Tuesday, July 30, 2013

Notes on Lake Whatcom Stormwater Infiltration

I had a geology hazard assessment project that took me out to the Lake Whatcom watershed east of Bellingham. Dug a few test pits with some interesting results. Not completely unexpected, but not expected either. Besides the geology I got a chance to check out some of the ways home builders have addressed stormwater in this sensitive watershed.
Probable glacial drift
A policy vote took place in the Lake Whatcom watershed last week. The County Council passed new updated development regulations to minimize potential phosphorus run off from new development in the watershed. A fair bit of the new language was simply clarification of existing regulations and got rid of some exemptions. The goal: any new development will not release phosphorus from the site at levels greater than natural background conditions. Lake Whatcom has dissolved oxygen issues that are linked to excess phosphorus inputs.
The County has made several upgrades to stormwater regulations in the Lake Whatcom watershed in the past. However, previous efforts were done without the mandated phosphorus pollution reduction requirements that are required through the Clean Water Act being implemented by the Washington State Department of Ecology.
There was some interesting dialog on phosphorus sources and how Ecology has approached this problem during the debate before the new rules were voted on that might be worth a post, but in the end the simplest approach to phosphorus in stormwater is to get the stormwater  into the ground versus having it run off the site and that is in fact the primary goal of the new regulations and really not significantly different than what was already required. 
Infiltration of stormwater is often an easy thing to do on large lots, but it gets tougher on small lots or lots with soils that are resistant to infiltration. Thought ahead of time on design and layout will make it easier and save a lot of money. Stormwater infiltration is not unique to Lake Whatcom and if stormwater is considered at the very beginning of the design phase for a home versus as an after thought, costs will be much less or one can avoid major redesigns or complicated engineered stormwater treatment facilities.
While getting the lay of the land for my geology assessment, I observed numerous driveway projects that had been installed to meet the existing stormwater rules on small lots. Pervious pavement surfaces all designed to get stormwater into the ground versus delivering phosphorus via soil particles and organic material carried by surface water flow.
New pervious concrete 
Pervious pavers

Pervious pavers

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