000 ft 5.0000 cfs
20.0000 ft 5.0000 cfs
Part D Water Quality
Water quality could be provided by use of a wet pond.
The preliminary size was determined using the volume calculated for 6-month/24-hour
storm event, and assuming a maximum depth of 6 feet.
The following was assumed:
• SCS/SBUH method per DOE
• 2-year precipitation value = 2.8". 6-month percip. Value = (2.8" * 0.64) _
1.8"
• Pervious Area CN = 80, for lawns under hydrologic soils Group B. The
Higer value was preliminarily used assuming topsoil will be placed over
the lots.
• Time of concentration was assumed to be 5 min.
• StormShed software
WQ required volume = 51,932 ft3.
From the stage/storage table 68,400 ft3 can be provided. Therefore, the preliminary pond
would be adequate. Final volumes will have to account for access roads and dividing
berms, if any.
Other BMP's maybe used and will be determined at final design.
p.,ex
DV1-24hr Water quality Event Summary:
BasinlD Peak Q Peak T Peak Vol Area
------- (cfs) (hrs) (ac-ft) ac
DV1-24hr 4.16 8.00 1.1922 15.40
Drainage Area: DV1-24hr '~ ~
% ~ "~ -
Hyd Method: SBUH Hyd Loss Method
Peak Factor: 484.00 SCS Abs:
Method Raintype Event
/Loss
SBUH/SCS THUR100Y WQ
SCS CN Number
0.20
Storm Dur 24.00 hrs
Area CN
Pervious 9.8000 ac 80.00
Impervious 5.6000 ac 98.00
Total 15.4000 ac
Supporting Data:
Pervious CN Data:
PERVIOUS AREA 80.00
Impervious CN Data:
IMPERVIOUS AREAS 98.00
Pervious TC Data:
Flow type: Description:
Fixed ASSUME
Impervious TC Data:
Flow type: Description:
Fixed ASSUME
TC
0.08 hrs
0.08 hrs
9.8000 ac
5.6000 ac
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
Length: Slope: Coeff: Travel Time
0.00 ft 0.00% 5.0000 5.00 min
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SECTION V -SPECIAL REPORTS AND STUDIES
At this time, no geotechnical analysis was prepared/obtained regarding the infiltration
capability of the soils. A geotechnical report/analysis can be prepared at final design.
Ppe~x
SECTION VI -OTHER PERMITS
At this time, the following permits are anticipated:
1. Right-of--Way from the City of Yelm.
2. Shoreline Management -substantial development.
NPDES permit from Washington State Dept. of Ecology.
pfl9ex
SECTION VII -MAINTENANCE AND OPERATIONS MANUAL
For informational purposes, the following items are anticipated. These were obtained
from the DOE Manual.
P,e~x
4.6 Maintenance Standards for Drainage Facilities
The facility-specific maintenance standards contained in this section are
intended to be conditions for determining if maintenance actions are
required as identified through inspection. They are not intended to be
measures of the facility's required condition at~all times between
inspections. In other words, ezceedence of these conditions at any time
between inspections and. or maintenance does not automatically constitute
a violation of these standards. However, based upon inspection
observations. the inspection and maintenance schedules shall be adjusted
to minimize the length of time that a facility is in a condition that requires
a maintenance action.
No. 1 - _ _ Ponds
Maintenance Defect Conditions When Maintenance Is Results Expected When
Component Needed Maintenance Is Performed
General Trash & Debris Any trash and debris which exceed 5 Trash and debris cleared from site.
cubic feet per 1,000 square feet (this
is about equal to the amount of trash
it would take to fill up one standard
size garbage can). In general, there
should be no visual evidence of
dumping.
If less than threshold all trash and
debris will be removed as part of next
scheduled maintenance.
Poisonous Any poisonous or nuisance No danger of poisonous vegetation
Vegetation and vegetation which may constitute a where maintenance personnel or the
noxious weeds hazard to maintenance personnel or public might normally be. (Coordinate
the public. with local health department)
Any evidence of noxious weeds as Complete eradication of noxious weeds
defined by State or local regulations. may not be possible. Compliance with
(Apply requirements of adopted IPN1 State or local eradication policies
policies for the use of herbicides). required
Contaminants Any evidence of oil, gasoline. No contaminants or pollutants present.
and Pollution contaminants or other pollutants
(Coordinate removal/cleanup with
local water quality response agency).
