Construction and stormwater

proper erosion control with silt fence and straw
Good: A silt fence and straw help to
prevent erosion at this construction site.

Developers, contractors, and others in the construction industry have some of the highest levels of responsibility regarding stormwater pollution prevention.  Stormwater runoff from construction sites can carry muddy water, debris, and chemicals into local waterways. Sediments, chemicals, and debris can harm aquatic life and reduce water quality.   

Knowing and following best management practices that prevent pollution can save you money by keeping your project on track and avoiding penalties.  Be sure to know the codes and stormwater development requreiments of the jurisdiciton in which work is being performed before undergoing any land distrubing activiites.  

 

Erosion and sediment control

When construction activities leave soils exposed to the elements muddy water from sites can

potential sediment pollution at construction site
Silt barriers and straw should be used to
control erosion and prevent sediment from
running off.

empty directly into a storm drain and pollute nearby waterways.  Here are some quick tips for reducing erosion and sediment pollution:

Do not disturb more area than needed for construction.

Stabilize exposed soils to minimize erosion with straw or temporary or permenant seeding. 

Protect drainage inlets in roadways with biofilter bags, silt catch basin inserts or block and gravel barriers.

Shovel or sweep soil and debris off of the roadway or sidewalk and back onto the site where it won't runoff in a rain event.

Maintain vegetation that will help trap sediment and minimize erosion

The Washington State Construction Stormwater General Permit requires that site inspections be conducted by a Certified Erosion and Sediment Control Lead (CESCL). Washington Department of Ecology keeps a list of CESCL inspectors and training programs. Certificates last three years from the training date. Find a Certified Erosion and Sediment Control Lead or learn how to become one here.

Construction stormwater pollution prevention

Washington Department of Ecology requires the 12 Elements listed below be considered in the development of the Construction Stormwater Pollution Prevention Plan (SWPPP) unless site conditions render the element unnecessary. If an element is considered unnecessary, the Construction SWPPP must provide the justification. 

  • Prior to beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits, sensitive areas and their buffers, and trees that are to be preserved within the construction area. These shall be clearly marked, both in the field and on the plans, to prevent damage and offsite impacts.
  • Plastic, metal, or stake wire fence may be used to mark the clearing limits.
  • The duff layer, native top soil, and natural vegetation shall be retained in an undisturbed state to the maximum extent practicable. If it is not practicable to retain the duff layer in place, it should be stockpiled onsite, covered to prevent erosion, and replaced immediately upon completion of the ground disturbing activities. 

Suggested BMPs: 

  • BMP C101: Preserving Natural Vegetation
  • BMP C102: Buffer Zones
  • BMP C103: High Visibility Plastic or Metal Fence
  • BMP C104: Stake and Wire Fence
  • Construction vehicle access and exit shall be limited to one route, if possible, or two for linear projects such as roadways where more than one access is necessary for large equipment maneuvering.
  • Access points shall be stabilized with a pad of quarry spalls or crushed rock prior to traffic leaving the construction site to minimize the tracking of sediment onto public roads.
  • Wheel wash or tire baths should be located on site, if applicable. February 2005 Volume II – Construction Stormwater Pollution Prevention 3-7
  • If sediment is tracked off site, public roads shall be cleaned thoroughly at the end of each day, or more frequently during wet weather, if necessary to prevent sediment from entering waters of the state. Sediment shall be removed from roads by shoveling or pickup sweeping and shall be transported to a controlled sediment disposal area. Street washing will be allowed only after sediment is removed in this manner.
  • Street wash wastewater shall be controlled by pumping back on site or otherwise be prevented from discharging into systems tributary to state surface waters.

