City of Bozeman. Construction Site Management Program

Transcription

1 City of Bozeman Construction Site Management Program Best Management Practice (BMP) Manual for Construction Sites Version 3 September 1, 2016

2 Section 1 Overview Table of Contents Manual Introduction 3 Local Requirements 4 Minimum Standards 5 Operational and Administrative Controls 6 Section 2 - Perimeter Control Wattle 7 Silt Fence 9 Compacted Earthen Berm 11 Section 3 - Infrastructure Protection Inlet Protection 13 Tracking Control 15 Sediment Trap 17 Dewatering Control 18 Section 4 - Pollutant Management Concrete Washout and Waste Management 21 Section 5 Stabilization Measures Stabalization Measures 24 2

3 Overview Manual Introduction Stormwater is rain that flows over hard surfaces and landscapes that does not infiltrate into the ground. Stormwater picks up pollutants, such as sediment, trash, animal waste, fertilizers, oils, hydrocarbons, and grease, as it moves over these surfaces. Stormwater then enters curb inlets, passes through a network of underground pipes, and dumps into local rivers. City of Bozeman staff works to improve the quality of stormwater to ensure local waterways stay clean enough to fish, recreate, and swim in. One of the largest sources of pollution staff encounters is uncontrolled stormwater runoff from construction sites. Uncontrolled stormwater runoff from construction sites displaces and deposits sediment and other pollutants offsite, causing degradation of rivers and infrastructure. A one-acre construction site can lose tons of sediment per year. This manual provides numerous approved best management practice (BMP) options for contractors, project owners, and engineers to mitigate adverse impacts and meet local requirements. 3

4 Overview Local Requirements The City of Bozeman requires that project owners submit one of the following stormwater permits before initiating ground disturbance activities. Stormwater staff highly encourages project owners or their agents to set up a pre-submittal meeting, which includes a conversation regarding minimum expectations, recommendations, and areas of concern saving both parties preparation and review time. Stormwater staff review, comment on, and, when deemed adequate, approve all permits. Project owners that do not submit or submit inadequate permits will experience a delay in building permit issuance, site plan approval, or notice to proceed until an approved permit is in place. Single-family home construction: Project owners must submit a Drainage and Stormwater Self-Certification with their building permit application. There is no fee associated with this permit. Multi-family, commercial, utility, demolition, and paving projects with a total land disturbance less than one acre: Project owners must submit an Erosion and Sediment Control Construction Permit for Projects Less than 1 Acre. There is no fee associated with this permit. Multi-family, commercial, utility, demolition and paving projects with a total land disturbance greater than one acre: Project owners must submit a Montana Department of Environmental Quality Notice of Intent, Stormwater Pollution Prevention Plan, and a Notice of Termination. There is no City of Bozeman fee associated with this permit. 4

5 Overview Minimum Standards The City of Bozeman requires that project owners meet the following minimum standards when preparing and enacting a stormwater permit for their site. Minimum standards exist to provide a consistent message to contractors, improve permit content, and promote cleaner sites. Project owners must: 1. Protect inlets: Inlets receiving site runoff require BMPs that filter stormwater before flowing into underground infrastructure. Approved options include drop inlet protection (pg. 14). 2. Contain disturbed areas: Project boundaries require BMPs that contain stormwater flowing from disturbed areas. Approved options include wattle (pg. 8), silt fence (pg. 10), and compacted earthen berm (pg. 12). 3. Mitigate tracking: Exit points require BMPs that prevent the tracking of debris offsite. Approved options include angular rock and a cattle guard/rock hybrid trackpads (pg. 16). 4. Control concrete waste: Concrete activities require BMPs that allow for the capture and disposal of generated pollutants to prevent environmental contamination. Approved options include reusable/disposable products, prefabricated roll-offs or containers, lined below-ground containment, and lined above ground containment (pg. 22). 5. Contain material stockpiles: Material stockpiles, not already contained within an existing perimeter control, require perimeter BMPs that prevent erosion and displacement of loose material. Approved options include wattle (pg. 8), silt fence (pg. 10), compacted earthen berm (pg. 12), and tarps/plastic sheeting. 6. Manage dewatering flows: Pumping activities require BMPs that filter water before entering underground infrastructure or waterways. Approved options include a series of inline treatment BMPs, land application, or wells (pg. 19). Dewatering discharges to state waters are a permitted activity under the authority of the MDEQ. 7. Protect post-construction stormwater features: Post-construction stormwater features, such as retention and detention ponds, require BMPs that protect and stabilize their side slopes and bases during and after construction activities. Approved BMPs include riprap, reinforced fore-bays, check dams, crimped straw mulch, and rolled erosion control products. 8. Stabilize disturbed areas: Disturbed areas require BMPs that prevent erosion of barren ground. Approved options include surface roughening, crimped straw mulch, wood mulch, rolled erosion control products, riprap, and sod (pg. 25). 5

