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• Marie McKinsey

How Much Sewage Will the Alki 11 Generate?

Updated: Oct 2, 2021

Originally published 6/19/2013

In an earlier post, I explained how to calculate the amount of stormwater runoff this project will produce. Now let's look at the amount of waste water (aka sewage) that will be going down the drain if these rowhouses are built.

According to a King County study done in 2010, per capita water usage in our area is 80 gallons per person. Nearly all of that water ends up in the sanitary sewer system by way of showers, baths, toilet flushes, handwashing, toothbrushing, dishwashing, cooking, laundry, etc.

The developer of the Alki 11 expects that this project will house 33 people.

33 people x 80 gallons of water = 2,640 gallons of waste water generated per day

2,640 gallons per day x 365 days in a year = 963,600 gallons of waste water per year

In addition to all that wastewater, stormwater runoff from this development will flow into the sewer system, too.

Every inch of rain running off the buildings and autocourt of the Alki 11 will produce a combined total of 5,457 gallons.

Rainfall in Seattle averages 38 inches per year.

38 inches x 5,457 gallons of runoff per inch = 207,366 gallons of stormwater per year

The grand total of waste and storm water from these rowhouses = 1,170,966 gallons per year

Compare that number with the volume that has historically been generated on this site:

Zero storm water drained into the sewer because downspouts emptied into yards, and off street parking was on a permeable surface

5 residents x 80 gallons per day = 400 gallons waste water per day

The grand total of waste and storm water from previous housing = 400 gallons x 365 days in a year = 146,000 gallons per year

If built, these rowhouses will introduce 8 times more waste/storm water into the sewer system than before. Even with the recently completed upgrade to the 53rd Ave Pump Station (which increased capacity by only two or three times), this 8-fold increase is way too much.

If sustainability is a goal for the city of Seattle, this is not the way to get there.

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