In addition to the substantive requirements of SMC 14.255.120, the following requirements shall apply to geologic hazard areas:
A. Alteration of geologically hazardous areas and buffers shall be prohibited except as expressly allowed in this chapter;
B. Proposed developments shall not increase the long-term risk of or exposure to a geologic hazard on-site or off-site;
C. Hazard mitigation shall not rely on actions that require extensive maintenance;
D. Development near an erosion or landslide hazard area shall:
1. Observe a buffer from the edges thereof, of adequate width to comply with the substantive requirements;
2. Not decrease the factor of safety for landslides below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. Analysis of dynamic conditions may be based on a minimum horizontal acceleration as established by the International Building Code;
3. Cluster structures and improvements as necessary to avoid hazard areas;
4. Use retaining walls that allow the retention of existing natural slopes when possible rather than graded artificial slopes;
5. Place utility lines and pipes in erosion and landslide hazard areas only when no other alternative is available and when the line or pipe can be installed above ground in such a manner as to remain intact without leaks in the event of a slide;
6. Discharge water from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area only if:
a. Discharged at flow durations matching pre-developed conditions, with adequate energy dissipation, into existing channels; or
b. Dispersed upslope of the steep slope onto a low-gradient undisturbed buffer of adequate infiltrate capacity without increasing saturation of the slope.
7. Locate any on-site sewage drain fields outside the hazard area and related buffers.