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HomeMy WebLinkAbout009.1 Stormwater Operations and MaintenanceStormwater Operation and Maintenance Plan 14th & Patrick Affordable Housing – Bozeman, MT WGM Project Number: 221213 08.22.2023 109 E. Main St. Suite B, Bozeman, MT 59715 I OFFICE 406.728.4611 I EMAIL wgm@wgmgroup.com 14th & Patrick Affordable Housing Stormwater Operation and Maintenance Plan STORMWATER OPERATION & MAINTENANCE PLAN LOCATION The development project is located on Lot 1, Block 2 of Amended Subdivision Plat No. J-498B, generally located between Patrick Street, Tschache Lane, N. 15th and N. 14th Avenues, just south of Interstate 90 in Bozeman, MT. The site is located within the City approved PT Land Subdivision in th Northwest ¼ of Section 1, Township 2S, Range 5E. The development will be comprised of a single, 5- story apartment building with onsite parking lot and open space. 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. STORMWATER SYSTEM OVERVIEW The stormwater facilities used on this developed site are limited to three separate systems of curb inlets, manholes, and storm conveyance piping, in addition to the parking lot’s surface and curb & gutters. Additionally, this development site, along with all other development sites, within the overall PT Land Subdivision relies on offsite “regional” wet detention basins. A wet detention basin is a constructed stormwater basin designed to capture, detain, and slowly release runoff to promote pollutant removal through sedimentation and biological uptake. This development site collects its onsite runoff and conveys it to the existing Ponds 1A and 1B, located on the northwest and southwest corners of the intersection of N. 15th Ave. and Tschache Lane, immediately west of the developed site. In order to promote optimal function of Ponds 1A and 1B, it is important that this site’s stormwater facilities are regularly checked and maintained. In combination with each other, this site’s stormwater facilities have the following general objectives:  Efficient internal capture and conveyance of stormwater runoff to offsite wet detention basins.  Safely collect and convey runoff from the 25-Year design storm event to minimize potential of localized flooding on the site.  Drainage structures include sumps which provide intermediate locations for sediment deposition and capture. 14th & Patrick Affordable Housing Stormwater Operation and Maintenance Plan RESPOSIBILITY TO MAINTAIN Designation of a responsible party is important to assure proper operation of your stormwater facilities. In this instance it is the responsibility of the property owner for the correct operation and proper maintenance of the facilities. The owner shall designate a qualified professional entity or individual to perform all monitoring and maintenance. The City of Bozeman Public Works Department is not responsible for the maintenance of the facilities located outside of the right-of-way including any 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. The owner’s representative shall be required to keep a log of all required inspections and maintenance required. The log shall be made available to the City of Bozeman Public Works Department for review as requested. INSPECTION & MAINTENANCE The onsite stormwater facilities have unique requirements for maintenance activities and intervals. The facility size, type and characteristics of the tributary area, and facility locations will all influence maintenance requirements. This section outlines 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 manholes) 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, as well as from pavement surfaces. 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. Inlets should be inspected four times per year and following large storm events and sumps should be cleaned annually or whenever basin sumps become filled with sediment to half of the depth. DO NOT ENTER confined spaces such as manholes and underground infiltration facilities for inspections. These facilities should be inspected from the surface.  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.  All piping should be inspected annually and following large storm events. Pipe should be cleaned and flushed as determined in the field.  All paved areas shall be swept twice a year, scheduled in the spring and fall. 14th & Patrick Affordable Housing Stormwater Operation and Maintenance Plan Routine Maintenance (seasonally to bi-annually): 1) 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, ponds, or pipes. Limit the use of fertilizers and pesticides around channels and rain gardens to minimize entry into subsequent downstream waters. 2) Snow Storage Management: Snow shall be stockpiled in locations where accumulations won’t limit or restrict the ability of the storm structures to collect and convey runoff. 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 manhole structures and clean floating debris as necessary. 