City of Coalinga Continuous GPS (CGPS) and Monitoring Well Installation

Description of Nature, Purpose and Beneficiaries of Project: In 2014, the Sustainable Groundwater Management Act (SGMA) was signed into law requiring local Groundwater Sustainability Agencies (GSAs) to manage groundwater in their service area that necessitates the development of an adequate network of appropriately spaced groundwater monitoring wells. With secured funding, the Department of Water Resources (DWR) has established the Technical Support Services (TSS) program to help GSAs meet their SGMA requirements by providing services to install groundwater monitoring wells, conduct downhole video logging, and training on methods to accurately monitor groundwater levels. The CGPS installation consists of installing a single CGPS station. The CGPS station will continuously measure the three-dimensional position at the site with the focus of monitoring for vertical movement, also known as land subsidence. A total area of 20' x 40' for equipment with a 50' x 50' staging area for vehicles and equipment is needed. The drilled holes will penetrate approximately 35' into the subsurface where stainless pipe is lowered and then grout is pumped through the legs to anchor the monument. The total height of the CGPS station equipment is approximately 6' tall. The Well Installation Project consists of installing a single, nested groundwater monitoring well. The well site location is TBD but will be marked by Underground Service Alert, then hand tools will be used to excavate to a minimum depth of 5'. The driller will use a truck-mounted drill rig to drill a pilot hole while using a mud cleaner to filter out solids and return drilling mud to the drill bit. When the pilot hole is at the desired depth, the driller will expand the borehole to a diameter of approximately 14". The nested well will consist of two or three PVC casings, and the base of each well, from the bottom up, will consist of sand, a filter pack, and a bentonite seal. Cement will be pumped from the support truck to place the sanitary seal in accordance with state and county requirements. A raised well monument and concrete pad approximately four square feet and four inches tall with four approximately 4-foot-high metal crash posts will be installed at ground level to protect the well from potential damage, or the well will be installed in a flush-mounted vault in accordance with county road ordinance. DWR or GSA staff may visit the well on a quarterly schedule to collect data. Operation and maintenance will be minimal and may consist of periodic servicing of equipment and replacing batteries as needed. Access to the well location will be by existing paved and dirt roads. Once installed, this facility will become part of the GSA's monitoring program.