The Rural Stormwater Code aims to limits applicability to large residental or moderate to large commercial or industrial projects. An application would have to propose a project of more than 10,000 square feet of impervious area AND 15% of the parcel size in order to trigger the residential threshold. Essentially, a Super Walmart size of impervious area, such as roofs, paved roadways, etc, would need to be proposed for a lot size of 5 acres before the new standards would apply. This handout (PDF) illustrates the concept.
Interested in all the nitty-gritty details?
The Rural Stormwater Code is located here, click Chapter 16 and then 16.20.
Still have questions? Patrick Harbison, P.E., is the Cowlitz County Stormwater Engineer. He can be reached at harbisonp@co.cowlitz.wa.us or (360) 577-3030.