1.4.2 Minimum Requirement 2 - Construction Stormwater Pollution Prevention
All new development and redevelopment projects are responsible for preventing erosion and discharge of sediment and other pollutants into receiving waters.
Projects that meet or exceed the thresholds in Applicability of the Minimum Requirements and Additional Protective Measures must prepare a Construction Stormwater Pollution Prevention Plan (SWPPP).
Projects below the thresholds in Applicability of the Minimum Requirements and Additional Protective Measures are not required to prepare a Construction SWPPP but must consider the 13 Elements of a SWPPP and develop controls for all SWPPP Elements that pertain to the project.
The Construction SWPPP shall include all information as required in Volume 2 - Documentation.
The Construction SWPPP shall be implemented beginning with initial land disturbance and continuing until final project site stabilization. Sediment and erosion control BMPs shall be consistent with those in Volume 3 of this manual.
1.4.2.1 The 13 Elements of Construction Stormwater Pollution Prevention
Element #1: Preserve Vegetation and Mark Clearing Limits
Element #2: Establish Construction Access
Element #3: Control Flow Rates
Element #4: Install Sediment Controls
Element #7: Protect Stormwater System Inlets
Element #8: Stabilize Channels and Outlets
Element #9: Control Pollutants
Element #10: Control Dewatering
Element #12: Manage the Project
Element #13: Protect Permanent Stormwater BMPs
Element #1: Preserve Vegetation and Mark Clearing Limits
Before beginning any 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 to prevent damage and offsite impacts. Mark clearing limits both in the field and on the plans.
Retain the duff layer, native topsoil, and natural vegetation in an undisturbed state to the maximum degree practicable. If it is not practicable to retain the duff layer in place, stockpile it onsite, cover it to prevent erosion, and replace it immediately upon completion of the ground-disturbing activities.
Plastic, metal, fabric fence, or other physical barriers may be used to mark the clearing limits.
Suggested BMPs (Refer to Volume 3):
BMP C101 - Preserving Natural Vegetation
BMP C103 - High Visibility Fence
Element #2: Establish Construction Access
Limit construction vehicle ingress and egress to one route, if possible.
Stabilize access points with a pad of quarry spalls, crushed rock, or other equivalent BMPs to minimize tracking of sediment.
Locate wheel wash or tire baths onsite if other measures fail to control sediment from leaving the site.
No tracking of sediment offsite is allowed. If sediment is tracked offsite, offsite areas (including roadways) shall be thoroughly and immediately cleaned by shoveling or pickup sweeping. Transport sediment to a controlled sediment disposal area.
Keep streets clean at ALL times. Clean tracked sediment immediately.
Washing of sediment to the stormwater system is not allowed.
Suggested BMPs (Refer to Volume 3):
BMP C105 - Stabilized Construction Entrance and Exit
BMP C107 - Construction Road/Parking Area Stabilization
Element #3: Control Flow Rates
Protect downstream properties, receiving waters, and conveyance systems from erosion and other damage due to increases in the velocity and peak volumetric flowrate of stormwater from the project site. A quantitative downstream analysis may be required to ensure no damage to the downstream conveyance system during construction. See Additional Protective Measure - Infrastructure Protection.
Where necessary, construct flow control facilities as one of the first steps in grading. Flow control facilities shall be functional prior to construction of site improvements (e.g. impervious surfaces). It may be necessary to install temporary flow control facilities to meet flow control requirements during construction.
Control structures designed for permanent flow control BMPs are not appropriate for use during construction without modification. If used during construction, modify the control structure to allow for long-term storage of runoff and enable sediments to settle. Verify that the BMP is sized appropriately for this purpose. Restore BMPs to their original design dimensions, remove sediment, and install a final control structure at completion of the project.
Velocity of water leaving the site shall not exceed 3 feet/second if the discharge is to a stream or ditch.
Permanent infiltration facilities shall not be used for flow control during construction unless lined. The bottom of the facility shall be scarified to ensure any compaction that occurred during construction is mitigated.
