13.46.220 Minimum Requirement No. 2 – Construction storm water pollution prevention plan (SWPPP).
A. If the site is covered under Ecology’s general NPDES permit for storm water discharges associated with construction activities, the requirements of that permit shall be fully implemented to fulfill this requirement.
B. All new development or redevelopment projects are responsible for preventing erosion and discharge of sediment and other pollutants into receiving waters. A construction storm water pollution prevention plan (SWPPP) is required for all projects which meet the thresholds in the Stormwater Manual. The SWPPP shall be implemented beginning with initial soil disturbance and until final stabilization.
C. Sediment and erosion control BMPs shall be consistent with the BMPs contained in Volume II of the Stormwater Management Manual for Western Washington and/or other equivalent BMPs contained in technical storm water manuals approved by the Department of Ecology.
D. From October 1st through April 30th, clearing, grading and other soil disturbing activities may only be authorized by the city if silt-laden runoff will be prevented from leaving the site through a combination of the following:
1. Site conditions including existing vegetative coverage, slope, soil type and proximity to receiving waters; and
2. Limitations on activities and the extent of disturbed areas; and
3. Proposed erosion and sediment control measures.
E. Based on information provided and/or local weather conditions, the city may expand or restrict the seasonal limitation on site disturbance. The following activities are exempt from the seasonal clearing and grading limitations:
1. Routine maintenance and necessary repair of erosion and sediment control BMPs;
2. Routine maintenance of public facilities or existing utility structures that does not expose the soil or result in the removal of the vegetative cover to soil; and
3. Activities where there is one hundred percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities.
F. The construction site operator shall include each of the twelve elements below in the SWPPP and ensure that they are implemented unless site conditions render the element unnecessary and the exemption from that element is clearly justified in the SWPPP. The SWPPP shall include both narrative and drawings. All BMPs shall be clearly referenced in the narrative and marked on the drawings. The SWPPP narrative shall include documentation to explain and justify the pollution prevention decisions made for the project.
1. Element One – Preserve Vegetation/Mark Clearing Limits.
a. 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.
b. The duff layer, native top soil, and natural vegetation shall be retained in an undisturbed state to the maximum degree practicable.
2. Element Two – Establish Construction Entrance.
a. Construction vehicle access and exit shall be limited to one route, if possible.
b. Access points shall be stabilized with quarry spalls, crushed rock or other equivalent BMP to minimize the tracking of sediment onto public roads.
c. Wheel wash or tire baths shall be located on-site, if stabilized construction entrance is not effective in preventing sediment from being tracked onto public roads.
d. If sediment is tracked off-site, affected roads shall be cleaned thoroughly at the end of each day, or more frequently during wet weather. Sediment shall be removed from roads by shoveling or pickup sweeping and shall by transported to a controlled sediment disposal area.
e. Street washing is allowed only after sediment is removed in accordance with subsection (F)(2)(d) of this section. Street wash wastewater shall be controlled by pumping back on-site or otherwise be prevented from discharging into systems tributary to waters of the state.
3. Element Three – Control Flow Rates.
a. Properties and waterways downstream from development sites shall be protected from erosion due to increases in the velocity and peak volumetric flow rate of storm water runoff from the project site.
b. Where necessary to comply with subsection (F)(3)(a) of this section, storm water retention or 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).
c. If permanent infiltration ponds are used for flow control during construction, these facilities should be protected from siltation during the construction phase.
4. Element Four – Install Sediment Controls.
a. Storm water runoff from disturbed areas shall pass through a sediment pond, or other appropriate sediment removal BMP, prior to leaving a construction site or prior to discharge to an infiltration facility. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but shall meet the flow control performance standard of subsection (F)(3)(a) of this section.
b. Sediment control BMPs (sediment ponds, traps, filters, etc.) shall be constructed as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place.
c. BMPs intended to trap sediment on-site shall be located in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages.
5. Element Five – Stabilize Soils.
a. Exposed and unworked soils shall be stabilized by application of effective BMPs that prevent erosion.
b. No soil should remain exposed and unworked for more than the time periods set forth below to prevent erosion:
i. During the dry season (May 1st through September 30th): seven days;
ii. During the wet season (October 1st through April 30th): two days.
c. Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast.
d. Soil stockpiles must be stabilized from erosion, protected with sediment-trapping measures, and, where possible, be located away from storm drain inlets, waterways and drainage channels.
