A. 
Application for any of the permit/approvals specified in Section 15.01.020 shall be accompanied by an interim erosion/sedimentation control plan and a drainage plan or a waiver therefrom granted by the city engineer in accordance with the provisions of subsection (C) of this section.
B. 
The plan submitted during one permit approval process may be subsequently submitted with further required applications.
C. 
The plan requirement established in this section will not apply when the engineering department determines that the proposed permit and/or activity:
1. 
Will neither seriously nor adversely impact the water quality conditions of any affected receiving bodies of water.
2. 
Will not alter the drainage patterns, increase the peak discharge and cause adverse effects in the drainage area.
3. 
Will not seriously nor adversely impact ground water quality, the recharge of a ground water aquifer and/or the capacities of nearby springs and wells.
(Ord. 743, 1997; Ord. 862, 2005)
A. 
All persons applying for any of the permits and/or approvals specified in Section 15.01.020 shall provide an interim erosion/sedimentation control plan and drainage plan for surface and pertinent subsurface water flows entering, flowing within, and leaving the subject property. Said plans shall present the following required information:
1. 
Interim Erosion/Sedimentation Control Plan. An interim erosion/sedimentation control plan will be required as set forth in the Langley comprehensive stormwater plan. At the discretion of the city engineer, plans prepared in conjunction with those actions not identified as categorical exemptions under SEPA, WAC 197-10-170 and/or occurring in lands classified as sensitive lands per Section 16.04.170 shall be prepared under the direction of a civil engineer, soil scientist, or other qualified individual(s). The plan for a proposed construction site shall describe:
a. 
Soils, topography, existing vegetation, the areas to be cleared and graded, and the location of major cuts and fills covered by the permit and/or approval for which application is made;
b. 
Computations and hazards associated with the area covered by the permit and/or approval for which application is made, the anticipated schedule of construction, and the proposed measures, including site management practices (such as check dams, slash removal, reseeding, or mulching) as appropriate for controlling erosion/sedimentation and runoff;
c. 
The city engineer may require interim erosion/sedimentation control measures to account for seasonal changes, alterations of the topography and watercourse during construction, and other such factors affecting site conditions which need to be constructed to ensure complete siltation control on the subject property. It shall be the obligation and responsibility of the person required to provide and maintain temporary erosion/sedimentation facilities pursuant to this section to address any new conditions that may be created by his activities and to utilize additional control measures as may be needed;
d. 
The interim erosion/sedimentation control facility shall be constructed prior to any grading or extensive land clearing in accordance with the approved temporary plan. These facilities must be satisfactorily maintained until construction and landscaping is completed and the potential of onsite erosion has passed.
B. 
Small Projects. All persons applying for and doing grading in conjunction with building permits for development or redevelopment with less than 5,000 square feet of impervious surface area shall employ one or more of the best management practices (BMPs) identified in Appendix A of this code prior to commencement of grading.
C. 
Preliminary Drainage Plan. A preliminary drainage control plan will be required unless waived by the city engineer. The preliminary drainage plan shall describe:
1. 
Background computations for sizing drainage facilities.
a. 
Depiction of the drainage area and the natural surface drainage system on a topographical map, with acreage indicated. A contour interval of two feet or five feet shall be required as directed by the city engineer.
b. 
Indication of the peak discharge and amount of surface water currently entering and leaving the subject property.
c. 
Indication of the peak discharge and amount of runoff which will be generated within the subject property if development is allowed to proceed.
d. 
Indication of how low-impact development measures will be incorporated into the site design in an effort to eliminate offsite discharge and mimic natural hydrologic functions.
e. 
For applications in which onsite detention is required, the preliminary drainage plan shall include the required storage volume, method of storage and an accurate cost estimate associated with furnishing and installing the detention facility. The cost estimate shall exclude the drainage conveyance system to the detention facility.
2. 
Proposed improvements for handling the additional computed runoff, and providing water quality treatment of runoff.
3. 
Arrangements by the developer to provide for continuing maintenance of the project drainage facilities.
D. 
As an alternate to onsite detention, upon the approval of the city engineer, the applicant may contribute to the city a sum of money equivalent to the estimated costs for furnishing and installing the sized detention facility for the proposed development. The cost estimate for the detention facility submitted by the applicant shall be reviewed by the city engineer for accuracy. This estimate, with any modifications by the city engineer, shall be the sum of money contributed to the storm drainage fund.