Suggested BMPs (Refer to Volume 3):
BMP C241 - Temporary Sediment Pond
BMP C253 - Portable Sediment Tank
Element #4: Install Sediment Controls
Design, install, and maintain effective erosion controls and sediment control to minimize the discharge of pollutants.
Minimize sediment discharges from the site. The design, installation and maintenance of erosion and sediment controls must address factors such as the amount, frequency, intensity and duration of precipitation, the nature of resulting stormwater, and soil characteristics, including the range of soil particle sizes expected to be present on the site.
Prior to leaving a construction site or prior to discharge to an infiltration facility, stormwater from disturbed areas shall pass through a sediment removal BMP.
Construct sediment control BMPs as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place.
Locate BMPs in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or conveyance channels.
Provide and maintain natural buffers around surface waters, direct stormwater to vegetated areas to increase sediment removal and maximize infiltration, where feasible.
Seed and mulch earthen structures such as dams, dikes, and diversions according to the timing indicated in Element #5.
Design outlet structures to withdraw impounded stormwater from the surface to avoid discharging sediment that is still suspended lower in the water column. If installing a floating pump structure, include a stopper to prevent the pump basket from hitting the bottom of the pond.
Full stabilization includes 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.
Suggested BMPs (Refer to Volume 3):
BMP C241 - Temporary Sediment Pond
BMP C250 - Construction Stormwater Chemical Treatment
BMP C251 - Construction Stormwater Filtration
Emerging technologies exist that can be used for sediment control. The applicant can utilize any BMP that has been approved by Ecology via the Construction Technical Assessment Protocol Ecology program.
Stabilize exposed and unworked soils by application of effective BMPs that prevent erosion.
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 stabilization requirement applies to all soils onsite, whether at final grade or not.
Stabilize soils at the end of the shift, before a holiday or weekend, if needed, based on the weather forecast.
Select appropriate soil stabilization measures for the time of year, site conditions, estimated duration of use, and the potential water quality impacts that stabilization agents may have on downstream waters or groundwater.
Stabilize soil stockpiles from erosion, protect stockpiles with sediment trapping measures, and where possible, locate piles away from stormwater system inlets, waterways, and conveyance channels.
Control stormwater volume and velocity within the site to minimize soil erosion.
Control stormwater discharges, including peak volumetric flowrates and total stormwater volume, to minimize erosion at outlets and to minimize downstream channel and stream bank erosion.
Minimize the amount of soil exposed during construction activity.
Minimize the disturbance of steep slopes.
Minimize soil compaction and, unless infeasible, preserve topsoil.
Ensure the gravel base used for stabilization is clean and does not contain fines or sediment.
Suggested BMPs: (Refer to Volume 3)
BMP C120 - Temporary and Permanent Seeding
BMP C127 - Polyacrylamide for Soil Erosion Protection
Design and construct cut-and-fill slopes in a manner to minimize erosion. Applicable practices include, but are not limited to, reducing continuous length of slope with terracing and diversions, reducing slope steepness, and roughening slope surfaces (for example, track walking).
Divert offsite stormwater (sometimes called run-on) or groundwater away from slopes and disturbed areas with interceptor dikes and/or swales. Manage offsite stormwater separately from stormwater generated on the site.
At the top of the slopes, collect stormwater in pipe slope drains or protected channels to prevent erosion. Size temporary pipe slope drains to convey either:
The peak volumetric flowrate calculated using a 10-minute time step from a Type 1A, 10-year, 24-hour frequency storm using a single event model, or
The 10-year return period flowrate, indicated by an Ecology-approved continuous simulation model, using a 15-minute time step.
Use the existing land cover condition for predicting flowrates from tributary areas outside the project limits. For tributary areas on the project site, use the temporary or permanent project land cover condition, whichever will produce the highest flowrate. If using, a continuous simulation model, model bare soils as landscaped areas.