Rodent Holes Any evidence of rodent holes if Rodents destroyed and dam or berm
facility is acting as a dam or berm, or repaired. (Coordinate with local health
any evidence of water piping through department; coordinate with Ecology
dam or berm via rodent holes. Dam Safety Office if pond exceeds 10
acre-feet.)
4-:~u Volume V -Runoff Treatment BMPs August 2001
No. 1- ._ _ Ponds
Maintenance Defect Conditions When Maintenance Is Results Expected When
Component Needed Maintenance Is Performed
Beaver Dams Dam results in change or function of Facility is returned to design function.
the facility.
(Coordinate trapping of beavers and
removal of dams with appropriate
permitting agencies)
Insects When insects such as wasps and Insects destroyed or removed from site.
hornets interfere with maintenance
activities. Apply insecticides in compliance with
adopted IPM policies
Tree Growth Tree growth does not allow Trees do not hinder maintenance
and Hazard maintenance access or interferes activities. Harvested trees should be
Trees with maintenance activity (i.e., slope recycled into mulch or other beneficial
mowing, silt removal, vactoring, or uses (e.g.. alders for firewood).
equipment movements). If trees are
not interfering with access or Remove hazard Trees
maintenance, do not remove
If dead, diseased, or dying trees are
identified
(Use a certified Arborist to determine
health of tree or removal
requirements)
Side Slopes Erosion Eroded damage over 2 inches deep Slopes should be stabilized using
of Pond where cause of damage is still appropriate erosion control measure(s);
present or where there is potential for e.g., rock reinforcement, planting of
continued erosion. grass, compaction.
Any erosion observed on a If erosion is occurring on compacted
compacted berm embankment. berms a licensed civil engineer should
be consulted to resolve source of
erosion.
Storage Area Sediment Accumulated sediment that exceeds Sediment cleaned out to designed pond
10% of the designed pond depth shape and depth; pond reseeded if
unless otherwise specified or affects necessary to control erosion.
inletting or outletting condition of the
facility.
Liner (If Liner is visible and has more than Liner repaired or replaced. Liner is fully
Applicable) three 1/flinch holes in it. covered.
Augusf 2001 Volume V -Runoff Treatment BMPs 4-31
No. 1 - Ponds
Maintenance Defect Conditions When Maintenance Is Results Expected When
Component Needed Maintenance Is Performed
Pond Berms Settlements Any part of berm ~+vhich has settled 4 Dike is built back to the design
(Dikes) inches lower than the design elevation.
elevation.
If settlement is apparent, measure
berm to determine amount of
settlement.
Settling can be an indication of more
severe problems with the berm or
outlet works. A licensed civil
engineer should be consulted to
determine the source of the
settlement.
Piping Discernable water flow through pond Piping eliminated. Erosion potential
berm. Ongoing erosion with potential resolved.
for erosion to continue.
(Recommend a Goethechnical
engineer be called in to inspect and
evaluate condition and recommend
repair of condition.
Emergency Tree Growth Tree growth on emergency spillways Trees should be removed. If root
Overflow/ creates blockage problems and may system is small (base less than 4
Spillway and cause failure of the berm due to inches) the root system may be left in
Berms over 4 uncontrolled overtopping. place. Otherwise the roots should be
feet in height.
Tree growth on berms over 4 feet in removed and the berm restored. A
licensed civil engineer should be
height may lead to piping through the consulted for proper berm/spillway
berm which could lead to failure of restoration.
the berm.
Piping Discernable water flow through pond Piping eliminated. Erosion potential
berm. Ongoing erosion with potential resolved.
for erosion to continue.
(Recommend a Goethechnical
engineer be called in to inspect and
evaluate condition and recommend
repair of condition.
Emergency
Overflow/ Emergency Only one layer of rock exists above Rocks and pad depth are restored to
S
illwa Overflow/ native soil in area five square feet or design standards.
p
y Spillway larger, or any exposure of native soil
at the top of out flow path of spillway.
