In the News

Export of Tahoe’s Treated Sewage Protects the Lake
date posted: December 22 2005

Lake Tahoe Report #87
Oct. 4, 2004
By John Cobourn and Heather Segale


While today’s residents at Lake Tahoe are learning about how to reduce nonpoint-source water pollution by implementing best management practices (BMPs), some might not know how Tahoe eliminated its “point source” pollution over 35 years ago.

Water pollution once entered the lake from easily identifiable sources, such as discharge pipes from sewage treatment plants. Septic tanks were used for many years, prior to the construction of wastewater treatment plants in 60s. Even before the Clean Water Act of 1968 was passed, the local jurisdictions knew that such discharges would not be allowed in the future. By 1968, all of Lake Tahoe’s treated sewage effluent was pumped out of the Tahoe Basin, and it remains so to this day.

The South Tahoe Public Utility District was formed in 1950 with the intention of treating sewage from the south shore, including Nevada’s casinos. Later in that decade, the Nevada side formed its own district (Douglas County Sewer Improvement District #1), and South Tahoe Public Utility District took responsibility for sewage from the city of South Lake Tahoe and from Eldorado County.

By 1965, an innovative advanced tertiary treatment plant was installed, which treated sewage to drinking water standards. However, even the effluent from this plant was not clean enough for discharge to Lake Tahoe. The district built a 27-mile pipeline over Luther Pass and constructed a storage reservoir in Alpine County. All effluent from the City of South Lake Tahoe and Eldorado County areas has been exported through this system since April 1968.

Once the export system was completed, the treatment plant reduced treatment to advanced secondary treatment, which disinfected the treated effluent water, but left trace amounts of nitrogen and phosphorus. This effluent water is stored in a reservoir near Woodfords during winter, and then released for use by ranchers to irrigate pastures and alfalfa crops in the summer. The small amounts of nitrogen and phosphorus are desirable nutrients for crops.

Similar systems have been built in Douglas County and Washoe County. The Douglas County Sewer Improvement District #1 treats all sewage from the casinos and from the Tahoe communities of Douglas County to advanced secondary levels. It then pumps the treated effluent over Kingsbury Grade to its holding ponds in the Carson Valley, in the foothills east of the Douglas County Airport. Again, this water is released during the hot, dry summer months for use by local ranchers to irrigate pasture and alfalfa fields.

In Washoe County, the Incline Village General Improvement District also treats sewage to advanced secondary levels. They pump the effluent over the Sierra to holding ponds in the north end of the Carson Valley. These ponds provide productive habitat for waterfowl, and the water is released for use by ranchers during the growing season.

On the California north and west shores, two local jurisdictions collect all the sewage in the sanitary sewers and pump it to Truckee. The Tahoe City Public Utility District and the North Tahoe Public Utility District cooperated under a Joint Powers Agreement to build a joint sewerage facility in 1968 to treat the sewage of both districts.

In 1978, the Tahoe-Truckee Sanitation Agency built a state-of-the-art tertiary treatment plant in Truckee. Since then, the Tahoe City and North Tahoe Public Utility Districts have collected all sewage between DL Bliss State Park at Emerald Bay and Kings Beach, and transported it to the Tahoe-Truckee Sanitation Agency plant through pipelines. The tertiary treated effluent from this plant is injected into the ground.

In addition to the liquid effluent, several of the plants on Tahoe’s south and east shores are now drying their solid waste materials (biosolids) and shipping them to the Carson Valley, instead of incinerating them. Bently Agrowdynamics is combining biosolids with other organic materials and composting them to form a fertilizer suitable for their pastures and alfalfa fields. With innovations like these, Tahoe has been in the vanguard of sewage treatment, water reclamation, reuse and recycling.