Gregg Drilling's Salton Sea Lakebed Project
Drainage SumpAt 227 feet below sea level, the sea is officially designated as a sump for agricultural drainage. Agricultural runoff from farms throughout the Imperial and Coachella valleys drain into the lake, replenishing water lost due to evaporation. This results in more salts, nutrients and contaminants retained by the lake as pure water is removed by evaporation. The Salton Sea currently is 25 percent saltier than the Pacific Ocean and boasts large amounts of fertilizer and minerals. The nutrients fuel plant and algae growth which at first, allowed the fish population to boom, but now is causing their demise. Fertilizers cause large algae blooms, which deplete the water of oxygen when they die and decompose. In summer, oxygen levels in the water disappear in all but the top few inches due to the heat, high salt content and decomposing algae. This causes massive fish die-offs, affecting birds and wildlife surviving in the area. Salt itself also aids fish extinction because an increasing content will soon hinder the ability for fish to reproduce. To add to these problems, representatives of Southern California's largest water agencies agreed last year to transfer 65 million gallons of water from the Imperial Irrigation District to the San Diego County Water Authority. This would reduce the inflow of water that maintains the Salton Sea, in effect, only adding to the problems outlined above by speeding up the process.
Is There Hope?Yes! The Salton Sea Authority, which is a coalition of Riverside and Imperial county governments and water districts, decided to take restoration plans into their own hands. A number of ideas were proposed to improve water quality and preserve the valuable habitat. It also was important that all designs account for possible seismic movement since the east side of the lake borders the San Andreas Fault. The plans revolve around creating a dike or dam to separate the lake into north and south sections. Desalination plants would reduce the salt content in the north lake, providing a recreational area and marine lake environment. The southern section also would benefit from water quality improvement, and could be turned into shallow wetlands for water birds and other wildlife. The plan would entail dam construction, wildlife preserves and one of the world's largest desalination plants. Initial estimates come in at almost $2 billion due to the hefty price tag on desalination. To assist with the cost of implementation, some of the water could be sold to California residents at $470/acre-foot. This is half the cost of desalinating ocean water but 60 percent more than just transferring water from the valley and not improving the Salton Sea. Enough water for up to 2 million people could be provided by this project, creating a win-win situation for the water agencies and the environmental conservationists. There still are some opponents to the plan who say that it is too centered on reducing the sea's salinity and stabilizing its elevation instead of other, more serious, water quality factors.
Regardless of this opposition, last year Congress gave the Salton Sea Authority $10 million for feasibility studies and design efforts. After more than 30 years of research, the Authority was eager to take action. It contracted Tetra Tech and URS Corp., environmental and engineering firms, to conduct investigations. Before engineers could get started on possible designs, exploration of the seabed for strength, stability and possible building materials had to be conducted.
Gregg Goes to WorkThe specialized nature of the project required engineers to engage Gregg Drilling and Testing of Signal Hill, Calif., to perform the over-water drilling operation. Gregg used a jack-up boat as a stable platform upon which they mounted their drilling rig. The benefit of the jack-up boat is that it is easily maneuvered to different locations across the lake and can be raised off the water surface to avoid disturbance by large waves. The jack-up boat was used to successfully drill and test sub-bottom soil in water up to 50 feet deep. A total of 28 locations were tested and sampled using standard penetration tests (SPT), cone penetration tests (CPT) and Shelby tube samplers.
The boreholes and CPT ranged from 30 feet to 50 feet in depth with one borehole extending to 200 feet below mudline. CPTs conducted in 15 locations provided a continuous soil behavior type profile of the sub-bottom environment. This was accomplished by pushing a cone penetrometer, attached to a data acquisition system, into the subsurface using a hydraulic ram. The cone penetrometer contains electronic sensors to measure tip resistance and sleeve friction, while a small filter behind the tip measures pore water pressure. The CPT provides a rapid, reliable and economical means of determining soil stratigraphy, relative density, strength and hydrogeologic information without generating soil cuttings. Geologists and engineers looked for strong and stable soils in the planned construction area to support large structures, and around the lake for possible fill materials for the proposed earthen structures (to reduce material importing costs). If the sub-bottom sediments are found to be soft fine-grained soils, extensive excavation and backfilling will be required to support construction of a dam.
Drilling and testing was completed in just over four weeks with samples sent to a URS geotechnical laboratory for further study. The data and information collected will provide valuable information for Salton Sea restoration designers and planners.