Dr. Lisa Thompson discusses the upgrades to Sacramento’s wastewater treatment plant; highlights a new study on the effects of wastewater effluent on phytoplankton
In 2010, the Sacramento Regional County Sanitation District was issued stringent new treatment requirements from the State Water Resources Control Board that required them to make significant upgrades to their wastewater treatment plant by 2021-2023.
The Sacramento Regional County Sanitation District (or Regional San) serves 1.4 million people in greater Sacramento, from West Sacramento to Folsom and south to Elk Grove.
The Sacramento Regional Wastewater Treatment plant was constructed from 1976 – 1982; there were 22 separate wastewater treatment plants operating around the region which were replaced with a single new plant built. “We’re the largest inland discharger, and our collection area is tied with San Diego, just to give you a sense of the scale,” she said.
She then presented a slide of the treatment area, noting the Sacramento River in the background. The process area in the middle is about 900 acres; it’s surrounded by 2600 acres of open space called the bufferlands which is managed for wildlife, although parts may be used for future process upgrades, she said. Stone Lakes National Wildlife Refuge is in the back of the slide, and parts of the bufferlands and the creeks connect to it. The discharge area is just downstream of the Freeport Bridge where a diffuser pipe with ports discharges the treated effluent into the river.
In 2010, Regional San was issued a new discharge permit which has led to a major upgrade of the treatment plant called Echo Water. “It’s the first time that we’ve been regulated for ammonia and nitrate in our discharge, and that’s what we’re addressing here,” she said. “The ammonia removal has to be completed by 2021 and the filtration disinfection by 2023. The black row is the interim limits that we have for ammonia between now and 2021, when the ammonia treating part of the new treatment plant gets installed; the new limits are down below.” She noted that the limits vary by season based on anticipated changes in river flow and dilution.
Ms. Thompson then presented a diagram of the upgrades, noting that the upper diagram is the current process of preliminary, primary, and secondary treatment followed by disinfection. The Echo Water process will build on the existing secondary treatment by adding biological nutrient removal (an air-activated process) followed by filtration and disinfection, she said.
The plant must remain operational while the new areas and processes are constructed and brought into operation. “The folks out at the plant liken this to converting your old pickup truck to a Ferrari while you’re driving it down the road, so it’s pretty interesting for the operations and maintenance staff and the support staff because they are maintaining the existing plant as well as learning everything about the new plant and how that’s going to work.”
The Echo Water project is expensive; it’s the largest public works project in the history of the Sacramento region, she said. It’s expected to somewhere between $1.5 – $2.1 billion total; at peak construction, costs will be as high as $28 million per month with an additional 600 people workers in addition to the usual staff. Most of the planning is complete and construction has begun.
Ms. Thompson then turned to adaptive management. “I was taught that you are supposed to be doing adaptive management in conjunction with management actions that managers are really planning to do and that you are talking to the managers while you are getting ready to gear up for this,” she said. “In reality, things are just kind of hairy; do you have funding and do you have time to get the management done before you actually have to get on and implement the management. Often managers and regulators are under various pressures and they have to get on and make the best decision they can, so I think it’s kind of like a carousel. I’m getting to the idea that you should just jump on wherever you are and try to catch up on the next go ‘round.”
“The idea is that you start off with some nutrient action that managers are thinking might work; there’s a fair bit of uncertainty, but they pick their best guess and they go out and try a pilot version of it,” she said. “You monitor while you are out there; this is in addition to routine monitoring programs because you want to be really specific. It might not be a lot of extra monitoring, but there may be particular things you need to know about the system to determine what mechanisms are at work, and often we’re just not sure which mechanisms are really key in a given system in a given time. Then you are evaluate your response based on that data. Then you update your model – it could be a conceptual model, it might be a numerical model, it just depends on what you need. It doesn’t have to be complicated, sometimes it does. Then you modify your strategy. You come back around and ask, is this working for me? If not, at least I know more about the system. What can I do better now that I know more about it?”
It’s the idea of learning by doing. “If you can’t say adaptive management experiment; if you can’t put that word after what you are doing, you may not being doing adaptive management as it was originally conceived,” she said. “You’re trying to seek outcome based actions; you are looking at what the outcomes are of the actions to see how effective they are for doing what you are trying to accomplish.”
