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A. Purpose. The purpose of minimum requirement 2 is to prevent erosion and the discharge of sediment and other pollutants into the storm and surface water system and receiving waters using appropriate BMPs and site management techniques.

B. Applicability.

1. Minimum Requirement 2. This section describes requirements for applicants to prepare a CSWPPP for new development, redevelopment, and land disturbing activities that meet the thresholds set forth in this chapter. Applicants and permittees are responsible for preventing erosion and discharge of sediment and other pollutants into the storm and surface water system and receiving waters. The city does not offer erosivity waivers.

2. Applicants and permittees shall comply with all applicable provisions of the Bellevue City Code, rules, standards, and manuals adopted for this chapter and Chapter 24.06 BCC including, but not limited to, Chapter 24.06 (Storm and Surface Water Code) and corresponding engineering standards, BCC Title 20 (Land Use Code), the clearing and grading development standards, all other applicable codes and standards, and the Ecology Manual, now or as hereafter amended.

3. Exemption. The director may exempt the following projects from the requirements of preparing a CSWPPP:

a. Projects that are covered under the Washington State Department of Ecology’s construction stormwater general permit and the permittee is fully implementing and in compliance with the requirements of that permit. To apply for this exemption, the applicant must provide with its permit application materials a copy of the permit coverage letter from the Washington State Department of Ecology, and a copy of the corresponding stormwater pollution prevention plan (SWPPP).

b. Projects that involve clearing of 1,000 square feet or less, and grading of 50 cubic yards or less, but require a clearing and grading permit in accordance with BCC 23.76.035(A), now or as hereafter amended.

C. General Requirements.

1. The CSWPPP shall include a narrative and drawings. All BMPs shall be clearly referenced in the narrative and marked on the drawings. The CSWPPP narrative shall include documentation to explain and justify the pollution prevention decisions made for the project. All elements listed below must be considered and included in the CSWPPP unless site conditions render the element unnecessary and the director determines that the exemption from that element is clearly justified based on the narrative of the CSWPPP.

2. 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, significant trees shall be maintained consistent with BCC Title 20, including, but not limited to, LUC 20.20.520 and 20.20.900, now or as hereafter amended. Consideration should be given to minimizing removal of other trees and minimizing disturbance and/or compaction of native soils except as needed for building purposes.

3. Applicants must prepare and submit a CSWPPP for all projects that meet the permitting thresholds in BCC 23.76.035, except as exempted in subsection (B)(3) of this section, now or as hereafter amended. The CSWPPP shall be implemented beginning with initial soil disturbance and until final stabilization. The permitted clearing and grading areas and any other areas required to preserve critical areas or critical area buffers, native growth protection areas, retained vegetation areas, or tree retention areas, as the city may require, shall be delineated on the site plans and the development site.

4. For projects with clearing totaling less than 7,000 square feet and grading less than 500 cubic yards, the CSWPPP may consist of a CSWPPP short form and a site plan. A turbidity and pH monitoring plan may also be required depending on site characteristics, such as topography, proximity to receiving waters, or critical areas and critical area buffers.

5. Sediment and erosion control BMPs shall be consistent with the BMPs contained in the clearing and grading development standards now or hereafter amended.

6. Seasonal Work Limitations. From October 1st through April 30th, clearing and grading activities shall only be authorized by the city if silt-laden runoff will be prevented from leaving the site through compliance with applicable provisions of BCC 23.76.093, now or as hereafter amended. Based on the information provided and/or local weather conditions, the director may expand or restrict the seasonal limitation on site disturbance.

a. The following activities are exempt from the seasonal clearing and grading limitations:

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

ii. 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

iii. Activities where there is 100 percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities.

b. Clearing, grading, and hauling are not allowed during periods of heavy rain.

D. CSWPPP Elements. The applicant shall include all elements below in the CSWPPP and ensure that they are implemented, unless site conditions render the element unnecessary and the director determines that the exemption from that element is clearly justified based on the CSWPPP.

1. Preserve Vegetation/Mark Clearing Limits.

a. Before beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits, critical areas and critical area buffers, and trees that are to be preserved within the construction area.

b. Retain the duff layer, native topsoil, and natural vegetation in an undisturbed state to the maximum degree practicable, and, where applicable, meet the requirements of LUC 20.20.520, now or as hereafter amended.