6 Overview Operational and Administrative Controls Introduction Operational and administrative control BMPs help keep construction sites clean and in compliance. The following are things to consider when preparing and implementing a stormwater permit: Site Barrier Utilize site barriers to control the flow of vehicles and equipment. Several types of site barriers exist, including concrete blocks, construction fencing, and cones. Off-Site Parking Utilize off-site parking to control tracking by reducing vehicle trips onto disturbed areas. Spill Prevention and Response Utilize a spill kit to clean up leaks and spills that occur. All parties should know its location and proper use. Fleet Management Utilize inspection techniques to identify and eliminate leaks and drips of hydraulic fluid, gas, oil, etc. from equipment and vehicles. Preservation of Existing Vegetation Utilize preservation of existing vegetation techniques to reduce the amount of erodible area on a job site. Image 1 Site Barrier Image 2 Spill Kit Image 3 Equipment Management 6

7 Introduction Wattle slows, ponds, filters, and disperses stormwater flowing from ground disturbance, pollutant storage, and material stockpile areas. Approved wattle consists of weed-free straw, flax, or coconut fiber wrapped in UV-degradable netting. Contractors must consider their site s size, soil condition, and topography before selecting and installing wattle. Installation Requirements Install wattle: before ground disturbance per the attached specification perpendicular to sheet flow direction 2 below grade and backfilled with compacted soil with 16 min. wooden stakes at alternating 45 angle every 3 with ends turned upslope for 2 min. with 1 min. of overlap when joining two sections 2 min. away from the toe of stockpiles or slopes Inspection and Maintenance Perimeter Control Wattle Image 1 Properly installed straw wattle. Inspect wattle per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following tasks: Repair or Replace torn, flattened, pulled out, or unraveled wattle. Repair holes by resecuring the netting using wire, twine, or rope. Cut out and replace degraded sections, ensuring to overlap with existing wattle. Replace stakes that have been broken, dislodged, or removed using a mallet or hammer. Maintain once sediment accumulation reaches a depth of 3. Remove collected sediment using hand tools. Remove once the site reaches final stabilization is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground and throw away waste. 7

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9 Introduction Silt fence slows, ponds, filters, and disperses stormwater flowing from land disturbance, pollutant storage, and material stockpile areas. Approved silt fence consists of woven geotextile fabric attached to wooden stakes. Contractors must consider their site s size, soil condition, and topography before selecting and installing silt fence. Installation Requirements Install silt fence: before ground disturbance per the attached specification perpendicular to sheet flow direction with stakes on the down gradient side 6 below grade in a J configuration and backfilled with compacted soil with 3 min. wooden stakes every 10 2 min. away from the toe of stockpiles with ends turned upslope for 5 min. with an adequate overlap when joining two sections Inspection and Maintenance Perimeter Control Silt Fence Image 1 Properly installed silt fence Image 1 Properly installed silt fence Inspect silt fence per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following tasks: Repair or Replace unraveled, flattened, slumped, bypassed, punctured, or torn silt fence. Repair by using a patch or duct tape to cover holes and a staple gun to re-secure fabric to the stakes. Cut out and replace severely degraded sections, ensuring to overlap with existing silt fence. Replace stakes that have been broken, dislodged, or removed using a mallet or hammer Maintain once sediment accumulation reaches a depth of 1/3 of its height. Remove collected sediment using hand tools. Remove once the site reaches final stabilization and is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground and throw away waste. 9

