Permeable Pavers in Yelm, WA — Infiltration Tested Against Nisqually Valley Outwash.

A permeable interlocking concrete pavement system moves water through the joints into an open-graded reservoir base and, ideally, into the native soil below. That last step is the one that is not automatic. If the native soil will not take the water, the system is a very expensive puddle. Yelm sits at the edge of the Nisqually delta, where sandy outwash gives way to heavier alluvial deposits as you move toward the river.

Most rural parcels here have no municipal storm system to tie into. Whatever water your hardscape sheds has to be retained, infiltrated, or routed on your own property — so on-site retention and swale design are part of the hardscape, not an afterthought. So we test infiltration before we design, and the design follows the answer. Where the soil accepts water, the reservoir infiltrates directly. Where it will not — which is common on the tighter ground in and around Yelm — the reservoir is sized to store the design storm and release it through a perforated underdrain, so the system still performs and still counts. That distinction also drives whether the project earns impervious-surface credit under Thurston County stormwater rules, which is the reason most Downtown Yelm homeowners come to us about permeable in the first place. Designed correctly, it also neutralizes runoff with nowhere legal or physical to go.