Challenges of Disposing of Tunneling Water

The San Diego County Water Authority (Water Authority) is currently constructing the San Vicente Pipeline connecting the San Vicente Reservoir to the Second Aqueduct Pipeline. This project is a key component of the Water Authority's Emergency Storage Program (ESP) to provide greater water reliability in the Water Authority's delivery system. The San Vicente Pipeline is approximately 11-miles in length and is being constructed as a 12.5 to 14-foot (3.81 to 4.27-meter) diameter tunnel through varying geology. The depth of the tunnel varies from 50 feet (15.24 meters) to over 500 feet (152.4 meters) below ground surface. There are four access sites to the tunnel. Each of these access sites has a unique set of parameters, site restrictions and expected groundwater inflows. It is difficult to predict the volume of groundwater that will be encountered, but 1000 gallons per minute is the upper limit in the project's Geotechnical Baseline Report. In addition, the current discharge regulations require high levels of groundwater treatment for discharge to surface waters. The majority of the groundwater that is currently being encountered is being treated and discharged to a local streambed. The cost of the treatment of groundwater is expensive and has led the Water Authority to look for other cost effective means of disposing groundwater. This paper addresses the other means of disposal and the various processes such as permit, community, and contract requirements that govern their implementation.