Provide temporary or permanent conveyance to remove groundwater seepage from the slope surface of exposed soil areas.
Place excavated material on the uphill side of trenches, consistent with safety and space considerations.
Place check dams at regular intervals within channels that are cut down a slope.
Stabilize soils on slopes, as specified in Element #5.
Suggested BMPs (Refer to Volume 3):
BMP C120 - Temporary and Permanent Seeding
BMP C200 - Interceptor Dike and Swale
BMP C201 - Grass-Lined Channels
BMP C208 - Triangular Silt Dike (Geotextile-Encased Check Dam)
Element #7: Protect Stormwater System Inlets
Protect all stormwater system inlets that are operable during construction so that stormwater does not enter the conveyance system without first being filtered or treated to remove sediment.
Clean or remove and replace inlet protection devices when sediment has filled 1/3 of the available storage (unless a different standard is specified by the product manufacturer).
Keep all approach roads clean. Do not allow sediment to enter the stormwater system.
Inspect inlets weekly at a minimum and daily during storm events.
Suggested BMPs (Refer to Volume 3):
BMP C220 - Stormwater System Inlet Protection
Element #8: Stabilize Channels and Outlets
Design, construct, and stabilize all temporary onsite conveyance channels to prevent erosion from either:
The peak volumetric flowrate calculated using a 10-minute time step from a Type 1A, 10-year, 24-hour frequency storm using a single event model, or
The 10-year return period flowrate, indicated by an Ecology-approved continuous simulation model, using a 15-minute time step.
Use the existing land cover condition for predicting flowrates from tributary areas outside the project limits. For tributary areas on the project site, use the temporary or permanent project land cover condition, whichever will produce the highest flowrate. If using a continuous simulation model, model bare soils as landscaped areas.
Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches at the outlets of all conveyance systems.
Suggested BMPs (Refer to Volume 3):
BMP C202 - Rip Rap Channel Lining
Element #9: Control Pollutants
Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants.
All discharges to the City of Tacoma wastewater system require City approval. Some discharges to the City of Tacoma stormwater system require City approval. The approval may include a separate Special Approved Discharge (SAD) permit. Visit https://www.cityoftacoma.org/government/city_departments/environmentalservices/wastewater/wastewater_permits_and_manuals for additional information about SAD permits.
Handle and dispose of all pollutants, including waste materials and demolition debris that occur on site in a manner that does not cause contamination of stormwater.
Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health and the environment. Provide secondary containment for tanks holding pollutants including onsite fueling tanks. Secondary containment means placing tanks or containers within an impervious structure capable of containing 110% of the volume contained in the largest tank within the containment structure. Double-walled tanks do not require additional secondary containment.
Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident.
Conduct oil changes, hydraulic system drain down, solvent and degreasing 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 using spill prevention measures, such as drip pans.
Discharge wheel wash or tire bath wastewater to a separate onsite treatment system that prevents discharge to surface water. Alternatively, discharge wheel wash or tire bath wastewater to the wastewater system (only allowed with SAD Permit approval).
Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of chemicals to stormwater. Follow manufacturers’ recommendations for application rates and procedures.
Use BMPs to prevent or treat contamination of stormwater by pH modifying sources. These sources include, but are not limited to, recycled concrete stockpiles, bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, and concrete pumping and mixer washout waters.
Adjust the pH of stormwater if necessary to prevent violations of water quality standards.
Manage concrete washout appropriately.
Washout concrete truck drums or concrete handling equipment in onsite or offsite designated concrete washout areas only.
Do not washout concrete truck drums or concrete handling equipment to streets, the stormwater system, receiving waterbodies, or the ground.
Washout of small concrete handling equipment may be disposed of in a formed areas awaiting concrete where it will not contaminate stormwater and surface water or groundwater.
Do not use upland land applications for discharging wastewater from concrete washout areas.
Do not dump excess concrete onsite, except in designated concrete washout areas.