(Rip-rap on inside slopes need not be
replaced. )
Erosion See "Side Slopes of Pond"
4-32
Volume V -Runoff Treatment BMPs August 2001
No. 2 -Infiltration
Maintenance Defect Conditions When Maintenance Is Results Expected When
Component Needed Maintenance Is
PPrf~rmc+~i
General Trash & Debris See "Detention Ponds" (No. 1). See "Detention Ponds"
(No. 1).
Poisonous/Noxious See "Detention Ponds" (No. 1). See "Detention Ponds"
Vegetation (No. 1).
Contaminants and See "Detention Ponds" (No. 1). See "Detention Ponds"
Pollution (No 1)
Rodent Holes See "Detention Ponds" (No. 1). See "Detention Ponds"
(No. 1)
Storage Area Sediment Water ponding in infiltration pond after Sediment is removed
rainfall ceases and appropriate time and/or facility is cleaned
allowed for infiltration. so that infiltration system
(A percolation test pit or test of facility works according to
design.
indicates facility is only working at 90% of
its designed capabilities. If two inches or
more sediment is present, remove).
Filter Bags (if Filled with Sediment and debris fill bag more than 1/2 Filter bag is replaced or
applicable) Sediment and full. system is redesigned.
Debris
Rock Filters Sediment and By visual inspection, little or no water flows Gravel in rock filter is
Debris through filter during heavy rain storms. replaced.
Side Slopes of Erosion See "Detention Ponds" (No. 1). See "Detention Ponds"
Pond
(No. 1).
Emergency Tree Growth See "Detention Ponds" (No. 1). See "Detention Ponds"
Overflow Spillway (No 1)
and Berms over 4
feet in height.
Piping See "Detention Ponds" (No. 1). See "Detention Ponds"
(No. 1).
Emergency Rock Missing See "Detention Ponds" (No. 1). See "Detention Ponds"
Overflow Spillway (No. 1).
Erosion See "Detention Ponds" (No. 1). See "Detention Ponds"
(No. 1).
Pre-settling Facility or sump 6" or designed sediment trap depth of Sediment is removed
Ponds and Vaults
filled with Sediment
sediment. .
andlor debris
August ZUU1
Volume V -Runoff Treatment BMPs
4-33
..:-
No. 4 -Control Structure/Flow Restrictor
Maintenance Defect Condition When Maintenance is Needed Results Expected
Component When Maintenance
is Performed
General Trash and Debris Material exceeds 25% of sump depth or 1 Control structure
(Includes Sediment) foot below orifice plate. orifice is not blocked.
All trash and debris
removed.
Structural Damage Structure is not securely attached to Structure securely
manhole wall. attached to wall and
outlet pipe.
Structure is not in upright position (allow up Structure in correct
to 10% from plumb). position.
Connections to outlet pipe are not watertight Connections to outlet
and show signs of rust. pipe are water tight;
structure repaired or
replaced and works
as designed.
Any holes--other than designed holes--in the Structure has no
structure. holes other than
designed holes.
Cleanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight
and works as
designed.
Gate cannot be moved up and down by one Gate moves up and
maintenance person. down easily and is
watertight.
Chain/rod leading to gate is missing or Chain is in place and
damaged. works as designed.
Gate is rusted over 50% of its surface area. Gate is repaired or
replaced to meet
design standards.
Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and
missing, out of place, or bent orifice plate. works as designed.
Obstructions Any trash, debris, sediment, or vegetation Plate is free of all
blocking the plate. obstructions and
works as designed.
OverFlow Pipe Obstructions Any trash or debris blocking (or having the Pipe is free of all
potential of blocking) the overflow pipe. obstructions and
works as designed.
Manhole See "Closed See "Closed Detention Systems" (No. 3). See "Closed
Detention Systems" Detention Systems"
(No. 3). (No. 3).
Catch Basin See "Catch Basins" See "Catch Basins" (No. 5). See "Catch Basins"
(No. 5). (No. 5).
