/Comments Period: March 31, 2020 – April 30, 2020
SUBJECT: The U.S. Army Corps of Engineers, Sacramento District (Corps) is evaluating a permit application to construct the Fordyce Dam Seepage Repairs project, which would result in permanent impacts to approximately 4.46 acres, and temporary impacts to 0.10 acre, of waters of the United States in or adjacent to Fordyce Lake, Fordyce Creek, and other unnamed drainages. This notice is to inform interested parties of the proposed activity and to solicit comments.
AUTHORITY: This application is being evaluated under Section 10 of the Rivers and Harbors Act of 1899 for structures or work in or affecting navigable waters of the United States and Section 404 of the Clean Water Act for the discharge of dredged or fill material in waters of the United States
APPLICANT: Pacific Gas and Electric Company, Attn: Mr. Matt Walker, 3600 Meadowview Drive, Redding, California, 96002
LOCATION: The approximately 70-acre project area is located in and around Fordyce Lake within Tahoe National Forest approximately 16 miles northwest of Truckee, Latitude 39.3798°, Longitude -120.4964°, Nevada and Placer Counties, California, and can be seen on the Webber Peak, Cisco Grove, and Soda Springs USGS Topographic Quadrangles.
PROJECT DESCRIPTION: Fordyce Dam has a long history of seepage issues, and the proposed project would provide permanent repairs, thus improving the overall safety of the dam and reducing the need for maintenance. Pacific Gas and Electric Company (PG&E) is proposing to mitigate seepage flows at Fordyce Dam to below the acceptable 30 cubic feet per second threshold established by the California Department of Water Resources Division of Safety of Dams, and protect the erodible upstream toe of the dam. The project is anticipated to take three years to complete, if annual precipitation levels are favorable. Work at Fordyce Dam is expected to occur approximately between July and October of each year, with specific durations informed by weather conditions and annual precipitation levels. The dam would function and perform in its normal and safe capacity outside the annual construction window.
The proposed project would involve removal of debris-laden fill from the upstream toe of the dam down to bedrock, and permanent fill of portions of the reservoir at the upstream toe of the dam. The permanent fills would include granular engineered fill, a concrete plinth, a grout curtain, and an impermeable liner on the upstream face of the dam. A grouting program would be implemented to seal potential voids in the bedrock at the upstream toe of the dam and at the abandoned, original low level outlet pipe. Two or more ramps of granular fill would be installed to access the reservoir bed. Existing debris-laden fill excavated from the upstream toe of the dam would have the debris removed and disposed of in uplands, and the clean fill would be discharged within the bed of the reservoir, between the dam and the cofferdam, over an approximately 2.30-acre area.
A cofferdam and flow bypass system would be installed to allow dewatering of the work area on the upstream side of Fordyce Dam and provide a “dry” workspace, while maintaining the minimum in-stream flow requirement. The location of the cofferdam would be at a natural constriction in the reservoir bathymetry, approximately 700 feet upstream from Fordyce Dam. Before installation of the cofferdam, Lake Fordyce would be drained to the minimum level allowed under the terms and conditions of the Drum-Spaulding license. The cofferdam would be constructed using steel and interlocking slide rail (bin-wall) segments. This system would consist of steel walls with bracing between them. Granular fill material would be placed in the spaces between the bin walls to form the cofferdam. This system can be constructed with water remaining in the reservoir; therefore, the reservoir would not have to be lowered below the minimum pool elevation. The cofferdam would be approximately 25 feet wide, and would span approximately 450 feet across the reservoir. The height of the cofferdam could vary based on the profile of the reservoir, but is expected to be a maximum of 23 feet tall. The cofferdam would include an impermeable liner on the upstream face, and would be rip-rapped on the downstream face. A concrete curb and ramp, and removable up- and downstream handrails would be installed on the crown of the cofferdam. The total filled area of the cofferdam would be approximately 0.88 acre. After being constructed, the cofferdam would be left in place throughout the three-year construction phase. In preparation for the winter season, the area between the cofferdam and Fordyce Dam would be rewatered and equalized with the water level in the lake. The cofferdam would remain submerged until the next construction season, when reservoir dewatering would be conducted in preparation for the construction season. The cofferdam also would be left in place for a 2-year monitoring period following completion of construction, while the performance of the repairs at Fordyce Dam are evaluated.