6. Element Six – Protect Slopes.
a. Design and construct cut and fill slopes in a manner that will minimize erosion.
b. Off-site storm water (run-on) or ground water shall be diverted away from slopes and undisturbed areas with interceptor dikes, pipes and/or swales. Off-site storm water should be managed separately from storm water generated on the site.
c. At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. Temporary pipe slope drains shall handle the expected peak ten-minute flow velocity from a Type 1A, ten-year, twenty-four-hour frequency storm for the developed condition. Alternatively, the ten-year, one-hour flow rate predicted by an approved continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic analysis shall use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis shall use the temporary or permanent project land cover condition, whichever will produce the highest flow rates. If using the Western Washington Hydrology Model to predict flows, bare soil areas should be modeled as “landscaped area.”
d. Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations.
e. Check dams shall be placed at regular intervals within constructed channels that are cut down a slope.
7. Element Seven – Protect Drain Inlets.
a. Storm drain inlets made operable during construction shall be protected so that storm water runoff does not enter the conveyance system without first being filtered or treated to remove sediment.
b. Inlet protection devices shall 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).
8. Element Eight – Stabilize Channels and Outfalls.
a. All temporary on-site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from the following expected peak flows. Channels shall handle the expected peak ten-minute flow velocity from a Type 1A, ten-year, twenty-four-hour frequency storm for the developed condition. Alternatively, the ten-year, one-hour flow rate predicted by an approved continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic analysis shall use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis shall use the temporary or permanent project land cover condition, whichever will produce the highest flow rates. If using the Western Washington Hydrology Model to predict flows, bare soil areas should be modeled as “landscaped area.”
b. Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems.
9. Element Nine – Control Pollutants.
a. All pollutants, including waste materials and demolition debris that occur on-site, shall be handled and disposed of in a manner that does not cause contamination of storm water.
b. Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks shall include secondary containment.
c. Maintenance, fueling and repair of heavy equipment and vehicles shall be conducted using spill prevention and control measures. Contaminated surfaces shall be cleaned immediately following any spill incident.
d. Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system or to the sanitary sewer with local sewer district approval.
e. Application of fertilizers and pesticides shall be conducted in a manner and at application rates that will not result in loss of chemical to storm water runoff. Manufacturers’ label requirements for application rates and procedures shall be followed.
f. BMPs shall be used to prevent or treat contamination of storm water 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, dewatering concrete vaults, concrete pumping and mixer washout waters. Construction site operators are required to adjust the pH of storm water if necessary to prevent violations of water quality standards.
g. Construction site operators are required to obtain written approval from the city prior to using chemical treatment other than CO2 or dry ice to adjust pH.
10. Element Ten – Control De-Watering.
a. Foundation, vault, and trench de-watering water, which have similar characteristics to storm water runoff at the site, shall be discharged into a controlled conveyance system prior to discharge to a sediment trap or sediment pond.
b. Clean, nonturbid de-watering water, such as well-point ground water, can be discharged to systems tributary to, or directly into, surface waters of the state, as specified in subsection (F)(8) of this section, provided the de-watering flow does not cause erosion or flooding of receiving waters. Clean de-watering water should not be routed through storm water sediment ponds.
c. Other de-watering disposal options may include:
i. Infiltration;
ii. Transport off-site in vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters;
iii. On-site chemical treatment or other suitable treatment technologies approved by the city;
iv. Sanitary sewer discharge with local sewer district approval, if there is no other option; or
v. Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized de-watering.
d. Highly turbid or contaminated dewatering water shall be handled separately from storm water.
11. Element Eleven – Maintain BMPs.
a. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired as needed to assure continued performance of their intended function in accordance with BMP specifications.
b. All temporary erosion and sediment control BMPs shall be removed within thirty days after final site stabilization is achieved or after the temporary BMPs are no longer needed.
12. Element Twelve – Manage the Project.
a. Development projects shall be phased to the maximum degree practicable and shall take into account seasonal work limitations.
b. Construction site operators are required to maintain, and repair as needed, all sediment and erosion control BMPs to assure continued performance of their intended function.
c. Construction site operators are required to periodically inspect their sites. Site inspections shall be conducted by a certified erosion and sediment control lead who shall be identified in the SWPPP and shall be present on-site or on-call at all times.
d. Construction site operators are required to maintain, update and implement their SWPPP. Construction site operators are required to modify their SWPPP whenever there is a change in 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. Such modifications shall be submitted and approved by the city prior to implementation. (Ord. 1205-22 § 7, 2022; Ord. 1032-10 § 2).