SCH Number 2022120399

Project Info

Title

Grading Permit GR 22-36; Initial Study IS 22- 37, Lucerne Harbor Dredging Project

Description

Project Location Lucerne Harbor Park is located in the unincorporated community of Lucerne in Lake County approximately 132 north of San Francisco and 110 miles west of Sacramento. The park is accessed from State Highway 20 on the northeast side of Clear Lake. The physical address is 6215 E. Hwy 20, Lucerne, CA 95458. Project Description The County of Lake is proposing a maintenance dredging project to remove approximately 2,500 cubic yards of sediment from Lucerne Harbor in the Lucerne Harbor Park. Site Photos taken on July 8, 2021, begin on page 9. Figure 1 includes an aerial photo of assessor’s parcel numbers (APNs) 034-121-11 & 034-141-01 outlined in yellow. Figure 2 includes dredging plan sheet C-1 which is an aerial photo showing three profiles of the water surface on the date of surveying, and the existing ground or lakebed with other information. Sidewall sediment will be excavated at a slope 2.5:1 with an approximate entrance width of 20 ft. Shifting sediment will occur over time and future maintenance will be required. The dredge site encompasses an area of approximately 0.8 acres. Dredging is anticipated to be accomplished using a floating clamshell dredge paired with one to two barges pushed by a shallow water tugboat. Dredge depth will be to approximately the original design depth of 1316 feet National standard reference datum (NGVD) with a 6-inch maximum over dredge allowance. Material dredged from the harbor will be loaded onto a barge using the dredge backhoe and then the loaded barge will be pushed to the boat ramp area by the tugboat. At the boat ramp area, the dredged material will be loaded into dump trucks using an excavator located on the shore. Much of the water will decant from the dredged material during this initial transfer to the trucks. The County will close portions of the park in the area of the harbor during dredging operations. A turbidity curtain will be installed by the contractor at the harbor entrance during the dredging work to prevent any sediment from returning to the lake. The system would be installed and relocated based on the area of work. The deepest depth of in-water work for this project is less than 5 feet. The length of the curtain can be adjusted by adding or removing sections. A turbidity curtain is a temporary Best Management Practice (BMP) that can be adjusted and relocated to accommodate the area of work. A floatation boom and bottom ballast keep the curtain vertical in water. For work at the harbor entrance, the curtain would be relocated to enclose the excavation area using the piers or nearby shoreline if necessary. Water conditions will be monitored for turbidity prior to and during the project operations. Water board guidance in previous dredging operations prohibit 20% increase from existing background conditions. For a turbidity curtain to be removed, these conditions would have to be met. The expected functional use of the harbor after this dredging will be more than 30 years based on previous depositional rates. The source of deposited sediment is from open water as no surface water drainage is directed to the harbor. Construction Timing To protect the state-listed threatened Clear Lake hitch, the work period for the dredging will be confined to periods when the water level in Clear Lake is below a Rumsey Gauge height of 3.5 feet (1321.8 NGVD). The water level in Clear lake is expected to be below Rumsey Gauge 3.5 during the planned work window. Should these expected conditions change, work will be reevaluated for potential rescheduling. Deposal of Dredged Materials Dredged material is proposed for disposal and drying at the Eastlake Sanitary Landfill in Clearlake, CA. Saturated sediments will be transported to Eastlake Landfill from the project site in lined truck beds or self-contained roll-off bins to prevent leakage while in route. The landfill has a soil borrow area that will be used as a drying area for the dredged material and will require the installation of silt fence and/or the use of straw wattles surrounding the disposal area to ensure any residual water or sediments are contained onsite while the material undergoes a period of further drying. Once the material has dried sufficiently the dredge material will be used for daily landfill cover and other on-site beneficial reuse purpose in accordance with the landfill permits. Construction Details There are two driveway encroachments into Lucerne Harbor Park from State Highway 20. The western-most driveway will be closed to the general public and used only for hauling operations. Barricades, cones, and other standard traffic control measures will be in place to alert the public. The anticipated work sequence will be as follows: 1. Mobilize equipment to the site. 2. Install turbidity curtain at harbor entrance to the lake. 3. Launch clamshell dredge(s), barge(s), and tugboat. 4. Remove sediment from the harbor and bring material to boat ramp for hauling and disposal at Eastlake Sanitary Landfill. 5. During removal, conduct intermediate surveys to verify dredge quantities. 6. After removal, conduct final survey and calculate total volume removed. Volume to be calculated at the nearest cost/cubic yard interval. 7. Remove turbidity curtains, demobilize, and site cleanup.

3 documents in project