March 30, 2011
A 13ft diameter Tunnel Boring Machine is now directly under the District aquifer heading East towards Kennmore. After delays of several months the TBM is making better than expected progress. Latest data from King County show the TBM is presently under 37th Avenue as it heads East along the 195th St. corridor. It appears that the TBM will be in the most critical zone under the aquifer starting in mid April and through the end of May.
The District is working intently to monitor the Brightwater tunnel construction and determine if the tunnel boring machine disturbs the Lake Forest Park aquifer. Provisions of a 2003 agreement require the County to double line a portion of the tunnel if it is found to enter the District aquifer.
Test wells along the tunnel route are being monitored closely for any indication of hydraulic connection and soil samples from the TBM are being examined along with numerous other parameters from the TBM. We appreciate the help our customers have offered for this project and we will keep you informed of progress over the coming months.
