Project:      New Bullards Bar Dam
                   Grout Curtain Remediation
Location:   Yuba and Nevada Counties, California
Client:        Yuba County Water Agency
                   Christensen Associates, Inc.
Year:           2013 - 2014

Geoinsite provided design support and onsite geology expertise for extensive field program to investigate and remediate a leaking grout curtain beneath the tallest concrete arch dam in the United States.

Project elements included: 1) investigation of foundation seepage, 2) sealing of flowing grout holes from the original grout curtain, 3) remedial grouting to reduce excessive seepage, and 4) drilling/installing instrumentation to monitor foundation deformation and uplift pressures.

Project work involved review of original construction records; development of detailed work plan and testing/monitoring program; monitoring/recording of drilling, water testing and grouting; monitoring of foundation drain holes and uplift pressure instruments throughout the exploration drilling and remedial grouting operations; and interaction with FERC and DSOD.  

Constraints to achieving project objectives included high hydrostatic pressures at the toe of the 650-ft-high dam, hydraulic communication between drains and grout holes, and water quality standards set forth by the State Regional Water Quality Control Board.

The project successfully reduced foundation seepage without increasing uplift pressures beneath the lowest block in the dam. Future work is planned for other parts of the dam.

Project:      Fault Hazards Evaluation
Location:   Washoe County, Nevada
Year:           2012

Geoinsite performed a geomorphic and paleoseismic investigation of a critical segment of the Olinghouse fault zone located in alluvial fans emanating from the Pah Pah Range in eastern Washoe County, Nevada. The Olinghouse fault zone is one of several northeast-trending fault zones in western Nevada that exhibit left-lateral strike-slip movement. The orientation and left-lateral motion are conjugate to the northwest-trending right-lateral faults of the Walker Lane shear zone.Previous studies by researchers at the University of Nevada at Reno (UNR) defined the fault zone as a narrow, curvilinear zone of interconnected fault traces with a combined length of approximately 25 km.

Geoinsite’s scope involved mapping Quaternary deposits (e.g., coalescing alluvial fans and debris flow deposits, Lake Lahontan lacustrine and sand dune deposits); analysis of surface geomorphology using aerial photographs and DEM’s prepared from LiDAR datasets; identification of geomorphic lineaments attributed to probable Holocene faulting; supervising and logging trenches excavated across fault traces; identification of two colluvial wedges that are truncated by a wide fault zone consisting of multiple fault strands; sampling and radiocarbon age determination of faulted colluvial deposits; and evaluation of potential fault rupture impacts. The field work was reviewed by UNR faculty. Results of the investigation identified at least two ground-rupturing events within the past 5,000 years along one prominent trace.

Project:      Seismic Hazards Evaluation
Location:   Miners Ranch and Little Grass Valley Dams
Client:        South Feather Water and Power Agency
Year:          2010 - 2011

Geoinsite participated in a collaborative study to evaluate the seismic geology of faults in the vicinity of two dams owned by the South Feather Water and Power Agency (SFWPA) in the Feather River region of northern California. The dams are located in the northwestern portion of the Foothills Fault System (FFS), which includes a number of Cenozoic-reactivated ancient bedrock structures extending from Merced northwestward to Red Bluff along the margin of the Sierra Nevada.
 
The FFS exhibits extremely low rates of slip and associated seismicity, as demonstrated by unbroken c.10 million-year old basalt and volcaniclastic rock overlying faults in many (but not all) crossings, and by the lack of deflection of major river canyons at fault crossings. The study involved assessment of fault activity and determination of whether fault traces pass through the dams, fault displacement estimates, development of seismic parameters for ground motion estimates using NGA models, and review of seismic slope stability analyses.  Part of Geoinsite’s scope involved re-examination of fault and seismicity data from the 1975 Oroville Earthquake, which was centered in the vicinity of Miners Ranch Dam. Geomorphic mapping from aerial photographs and field observations resulted in revised fault locations, fault segmentation evaluations, and associated maximum earthquake scenarios. Findings of the study were generally favorable for the dams, in that possible triggered displacement on secondary faults were tolerable and seismic ground motions were within ranges previously analyzed to be acceptable with respect to dam stability.

