Pomona Municipal Code § 74-314 Applicability

These procedures and standards set forth in this article, the BMP design information found in the Los Angeles County municipal storm water permit, and the County of Los Angeles department of public works low impact development standards manual (February 2014), and any amendment, revision, or reissuance thereof provide minimum standards to be complied with by developers and in no way limit the city's authority to adopt and publish or enforce higher standards as a condition of approval of developments.

(a) New development projects. Development projects subject to city conditioning and approval for the design and implementation of post-construction controls to mitigate stormwater pollution prior to completion of the project(s) include:

(1) All development projects equal to one acre or greater of disturbed area and adding more than 10,000 square feet of impervious surface area;

(2) Industrial parks 10,000 square feet or more of surface area;

(3) Commercial malls ten thousand (10,000) square feet or more of surface area;

(4) Retail gasoline outlets 5,000 square feet or more of surface area.

(5) Restaurants (SIC 5812) 5,000 square feet or more of surface area;

(6) Parking lots 5,000 square feet or more of impervious surface area, or with 25 or more parking spaces;

(7) Street and road construction of 10,000 square feet or more of surface area shall follow the city green street policy to the maximum extent practicable. Street and road construction applies to standalone streets, roads, highways, and freeway projects, and also applies to streets within larger projects;

(8) Automotive service facilities (SIC 5013, 5014, 5511, 5541, 7532-7534 and 7536-7539) with 5,000 square feet or more of surface area;

(9) New development projects located in or directly adjacent to, or discharging directly to the proposed significant ecological area ("SEA") which will:

a. Discharge stormwater runoff that is likely to impact a sensitive biological species or habitat; and

b. Create two thousand 2,500 square feet or more of impervious surface area; and

(10) Redevelopment projects in subject categories that meet redevelopment thresholds identified in Part B—Redevelopment projects, below;

(11) Redevelopment projects located in or within 200 feet of, or discharging directly to a significant ecological area (SEA) where the development will:

a. Discharge stormwater runoff that is likely to impact a sensitive biological species or habitat; and

b. Create 2,500 square feet or more of impervious surface area.

(12) Single-family hillside homes. During the construction of a single-family hillside home, the following measures shall be considered to the maximum extent practicable:

a. Conserve natural areas.

b. Protect slopes and channels.

c. Provide storm drain system stenciling and signage.

d. Divert roof runoff to vegetated areas before discharge unless the diversion would result in slope instability.

e. Direct surface flow to vegetated areas before discharge unless the diversion would result in slope instability.

(b) Redevelopment projects. Redevelopment projects subject to conditioning and approval requirements outlined in this article for the design and implementation of post-construction controls to mitigate stormwater pollution prior to completion of the project(s) include:

(1) Land disturbing activity that results in the creation or addition or replacement of 5,000 square feet or more of impervious surface area on an already developed site.

(2) Redevelopment project that result in an alteration to more than 50 perfect of impervious surfaces of an existing development which had not been subject to post-construction stormwater quality control requirements at the time of the previous development shall be required to mitigate the entire project site.

(3) Redevelopment project that result in an alteration of less than 50 perfect of impervious surfaces of an existing development which had not been subject to post-construction stormwater quality control requirements at the time of the previous development shall be required to mitigate only the alteration and shall not be required to mitigate the entire project site.

(4) 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.

(5) Existing single-family dwelling and accessory structures are exempt from the redevelopment requirements unless such projects create, add, or replace 10,000 square feet of impervious surface area.

(Ord. No. 4185, § 1, 6-2-2014)

All development projects that fit the project criteria listed above in section 74-331 of this article shall control pollutants, pollutant loads, and runoff volume by retaining the stormwater quality design volume (SWQDv) (as defined in definitions) on-site through:

(1) Minimizing the impervious surface area; and

(2) Controlling runoff from impervious surfaces through infiltration, bioretention and/or rainfall harvest and use.

(Ord. No. 4185, § 1, 6-2-2014)

(a) To demonstrate technical infeasibility, the project applicant shall demonstrate to the city engineer 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 the compliance with the applicable post-construction requirements would be technically infeasible. This shall be demonstrated by submitting a site-specific hydrologic and/or design analysis conducted and endorsed by a registered professional engineer and shall be subject to review and approval by the city engineer.

(b) When evaluating the potential for on-site retention, each applicant shall consider the maximum potential for evapotranspiration from green roofs and rainfall harvest and use. Alternative compliance measures include the following:

(1) On-site biofiltration. Biofiltration systems shall meet the design specifications provided in Attachment H of the Los Angeles County Municipal Storm Water Permit Order N. R4-2012-0175, and any amendment, revision, or reissuance thereof. If using biofiltration due to demonstrated technical infeasibility, then the new project must biofiltrate 1.5 times the portion of the SWQDv that is not reliably retained on site, as calculated by Equation 1 below:

Equation 1: Bv=1.5* [SWQDv-Rv)

Where: Bv = Biofiltraton volume SWQDv= the stormwater runoff from a 0.75 inch, 24-hour storm or the 85th percentile storm, whichever is greater Rv=volume reliably retained on-site

(2) Off-site infiltration. Use infiltration or bioretention BMPs to intercept a volume of stormwater runoff equal to the SWQDv, less the volume or stormwater runoff reliably retained on-site, at an approved offsite project. The required off-site mitigation volume shall be calculated by Equation 2 below:

Equation 2: Mv=1.0*[SWQDv-Rv]

Where: Mv=Mitigation Volume SWQDv=Runoff from the 0.75 inch, 24-hour storm event or the 85th percentile storm, whichever is greater Rv=the volume of stormwater runoff reliably retained on-site

(3) Offsite project. Retrofit existing development. Use infiltration, bioretention, rainfall harvest and use and/or biofiltration BMPs to retrofit an existing development, with similar land uses as the new development or land uses associated with comparable of higher stormwater runoff event mean concentrations (EMCs) than the new development. The retrofit plan shall be designed and constructed as described in the Los Angeles County Municipal Storm Water Permit Order N. R4-2012-0175, and any amendment, revision, or reissuance thereof.

(4) Other alternative compliance requirements are detailed in the Los Angeles County Municipal Stormwater Permit Order No. R4-2012-0175.

(c) Applicants and/or designers may select any combination of stormwater BMPs which meet the performance standards provided in this section and identified in the Los Angeles Municipal Storm Water Permit Order N. R4-2012-0175, and the County of Los Angeles Department of Public Works Low Impact Development Standards Manual (February 2014), and any amendment, revision, or reissuance thereof.

(Ord. No. 4185, § 1, 6-2-2014)