Clark County Stormwater Manual
Clark County Stormwater ManualBook 4Stormwater FacilityOperations and MaintenanceJuly 2021
Clark County Stormwater ManualBook 4 – Stormwater Facility Operations and MaintenanceJuly 2021
The Clark County Stormwater Manual: Book 4 – Stormwater Facility Operations and Maintenance is adaptedfrom the Clark County Stormwater Facility Maintenance Manual, 2009 and the Stormwater ManagementManual for Western Washington, Volume V, (Ecology, 2019).Illustrations are courtesy Washington Department of Ecology or redrawn from WashingtonDepartment of Ecology, unless otherwise noted. Illustrations are simplified representations ofstormwater facilities; they are not to scale and not for engineering design or construction.
Tables of ContentsTable of ContentsIntroduction . 1Background . 1Purpose . 1Why Maintain Stormwater Facilities? . 1Maintenance Resources and Standards . 2Organization of this Book . 2Emerging Treatment Technologies . 3Mosquito Control . 3References . 3Stormwater Treatment, Flow Control, and Conveyance Facility Components . 5Field Inlet . 6Catch Basin . 10Manhole . 15Catch Basin Insert . 18Control Structure/Flow Restrictor . 21Debris Barrier & Access Barrier (e.g. Trash Rack). 24Energy Dissipater / Outfall Protection . 27Stormwater Conveyance Pipe. 29Stormwater Facility Discharge Points / Pipe Outlets. 30Hydrodynamic Separator System . 33Sediment Trap . 35Oil/Water Separator (API Type) . 39Coalescing Plate Oil/Water Separator . 42Presettling Basin (Forebay or Pretreatment) . 46Detention Pond . 49Wetpond . 55Filter Strip . 60Compost-Amended Vegetated Filter Strip (CAVFS) . 64Media Filter Drain (MFD) . 67Basic Biofiltration Swale. 69Wet Biofiltration Swale. 74Treatment Wetland . 78Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenancei
Closed Detention System (Tank/Vault) . 84Wet Vault . 88Modular Detention Systems . 92Media Cartridge Filters . 95Planter Box Media Filters . 84Bioretention System .101Permeable Pavement.109Vegetated Roof .100Sand Filter Open (Above Ground).121Sand Filter Vault (Below Ground/Enclosed) .125Infiltration Trench .129Infiltration Basin .131Drywell .137Access Road and Easement .140Fence, Gate, and/or Water Quality Sign .143Vegetation.144On-site Stormwater Management . 149Downspout Infiltration .150Downspout Dispersion .154Sheet Flow and Concentrated Dispersion .159Compost-Amended Soil .162Rain Garden .165Table of TablesTable 1: Stormwater Tract "Low Grow" Seed Mix* for Detention Pond .51Table 2: Emergent Wetland Plant Species Acceptable for Wetponds .57Table 3: Plant Mixes for Biofiltration Swale Treatment Area .71Table 4: Groundcovers and Grasses Suitable for Upper Side Slopes of a Swale .72Table 5: Acceptable Plants for Wet Biofiltration Swale .76Table 6: Emergent Wetland Species for Treatment Wetlands .81Table 7: Plant List for Bioretention System. 103Table 8: Stormwater Tract "Low Grow" Seed Mix for Infiltration Basin . 133Table 9: Plant List for Rain Garden* . 166iiClark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
IntroductionIntroductionBackgroundStormwater facilities include pipes, catch basins, manholes, grassy treatment swales, ditches,drywells, ponds, oil/water separators, and any other structures that collect, convey, control, or treatstormwater drainage. More recently, on-site or low impact development (LID) facilities such as raingardens and permeable pavement are included in the list of stormwater facilities. Stormwaterfacilities are found in a variety of locations, including business sites, residential areas, governmentfacilities, and roadways. Stormwater facilities on private sites often drain to roadside ditches, countystorm sewer pipes, streams, or to groundwater from infiltration facilities.The federal Clean Water Act, the federal Safe Drinking Water Act, and rules to protect threatenedsalmon under the federal Endangered Species Act require Clark County to ensure that stormwaterfacilities in unincorporated Clark County are properly operated and maintained.PurposeStormwater facility owners and operators are required to maintain the stormwater facilities in theircare in compliance with the standards of this book and the Clark County codes listed below.This book is intended to meet all stormwater facility operation and maintenance requirements underClark County Code (CCC) Chapter 13.26A, Water Quality, and Chapter 40.386, Stormwater andErosion Control. It applies to County operations, as well as to public or privately owned andoperated stormwater facilities in unincorporated areas of Clark County.Stormwater facilities are often in or near areas that are also fish and wildlife habitat. This book helpsmake sure that owners perform maintenance in a way that conforms to regulations protecting fishand wildlife.Why Maintain Stormwater Facilities?Along with helping to prevent flooding, properly maintained stormwater facilities can help reducepollution of surface water and groundwater.Stormwater facility maintenance is necessary to protect streams, lakes, wetlands, and groundwater.Proper maintenance helps ensure that facilities operate as they were designed and that trappedpollutants, such as sediment and oils, are cleaned out so that the facilities do not become pollutantsources.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance1
