There are some truly awesome–even sublime–figures associated with sewage treatment. Seattle’s West Point treatment plant, on a normal rainy day, can handle about 133 million gallons of sewage. It tops out at 440 million gallons. The human mind cannot really process 440 million gallons of anything, let alone…stinky brown water. The West Point site covers 32 acres.

And of course things go wrong. Last December, a faulty sensor let 10 million gallons pump into Puget Sound from West Point in one night. Due to a possible mechanical failure at a Kirkland pump station the day before yesterday, 25,000 gallons flowed into Lake Washington.

But a large part of what King County (and Seattle) is still wrestling with are the overflows that were designed to happen. CSOs are combined sewer overflows, an intermediate step in sewage evolution between the stage when everything (storm drains and residential sewage) poured into the nearest large body of water, and today’s Felix-Unger-style set-up, in which sewage is neatly separated from storm water.

King County has 38–and Seattle has 88 (map)–CSOs that allow overflows of a mix of storm water and raw sewage when the system is overwhelmed by rain. The thinking back in the day was that the storm water would dilute the sewage enough, you’d hardly notice. They discharge to Lake Washington, Lake Union, the Lake Washington Ship Canal, the Duwamish River, Elliott Bay, and Puget Sound, to name a few places.

Seattle Pacific University students have learned the rashy way that just because a canal looks cool and inviting, that doesn’t mean it’s safe to dive in. In fact, because these overflows have been operating for decades, no one knows precisely what might be in the sediment near overflow outlets. As I type this (Wednesday), a CSO is discharging into the canal.

King County’s CSO control program is supposed to rein in the raw sewage entering our waterways, but it’s a huge project, and will not be completed until 2030. Still, the county and city have made substantial progress. In 1988, 470 million gallons of wastewater were discharged in Seattle–in 2008, thanks partly to a drier than normal year, the overflows amounted to “just” 24 million gallons.

Sightline has been doing a series on stormwater run-off, and one spectacular entry deals with the in-home sewage overflow: “Geysers of sewage and water gushed from the drains and toilets….” Depending on where you live in Seattle (it’s all about topography and hydrodynamics), you can get sewage geysers more often than you’d like.

Sightline proposes some “smart, cheap stormwater fixes,” and King County urges you to disconnect gutters and drains that may enter the sewer system, and maybe invest in a rain barrel (it’s Seattle, you might need a bigger rain barrel) or rain garden.

Well, maybe wait for it to stop raining first.