A flow bypass system would include an approximately 60-inch diameter, 700-foot-long pipeline connecting the upstream side of the cofferdam to the inlet of the existing Fordyce Dam low level outlet. Three 8-foot-long by 8-foot-wide temporary barge-mounted pumps would be located in Lake Fordyce upstream of the cofferdam, to pump water through the bypass system.
The project would involve temporary fills in portions of the reservoir, including materials associated with the cofferdam (i.e., steel bins, membrane, and ballast), in-stream flow bypass system materials, and turbidity curtains. In addition, temporary granular fill would be used for staging areas, and would be later converted to permanent granular fill along the upstream toe of the dam.
Impacts to Fordyce Creek would also occur downstream from the dam. These impacts would be associated with a water quality control system to mitigate for potential seepage of high pH water downstream from the dam during grouting operations. The water quality control system would involve temporary placement of supersacks in Fordyce Creek necessary for installation of three ponds: a seepage collection pond, a treatment pond, and a post-treatment discharge pond. In addition, a temporary check dam would be installed downstream from these ponds and would be made from existing rocks, to act as a dissipation structure. Furthermore, the existing LLO pipe would be extended temporarily beyond the treatment pond area.
Culvert extensions would be installed within three drainages along the access roads to Lake Fordyce (i.e., Rattlesnake Road and Lake Fordyce Road). The culvert extensions would be required to widen the roads to allow truck passage. Four additional drainages would be affected by grading activities along the road, which would involve filling the drainages with granular fill to create drainage dips.
The applicant’s stated project purpose is to improve the safety of Fordyce Dam by providing a permanent repair to reduce dam seepage in accordance with California Division of Safety of Dams requirements, while maintaining the existing capacity of Fordyce Lake. The applicant believes there is a need for Fordyce Dam to be maintained as a safe and reliable component of the water storage and delivery infrastructure serving downstream uses including power production, irrigation, and domestic consumption. The attached drawings provide additional project details.
Environmental Setting. The aquatic resources study area is larger than the project area, and includes the entirety of Lake Fordyce to account for potential effects of the reservoir draw-down required for the project. There are approximately 0.08 acre of wetlands, and 720.16 acres of other waters of the United States within the aquatic resources study area. The project area is characterized as a higher-elevation reservoir impounded by a 156-foot-high, 1,220-foot-long soil and rock-fill dam, which are both part of PG&E’s Drum-Spaulding Hydroelectric Project, under the jurisdiction of the Federal Energy Regulatory Commission (FERC). Upland vegetation communities within the project area are predominantly forested, with some areas of chaparral. Aquatic habitats within the project area include lacustrine impoundment, palustrine emergent wetlands, palustrine scrub-shrub wetlands, and perennial, intermittent, and ephemeral streams.
Alternatives. The applicant has provided information concerning project alternatives. Additional information concerning project alternatives may be available from the applicant or their agent. Other alternatives may develop during the review process for this permit application. All reasonable project alternatives, in particular those which may be less damaging to the aquatic environment, will be considered.
Mitigation. The Corps requires that applicants consider and use all reasonable and practical measures to avoid and minimize impacts to aquatic resources. If the applicant is unable to avoid or minimize all impacts, the Corps may require compensatory mitigation. The applicant is not proposing compensatory mitigation for the project.
OTHER GOVERNMENTAL AUTHORIZATIONS: Water quality certification or a waiver, as required under Section 401 of the Clean Water Act from the Central Valley Regional Water Quality Control Board is required for this project. The applicant has indicated they are currently preparing an application for certification.
