The Plant Operations and Maintenance Section of the wastewater Division is
responsible for the operations and maintenance of Wastewater of all Treatment
Facilities and Lift Stations. Wastewater treatment plant operators monitor
and staff the treatment plant 24 hours a day, 7 days a week to ensure compliance
and safety of the processes. The wastewater treatment plant operators are
certified Grades 1 through 5, as required by the California Water Resources
Control Board, Office of Operator Certification. The maintenance staff is
responsible for keeping all of the machinery working to original equipment
and design standards. This allows the operations staff to make sure all
processes run smoothly. Staff performs preventative maintenance and works
closely with the operations staff to resolve issues that may arise during the
operation process. The maintenance staff working at the treatment facilities
and lift stations are certificated technicians. All of the operations and
maintenance staff are trained on confined space entry, chemical response
training and are First Responders that can assist with an emergency involving
chemicals used in the treatment process.
Prior to the year 1910, wastewater from the City of Modesto was discharge without treatment
directly into the Tuolumne River at 9th street. In 1910, the City installed a septic tank at
the foot of Sutter Avenue with outfall to river. In 1919, the City purchased 38
acres of land at the foot of Sutter Avenue. With this an outfall line was built. City wastewater
flow was re-routed to what was equal to a giant septic tank. The tank’s overflow was then
discharged into the Tuolumne River and in 1928 approximately 12 acres of oxidation and percolation
beds were constructed.
Between 1930 and 1950, the City constructed a 62 ft foot diameter clarifier
and the pre-existing septic tank was converted into a sludge digester. Also, the facility
was modified for secondary treatment with the installation of a bio-filter. During this era
approximately 37 industries had developed in Modesto. Most of these industries
were related to food processing. With no pretreatment and the inability of the Sutter Facility
to treat the volume of industrial waste, the Tuolumne River during the canning season became
In an attempt to improve the discharge quality of the wastewater, a Control Structure and
2 digestion tanks were built. Other construction projects over the ensuing two decades
would be developed due the stringency of the regulatory agencies. During the canning season,
it was common practice to operate the Sutter Facility differently than the rest of the season,
when most industries ceased production. This is a cycle that continues today. An Industrial
pumping plant was established and bar-screens were installed as well as the deck aeration, 21
acres of oxidation ponds and 53 acres of percolation ponds were established.
During the 1950’s and1960’s, a 50’ vacuator, a 90’ – 100’ bio-filter enlargement and a
domestic detritor, bar rakes, comminutor and a 90 ft digester were installed.
Construction of the advanced (for its era) Bio-filter was completed. A 200’ secondary
clarifier and Vortex tank were constructed along with installation of a secondary 200’
clarifier and vortex Tank and supplemental aeration of vortex tank with Inka Grid System,
buffalo blowers and Waukesha engines using digester were also installed during this time.
In 1969, the City purchased 1200 acres of land off of Jennings Rd located 7 miles
southwest of Modesto. A new trunk line connected the primary facility and the 843 surface acre
pond system that was being developed for secondary treatment. Ultimately, discharge would be
rerouted from the Tuolumne River to the San Joaquin River. This new facility and treatment
process would be known as Jennings Secondary plant. The Sutter facility was converted back
to primary treatment only. Modifications included conversion of 1930 clarifier to a gravity
thickener, and the 1955 bio-filter converted to a 2nd secondary clarifier. A 104’ Digester
was installed and a new control building. The vortex tank, bio-filter, oxidation, and
percolation ponds were taken out of service.
During the 1970’s, modifications to DAFT’s were done at Sutter and mechanical aeration
was added at Jennings (16 aerators) and there was the addition of several more mechanical
aerators at Jennings.
The next phase of improvements happened during the 1980’s which led to effluent land
application a Jennings. Between land application and river discharge the City of Modesto
was able to move a greater volume effluent. Jennings facility received additional aerators,
chlorine contact tank, chlorination and de-chlorination facility, two fixed film reactors
and land application system consisting of irrigation fore bay, irrigation pump station
and ranch reservoir.
The 1980’s also saw the Jennings chlorine contact basin baffles and mixer installation
and at Sutter, a digester and methane recovery system for vehicle fuel was installed.
Other events were the Sutter, 2 flotation thickeners, additional influent capacity,
a parallel outfall line and Administrative building, an irrigation project at Jennings
adding 275 acres from local rancher (Trinkler), 2 fixed film reactors, and more
aerators, storage ponds and de-chlorination facility up grades, Fixed film reactor #3
on line, Storage pond wave protection, polymer system added to thickeners, and new
influent bar screens.
In 1998, the Cannery segregation force mane project completed allowing industry
complete isolation for the domestic influent line. New head-works screw pumps completed
and put into service.
Since 2000, the Jennings and Sutter have seen the Sutter DAFT units permanently
removed from service and the DAF units at Jennings for algae removal placed in service.
In 2009, the begin construction of Phase 1 2.3 MGD Tertiary facility which started up
in July 2010. 2010 saw the completion of the Sutter Laboratory remodel complete and
in 2011 the installation of gas scrubber system at Sutter (using grant funds), Jennings
communication tower installation.
The City continues to meet the needs of the growing population of the City of Modesto
by starting construction on Phase 2 of the Tertiary facility which will meets the needs
of Modesto for the next 20 years.