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HomeMy WebLinkAboutStormwaterMaintenancePlan_06-24-21 1 BOZEMAN COHOUSING Stormwater System Operation and Maintenance Plan   STORMWATER OPERATION & MAINTENANCE PLAN PURPOSE Stormwater runoff is a significant source of water pollution in urbanizing areas. In addition, increasing impervious area causes increased runoff flow rates and runoff volumes discharged to receiving drainageways. The proposed stormwater facilities help mitigate negative effects by providing treatment for pollutant removal as well as storage and infiltration functions to help control release rates downstream. Properly maintained stormwater facilities are effective at removing certain pollutants and providing necessary management of stormwater volumes during larger storm events. Improperly maintained facilities can increase the discharge of pollutants downstream, increase the risk of flooding downstream, increase the instability of downstream channels, and lead to aesthetic and nuisance problems. Studies show that poor operation and maintenance is the leading cause of facility failure. Poor maintenance of the stormwater facilities can also create unpleasant odors, nuisance insects, and a generally unsightly, unkempt appearance. Failure can be caused by:  poor maintenance in relation to sediment and debris removal,  clogged inlets resulting from sediment accumulation or trash and debris,  inadequate access for routine maintenance activities. Proper maintenance and knowing the functionality of the facilities and the importance of all the system components reduces the chance of flooding and stormwater management deficiencies. STORMWATER SYSTEM OVERVIEW The stormwater features used at this site are: catch basins, stormwater conveyance pipes, cobble bed conveyance channels (ditches), culverts, rain gardens, drywell structures, and underground stormwater infiltration facilities, and outflow control structures. In combination with each other, the site’s stormwater facilities have the following general objectives:  Efficient internal conveyance of stormwater runoff to final infiltration and treatment facilities.  Treatment and infiltration of runoff to improve water quality.  Protection of the downstream (i.e. offsite) drainage system through reduction of runoff peak flow rates and volumes via storage and infiltration. Properly functioning stormwater features reduce flood damage risk, protect downstream drainageways, and enhance water quality of discharges to receiving water bodies. The stormwater facility owner must understand the importance of the designated onsite 2 BOZEMAN COHOUSING Stormwater System Operation and Maintenance Plan   stormwater facilities and the obligation to assure their continued proper function. This Stormwater System Operation and Maintenance Plan will provide the information needed to operate a fully functional stormwater treatment facility on the property. RESPOSIBILITY TO MAINTAIN Designation of a responsible party is important to assure proper operation of your stormwater detention and control features. In this instance it is a responsibility of the property owner for the correct operation and proper maintenance of the facilities. The City of Bozeman Public Works Department is not responsible for the maintenance of these facilities or their structural components, including the water quality devices, flow control structures, and outlet pipes. However, the City of Bozeman Public Works Department does have the authority to inspect and review maintenance activities to ensure the viability of your facilities. RECOMMENDED MAINTENANCE Each onsite stormwater facility will have unique requirements for maintenance activities and intervals. The facility size, type and characteristics of the tributary area, and facility location will all influence maintenance requirements. This section outlines suggested maintenance activities, intervals, and procedures for the stormwater system. The site’s maintenance program should be adjusted as necessary to keep the stormwater system functioning properly.  Regular maintenance activities should focus on the care of upstream pre-treatment facilities (i.e. catch basins and rain gardens) to protect the viability of larger downstream treatment features. This maintenance includes seasonal removal of any trash, debris, and sediment that accumulates within pipes, catch basins, curb and gutters, drywells, and rain gardens. Excessive accumulations of trash, debris, and sediment may cause clogging in the system and result in reduced lifespan of infiltration facilities, overflow and flooding, and damage risk to nearby structures.  