SU0006254 - Laserfiche WebLink

Home Browse Search

MOUNTAIN HOUSE PROPOSED ALTAMONT HEIGHTS TENTATIVE MAP 4. ENVIRONMENTAL CHECKLIST 4.8 HYDROLOGY AND WATER QUALITY one-percent chance of occurring each year,while a 10-year storm event has a 10-percent chance of occurring each year. The MEIR indicates that,with construction of the storm drain system planned in the Mountain House Master Drainage Plan and implementation of mitigation measures identified in the MHMP, development of the Mountain House Community(including the proposed - project)would result in less-than-significant flooding impacts. Mitigation Measures The proposed project would increase the rate and amount of runoff,but the storm drain system would ensure that the increase would not result in significant flooding on or off the project site.No mitigation measures are required. e) Create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff? Increase in runoff and the hydraulic capacity of the storm drain system are addressed in Item d)above. Since the project site was formerly used for dry farming(mainly oats), it is likely that the non-point source(NPS)pollutants formerly found in runoff from the site were sediments and oxygen-demanding constituents from decaying dry oats. When completed,the proposed land use will be residential. The conversion of the project site would result in a decrease in sediments and oxygen-demanding constituents in the site runoff while increasing levels of oils, grease,metals, and petroleum hydrocarbons. All "urban" runoff originating from the project site would be treated in WQB No.1 prior to discharge to Mountain House Creek and Old River. This treatment is particularly important for the first flush that occurs at the beginning of a strong storm when pollutants that are on the streets are washed into the storm drains. Mitigation Measures The Mountain House Community storm drainage system includes facilities to adequately treat the storm runoff to reduce pollutants to a less than significant level. No additional mitigation measures are required. f) Otherwise substantially degrade water quality? Refer to discussions for Items a),c), d)and c)above. Mitigation Measures No additional mitigation measures are required. g) Place housing within a 100 year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood.Insurance Rate Map or other flood hazard delineation map? 4-45