Do not washout anything contaminated with concrete into formed areas awaiting infiltration BMPs.
Concrete spillage or concrete discharge directly to groundwater or surface waters of the State is prohibited.
Written approval from the Department of Ecology is required prior to using chemical treatment other than CO2, dry ice, or food grade vinegar to adjust pH.
Clean contaminated surfaces immediately following any discharge or spill incident.
Uncontaminated water from water-only based shaft drilling for construction of building, road, and bridge foundations may be infiltrated provided the wastewater is managed in a way that prohibits discharge to surface waters. Prior to infiltration, water from water-only based shaft drilling that comes into contact with curing concrete must be neutralized until pH is in the range of 6.5 to 8.5.
Suggested BMPs (Refer to Volume 3):
BMP C152 - Sawcutting and Surfacing Pollution Prevention
BMP C153 - Material Delivery, Storage and Containment
BMP C154 - Concrete Washout Area
BMP C250 - Construction Stormwater Chemical Treatment
BMP C251 - Construction Stormwater Filtration
BMP C252 - Treating and Disposing of High pH Water
Source Control BMPs from Volume 6, as appropriate.
Element #10: Control Dewatering
Dewatering discharges to the City of Tacoma stormwater conveyance system or the City of Tacoma wastewater system may require City approval through a Special Approved Discharge (SAD) Permit. See https://www.cityoftacoma.org/government/city_departments/environmentalservices/wastewater/wastewater_permits_and_manuals for more information on the SAD Permit Process.
Discharge foundation, vault, and trench dewatering water that has similar characteristics to site stormwater into a controlled conveyance system prior to discharge to a sediment trap or sediment pond. Stabilize channels as specified in Element #8.
Clean, non-turbid dewatering water, such as well-point groundwater, can be discharged to systems tributary to state surface waters, as specified in Element #8, provided the dewatering flow does not cause erosion or flooding of receiving waters. Do not route clean dewatering water through TESC BMPs.
Handle highly turbid or contaminated dewatering water separately from stormwater at the site.
Other disposal options, depending on site constraints, may include:
Transport offsite in vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters
Ecology approved onsite chemical treatment or other suitable treatment technologies
Use of a sedimentation bag that discharges to a ditch or swale for small volumes of localized dewatering
Suggested BMPs (Refer to Volume 3):
BMP C236 - Vegetative Filtration
BMP C250 - Construction Stormwater Chemical Treatment
BMP C251 - Construction Stormwater Filtration
Maintain and repair as needed all temporary and permanent erosion and sediment control BMPs to assure continued performance of their intended function. Conduct maintenance and repairs in accordance with BMP specifications.
Remove temporary erosion and sediment control BMPs 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 onsite. Permanently stabilize disturbed soil resulting from removal of BMPs or vegetation.
Suggested BMPs (Refer to Volume 3):
BMP C160 - Erosion and Sediment Control Lead
Element #12: Manage the Project
Phasing of Construction – Phase development projects in order to prevent soil erosion and the transport of sediment from the project site during construction, unless the Erosion and Sediment Control Lead can demonstrate that construction phasing is infeasible. Revegetation of exposed areas and maintenance of that vegetation shall be an integral part of the clearing activities for any phase.
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 City that silt-laden stormwater will be prevented from leaving the site through a combination of the following:
Site conditions including existing vegetative coverage, slope, soil type, and proximity to receiving waters;
Limitations on activities and the extent of disturbed areas; and
Proposed erosion and sediment control measures.
Based on the information provided and local weather conditions, the City may expand or restrict the seasonal limitation onsite disturbance. The following activities are exempt from the seasonal clearing and grading limitations:
Routine maintenance and necessary repair of erosion and sediment control BMPs
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
Activities where there is one hundred percent infiltration of stormwater within the site in approved and installed erosion and sediment control facilities
Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Projects regulated under the Construction Stormwater General Permit (CSWGP) must conduct site inspections and monitoring in accordance with Special Condition S4 of the CSWGP.
