Wastewater Treatment


Beginning in the 1920s up to the late 1950s, the Redlands “Sewer Farm” (a common term during that time) was located north and west of the City, on the north side of the Santa Ana River, near Alabama Street. Up until this time, an acceptable form of wastewater treatment was the Imhoff Technology. Raw sewage was placed in an Imhoff Tank where solids are separated from the liquid. The solids were then transferred to large drying lagoons, and the liquid portion, without further treatment, was discharged to the Santa Ana River. Due to the Federal Water Pollution Control Act of 1948, it was unlawful for any person to discharge any pollutant to navigable waters.

As a result of these new regulations, the City of Redlands facility was relocated in the early 1960s to the south side of the river at the north end of Nevada Street and a secondary wastewater treatment was constructed. With this method of treatment the wastewater solids are settled in large tanks and then removed, dried and disposed of off-site. The liquid portion is transferred to an activated sludge process where different chambers within this process help remove conventional pollutants. The discharge of the treated wastewater was to be treated in such a degree that disposal to navigable waters or direct disposal to the groundwater table will not endanger public health or degrade groundwater quality.  Development of population and water use (i.e., water conservation) have drastically changed the incoming wastewater matrix to treatment plants.  Consequently, over the years the City of Redlands has undergone many upgrades to the original wastewater treatment plant.

The Redlands Wastewater Treatment Facility is located on approximately 50 acres. The facility currently employs a staff of 25 on a continuous basis. The City’s wastewater treatment facility has a rated treatment capacity of 9.5 million gallons per day annual dry weather flow.  Approximately 6 million gallons of that capacity is in a membrane bioreactor system, the remaining 3.5 million gallons is in a conventional activated sludge process.


The City of Redlands operates a certified environmental laboratory for monitoring its drinking water supply and wastewater effluent. The laboratory is certified by the State Water Resources Control Board under Environmental Laboratory Accreditation Program (ELAP). The laboratory has two objectives: First, the laboratory provides information to the operational staff of the City’s water and wastewater treatment facilities, and sanitary landfill. Second, the laboratory provides monitoring information to the State of California’s environmental regulatory agencies. The laboratory staff is trained in highly technical testing procedures, and uses sophisticated instrumentation, such as ion chromatography and total organic carbon, to perform required laboratory analysis.

The City’s laboratory is located in the Training Center Building at the City’s Wastewater Treatment Plant. The laboratory is in operation every day of the year to provide the laboratory analyses and reports required for daily water and wastewater operations to meet all regulatory standards. The laboratory is currently staffed by a Laboratory Manager and four Laboratory Analysts.

The City’s laboratory operates cost-effectively and responsively to meet the joint needs of the City’s three municipal utilities: water, wastewater, and solid waste (landfill), to ensure compliance with regulatory requirements for safe drinking water, for a high degree of wastewater treatment and disposal, and protection of groundwater quality.

Wastewater Collection System

The City owns and operates a Publicly Owned Treatment Works  which includes a wastewater collection system that consists of approximately 250 miles of gravity pipelines, ranging from 6 inches to 48 inches in diameter. Dischargers into the wastewater collection system include residential, commercial, and industrial sources thorough approximately 20,000 private lateral connections.

To overcome hydraulic challenges, a portion of the wastewater collection system is diverted to a lift station that receives an average flow of 3.0 Million Gallons per Day (MGD), and has a maximum capacity of 7.8 MGD. The sewage flow from the lift station is pumped through a pressure force main that is 12 and 14 inches in diameter and approximately 3.5 miles in length.  Discharges into the wastewater collection system are conveyed to the City’s Wastewater Treatment Plant (WWTP) which was constructed in 1963.

State Water Resources Control Board Order No. WQ 2022-0103-DWQ requires wastewater collection agencies to have a Sewer System Emergency Response Plan (SERP). Under this order, City employees are required to report all wastewater overflows found and to take the appropriate action to secure the wastewater overflow area, properly report to the appropriate regulatory agencies, relieve the cause of the overflow, and ensure that the affected area is cleaned as soon as possible to minimize health hazards to the public and protect the environment. As such, the City’s goal is to respond to sewer system overflows as soon as possible following notification and in accordance with the City’s SERP.

Redlands Sewer System Emergency Response Plan

Redlands Sewer System Management Plans (SSMP) 2023