About Truckee Meadows Water Authority
The Truckee Meadows Water Authority (TMWA) is a not-for-profit, community-owned water utility in Northern Nevada comprised of three member agencies: City of Reno, City of Sparks and Washoe County. TMWA treats and delivers water supply to more than 400,000 residents of the Truckee Meadows region.
Nitrate is one of the most serious water utility challenges, as violations can lead to Tier 1 acute violations which is alarming for water utility customers and can pose health risks. Water utilities do not want to have a nitrate violation on the public record, nor do they want to have to tell their customers that nitrate levels have been climbing or that the utility may have received a violation. It’s very important for any utility to first get an understanding of their water quality and then act proactively to manage it.
If a water utility is seeing a rising nitrate level, the utility must assess the level of concern and the level of risk. Utilities do extensive monitoring for nitrate, and if they see levels going up, they are forced to take those wells out of service. They need to ensure the water is safe and that they don’t have a risk of sending water out that is contaminated. It is important for the utility to trend out what the nitrate levels are and understand any vulnerable aquifers.
The area of Spanish Springs in northern Nevada has grown quite a bit over the last twenty years. TWMA now serves that community but it was previously run by the Washoe County Department of Water Resources (DWR). Once TMWA and DWR consolidated in 2015, TMWA brought a closer eye to the nitrate levels within the Desert Springs system. Enhanced aquifer modeling and drilling additional monitoring wells allowed TMWA to better understand what was going on in the basin. According to TMWA, there is a lot of septic in that area and that is likely the biggest factor leading to the elevated nitrate levels in the basin.
For TMWA, if the nitrate levels continue to rise to the point where nitrate compliance is threatened, the affected well would proactively be removed from service. The utility begins to ask questions including: Are the nitrate levels going to change? Are they going to do screen interval monitoring? What are the nitrate point sources? Is the well going to continue to be a reliable source of water supply or is it just going to be stranded resource?
If an affected well were to become a stranded resource, the utility must then decide the best way to replace that resource. A stranded well due to water quality reasons is not as simple as just drilling another well. Drilling a new well in this area is not really feasible because of nitrate levels throughout the basin. Many times, you can drill a good producing well which has very poor water quality or you may find good water quality but very little production.
An alternative solution may be to research and implement a technology that will allow the utility to treat and safely remove the nitrate from the well. If you can clean up and treat a well that has already been demonstrated to be a good producer, that’s the best thing for the basin and for the water utility. As TMWA has not had any nitrate-threatened wells in their system in the past, this research project is essentially their first attempt at developing a nitrate removal process.
WaterStart facilitated the development of a potential pilot project between TMWA and Carollo. Once all of the entities (WaterStart, TMWA and Carollo) started digging into the issue, multiple potential treatment options were identified, including ion-exchange (IX), reverse osmosis (RO), and biological treatment that would allow lowering the nitrate levels to the desired levels before sending the water to the distribution system. However, since biological treatment would convert nitrate to innocuous nitrogen gas without generating concentrated wastes, a two-stage biologically active carbon (BAC) biotreatment system was selected for pilot-scale testing with the well water in Desert Springs. Since the water also contained arsenic, physical-chemical removal of arsenic with the use of iron hydroxides as the adsorbent was also evaluated during the pilot study.
The pilot study included sustained contaminant removal demonstration and system robustness under simulated process upsets. Rigorous process monitoring was conducted, using in-line nitrate and arsenic analyzers and grab samples. The results collected during the pilot study were shared and discussed with the regulatory agencies with the intent of obtaining an approval for full-scale implementation in Nevada.
“The Carollo process is very intriguing to TMWA because we can address a large scale production site with limited footprint space for the treatment technology, as opposed to other resources such as ion exchange or reverse osmosis,” said Will Raymond, Operations and Water Quality Manager at TMWA. The well (production capacity 750 gallons/min) TMWA needed to address is in an established neighborhood with limited available space. However, the modular and compact pilot skid allowed assessing the possibility of simultaneously removing nitrate and arsenic from the well water. The design criteria developed during the pilot study are scalable for a full-scale implementation.
