CONSTRUCTION SITE EROSION CONTROL
METHODS AND REGULATIONS
ATACHMENT: “Storm Water Pollution Prevention, Practices for Construction” A PDF visual presentation compiled by North Central Texas Council of Governments
BACKGROUND
Construction activity, the latest building permit numbers reflect 12,443 permits issued in Honolulu in the year 2000, of which residential and duplex construction accounted for 1,774. Allocating this by population, Koolaupoko would account for 1,635 permits, and 238 new housing units in a year. Many building projects require grading, as well as cut/fill for driveways.
There are few large projects in the pipeline requiring substantial grading (excepting agricultural practices) at the present time, so for now, most projects are likely to be of the small variety.
Smaller projects individually have the potential to cause substantial environmental damage to marine communities on a local scale, say in the vicinity of a stream mouth or drainage outfall. In the aggregate, a number of such projects pose risks to larger embayments. In Koolaupoko, nearly all land classified for residential or commercial use is within 1 mile of marine waters, and agricultural parcels largely within two miles. Severe construction site erosion has immediate impacts on those waters.
The pollutants of concern from construction sites are primarily total suspended solids, sediments (as measured in receiving waters by a light defraction standard called N.T.U.). These sediments often entrain other pollutants, if other pollutants such as oil, grease, or chemicals are present.
In addition to opacity, sediment in the marine environment is also regulated based on depth of accumulation on the bottom persisting more than a certain time period following a storm event. These standards are after the fact measures of pollution applicable in Department of Health Rules (HAR 11-54, various).
Runoff and erosion from a parcel of land are a function of several factors, comprised in the Universal Soil Loss Equation. These include:
a. Type of soil, its porosity and erodibility factor (K). Erodibility factors can be as high as 0.6 for fine silty loam, or as low as 0.1 for sandy clay.
b. Rainfall factor, a function both of volume per unit time, and of drop size.
c. Length and steepness of slopes. The longer or steeper a slope, the greater the erosion potential. Water running onto a parcel from above is a factor that needs to be separately estimated.
d. Vegetation cover of the slopes. The effects of vegetation can reduce erosion by a factor of a thousand (between bare soil and a mature forest)
e. Erosion control practices
Rainfall and soil types differ significantly across the island of Oahu, as well as within Koolaupoko. One size (design storm event for example) does not fit all circumstances. Likewise, some areas have more sensitive receiving waters for which more stringent standards may be appropriate.
Lets go through a short primer on how these factors should be managed on construction sites:
GO THROUGH THE VISUALS
The most effective regulation comes about through zoning. Sites too steep or too erosion prone, and which are near sensitive waters should not be zoned to allow development.
State Land Use has categories for such lands in the Conservation District sub-zones.
County zoning would put such lands in the Preservation (P20 zone)
However, once construction is allowed, application of all practical measures to control site erosion is required by City regulations, even if no permit is needed. In practice, most small sites get little erosion control attention.
DOH – Clean Water Act, regulates receiving waters. Ours in Koolaupoko are AA and A, which set standards tolerating little pollution. Some bottom types, especially fringing coral reef flats are very susceptible to construction site pollution, as heavy sediment discharges can smother inshore reefs. As mentioned previously, the state also has established standards for various bottom types. Unfortunately, these types of regulation are of little effect in individual enforcement actions.
The state’s direct effort to control construction site impacts arise Under Non Point Source Pollution regulations of the Clean Water Act. The State issues permits for construction activity exceeding 5 acres; this criteria is very shortly to become 1 acre. Construction activities may apply for and comply with conditions of standard permits.
The City DPP issues permits for construction and grading. Depending on the scope of the work planned, various levels of permits, erosion control planning, and bonding may be required. In summary:
No grading permit required:
Excavation within building line
Cut/fill less than 50 cy/ 3 vertical feet if off site drainage not modified
Grubbing less than 15,000 sf
Grading permit required but NO erosion control plan required:
Grading area < 15,000sf (about a third of an acre) and maximum cut/fill < 15 (7.5 other than residential) vertical feet
Grading permit required and erosion control plan required:
Grading area> 15,000sf or max cut/fill > 15 (7.5) vertical feet
Grading permit with erosion control plan and soils report required:
Slope >15% or max cut/fill >15 (7.5) vertical feet
Performance Bond required:
Volumes of cut/fill exceed 500 cy
Project owners are not prohibited by construction regulations from polluting; they are only required to employ practical methods to control it. That’s the rub: on some sites, it is not practical to control erosion because of steepness and lack of space, so proper zoning is the best approach for these.
The City DES and State DOT have regulatory clout because of their need to obtain permits for storm water discharge through their respective storm drain system. What goes in also comes out, so the erosion that enters a city or state roadway and then into the ocean becomes a problem for the agency managing the system.
WHERE DO YOU GO IF YOU NEED HELP (also available here)
A.
Department of Planning and Permitting
City & County of Honolulu
650 S King Street, Permit Center
Honolulu, Hawaii 96813
808-523-4164
email to: jnolan@co.honolulu.hi.us
Permitting Web sites:
B. Best Management Practices
Refer to DPP's "Rules Relating to Soil Erosion Control Standards and Guidelines, ” which is available at the City’s municipal bookstore (523-4780) for $2.50 per copy DPP also has handouts on BMP requirements at its counter.
Refer to the Department of Environmental Services “Best Management Practices for Construction Sites in Honolulu.” Hard copies are available at the City’s municipal bookstore (523-4780) for $2.50, or may be downloaded at the following web site: www.cleanwaterhonolulu.com
Common Complaints and errors:
Where to Report Violations:
What to Report: