County of Asotin

Regional Stormwater Program

Inform. Educate. Prevent.

Large Construction Projects

Local Stormwater Permit Required

  • All earth disturbing activities ≥ 1 acre
  • Requires Stormwater Pollution Prevention Plan (SWPPP) and map
  • Daily inspections by Certified Erosion & Sediment Control Lead (CESCL)
  • Stormwater staff will conduct inspections
  • May require Ecology Stormwater Construction Permit

Stormwater Pollution Prevention Plan (SWPPP)

Large Projects shall prepare a SWPPP for land disturbing activity as part of the Core Elements of stormwater management. The SWPPP shall be implemented beginning with initial soil disturbance and continue until final stabilization. A Certified Erosion and Sediment Control Lead (CESCL) shall be on site or on call on all days when construction or grading activity takes place. The SWPPP and inspection records shall be maintained at the site during the progress of work.

Each of the twelve elements below shall be included in the SWPPP and must be implemented unless site conditions render the element unnecessary and the exemption is clearly justified in the SWPPP.

  • Preserve Vegetation/Mark Clearing Limits
  • Establish Construction Access
  • Control Flow Rates
  • Install Sediment Controls
  • Stabilize Soils
  • Protect Slopes
  • Protect Drain Inlets
  • Stabilize Channels and Outlets
  • Control Pollutants
  • Control De-Watering
  • Maintain BMPs
  • Manage the Project


The SWPPP shall also include a legible site map (or maps) showing the entire construction site. The following features shall be identified:

  • The direction of north, property lines, and existing structures and roads;
  • Cut and fill slopes indicating the top and bottom of slope catch lines;
  • Approximate slopes, contours, and direction of stormwater flow before and after major grading activities;
  • Areas of soil disturbance and areas that will not be disturbed;
  • Locations of structural and nonstructural controls (BMPs) identified in the SWPPP
  • Locations of off-site material, stockpiles, waste storage, borrow areas, and vehicle/equipment storage areas;
  • Locations of all surface water bodies, including wetlands;
  • Locations where stormwater or non-stormwater discharges off-site and/or to a surface water body, including wetlands;
  • Location of water quality sampling station(s), if sampling is required by state or local permitting authority; and
  • Areas where final stabilization has been accomplished and no further construction-phase requirements apply.

Core Elements

Large projects are required to include the applicable minimum technical requirements of the core elements outlined below. This is only a summary and details of all elements can be found in the Stormwater Manual for Eastern Washington located on Department of Ecology’s website at

#1: Preparation of a Stormwater Site Plan – Used to integrate stormwater management into project planning and design, demonstrate compliance with other applicable Core Elements, and illustrate and validate the design of the permanent stormwater management facilities.

#2: Construction Stormwater Pollution Prevention – The purpose is to control erosion and prevent sediment and other pollutants from leaving the site.

#3: Source Control of Pollution – The purpose is to prevent stormwater from coming into contact with potential pollutants.

#4: Preservation of Natural Drainage Systems – The purpose is to maximize the extent to which stormwater discharge patterns, rates, and outfall locations remain the same after a development project.

#5: Runoff Treatment – The purpose is to protect water quality in the receiving water by reducing the loads and concentrations of pollutants in stormwater using biological, physical and chemical removal methods.

#6: Flow Control – The purpose is to protect stream morphology and habitat by mitigating the impacts of increased storm runoff volumes and flow rates to streams.

#7: Operation and Maintenance – The purpose is to prevent failure of stormwater treatment facilities or improper discharges due to inadequate maintenance or improper operation.

Ecology Construction Stormwater Permit

Contractors may be required to apply for the Ecology construction stormwater permit in addition to the local permit. Click here to find out.
See information on Ecology’s Construction Stormwater Permit.