A. Site Design Measures.
1. All projects that create and/or replace (including projects with no net increase in impervious footprint) between 2,500 square feet and 5,000 square feet of impervious surface, including detached single family homes that create and/or replace 2,500 square feet or more of impervious surface and are not part of a larger plan of development are required to implement one or more of the following site design measures to reduce project site runoff:
a. Stream setbacks and buffers – a vegetated area including trees, shrubs, and herbaceous vegetation, that exists or is established to protect a stream system;
b. Soil quality improvement and maintenance – improvement and maintenance soil through soil amendments and creation of microbial community;
c. Tree planting and preservation – planting and preservation of healthy, established trees that include both evergreens and deciduous;
d. Porous pavement – pavement that allows runoff to pass through it, thereby reducing the runoff from a site and surrounding areas and filtering pollutants;
e. Green roofs – a vegetated, open-channel management practice designed specifically to treat and attenuate storm water runoff; and/or
f. Rain barrels and cisterns – system that collects and stores storm water runoff from a roof or other impervious surface.
2. This section is not applicable to linear underground/overhead projects.
3. Project proponents shall use the State Water Board SMARTS post-construction calculator to quantify and submit to the City of Chico the runoff reduction resulting from implementation of site design measures.
4. The plans for the site design measures required in this section shall be stamped by:
a. A California civil professional engineer for rooftop and impervious area disconnections, porous pavement, rain cisterns, bioretention and rain gardens, infiltration trenches, retention or detention basins, or green roofs; and
b. A California landscape architect for soil quality improvements, vegetated swales, or biorentention and rain gardens.
B. Regulated Projects – Projects that create and/or replace 5,000 square feet or more of impervious surface.
1. All projects that create and/or replace 5,000 square feet or more of impervious surface are required to implement measures for site design, source control, runoff reduction, storm water treatment and baseline hydromodification management. These projects are considered regulated projects.
a. Regulated projects do not include detached single family home projects that are not part of a larger plan of development; interior remodels; routine maintenance or repairs such as exterior wall surface replacement or pavement resurfacing within the existing footprint; and LUPs.
i. LUPs that have a discrete location of 5,000 square feet or more of newly constructed contiguous impervious surface are considered a regulated project for that specific discrete location.
2. Regulated projects include development projects. Development includes new and redevelopment projects on public or private land that fall under the permitting authority of the city. Redevelopment is any land-disturbing activity that results in the creation, addition, or replacement of exterior impervious surface area on a site on which some past development has occurred. Redevelopment does not include trenching, excavation and resurfacing associated with LUPs; pavement grinding and resurfacing of existing roadways; construction of new sidewalks, pedestrian ramps, or bike lanes on existing roadways; or routing replacement of damaged pavement such as a pothole repair or replacement of short, non-contiguous sections of roadway. The following describe specific regulated project requirements:
a. Redevelopment Projects –
i. Where a redevelopment project results in an increase of more than 50 percent of the impervious surface of a previously existing development, runoff from the entire project, consisting of all existing, new, and/or replaced impervious surfaces, must be included to the extent feasible.
ii. Where a redevelopment project results in an increase of less than 50 percent of the impervious surface of a previously existing development, only runoff from the new and/or replaced impervious surface of the project must be included.
b. Road Projects and LUPs – Any of the following types of road projects and LUPs that create 5,000 square feet or more of newly constructed contiguous impervious surface and that are public road projects and/or fall under the permitting authority of the city shall comply with Section 15.50.080(D) Low impact development design standards, except that treatment of runoff of the 85th percentile that cannot be infiltrated onsite shall follow U.S. Environmental Protection Agency’s guidance regarding green infrastructure to the extent feasible.
i. Construction of new streets or roads, including sidewalks and bicycle lanes built as part of the new streets or roads.
ii. Widening of existing streets or roads with additional traffic lanes.
a. Where the addition of traffic lanes result in an alteration of more than 50 percent of the impervious surface of an existing street or road, runoff from the entire project, consisting of all existing, new, and/or replaced impervious surfaces, must be included in the treatment system design.
b. Where the addition of traffic lanes result in an alteration of less than 50 percent (but 5,000 square feet or more) of the impervious surface of an existing street or road, only the runoff from new and/or replaced impervious surface of the project must be included in the treatment system design.
iii. Construction of linear underground/overhead projects (LUPs).
iv. Specific exclusions are:
a. Sidewalks built as part of new streets or roads and built to direct storm water runoff to adjacent vegetated areas.
b. Bicycle lanes that are built as part of new streets or roads that direct storm water runoff to adjacent vegetated areas.
c. Impervious trails built to direct storm water runoff to adjacent vegetated areas, or other non-erodible permeable areas, preferably away from creeks or towards the outboard side of levees.
d. Sidewalks, bicycle lanes, or trails constructed with permeable surfaces.
e. Trenching, excavation and resurfacing associated with LUPs; pavement grinding and resurfacing of existing roadways and parking lots; construction of new sidewalks, pedestrian ramps, or bike lanes on existing roadways; or routine replacement of damaged pavement such as pothole repair or replacement of short, non-contiguous sections of roadway.
C. Source Control Measures.
1. Regulated projects with pollutant-generating activities and sources are required to implement standard permanent and/or operation source control measures. The measures for the following pollutant generating activities and sources shall be designed consistent with recommendations from the CASQA Storm Water BMP Handbook for New Development and Redevelopment or equivalent manual:
a. Accidental spills or leaks
b. Interior floor drains
c. Parking/storage areas and maintenance
d. Indoor and structural pest control
e. Landscape/outdoor pesticide use
f. Pools, spas, ponds, decorative fountains, and other water features
g. Restaurants, grocery stores, and other food service operations
h. Refuse areas
i. Industrial processes
j. Outdoor storage of equipment or materials
k. Vehicle and equipment cleaning
l. Vehicle and equipment repair and maintenance
m. Fuel dispensing areas
n. Loading docks
o. Fire sprinkler test water
p. Drain or wash water from boiler drain lines, condensate drain lines, rooftop equipment, drainage sumps, and other sources
q. Unauthorized non-storm water discharges
r. Building and grounds maintenance
D. Low Impact Development (LID) Design Standards – All regulated projects are required to implement LID standards as listed below.
1. Site Assessment – Regulated projects are required to assess and evaluate how site conditions, such as soils, vegetation, and flow paths, will influence the placement of buildings and paved surfaces. The evaluation will be used to meet the goals of capturing and treating runoff and assuring these goals are incorporated into the project design. The following methods are required to be completed to optimize the site layout of the project site:
a. Define the development envelope and protected areas, identifying areas that are most suitable for development and areas to be left undisturbed.
b. Concentrate development on portions of the site with less permeable soils and preserve areas that can promote infiltration.
c. Limit overall impervious coverage of the site with paving and roofs.
d. Set back development from creeks, wetlands, and riparian habitats.
e. Preserve significant trees.
f. Conform the site layout along natural landforms.
g. Avoid excessive grading and disturbance of vegetation and soils.
h. Replicate the site’s natural drainage patterns.
i. Detain and retain runoff throughout the site.
2. Drainage Management Areas – Each regulated project is required to provide a map or diagram dividing the developed portions of the project site into discrete drainage management areas (DMAs), and to manage runoff from each DMA using site design measures, source controls and/or storm water treatment and baseline hydromodification measures.
3. Numeric Sizing Criteria for Storm Water Retention and Treatment – Facilities designed to evapotranspire, infiltrate, harvest/use, and biotreat storm water are required to meet at least one of the following hydraulic sizing design criteria:
a. Volumetric Criteria:
i. The maximized capture storm water volume for the tributary area, on the basis of historical rainfall records, determined using the formula and volume capture coefficients in Urban Runoff Quality Management, WEF Manual of Practice No. 23/ASCE Manual of Practice No. 87 (1998) pages 175-178 (that is, approximately the 85th percentile 24-hour storm runoff event); or
ii. The volume of annual runoff required to achieve 80 percent or more capture, determined in accordance with the methodology in Section 5 of the CASQA’s Storm Water Best Management Practice Handbook, New Development and Redevelopment (2003), using local rainfall data.
b. Flow-based Criteria:
i. The flow of runoff produced from a rain event equal to at least 0.2 inches per hour intensity; or
ii. The flow of runoff produced from a rain event equal to at least 2 times the 85th percentile hourly rainfall intensity as determined from local rainfall records.
4. Site design measures as defined in Section 15.50.080(A) above, site layout, and design measures shall be implemented on the objective of achieving infiltration, evapotranspiration and/or harvesting/reuse of the 85th percentile 24-hour storm runoff event. Site design measures shall be used to reduce the amount of runoff, to the extent technically feasible, for which retention and runoff is required. Any remaining runoff from impervious DMAs may then be directed to one or more bioretention facilities as specified in Section 15.50.080(D)(6) below.