2. Establish Construction Access.

a. Limit construction vehicle access and exit to one route, if possible.

b. Stabilize access points with a pad of quarry spalls, crushed rock, or other equivalent BMPs to minimize the tracking of sediment onto public roads.

c. Locate wheel wash or tire baths on site, if the stabilized construction entrance is not effective in preventing tracking sediment onto roads.

d. If sediment is tracked off site, clean the affected roadways thoroughly as directed by the city or at a minimum at the end of each day, or more frequently as necessary (for example during wet weather). Remove sediment from roads by shoveling, sweeping, or pickup and transport the sediment to a controlled sediment disposal area.

e. Conduct street washing only after sediment is removed in accordance with subsection (D)(2)(d) of this section. Street wash wastewater shall be controlled by pumping back on site or otherwise be prevented from discharging into the storm and surface water system or receiving waters.

f. Control street wash wastewater by pumping back on site, or otherwise prevent it from discharging into systems tributary to waters of the state.

3. Control Flow Rates.

a. Protect properties and waterways downstream of development sites from erosion and the associated discharge of turbid waters due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the project site.

b. Where necessary to comply with subsection (D)(3)(a) of this section, construct stormwater retention or detention facilities as one of the first steps in grading. Assure that detention facilities function properly before constructing site improvements (e.g., impervious surfaces).

c. If permanent infiltration ponds are used for flow control during construction, protect these facilities from siltation during the construction phase.

4. Install Sediment Controls.

a. Design, install and maintain effective erosion controls and sediment controls to minimize the discharge of pollutants.

b. Construct sediment control BMPs (sediment ponds, traps, filters, etc.) as one of the first steps in grading. These BMPs shall be functional before other land-disturbing activities take place.

c. 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 runoff, and soil characteristics, including the range of soil particle sizes expected to be present on the site.

d. Direct stormwater runoff from disturbed areas through a sediment pond or other appropriate sediment removal BMP, before the runoff leaves a construction site or before discharge to an infiltration facility. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but must meet the flow control performance standard in subsection (D)(3)(a) of this section.

e. Locate BMPs intended to trap sediment on site in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages.

f. Where feasible, design outlet structures that withdraw impounded stormwater from the surface to avoid discharging sediment that is still suspended in the water column.

5. Stabilize Soils.

a. Stabilize exposed and unworked soils by application of effective BMPs described in the clearing and grading development standards that prevent erosion. Applicable BMPs 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 early on areas to be paved, and dust control.

b. Control stormwater volume and velocity within the site to minimize soil erosion.

c. Control stormwater discharges, including both peak flow rates and total stormwater volume, to minimize erosion at outlets and to minimize downstream channel and stream bank erosion.

d. Soils must not remain exposed and unworked for more than the time periods set forth below:

i. During the dry season (May 1st – September 30th): seven days.

ii. During the wet season (October 1st – April 30th): two days.

e. Stabilize soils at the end of the shift before a holiday or weekend, if needed, based on the weather forecast.

f. Stabilize soil stockpiles from erosion, protect with sediment trapping measures, and, where possible, locate away from the storm and surface water system and receiving waters.

g. Minimize the amount of soil exposed during construction activity.

h. Minimize the disturbance of steep slopes.

i. Minimize soil compaction and, unless infeasible, preserve topsoil.

6. Protect Slopes.

a. Comply with applicable provisions of BCC 23.76.080, now or as hereafter amended.

b. 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 diversion, reducing slope steepness, and roughening slope surfaces (for example, track walking).

c. Divert off-site stormwater (run-on) or groundwater away from slopes and disturbed areas with interceptor dikes, pipes, and/or swales. Off-site stormwater should be managed separately from stormwater generated on the site.

d. At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion.

e. Temporary pipe slope drains must handle the peak 10-minute velocity of flow from a Type 1A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10-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 must 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 must 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 shall be modeled as “landscaped area.”

f. Place excavated material on the uphill side of trenches, consistent with safety and space considerations.

g. Place check dams at regular intervals within constructed channels that are cut down a slope.

7. Protect Drain Inlets.

a. Protect storm drain inlets made operable during construction so that stormwater runoff does not enter the conveyance system without first being filtered or treated to remove sediment.

b. Clean or remove and replace inlet protection devices when sediment has filled one-third of the available storage (unless a different standard is specified by the product manufacturer).

8. Stabilize Channels and Outlets.

a. Design, construct, and stabilize all on-site conveyance channels to prevent erosion from the following expected peak flows. Channels must handle the indicated peak 10-minute flow velocity from a Type 1A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10-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 must 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. 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.