August 2009 Volume V -Runoff Treatment BMPs 4-35
No. 5 -Catch Basins
Maintenance Defect Conditions Whe Maintenance is Needed Results Expected When
Component Maintenance is
performed
General Trash & Trash or debris •: ch is located immediately No Trash or debris located
Debris in front of the ca' basin opening or is immediately in front of
blocking inlettinc 3pacity of the basin by
~ catch basin or on grate
more than 10% opening.
Trash or debris the basin) that exceeds 60 No trash or debris in the
percent of the s~ p depth as measured from catch basin.
the bottom of ba ~ to invert of the lowest
pipe into or out c ne basin. but in no case
less than a minir m of six inches clearance
from the debris : 'ace to the invert of the
lowest pipe.
4-36
Trash or debris a any inlet or outlet pipe Inlet and outlet pipes free
blocking more th : ~ 1/3 of its height. of trash or debris.
Dead animals or egetation that could No dead animals or
generate odors `~ -t could cause complaints vegetation present within
or dangerous ga~. s (e.g.. methane). the catch basin.
Sediment Sediment (in the 3sin) that exceeds 60 No sediment in the catch
percent of the su o Cepth as measured from basin
the bottom of bay to invert of the lowest
pipe into or out o ne basin, but in no case
less than a minim m of 6 inches clearance
from the sedimer surface to the invert of the
lowest pipe.
Structure
Damage to
Frame and/or
Top Slab
Top slab has holy larger than 2 square
inches or cracks .der than 1/4 inch
Top slab is free of holes
and cracks.
Fractures or
Cracks in
Basin Walls/
Bottom
(Intent is to mak4 ure no material is running
into basin).
Frame not sitting ash on top slab, i.e., Frame is sitting flush on
separation of me than 3/4 inch of the frame the riser rings or top slab
from the top slat ~rame not securely and firmly attached.
attached
Maintenance pe ~n judges that structure is
unsound.
Grout fillet has s _
than 1/2 inch anc
joint of any inlet/
soil particles ente
cracks.
SettlemenU I If failure of basir.
Misalignment function, or desi~.
Vegetation Vegetation grow
than 10% of the
Vegetation grow
that is more thar
six inches apart.
=sated or cracked wider
ginger than 1 foot at the
-let pipe or any evidence of
.g catch basin through
Basin replaced or repaired
to design standards.
Pipe is regrouted and
secure at basin wall.
~s created a safety, I Basin replaced or repaired I
xoblem, to design standards.
across and blocking more No vegetation blocking
yin opening. opening to basin.
in inlet/outlet pipe joints No vegetation or root
.x inches tall and less than growth present.
Volume V - ~noff Trearmenr BMPs
August 2001
No. 5 -Catch Basins
Maintenance Defect Conditions When Maintenance is Needed Results Expected When
Component Maintenance is
performed
Contamination See "Detention Ponds" (No. 1). No pollution present.
and Pollution
Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is
Cover Place Any open catch basin requires maintenance. closed
Locking Mechanism cannot be opened by one Mechanism opens with
Mechanism maintenance person with proper tools. Bolts proper tools.
Not Working into frame have less than 1/2 inch of thread.
Cover Difficult One maintenance person cannot remove lid Cover can be removed by
to Remove after applying normal lifting pressure. one maintenance person.
(Intent is keep cover from sealing off access
to maintenance.)
Ladder Ladder Rungs Ladder is unsafe due to missing rungs, not Ladder meets design i
Unsafe securely attached to basin wall, standards and allows
misalignment, rust, cracks, or sharp edges. maintenance person sale
access.
Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets
(If Applicable) Unsafe design standards.
Trash and Trash and debris that is blocking more than Grate free of trash and
Debris 20% of grate surface inletting capacity. debris.
Damaged or Grate missing or broken member(s) of the Grate is in place and
Missing. grate. meets design standards.
No. 6 -Debris Barriers (e.g., Trash Raclcs)
Maintenance Defect Condition When Maintenance is Results Expected When
Components Needed Maintenance is Performed
General Trash and Trash or debris that is plugging more Barrier cleared to design flow
Debris than 20% of the openings in the barrier. capacity.
Metal Damaged/ Bars are bent out of shape more than 3 Bars in place with no bends more
Missing inches. than 3/4 inch.
