• Introduction
• Collection Systems
• Pump Stations
• Treatment Plants

• Huston Creek

• Seeley Creek

• Cleghorn

• Effluent Outfall System
• Effluent Disposal Site

• Discharge Requirements

Cleghorn Treatment Plant

The Cleghorn Plant is the smallest of the District's three wastewater treatment plants with a design capacity of 0.2 mgd. The facility was originally constructed in 1974 by the District to serve the needs of the California Department of Parks and Recreation campgrounds at Lake Silverwood and the administrative and housing facilities upstream of the plant. The Cleghorn WWTP is owned and operated by the District. By agreement, the State Parks and Recreation Department reimburses the District for annual operation and maintenance costs. The State Parks and Recreation Department still maintains and operates the collection system that includes five lift stations. Only one of these pump stations has emergency power, which is supplied from the Cleghorn Plant.  Periodic dewatering, cleaning and recoating is carried out on a scheduled basis to avoid failures. 

The Cleghorn Wastewater Treatment Plant is an extended aeration (i.e., oxidation ditch) activated sludge plant with effluent chlorine disinfection. All wastewater flow from the majority of the park campground enters the plant though a 4-inch force main. An 8-inch gravity main serves the administration center, staff housing and group campgrounds. Final effluent is pumped via force main into the District's effluent outfall system for disposal at the Los Flores site.

Pretreatment - The headworks are designed to provide coarse screening followed by comminution. A bar rack is installed upstream to prevent damage to the comminutor. Once the comminutor shreds solids, raw wastewater enters the oxidation ditch process for biological treatment. The headworks structure also provides for the return of activated sludge from the secondary clarifier for blending with raw wastewater prior to entry into the ditch. No influent flow meter is provided at the plant.

Primary Treatment - As is typical of most extended aeration facilities, the Cleghorn plant does not have primary treatment facilities.

Secondary Treatment - Secondary treatment is accomplished in a 0.20-mgd oxidation ditch using one 30 HP brush aerator. The brush aerator operates continuously to provide sufficient mixing and aeration of mixed liquor. Both mixing energy and aeration capacity are controlled simultaneously by varying the level of mixed liquor in the ditch. Mixed liquor from the oxidation ditch flows into a single 22-foot diameter secondary clarifier with a 10-foot side water depth.

A single RAS pump intermittently pumps return activated sludge from the secondary clarifier to the headworks. This same pump is used to pump skimmings on an as-needed basis from the secondary clarifier and is used to pump waste activated sludge into a tank truck for transport to the Huston Creek sludge dewatering facilities.

Effluent Disinfection - Disinfection occurs within a rectangular, baffled, serpentine-style chlorine contact tank. As with the Seeley Creek WWTP, the chlorinators provide a constant feed to the contact tank. Chlorine dilution water is supplied by using potable water from the State Parks and Recreation Department system. Chlorine gas is supplied by one of two 150-pound cylinders with tank mounted remote vacuum chlorinators. In addition to the two chlorinators, the facility has two injectors (one duty, one standby). Should the duty injector become plugged, operators can manually switch operation over to the standby unit.

Effluent Flow Metering - Plant flow is continuously recorded using a 90-degree V-notch weir at the end of the chlorine contact tank. The water level upstream of the weir is monitored by a sonic meter.  The Huston Creek Treatment Plant has an identical system.

Solids Handling - There are no solids handling facilities at the Cleghorn WWTP. As with the Seeley Creek plant, waste solids are hauled as a liquid to the Huston Creek plant for dewatering.

Effluent Pumping - Effluent from the facility must be pumped into the Effluent Outfall, which operates at approximately 90 psi at the connection point. There are two constant speed effluent pumps (one lead, one lag). Both pumps are nine-stage vertical turbine pumps of identical design and manufacturer. Should the effluent pumping system fail, effluent will back up in the contact tank discharge channel resulting in activation of a flow switch alarm.  Occasional failures have been experienced on the plant effluent discharge pipeline requiring repairs.  District staff is watching this closely and will need to provide for a future replacement of all or part of the forcemain.

 Introduction | BACK | NEXT: Effluent Outfall System