Water Pollution Control Facility

Wastewater Treatment at Woodland’s Water Pollution Control Facility


Sewers have been used to remove wastewater as far back as ancient Rome, and by the late 19th century, people began to make the connection between raw sewage and its effect on public health and the environment. In the early 20th century, large cities (London, Chicago) began to treat wastewater in order to reduce the amount of pollutants discharged to the environment.

The City of Woodland has had a municipal wastewater treatment system in place for over 60 years (Treatment Ponds at Beamer & Rd 102, 1950; North Ponds in the 1970s). The WPCF, originally built in 1988, was expanded in 1997 and again in 1999 in response to population growth. In 2007, the plant was upgraded to its present configuration when a major expansion, driven by new regulatory requirements, was completed.   

Homes and businesses in Woodland are connected to a sanitary sewer system which conveys wastewater to the WPCF (sanitary sewer systems, like Woodland’s, carry only domestic and industrial wastewater, while combined sewer systems, for instance those in the older parts of Sacramento, also carry stormwater runoff). The wastewater flows mostly by gravity, but gets a little help from pumps, until it reaches the plant where it is treated and then returned to the environment. In our case, treated wastewater is discharged to Tule Canal in the Yolo Bypass (about 5 miles east of here).

What Happens in the Treatment Process?

The wastewater treatment process is essentially the same as occurs naturally in lakes, rivers, or streams. The function of a wastewater treatment plant is to speed up this natural process by creating ideal conditions for breaking down waste products and purifying water. Like most treatment plants, the WPCF operates 24 hours a day. We are committed to protecting public health and the environment while operating the plant in the most efficient and cost-effective manner possible.

Wastewater treatment at the WPCF is combination of physical, biological, and chemical processes:

  • At the Influent Pump Station, Screw Pumps lift raw sewage from the sanitary sewer system into the plant.
  • Preliminary (or Mechanical) Treatment removes inorganic material by using Bar Screens to exclude large objects such as sticks, rags, and trash. The Grit Basin allows heavy, sandy, or abrasive matter to settle out. These materials are collected by Grinders and Classifiers and discarded at the landfill.
  • Secondary Treatment creates optimum conditions for the growth of naturally occurring microorganisms, which digest organic material and remove nutrients, in the Oxidation Ditches. Organic solids are removed by settling to the bottom of Secondary Clarifiers. A return Sludge Pump re-circulates active microorganisms back into the system (like starter in sourdough bread). After secondary treatment 90% to 95% of solids have been removed from the wastewater.
  • Tertiary (or Advanced) Treatment is required because we are subject to very stringent effluent discharge limits. In tertiary treatment, effluent from the secondary treatment process is chemically conditioned and directed through Cloth Media Filters to remove particles. 
  • Disinfection destroys pathogenic organisms in the tertiary effluent before it is discharged to the receiving water. This step helps protect the public from exposure to disease-causing organisms and further insures that the environmental impact of our discharge will be minimal. The plant has two Ultraviolet (UV) Light Disinfection Channels that inactivate bacteria and viruses prior to discharge.  The final effluent is tested to confirm full treatment and to demonstrate compliance with the City’s discharge permit.  

Two additional steps complete the treatment process:

  • Solids Processing makes the solids which were removed from the secondary treatment process suitable for beneficial use or for disposal at a landfill. Waste sludge from the secondary treatment process is directed to a series of Facultative Sludge Lagoons (over 200 acres) for stabilization and drying. Wind action and the growth of naturally occurring algae minimize odors and further break down the sludge.  After drying, the waste solids are tested to confirm full treatment before being trucked offsite.
  • Overflow Pond.  During emergencies, water can be sent to the 43 acre Overflow Pond instead of being discharged to the environment.

Monitoring, Reporting and Discharge Permits

  • Process Monitoring - Each step in the treatment process has its own sampling and monitoring requirements and we use a variety of laboratory tests to make sure everything is running smoothly. Plant operators use process monitoring data to optimize plant performance.
  • Discharge Monitoring and Reporting - Since 1972, treatment plants that discharge directly water have been required to have a National Pollutant Discharge Elimination System (NPDES) permit issued by the USEPA or an approved State agency. In California, NPDES permits are administered through the Regional Water Quality Control Boards. Our NPDES permit tells us how often to monitor and report on the quality of the water we’re discharging. It dictates approved testing methods and even some operational parameters. Under the NPDES program, the state can establish even more stringent requirements than those applied by federal EPA. California’s Basin Plans are the most stringent water quality regulations in the country.

Who Works at the WPCF?

The WPCF is the City of Woodland’s largest asset – if we had to build it today, it would cost over $70 million. With that kind of price tag, it’s important to have qualified crew to operate and maintain the facility. The WPCF receives an incoming flow of 5 MGD (equivalent to the volume in 8 Olympic-sized swimming pools) with characteristics that can change daily or even hourly. To consistently meet clean water standards, the plant is operated 24 hours a day, but it’s only staffed from 6:30 – 5:00. The rest of the time it’s run remotely through the SCADA system. This automated system allows up to have only 1 crew, a day crew. We have a crew of 13.5 people directly involved in running the plant:

  • Pretreatment – The City implements a Regional Board-approved pretreatment program as required by our NPDES permit. Our Pretreatment group works directly with industrial and commercial dischargers to minimize their impact on the sewer system and the WPCF by controlling water pollution at the source. In addition, the Pretreatment group does outreach to residential customers to inform and educate on pollution prevention strategies for the home & office.
  • Operations & Maintenance – Our Plant Operators, Electricians, Instrument Technicians, and Mechanics are responsible for the safe, efficient and effective operation of the WPCF. The wastewater treatment process is designed to mimic natural processes however, doing so requires extensive use of complex (and expensive) mechanical and electrical equipment. The Plant O&M group protects the City’s investment in the WPCF by maintaining and repairing this equipment and keeps costs in check by optimizing its operation.
  • Laboratory – Our Laboratory group performs over 10,000 routine process and discharge monitoring tests every year. In addition, they collect samples for special monitoring studies, prepare regulatory reports, and work closely with plant operators to optimize the treatment process.

A community’s quality of life and economic vitality are enhanced by wastewater systems that work efficiently and effectively. Citizens can make a difference by educating themselves in order to make informed decisions about initiatives to protect and improve our wastewater infrastructure. For more detailed information on wastewater treatment, visit the Water Environment Federation website http://www.wef.org/.