Bars.
Bars are missing or entire barrier Bars in place according to design.
missing.
Bars are loose and rust is causing 50% Barrier replaced or repaired to
deterioration to any part of barrier. design standards.
Inlet/Outlet Debris barrier missing or not attached to Barrier firmly attached to pipe
Pipe pipe
August 2001 Volume V -Runoff Treatment BMPs 4-37
~~
No. 7 -Energy Dissipaters
Maintenance Defect Conditions When Maintenance is Results Expected When
Components Needed Maintenance is Performed
External:
Rock Pad Missing or Only one layer of rock exists above Rock pad replaced to design
Moved Rock native soil in area five square feet or standards.
larger, or any exposure of native soil.
Erosion Soil erosion in or adjacent to rock pad. Rock pad replaced to design
standards.
Dispersion Trench Pipe Accumulated sediment that exceeds Pipe cleaned/flushed so that it
Plugged with 20°% of the design depth. matches design.
Sediment
Not Visual evidence of water discharging at Trench redesigned or rebuilt to
Discharging concentrated points along trench (normal standards.
Water condition is a "sheet flow" of water along
Properly trench). Intent is to prevent erosion
damage.
Perforations Over 1/2 of perforations in pipe are Perforated pipe cleaned or
Plugged. plugged with debris and sediment. replaced.
Water Flows Maintenance person observes or Facility rebuilt or redesigned to
Out Top of receives credible report of water flowing standards.
"Distributor" out during any storm less than the design
Catch Basin. storm or its causing or appears likely to
cause damage.
Receiving Water in receiving area is causing or has No danger of landslides.
Area Over- potential of causing landslide problems.
Saturated
Internal:
Manhole/Chamber Worn or Structure dissipating flow deteriorates to Structure replaced to design
Damaged 1/2 of original size or any concentrated standards.
Post, worn spot exceeding one square foot
Baffles, Side which would make structure unsound.
of Chamber
Other See "Catch Basins" (No. 5). See "Catch Basins" (No. 5).
Defects
4-38
--
Volume V -Runoff Treatment BMPs August 2001
-~
No. 11 - Wetponds
Maintenance Defect Condition When Maintenance Results Expected When Maintenance is
Component is Needed Performed
General Water level First cell is empty. doesn't hold Line the first cell to maintain at least 4 feet
water. of water. Although the second cell may
drain, the first cell must remain full to
control turbulence of the incoming flow
and reduce sediment resuspension.
Trash and Accumulation that exceeds 1 Trash and debris removed from pond.
Debris CF per 1000-SF of pond area.
Inlet/Outlet Inlet/Outlet pipe clogged with No clogging or blockage in the inlet and
Pipe sediment and/or debris material. outlet piping.
Sediment Sediment accumulations in Sediment removed from pond bottom.
Accumulation pond bottom that exceeds the
in Pond depth of sediment zone plus 6-
Bottom inches. usually in the first cell.
Oil Sheen on Prevalent and visible oil sheen. Oil removed from water using oil-
Water absorbent pads or vactor truck. Source of
oil located and corrected. If chronic low
levels of oil persist. plant wetland plants
such as Juncus effusus (soft rush) which
can uptake small concentrations of oil.
Erosion Erosion of the pond's side Slopes stabilized using proper erosion
slopes and/or scouring of the control measures and repair methods.
pond bottom, that exceeds 6-
inches, or where continued
erosion is prevalent.
Settlement of Any part of these components Dike/berm is repaired to specifications.
Pond that has settled flinches or
Dike/Berm lower than the design elevation,
or inspector determines
dike/berm is unsound.
Internal Berm Berm dividing cells should be Berm surface is leveled so that water
level. flows evenly over entire length of berm.
Overflow Rock is missing and soil is Rocks replaced to specifications.
Spillway exposed at top of spillway or
outside slope.
4-42
Volume V -Runoff Treatment BMPs August 2001
~ r
SECTION VII -BOND QUANTITIES, RETENTION/DETENTION SUMMARY
SHEET AND DECLARATION OF COVENANT
These items will be provided, if required, at the final design phases.
1/29177/Does-rpts/RptsJb010705
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