5. Source Controls – All regulated projects shall implement source controls as defined in Section 15.50.080(C) above.
6. Storm Water Treatment Measures and Baseline Hydromodification Management Measures – After implementation of site design measures on regulated projects, the remaining runoff from impervious DMAs must be directed to one or more facilities designed to infiltrated, evapotranspire, and/or bioretain the amount of runoff specified in Section 15.50.080(D)(3) Numeric sizing criteria for storm water retention and treatment. The facilities must be demonstrated to be at least as effective as a bioretention system with the following design parameters:
a. Maximum surface loading rate of 5 inches per hour, based on the flow rates calculated. A sizing factor of 4% of tributary impervious area may be used.
b. Minimum surface reservoir volume equal to surface area times a depth of 6 inches.
c. Minimum planting medium depth of 18 inches. The planting medium must sustain a minimum infiltration rate of 5 inches per hour throughout the life of the project and must maximize runoff retention and pollutant removal. A mixture of sand (60%-70%) meeting the specifications of American Society for Testing and Materials (ASTM) C33 and compost (30%-40%) may be used.
d. Subsurface drainage/storage (gravel) layer with an area equal to the surface area and having a minimum depth of 12 inches.
e. Underdrain with discharge elevation at top of gravel layer.
f. No compaction of soils beneath the facility, or ripping/loosening of soils if compacted.
g. No liners or other barriers interfering with infiltration.
h. Appropriate plant palette for the specified soil mix and maximum available water use.
7. Alternative Designs – Facilities, or a combination of facilities, of a different design than in Section 15.50.080(D)(6) may be permitted if all of the following measures of equivalent effectiveness are demonstrated:
a. Equal or greater amount of runoff infiltrated or evapotranspired;
b. Equal or lower pollutant concentrations in runoff that is discharged after biotreatment;
c. Equal or greater protection against shock loadings and spills;
d. Equal or greater accessibility and ease of inspection and maintenance.
8. Allowed Variations for Special Site Conditions – The bioretention system design parameters Section 15.50.080(D)(6) may be adjusted for the following special site conditions:
a. Facilities located within 10 feet of structures or other potential geotechnical hazards established by the geotechnical expert for the project may incorporate an impervious cutoff wall between the bioretention facility and the structure or other geotechnical hazard.
b. Facilities with documented high concentrations of pollutants in underlying soil or groundwater, facilities located where infiltration could contribute to a geotechnical hazard, and facilities located on elevated plazas or other structures may incorporate an impervious liner and may located the underdrain discharge at the bottom of the subsurface drainage/storage layer (this configuration is commonly known as a “flow-through planter”).
c. Facilities located in areas of high groundwater, highly infiltrative soils or where connection of underdrain to a surface drain or to a subsurface storm drain are infeasible, may omit the underdrain.
d. Facilities serving high-risk areas such as fueling stations, truck stops, auto repairs, and heavy industrial sites may be required to provide additional treatment to address pollutants of concern unless these high-risk areas are isolated from storm water runoff or bioretention areas with little chance of spill migration.
9. Exceptions to Requirements of Bioretention Facilities –
Contingent on a demonstration that use of bioretention or a facility of equivalent effectiveness is infeasible, other types of biotreatment or media filters (such as tree-box-type biofilters or in-vault media filters) may be used for the following categories of regulated projects:
a. Projects creating or replacing an acre or less of impervious area, and located in a designated pedestrian-oriented commercial district, and having at least 85% of the entire project site covered by permanent structures;
b. Facilities receiving runoff solely from existing (pre-project) impervious areas; and
c. Historic sites, structures or landscapes that cannot alter their original configuration in order to maintain their historic integrity.
E. Hydromodification Management – Hydromodification management projects are regulated projects that create and/or replace one acre or more of impervious surface. A project that does not increase impervious surface area over the pre-project condition is not a hydromodification management project. Post-project runoff for hydromodification management projects shall not exceed estimated pre-project flow rate for the 2-year, 24-hour storm.
F. Operations and Maintenance of Post-Construction Storm Water Management Measures – All regulated projects shall at a minimum, require from all project proponents and their successors in control of the project or successors in fee title:
1. The property owner or responsible party shall sign a statement of responsibility accepting responsibility for the on-going operation, inspection, and maintenance of the treatment control measures until the property and/or responsibility is legally transferred to another entity. The statement of responsibility shall be on a form approved by the city.
a. The transfer of property to a new owner shall contain conditions requiring the recipient to assume responsibility for maintenance of any treatment control measures to be included in the sales or lease agreement for that property and will be the owner’s responsibility. The new owner or responsible party will be obligated to maintain the operations and maintenance of the treatment control measures.
2. The city will send the responsible party an operation and maintenance self- certification form. The responsible party will certify that the operations and maintenance program is being implemented and that the treatment control measures are in an effective operational condition. The responsible party will have sixty (60) days to complete and return the annual operation and maintenance self-certification form.
a. If the operation and maintenance self-certification form is not received within the sixty (60) day period, the city will perform the inspection and assessment. The responsible party will be billed for the inspection and assessment as applicable.
G. All projects subject to this section shall submit a completed post construction storm water worksheet to the city.
(Ord. 2468 §5)