E. 
Modifications. The requirements of this section may be modified if, in the city engineer's professional opinion, such additional or reduced amount of information is necessary or appropriate to carry out the expressed purpose and intent of this chapter.
F. 
Large tract subdivisions shall be exempt from the detailed drainage plan requirements in subsection (C) of this section, except in critical drainage areas.
(Ord. 743, 1997; Ord. 862, 2005; Ord. 921, 2009; Amended during 2013 reformat)
A. 
A detailed drainage plan shall be prepared by a registered civil engineer based upon the city engineer's determination as provided in Section 15.01.425(E). Detailed drainage plans are not required for single-family or duplex development or redevelopment that includes the creation of less than 5,000 square feet of impervious surface area. Detailed drainage plans are also not required for commercial/industrial or multifamily development or redevelopment that includes the creation of less than 5,000 square feet of impervious surface area except if the development is located in the critical drainage sub-basins DB-3B-3East.
B. 
The use of all reasonable and appropriate low-impact development measures shall be required prior to consideration of conventional stormwater management methods.
C. 
Surface water entering the subject property shall be received at the naturally occurring location, and surface water exiting the subject property shall be discharged at the natural location, with adequate energy dissipaters within the subject property to eliminate downstream damage and with no diversion at any of these points. Deviations consistent with law may be permitted.
D. 
The peak discharge from the subject property due to the design storm may not be increased due to the proposed development. Further control may be required as specified in Section 15.01.440. See alternative to detention, Section 15.01.425(D).
E. 
Retention/detention facilities or other drainage facilities shall be in accordance with Section 15.01.445.
F. 
Provide stormwater quality treatment facilities to accommodate runoff produced by the design storm, defined as the six-month, 24-hour return period storm event which is approximately equal to 64 percent of the two-year, 24-hour storm. The first priority for treatment shall be to infiltrate as much as possible of the storm, if site conditions are appropriate and ground water quality will not be impaired. Direct discharge of untreated stormwater to ground water is prohibited. All treatment BMPs shall be selected, designed, and maintained according to the Department of Ecology's Stormwater Management Manual for Western Washington (Publication Nos. 05-10-029 through 05-10-033 as they now exist or are hereafter amended).
G. 
All development projects shall conduct an analysis of offsite water quality impacts resulting from the project and shall mitigate these impacts. The analysis shall extend a minimum of one-fourth of a mile downstream from the project. The existing or potential impacts to be evaluated and mitigated shall include, at a minimum, but not be limited to: excessive sedimentation, stream bank erosion, discharges to ground water contributing or recharge zones, violations of water quality standards, and spills and discharges of priority pollutants.
H. 
Source Control of Pollution. Source control BMPs shall be applied to all projects to the maximum extent practicable. Source control BMPs shall be selected, designed and maintained according to the DOE Technical Manual.
I. 
Wetlands. The following requirements apply only to situations where stormwater discharges directly or indirectly through a conveyance system into a wetland.
1. 
Stormwater discharges to wetlands must be controlled and treated to the extent necessary to meet the State Water Quality Standards, Chapter 173-201 WAC, or Ground Water Quality Standards, Chapter 173-200 WAC, as appropriate.
2. 
Discharges to wetlands shall maintain the hydroperiod and flows of existing site conditions to the extent necessary to protect the characteristic uses of the wetland. Prior to discharging to a wetland, alternative discharge locations shall be evaluated, and natural water storage and infiltration opportunities outside the wetland shall be maximized and shall be subject to review by the planning official and the city engineer.
3. 
Created wetlands that are intended to mitigate for loss of wetland acreage, function and value shall not be designed to also treat stormwater.
4. 
In order for constructed wetlands to be considered treatment systems, they must be constructed on sites that are not wetlands and they must be managed for stormwater treatment. If these systems are not managed and maintained in accordance with the Department of Ecology's Stormwater Management Manual for Western Washington (Publication Nos. 05-10-029 through 05-10-033 as they now exist or are hereafter amended) for a period exceeding three years these systems may no longer be considered constructed wetlands. Discharges from constructed wetlands to waters of the state (including discharges to natural wetlands) are regulated under Chapter 90.48 RCW and Chapters 173-200 and 173-201 WAC.
5. 
Stormwater treatment BMPs shall not be built within a natural vegetated buffer, except for necessary conveyance systems as approved by the city of Langley.
