by Stan Penkin
After four months of impact hammer pile driving at Block 20, neighbors are relieved that this activity is finally over. Thanks to the foundation contractor, DeWitt Construction, the noise impacts were diminished by utilizing a sound barrier shroud around the equipment and erecting an acoustical wall at the nearby elementary school. Decibel readings taken during the course of the work registered from 82 to 86. Readings taken during the Block 17 project that had last used the impact hammer registered as high as 110, a level known to be harmful to hearing.
The city’s noise ordinance allows for a maximum decibel level of 85 for construction activity, but pile driving is exempted. Advocates for noise mitigation have argued that the far quieter augur cast method should be used in lieu of the harmful impact hammer. Most developers in the Pearl District agreed, as the most recent fourteen and upcoming projects chose that method. Block 20 was the exception.
What does this all mean? There is now evidence that sound mitigation of the impact hammer is possible and can have a beneficial effect. The Noise Review Board has been reviewing this issue and is preparing a proposal to City Council in the coming months that would eliminate the pile driving exemption.
The decision to use the impact hammer is often a financial one, although there are sometimes geotechnical reasons. The impact hammer is a cheaper alternative, but by eliminating the pile driving exemption, the cost of both methods will be more equalized if mitigation has to be included to meet the code.
The next Noise Review Board meeting where this topic is expected to be on the agenda will take place on April 12th at 6:00 PM. For more information