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11 Introduction Perimeter Control Earthen Berm An earthen berm slows, ponds, filters, and, in some cases, conveys stormwater flowing from ground disturbance, pollutant storage, and material stockpile areas. Approved earthen berms consist of compacted soil or stone. Contractors must consider their site s size, soil condition, and topography before selecting, sizing, and installing earthen berms. Installation Requirements Install earthen berms: before ground disturbance per the attached specification with a height of 2 min. and width of 3 min. with ends turned upslope for 5 min. with crimped mulch, compaction, or surface roughening for temporary stabilization Inspection and Maintenance Inspect earthen berm per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following tasks: Repair washed out, eroded, flattened, or bypassed earthen berms. Repair with a piece of equipment or hand tool capable of excavating, contouring, and compacting back to its original shape. Maintain once sediment accumulation reaches 1/3 of its height. Use equipment or hand tools to remove. Remove once the site reaches final stabilization and is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground. Image 1 Installed compacted earthen berm Image 2 Conveyance ditch and compacted earthen berm 11

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13 Introduction Infrastructure Protection Inlet Protection Inlet protection filters stormwater before flowing into the City s infrastructure. Premanufactured devices designed to drop inside inlets are the only approved types. Multiple options exist online and at local retailers. Installation Requirements Install inlet protection: before ground disturbance per the manufacturer s recommendation Inspection and Maintenance Image 1 Properly installed drop inlet protection Inspect inlet control per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following tasks: Replace driven over, torn, or displaced inlet protection. Maintain by removing accumulated sediment using equipment or hand tools. Remove once the site reaches final stabilization and is no longer required. 13

14 Introduction Offsite tracking control agitates and removes sediment from vehicle tires before exiting construction sites. Two types are allowed. Both utilize geotextile and angular rock. One option includes a cattle guard platform. Contractors must consider their site s volume of traffic, underlying soil condition, and site constraints before selecting and installing tracking control. Approved Options 1. Install angular rock: Infrastructure Protection Tracking Control before ground disturbance per the attached specification with a geotextile for separation between undisturbed soils and rock with 1 min. depth of 3-6 angular rock with a length that allows for two full tire rotations 2. Install cattle guard and cobble hybrid: before ground disturbance per the attached specification with a geotextile for separation between undisturbed soils and rock with a 12 min. by 20 min. cattle guard with sediment trap below with 1 min. depth of 3-6 angular rock Inspection and Maintenance Image 1 Properly installed cattle guard entrance Inspect tracking control per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following tasks: Maintain once the aggregate and cattle guard fill with sediment. Refresh the surface by uncompacting and turning over the aggregate. Remove once the site reaches final stabilization and is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground. 14

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16 Introduction A sediment trap captures and holds stormwater flowing from construction sites. An approved sediment trap consists of an excavated basin and a riprapped overflow channel. Contractors must consider their site s size, soil condition, and topography before selecting, sizing, and installing sediment traps. Installation Requirements Install sediment traps: before ground disturbance with a size adequate for its contributing drainage area with a rip-rap outfall made of 3-6 angular rock with temporary stabilization, such as mulch or seeding Inspection and Maintenance Inspect sediment trap per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning as planned. If not, complete one of the following tasks: Infrastructure Protection Sediment Trap Image 1 Properly installed sediment trap Image 2 Rip-rap outlet channel Repair washed out and eroded sediment traps. Repair the sediment trap with a piece of equipment or hand tool to excavate, contour, and compact back to its original shape. Maintain sediment trap once sediment accumulation reaches 1/3 of its height. Use equipment or hand tools to remove. Remove sediment trap or convert to post construction stormwater basin once the site reaches final stabilization and is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground. 16