Inlet grates should remain free of obstructions to flow from debris. Clogged inlets can lead to flooding risk and damage to onsite and offsite structures. Inlet grates are particularly prone to clogging from leaf litter in the fall and from road sanding/de- icing material in the spring.  Keeping underground infiltration facilities and drywells clear of accumulating sediment and debris is critical for their proper function and lifespan. If the underlying gravel pack and soils become clogged with fine sediments, the cobble galleries and drywells will not function as designed and may require complete replacement. Drywells should be inspected frequently and cleaned as necessary via hydraulic vacuum truck. Routine Maintenance (seasonally to bi-annually): 1) Inspections: Scheduled inspections with a specified checklist should be performed during the year. Inspections after major rainfall events are also recommended to check for obstructions or damage and to remove debris/trash. Example inspection checklists are included as an attachment to this plan for reference purposes that 3 BOZEMAN COHOUSING Stormwater System Operation and Maintenance Plan   can be customized to project specific infrastructure. DO NOT ENTER confined spaces such as manholes and underground infiltration facilities for inspections. These facilities should be inspected from the surface. 2) Vegetation Management: When mowing, collect grass clippings and all other clippings/trimmings and take offsite for disposal or dispose in trash on site. Do not leave clippings in an area that will clog catch basin inlet grates and French drains. This includes removing clippings from roadside ditches that are throughout the development. Removing clippings, leaf litter, and sediment from the cobble drainage channels is necessary to sustain infiltration capabilities. Channel cobble should be open to the surface and should never be covered with mulch or sod. Limit the use of fertilizers and pesticides around channels and rain gardens to minimize entry into subsequent downstream waters. 3) Trash, Debris and Litter Removal: Removal of any trash, etc. causing any obstructions to the stormwater facilities during periodic inspections and especially after every significant runoff event. In general, pick up trash, etc. in and around the facilities during all inspections. Inspect all catch basins and drywell structures and clean floating debris as necessary. 4) Parking Lot Sweeping: Each parking lot is recommended to be swept on an annual basis in the spring to reduce the winter traction sands, de-icing materials, and sediment that would otherwise be washed into the stormwater system during runoff events. Sweeping via vacuum broom truck is the preferred alternative so that fine sediments are fully removed from the site. 5) Structural Component Check: Perform structural inspection of catch basins, drywells, inlets, grates, pipes, and culverts on a regular basis for potential additions to the Non-routine Maintenance list. Non-Routine Maintenance includes (annually to 5 years): 1) Sediment Removal: Accumulated sediment in the bottom of catch basins, drywells, and rain gardens may need to be removed as frequently as once annually. Sediment removal in the drywell should be performed at frequencies of approximately once every three to five years, or as necessary, to ensure that sediment depth or debris accumulation in the bottom at any location does not exceed twelve inches. Sediment removal in the rain garden bioretention areas may be required every 3 to 5 years to ensure that vegetation is not ‘smothered’ and underlying soils are not clogged with fine sediments. 2) Structural Repair/Replacement: Eventually structural components may need to be repaired or replaced to ensure proper function. Monitor metal structures for excessive rust and corrosion. Monitor concrete structures for large cracking and/or spalling. Repair and replace as necessary. BOZEMAN COHOUSING Stormwater System Operation and Maintenance Plan   EXAMPLE INSPECTION CHECKLISTS Closed Detention & Infiltration Systems Date Inspected _________ (Tanks/Vaults/Drywells) Drainage  System  Feature  Potential  Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is  Performed Or Not Needed   Plugged Air  Vents  One‐half of the cross section of a vent is  blocked at any point or the vent is  damaged.  Vents open and functioning.   Accumulated sediment depth exceeds 10%  of the diameter of the storage area for 1/2  length of storage vault or any point depth  exceeds 15% of diameter.     Debris and  Sediment (Example: 72‐inch storage tank would  require cleaning when sediment reaches  depth of seven inches for more than 1/2  length of tank).  Remove all sediment and debris from  storage area.    