overflow discharge events compared with current conditions. Please see pages 4.H-26 through 4.H-35, and 4.O-51 to 4.O-52, for additional information on proposed stormwater drainage system improvements, as well as Appendix B, Brisbane Baylands Infrastructure Plan for information specific to the DSP and DSP-V scenarios.
[See page 5-77 for the original comment] The 2004 American Association of State Highway and Transportation Officials (AASHTO) guidelines include references for underground utility criteria, citing studies that indicate vibration under the ground surface is lower than that measured at the ground surface. One major utility (AASHTO 2004) has adopted a criterion of 4.0 in/sec (100 mm/s) for underground optical-fiber cables. Underground or restrained concrete structures can withstand vibration of 10.0 in/sec (254 mm/s) before the appearance of threshold cracks. Thus, underground utilities are less sensitive than surface structures.
As discussed on Draft EIR page 4.J-22, pile driving can result in peak particle velocity (PPV) of up to 1.5 in/sec at a distance of 25 feet (FTA, 2006), but typically average about 0.644 PPV at that distance. All other construction activities would have substantially lower vibration inducing potential. Vibration from pile driving could potentially reach levels in excess of the 4.0 in/sec AASHTO criteria at distances between 10 to 15 feet. Consequently additional mitigation measures are identified to implement alternatives to impact pile driving, as needed. These alternative methods produce substantially less vibration than pile driving, with drilling feasible of being conducted within two feet of utilities and complying with the most stringent threshold. Mitigation Measure 4.J-2c is added to the Draft EIR to read as follows:
Mitigation Measure 4.J-2c: All development sites requiring pile driving shall have underground utility1 surveys completed before a building permit is issued to demonstrate that pile driving will be located a minimum 15 feet from buried utilities. Underground utilities surveys shall be submitted to the City for review and consultation with affected utilities a minimum of two weeks prior to commencement of construction activities. If underground utilities are identified within 15 feet of proposed pile driving activities, alternative pile installation methods shall be required. Alternative methods may include use of sonic drivers or drilled and cast-in-place piles. All pile driving shall be designed so as to result in peak particle velocity of less than 4.0 in/sec (100 mm/s) at the location of underground utilities.