Implementing the Pilot
The Desert Springs well being addressed has a production capacity of 750 gallon/minute (gpm) and was already out of service due to the high nitrate levels. For the pilot testing, the 750 gpm pump was replaced with a 7 gpm pump. Water was collected in an equalization tank, from which the water was pumped into the pilot skid for the assessment of the technology and evaluating the possibility of bringing the well back into production mode.
The treatment approach relies on enhancing the growth and activity of microorganisms indigenous to the groundwater to turn the nitrate into nitrogen gas. Arsenic removal is achieved through adsorption on iron hydroxides and separating the arsenic-containing iron hydroxides during the treatment. “There was a lot of bang for your buck to demonstrate what you can do without producing a whole bunch of wastewater stream and without trying to build a whole bunch of infrastructure, ” said Raymond. This new technology is also easily deployable which was very important for TMWA. A major objective of the study was to demonstrate that the process works even under challenged operating conditions. The process can be used at a large scale for a utility such as TMWA that needs to treat a large production well, or at a private well for an individual homeowner that might be facing nitrate challenges.
Results of the Pilot
Since the Maximum Contaminant Level (MCL) for nitrate is 10 milligrams per liter, years ago TMWA removed the ability for the well to pump straight to customers to ensure that no customers would receive water nearing the MCL. Replacing the production pump with the 7 gpm test pump set the stage to be able to put the biological filters to the test.
“We had a fantastic pilot,” Raymond said. ?Piloting the Carollo technology brought the nitrate levels down to less than one milligram per liter. When you look at performance of just nitrate levels alone, going from a 30 to less than a 1 is a fantastic demonstration. I truly didn’t expect to see the performance that it gave us.” said Raymond. According to TMWA, the piloted biological treatment technology worked like a champ even through cold temperatures.
The reduced waste stream was also a benefit realized from this system. When using a typical IX or RO, you are essentially just filtering out water and will have waste as a result. Utilizing Carollo?s biotreatment technology, the microorganisms are consuming nitrate and producing an off gas. It’s also a dual stage treatment that treats other contaminants beyond nitrate. A lot of areas, especially in the West Coast and the Southwest, have arsenic along with nitrate in the groundwater well. The tested treatment technology lowered the arsenic levels from approximately 15 micrograms/liter to less than 5 micrograms/liter.
The process was robust even under challenged process upsets, consistently lowering nitrate and arsenic to less than 1 mg/L and 5 micrograms/liter respectively. The results also confirmed that the treatment system can be implemented either at a centralized full-scale plant or isolated rural areas with minimal operation attention.
Part of this pilot project was to come up with a conceptual design that TMWA could bring to the regulatory agencies for larger adoption, which would be a full-scale application. The regional issue for TMWA is that there really aren’t many other areas for drilling new wells. As a result, TMWA is currently exploring the possibility of a much larger treatment plant at one of their properties where they could bring potentially 4-5 different wells together for a total of 2,000 gallons/minute with nitrate levels around 30 milligrams/liter each, and to construct a biological treatment system that would remove as much nitrate as possible from a larger area of concern, rather than just treating a single well. The most cost-effective approach would be to build a consolidated treatment plant to serve the outlying area, because it’s much easier to treat and deliver in the affected area rather than to send the nitrate-containing water through miles of water mains into another basin for treatment.
TMWA brought in the regulatory agencies into this project from the beginning. “We can demonstrate as much as we want, but if it’s not going to get regulatory approval, it really wouldn’t behoove us to continue on this path. At this point, we’ve received good feedback from Washoe County Health District and the Nevada Division of Environmental Protection that it’s an intriguing process for them and they’re very closely monitoring it. We hope to collaborate with them, get their approval and get this full-scale system going,” said Raymond.
At Carollo Engineers, water is their focus, business and passion. For more than 80 years, Carollo has provided a full range of innovative planning, design and construction management services to meet the water and wastewater needs of municipalities, public agencies, private developers and industrial firms.