Suggested BMPs

  • BMP C105: Stabilized Construction Entrance
  • BMP C106: Wheel Wash
  • BMP C107: Construction Road/Parking Area Stabilization
  • Properties and waterways downstream from development sites shall be protected from erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site, as required by local plan approval authority.
  • Downstream analysis is necessary if changes in offsite flows could impair or alter conveyance systems, streambanks, bed sediment, or aquatic habitat. See Chapter 3 for offsite analysis guidelines.
  • Where necessary to comply with Minimum Requirement #7, stormwater retention/detention facilities shall be constructed as one of the first steps in grading. Detention facilities shall be functional prior to construction of site improvements (e.g. impervious surfaces).
  • The local permitting agency may require pond designs that provide additional or different stormwater flow control if necessary to address local conditions or to protect properties and waterways downstream from erosion due to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site.
  • If permanent infiltration ponds are used for flow control during construction, these facilities should be protected from siltation during the construction phase.

Suggested BMPs

  • BMP C240: Sediment Trap
  • BMP C241: Temporary Sediment Pond Refer to Volume 3, Detention Facilities, Infiltration Stormwater Quantity and Flow Control
  • Prior to leaving a construction site or prior to discharge to an infiltration facility, stormwater runoff from disturbed areas shall pass through a sediment pond or other appropriate sediment removal BMP. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but must meet the flow control performance standard of Element #3, bullet #1. Full stabilization means concrete or asphalt paving; quarry spalls used as ditch lining; or the use of rolled erosion products, a bonded fiber matrix product, or vegetative cover in a manner that will fully prevent soil erosion. The Local Permitting Authority shall inspect and approve areas fully stabilized by means other than pavement or quarry spalls.
  • Sediment ponds, vegetated buffer strips, sediment barriers or filters, dikes, and other BMPs intended to trap sediment on site shall be constructed as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place.
  • Earthen structures such as dams, dikes, and diversions shall be seeded and mulched according to the timing indicated in Element #5.
  • BMPs intended to trap sediment on site must be located in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages, often during nonstorm events, in response to rain event changes in stream elevation or wetted area.

Suggested BMPs

  • BMP C230: Straw Bale Barrier
  • BMP C231: Brush Barrier
  • BMP C232: Gravel Filter Berm
  • BMP C233: Silt Fence
  • BMP C234: Vegetated Strip
  • BMP C235: Straw Wattles
  • BMP C240: Sediment Trap
  • BMP C241: Temporary Sediment Pond
  • BMP C250: Construction Stormwater Chemical Treatment
  • BMP C251: Construction Stormwater Filtration
  • All exposed and unworked soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrop impact, flowing water, and wind.
  • From October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days. From May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. This condition applies to all soils on site, whether at final grade or not. February 2005 Volume II – Construction Stormwater Pollution Prevention 3-9 These time limits may be adjusted by the local permitting authority if it can be shown that the average time between storm events justifies a different standard.
  • Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast.
  • Applicable practices include, but are not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics and matting, soil application of polyacrylamide (PAM), the early application of gravel base on areas to be paved, and dust control.
  • Soil stabilization measures should be appropriate for the time of year, site conditions, estimated duration of use, and potential water quality impacts that stabilization agents may have on downstream waters or ground water.
  • Soil stockpiles must be stabilized from erosion, protected with sediment trapping measures, and when possible, be located away from storm drain inlets, waterways and drainage channels.
  • Linear construction activities, including right-of-way and easement clearing, roadway development, pipelines, and trenching for utilities, shall be conducted to meet the soil stabilization requirement. Contractors shall install the bedding materials, roadbeds, structures, pipelines, or utilities and re-stabilize the disturbed soils so that: − from October 1 through April 30 no soils shall remain exposed and unworked for more than 2 days and − from May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days.

