If you’ve compressed a few vertebrae negotiating the dips and rises around the traffic islands on 87th west of Greenwood Avenue, you’ve had first-hand experience with a “peat settlement-prone area.”
When settling started in that area around 2001, the City of Seattle did some research and came up with new regulations for areas prone to ground settlement due to subsurface deposits of peat. Peat is plant material that typically forms in wetland environments where acid conditions keep it from completely decaying.
Peat deposits tend to compress and settle when you put new buildings on them or lower the groundwater table. That settlement can result in serious damage to buildings, roads, sidewalks and utilities, hence the damage on 87th, cross streets and some nearby homes.
The city council has passed a bill that would call for identifying areas of the city that are settlement-prone. It would also then ensure that new development in these areas doesn’t hurt neighboring properties. The legislation is expected to take effect in August.