Projects that disturb one or more acres must have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL) or Certified Professional in Erosion and Sediment Control (CPESC).
Projects disturbing less than one acre must have an Erosion Sediment Control Lead (ESC) conduct inspections. The ESC Lead does not have to have CESCL or CPESC certification.
The CESCL, CPESC, or ESC Lead shall be identified in the SWPPP and shall be onsite or on-call at all times.
The CESCL, CPESC, or ESC Lead must examine stormwater visually for the presence of suspended sediment, turbidity, discoloration, and oil sheen and evaluate the effectiveness of BMPs to determine if it is necessary to install, maintain, or repair BMPs.
The CESCL, CPESC, or ESC Lead must inspect all areas disturbed by construction activities, all BMPs, and all locations where stormwater leaves the site at least once every calendar week and within 24 hours of any discharge from the site. (Individual discharge events that last more than one day do not require daily inspections). The CESCL, CPESC, or ESC Lead may reduce the inspection frequency for temporary stabilized, inactive sites to once every calendar month.
Construction site operators must correct any problems identified by the CESCL, CPESC, or ESC Lead by:
Reviewing the SWPPP for compliance with the 13 construction SWPPP elements and making appropriate revisions within 7 days of the inspection.
Fully implementing and maintaining appropriate source control and/or treatment BMPs as soon as possible but correcting the problem within 10 days.
Documenting BMP implementation and maintenance in the site log book. (Required for sites larger than 1 acre but recommended for all sites).
Sampling and analysis of the stormwater discharges from a construction site may be necessary on a case-by-case basis to ensure compliance with standards. Ecology or the City will establish these monitoring and associated reporting requirements.
Responsible Party – For all projects, a 24-hour responsible party shall be listed in the SWPPP, along with that person’s telephone number and email address.
Maintenance of the Construction SWPPP – Keep the Construction SWPPP onsite or within reasonable access to the site. Modify the SWPPP 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.
Modify the SWPPP if, during inspections or investigations conducted by the owner/operator, City staff, or by local or state officials, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. Modify the SWPPP as necessary to include additional or modified BMPs designed to correct problems identified. Complete revisions to the SWPPP within seven (7) days following the inspection. City of Tacoma Environment Services (review staff or inspector) may require that a modification to the SWPPP go through additional City review.
Suggested BMPs (Refer to Volume 3):
BMP C160 - Erosion and Sediment Control Lead
Element #13: Protect Permanent Stormwater BMPs
Protect all permanent stormwater BMPs from sedimentation through installation and maintenance of erosion and sediment control BMPs on portions of the site that drain into the BMPs. Restore all BMPs to their fully functioning condition if they accumulate sediment during construction. Sediment impacting Best Management Practices shall be removed before system start-up. Restoring the BMP shall include removal of all sediment and full replacement of treatment media.
Prevent compacting infiltration facilities by excluding construction equipment and foot traffic.
Keep all heavy equipment off native soils under infiltration BMPs that have been excavated to final grade to retain the infiltration rate of the soils.
Protect lawn and landscaped areas from compaction due to construction equipment and material stockpiles.
Do not allow muddy construction equipment on the base material of permeable pavement or on the permeable pavement section.
Do not allow sediment laden runoff onto permeable pavements or base materials of permeable pavements.
Permeable pavements fouled with sediment or that can no longer pass an initial infiltration test must be cleaned prior to final acceptance.
Suggested BMPs (Refer to Volume 3):
BMP C103 - High Visibility Fence
BMP C200 - Interceptor Dike and Swale
BMP C201 - Grass-Lined Channels
BMP C208 - Triangular Silt Dike (Geotextile-Encased Check Dam)
The intent of Stormwater Pollution Prevention is to control erosion and prevent sediment and other pollutants from leaving the site during the construction phase of a project and to have fully functional stormwater facilities and BMPs for the developed site upon completion of construction.