Studying phytoplankton dynamics in the Sacramento River
Studies have suggested that ammonium in treated wastewater effluent entering rivers and estuaries negatively affects phytoplankton growth and alters species composition, but much of this evidence comes from laboratory studies and hasn’t really been tested in the environment. In October of 2013 and in June of 2014, discharges from the Sacramento Regional Wastewater Treatment Plant were diverted, and a Lagrangian approach used to compare changes in nutrients and phytoplankton in both the absence and presence of effluent as water traveled downstream. Changes in phytoplankton chlorophyll, species composition, and productivity were tracked, along with nutrients, zooplankton, and benthic grazer abundances.
The Sacramento River Lagrangian study was led by the USGS and was a collaboration of a number of groups. The project was funded in part by the Interagency Ecological Program and Regional San; Regional San picked up a lot of the costs in the second year as funding was depleted, Dr, Thompson noted. The study came about in response to concerns about declines in abundance of phytoplankton along the length of the Sacramento River near the treatment plant and potential changes in species composition. “The idea was to look at the relationship between nutrients and phytoplankton and to be able to do that in the presence and absence of wastewater,” she said.
Dr. Thompson explained that since the Freeport area where the treatment plant discharges is still tidal, the plant was constructed with large emergency storage basins that hold treated effluent while the tide is coming in and the river is flowing backwards until the tide goes out and the river starts flowing downstream again. “So our operating staff were able to actually hold effluent in the storage basins for 20 hours, which is a lot longer than they normally would do it, and then run it back through the treatment process before it went back in the river,” she said. “That 20 hour hold time gave us a 6 mile long section of the river that had no effluent in it all, that’s indicated by the yellow section. The purple is the parts of the river that had the effluent coming in before and after that diversion hold. There were 5 days of tracking; it was done both fall and spring.”
A Lagrangian study is a technique for analyzing currents and flows of various materials by utilizing data collected from gauges and sensors that move with the motion of the water; it is commonly used to study ocean currents. For this study, floaters were deployed to follow the current, and phytoplankton and nutrient concentrations were measured every four hours.
The study found that there was no statistical difference in phytoplankton or species composition whether in the presence or absence of effluent during either experimental periods, indicating that declines in phytoplankton were not attributable to effluent effects, including elevated ammonium. Diatoms, a preferred food source, were the most common type of phytoplankton, suggesting that wastewater is not causing an immediate change in phytoplankton species composition from preferred to non-preferred species. These results, together with the prevalence of benthic and diatoms, suggest that hydrodynamic factors may play an underappreciated role in phytoplankton losses through settling during slack periods. (Read the report here.)
“I think it’s a neat example of how we can go out and do an experiment to test management actions, and I’m just seeing so many other cool examples of where we could be doing that in the Delta,” said Ms. Thompson. “Hopefully we’ll be getting more tidal wetland restoration and inundation and looking at how that’s going to work. I can see situations where you might have control in active restoration areas and be comparing those over time, and we’ll also have the data from the Delta Regional Monitoring Program to give us better baseline data which is always a nice thing when you are embarking on one of these projects.”
Other studies underway …
Regional San is involved in a number of other projects, including studying phytoplankton stress along Sacramento River and Suisun Bay, lab and mesocosm studies of phytoplankton growth in relation to light, nutrient form and concentration, and a clam survey of the distribution and phytoplankton grazing rates from I-80 bridge to Rio Vista; they have also been funding the USGS monitoring station at Feeport. (More on Regional San’s research studies and collaborations by clicking here.)
Regional San is also involved in a study of freshwater mussels with the Central Valley Clean Water Association, a consortium of treatment plants which is funding the work. The mussels are influenced by ammonia, but there’s not a lot of data, she said. “We don’t know very much about where they are relative to the treatment plants and that makes a big difference for how far down the stream you might be wanting to mix in your ammonia coming out of a plant, and so we’re going to be using environmental DNA for that.”
Regional San staff participate in a number of different policy workgoups, forums, and conferences. “We’re really looking for places where we can get out, learn more about the research ourselves, contribute to the policy, and come in with the managed perspective on it,” she said. “Obviously we’re not the decision makers on the management, but we know a fair bit about the implementation and what’s possible from an infrastructure standpoint.”
“If you want more information about the treatment plant, I encourage you to go to our website, there’s a virtual tour of the current plant and information about the new Echo Water project and also you can come and get an actual tour of the treatment plant,” she said.