Maintenance Resources and StandardsThis book will help facility owners and operators follow requirements for maintenance. This bookdescribes potential maintenance problems (defects), conditions when maintenance is needed, andminimum performance standards for each type of stormwater facility found in Clark County. If asite was approved for construction under county stormwater requirements adopted in 1994 or later,then the stormwater facilities should have an approved plan for maintenance.Additional guidance on procedures for LID facilities may be found in the Western Washington LowImpact Development (LID) Operation and Maintenance (O&M) (Ecology, 2013) guidance document.The maintenance standards contained in this book are minimum performance standards. Inspectionof a stormwater facility will determine if conditions require a maintenance action. Maintenancestandards are not intended to describe a facility's required condition at all times between inspections.Exceeding a condition at any time between inspections and/or maintenance does not automaticallyconstitute a violation of these standards. However, based upon inspection observations, theinspection and maintenance schedules shall be adjusted to minimize the length of time that a facilityis in a condition that requires maintenance.Many defects listed in this Book are not specifically related to facility performance to treat pollutantsand control runoff rates. The presence of a defect that does not hinder treatment, flow control, orpublic safety is not a violation of county code.Organization of this BookThis book is divided into two sections: The Stormwater Treatment, Flow Control and Conveyance Facility Components sectioncontains facility types that are common in subdivisions, commercial property, and roads. Thesefacilities are commonly maintained by County staff, professional landscapers, propertymanagement personnel, or Homeowners’ Associations. The On-site Stormwater Management section contains LID facility types such as rain gardensthat are becoming common on residential lots. These facilities are commonly maintained by theresidential property owners.Each facility type contains: A brief description of the type of facility, often including an illustration. Key operations and maintenance considerations, which are suggested maintenance methods. An inspection and maintenance table describing minimum performance standards formaintenance.2Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
IntroductionEmerging Treatment TechnologiesSome stormwater treatment facilities are designed and installed with emerging technologies that arenot (or were not) standard at the time of their installation. If not found in this manual, a treatmentfacility may be an emerging technology approved by Washington Department of Ecology in aGeneral Use Level Designation. Maintenance standards in General Use Level Designation approvalsfor emerging technologies not found in this manual are adopted by reference and can be found dex.html.Mosquito ControlMosquitoes can be annoying and sometimes pose a serious risk to public health. They can transmitdiseases such as West Nile Virus and equine encephalitis.Above-ground stormwater facilities should be designed to allow water to flow through or infiltratein less than 48 hours. Presence of mosquitos in a stormwater facility may indicate a clogged outlet,compromised infiltration capacity, or other defect that should trigger inspection and may requiremaintenance.To combat mosquitoes, Clark County has established a mosquito control program. Information onthe Clark County Mosquito Control District can be accessed online at trict.If mosquitoes are identified during stormwater facility maintenance or inspection and are a concern,a request to the Clark County Mosquito Control District for service or information regardingmosquito control can be made online or at the 24-hour request line, (360) 397-8430.ReferencesThis book draws on other maintenance manuals. Along with documenting current county standardsand practices, this book includes maintenance practices from or refers to the following documents: Washington Department of Ecology Stormwater Management Manual for Western Washington(SMMWW) (December 2019) Washington Department of Ecology Western Washington Low Impact Development (LID) Operationand Maintenance (O&M) (July 2013)Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance3
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Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsStormwater Treatment, Flow Control, and Conveyance FacilityComponentsThe BMPs in this section are stormwater treatment, flow control, and conveyance facilities (andtheir components) that commonly serve subdivisions, commercial developments, and roads. BMPsthat typically serve individual residential lots are listed in the next section, On-site StormwaterManagement.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance5
6Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsField InletA field inlet is a concrete structure fitted with a slotted grate to collect stormwater runoff and routeit through underground pipes.Field inlets typically provide a storage volume (sump) below the outlet pipe to allow sediments anddebris to settle out of the stormwater runoff. Some field inlets are fitted with a spill control device(inverted elbow on outlet pipe) intended to contain large quantities of grease or oils.Facility objects that are typically associated with a field inlet include: access road or easement control structure/flow restrictor biofiltration swale detention pond infiltration trenchKey Operations and Maintenance Considerations The most common tool for cleaning field inlets is a truck with a tank and vacuum hose(Vactor truck) to remove sediment and debris from the sump.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance7
A field inlet may be an enclosed space where harmful chemicals and vapors can accumulate.Therefore, if the inspection and maintenance requires entering a field inlet, it should beconducted by an individual trained and certified to work in hazardous confined spaces.Field InletDrainageSystem FeaturePotentialDefectConditions When Maintenance IsNeededMinimum Performance StandardNote: table spans multiple pages.General8Trash andDebrisTrash or debris which is locatedimmediately in front of the catch basinopening or is blocking inletting capacityof the field inlet by more than 10%.No trash or debris locatedimmediately in front of field inlet or ongrate opening.Trash or debris (in the field inlet) thatexceeds 60 percent of the sump depthas measured from the bottom of basin toinvert of the lowest pipe into or out of thebasin, but in no case less than aminimum of six inches clearance fromthe debris surface to the invert of thelowest pipe.No trash or debris in the field inlet.Trash or debris in any inlet or outlet pipeblocking more than 1/3 of its height.Inlet and outlet pipes free of trash ordebris.Dead animals or vegetation that couldgenerate odors that could causecomplaints or dangerous gases (e.g.,methane).No dead animals or vegetationpresent within the field inlet.SedimentSediment (in the basin) that exceeds 60percent of the sump depth as measuredfrom the bottom of basin to invert of thelowest pipe into or out of the basin, but inno case less than a minimum of 6 inchesclearance from the sediment surface tothe invert of the lowest pipe.No sediment in the field inlet.StructureDamage toFrame and/orTop SlabTop slab has holes larger than 2 squareinches or cracks wider than 1/4 inch.(Intent is to make sure no material isrunning into basin).Top slab is free of holes and cracks.Frame not sitting flush on top slab, i.e.,separation of more than 3/4 inch of theframe from the top slab. Frame notsecurely attached.Frame is sitting flush on the riserrings or top slab and firmly attached.Fractures orCracks in BasinWalls/ BottomMaintenance person judges thatstructure is unsound.Basin replaced or repaired to designstandards.Grout fillet has separated or crackedwider than 1/2 inch and longer than 1foot at the joint of any inlet/outlet pipe orany evidence of soil particles enteringfield inlet through cracks.Pipe is regrouted and secure at basinwall.Settlement/MisalignmentIf failure of basin has created a safety,function, or design problem.Basin replaced or repaired to designstandards.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsField InletDrainageSystem FeaturePotentialDefectConditions When Maintenance IsNeededMinimum Performance StandardNote: table spans multiple pages.VegetationInhibitingSystemVegetation growing across and blockingmore than 10% of the basin opening.No vegetation blocking opening tobasin.Vegetation growing in inlet/outlet pipejoints that is more than six inches talland less than six inches apart.No vegetation or root growth present.Contaminantsand PollutionAny evidence of oil, gasoline,contaminants, or other pollutants.Sheen, obvious oil, or othercontaminants present.No contaminants or pollutantspresent. Metal GratesIdentify and remove source, ANDReport to Clark County Clean WaterProgram.Grate Not inPlaceCover is missing or only partially inplace. Any open field inlet requiresmaintenance.Field inlet cover is closed.Grate OpeningUnsafeGrate with opening wider than 3 inches.Grate opening meets designstandards.Trash andDebrisTrash and debris that is blocking morethan 20% of grate surface inlettingcapacity.Grate free of trash and debris.Damaged orMissingGrate missing or broken member(s) ofthe grate.Grate is in place and meets designstandards.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance9
10Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsCatch BasinA catch basin is an underground concrete structure typically fitted with a slotted grate to collectstormwater runoff and route it through underground pipes. Catch basins can also be used as ajunction in a pipe system and may have a solid lid. There are two types.A Type 1 catch basin is a rectangular box with approximate dimensions of 3’x2’x5’. Type 1 catchbasins are utilized when the connected conveyance pipes are less than 18 inches in diameter and thedepth from the gate to the bottom of the pipe is less than 5 feet.A Type 2 catch basin, also commonly referred to as a storm manhole, is listed separately under“Manhole” in this book.Catch basins typically provide a storage volume (sump) below the outlet pipe to allow sediments anddebris to settle out of the stormwater runoff. Some catch basins are also fitted with a spill controldevice (inverted elbow on outlet pipe) intended to contain large quantities of grease or debris.Catch basins are frequently associated with all stormwater facilities.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance11
Key Operations and Maintenance Considerations The most common tool for cleaning catch basins is an industrial vacuum truck with a tank andvacuum hose (e.g. Vactor truck) to remove sediment and debris from the sump. A catch basin may be an enclosed space where harmful chemicals and vapors can accumulate.Therefore, if the inspection and maintenance requires entering a catch basin, it should beconducted by an individual trained and certified to work in hazardous confined spaces.Catch BasinDrainageSystem FeaturePotentialDefectConditions When Maintenance IsNeededMinimum Performance StandardNote: table spans multiple pages.GeneralTrash andDebrisTrash or debris which is locatedimmediately in front of the catch basinopening or is blocking inletting capacityof the basin by more than 10%.No trash or debris located immediately infront of catch basin or on grate opening.Trash or debris (in the basin) thatexceeds 60 percent of the sump depth asmeasured from the bottom of basin toinvert of the lowest pipe into or out of thebasin, but in no case less than aminimum of six inches clearance from thedebris surface to the invert of the lowestpipe.No trash or debris in the catch basin.Trash or debris in any inlet or outlet pipeblocking more than 1/3 of its height.Inlet and outlet pipes free of trash or debris.Dead animals or vegetation that couldgenerate odors that could causecomplaints or dangerous gases (e.g.,methane).No dead animals or vegetation present withinthe catch basin.SedimentSediment (in the basin) that exceeds 60percent of the sump depth as measuredfrom the bottom of basin to invert of thelowest pipe into or out of the basin, but inno case less than a minimum of 6 inchesclearance from the sediment surface tothe invert of the lowest pipe.No sediment in the catch basin.StructureDamage toFrame and/orTop SlabTop slab has holes larger than 2 squareinches or cracks wider than 1/4 inch.Top slab is free of holes and cracks.Fractures orCracks in12(Intent is to make sure no material isrunning into basin.)Frame not sitting flush on top slab, i.e.,separation of more than 3/4 inch of theframe from the top slab. Frame notsecurely attached.Frame is sitting flush on the riser rings or topslab and firmly attached.Maintenance person judges that structureis unsound.Basin replaced or repaired to designstandards.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance
Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsBasin Walls/BottomGrout fillet has separated or crackedwider than 1/2 inch and longer than 1 footat the joint of any inlet/outlet pipe or anyevidence of soil particles entering catchbasin through cracks.Pipe is regrouted and secure at basin wall.Settlement/MisalignmentIf failure of basin has created a safety,function, or design problem.Basin replaced or repaired to on growing across and blockingmore than 10% of the basin opening.No vegetation blocking opening to basin.Vegetation growing in inlet/outlet pipejoints that is more than six inches tall andless than six inches apart.No vegetation or root growth present.Contaminantsand PollutionAny evidence of oil, gasoline,contaminants, or other pollutants. Sheen,obvious oil, or other contaminantspresent.No contaminants or pollutants present. Catch BasinCoverMetal Grates(If Applicable)Oil/Debris Trap (IfApplicable)Identify and remove source, ANDReport to Clark County Clean WaterProgram.Cover Not inPlaceCover is missing or only partially in place.Any open catch basin requiresmaintenance.Catch basin cover is closed.LockingMechanismNot WorkingMechanism cannot be opened by onemaintenance person with proper tools.Bolts into frame have less than 1/2 inchof thread.Mechanism opens with proper tools.CoverDifficult toRemoveOne maintenance person cannot removelid after applying normal lifting pressure(Intent is to keep cover from sealing offaccess to maintenance).Cover can be removed by one maintenanceperson.GrateOpeningUnsafeGrate with opening wider than 7/8 inch.Grate opening meets design standards.Trash andDebrisTrash and debris that is blocking morethan 20% of grate surface inlettingcapacity.Grate free of trash and debris.Damaged orMissingGrate missing or broken member(s) ofthe grate.Grate is in place and meets designstandards.DislodgedOil or debris trap is misaligned with ordislodged from the outlet pipe.Trap is connected to and aligned with outletpipe.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance13
