Hawaiian Gardens Municipal Code Ch. 13.20 Low Impact Development Standards

The provisions of this chapter establish requirements for development and redevelopment to comply with the latest NPDES MS4 permit to lessen water quality impacts by using smart growth practices, and integrate low impact development (LID) practices and standards for storm water pollution mitigation through means of infiltration, evapotranspiration, bioretention, biofiltration, and rainfall harvest and use.

(Ord. 545 § 1, 2013; Ord. No. 2024-617, § 5(Att. C), 6-12-2024)

For purposes of this chapter, the following terms shall be defined as follows. If the definition of any term contained in this chapter conflicts with the definition of the same term in the latest NPDES MS4 permit, then the definition contained in the NPDES MS4 permit shall apply.

Biofiltration means a LID BMP that reduces storm water pollutant discharges by intercepting rainfall on vegetative canopy, and through incidental infiltration and/or evapotranspiration, and filtration. Incidental infiltration is an important factor in achieving the required pollutant load reduction. Therefore, the term "biofiltration" as used in this chapter is defined to include only systems designed to facilitate incidental infiltration or achieve the equivalent pollutant reduction as biofiltration BMPs with an underdrain (subject to approval by the Regional Board's Executive Officer). Biofiltration BMPs include bioretention systems with an underdrain and bio-swales.

Bioretention means a LID BMP that reduces storm water runoff by intercepting rainfall on vegetative canopy, and through evapotranspiration and infiltration. The bioretention system typically includes a minimum two-foot top layer of a specified soil and compost mixture underlain by a gravel-filled temporary storage pit dug into the in-situ soil. As defined in this chapter, a bioretention BMP may be designed with an overflow drain, but may not include an underdrain. When a bioretention BMP is designed or constructed with an underdrain it is regulated by the NPDES NS4 permit as biofiltration.

Bio-swale means a LID BMP consisting of a shallow channel lined with grass or other dense, low-growing vegetation. Bioswales are designed to collect storm water runoff and to achieve a uniform sheet flow through the dense vegetation for a period of several minutes.

City means the City of Hawaiian Gardens.

Clean Water Act or CWA means the Federal Water Pollution Control Act enacted in 1972, by Public Law 92-500, and amended by the Water Quality Act of 1987. The Clean Water Act prohibits the discharge of pollutants to waters of the United States unless the discharge is in accordance with an NPDES MS4 permit.

Development means construction, rehabilitation, redevelopment or reconstruction of any public or private residential project (whether single-family, multi-unit or planned unit development); industrial, commercial, retail, and other non-residential projects, including public agency projects; or mass grading for future construction. It does not include routine maintenance to maintain original line and grade, hydraulic capacity, or original purpose of facility, nor does it include emergency construction activities required to immediately protect public health and safety.

Discharge means any release, spill, leak, pump, flow, escape, dumping, or disposal of any liquid, semi-solid, or solid substance. When used without qualification the release of a pollutant or pollutants from the MS4.

Flow-through treatment BMPs means modular, vault type "high flow biotreatment" devices contained within an impervious vault with an underdrain or designed with an impervious liner and an underdrain.

Green roof means a LID BMP using planter boxes and vegetation to intercept rainfall on the roof surface. Rainfall is intercepted by vegetation leaves and through evapotranspiration. Green roofs may be designed as either a bioretention BMP or as a biofiltration BMP. To receive credit as a bioretention BMP, the green roof system planting medium shall be of sufficient depth to provide capacity within the pore space volume to contain the design storm depth and may not be designed or constructed with an underdrain.

Infiltration means a LID BMP that reduces storm water runoff by capturing and infiltrating the runoff into in-situ soils or amended on-site soils. Examples of infiltration BMPs include infiltration basins, dry wells, and pervious pavement.

Low impact development (LID) means the implementation of systems and practices that use or mimic natural processes to: 1) infiltrate and recharge, 2) evapotranspire and/or 3) harvest and use precipitation near to where it falls to earth.

