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GRD-011 Erosion Prevention and Sediment Control Notes

Permit and Resource Management Department Banner 750

These notes provide information on the County’s requirements for erosion prevention and sediment control during building and construction activities.

Version: December 16, 2020

  1. Perform erosion prevention and sediment control in accordance with Chapter 11 and Chapter 11A of the Sonoma County Code (SCC).
  2. The approved plans shall conform to Permit Sonoma erosion prevention and sediment control best management practices (BMP’s) guide as posted on the Permit Sonoma website.
  3. The property owner is responsible for preventing storm water pollution generated from the construction site year round. Work sites with inadequate erosion prevention and/or sediment control may be subject to a stop work order and/or additional inspection fees to verify compliance with the SCC.
  4. If discrepancies occur between these notes, material referenced on the approved plans or manufacturer’s recommendations, then the most protective shall apply.
  5. At all times the property owner is responsible for obtaining and complying with the state of California national pollutant discharge elimination system (NPDES) general permit for storm water discharges associated with construction and land disturbing activities such as clearing, grading, excavation, stockpiling, and reconstruction of existing facilities involving removal and replacement.
  6. The property owner must implement an effective combination of erosion prevention and sediment control on all disturbed areas during the rainy season (October 1 - April 30). Grading and drainage improvement shall be permitted during the rainy season only when on-site soil conditions permit the work to be performed in compliance with the SCC.
  7. During the rainy season, storm water BMPs referenced or detailed in Permit Sonoma’s BMPs guide shall be implemented and functional on the site at all times and the area of erodible land exposed at any one time during the work shall not exceed one acre or 20 percent of the permitted work area, whichever is greater, and the time of exposure shall be minimized to the maximum extent practicable.
  8. During the non-rainy season, on any day when the national weather service forecast is a chance of rain of 30 percent or greater within the next 24 hours, storm water BMPs referenced or detailed in Permit Sonoma’s BMPs guide shall be implemented and functional on the site to prevent soil and other pollutant discharges. At all other times, BMPs should be stored on site in preparation for installation prior to rain events.
  9. Erosion prevention and sediment control BMPs shall be inspected by the property owner before foretasted storm events and after storm events to ensure BMPs are functioning properly. Erosion prevention and sediment control BMPs that have failed or are no longer effective shall be promptly replaced. Erosion prevention and sediment control BMPs shall be maintained until disturbed areas are stabilized.
  10. The limits of grading shall be defined and marked on site to prevent damage to surrounding trees and other vegetation. Preservation of existing vegetation shall occur to the maximum extent practicable. Any existing vegetation within the limits of grading that is to remain undisturbed by the work shall be identified and protected from damage by marking, fencing, or other measures.
  11. Changes to the erosion prevention and sediment control plan may be made to respond to field conditions if the alternative BMPs are equivalent or more protective than the BMPs shown on the approved plans. Alternative BMPs are subject to review and approval by Permit Sonoma staff.
  12. Discharges of potential pollutants from construction sites shall be prevented using source controls to the maximum extent practicable. Potential pollutants include but are not limited to: sediment, trash, nutrients, pathogens, petroleum hydrocarbons, metals, concrete, cement, asphalt, lime, paint, stains, glues, wood products, pesticides, herbicides, chemicals, hazardous waste, sanitary waste, vehicle or equipment wash water, and chlorinated water.
  13. Entrance(s) to the construction site shall be maintained in a condition that will prevent tracking or flowing of potential pollutants off site. Potential pollutants deposited on paved areas within the county right-of- way, such as roadways and sidewalks, shall be properly disposed of at the end of each working day or more frequently as necessary. The contractor shall be responsible for cleaning construction vehicles leaving the site on a daily basis to prevent dust, silt, and dirt from being released or tracked off site. All sediment deposited on paved roadways shall be removed at the end of each working day or more often, as necessary.
  14. All disturbed areas shall be protected by using erosion prevention BMPs to the maximum extent practicable, such as establishing vegetation coverage, hydroseeding, straw mulch, geotextiles, plastic covers, blankets, or mats. Temporary Revegetation shall be installed as soon as practical after vegetation removal, but in all cases prior to October 1. Permanent revegetation or landscaping shall be installed prior to final inspection.
  15. Whenever it is not possible to use erosion prevention BMPs on exposed slopes, sediment control BMPs such as fiber rolls and silt fences shall be installed to prevent sediment migration. Fiber rolls and silt fences shall be trenched and keyed into the soil and installed on contour. Silt fences shall be installed approximately 2 to 5 feet from toe of slope.
  16. Hydroseeding shall be conducted in a three step process. First, evenly apply seed mix and fertilizer to the exposed slope. Second, evenly apply mulch over the seed and fertilizer. Third, stabilize the mulch in place. An equivalent single step process, with seed, fertilizer, water, and bonded fibers is acceptable.

    Applications shall be broadcasted mechanically or manually at the rates specified below. Seed mix and fertilizer shall be worked into the soil by rolling or tamping. If straw is used as mulch, straw shall be derived from wheat, rice, or barley and be approximately six to eight inches in length. Stabilization of mulch shall be done hydraulically by applying an emulsion or mechanically by crimping or punching the mulch into the soil. Equivalent methods and materials may be used only if they adequately promote vegetation growth and protect exposed slopes.

    Materials and Application Rate (pounds per acre)
    • Seed mix
      • Bromus mollis (blando brome) - 40 pounds
      • Trifolium hirtum (hykon rose clover) - 20 pounds
      • 16-20-0 & 15% sulphur - 500 pounds
      • Straw - 4000 pounds
      Hydraulic stabilizing
      non-asphaltic, derived from plants
      • M-binder or sentinel - 75-100 pounds
      Equivalent material
      • Per manufacturer
  17. Dust control shall be provided by the contractor during all phases of construction.
  18. Storm drain inlets shall be protected from potential pollutants until drainage conveyance systems are functional and construction is complete.
  19. Energy dissipaters shall be installed at storm drain outlets which may convey erosive stormwater flow.
  20. Soil, material stockpiles, and fertilizing material shall be properly protected with plastic covers or equivalent BMP's to minimize sediment and pollutant transport from the construction site.
  21. Solid waste, such as trash, discarded building materials, and debris, shall be placed in designated collection areas or containers. The construction site shall be cleared of solid waste daily or as necessary. Regular removal and proper disposal shall be coordinated by the contractor.
  22. A concrete washout area shall be designated to clean concrete trucks and tools. At no time shall concrete products and waste be allowed to enter county waterways such as creeks or storm drains. No washout of concrete, mortar mixers, or trucks shall be allowed on the soil. Concrete waste shall be properly disposed.
  23. Proper application, cleaning, and storage of potentially hazardous materials, such as paints and chemicals, shall be conducted to prevent the discharge of pollutants.
  24. Temporary restrooms and sanitary facilities shall be located and maintained during construction activities to prevent the discharge of pollutants.
  25. Appropriate vehicle storage, fueling, maintenance, and cleaning areas shall be designated and maintained to prevent the discharge of pollutants.