(4) Site Design Best Management Practices (BMP) Requirements
(a) The City of Laguna Beach must require each Priority Development Project to
implement site design BMPs which will collectively minimize directly
connected impervious areas, limit loss of existing infiltration capacity, and
protect areas that provide important water quality benefits necessary to
main riparian and aquatic biota, and/or are particularly susceptible to
erosion and sediment loss.
(b) The following Site Design BMPs must be implemented at all Priority
Development Projects as required below:
(i) Maintain or restore natural storage reservoirs and drainage corridors
(including depressions, areas of permeable soils, swales, and
ephemeral and intermittent streams) in drainage networks in
preference to pipes, culverts, and engineered ditches.
(ii) For Priority Development Projects with landscaped or other pervious
areas, properly design and construct the pervious areas to effectively
receive and infiltrate or treat runoff from at least a portion of impervious
areas prior to discharge to the MS4 (storm system). The amount of the impervious
areas that are to drain to pervious areas must be based upon the total
size, soil conditions, slopes, and other pertinent factors of the project.
(iii) For Priority Development Projects with low traffic areas and
appropriate soil conditions, construct a portion of walkways, trails,
overflow parking lots, alleys, or other low-traffic areas with permeable
surfaces, such as pervious concrete, porous asphalt, unit pavers, and
granular materials. |
(c) The following Site Design BMPs listed below must be implemented at all
Priority Development Projects where applicable and feasible. Each
Copermittee must require each Priority Development Project to
demonstrate applicability and feasibility, or lack thereof, for each site
design BMP listed below.
(i) Minimize disturbances to natural drainages (e.g., creeks, natural
swales, topographic depressions, etc.);
(ii) Conserve natural areas, including existing vegetation and soils;
(iii) Protect slopes and channels;
(iv) Minimize soil compaction of permeable soils;
(v) Construct streets to the minimum widths necessary based on
anticipated usage and public safety;
(vi) Design parking lots to reduce the impervious land coverage of
parking areas and to filter runoff before it reaches the storm drain
system;
(vii) Minimize the impervious footprint of the project;
(viii) Disconnect impervious surfaces through distributed pervious
areas;
(ix) Provide pervious areas for parking and walking; and
(x) Design the layout of buildings to reduce street length and
preserve open space. |
(5) Source Control BMP Requirements
Each Copermittee must require each Priority Development Project to
implement source control BMPs. The source control BMPs to be required
must:
(a) Prevent illicit discharges into the MS4;
(b) Minimize storm water pollutants of concern in urban runoff;
(c) Minimize irrigation runoff;
(d) Include storm drain system stenciling or signage;
(e) Include properly designed outdoor material storage areas;
(f) Include properly designed outdoor work areas;
(g) Include properly designed trash storage areas; and
(h) Include water quality requirements applicable to individual priority project
categories. |
(6) Treatment Control BMP Requirements
Each Copermittee must require each Priority Development Project to
implement treatment control BMPs which meet the following requirements:
(a) All treatment control BMPs for a single Priority Development Project must
collectively be sized to comply with the following numeric sizing criteria:
(i) Volume-based treatment control BMPs must be designed to mitigate
(infiltrate, filter, or treat) the volume of runoff produced from a 24-hour
85th percentile storm event, as determined from the County of
Orange’s 85th Percentile Precipitation Isopluvial Map; or
(ii) Flow-based treatment control BMPs must be designed to mitigate
(infiltrate, filter, or treat) either: a) the maximum flow rate of runoff
produced from a rainfall intensity of 0.2 inch of rainfall per hour, for
each hour of a storm event; or b) the maximum flow rate of runoff
produced by the 85th percentile hourly rainfall intensity (for each hour
of a storm event), as determined from the local historical rainfall
record, multiplied by a factor of two.
(b) Treatment control BMPs for all Priority Development Projects must
mitigate (infiltrate, filter, or treat) the required volume or flow of runoff from
all developed portions of the project, including landscaped areas.
(c) All treatment control BMPs must be located so as to infiltrate, filter, or treat
runoff prior to its discharge to any waters of the U.S. Multiple Priority
Development Projects may use shared treatment control BMPs as long as
construction of any shared treatment control BMP is completed prior to the
use or occupation of any Priority Development Project from which the
treatment control BMP will receive runoff.
(d) All treatment control BMPs for Priority Development Projects must, at a
minimum:
(i) Be ranked with high or medium pollutant removal efficiency for the
project’s most significant pollutants of concern, as the pollutant
removal efficiencies are identified in the Copermittees’ Model SUSMP
or in the Copermittees’ local SUSMPs as they are updated. Treatment
control BMPs with a low removal efficiency ranking must only be
approved by a Copermittee when a feasibility analysis has been
conducted which exhibits that implementation of treatment control
BMPs with high or medium removal efficiency rankings are infeasible
for a Priority Development Project or portion of a Priority Development
Project.
(ii) Be correctly sized and designed so as to remove pollutants to the
Maximum Extent Practicable.
(e) Target removal of pollutants of concern from urban runoff.
(f) Be implemented close to pollutant sources (where shared BMPs
are not proposed), and prior to discharging into waters of the U.S.
(g) Not be constructed within a waters of the U.S. or waters of the
State.
(h) Include proof of a mechanism under which ongoing long-term
maintenance will be conducted to ensure pollutants are reduced to
the MEP for the life of the project. The mechanisms may be
provided by the project proponent or Copermittee. |
More information is available from the County of Orange and the Regional Water Quality Control Board fact sheet. Low Impact Development (LID) techniques are encouraged in Laguna Beach!
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