StormwaterPRELIlVIINARY STORMWATER SITE PLAN
FOR THE
BENUM & COYNE PROPERTY
Prepared for:
Mr. Robert L. Coyne
c/o Benum Enterprises
P.O. Box 73130
Puyallup, Washington 98372
Project
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Prepared by:
Apex Engineering PLLC
2601 South 35th, Suite 200
Tacoma, Washington 98409
(253) 473-4494
File #27002/0
October 28, 2002
TABLE OF CONTENTS
Section I -Project Overview .................................................................................................. 3 - S
Section II -Existing Condition Summary ............................................................................. (o
Section III -Off-Site Analysis Report ..................................................................................
"" Section IV -Permanent Stormwater Control Flow ............................................................... / D - / 7
Section V -Special Reports and Studies ............................................................................... / $ - /~
Section VI -Other Permits .................................................................................................... ~ O
Section VII -Maintenance and Operations Manual .............................................................. c~ ~ O
Section VIII -Bond Quantities, Retention/Detention Summary Sheet
And Declaration of Covenant ........................................................................ ~ ~
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SECTION I -PROJECT OVERVIEW
This preliminary report format will 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).
Site Locations
• Portions of the Southwest quarter of Section 17, Township 17 North, Range 2 East,
Willamette Meridian, City of Yelm.
• West of Wilkerson Road S.E.. and north east of the Burlington Northern Railroad
right-of--way and south of the Centralia power canal.
See Figure 1 for Vicinity Map.
See Figure 2 -Preliminary Storm Drainage Plan.
Site Area = 28+ acres.
The proposed project is to improve the site into 108 lots for single-family dwellings.
Included are roadways and utilities to serve the individual lots. Lot sizes average 7,636
ftZ. 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) latest edition. This preliminary report
is to show that requirements for runoff control and water quality is feasible.
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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 Soils Survey of the Thurston County Area, the site situates within the Spanaway
gravelly sandy loam 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
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SECTION III -OFF-SITE ANALYSIS report
The intent is to infiltrate stormwater runoff on-site. Therefore, anoff--site analysis is not
required per Optional Guidance #2, Section 2.6.2 D.O.E. However, an analysis can be
provided at final design if required by the City of Yelm.
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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:
• Western Washington Hydrology Model (WWHM)
• The standard parameters per DOE.
• Non-standard residentiaUcommercial assumptions. This allows for input of
impervious and pervious areas directly.
• Outwash soil type.
Part A - Existing Conditions
The existing site is grasses and shrubs. Land slopes from 0.5% to 10%+, generally in the
northern direction. Because infiltration is proposed, existing condition calculations are
unnecessary. However, the WVVHM does include it as part of the software.
Part B -Developed Conditions
For the developed site the following was assumed:
• Individual on-site roof drains infiltration systems would be used for roof runoff.
The area was excluded from the infiltration analysis.
• Right-of--way to be 24 feet paved, 2 feet curb and gutter, 10 feet sidewalk; total
width = 36 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.
Total impervious area = 5.0 Ac.
Total pervious area = 10.7 Ac.
• The remaining lot was assumed to be lawn. This area would enter the stormwater
facility.
The outlets should be protected from erosion. As a minimum. riprapping is required.
Stilling basins or gabon outfalls protection may be required.
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Part C -Infiltration Analysis
General Methodolo~v
The developed conditions basins were routed through preliminary infiltration pond using
the VVWHM and the level pool routing technique. The preliminary pond is larger than
required to anticipate access roads and dividing berms.
Assumptions
• No bypass areas were included. Final designs are yet to be prepared. Bypass areas
may require separate stormwater facilities.
Generally, the assumption Qout through the pond bottom is constant. However, the
preliminary pond size shown on the preliminary plan allows a Qout exceeding the 100-yr.
flow entering the pond. Therefore, at the lower elevations, the pond Qout was reduced to
allow the VWVHM to compute a preliminary water surface elevation.
Figure 5 is the project summary printout from the WWHM. The 100-yr. Qout is 1.6 cfs,
which is about water elevation 316.4, below the design water surface elevation of 321.00.
