The Plant Operations and Maintenance Section of the Wastewater Division is
responsible for the treatment facilities and lift stations. Wastewater treatment plant operators monitor
the treatment plant 24 hours a day, 7 days a week to ensure regulatory compliance
and maintain process control. The wastewater treatment plant operators are
certified Grades I through V, as required by the California Water Resources
Control Board, Office of Operator Certification and the maintenance staff are CWEA certified technicians.
The maintenance staff is
responsible for performing preventative maintenance tasks keeping all of the equipment in excellent working condition.
This allows the operations staff to make sure all
processes run smoothly. Maintenance staff works closely with the operations staff to resolve issues that may
arise as to keep disruptions in the process to a minimum. The treatment process and liftstations contain confined
spaces and hazardous chemicals. All of the operations and
maintenance staff are trained in confined space entry, and are First Responders that can assist with
an emergency involving hazardous chemical releases.
Prior to the year 1910, wastewater from the City of Modesto was discharged 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 an outfall to the river. In 1919, the City purchased 38
acres of land to build an outfall line at the foot of Sutter Avenue. The tank’s overflow was then
discharged into the Tuolumne River. In 1928 approximately 12 acres of oxidation and percolation
beds were constructed as the first steps in primary treatment of the wastewater.
Between 1930 and 1950, the City constructed a 62 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 which
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
two digestion tanks were built. Other construction projects over the ensuing two decades
would be developed due the stringency of the regulatory agencies. An industrial
pumping plant was established and bar-screens were installed as well as a deck aeration, 21
acres of oxidation ponds and 53 acres of percolation ponds were established.
During the 1950’s and 1960’s, a 50 foot vacuator, a 90 – 100 foot bio-filter enlargement,
bar rakes, and a 90 foot digester were installed.
Construction of the advanced (for its era) Bio-filter was completed. A 200 foot secondary
clarifier and Vortex tank were constructed along with a
supplemental aeration of the vortex tank with Inka Grid System,
buffalo blowers and Waukesha engines using digester gas were also installed during this time.
In 1969, the City purchased 1200 acres of land off of Jennings Rd located seven miles
southwest of Modesto. A new trunk line connected the primary facility located at Sutter and the 843 surface acre
pond system located at Jennings that were 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 secondary clarifier. A 104 foot digester
was installed as well as a new control building. The vortex tank, bio-filter, oxidation, and
percolation ponds were taken out of service as well as a 100 foot biofilter.
During the 1970’s, a pressurization system was added to the vacuators and aerators were added to the ponds for a
total of 3200 hp mechanical aeration.
The next phase of improvements happened during the 1980’s which led to wastewater, also referred to as effluent, land
application at Jennings. Between land application and river discharge the City of Modesto
was able to move a greater volume of effluent. The Jennings facility received additional aerators,
chlorine contact tank, a 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 chlorination facility and mixer installation.
A digester and methane recovery system for vehicle fuel was installed at the Sutter facility.
Other installations at Sutter included two flotation thickeners, additional influent capacity,
a parallel outfall line and the Administrative building. An irrigation project at Jennings
adding 275 acres from local rancher (Trinkler) and an additional 2,900 acres from the Chase Ranch.
Two fixed film reactors, additional
aerators, storage ponds, 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 were improvements seen at the Jennings and Sutter facilities.
In 1998, the cannery segregation force mane project was completed allowing industry
complete isolation from the domestic influent line. New head-works screw pumps were completed
and put into service.
Since 2000, the Jennings and Sutter facilities have seen the Sutter DAFT units permanently
removed from service and the DAF units at Jennings for algae removal placed in service.
In 2009, construction began on Phase 1, a 2.3 MGD tertiary facility.
2010 saw the completion of the Sutter laboratory remodel.
2011 saw the installation of a gas scrubber system at Sutter (using grant funds),
and a communication tower installation at Jennings.
The City has continued 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 meet the regulatory and growth needs
of Modesto for the next 20 years.