HISTORIC PROPERTIES: Based on the available information (including applicant's December 2019 report titled PG&E’s Fordyce Dam Seepage Mitigation Project: Cultural Resource Inventory, NRHP and CRHR Evaluations, Nevada and Placer Counties, prepared by Browning Cultural Resources), potentially eligible cultural resources may be affected by the proposed project. The FERC, acting as the federal lead agency, has designated PG&E as their non-federal representative for purposes of consulting with the State Historic Preservation Officer (SHPO) under Section 106 of the National Historic Preservation Act. PG&E initiated consultation with the SHPO on January 17, 2020. On March 3, 2020, PG&E received a letter from the SHPO concurring with PG&E’s findings of eligibility and determination that no historic properties would be adversely affected.
ENDANGERED SPECIES: The proposed activity may affect Federally-listed threatened or endangered species or their critical habitat. PG&E, acting as the FERC’s non-federal representative, will initiate consultation with the U.S. Fish and Wildlife Service, pursuant to Section 7 of the Endangered Species Act, as appropriate.
ESSENTIAL FISH HABITAT: The proposed project would not adversely affect Essential Fish Habitat as defined in the Magnuson-Stevens Fishery Conservation and Management Act.
The above determinations are based on information provided by the applicant and our preliminary review.
EVALUATION FACTORS: The decision whether to issue a permit will be based on an evaluation of the probable impacts, including cumulative impacts, of the described activity on the public interest. That decision will reflect the national concern for both protection and utilization of important resources. The benefit, which reasonably may be expected to accrue from the described activity, must be balanced against its reasonably foreseeable detriments. All factors which may be relevant to the described activity will be considered, including the cumulative effects thereof; among those are conservation, economics, aesthetics, general environmental concerns, wetlands, historic properties, fish and wildlife values, flood hazards, floodplain values, land use, navigation, shoreline erosion and accretion, recreation, water supply and conservation, water quality, energy needs, safety, food and fiber production, mineral needs, consideration of property ownership and, in general, the needs and welfare of the people. The activity's impact on the public interest will include application of the Section 404(b)(1) guidelines promulgated by the Administrator, Environmental Protection Agency (40 CFR Part 230).
The Corps is soliciting comments from the public, Federal, State, and local agencies and officials, Indian tribes, and other interested parties in order to consider and evaluate the impacts of this proposed activity. Any comments received will be considered by the Corps to determine whether to issue, modify, condition, or deny a permit for this proposal. To make this decision, comments are used to assess impacts on endangered species, historic properties, water quality, general environmental effects, and other public interest factors listed above. Comments are used in the preparation of an Environmental Assessment and/or an Environmental Impact Statement pursuant to the National Environmental Policy Act. Comments are also used to determine the need for a public hearing and to determine the overall public interest of the proposed activity.
SUBMITTING COMMENTS: Written comments, referencing Public Notice SPK-2018-00549 must be submitted to the office listed below on or before April 30, 2020.
Senior Project Manager
U.S. Army Corps of Engineers
Sacramento District, Regulatory Division
1325 J Street, Suite 1350
Sacramento, California 95814-2922
The Corps is particularly interested in receiving comments related to the proposal's probable impacts on the affected aquatic environment and the secondary and cumulative effects. Anyone may request, in writing, that a public hearing be held to consider this application. Requests shall specifically state, with particularity, the reason(s) for holding a public hearing. If the Corps determines that the information received in response to this notice is inadequate for thorough evaluation, a public hearing may be warranted. If a public hearing is warranted, interested parties will be notified of the time, date, and location. Please note that all comment letters received are subject to release to the public through the Freedom of Information Act. If you have questions or need additional information please contact the applicant or the Corps' project manager Zachary Fancher at (916) 557-6643 or Zachary.J.Fancher@usace.army.mil.
Attachments: 20 drawings