Mahonia Glen Affordable Housing Project (Notification of Lake or Streambed Alteration, No. EPIMSSON-26045-R3 Amendment No. 1

Mahonia Glen Affordable Housing Project (Notification of Lake or Streambed Alteration, No. EPIMSSON-26045-R3 Amendment No. 1

The project is limited to the removal of four existing culverts in the unnamed drainage channel that bisects the property and installing a single full-span arch culvert, extension of an existing storm drain culvert that crosses under Calistoga Road for the widening of Calistoga Road, and widening of the existing drainage channel to reduce erosion and sediment inputs. The four culverts occupy 89 linear feet and 203 square feet of in-channel riparian habitat. The new full-span arch culvert will span 7-feet and occupy 40 linear feet and approximately 300 square feet of the channel including associated wingwalls and rock riprap at the inlet and outlet. An existing 30-inch diameter reinforced concrete pipe (RCP) culvert crosses under Calistoga Road and conveys storm drainage under the road, discharging onto the property. The existing culvert will end at a new manhole that will be constructed within the widened Calistoga Road, and a 40-foot long, 36-inch diameter RCP culvert will continue under Calistoga Road from the manhole to the west to discharge into the unnamed drainage on-site. The culvert and associated headwall and riprap will permanently impact 118 square feet of riparian habitat, with a portion of the new culvert to be located within the existing road prism. In total, the project will remove 89 linear feet and 203 square feet of existing culverts and construct 80 linear feet and 418 square feet of new culverts and associated infrastructure. A total of 15 riparian trees will be removed. Approximately 502 linear feet (2,571 square feet) of the channel will be restored by laying back the banks to a more gradual slope to reduce erosion and sediment inputs into Austin Creek. This channel rehabilitation includes the removal of approximately 5,250 square feet of Himalayan blackberry (Rubus armeniacus) and bamboo (Bambusa sp.), both invasive species, when laying back the banks. Approximately 1,380 square feet of native riparian including wetland vegetation will be temporarily impacted to lay back the banks. Also included is the revegetation of approximately 10,040 square feet of riparian habitat with native riparian plants within the unnamed drainage. The project as amended includes the addition of fire escape ladders and pads to the project design, which will increase the permanent impacts to riparian habitat by 370 square feet and will increase temporary impacts to riparian habitat by 580 square feet. In addition, two more trees will need to be removed.

Santa Rosa

Sonoma

Northern California, San Francisco Bay Area

Sonoma