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Stormwater Treatment, Flow Control, and Conveyance Facility ComponentsManholeA manhole is an underground concrete structure typically fitted with a slotted grate to collectstormwater runoff and route it through underground pipes. Manholes can also be used as a junctionin a pipe system and may have a solid lid. A manhole is also known as a Type 2 catch basin.Manholes are round concrete structures ranging in diameter from 4 feet to 8 feet. They are usedwhen the connecting conveyance pipe is 18 inches or greater or the depth from grate to pipe bottomexceeds 5 feet. Manholes typically have steps mounted on the side of the structure to allow access.Manholes typically provide a storage volume (sump) below the outlet pipe to allow sediments anddebris to settle out of the stormwater runoff. Some manholes are also fitted with a spill controldevice (inverted elbow on outlet pipe) intended to contain large quantities of grease or oils.Manholes are often associated with other stormwater facilities.Clark County Stormwater Manual 2021Book 4 – Stormwater Facility Operations and Maintenance15
Key Operations and Maintenance Considerations The most common tool for cleaning manholes is a truck with a tank and vacuum hose (Vactor truck) to remove sediment and debris from the sump. A manhole may be an enclosed space where harmful chemicals and vapors can accumulat
The Clark County Stormwater Manual: Book 4 - Stormwater Facility Operations and Maintenance is adapted from the Clark County Stormwater Facility Maintenance Manual, 2009 and the Stormwater Management Manual for Western Washington, Volume V, (Ecology, 2019). Illustrations are courtesy Washington Department of Ecology or redrawn from Washington
The Journals of Lewis and Clark. By Meriwether Lewis and and William Clark, 1804-1806. Note: These Journals are from May 14, 1804, the day the expedition left the Mississippi River, to September 26, 1806, a day or two after they arrived back in St. Louis. It includes all possible Journal entries of Lewis and Clark. Most of the "courses andFile Size: 4MBPage Count: 1023Explore furtherJournal Entries from the Lewis and Clark Expeditionwww.lewisandclarkexhibit.orgThe Journals of Lewis and Clark, by Meriwether Lewis and .www.gutenberg.orgThe Journals of the Lewis & Clark Expedition Center for .www.unl.eduHome Journals of the Lewis and Clark Expeditionlewisandclarkjournals.unl.eduJournal Excerpts Discovering Lewis & Clarklewis-clark.orgRecommended to you b
NPDES: Stormwater Best Management Practice— — Stormwater Wetland Stormwater Retrofit A stormwater retrofit is a stormwater control (usually structural) that a community puts into place after development to improve water quality, protect downstream channels, reduce flooding or meet other specific objectives.
Green Stormwater Infrastructure Maintenance Manual 7 1.1 Introduc on The City of Philadelphia relies in part on Green Stormwater Infrastructure (GSI) systems—comprised of one or more decentralized stormwater management prac ces (SMPs) such as rain gardens, stormwater tree trenches, and green roofs—to reduce stormwater volume and pollutants
Green Stormwater Infrastructure Maintenance Manual 7 1.1 Introduc on The City of Philadelphia relies in part on Green Stormwater Infrastructure (GSI) systems—comprised of one or more decentralized stormwater management prac ces (SMPs) such as rain gardens, stormwater tree trenches, and green roofs—to reduce stormwater volume and pollutants
Chisholm, Paul & Michelle 72 Christie, Russell J. 114 Clanton, David 19 Clark, Eddie And Linda 19 Clark, Ernie 27 Clark, Fredrick 30 Clark, Geoffrey 29 Clark, Geoffrey 33 Clark, Jeff and Angie 15 Clark, Jonathan 76 Clark, Nick 16 Clay, Dixie H. 87 Clegg, Larry 61 Coghlan, Sr., F. H. 98 Coker, Randall 17 Cole, Bobby 106 Cole, Bobby 123 Cole .
Adiba Ali, MPH, Clark County Public Health Janis Koch, MPA, Clark County Public Health Leigh Radford, Clark County Public Information and Outreach Christine Sorvari, MS, Healthy Columbia Willamette Collaborative, Multnomah County Health Department Contact Melanie Payne, MPH Health Assessment and Evaluation Clark County Public Health 360-397 .
1.3 New Jersey Stormwater Best Management Practices (BMPs) Manual The New Jersey Stormwater Best Management Practices Manual (BMP Manual) of April 2004, as amended, was developed to provide guidance to implement the standards in the Stormwater Rules. The BMP manual provides examples of ways to meet the standards required by the Stormwater R
a result of poor understanding of human factors. Patient deaths have occurred as a result. Example: unprotected electrodes n Problems: Device use errors - improper hook ups, improper device settings n Solutions: “Ergonomic or Human factors engineering - See “Do it by Design” and AAMI Human Factors Engineering Guidelines.
