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Compost and topsoil calculator for meeting post-construction soil standards (King County Code 16.82)

The Compost and Topsoil Calculator below is for use by permit applicants to determine the compost and/or topsoil needs for site development projects to meet the post-construction soil standard required by King County's Clearing and Grading regulations KCC 16.82. This information must be included on the Soil Management Plan Download Microsoft Word document 900 K form required as part of the permitting process. Steps for preparing a Soil Management Plan are found on pp. 8-9 in the Achieving the Post-construction Soil Standard brochure Download PDF 1 MB.

The calculator can calculate:

  • a custom compost amendment rate (i.e., number of inches of compost to be layered over the site surface and mixed in)
  • quantity of compost (in cubic yards) needed
  • quantity of site soil (in cubic yards) to be stockpiled, and/or
  • quantity of imported topsoil (in cubic yards) needed.

Follow these four steps to determine compost or topsoil needs and provide results as required by the permitting process:

Step 1: Determine which soil management option(s) are needed for each area marked on project site map by reading Achieving the Post-construction Soil Standard brochure Download PDF 1 MB (pp. 4-6).

Step 2: Choose Turf or Planting beds and determine Amendment rate of compost needed:

  • For soil treatment options that involve adding compost to the soil, permit applicants must choose to use a pre-approved amendment rate of application or a custom amendment rate.
  • On many sites, a custom amendment rate will be lower than the pre-approved rate. To calculate a custom amendment rate, you will need to enter information from laboratory tests* of the site soil and specified compost products.
  • Are you performing a turf or planting application? (choose one)
    Turf   Planting beds
  • Pre-approved or Custom compost amendment rate? (choose one)
    Pre-approved   Custom
 

Step 3: For each option needed, enter the following into the table below and click Calculate:

  • identification of site area(s) marked on site map (for example, A, B, C)
  • total square footage for all areas on map where the options will be implemented.
Soil managment options Areas on site map using this option (example: A, B, C) Total square footage for all areas, in thousands. Do not use commas (example: enter 4,525 square feet as 4525)
Option 1: Leave native soil undisturbed Not Applicable Not Applicable
Option 2: Amend existing soil in-place
Option 3: Import topsoil mix
Option 4: Disturbed Soil - stockpile, reapply and amend
  Amount of soil to stockpile Amount compost needed Amount topsoil needed
Option 1: Leave native soil undisturbed N/A N/A N/A
Option 2: Amend existing soil in-place
Areas:
Square footage in thousands =
* *
Option 3: Import topsoil mix
Areas:
Square footage in thousands =
* *
Option 4: Disturbed Soil - stockpile, reapply and amend
Areas:
Square footage in thousands =
*
Totals
 
 

Step 4: Enter the results of the calculations for compost and/or topsoil needed from the table above on the Soil Management Plan Download PDF 1 MB, and attach a print-out of the calculation results to the Plan. Submit to Department of Local Services, Permitting Division as part of the permitting process.

Department of Local Services, Permitting Division reviewers will also use the calculator to verify the compost and/or soil quantities that permit applicant must enter in the Soil Management Plan.

Note that separate calculation sheets are needed for turf and planting beds.

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