was a joint project between the US Bureau of Reclamation (USBR) and Placer County Water Agency (PCWA). The project includes reconstruction (grading,
placement of riprap, and subsurface cutoffs) of approximately 1.5 miles of
river channel, design and construction of new intake facilities for PCWA, and closure of the dam diversion tunnel.
Blackburn Consulting evaluated subsurface
conditions including alluvial depth/composition and structural geology, and provided
options for excavation and fill placement, rock slope stability, design and construction
of structures, and construction testing/inspections. We also assisted in preparation
of specifications for grading, foundation construction, blasting, and rock
bolting. Significant challenges included
site access and methods to determine depth of fill/alluvium overlying bedrock
(for foundations and cutoffs), and defining the variety of materials within the
site and their reuse within the project.
We coordinated with the USBR in obtaining borehole and excavator data
on bedrock depth and quality and groundwater elevation. Exposed rock structure/extent mapping was
completed and extrapolated to covered areas and combined with subsurface data
for preliminary evaluation and design recommendations.