17 Introduction Infrastructure Protection Dewatering from Excavated Areas and Wells Dewatering control filters pumped water before flowing into underground infrastructure. Contactors must consider the expected volume of water, duration, and site condition before selecting and installing dewatering BMPs. Approved Options 1) Well Pumping Used to lower the water table during utility line and foundation installs. Achieved through the install of well(s) and pumps tied together in a network Image 1 Dewatering filter bag that discharge to a predetermined location(s). Discharge location(s) may include waterways, stormwater infrastructure, or vegetated lands. Installation requirements include: placed in 15 x 15 undisturbed area contained initial discharge (purging of well) reinforced discharge location preventing erosion 3. Excavation Pumping Used to remove accumulated water in an excavated trench, poured foundation, or subsurface sump. Achieved through the placement of a pump in the dug our area, which pushes water through a hose to a predetermined discharge location(s). Discharge location(s) may include stormwater infrastructure and vegetated lands. Installation requirements include: filter sock secured to the discharge hose and placed on a vegetated, riprapped, or solid surface. three rock sock curb checks in place within the downstream curb line rock sock inlet protection in place for the inlet receiving the water Maintenance and Install Requirements Image 1 Below ground containment are Inspect routinely to ensure dewatering controls are functioning resulting in a clear discharge. If not, halt dewatering immediately and: Maintain filter socks, curb checks, or inlet by removing accumulated debris. Maintain discharge location(s) if any noticeable erosion is identified by moving the hose or refortifying the ground surface using 3-6 cobble or stone. Remove once the site reaches final stabilization and is no longer required. Fill, compact, and seed areas of ground disturbance to blend with adjacent ground. 17

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20 Introduction Pollutant Management Concrete Washout and Waste Management A concrete washout contains and dried waste generated from mixer chutes, pump trucks, and other masonry activities. Staff approves several types of concrete washouts. Contractors must consider their sites expected volume of washout and site constraints prior to selecting and installing concrete washouts. Approved Options 1) Reusable or Disposable Product 2) Prefabricated Roll Off or Container 3) Lined Below Ground Containment 4) Lined Above Ground Containment Installation Requirements Install concrete washouts: before concrete and masonry work installed per the attached specification or manufacturer s requirements clearly marked with signage stating Concrete Washout Area of adequate depth and structure to prevent spill and splash over Maintenance and Inspection Requirements Inspect concrete washout per the frequency required in your permit, before rain events, and after rain events to ensure it is functioning. If not, complete one of the following: Image 1 Properly installed below ground containment Image 2 Properly installed disposable product Repair if the liner is leaking or washout is in a state of disrepair. Maintain when the facility reaches 75% capacity. Vacuum or evaporate washout water. Remove all solids and dispose into a roll off dumpster, haul trailer, or solid waste receptacle. Remove concrete washout once the site reaches stabilization and is no longer required. If applicable, fill, compact, and seed areas of ground disturbance to blend with adjacent ground. 20

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23 Stabilization Measures Introduction Stabilization measures reduce erosion, increase infiltration, shorten slope lengths, slow the flow of water, and minimize raindrop impact of disturbed areas during and after construction activities. Approved Options 1. Surface Roughening: Consists of 3 min. depressions running perpendicular to slopes using equipment, such as a grouser or sheep s foot. 2. Crimped Straw Mulch: Consists of weed-free straw with a 12 min. length evenly distributed at a rate of 4000 lbs/acre and crimped into the soil. Straw blowers and hand broadcasting are useful distribution methods. Flat shovels and disc plows work well for crimping. Image 1 Surface Roughening Image 2 Crimped Straw Mulch 3. Wood Mulching: Consists of shredded wood and compost evenly distributed. Apply wood mulch and compost to a depth of Rolled Erosion Control Products: Consists of biodegradable erosion control blanket composed of fibers such as jute, straw, coconut, or a combination of straw and coconut fibers. Installation criteria to consider: anchor slots, overlapping adjacent blankets, check dams, and staking. Image 3 Wood Mulching 5. Sod: Immediately stabilizes disturbed areas. Consider sod type, soil preparation, soil amendments, and irrigation until establishment. Image 4 Erosion Control Product 23