Suggested BMPs

  • BMP C120: Temporary and Permanent Seeding
  • BMP C121: Mulching
  • BMP C122: Nets and Blankets
  • BMP C123: Plastic Covering
  • BMP C124: Sodding
  • BMP C125: Topsoiling
  • BMP C126: Polyacrylamide for Soil Erosion Protection
  • BMP C130: Surface Roughening
  • BMP C131: Gradient Terraces
  • BMP C140: Dust Control
  • BMP C180: Small Project Construction Stormwater Pollution Prevention
  • Design and construct cut and fill slopes in a manner that will minimize erosion.
  • Consider soil type and its potential for erosion.
  • Reduce slope runoff velocities by reducing continuous length of slope with terracing and diversions, reduce slope steepness, and roughen slope surface.
  • Off-site stormwater (run-on) shall be diverted away from slopes and disturbed areas with interceptor dikes and/or swales. Off-site stormwater should be managed separately from stormwater generated on the site.
  • At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. Temporary pipe slope drains shall handle the peak flow from a 10 year, 24 hour event assuming a Type 1A rainfall distribution. Alternatively, the 10-year and 25-year, 1-hour flow rates indicated by an approved continuous runoff model, increased by a factor of 1.6, may be used. Consult the local drainage requirements for sizing permanent pipe slope drains.
  • Provide drainage to remove ground water intersecting the slope surface of exposed soil areas.
  • Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations.
  • Check dams shall be placed at regular intervals within channels that are cut down a slope.
  • Stabilize soils on slopes, as specified in Element #5.

Suggested BMPs

  • BMP C120: Temporary and Permanent Seeding
  • BMP C130: Surface Roughening
  • BMP C131: Gradient Terraces
  • BMP C200: Interceptor Dike and Swale
  • BMP C201: Grass-Lined Channels
  • BMP C204: Pipe Slope Drains
  • BMP C205: Subsurface Drains
  • BMP C206: Level Spreader
  • BMP C207: Check Dams
  • BMP C208: Triangular Silt Dike (Geotextile-Encased Check Dam)
  • All storm drain inlets made operable during construction shall be protected so that stormwater runoff does not enter the conveyance system without first being filtered or treated to remove sediment.
  • All approach roads shall be kept clean. Sediment and street wash water shall not be allowed to enter storm drains without prior and adequate treatment unless treatment is provided before the storm drain discharges to waters of the state.
  • Inlets should be inspected weekly at a minimum and daily during storm events. Inlet protection devices should be cleaned or removed and replaced when sediment has filled one-third of the available storage (unless a different standard is specified by the product manufacturer).

Suggested BMPs

  • BMP C220: Storm Drain Inlet Protection
  • All temporary on-site conveyance channels shall be designed, constructed and stabilized to prevent erosion from the expected peak 10 minute velocity of flow from a Type 1A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10- year, 1-hour flow rate indicated by an approved continuous runoff model, increased by a factor of 1.6, may be used. 
  • Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent streambanks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems.

Suggested BMPs

  • BMP C202: Channel Lining
  • BMP C209: Outlet Protection
  • All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Woody debris may be chopped and spread on site.
  • Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304 WAC for the definition of inert waste). On-site fueling tanks shall include secondary containment. 3-12 Volume II – Construction Stormwater Pollution Prevention February 2005
  • Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff must be conducted using spill prevention measures, such as drip pans. Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Emergency repairs may be performed on-site using temporary plastic placed beneath and, if raining, over the vehicle.
  • Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system or to the sanitary sewer.
  • Application of agricultural chemicals, including fertilizers and pesticides, shall be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers’ recommendations for application rates and procedures shall be followed.
  • BMPs shall be used to prevent or treat contamination of stormwater runoff by pH modifying sources. These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters. Stormwater discharges shall not cause or contribute to a violation of the water quality standard for pH in the receiving water.
  • Construction sites with significant concrete work shall adjust the pH of stormwater if necessary to prevent violations of water quality standards.

Suggested BMPs

  • BMP C151: Concrete Handling
  • BMP C152: Sawcutting and Surfacing Pollution Prevention See Volume IV – Source Control BMPs

Foundation, vault, and trench de-watering water, which have similar characteristics to stormwater runoff at the site, shall be discharged into a controlled conveyance system prior to discharge to a sediment trap or sediment pond. Channels must be stabilized, as specified in Element #8.

Clean, non-turbid de-watering water, such as well-point ground water, can be discharged to systems tributary to state surface waters, as specified in Element #8, provided the de-watering flow does not cause erosion or flooding of receiving waters. These clean waters should not be routed through stormwater sediment ponds. February 2005 Volume II – Construction Stormwater Pollution Prevention 3-13

Highly turbid or contaminated dewatering water from construction equipment operation, clamshell digging, concrete tremie pour, or work inside a cofferdam, shall be handled separately from stormwater.

