The project is limited to the removal and replacement of two existing gas transmission pipelines that cross the Petaluma River. The existing dual 12-inch diameter pipelines will be removed from beneath the Petaluma River. To remove the existing pipelines, approximately 16 linear feet from each bank of the river will be excavated to expose
the pipelines. Once exposed from the banks, a barge-mounted dredging operation located in the Petaluma River will excavate approximately 8 feet in depth of the native material within the riverbed from on top of the pipeline.
Dredge material will be loaded onto a barge and then stored in uplands until it can be hauled to an approved disposal site. After dredging, each pipe will be dislodged from the soil using slings attached to a barge-mounted crane and then pulled out at the south side of the river. Following pipe removal, crews will backfill each bank
excavation site using clean native material and original contours would be reestablished. Pipeline removal will cause temporary impacts to the riparian and salt marsh habitat along the riverbanks of approximately 130 square feet, and temporary impacts to the open channel habitat in the Petaluma River of approximately 4,000 square feet.
In addition to removing the existing pipelines, a new gas transmission pipeline will be installed. The new pipeline will cross under the Petaluma River just upstream of the existing pipes. It will entail installing approximately 492 feet of 16-inch diameter steel pipe with open trench in an upland portion of the site and approximately 1,360 feet of the steel pipe utilizing horizontal directional drilling (HDD) under the Petaluma River at a depth of 61 feet The HDD will require excavation of a bell hole on either side of the river, located in the upland portion of the site. Pipeline installation activities will not result in temporary or permanent impacts to stream and riparian habitat.