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SEPA checklist guidance, Section B: Earth

We provide guidance to help applicants complete the Earth section of the SEPA Section B: Environmental elements checklist.

1. Earth

a. General description of the site: Flat, rolling, hilly, steep slopes, mountainous, other:

Ignoring structures and vegetation, describe the general shape or contour of the land including the project site and surrounding area. When proposals cover multiple areas, describe the general predominate landform types. It is important to note:
  • Steep or hazardous slopes. Describe hazardous slopes, including slope percentage and vertical height. Identify any large, deep-seated slumps, unstable areas, and any mass wasting features.
  • Tidelands, bedlands, harbor areas, or freshwater shorelands. Tidelands are located between the ordinary high tide and extreme low tide lines. Bedlands lie waterward of and below the navigability line for non-tidal rivers and lakes. The harbor area is the line where a harbor has been created. Shorelands are submerged lands lying along the edge of lakes or rivers.
  • Other nearshore features. These include feeder bluffs directly impacting the nearshore ecosystem on aquatic lands. Provide location information for feeder bluffs as well as drift cells.   
b. What is the steepest slope on the site (approximate percent slope)?

Slope refers to the number of units the land falls or rises in 100 units of horizontal distance. The higher the percentage, the steeper the slope. This calculation is critical for proposals to remove vegetation or disturb soils. Percent slope is typically measured by professionals with a clinometer but can be measured in the field. Field measurements or a topographic map must be used to determine the rise and run of the steepest on-site slope.
Calculate the percent slope using this formula: Percent Slope = (Rise/Run) x 100.  A 45 degree angle, where rise and run are equal, results in a 100 percent slope. 
 
c. What general types of soils are found on the site (for example, clay, sand, gravel, peat, muck)? If you know the classification of agricultural soils, specify them and note any agricultural land of long-term commercial significance and whether the proposal results in removing any of these soils:

A site can have multiple types of soil. Applicants need to list the average soil profile to a depth of four feet. More information is available through local governments, colleges and universities, and other sources.  

d.  Are there surface indications or history of unstable soils in the immediate vicinity? If so, describe:

Unstable soils refers to areas subject to mass wasting or landslides. Landslides occur when gravity pushes a mass of soil or rock moves down the slope. A proposal may need further evaluation if unstable soils are found. This question also applies to land under water. Past fill activities including filled wetlands and tide lands, reclaimed surface mines as well as destabilization from vegetation removal, evidence of high groundwater, or concentrated stormwater infiltration are all indicators of potential soil non-stability.

e. Describe the purpose, type, total area, and approximate quantities and total affected area of any filling, excavation, and grading proposed. Indicate source of fill: 

Fill type describes the materials to be imported to the site such as large rocks, gravel, sand, clay, top soil, mixed soil and rock, etc. Fill source is the original location of the imported material and must be checked for invasive species to keep them from spreading. Include the specific location of the area to be filled on the project site.  Most proposals to fill in aquatic lands require additional permits and approvals. Provide the quantities of grading, excavation, or fill in cubic yard measures. Professionals may need to be consulted for this information.
 
f. Could erosion occur as a result of clearing, construction, or use? If so, generally describe:

If erosion could occur during construction activities such as filling, excavation, grading, or removing vegetation, describe the total area of exposed soil and duration of expected activities during the life of the proposal. The following circumstances could lead to site erosion including:
  • Changes in geometry of the slope.
  • Changes in material characteristics of the slope or soil.
  • Increased water on the slope or in the soil.
  • Increased or re-directed energy in a stream, river, lake or marine waters.
g. About what percent of the site will be covered with impervious surfaces after project construction (for example, asphalt or buildings)?

Include any square foot where rain cannot percolate into the ground such as building footprints, asphalt and concrete areas, covered or capped ground, and lined ditches or ponds.
Include areas of impervious soil cover during and / or after project construction. Stockpile areas and pit floors often become impervious surface. Other examples of impervious or nearly impervious surfaces include paved roads, piling supported structures, bridges and pier, and hard packed grass, roads and parking lots.
 
h. Proposed measures to reduce or control erosion, or other impacts to the earth, if any:

General mitigation possibilities include:
  • Avoidance (stay away from the area).
  • Alternative on-the-ground operational systems.
  • Removing unstable material.
  • Engineering to reinforce the slope, drain water, etc.
  • Vegetation management (such as mulching, grass seeding, slash placement).
  • Reducing slopes.
  • Ripping or tilling compacted area.
  • Road design, drainage structures, and water dispersion or fill armoring techniques.
  • Silt curtains for in-water work.
Control methods to defray the potential erosion effects:
  • Minimizing vegetation removal or actions in disturbed areas during construction and operation, especially steep slopes or previous destabilized areas.
  • Planting or maintaining vegetative cover.
  • Moistening exposed soils or applying stabilizing compounds.
  • Placing straw, rip rap, or other materials to reduce exposure to the elements. 
  • Putting roads and structures away from unstable areas or geological hazards.
  • Managing stormwater after construction is completed.
Tip: Before selecting plant material for vegetative cover, check the Washington State Noxious Weed list to avoid using any noxious weed species. The board also maintains a list of certified weed-free hay and mulch providers.