Water Quality and Treatment

When Metropolitan first began delivering desalted Colorado River water to Southern California cities in 1941, the “softened” water was touted for its ability to reduce laundry suds. Today, salinity control remains a high priority. Colorado River water has the highest level of salinity of all of Metropolitan’s sources of supply (averaging approximately 625 mg/L since 1976). Metropolitan’s board in 1999 approved a Salinity Management Policy that set of goal of reaching salinity concentrations in delivered water of less than 500 mg/L when hydrological conditions allow.

One of the reasons the river is so salty is because many of the salts are indigenous and date to prehistoric marine environments that left deposits of saline sediments. Salts erode easily, dissolve and get transported in the river system. Metropolitan works with the Colorado River Basin Salinity Control Forum, an organization of the seven Colorado River Basin states of Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming to coordinate ways to prevent salts from moving into the river system. Measures include better irrigation practices and rangeland management. Since the 1970s, the salt load has been reduced by 20 percent.

The start of State Water Project deliveries to Southern California in the 1970s gave Metropolitan an additional tool of blending less salty (250 to 325 mg/L) SWP supplies with Colorado River water. Like the Colorado River, SWP salinity can vary greatly depending on hydrologic conditions.

High salinity levels can also occur in groundwater (referred to as brackish water). The desalination of brackish groundwater and other local supplies enhances the continued supply reliability of the region by maximizing local groundwater resources. For this reason, since 1991 Metropolitan funding has helped recover a little more than 1 million acre-feet of groundwater, cleansing it of salts, metals, nitrates, viruses and bacteria and creating another source of water that lessens our dependence on imported supplies.

In addition to desalinating brackish groundwater, Metropolitan has explored the development of seawater desalination since the 1950s. Since 2014, we have offered financial incentives as part of the Local Resources Program.

From the first discovery of quagga mussels in Lake Mead in January 2007 and their subsequent spread into parts of Metropolitan’s water system, the district has devoted countless hours and tens of millions of dollars toward containing and managing the invasive pest. Spread by commercial ships and inadequately cleaned and dried recreational boats, quagga and zebra mussels had already wreaked havoc in other parts of the country before arriving in the west.

The mussels rapidly reproduce, clogging pipes, water pumps and siphons, and growing on the walls of canals and other submerged infrastructure impeding flow. Soon after their discovery in Lake Mead, Metropolitan created a Quagga Mussel Control Plan.

Crews constructed continuous chlorination facilities at Copper Basin Reservoir, Lake Mathews and Lake Skinner, all of which take Colorado River water and, therefore, have quagga mussels. During Metropolitan’s yearly Colorado River Aqueduct shutdowns, Metropolitan crews dry up (desiccate) quagga mussels and remove them from the system, clean tunnels, and chlorinate strategic sites (sometimes using a mobile chlorinator). Divers perform underwater maintenance, stripping layers of quagga mussels from intake structures.

Routine inspections have demonstrated that the combined use of chlorine and regularly scheduled shutdowns effectively control mussel infestation along the length of the CRA and downstream systems.

We have been able to avoid infestation at our Diamond Valley Lake storage reservoir because CRA deliveries into the reservoir stopped prior to the arrival of quagga mussels in our CRA system in 2007. Our success also is due to a rigorous boater education and inspection campaign that enlists our Diamond Valley Lake marina operators to enforce launch requirements for visiting boats, and interview boaters to ensure requirements listed here have been followed. Recently, quagga mussels have been found in the State Water Project system at Pyramid and Castaic Lakes.