PD-17-00001 Marian Meadows Full Record with Index (2)

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Marian Meadows Rezone and Subdivision Final Environmental Impact Statement 1-28 If contaminated soils are encountered during development, the response is likely to be excavation and disposal of contaminated soils at an approved disposal facility. To control accidental discharge of hazardous materials during construction, a Spill Prevention, Control and Countermeasure (SPCC) Plan is likely to reduce potential impacts. Historic, Cultural, and Archaeological Resources No cultural resources have been identified on site. It is possible, however, that resources could be uncovered during construction. Mitigation measures available to ensure protection of all significant cultural resources on the site include stopping work, identifying resources, and avoiding or conserving the resources identified. Geology, Topography, and Soils The greatest potential for seismic hazards on the site are rockfall, shallow landslides, and debris flow across alluvial fans, as well as water flow downgradient of the fans where water is likely to flow after dropping sediments on the fan. The most effective means of mitigating potential hazards is avoidance of these areas. Alternatives that avoid the steeper eastern portion of the site avoid much of the hazard area. On the western flatter portion of the site, the greatest potential impact is from debris flow and debris flow conveyance across the site. The most effective mitigation for alluvial fans and debris flows is to avoid any human occupancy or improvements on the fan and its downstream conveyance area as well as providing channels or other measures such as berms to direct high lows away from developed areas. Addressing geologic hazards on the steeply sloping eastern portions of the site would require more detailed on-site assessment of conditions, risk and mitigation at the time of specific development proposals. Surface Water Resources It is unlikely that water from the site would reach surface water streams except under the most extreme rain-on-snow conditions. All alternatives are likely to handle normal stormwater up to typical 2- and 10- year storms through standard facilities. It is likely that infiltration would be utilized as well as conveyance in roadside ditches. The most significant hazard not addressed in standard engineering design is from isolated events leading to unpredictable volumes of water collecting in narrow canyons leading to catastrophic debris flows. This event has happened periodically on the site as is evidenced by alluvial fans that have formed at the base of several drainages and discontinuous drainage courses across the site. The most effective mitigation for alluvial fans and debris flows is to avoid any human occupancy or improvements on the fan and its downstream conveyance area as well as providing channels or other measures such as berms to direct high lows away from developed areas.