Runoff
from construction sites can contain significant
pollution including sediment, concrete fines,
lubricants and fuels, solvents, fertilizers,
pesticides and many other contaminants which,
if allowed to enter storm drains, will pollute
Santa Monica Bay. Mitigation steps must
be taken to ensure that no runoff leaves
the site during the dry season and that
stormwater contamination during rain events
is minimized.
All
construction projects in the City of Santa
Monica must follow specific construction
Best Management Practices, or BMPs. BMPs
ensure that hazardous materials and pollutants
stay onsite and don’t get washed or
dumped into the storm drain system. The
BMPs in the list below are required by City
Ordinance. BMPs must be put into practice
at the time of demolition of an existing
structure, or at the start of new construction,
and will remain in place until a certificate
of occupancy has been issued. In addition,
depending on the size of the project, there
may be state requirements above and beyond
those of the City of Santa Monica. Check
with the Engineering Division to determine
if state regulations apply to the project.
- Runoff,
sediment and construction waste from construction
sites and parking areas shall not leave
the site.
- Any
sediments or other materials that are
tracked onto adjacent streets or properties
shall be removed the same day.
- On
an emergency basis only, plastic covering
may be utilized to prevent erosion of
an otherwise unprotected area, along with
runoff devices to intercept and safely
convey the runoff.
- Excavated
soil shall be located on the site in a
manner that eliminates the possibility
of sediments running into the street or
adjoining properties. Soil piles shall
be covered until the soil is either used
or removed.
- No
washing of vehicles shall be allowed adjacent
to a construction site. No runoff from
washing vehicles on a construction site
is allowed to leave the site.
- Drainage
controls shall be utilized as needed,
depending on the extent of proposed grading
and topography of the site.
Typical
techniques used to contain runoff are swales,
diversion ditches, and stormwater treatment
devices such as dry wells, sediment control
ponds (on large sites) and several proprietary
fixtures. Where storm water is collected
on site it can be recycled for dust control
and irrigation.
Stabilizing
excavated material, stockpiled soil and
fill to prevent wind loss and erosion by
storms is essential to stormwater protection.
It is far easier and more economical to
prevent stormwater contamination at the
source than to attempt to capture and clean
it later.
On
some sites a wheel-cleaning strip of coarse
gravel where trucks leave the site will
help control soil loss and reduce the amount
deposited on streets. A strip the full width
of the site access road and at least 12
ft. long is generally adequate. The strip
should be graded to slope into the site,
and should be made from 3/4“ to 1-1/2”
rock (“drain rock” material).
After construction, the rock may be used
for non-critical drainage, landscaping or
fill uses.
Cautions
- Arrangements
must be made for wash-down of concrete
and excavation equipment off-site where
sediment capture facilities exist.
- Straw
bales, often used as a sediment barrier,
are not very effective.
- Oversized
rock (over 3 in.) should not be used in
a wheel-cleaning strip due to possible
road hazards from becoming stuck between
dual truck wheels.
