|Station House Lofts -- This "deep-dig" sits over and in our aquifer|
To help scale the size of the dig look for the workers...those orange and yellow specks. (Click on the photo to see the influence of the camera angle on size.) The city aquifer is close to the surface so the site has to be "dewatered" and sealed off. Notice the white water pipe in the foreground. Six inch diameter water pipes also surround the site, and can't be seen in this picture. Owing to extreme rains there's a lot of aquifer water that must be pumped out. The mixed aquifer and rain water are tested every two weeks for oil and lubricants before it's dumped into the stormwater system. Many downtown developments need dewatering.
Public Works is somewhat concerned about contaminated construction water entering the aquifer -- the aquifer being a major source of our drinking water. Thus, the city wrote a new ordinance to protect the aquifer during development; and to bill those developers who excessively drain the aquifer and our wells.
In a few places around the city, the aquifer can be as close as 3 feet from the surface. According to the Superintendent it's my understanding they had to dig 2-3 feet into the alluvial aquifer in places.
Since publishing this post and alerting the City Ombuds. a new policy was instituted requiring some future developers to build their parking above grade, rather than subterranean. Building height could increase up to 2 levels as a result.
This is an excellent article explaining the process and challenges of dewatering construction sites.
This is an archive of all my aquifer and groundwater posts over the years. .