Municipal separate storm sewer system or MS4 means a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) (40 CFR Section 122.26(b)(8)):

1. Owned or operated by a state, city, town, borough, county, parish, district, association, or other public body (created by or pursuant to state law) having jurisdiction over disposal of sewage, industrial wastes, storm water, or other wastes, including special districts under state law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under Section 208 of the CWA that discharges to waters of the United States;

2. Designed or used for collecting or conveying storm water;

3. Which is not a combined sewer; and

4. Which is not part of a publicly owned treatment works (POTW) as defined at 40 CFR Section 122.2 (40 CFR Section 122.26(b)(8)).

National Pollutant Discharge Elimination System or NPDES means the national program for issuing, modifying, revoking and reissuing, terminating, monitoring and enforcing permits, and imposing and enforcing pretreatment requirements, under CWA Sections 307, 402, 318, and 405. The term includes an "approved program."

Natural drainage system means a drainage system that has not been modified using engineering controls (e.g., channelized or armored). The clearing or dredging of a natural drainage system does not cause the system to be classified as modified for purposes of the "Hydromodification Management Requirements" in the MS4 Permit.

Parking lot means land area or facility for the parking or storage of motor vehicles used for businesses, commerce, industry, or personal use, with a lot size of 5,000 square feet or more of surface area, or with 25 or more parking spaces.

Pollutant means any "pollutant" defined in Section 502(6) of the Federal Clean Water Act or incorporated into the California Water Code Section 13373.

Project means all development, redevelopment, and land disturbing activities. The term is not limited to "project" as defined under CEQA (Public Resources Code Section 21065).

Rainfall harvest and use means a LID BMP system designed to capture runoff, typically from a roof but can also include runoff capture from elsewhere within the site, and to provide for temporary storage until the harvested water can be used for irrigation or non-potable uses. The harvested water may also be used for potable water uses if the system includes disinfection treatment and is approved for such use by the local Building Department.

Redevelopment means activity that includes, but is not limited to: the expansion of a building footprint; addition or replacement of a structure; replacement of impervious surface area that is not part of routine maintenance activity; and land disturbing activity related to structural or impervious surfaces. It does not include routine maintenance to maintain original line and grade, hydraulic capacity, or original purpose of facility, nor does it include emergency construction activities required to immediately protect public health and safety.

Regional Board means the California Regional Water Quality Control Board, Los Angeles region.

Routine maintenance includes, but is not limited to, projects conducted to:

1. Maintain the original line and grade, hydraulic capacity, or original purpose of the facility.

2. Perform as needed restoration work to preserve the original design grade, integrity and hydraulic capacity of flood control facilities.

3. Includes road shoulder work, re-grading dirt or gravel roadways and shoulders and performing ditch cleanouts.

4. Update existing lines* and facilities to comply with applicable codes, standards, and regulations regardless if such projects result in increased capacity.

5. Repair leaks.

6. Routine maintenance does not include construction of new** lines or facilities resulting from compliance with applicable codes, standards and regulations.

* Update existing lines includes replacing existing lines with new materials or pipes.

** New lines are those that are not associated with existing facilities and are not part of a project to update or replace existing lines.

Site means land or water area where any facility or activity is physically located or conducted, including adjacent land used in connection with the facility or activity.

Storm water or stormwater means storm water runoff, snow melt runoff, and surface runoff and drainage related to precipitation events (pursuant to 40 CFR Section 122.26(b)(13); 55 Federal Regulations 47990, 47995 (Nov. 16, 1990)).

(Ord. 545 § 1, 2013; Ord. No. 2024-617, § 5(Att. C), 6-12-2024)

A. New development and redevelopment projects listed in Part VIII.F.1.a-b of the NPDES MS4 permit fall under the permittee's planning and building authority for which the City must impose specific requirements, including the implementation of structural BMPs to meet the performance requirements described in Part VIII.F.4 of the NPDES MS4 permit.

1. Redevelopment projects:

a. Where redevelopment results in an alteration to more than 50 percent of impervious surfaces of a previously existing development, and the existing development was not subject to post-construction storm water quality control requirements, the entire project must be mitigated.

b. Where redevelopment results in an alteration of less than 50 percent of impervious surfaces of a previously existing development, and the existing development was not subject to post-construction storm water quality control requirements, only the alteration must be mitigated, and not the entire development.

c. Redevelopment does not include routine maintenance activities that are conducted to maintain original line and grade, hydraulic capacity, original purpose of facility or emergency redevelopment activity required to protect public health and safety. Impervious surface replacement, such as the reconstruction of parking lots and roadways which does not disturb additional area and maintains the original grade and alignment, is considered a routine maintenance activity. Redevelopment does not include the repaving of existing roads to maintain original line and grade.

