Ogier Ponds Separation from Coyote Creek Planning Study, Subsurface Hazardous Substances and Geotechnical Investigations

Ogier Ponds Separation from Coyote Creek Planning Study, Subsurface Hazardous Substances and Geotechnical Investigations

Valley Water proposes a project to collect data and information on the site conditions on at Ogier Ponds. The project would consist of subsurface hazardous substances investigation and geotechnical investigation. The project would consist of three data collection activities, which include geophysical screening, field exploration drilling, and test pits. The purpose of this project is to collect data to inform the planning and design of the proposed Ogier Ponds Separation from Coyote Creek Project. The project was included in an on-call geotechnical investigation contract that Valley Water executed in 2023 and now has an updated schedule. The project site is located at and near the Ogier Ponds in Morgan Hill, approximately four miles downstream of Anderson Dam. Project activities would involve data collection at four out of the six instream ponds. Geotechnical and geophysical investigations would be conducted at the Borrow Hill Area and near Ponds 2, 3, 4, and 5. The description for each data collection activity is provided below Geophysical Screening To collect information on buried steel pipes and other relics of the former mine on site, Valley Water would conduct a geophysical screening of the project site. The geophysical screening activity includes surface geophysical methods such as Electrical Resistivity Profiling and Ground Penetrating Radar to potentially locate buried objects or voids resulting from previous mining activities. The Electrical Resistivity Profiling (ERP) method measures the lateral and vertical variation of electrical resistivity (ER) beneath a given transect (line). The geophysical screening would provide results of a depth of detection of approximately 65 feet to 110 feet depending on the length of the proposed transect (line). Ground penetration radar (GPR) will be used to detect any shallow subsurface material up to about 10 feet. The proposed exploration locations would be conducted in the Borrow Hill area of Ogier Ponds. Equipment used for the geophysical screen be limited to two 4x4 trucks and a large van carrying equipment. Access to the site would be located along Ogier Avenue. The equipment will be stored in the vehicles when not in use. This activity is not anticipated to generate excess dust or spoils materials Prior to geophysical screening field work, Valley Water and its subcontractors would prepare an internal Health and Safety Plan, conduct pre-activity biological surveys, and coordinate access and location with the County Ranger with 72 hours advanced notice. Work would occur during normal business hours and would take approximately five days to complete. The work would occur between May 2025 to October 2028 depending on access rights and contractors’ availability. Field Exploration Drilling To collect soil information, the project includes field exploration drilling to collect soils samples at Ogier Ponds. The soil sample collection involves installing up to nine shallow boreholes with a depth up to 60 feet using a truckmounted drill rig. All boring holes would be conducted using the mud-rotary method, which including using a mudrotary to drill up to a depth of 60 feet. If needed, air-rotary drilling or sonic drilling techniques may be used to advance the borings to their target depth. The mud-rotary method would require the support vehicles and drill rig to have a staging area of approximately 10 feet by 40 feet (or 400 square feet) at each bore site. No trees on site would be removed. The mud-rotary drilling activities would be performed in accordance with ASTM D5783 standards and conducted with a 4.5-inch diameter drag or tricone bit at the end of N-size rods. A conductor casing (4 or 5-inch diameter) may be installed to facilitate and control fluid circulation. The bentonite drilling mud would be used as the drilling fluid and the drill cuttings would be placed into drums or bins. Waste material would be properly disposed of off-site according to all applicable waste disposal laws. Drill water would be contained and disposed of in a shallow excavated water sump on-site. Soil samples would be collected at 2 to 10 feet intervals using either Standard Penetration Test (SPT) or Modified California (MC) drive samplers. The soil samples would be transported to a laboratory for testing and evaluation. All boreholes have been proposed in locations to avoid environmentally sensitive areas identified in a 2022 cultural resources survey,and be located outside a 50 feet buffer area surrounding these environmentally sensitive areas. In the unlikely event that an archaeological artifact is accidentally encountered during construction, work in affected areas would be halted and a no work zone would be established. A no work zone area would be established within the 30 feet of the encounter. Valley Water or the contractor would consult with an archaeologist immediately after the encounter to determine the significance of the artifact and appropriate avoidance or minimization procedures if the artifact is significant, consistent with Valley Water Best Management Practice (BMP) CU-1 (Stop Work and Report if Archaeological Artifacts are Found). Following boring completion, boreholes would be backfilled with cement grout in accordance with the standards and requirements per Valley Water. Access to the work areas would be from Ogier Avenue and Coyote Creek Golf Drive. Prior to test pits field work, Valley Water and its subcontractors would prepare an internal Health and Safety Plan, schedule a USA Utility Locate, conduct pre-activity surveys, and coordinate site access and locations of drilling work with the County Ranger with 72 hours advanced notice. Neighbors within 500 feet of the drilling locations will be provided with three days advanced notice prior to generating noticeable noise, dust, or vibration. Field exploration drilling would take seven days to complete and would occur between May 2025 to October 2028 depending on access rights and contractor’s availability. Project activities would occur from Monday through Friday, 7:00 am. to 7:00 pm. Test Pits To evaluate the ground conditions for potential use as borrow sites, Valley Water would conduct a geotechnical investigation that consists of up to seven test pits. Three of the test pits will include sampling, requiring minor extra work using a 4 x 4 truck and hand auger to collect samples for analysis in conjunction with the test pit excavation. Each test pit would be about 10 to 15 feet long, 3 feet wide, up to 10 feet deep. To install the test pits, a flatbed truck, a track-mounted backhoe, and a 4x4 truck would access the site. Equipment used for conducting the test pits be limited to two 4x4 trucks, large van carrying equipment, drill rig, a flatbed truck support vehicle, a small water truck. In the unlikely event that an archaeological artifact is accidentally encountered during construction of a test pit, work in affected area would be halted, and procedures for evaluating and protecting archaeological resources described above in “Field Exploration Drilling” would be followed. The test pits would be installed near Ponds 2, 3, 4, and 5. Locations of the test pits may be slightly adjusted to avoid underground utilities that have not yet been identified. A biological pre-construction survey will be conducted prior to the work to ensure that biological resources are avoided. Exact test pit locations will be sited to avoid jurisdictional features. Native soil would be used as backfill material. No trees on site would be removed. The test pit locations would be restored to preconstruction conditions. Prior to test pits field work, Valley Water and its subcontractors would prepare an internal Health and Safety Plan, schedule a USA Utility Locate, conduct pre-activity surveys, and coordinate site access and locations of drilling work with the County Ranger with 72 hours advanced notice. The test pits would take about two weeks to complete. The proposed work would occur between May 2025 to October 2028 depending on access rights and contractors’ availability. Project activities would occur from Monday through Friday, 7:00 am to 5:00 pm. Access to Work Areas Access to the work areas would be from Ogier Avenue and Coyote Creek Golf Drive. Access to the site would be located on existing roads, parking lots, trails, and pedestrian bridges to reach the areas of activity. Trails may be temporarily blocked during access. Control measures would be implemented to maintain trail safety. During ingress and egress of equipment, crews will be in front of and trailing equipment to direct pedestrian and bicycle traffic, and to notify them when it is safe to pass the equipment. Signs, flaggers, cones, and/or blockades will be placed around work areas to keep the public at a safe distance

Morgan Hill

Santa Clara

Countywide

Santa Clara