9. Control Pollutants.

a. Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants.

b. 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.

c. 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 or the environment. On-site fueling tanks must include secondary containment. Secondary containment means placing tanks or containers within an impervious structure capable of containing 110 percent of the volume contained in the largest tank within the containment structure. Double walled tanks do not require additional secondary containment.

d. Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident.

e. Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that prevents discharge to surface water, such as closed loop recirculation or upland application, or to the sanitary sewer upon approval by the King County Wastewater Treatment Division and the city’s utilities department.

f. Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of chemicals to stormwater runoff. Follow manufacturers’ label requirements for application rates and procedures.

g. Use BMPs to prevent contamination of stormwater runoff by pH modifying sources. The sources for this contamination 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.

h. Adjust the pH of stormwater if necessary to prevent violations of water quality standards.

i. Assure that washout of concrete trucks is performed off site or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets or streams. Do not dump excess concrete on site, except in designated concrete washout areas. Concrete spillage or concrete discharge to surface waters of the state is prohibited.

j. Obtain written approval from Ecology before using chemical treatment other than CO2 or dry ice to adjust pH. Permittees shall provide the city with a copy of Ecology’s written approval before commencing treatment.

10. Control Dewatering.

a. Discharge foundation, vault, and trench dewatering water, which have similar characteristics to stormwater runoff at the site, into a controlled conveyance system before discharge to a sediment trap or sediment pond.

b. Discharge clean, nonturbid water from dewatering activities, such as well-point ground water, to the storm and surface water system or directly into receiving waters; provided the dewatering flow does not cause erosion or flooding of receiving waters. Do not route clean dewatering water through stormwater sediment ponds. Note that “surface waters of the state” may exist on a construction site; for example, a creek running through the site.

c. Handle highly turbid or otherwise contaminated dewatering water separately from stormwater.

d. Other treatment or 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 receiving waters;

iii. Ecology-approved on-site chemical treatment or other suitable treatment technologies;

iv. Sanitary sewer discharge upon approval from the King County Wastewater Treatment Division and the city’s utilities department, 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 dewatering.

11. Maintain BMPs.

a. Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications.

b. Remove all temporary erosion and sediment control BMPs within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed.

12. Manage the Project.

a. Phase development projects to the maximum degree practicable and take into account seasonal work limitations.

b. Inspection and Monitoring. Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function.

c. Maintaining an Updated CSWPPP. Maintain, update, and implement the CSWPPP.

d. Projects that disturb one or more acres must have site inspections conducted by a certified erosion and sediment control lead (CESCL). By the initiation of construction, the CSWPPP must identify the CESCL or inspector who must be present on site or on call at all times.

13. Protect Low Impact Development BMPs.

a. Protect all bioretention and rain garden BMPs from sedimentation through installation and maintenance of erosion and sediment control BMPs on the portions of the site that drain into bioretention and/or rain garden BMPs. Restore the BMPs to their fully functioning condition if they accumulate sediment during construction. Restoring the BMP must include removal of sediment and any sediment-laden bioretention/rain garden soils, and replacing the removed soils with soils meeting the design specification.

b. Prevent compacting bioretention and rain garden BMPs by excluding construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment.

c. Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements or base materials.

d. Pavements fouled with sediments or no longer passing an initial infiltration test must be cleaned using procedures from the city of Bellevue stormwater manual (now or hereafter amended), or the manufacturer’s procedures.

e. Keep all heavy equipment off existing soils under LID BMPs that have been excavated to final grade to retain the infiltration rate of the soils.

E. Additional Erosion and Sedimentation Control Requirements.

1. In addition to the CSWPPP elements listed in subsection D of this section, the director may impose the following extraordinary BMPs or other additional measures, as appropriate for the project:

a. Funding additional city inspection time, up to a full-time inspector;

b. Stopping work if necessary to control erosion and sedimentation; or

c. Constructing additional erosion and sedimentation BMPs.

2. If the initially implemented BMPs do not adequately control pollutants, erosion, and sedimentation, additional BMPs shall be installed, including but not limited to the extraordinary BMPs described in subsection (E)(1) of this section. It is the permittee’s responsibility to ensure sediment or other pollutants do not leave the site and enter the storm and surface water system or receiving waters in an amount that would violate the discharge prohibitions set forth in BCC 24.06.125, now or as hereafter amended.

F. Permanent Erosion and Sedimentation Control.

1. Permanent erosion and sedimentation control shall be provided per the clearing and grading development standards. Disturbed areas of the site that are not covered by permanent improvements such as buildings, parking lots, and decks shall be mulched or vegetated.

2. The permittee must complete the required permanent erosion control within seven days of completed grading unless the weather is unsuitable for transplanting. In that case, the permittee must maintain temporary erosion control until permanent restoration can be completed. The period between work completion and final planting shall not exceed six months without written authorization from the director. (Ord. 6318 § 25, 2016; Ord. 6196 §§ 3 – 6, 2014; Ord. 5906 § 15, 2009; Ord. 5452 § 13, 2003; Ord. 4754 § 2, 1995.)