Timber Bridge Replacements at Basalt Creek (MP 29.31) and San Antonio Slough (MP 31.74) (Lake or Streambed Alteration Agreement No. EPIMS-MAN-31623-R3)

Timber Bridge Replacements at Basalt Creek (MP 29.31) and San Antonio Slough (MP 31.74) (Lake or Streambed Alteration Agreement No. EPIMS-MAN-31623-R3)

The California Department of Fish and Wildlife (CDFW) has executed Lake and Streambed Alteration Agreement (EPIMS-MAN-31623-R3), pursuant to Fish and Game Code section 1602, to the project Applicant, SMART. The Project is limited to replacing two creosote-treated timber bridges on the SMART right-of-way. At Basalt Creek, the SMART railroad will be temporarily removed and staged on the track bed. The existing 15-footlong and 20-foot-wide timber bridge, including abutments, will be removed to at least the level of grade and disposed of properly. Substrate below each bridge abutment will be removed, widening the channel and creating approximately 160 square feet of shaded stream channel. Two sheet piles and six H-piles will be installed using a vibratory hammer, followed by installation of the abutments. After abutment placement is complete, a 27-foot-and-2-inch-long and 20-foot-wide prefabricated steel bridge will be installed and the railroad re-installed. At San Antonio Slough, the SMART railroad will be temporarily removed and staged on the track bed. The existing 44-foot-and-11-inch-long and 20-foot-wide timber bridge, including twenty 15-inch-diameter post piles and abutments, will be removed to at least the level of grade and disposed of properly. Substrate below each bridge abutment will be removed, widening the channel and creating approximately 200 square feet of shaded stream channel. Two sheet piles, three steel pipe piles, and six H-piles will be installed using a vibratory hammer, followed by installation of the abutments and bents. After abutment placement and bent construction is complete, a 58-footand-2-inch-long and 20-foot-wide prefabricated steel bridge will be installed and the railroad re-installed. The Project will result in 26 square feet and 10 linear feet of permanent impacts to San Antonio Slough as a result of installation of new piles, however this impact will be offset by the creation of 298 square feet and 20 linear feet of shaded stream channel, and the removal of creosote-treated timber piles and abutments. The Project will not result in permanent impacts to Basalt Creek. The Project will create 20 linear feet and approximately 160 square feet of shaded stream channel and will remove creosote-treated timber abutments at Basalt Creek. As the project is widening the stream, and the widened section will be shaded, no new shading impacts will be caused to existing stream channel. The Project will result in approximately 3,287 square feet and 70 linear feet of temporary impacts to San Antonio Slough and associated salt marsh habitat, of which 3,049 square feet is vegetated, and approximately 218 square feet and 15 linear feet of temporary impacts to Basalt Creek and associated salt marsh habitat, all of which is vegetated. The Project does not include any in-water work, with the exception of the use of a small boat to weld the new bents to the superstructure of the bridge at San Antoino Slough which would occur during a high tide to ensure workers are able to reach the underside of the structure. Piles will be installed when no water is present at the base of the pile. No trees will be removed as part of the Project. Work will take place primarily at night due to SMART operational requirements.

Marin

San Francisco Bay Area

Marin