Geotechnical boring is required as part of a subsurface exploration program for site characterization of bridge foundation materials. Caltrans proposes to collect subsurface data necessary in the preparation of the future twerlve mud rotary borings will be drilled at the Cosumnes River Bridge site with two holes under the OHWM in the dry river bed. It is anticipated that each boring will take approximately two working days to complete. The maximum depth from the ground surface of the borings will not exceed 175 feet.
All work will be done when teh river is dry, which is generally from late June to late October. Access to the borehole sites north of the river will be from maintenance roads. Access to the river will be from a river access road adjacent to the railroad. The equipment will drive from the access point 500 feet northwest on the dry riverbed to the borehole location. The borehole locations south of the river will be accessed from the river up the southern bank.
In order to obtain quality soil and rock samples at the depths needed, advancement of the test borings will require the use of the mud rotary self-casing drilling system. This drilling system requires the use of drilling fluid to maintain hole stability, bring drill cuttings to the surface, as well as lubricate and cool the drill bit. Drilling fluid may consist of water, water mixed with bentonite clay based powder and/or liquid polymer. The drilling fluid is contained and recirculated through a close system utilizing a drill rod and a primary containment system. After total bore depth is reached, the boreholes will be backfilled appropriately and will likely consist of bentonite chips and/or grout.
This activity consists of basic data collection and resource evaluation activities which do not result in a serious or major disturbance to environmental resources. These activities are for information gathering purposes and studies that will lead to a project that Caltrans has not yet approved or funded.