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Project File: 27002.prj
tame
address
city
?redevelop2d Land Use (acres)
3asin Outwash Till Saturated/Wetland
Design Basin 15.7 0 0
DEVELOPED LAND USE
CYPE: Non-Standard Residential/Commercial (acres)
BASIN LAND USE OUTWASH TILL
resign Basin Landscaped Area 10.7
design Basin Streets/Sidewalks/Parking 5
2ETURN PERIOD VALUES FOR PREDEVELOPED CONDITIONS (CFS)
TEAR: 2 5 10 25 50 100
CFS 0.003 0.004 0.005 0.007 0.006 0.01
2ETURN PERIOD VALUES FOR DEVELOPED CONDITIONS W/ NO DETENTION FACILITY(CFS)
YEAR: 2 5 10 25 50 100
.FS 1.277 1.648 1.921 2.296 2.599 2.923
RETURN PERIOD VALUES FOR POST-DEVELOPED CONDITIONS W/POND (CFS)
GEAR: 2 5 10 25 50 100
.FS 1.007 1.196 1.305 1.431 1.518 1.6
7ETENTION FACILITY INFORMATION:
.dAME OF FACILITY: PREL
TYPE OF FACILITY: INFILTRATION
Depth Area Volume Outflows
(f t) (acres) (acre-ft) (cfs) ~
00.1 00.01 00.076 01.O~R ,~.,~,j,e~,
00.5 00.02 00.38 02.0 ~S//~~
00.75 00.03 00.608 03.0
01.0 00.04 00.76 03.0
02.0 00.05 01.52 03.0
03.0 00.06 02.28 03.0
04.0 00.07 03.04 03.0
05.0 00.08 03.799 03.0
06.0 00.09 04.559 03.0
06.1 00.1 05.0 10.0
STATISTICAL ANALYSIS FOR PREDEVELOPED
.AND DEVELOPED WITH FACILITY
analysis from 50~ of the 2 Year to the 50 Year.
r'lows ~# of times ~# of times ~k developed Pass/Fail
flow exceeds flow exceeds compared to ~
~predeveloped~developed ~predeveloped~
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1601 South 35th, Suite 200
Tacoma,4Vashington 98409
(253) 413-4494
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Part D Water Ouality
Water quality could be provided by use of a wet pond, below the live storage.
The preliminary sizes are determined by using the detention pond bottom areas and
calculating a depth. The maximum depth is 6 feet.
The preliminary size was determined by using the volume calculated for 6-month storm.
The following was assumed:
A SCS/SBiJH 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.
• Water Works software
See Figure 6 for the basin summary.
See Figure 7 for the wet pond stage/storage table.
WQ required volume = 52,707 ft3.
From the stage/storage table 57,000 ft3 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 may be used and will be determined at final design.
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10/24/02 8:18:58 am Apex Engineering PLLC page 1
BENUM AND COYNE PROPERTY
PRELIMINARY STORM DRAINAGE ANALYSIS
27002/0, 10-22-2002, J.B.
BASIN SUMMARY
BASIN ID: DVWQ NAME: DEV SITE WATER QUALITY
SCS METHODOLOGY
TOTAL AREA.......: 15.70 Acres BASEFLOWS: 0.00 cfs
`~" RAINFALL TYPE....: THUR6M0 PERV
PRECIPITATION....: 1.80 inches AREA..: 10.70 Acres
TIME INTERVAL....: 10.00 min CN....: 85.00
_.,~ TC..... 5.00 min
ABSTRACTION COEFF: 0.20
PEAK RATE: 4.95 cfs VOL: 1.21 Ac-ft TIME: 450 min
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5.00 Acres
98.00
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SECTION V -SPECIAL REPORTS AND STUDIES
At this time, no geotechnical analysis was prepared regarding the infiltration capability of
the soils. For this preliminary analysis, Table 3.7, DOE, was used for rates. Assuming
sandy gravel, 10-inch/hr. was used. See Figure 8.
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Table 3.7 -- Recommended Infiltration Rates
based on USDA Soil Textural Classification.
Estimated Long-
*Short-Term Term (Design)
Infiltration Correction Infiltration Rate
Rate (in./hr Factor, CF (in./hr)
20 2 10
Clean sandy gravels and __._
gravelly sands (i.e., 90% of '--"~'
the total soil sample is
retained in the #10 sieve)
Sand 8 4 2
Loam Sand 2 4 0.5
Sand Loam 1 4 0.25
Loam 0.5 4 0.13
*From WEF/ASCE, 1998.
Based on experience with long-teen full-scale infiltration pond
performance, Ecology's Technical Advisory Committee (TAC)
recommends that the short-term infiltration rates be reduced as shown in
Table 3.7, dividing by a correction factor of 2 to 4, depending on the soil
textural classification. The correction factors provided in Table 3.7
represent an average degree of long-term facility maintenance, TSS
reduction through pretreatment, and site variability in the subsurface
conditions. These conditions might include deposits of ancient landslide
debris, buried stream channels, lateral grain size variability, and other
factors that affect homogeneity).
These correction factors could be reduced, subject to the approval of the
local jurisdiction, under the following conditions:
• For sites with little soil variability,
• Where there will be a high degree of long-term facility maintenance,
• Where specific, reliable pretreatment is employed to reduce TSS
entering the infiltration facility
In no case shall a correction factor less than 2.0 be used.
