piles versus driven piles), alternative foundation types for the new construction (e.g., spread footings versus driven piles), alternative compaction methods, and physical measures (intervening trench, increased distance).
- Require monitoring to be conducted at the building during construction. This monitoring can include crack gages on existing cracks and vibration amplitude monitoring. Establish warning and stop work thresholds for monitoring. Implement visual and audible signals that are triggered by a vibration monitor when exceedances of warning and stop work thresholds occur. If warning thresholds are exceeded routinely, consider alternative construction approaches.
- If the stop work threshold is exceeded, evaluate the condition of the building for damage. If no damage is indicated consult with structural engineer and/or architectural historian to assess whether higher thresholds are possible and adjust as appropriate.
- If damage occurs determine if any other construction approaches are feasible to reduce vibration. If none is available examine the severity of the damage to determine if damage is minor and repair is feasible. If repair is feasible continue with construction, but monitor vibration and damage closely to ensure that damage remains repairable. Consider whether a lower stop work threshold is feasible.
- If damage approaches becoming unrepairable and vibration levels have approached or exceeded the stop work threshold repeatedly, reconsider construction of the project.
- Repair any damage that has occurred.
[See page 5-247 for the original comment] The purpose of monitoring is to ensure the effectiveness of mitigation measures. The measures added to Mitigation Measure 4.J-2b in Response BCC-435 will establish both warning and stop-work thresholds. The warning threshold would provide a direct feedback to the equipment operators when vibration limits are being approached and allow equipment operators to adjust their activity. See Response BCC-435.
[See page 5-247 for the original comment] Noise increases presented in Draft EIR Table 4.J-4 are based on a comparison of roadway traffic volumes with and without development of the Baylands under each scenario. For Roadway #3 (Old County Road), average daily traffic volumes on Old County Road are estimated to increase from 6,045 under existing conditions to 10,490 under the DSP-V scenario with an event. This increase translates to an increase of 2.4 dBA, which would be a less-than-significant impact, as identified in the Draft EIR (a less than 3 dBA increase in an area where existing levels are less than 65 dBA).
[See page 5-247 for the original comment] Noise increases presented in Table 4.J-4 of the Draft EIR are based on a comparison of roadway traffic