J. 
Operation and Maintenance. An operation and maintenance schedule shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified.
K. 
The developer will obtain the necessary easements from all affected properties for the flow of storm drainage between the development and a drainage way or receiving body of water necessary to comply with the foregoing requirements.
L. 
Drainage from roofs, downspouts, surface drains, and sub-drains shall not be discharged into a city road or drainage ditch without first having received approval from the city engineer.
M. 
Variances from any or all of the foregoing requirements of this section may be permitted only after a determination by the city engineer and the planning official, employing the following criteria: (1) capacity of downstream facilities, (2) acceptability of receiving bodies of water, (3) possibility of adverse effects of retention, (4) utility of regional retention facilities, and (5) capability of maintaining the system.
N. 
Exceptions:
1. 
Those areas designated in the city of Langley comprehensive stormwater plan as not benefiting from stormwater runoff control (sub-basins C and D2 which discharge directly to the Sound and have short travel times in comparison to uphill basins) may be exempt from the runoff control/detention requirements of this chapter and eligible for the alternative described in Section 15.01.425(D).
2. 
Increased mitigation measures may be required based on downstream flooding problems or the limited capacity of the downstream conveyance system.
(Ord. 743, 1997; Ord. 862, 2005; Ord. 921, 2009)
Development in a critical drainage area shall meet special drainage conditions set by the city engineer until such time as the community hazard is alleviated. Such conditions may include the limitations of the volume of discharge from subject property to predevelopment levels, preservation of wetlands or other natural drainage features, or other controls necessary to protect against community hazard.
(Ord. 743, 1997)
A. 
The methods for predicting runoff from a given basin that are acceptable to the city are the Soil Conservation Service (SCS) method or the Santa Barbara Urban Hydrograph (SBUH) method. In addition, for basins smaller than 25 acres, the rational method is acceptable for sizing conveyance systems.
B. 
Stormwater quantity conveyance systems connected to the present piping system shall be designed to convey a 25-year, 24-hour storm as computed using the Soils Conservation Service (SCS) method or the Santa Barbara Urban Hydrograph (SBUH) method. In basins smaller than 25 acres the Rational Method is acceptable. Stormwater runoff that is discharged directly or indirectly to a stream shall be regulated as follows:
1. 
The peak rate of runoff from individual development sites shall be limited to 50 percent of the existing condition two-year, 24-hour design storm while maintaining the existing condition peak runoff rate for the 10-year, 24-hour, and 100-year, 24-hour design storm. In cases where discharge is directly to Puget Sound and the downstream conveyance system has adequate capacity to carry the 25-year, 24-hour peak flow the requirement to limit peak rates to pre-development values may be waived based on the city engineer's approval. In cases where discharge is directly to Puget Sound but the downstream conveyance system has limited capacity, post-development peak runoff rates shall be limited to the magnitudes of the pre-development 10-year, 24-hour and 100-year, 24-hour peak runoff rates.
C. 
Water Quality Facilities. Water quality facilities shall be designed for the six-month, 24-hour storm event which is approximately equal to 64 percent of the two-year, 24-hour storm.
(Ord. 743, 1997; Amended during 2013 reformat)
A. 
All reasonable and appropriate low-impact development measures shall be incorporated into site design before conventional onsite detention and infiltration methods are considered.
B. 
Open retention/detention facilities and infiltration facilities shall not be located in public road right-of-way. The city engineer is authorized to require all persons, associations, and/or corporations constructing new or maintaining retention/detention facilities to secure a liability insurance policy for the duration of the operation of the facility.
C. 
An emergency overflow system is required for all retention/detention facilities.
D. 
Detention basin design must account for antecedent conditions which may contribute to a partially full basin at the beginning of the design storm, i.e., a minimum of one foot of freeboard above the maximum design water surface.
E. 
Existing wetlands may function as both a control feature in the natural surface drainage system and as areas of ground water recharge. Any reduction of such features shall be replaced with equivalent drainage controls.
F. 
Infiltration is preferred where practical because it reduces the demand for conveyance capacity and hence, reduces potential flooding. It also recharges the aquifer and has water quality benefits. Figure 2.7 of the City of Langley Comprehensive Stormwater Management Plan and Section 5 of that document discuss areas where infiltration shall be considered. The Low Impact Development Technical Guidance Manual For Puget Sound (Puget Sound Action Team Publication No. PSAT 05-03 as it now exists or is hereafter amended) and the Department of Ecology's Stormwater Management Manual for Western Washington (Publication Nos. 05-10-029 through 05-10-033 as they now exist or are hereafter amended) provide general guidelines for analyzing the feasibility of the infiltration systems, which shall be recognized as minimum standards. The basic design shall follow the Stormwater Manual for Western Washington.
