SU0014674 - Laserfiche WebLink

Home Browse Search

MOUNTAIN HOUSE NEIGHBORHOOD' 'PROJECT INITIAL STUDY even under existing conditions, cannot handle all of the runoff. The project applicant has proposed interim measures to be taken to handle the increased runoff from the project development. These measures include diversion berms and channels as well as mobile rented pumps. Refer to Condition of Approval HYDRO-2 regarding an interim storm water pumping plan which would mitigate any potential impacts related to drainage system capacity. Refer to Condition of Approval HYDRO-1 and HYDRO-3 regarding measures to minimize polluted runoff. fi Otherwise substantially degrade water quality? There has been no known water quality monitoring of runoff from the project site or vicinity. Given the current land use of the project site, open grassland and agricultural area and the soil and topography characteristics, the non-point source pollutants likely found in runoff from the site are sediment, nutrients, pathogens, and oxygen-demanding solids. Non-point source pollution consists of materials and chemicals that are washed from diffuse locations within a watershed and washed into a storm drainage network. Due to variable land area, soil conditions, vegetative cover, and agricultural practices, however, it is difficult to estimate pollutant concentrations. Conversion of the site from agricultural use to a suburban development would increase the levels of oil and grease, petroleum hydrocarbons, and metals, entering the Old River channel and ultimately the San Joaquin River Delta. Pollutants from the proposed project would be consistent with typical suburban non- point source pollution. Suburban non-point source pollutants come from a variety of sources including household products and home maintenance supplies, landscape materials and products(pesticides, herbicides, and fertilizers), automobiles, and fuels. The pollutants of primary concern for the proposed project include fertilizers and pesticides from landscaped areas and oil, grease, and petroleum hydrocarbons from automobiles and fuels. The project's Master Storm Water Plan and Neighborhood F Storm Water Report proposes post- construction storm water pollution prevention best management practices(BMPs)including first-flush water quality basins. Other programs such as regular street sweeping, inlet stenciling, and home buyer education are not specifically mentioned. Due to the change in land use and the size of the development, the anticipated pollutant loads would likely be substantial. Construction site erosion could be another impact to water quality. Site grading during construction could significantly increase erosion on the site(discussed above)and represents a potential impact to water quality. Refer to Conditions of Approval HYDRO-1 and HYDRO-3 regarding measures to minimize polluted runoff. 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? The project would not place housing within any official designated Flood Hazard Zone. However, a series of berms would be placed or heightened along portions of Mountain House Creek to increase the amount of freeboard between the 100-year flood elevation and the top of the berm. In many cases this freeboard is between 1 and 2 feet. Current Federal Emergency Management Agency(FEMA)guidelines require 3 feet of freeboard on a levee or berm to be certified safe from breaching. If the structure does not have three feet of freeboard, the floodplain area is mapped assuming the levee fails. Under this scenario, it is likely that a portion of the 100-year flood flow would spill from the Mountain House Creek channel and flow towards Neighborhood"I"'. In theory, the proposed ditchlberm along the Central Parkway alignment would capture these flows and return them to Mountain House Creek. However, if that ditch/berm system is not designed with the appropriate freeboard, it would not be recognized as a regulatory levee. C:U0B=C\1NMAL MMYONALINMALMDY-PARMDOC(7(!7100) 99 V.J. HYDROLOGY AND WATER QUALrrY