By 1959, the District's first wastewater treatment plant was brought on line, greatly reducing the amount of untreated sewage discharged to the Mare Island Strait. Sewage flows through pipes to our modern wastewater treatment plant at 450 Ryder Street in southwestern Vallejo. The plant has a dry weather capacity of 15.5 million gallons per day (mgd) and a wet weather capacity of 60 mgd.

WASTEWATER SYSTEM IMPROVEMENTS

Early 1970s
The original 1959 plant was designed to treat sewage only to a primary level, clarifying the wastewater by removal of material by settlement and skimming. In 1972, new regulations from the U.S. Environmental Protection Agency necessitated the construction of a secondary treatment plant. Secondary treatment removes the biological elements remaining in wastewater after primary treatment.

1977 - 1985
Vallejo's secondary facility was completed in 1977. During initial efforts to bring the new plant on-line, it became obvious that the plant was not going to work properly. The plant used an innovative physical/chemical process, hailed at the time by federal and state regulators as the "process of the future." In 1981, this process was declared a failure by the regulators who once praised it.

In 1985, after considerable legal battling and political effort, the federal and state governments acknowledged their responsibility to assist in correcting the failed plant.

The new plant uses the same process that nature does to clean water in streams and rivers. Once the water is cleaned and returned to the Bay, the dried biosolids that are left are treated and used as a soil amendment and fertilizer at the District-owned Tubbs Island farm in Sonoma County.

Secondary treatment dramatically improves the plant's effluent quality. To address long-term wastewater treatment needs, the District developed a 20-year Master Plan for wastewater capital facilities that included a program to eliminate wet weather sewage overflows to surface waters entering San Francisco Bay. This effort involved the construction of new wet weather treatment facilities at the existing wastewater treatment plant as well as improvements to the District's collection system. The new plant facilities were brought on line in 1991. These improvements increased the plant's capacity from 30 mgd to 60 mgd during wet weather flows. The District also increased the size of several pipes within the collection system between 1988 and 1995. In 1992, an Inflow/Infiltration Control Program was prepared. The District currently follows this program as a means to reduce the entrance of rainwater into the sanitary sewer system.

SANITARY SEWER OVERFLOWS
Pipes that carry wastewater to the plant are made out of various materials ranging from clay and cement to materials made of paper and tar called Orangeburg that were installed during World War II. Over time, tree roots and ground settling can cause the pipes to develop small cracks that allow excess rainwater and ground water to flow in. Wastewater flows can increase from an average of 13 million gallons per day in dry weather to 60 million gallons per day during heavy rains. The District is currently in the process of implementing a $60 million program to make the system repairs and improvements necessary to eliminate overflows.

STORM DRAIN SYSTEM
The District has also made improvements to the storm drainage system. There are more than 150 miles of pipes and channels, as well as four pump stations that provide drainage in the Vallejo area. The District maintains these storm drains. Severe flooding in the Vallejo area has been reduced substantially. Major facilities constructed include Lake Dalwigk and Austin Creek in the 1950s, and facilities below Lake Chabot Dam in the late 1980s and early 1990s. Engineers use a formula to measure the intensity and quantity of rain that falls during a storm. Each storm is given a rating that is measured by "years." A 15-year storm means that the area is likely to experience a storm of similar capacity only once in 15 years. Likewise a 100-year storm means that a similar storm would be expected in the area only once in 100 years. The District has a minimum capacity requirement for new drainage systems. New public systems must have a capacity to convey the 15-year storm design. Since 1988, if the area drained is one square mile or larger, the required capacity is conveyance for a 100-year storm. The District continues to follow the Storm Drain Master Plan prepared in 1987 and updated in 2003.