Background & History

1800s – Sewer Collection System

In 1888 there were no sewers in San Luis Obispo, only minor, scanty trenches that took human and other waste from town to San Luis Obispo Creek (Creek), carrying muck and disease through the waters where children played and dumping it into the ocean. In February 1890, City of San Luis Obispo (City) leaders took the first step to reduce illnesses contracted from the Creekby installing the City’s first sewer pipe along Chorro Street to the corner of Palm Street. The pipe, however, still emptied into San Luis Obispo Creek. The City knew that additional treatment was needed, and reviewed different proposals for a sewage farm. By the end of 1890, the second component of the wastewater collection system, designed by Colonel Waring of San Luis Obispo, was approved, built, and used to rid downtown San Luis Obispo of sewage. The City purchased 10 acres at “the Schow Place” along San Luis Obispo Creek for $2,000 to be used as space for sewage treatment.

1900s – Disposal Grounds to Water Reclamation Facility

The purchase of “the Schow Place” marked the humble beginning of the Water Resource Recovery Facility (WRRF) as the then-called Disposal Grounds that was designed in 1900 by the City Engineer, George Story. In 1910, the Disposal Grounds and the sewer system expansion was designed.

Original plans for the Disposal Grounds from 1900.
Original plans for the 1910 expansion of the Disposal Grounds.


In the 1920s, two city bonds allowed for additional land purchase for the Disposal Grounds and the construction of a larger City sewer collection system. During 1920, San Luis Obispo built one of the earliest sewage treatment plants in California, transforming the Disposal Grounds into a treatment plant. It consisted of a preliminary clarifier and open digester ahead of sugar beet fields irrigated by the effluent.


The City of San Luis Obispo Disposal Grounds (1926).

In 1940, the U.S. entered World War II. Along with this came construction of Camp San Luis Obispo and a resulting population boom. The Disposal Grounds now could not land apply all of its effluent and had to look to San Luis Obispo Creek or other means of discharging its effluent.


Photographed in the 1940s, the photo features two newly constructed clarifiers and two unidentified gentlemen.

In 1945, the Disposal Grounds was enlarged to 35 acres which included two primary clarifiers, two biofilters, an additional digester. This allowed the City to treat 2.0 million gallons per day of wastewater and With the expansion, the plant also began discharging effluent to San Luis Obispo Creek. Today, the biofilter is off-line and the filter rock has been recycled throughout the site for landscaping purposes.

By 1951, the sewage effluent pond was constructed. By then the plant included two clarifiers, two biofilters, two digesters, a primary clarifier, chlorination facilities, an effluent pond, and sludge drying beds. The City added a third digester and a new laboratory facility in 1952, and the plant was renamed the City of San Luis Obispo Sewer Farm in 1954.


Featured are the primary clarifiers, trickling biofilter, and two unidentified gentlemen (1951).

The plant was renamed the City of San Luis Obispo Sewage Treatment Plant in 1962, after adding an influent pumping station that included grinders, a control house, two new biofilters (now totaling four), two new clarifiers (now totaling four), two treatment ponds, a chlorine contact pond, and an electrical control center. In 1964, the original operations building was constructed, which is still in use today.

The plant was renamed from the Sewage Treatment Works in 1967, to the Sewage Treatment Plant in 1970, and again to the Wastewater Treatment Plant in 1974.


Aerial view of the Water Resource Recovery Facility taken in 1970.

In 1982, the City added an equalization pond with a control structure, additional sludge drying beds, and an effluent structure located south of the facility for chlorination and dechlorination with chlorine and sulfur dioxide gas, respectively. The existing pond was divided into two smaller ponds to allow for rotation as polishing ponds.

From 1992 to 1994, the Wastewater Treatment Plant went through massive upgrades to meet permit requirements to protect the San Luis Obispo Creek’s freshwater habitat. The name was changed from the Wastewater Treatment Plant to the Water Reclamation Facility (WRF). The following structures were abandoned: two biofilters, the chlorine contact pond, and the chlorine and sulfur dioxide gas facilities. In their place, the following processes were added: two aeration basins (replacing the two treatment ponds), four dual media filters, two equalization tanks, and two chlorine contact channels. The effluent structures were also upgraded.


Construction of the two chlorine contact channels in the 1992 to 1994 upgrade.

2000s – Water Reclamation Facility

Water reuse facilities were constructed in 2004, and recycled water was used to irrigate parks, schools, and retail landscaping. Recycled water is still used for these purposes today.


Proposed recycle water layout (prior to 2004). 1 – Recycled water 2 – Motor Control Center 3 – Recycled water storage tank 4 – Recycled water discharge line 5 – Aqueous ammonia storage tanks 6 – Chlorine residual monitoring shed 7 – Chlorine Contact Channels #3 and #4 8 – Water reuse production metering vault 9 – Chlorine dosing pumps 10 – Alum and polymer pumping station 11 – New Laguna Lift Station 12 – Proposed additional recycled water storage tank site


The recycled water tank was constructed partially underground to reduce visual impacts.


The completed recycled water tank and pump station (2012).

2010s – Water Reclamation Facility to Water Resource Recovery Facility

In 2011, the WRF initiated the WRF Energy Efficiency Project to reduce energy usage, reduce the carbon footprint, and increase operational efficiencies at the plant. The project, in partnership with PG&E, included process and equipment changes and upgrades and was completed in 2015.

The Energy Efficiency Project replaced the existing non-functional microturbine cogeneration system with a new cogeneration system to provide more reliable electricity and heating for the existing anaerobic digesters. The cogeneration system covers approximately 25% of the WRF’s energy use.


Top – The cogeneration generator is shown inside the unit. Bottom – The metal vessels are carbon filters which provide air filtration to meet air quality requirements (2014).

Energy Efficiency Project Screw Press Addition: A screw press was installed to replace the existing belt press that was underperforming due to age. The new screw press dewaters the freshly digested Biosolids to achieve a higher solids concentration, therefore reducing hauling costs that are based on weight. The Biosolids are transported a local compost facility.


A large crane was used to install the screw press for biosolids dewatering (2015).

As part of the Energy Efficiency Project, the WRF headworks was upgraded to remove more grit and large non-organic debris brought to the plant through the collections system. This upgrade improves the flow through the system by reducing blockages and clogs.

In 2011, Cal Poly landscape architecture students and City staff designed and constructed a bioswale to treat storm water runoff.


Bisowale construction using native vegetation (2011).

In 2014, the plant was renamed as the Water Resources Recovery Facility (WRRF), as it is known today. It is intersting to note that throughout time the facility’s name changes reflect social perception of water as a resource.


Pictured here is a handful of the dedicated WRRF staff (2014). From left: Keith Powers, Marty Maloney, James Austin, Chris Lehman, Glenn Lubak, Dave Wharton, Ernie Redman, and Tom Tingley.

The WRRF Project was initiated in 2015 to improve existing treatment processes to meet the City’s new National Pollutant Discharge Elimination System permit, treat future flows and loading, replace aging equipment, maximize the production of recycled water, and incorporate interpretive features and public amenities. For more information, visit the Project Overview page.


The signing of the Program Charter for the WRRF Project (2014). Pictured here from left to right: James Austin, Jasmine Diaz, Vance Trimble, and Christina Claxton.