4) Parking Lot Sweeping: Each parking lot is recommended to be swept on a semi-annual basis in the spring and fall to reduce the winter traction sands, de-icing materials, leaves 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, manholes, inlets, grates, pipes, and culverts on a regular basis. Non-Routine Maintenance (annually to 5 years): 1) Sediment Removal: Accumulated sediment in the bottom of catch basins, manholes, and pipes may need to be removed as frequently as once annually. Sediment removal in the sumps of drainage structures 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. 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. 14th & Patrick Affordable Housing Stormwater Operation and Maintenance Plan - 34 - Inspection Schedule & Checklist Activity Schedule/Frequency Inspect pond area for oil sheens or trash Monthly Inspect exterior of catch basins Monthly and after storm Inspect pond area, sidewalls, and shoreline for erosion, settlement, ro- dent damage, and insects Quarterly Inspect fences, gates and locks Quarterly Inspect bioswales for vegetation cover and bare areas Quarterly Inspect ditches, check dams, and all visible pipes and culverts for trash, obstructions and other problems Quarterly and after storm events Inspect inlets and outlets for trash, obstructions, and vegetation Quarterly and after storm events Inspect trash racks, debris barriers, and energy dissipaters Quarterly and after storm events Inspect water levels in the pond After storm events Inspect pond area for undesirable or poisonous vegetation and noxious weeds Semi-annually, during growing season Pond area sediment accumulation (pond bottom) Annually Inspect interior of catch basins for debris and sediment Annually Inspect spillway for vegetation overgrowth and ease of heavy equipment access Annually Inspect inside type 2 catch basins, including flow restrictor/orifice plate Annually Inspect access ramps for ease of heavy equipment access Annually Typical Inspection / Maintenance Schedule for Stormwater Pond Facilities - 35 - Stormwater System Inspection Checklist INSPECTOR’S NAME & DATE: NAME & ADDRESS OF FACILITY: GENERAL OBSERVATIONS (IS WATER FLOWING?): WEATHER: Checked? (Y/N) Maintenance Needed? (Y/N) Maintenance Completed/ Observations & Remarks Type 1 catch basins Look for debris and sediment blocking catch basin grate. If found, remove. Inspect filter. Change if torn; clean if clogged; monitor for blockages. Look for sediment and trash in catch basin sump. Clean out if sediment fills 60% of the sump or comes within 6” of a pipe. Look for damage or cracks to frame, grate, basin walls or bottom. If found, repair or replace. Type 2 catch basins Remove trash blocking grates or inlets; replace if broken. Remove lid and check for sediment accu- mulation. Remove trash. Remove sedi-ment if more than 1/3 full. Check integrity of ladder rungs, cleanout gate, and orifice plate. If bent or ob-structed, take appropriate action. Have cracks in wall or bottom repaired as necessary. Conveyances (ditches, bioswales, culverts, and pipes) Check for undercutting, scouring, and slumping. If found, repair or maintain. Remove all trash and loose sediment. Re- move sediment if it will impede water flow or clog downstream structures. Maintain vegetation; mow or cut back if impedes water movement or grass health. Repair check dams as necessary. Remove any dumped yard waste. In ditches and swales, check for integrity of grass, check dams, inlets, and outlets. Remove shrubs and trees. - 35 -- 34 - - 36 - Checked? (Y/N) Maintenance Needed? (Y/N) Maintenance Completed/ Observations & Remarks Components of the pond Inlets and outlets: remove vegetation and debris. Fix erosion and scouring. Fix cause of sediment found below outlet. Remove vegetation and debris from trash rack. Add rock to energy dissipater if missing. If necessary, repair rock on spillway. Remove trees, shrubs, and vegetation over 4”. If piping or erosion is visible, consult engineer. Pond Check for slumping or sloughing of walls. If over 4” of slumping, consult with an engineer. Fix any ero- sion or scouring. If leaks, piping, or soft spots are found, consult with an engineer. If liner visible on bottom, check for holes or replace. Clean any oil sheen from water with oil-absorbent pads or vactor truck. Check sediment depth near inlet. If more than one foot exists, or there is build up near inlet, the pond needs to be cleaned. Vegetation On the pond walls/side slopes, mow grass to 4 – 9”. Remove clippings. Reseed bare areas. On pond surface, emergent vegetation over 50% of the area indicates sediment removal needed. On pond bottom, remove tree seedlings. Around the pond, remove trees and shrubs that shade sidewall grass or that might have problem roots near pipes and structures. Remove invasive and poisonous plants. Remove algae if over 10% of surface. Access and Safety Check integrity of access ramp; ensure stable and clear for heavy equipment. Check integrity and operation of all fences, gates, and locks. Repair as needed for ease of access. Remove rodents and insects if evidence found. Remove vegetation on fences. Attach pictures, summary, sketches, and notes as appropriate. - 37 - Photo: Whatcom County - 37 -- 36 -