1. Yesterday morning’s item about the Wallingford Community Council’s concern that more density would add too much poop to the sewage system—and overwhelm our water supply with combined sewer overflows—got a strong reaction from readers. (Check the lengthy comments thread.) And from the mayor’s office (which is pushing for upzones to facilitate growth by promoting density.)

Basically, they said the community council was full of s—.

(More politely and literally, the mayor's office identified the concern as the "the development/CSO canard.")

For starters, mayor Ed Murray’s spokesman Jeff Reading pointed out that “the city of Seattle’s storm water code says that all new development needs to take care of its storm water onsite through methods such as underground detention or infiltration.”

Storm water is different than poop, you say? True. But raw sewage only makes up 10 percent of the city sewer flows that create the combined sewer overflow problem. 90 percent of the overload, according to Seattle Public Utilities, comes from storm water runoff.

Second, the city is already designing the Ship Canal Water Quality Facility to bring CSOs in Ballard, Fremont and Wallingford into compliance with health standards. “It has been sized to fully control the area’s outfalls,” Reading told me. SPU's project overview explains, "the 2.7-mile, tunnel will capture and temporarily hold more than 15 million gallons of storm water mixed with some sewage that over flows during heavy rains. When the storm passes, overflows will be sent to the existing West Point Wastewater Treatment Plant in Magnolia." SPU estimates that will keep 50 million gallons of overflow out of the Ship Canal, Salmon Bay, and Lake Union every year and prevent the nearly all of the 130 CSOs that hit Ballard, Fremont, and Wallingford every year



Additionally, one reader pointed me to a study which confirms what I call the Green Metropolis Effect—the idea that density actually eases the burden on infrastructure by making infrastructure more efficient. By way of example: it takes less energy to provide heating for 50 families living in a multifamily building than it does to keep the same 50 families warm if they’re all living in a dispersed set of single family homes in a suburban swath.

According to the EPA, the same concept works for managing storm water and poop.

The findings indicated that "low-density development may not always be the preferred strategy for protecting water resources. Higher densities may better protect water quality - especially at the lot level and watershed scale," the EPA said. The study found that higher-density scenarios generate less storm water runoff per house at all scales - one acre, lot, and watershed - and time series build-out examples. For the same amount of development, the EPA says, higher-density development produces less runoff and less impervious cover than low-density development. For a given amount of growth, the agency found, lower-density development impacts more of the watershed. … dispersed development patterns cost more to serve because of the length of pipe required, pumping costs, and other factors. The literature reviewed shows how large-lot, dispersed development uses more water than smaller lot, higher density development. This publication concludes with policy options for states, localities, and utilities that directly reduce the cost and demand for water, while indirectly promoting smart growth.

2. The city council's affordable housing and neighborhoods committee is taking up committee chair Tim Burgess's proposal to regulate Airbnb this morning. The key component of the proposal is to cap the number of days that off-site property owners can rent rooms; the proposed cap is 90 days.

Part of Burgess's pitch is that those rentals are hurting the city's housing supply.

Sightline's Dan Bertolet has a timely report this morning that raises questions about Burgess's logic.

The key excerpt: