some existing flooding issues. The drainage improvements required in the Draft EIR include LID drainage features, which could include detention basins or cisterns as required by C.3 requirements to minimize the amount of offsite flow. The requirements are designed to ensure that existing water resources and receiving waters of offsite stormwater discharges are protected from degradation of water quality. See Section 4.C, Biological Resources, for a full analysis of biota impacts related to the proposed improvements.
[See page 5-239 for the original comment] As stated in the Draft EIR on page 4.H-21, any dewatering activities that would occur as part of construction would be temporary in nature and conducted in accordance with RWQCB requirements, which would address any concerns regarding influences on existing contaminated groundwater. In addition, considering that the dewatering would only be temporary, any effects would also be temporary and would cease once that stage of construction is complete. In addition, dewatering activities would be planned in accordance with the recommendations of the design level geotechnical report as required by law which would include safeguards to ensure that secondary effects such as “slumping” would not occur. To clarify its intent, Mitigation Measure 4.H-1b is revised to read as follows
Mitigation Measure 4.H-1b: Prior to issuance of a grading permit, an applicant for any site specific development project to be constructed within the Project Site shall comply with any site-specific NPDES permit requirements for dewatering activities, as administered by the RWQCB. The RWQCB could require compliance with certain provisions in the permit, such as treatment of the flows prior to discharge, depending on the particular site conditions. Discharge of the groundwater generated during dewatering to the sanitary sewer or storm drain system shall only occur with authorization of and required permits from the applicable regulatory agencies, including the Bayshore Sanitary District or the RWQCB. Site dewatering activities shall also be monitored by a state licensed geotechnical engineer in such a manner as to avoid the potential for damaging buildings or infrastructure due to potential subsidence of the ground surface in accordance with any requirements from the City Engineer.
[See page 5-239 for the original comment] Mudflows are debris flows that involve large volumes of water mixed with soil, and are typically associated with heavy rainfall or sudden snow melts. While an existing waterline break could theoretically occur, it would be speculative to assume such an event would actually occur within an area that is outside of the Baylands Project Site. The relatively flat topography of the area, even with the presence of Icehouse Hill, is not prone to substantive debris flows or mudflows due to the lack of any substantive nearby upland slopes.