The California Department of Transportation (Caltrans), using state funding only, plans to conduct a geotechnical investigation on State Route (SR) 97 in Siskiyou County at post mile (PM) 19.8. The purpose of the geotechnical investigation is to collect data on subsurface conditions at the location of a proposed wildlife overcrossing that would be constructed as part of the Wildlife Crossing project. The geotechnical investigation is needed because the data collected would be used to design the foundation of the wildlife overcrossing.
The proposed subsurface investigation would consist of drilling a maximum of two (2) borings. The borings would not extend deeper than 120 feet below the ground surface. The drilling operations would be performed by a Caltrans drill crew or contracted drilling crew. The drilling operation would utilize a truck-mounted or track (trailer)-mounted drill rig equipped with a Standard Penetration Test (SPT) hammer. Other equipment used would include a water tender (water truck) and a crew cab with trailer. In addition, one or two Engineering Geologist/Engineer’s vehicles are required to support the drilling operation.
Drilling would be conducted with a hollow stem auger boring (with a maximum eight-inch diameter) until practical refusal or groundwater is encountered. If refusal or the presence of free groundwater is encountered before the maximum proposed depth, the mud rotary self-casing drilling system (four-inch diameter) would then be conducted to achieve the required depth of the investigation. This mud rotary technique requires the use of drilling fluid to maintain hole stability, bring drill cuttings to the surface, and lubricate and cool the drill bit. The drilling fluid consists of water mixed with bentonite clay-based powder and/or liquid polymer. The drilling fluid is contained and recirculated through a closed system utilizing drill rod and a mud tank. The mud tank would be positioned on the surface of the ground and serve as a settlement tank for the soil cuttings, which are periodically removed and placed in 55-gallon steel drums. Once the desired boring depth has been reached, the holes would be flushed with clear water to displace the drilling fluid back into the mud tank. The drilling fluid and water would then be pumped from the mud tank into 55-gallon steel drums for disposal. After the total depth is reached, the bore holes would be sealed/destroyed in accordance with California Water Code and the LEA permit requirements.
The drilling operation for this project may take up to two weeks to complete. The driller’s work schedule is four ten-hour days, Monday through Thursday. Working during daylight hours is preferred to perform the drilling operations.
Equipment storage for the drilling operation is typically located at the local Caltrans maintenance yard. Typically, the water tender and trailer are stored at the nearest Caltrans yard at the end of each workday. However, the drilling rig might remain at the investigation location overnight, if required. The crew cab and geologist/engineer’s vehicles would be transported off site at the end of each workday.
The total area of topsoil disturbance associated with the geotechnical investigation would be negligible. The geotechnical investigation does not require the use of a borrow site. Soil (“cuttings”) removed from the boring holes would be placed into 55-gallon drums and temporarily stored at a nearby Caltrans maintenance yard or at the Caltrans Trans-Lab facility in Sacramento. The material would then be disposed of at a landfill which has previously undergone environmental review and is approved for use.
The geotechnical investigation would be performed entirely within Caltrans’ right-of-way. No federal land is present within the project area.
No conflicts with utilities are anticipated.
No permits from regulatory agencies would be required.
Caltrans has performed a review of resource records and databases and consulted with applicable agencies and individuals.