Any openings or voids allowing material to  be transported into facility. Joints Between  Tank/Pipe  Section (Will require engineering analysis to  determine structural stability).  Seal all joint between tank/pipe sections.   Tank Pipe Bent  Out of Shape  Any part of tank/pipe is bent out of shape  more than 10% of its design shape. (Review  required by engineer to determine  structural stability).  Repair tank/pipe or replace to design.   Cracks wider than 1/2‐inch and any  evidence of soil particles entering the  structure through the cracks, or  maintenance/inspection personnel  determines that the vault is not structurally  sound.  Replace vault or repair to design  specifications and is structurally sound.   Storage  Area  Vault Structure  Includes Cracks  in Wall,  Bottom,  Damage to  Frame and/or  Top Slab  Cracks wider than 1/2‐inch at the joint of  any inlet/outlet pipe or any evidence of soil  particles entering the vault through the  walls.  No cracks more than 1/4 inch wide at the  joint of the inlet/outlet pipe.   Cover Not in  Place  Cover is missing or only partially in place.  Any open manhole requires maintenance. Manhole is closed.   Locking  Mechanism Not  Working  Mechanism cannot be opened by one  maintenance person with proper tools.  Bolts into frame have less than 1/2 inch of  thread (may not apply to self‐locking lids).   Mechanism opens with proper tools.   Cover Difficult  to Remove  One maintenance person cannot remove  lid after applying normal lifting pressure.  Intent is to keep cover from sealing off  access to maintenance.  Cover can be removed and reinstalled by  one maintenance person.   Manhole  Ladder Rungs  Unsafe  Ladder is unsafe due to missing rungs,  misalignment, not securely attached to  structure wall, rust, or cracks.  Ladder meets design standards. Allows  maintenance person safe access.   General Trash and  Debris   Trash or debris which is located  immediately in front of the catch basin  opening or is blocking inletting capacity of  the basin by more than 10%.  No trash or debris located immediately in  front of catch basin or on grate opening.  Drainage  System  Feature  Potential  Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is  Performed Or Not Needed   Trash or debris (in the basin) that exceeds  60% of the sump depth as measured from  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.  No trash or debris in the catch basin.   Trash or debris in any inlet or outlet pipe  blocking more than 1/3 of its height.  Inlet and outlet pipes free of trash or  debris.   Trash and  Debris  Dead animals or vegetation that could  generate odors that could cause  complaints or dangerous gases (e.g.,  methane).  No dead animals or vegetation present  within the catch basin.   Sediment  Sediment (in the basin) that exceeds 60%  of the sump depth as measured from 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 of clearance  from the sediment surface to the invert of  the lowest pipe.  No sediment in the catch basin.   Top slab has holes larger than two square  inches or cracks wider than 1/4 inch (Intent  is to make sure no material is running into  basin).  Top slab is free of holes and cracks.  Structure  Damage to  Frame and/or  Top Slab  Frame not sitting flush on top slab, i.e.,  separation of more than 3/4 inch of the  frame from the top slab. Frame not  securely attached.  Frame is sitting flush on the riser rings or  top slab and firmly attached.   Maintenance person judges that structure  is unsound.  Basin replaced or repaired to design  standards.   Fractures or  Cracks in Basin  Walls/ Bottom  Grout fillet has separated or cracked wider  than 1/2 inch and longer than one foot at  the joint of any inlet/outlet pipe or any  evidence of soil particles entering catch  basin through cracks.  Pipe is regrouted and secure at basin wall.   Settlement/  Misalignment  If failure of basin has created a safety,  function, or design problem.  Basin replaced or repaired to design  standards.   Vegetation growing across and blocking  more than 10% of the basin opening. No vegetation blocking opening to basin.   Vegetation Vegetation growing in inlet/outlet pipe  joints that is more than six inches tall and  less than six inches apart.  No vegetation or root growth present.   General  Contaminants  and Pollution  Any evidence of oil, gasoline, contaminants  or other pollutants (Coordinate  removal/cleanup with local water quality  response agency).   No contaminants or pollutants present.   Catch Basins Date Inspected_________ Drainage  System  Feature  Potential  Defect  Conditions When Maintenance Is  Needed  Results Expected When Maintenance Is  Performed Or Not Needed   Trash or debris which is located immediately  in front of the catch basin opening or is  blocking inletting capacity of the basin by  more than 10%.  