Other disposal options, depending on site constraints, may include:

  1. infiltration
  2. transport offsite in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters,
  3. Ecology-approved on-site chemical treatment or other suitable treatment technologies,
  4. sanitary sewer discharge with local sewer district approval, if there is no other option, or
  5. use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized dewatering.
  • All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with BMP specifications.
  • All temporary erosion and sediment control BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs or vegetation shall be permanently stabilized.

Phasing of Construction

Development projects shall be phased where feasible in order to prevent soil erosion and, to the maximum extent practicable, the transport of sediment from the site during construction. Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities for any phase.

Clearing and grading activities for developments shall be permitted only if conducted pursuant to an approved site development plan (e.g., subdivision approval) that establishes permitted areas of clearing, grading, cutting, and filling. When establishing these permitted clearing and grading areas, consideration should be given to minimizing removal of existing trees and minimizing disturbance/compaction of native soils except as needed for building purposes. These permitted clearing and grading areas and any other 3-14 Volume II – Construction Stormwater Pollution Prevention February 2005 areas required to preserve critical or sensitive areas, buffers, native growth protection easements, or tree retention areas as may be required by local jurisdictions, shall be delineated on the site plans and the development site.

Seasonal Work Limitations

From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if shown to the satisfaction of the local permitting authority that silt-laden runoff will be prevented from leaving the site through a combination of the following:

    A. Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters; and

    B. Limitations on activities and the extent of disturbed areas; and

    C. Proposed erosion and sediment control measures.

  • Based on the information provided and/or local weather conditions, the local permitting authority may expand or restrict the seasonal limitation on site disturbance. The local permitting authority shall take enforcement action - such as a notice of violation, administrative order, penalty, or stop-work order under the following circumstances:

   − If, during the course of any construction activity or soil disturbance during the seasonal limitation period, sediment leaves the construction site causing a violation of the surface water quality standard; or

   − If clearing and grading limits or erosion and sediment control measures shown in the approved plan are not maintained. The following activities are exempt from the seasonal clearing and grading limitations:

   A. Routine maintenance and necessary repair of erosion and sediment control BMPs;

   B. Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil; and

   C. Activities where there is one hundred percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities.

Coordination with Utilities and Other Contractors

The primary project proponent shall evaluate, with input from utilities and other contractors, the stormwater management requirements for February 2005 Volume II – Construction Stormwater Pollution Prevention 3-15 the entire project, including the utilities, when preparing the Construction SWPPP.

Inspection and Monitoring

All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections shall be conducted a person who is knowledgeable in the principles and practices of erosion and sediment control. The person must have the skills to 1) assess the site conditions and construction activities that could impact the quality of stormwater, and 2) assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges.

For construction sites one acre or larger that discharge stormwater to surface waters of the state, a Certified Erosion and Sediment Control Specialist shall be identified in the Construction SWPPP and shall be on-site or on-call at all times. Certification may be obtained through an approved training program that meets the erosion and sediment control training standards established by Ecology. Whenever inspection and/or monitoring reveals that the BMPs identified in the Construction SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant amount of any pollutant, appropriate BMPs or design changes shall be implemented as soon as possible.

Maintaining an Updated Construction SWPPP

The Construction SWPPP shall be retained on-site or within reasonable access to the site. The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection.

  • Protect all Bioretention and Rain Garden facilities from sedimentation through installation and maintenance of erosion and sediment control BMPs. 
  • Restore LID facilities to fully functioning condition if they accumulate sediment during construction. 
  • Maintain the infiltration capabilities of Bioretention and Rain Garden facilities by protecting against compaction. 
  • Control erosion and avoid introducing sediment into permeable pavements. Clean 12 permeable pavements fouled with sediments or no longer pass an initial infiltration test. 
  • Keep heavy equipment off existing soils under LID facilities that have been excavated to final grade to retain the soil infiltration rate.