Construction on a series of infrastructural upgrades is underway at the San Andreas Sanitary District (SASD) Wastewater Treatment Plant in San Andreas.
“We have an old treatment plant, and much of the equipment is at the end of its useful life,” said Hugh Logan, the district manager, on the site last week.
The $6.5 million project is funded through grants from the State Revolving Fund and the U.S. Department of Agriculture (USDA). That budget includes the cost of planning, design, procurement, environmental review and construction.
“Securing grant funds was critical so the district could afford the project, while still keeping sewer rates reasonable,” said Terry Strange, SASD board president. A new rate structure was adopted in 2016, and a 1.87% rate increase was approved for July 1, 2019, to keep up with inflation, Logan said.
At about $68 per month, the district offers some of the lowest sewer rates in the county.
“The philosophy from the board of directors is that we actively pursue grants and low-interest loans in order to keep sewer rates as low as we can,” Logan said.
One of the most significant upgrades is the replacement of a 60-year-old anaerobic digester, a massive cylindrical tank that processes solid waste, or biosolids.
Built in the early 1950s for a smaller population of residents, the machine is no longer large enough to treat and process the solids generated at the facility, Logan said. The district currently provides wastewater services to over 900 residential and commercial customers. On top of population growth since 1952, state-mandated upgrades to help remove ammonia from the water in 2009 added even more waste for the digester to process.
“We can’t get enough production and treatment through that digester, which means it stinks a little bit more and it’s not as well treated as it needs to be,” Logan said. “One reason we were able to get grant funds is that we demonstrated that it’s not just old, it’s old and not working.”
Logan likened the digester to the human digestive system: “It likes to be at 98 degrees; it likes to be fed regularly and to be well mixed. It will produce gas, solid and liquid material. Just like the human stomach, if you eat a lot, the digester can get upset. Our digester gets upset because we can’t keep it at the right temperature because we have really old equipment. We have to feed it too much so it doesn’t have time to digest properly, and it’s not mixed at all, so the byproduct is not a good product.”
With the replacement, an aerobic digester, there will be no methane emissions, and it will be able to treat more solid waste at a faster rate. Larger plants can recover methane from the digestion process and use it for power generation, but SASD doesn’t generate enough gas to justify buying a generator, Logan said.
Aerobic digestion is a biological process that takes place in the presence of oxygen, Logan said. Large electric blowers bubble air up through the liquid in the concrete-lined digester to help stabilize solid waste and reduce nuisance (odors, rodents), disease and the total mass of waste that requires disposal.
“The new technology will be safe; no gas production, easier treatment,” Logan said, peering over the edge of the gaping hole that will house the new digester. “There’s a higher power cost for aerating, but it’s less labor and less dangerous, so it’s about a wash in the end.”
Other grant-funded improvements include upgrades to the plant’s electrical system and installation of a new supervisory control and data acquisition system for process control and security.
Additionally, effluent storage ponds were cleaned out to protect pond levees from erosion and provide greater storage capacity during periods of heavy rainfall.
After the various stages of treatment at the plant are complete, the water is dispensed down a mile-long pipe to the North Fork of the Calaveras River when water is flowing in the river for dilution, or it’s sprayed through sprinklers for land application.
W.M. Lyles Contractors and KASL Construction Management team were selected to complete the improvement project, and construction is anticipated to be complete by spring of 2020.
“Our goal is to complete this project on time, on budget, and with the highest degree of safety and quality for the district,” said Jack Scroggs, the district’s construction manager.
Logan said SASD is also seeking $750,000 in grant funding to build a new channel and replace a screen in the headworks, the first set of filtering processes that wastewater entering the facility passes through.
It’s also seeking funding to replace the trickling filter, a 50-year-old tower of corrugated plastics that breaks down waste with a bacterial slime.
“By investing in the infrastructure of the facility, we have the ability to implement what the community wants,” Logan said. “If community or the county has plans they want to implement, it’s our job at the wastewater plant to keep infrastructure ready to receive. This project certainly helps in that regard. It’s a foundational step for any community to have infrastructure in place for clean water and wastewater treatment.”