This calculator may be used 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.
For soil treatment options that involve adding compost to the soil, permit applicants may choose to use the pre-approved amendment rate or a custom amendment rate. To calculate a custom amendment rate, you will need to enter information from laboratory tests of the site soil and specified compost products. On many sites, a custom rate will be lower than the pre-approved rate. Soil and compost sampling and testing must be preformed by an accredited soil testing laboratory.
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 to be ordered
quantity of site soil (in cubic yards) needed to be stockpiled, and/or
quantity of imported topsoil (in cubic yards) needed to be ordered.
The results of these calculations must be entered on the Soil Management Plan (see Achieving the Post-construction Soil Standard(PDF)), and a print-out of the calculation results should be attached to the Plan. DDES reviewers will also use the calculator to verify the Soil Management Plan information.