(Ord. 545 § 1, 2013; Ord. No. 2024-617, § 5(Att. C), 6-12-2024)

Each new development and redevelopment subject to the provisions of this chapter shall be designed to control pollutants, pollutant loads, and runoff volume to the maximum extent feasible by minimizing impervious surface area and controlling runoff from impervious surfaces through infiltration, evapotranspiration, bioretention and/or rainfall harvest and use. The minimum required standards shall be as follows:

A. Street and road construction of 10,000 square feet or more of impervious surface shall follow USEPA guidance regarding Managing Wet Weather with Green Infrastructure: Green Streets (December 2008 EPA-833-F-08-009), to the maximum extent practicable.

B. All other projects shall prepare a LID plan to comply with the following:

1. Retain storm water runoff on-site for the stormwater quality design volume (SWQDv) defined as the runoff from the greater of the following:

a. The 85th percentile 24-hour runoff event as determined from the Los Angeles County 85th percentile precipitation isohyetal map; or

b. The volume of runoff produced from a three-quarter-inch, 24-hour rain event.

2. Minimize hydromodification impacts to natural drainage systems as defined in the NPDES MS4 permit.

3. To demonstrate technical infeasibility, the project applicant must demonstrate that the project cannot reliably retain 100 percent of the SWQDv on-site, even with the maximum application of green roofs and rainwater harvest and use, and that compliance with the applicable post-construction requirements would be technically infeasible by submitting a site-specific hydrologic and/or design analysis conducted and endorsed by a registered professional engineer, geologist, architect, and/or landscape architect. Technical infeasibility may result from conditions including the following:

a. The infiltration rate of saturated in-situ soils is less than three-tenths-inch per hour and it is not technically feasible to amend the in-situ soils to attain an infiltration rate necessary to achieve reliable performance of infiltration or bioretention BMPs in retaining the SWQDv on-site;

b. Locations where seasonal high groundwater is within five to ten feet of surface grade;

c. Locations within 100 feet of a groundwater well used for drinking water;

d. Brownfield development sites or other locations where pollutant mobilization is a documented concern;

e. Locations with potential geotechnical hazards;

f. Smart growth and infill or redevelopment locations where the density and/or nature of the project would create significant difficulty for compliance with the on-site volume retention requirement.

4. If partial or complete on-site retention is technically infeasible, the project site may biofiltrate one and one-half times the portion of the remaining SWQDv that is not reliably retained on-site. Biofiltration BMPs must adhere to the design specifications provided in the NPDES MS4 permit.

a. Additional alternative compliance options such as off-site infiltration and groundwater replenishment projects may be available to the project site. The project applicant should contact the City to determine eligibility.

5. The remaining SWQDv that cannot be retained or biofiltered on-site must be treated on-site to reduce pollutant loading. BMPs must be selected and designed to meet pollutant-specific benchmarks as required per the NPDES MS4 permit. Flow-through treatment BMPs may be used to treat the remaining SWQDv and must be sized based on a rainfall intensity of:

a. Two-tenths of an inch per hour; or

b. The 85th percentile hourly storm event, as determined from the local historical rainfall record, multiplied by a factor of two.

(Ord. 545 § 1, 2013; Ord. No. 2024-617, § 5(Att. C), 6-12-2024)

Editor's note— Ord. No. 2024-617, § 5(Att. C), adopted June 12, 2024, amended the title of § 13.20.040 to read as herein set out. The former § 13.20.040 title pertained to low impact development standards for development and redevelopment planning and construction activities.

The requirements of this chapter shall become effective on August 12, 2013. This includes projects subject to discretionary permits or project phases that have not been deemed complete for processing or discretionary permit projects without vesting tentative maps that have not requested and received an extension of previously granted approvals.

(Ord. 545 § 1, 2013; Ord. No. 2024-617, § 5(Att. C), 6-12-2024)