Friday, June 21, 2013

Over One MILLION Gallons of Waste Water - Where's It All Going to Go?

In my last post, I explained how the Alki 11 rowhouse project on 55th Ave SW will add more than one million gallons of combined waste and stormwater to our local sewer system every year - 8 times the volume generated with the previous housing configuration. Where is all of that polluted water going to go?


Sewer manhole cover on Wickstrom Place SW

Our Alki Beach neighborhood has a combined sewer system, meaning that storm drains tie directly into the sanitary sewer. Buildings built in the past 10 years or so also have their downspouts and parking area drains tied into the sewer. 

The drainage and waste water map of 55th Ave and Wickstrom Place shows how this works. (55th Ave is the street shown on the left. Wickstrom is the dead end street on the right.) Water lines are shown as blue-black, sewer lines are red and stormwater drain lines, turquoise. The little black rectangles are storm drain catch basins. You can see that the older buildings do not have turquoise drain lines around them - they have natural drainage for stormwater runoff from roofs - downspouts empty into yards. This keeps a lot of stormwater out of the system, which reduces the likelihood of sewage overflows into the Sound, as I will explain later. 

According to documents filed by the developer with the city, all waste and stormwater from the Alki 11 rowhouse project will empty into the sewer line on Wickstrom Ave SW. From there, it will go to the 53rd Ave Pump Station, two blocks away. Waste and stormwater is pumped from this station to the West Point treatment plant

53rd Ave Pump Station on Alki Ave SW
Considering that stormwater runoff is now the number one source of pollution in  Puget Sound, you might think that sending it all off to a sewage treatment plant is a good idea. Unfortunately, it isn't that simple. When we have heavy rains, that extra volume of water overwhelms the system. To prevent flooding and sewage backups into homes, Combined Sewer Overflows (CSOs) release combined stormwater and raw sewage into the Sound. This 53rd Ave Pump Station is one of those CSOs. Here's a map of CSO locations in Seattle. Want to know if a CSO near you is discharging sewage? Here's real-time map showing CSO status.

The 53rd Ave Pump Station was recently upgraded to add two or three times the capacity it had before. But you have to wonder: how many projects like the Alki 11 rowhouses - which adds 8 times the volume and does nothing to absorb and mitigate stormwater onsite - can the system take on without serious environmental consequences?

Sign posted next to the 53rd Ave Pump Station

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