Project:      Leroy Anderson Dam FERC Safety Assessment
Location:   Santa Clara County, California
Owner:       Santa Clara Valley Water District
Year:          2007-2008 and 2011-2012

Geoinsite’s Principal Geologist served as the Engineering Geologist team member for the Fifth (2007) and Sixth (2011) FERC Pt12D inspections and safety evaluations for Leroy Anderson Dam, FERC Project 5737. The dam is a zoned earthfill embankment that impounds Coyote Creek. The dam has a maximum height of about 240 feet above the streambed, a crest length of 1,400 feet, and a crest width of 26 to 43 feet. The dam is a zoned earthfill and rockfill with a central impervious core, pervious upstream and downstream outer shells. The reservoir impounded by Anderson Dam has a surface area of approximately 1,245 acres and a storage capacity of 90,373 acre‐feet at a spillway crest El. 625 ft.
 
Geologic and seismic issues at Anderson Dam that are of concern to regulatory agencies include significant near-field seismic sources (Calaveras Fault), liquefaction potential of alluvial deposits underlying the shells, secondary fault displacement along fault traces under the dam and outlet works, reservoir rim landsliding, and erosion of the downstream spillway channel. Geoinsite provided review and assessment of these issues, and summarized current conditions and state of understanding in the 2007 and 2012 Pt12D reports, PFMA sessions and STID. Geoinsite also performed independent geologic mapping and evaluation of the spillway erosion issue to satisfy regulator concerns. Anderson Dam is currently the focus of seismic remediation studies due to the potential for liquefaction deformation associated with strong ground motion.

Project:      Rockfall And Foundation Erosion Assessment
Location:   Slab Creek and Junction Dams
Client:        Sacramento Municipal Utility District/GEI Consultants
Year:           2008-2009

Slab Creek and Junction Dams are concrete structures that were designed and constructed in the 1960s. Updated flood studies resulted in calculated overtopping of the dam crests, which led to the identification of potential failure modes involving erosion of foundation rock in recent Potential Failure Mode Analysis (PFMA) workshops for the two dams. Geoinsite completed engineering geologic evaluations of abutment stability and foundation erosion associated with the future crest overpour events to determine the validity of the potential failure modes.
 
The dams are located in relatively narrow, steep-walled canyons.  The geology at both sites is characterized by Paleozoic-age metamorphic rock and Mesozoic granitic rock.  Discontinuities in the metamorphic rocks include bedding-parallel foliation and several joint sets.
 
Engineering geologic field mapping was performed to measure and characterize rock discontinuities.  Kinematic analyses of rock discontinuities showed a low potential for the formation of significant wedges in the dam foundations. Current conditions do not appear capable of allowing development of foundation washout paths through which the reservoir would be lost (PFM scenario 1).  Further, a total loss of foundation support over a localized area in the abutment area, which would prevent “bridging” of the load across the eroded area, resulting in loss of the upper cantilevers in the localized area, was determined to be unlikely (PFM scenario 2). Recommendations were provided to monitor certain fractures in future inspections.

Project:     Bear River Canal-Flume Repair
Location:  Placer County, California
Client:       Sanders & Associates GeoStructural Engineering
Year:          2011

A canal-and-flume water conveyance structure in the Sierra Nevada failed catastrophically in April 2011, requiring rapid geologic evaluation of the underlying slope. Geoinsite provided geologic support services to SAGE to assist in site geology characterization for development of geotechnical design criteria for repair and replacement of failed canal-flume section. Responsibilities included geologic field mapping, logging of rock core, and characterization of rock slope parameters, including depth to competent rock, joint and shear orientations, RQD, and selection of samples for laboratory testing. Repair of the canal-flume structure was completed in July 2011.

Project:     Hawaii Dam Safety Program
Location:   Maui, Molokai
Client:        State of Hawaii/GEI Consultants, Inc.
Year:          2008

Geologic evaluation of 55 dams on the islands of Maui and Molokai to support updated Dam Safety Program for the State of Hawaii Department of Land and Natural Resources.

Scope included characterization of Hawaii earthquake hazards, field inspections of dams and water conveyance systems, and evaluations of slope instability and foundation conditions. Detailed evaluation and mitigation of embankment and foundation deficiencies are still to be performed for selected sites.