No trash or debris located immediately in  front of catch basin or on grate opening.  Trash or debris (in the basin) that exceeds 60%  of the sump depth as measured from 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.  No trash or debris in the catch basin.  Trash or debris in any inlet or outlet pipe  blocking more than 1/3 of its height. Inlet and outlet pipes free of trash or debris.  Trash and Debris   Dead animals or vegetation that could  generate odors that could cause complaints or  dangerous gases (e.g., methane).  No dead animals or vegetation present within  the catch basin.  Sediment  Sediment (in the basin) that exceeds 60% of  the sump depth as measured from 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 of clearance from the  sediment surface to the invert of the lowest  pipe.  No sediment in the catch basin.  Top slab has holes larger than two square  inches or cracks wider than 1/4 inch     (Intent is to make sure no material is running  into basin).  Top slab is free of holes and cracks.  Structure  Damage to  Frame and/or  Top Slab Frame not sitting flush on top slab, i.e.,  separation of more than 3/4 inch of the frame  from the top slab. Frame not securely  attached.  Frame is sitting flush on the riser rings or top  slab and firmly attached.  Maintenance person judges that structure is  unsound. Replace basin or repair to design standards.  Fractures or  Cracks in Basin  Walls/ Bottom  Grout fillet has separated or cracked wider  than 1/2 inch and longer than one foot at the  joint of any inlet/outlet pipe or any evidence  of soil particles entering catch basin through  cracks.  Regrout pipe and secure at basin wall.  Settlement/  Misalignment  If failure of basin has created a safety,  function, or design problem.  Replace basin or repair to design standards.  Vegetation growing across and blocking more  than 10% of the basin opening. No vegetation blocking opening to basin.  Vegetation Vegetation growing in inlet/outlet pipe joints  that is more than six inches tall and less than  six inches apart.  No vegetation or root growth present.  General  Contaminants  and Pollution  Any evidence of oil, gasoline, contaminants or  other pollutants (Coordinate removal/cleanup  with local water quality response agency).  No contaminants or pollutants present.   Drainage  System  Feature  Potential  Defect  Conditions When Maintenance Is  Needed  Results Expected When Maintenance Is  Performed Or Not Needed   Cover Not in  Place  Cover is missing or only partially in place. Any  open catch basin requires maintenance. Catch basin cover is closed.  Locking  Mechanism Not  Working  Mechanism cannot be opened by one  maintenance person with proper tools. Bolts  into frame have less than 1/2 inch of thread.  Mechanism opens with proper tools.  Catch  Basin  Cover  Cover Difficult to  Remove  One maintenance person cannot remove lid  after applying normal lifting pressure (Intent is  to keep cover from sealing off access to  maintenance).  Cover can be removed by one maintenance  person.  Ladder Ladder Rungs  Unsafe  Ladder is unsafe due to missing rungs, not  securely attached to basin wall, misalignment,  rust, cracks, or sharp edges.  Ladder meets design standards and allows  maintenance person safe access.  Grate Opening  Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards.  Trash and Debris Trash and debris that is blocking more than  20% of grate surface inletting capacity. Grate free of trash and debris.  Metal  Grates (If  Applicable)  Damaged or  Missing  Grate missing or broken member(s) of the  grate. Grate is in place and meets design standards.  Conveyance Storm Pipe Date Inspected_________ Drainage  System  Feature  Potential  Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is  Performed Or Not Needed   Obstructions,  Including Roots Root enters or deforms pipe, reducing flow. Use mechanical methods to remove root.  Do not put root‐dissolving chemicals in  storm sewer pipes. If necessary, remove  the vegetation over the line.    Pipe Dented or  Broken  Inlet/outlet piping damaged or broken and  in need of repair. Pipe repaired and/or replaced.   Pipe Rusted or  Deteriorated   Any part of the piping that is crushed or  deformed more than 20% or any other  failure to the piping.  Pipe repaired and/or replaced.   Sediment &  Debris  Sediment depth is greater than 20% of pipe  diameter.  Install upstream debris traps (where  applicable) then clean pipe and remove  material.    General  Debris barrier or  Trash Rack  Missing  Stormwater pipes > than 18 inches need  debris barrier.  Debris barrier present on all stormwater  pipes 18 inches and greater. 