Infiltration may be restricted or disallowed, as determined by the city engineer, in those areas designated and defined in the Langley Municipal Code as sensitive areas.
G. 
Detention systems shall be designed in accordance with Chapter III-4 of the Stormwater Manual for Western Washington. Water shall be released at a rate not to exceed the runoff which occurred before development.
(Ord. 743, 1997; Ord. 862, 2005; Ord. 921, 2009)
A. 
Publicly Owned Stormwater Facilities Located in City Rights-of-Way. Facilities are maintained by the city public works department. These facilities include catch basins, road side ditches, storm drains, detention facilities, and infiltration facilities.
B. 
Existing Privately Owned Stormwater Facilities Located on Private Property.
1. 
Facilities located on single lot private property shall be maintained by the property owners.
2. 
When a facility serves several properties, a homeowners association will provide an O&M agreement that the facilities will be inspected, with notice, by the city and paid for by the homeowners association. The facility shall be located in a tract or easement dedicated to that association.
3. 
Should private stormwater facilities not be maintained in accordance with city standards, then the city may choose to perform the necessary maintenance and charge the property owner/association or the city may condemn the property as a health and safety nuisance and assume ownership.
C. 
Public facilities shall be inspected by the city annually and cleared of debris, sediment and vegetation, when they affect the functioning and/or design capacity of the facility. All stormwater facilities shall be maintained in accordance with the DOE Technical Manual.
(Ord. 743, 1997; Ord. 921, 2009)
A. 
Mainline Storm Sewers.
1. 
Minimum diameter of storm drain pipe shall be 12 inches except that a maximum length of 60 lineal feet of eight-inch diameter pipe may be used between inlet and catch basin.
2. 
Minimum slope of storm drain pipe shall be 0.005 ft./ft.
3. 
Minimum velocity at design flow shall be three feet per second.
4. 
Maximum depth of liquid in culvert shall be d/D = 0.8.
5. 
Maintain line and grade between all catch basins/manholes.
6. 
Install catch basins/manholes at all changes of line or grade, at all pipe intersections and at both ends of all storm drain pipe, except driveway culverts and at maximum spacing of 300 feet.
7. 
Extend mainline storm sewers to boundary of project to serve adjacent upstream properties.
8. 
Design location of pipe shall be south and west of street centerline under street curb, except as required to match existing utilities.
9. 
Maximum depth of cover over top of pipe into catch basins shall be four feet except where approved by the city engineer. Where the depth to pipe invert is five feet or more, a manhole shall be installed at grade breaks and pipe intersections.
10. 
Provide six-inch tees to serve each adjacent land parcel or future lot. Extend service lines to property line where under future paving, curbs or sidewalks.
11. 
Note pipe size, length, slope and invert elevations in profile on each run between catch basins.
12. 
Drainage facilities must be designed to convey the surface water entering a drainage area at the naturally occurring location.
B. 
In areas where ditches are allowed, they shall be constructed with maximum depth of three feet, minimum side slope of one and one-half horizontal to one vertical, with driveway culverts 12-inch minimum diameter.
C. 
Footing and Downspout Drain.
1. 
Preference is to keep stormwater on site, through installation of rain gardens, or infiltration drywell next, over connection to the storm drain.
2. 
Minimum diameter shall be six inches to property line.
3. 
Minimum slope shall be one percent.
4. 
Provide three-foot minimum depth at property line, or deeper if required by lot topography.
5. 
Provide individual drain for each house or lot.
6. 
All drain lines shall enter mainline at a tee or catch basin.
7. 
Under no circumstances shall storm drain be connected to the sanitary sewer system.
8. 
In no event shall footing drains and downspout drains be allowed to be tied together within 10 feet of a structure.
D. 
Minimum materials requirements shall be as follows:
1. 
Pipe materials shall be in accordance with Section 7-04 of the APWA Standard Specifications.
2. 
Catch basins, inlets and grates shall be in accordance with the APWA Standard Plans.
(Ord. 743, 1997; Ord. 921, 2009)