Correction factors higher than those provided in Table 3.7 should be
considered for situations where long-term maintenance will be difficult to
implement, where little or no pretreatment is anticipated, or where site
conditions are highly variable or uncertain. These situations require the
use of best professional judgment by the site engineer and the approval of
the local jurisdiction. An Operation and Maintenance plan and a financial
bonding plan maybe required by the local jurisdiction.
~-8
August 2001 Volume 111 -Hydrologic Analysis and Flow Control BMPs ~-6 /
/9'
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.
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SECTION VII -MAINTENANCE AND OPERATIONS MANUAL
For informational purposes, the following items are anticipated. These were obtained
from the DOE Manual.
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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, exceedence 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 IPM State or local eradication policies
required
policies for the use of herbicides).
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. )
430 Volume V -Runoff Treatment BMPs August 2001
as
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.
August 2001 Volume V -Runoff Treatment BMPs 4-31
a3
No. 1- -... ~ Ponds
Maintenance Oefect Conditions When Maintenance Is Results Facpected When
Component Needed Maintenance Is Performed
Pond Berms Settlements Any part of berm which 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. removed and the berm restored. A
Tree growth on berms over 4 feet in licensed civil engineer should be
heigf~t 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 Emergency Only one layer of rock exists above Rocks and pad depth are restored to
Overflow/ Overflow/ native soil in area five square feet or design standards.
Spillway 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"
432 Volume V -Runoff Treatment BMPs August 2001
No. 2 -Infiltration
Maintenance Defect Conditions When Maintenance Is Results Expected When
Component Needed Maintenance Is
Performed
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
works according to
(A percolation test pit or test of facility 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.
and/or debris
~.
August 2001 Volume V -Runoff Treatment BMPs 433
as
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 2001 Volume V -Runoff Treatment BMPs 435
d t0
No. 5 -Catch Basins
Maintenance Defect Conditions When Maintenance is Needed Results Expected When
Component Maintenance is
performed
General Trash & Trash or debris which is located immediately No Trash or debris located
Debris in front of the catch basin opening or is immediately in front of
blocking inletting capacity of the basin by catch basin or on grate
more than 10%. opening.
Trash or debris (in the basin) that exceeds 60 No trash or debris in the
percent of the sump depth as measured from catch basin.
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
less than a minimum of six inches clearance
from the debris surface to the invert of the
lowest pipe.
Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free
blocking more than 1/3 of its height. of trash or debris.
Dead animals or vegetation that could No dead animals or
generate odors that could cause complaints vegetation present within
or dangerous gases (e.g., methane). the catch basin.
Sediment Sediment (in the basin) that exceeds 60 No sediment in the catch
percent of the sump depth as measured from basin
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
less than a minimum of 6 inches clearance
from the sediment surface to the invert of the
lowest pipe.
Structure Top slab has holes larger than 2 square Top slab is free of holes
Damage to inches or cracks wider than 1/4 inch and cracks.
Frame and/or
Top Slab (Intent is to make sure no material is running
into basin).
Frame not sitting flush on top slab, i.e., Frame is sitting flush on
separation of more than 3/4 inch of the frame the riser rings or top slab
from the top slab. Frame not securely and firmly attached.
attached
Fractures or Maintenance person judges that structure is Basin replaced or repaired
Cracks in unsound. to design standards.
Basin Walls/
Bottom
Grout fillet has separated or cracked wider Pipe is regrouted and
than 1/2 inch and longer than 1 foot at the secure at basin wall.
joint of any inleUoutlet pipe or any evidence of
soil particles entering catch basin through
cracks.
SetUemenU If failure of basin has created a safety, Basin replaced or repaired
Misalignment function, or design problem. to design standards.
Vegetation Vegetation growing across and blocking more No vegetation blocking
than 10% of the basin opening. opening to basin.
Vegetation growing in inlet/outlet pipe joints No vegetation or root
that is more than six inches tall and less than growth present.
six inches apart.
4-36 Volume V -Runoff Treatment BMPs August 2001
a~
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
Unsafe securely attached to basin wall, standards and allows
misalignment, rust, cracks, or sharp edges. maintenance person safe
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 Racks)
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 437
a~
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 Wom 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
a~
No. 11- Wetponds
Maintenance Defect Condition When Maintenance Results F~cpected 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.
InIeUOutlet InIeUOutlet 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/beret is repaired to specifications.
Pond that has settled flinches or
Dike/Beret lower than the design elevation,
or inspector determines
dike/beret 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
3D
SECTION VII -BOND QUANTITIES. RETENTION/DETENTION SUMMARY
SHEET AND DECLARATION OF COVENANT
These items will be provided, if required, at the final design phases.
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