After a rainy week in Seattle, and after SPU filled some of the non-functioning ponds with dirt, we have noticed new patterns that belie the ability of any of these ponds as a CSO resolution.
After filling in the non-functioning ponds that were below the water table, the once-functioning ponds are now full of water and have not drained since. Some of this water is from rain, but some of this water is from groundwater seeping into the hole. None of this water is from the street—the original intent of this curb bulb—since the curb inlet is still plugged with asphalt.
That volume of water has to go somewhere. Where it can’t go is into the clay ground underneath.
Building underground drainage would only attempt to push the water into cement-like clay, or drain this water into the sewer. The latter option is less of a CSO resolution than just holding this groundwater in a very soggy lawn.
After SPU has filled in some non-functioning cells, it has become clear to us this week this overwhelms the functioning cells, and then they become non-functioning cells as well…because it’s all built on top of clay.