This photo of the inside of a wetwell at the city’s sewage plant shows how hydrogen sulphide has eroded the concrete walls down to the rebar, some of which has disappearing, according to Stantec, hired by the city to inspect the system
The Madera Waste Water Treatment facility — aka sewage plant — is again approaching disaster with the potential failure of another key component, the concrete “wetwell,” the massive tank that collects and holds city sewage just prior to processing, according to an emergency repair study, performed in September by Stantec Consulting Services.
Built in the 1950s, the sewer plant dodged a crisis in 2017, but continues on.
The study was presented to the City Council Oct. 10.
With its decaying infrastructure, the plant, situated on Avenue 13, processes from 7 million gallons to as much as 10 million gallons per day and is barely keeping up with increasing population demands.
Some parts of the sewer plant and holding tanks were recently deemed unsafe by Stantec after examination. Damage to the upper concrete tank walls was considered extreme and more extensive than originally thought, due to years of exposure to hydrogen sulfide gases, the Stantec report said:
“Once the water level inside the wet well was lowered and Stantec had access to the Primary Effluent Pump Station, the extent of damage to the concrete baffle walls and ceiling (within the Wetwell) could be fully assessed and is identified as more severe than observed during the initial inspection. Years of exposure to hydrogen sulfide (H2S) has allowed the concrete inside the wetwell to corrode and expose much of the interior mat rebar, corroding the rebar and compromising the structural integrity of the top half of the wetwell.
“This wetwell supports three massive vertical turbine pumps on the top slab (each weighs over 5 tons with 20” columns, and is now considered unsafe. Stantec recommends that operators stay off the slab (to the extent possible) until structural remediation measures can take place.”
Photos submitted to the City Council showed rusting steel rebar protruding from decayed concrete walls in the upper portion of the wet well holding tank, risking the structural failure of the concrete holding tank wall and it’s massive concrete top structure.
The city barely dodged a bullet in mid 2017 after three of the plant’s massive gears which power the pumps churning the sewage effluent failed, and two others had to undergo a costly emergency retrofit, leaving the city with only one gear of six actually working for a time.
Without the gears working and only a day of emergency overflow storage outside in a ponding basin, all sewage processing could have come to a stop, causing toilets in Madera to cease to function, and a public health crisis no one wanted to contemplate.
The consultant’s study basically offered two options for consideration by the Madera City Council.
(1) Repair and reline the existing concrete walls of the old existing tank for roughly $600,000 to $700,000 or (2) add a new, larger holding tank for about twice the price, at around $1.2 million, which the consultants said would meet current building codes and the needs of future sewer operations.
The project can be funded out of water and sewer enterprise reserve funds — the small amounts of money collected each month from all residents for this purpose.
Observers of city operations said they were surprised at the situation, which they attributed to poor planning and apparent neglect.
One former city official went further to say city infrastructure maintenance, repair and improvement should have been a top priority of all city officials. “Where is the accountability? This reaches the level of investigation, possible malfeasance and reprimand. Somebody wasn’t doing their job. Without a working sewer plant you don’t even have a functional city.”