The U.S. has over 84,000 reservoirs, ranging from large-scale ones like Lake Mead to small municipal reservoirs. Their combined storage capacity exceeds 600 million acre-feet of water. These reservoirs serve various purposes, including drinking water supply, recreation, irrigation, flood control, and hydropower. Some are exclusively for drinking water, some are recreational, and many are multi-use.
As public utilities, reservoirs are subject to more stringent management standards and must meet requirements for a range of water quality parameters that are not typically a concern for recreational water bodies. Those responsible include federal agencies (e.g., U.S. Army Corps of Engineers, Bureau of Reclamation), state governments, municipal water districts, and private organizations. Drinking water reservoirs often fall under the jurisdiction of local water utilities and health departments.
For these agencies, maintaining consistent water quality is essential for the effective operation of water treatment plants. Seasonal changes such as stratification of the water column can result in reductions in dissolved oxygen levels and increases in pH, levels of dissolved metals such as iron and manganese, taste and odor problems due to geosmins, total organic content, algae levels and in extreme cases, toxic cyanobacteria bloom events.
Algae outbreaks can release toxins like microcystins, which contaminate drinking water supplies. This contamination can cause water treatment disruptions, increased costs, and health risks like live damage or gastrointestinal illness. Notable incidents include Toledo, Ohio’s 2014 crisis, where residents were unable to use their tap water for days.
With greater volatility in weather and climate, seasonal changes in water quality are becoming more frequent and pronounced. This leaves many treatment plant operators battling to respond and cope. Many are now actively seeking solutions that can minimize fluctuations in water quality consistency to reduce chemical costs, eliminate plant downtime for backwashing, and assist in meeting compliance standards for potable water.
ALGAE OUTBREAKS
Algae outbreaks are more common in areas with high nutrient runoff, such as agricultural regions in the Midwest and Southeast. Outbreaks have been reported annually in states like Florida, Ohio, Oregon and California, with increasing frequency due to rising temperatures and nutrient pollution.
High levels of algae in the upper water column and deoxygenated water in the lower column can create numerous issues. In the upper column, excessive aquatic plants and algae can clog plant intakes and filtration equipment. In the lower column, geosmins, high levels of dissolved metals, high organic content, and hydrogen sulfide can lead to taste and odor problems that result in customer complaints. The problem can become so severe that water drawn from deeper gates can become untreatable despite purification treatment.
Changes in raw water quality can result in elevated algae levels that block treatment plant filters, requiring frequent backwashing which disrupts production and increases chemical treatment and costs. Increased chlorination produces disinfection by products which can negatively impact compliance.
Algae blooms also contribute to the build-up of sediment, as well as fish kills that impact local wildlife in the food chain and can impact recreational activities such as fishing.
THE SEARCH FOR EFFECTIVE SOLUTIONS
Despite significant financial investments over many years, there has been little improvement in the condition of US lakes. In fact, according to a GAO report on water quality published in June of 2022 (https://www.gao.gov/products/gao-22-104449), the health of our lakes has deteriorated consistently over the past two decades.
Conventional approaches to addressing inconsistent water quality often involve the use of treatment chemicals and auxiliary treatment processes, which can increase plant operation costs and, in the case of chemical usage may generate potentially harmful byproducts.
Chemicals can also lead to a detrimental cycle that accelerates the deterioration of the reservoir’s ecosystem. The elimination of algae results in the release of toxins, leading to the destruction of more beneficial organisms and favoring the proliferation and dominance of the harmful organisms in the lake. Over time, the continued application of algaecides causes lake algae blooms to worsen. In other words, the symptoms are treated temporarily, but the patient never gets better.
“Fortunately, there are more effective natural, chemical-free processes that can be implemented to address the root causes of water quality degradation, not just the symptoms,” says Dave Shackleton, president of Clean-Flo International, a US-based leader in biological water management solutions for managing water quality,
“The focus should be on maintaining the reservoir’s balance of nutrients, organic matter, and dissolved oxygen, and promoting desirable aquatic organisms that help maintain a natural balance in the reservoir’s ecosystem that ensures nutrient clearance,” adds Shackleton.
To ensure a reservoir is suitable for public water supply, its quality must be consistent throughout the water column, and throughout the year, with a proper balance of nutrients and dissolved oxygen distributed evenly.
Sediment accumulation must also be addressed, which can become part of the permanent morphology of the lake. Simply physically removing and dumping sediment elsewhere through dredging techniques doesn’t allow the nutrients to be recycled within the lake ecosystem. Bioaugmentation, which involves the use of enzymes to break down organic muck, like a compost pile is a better solution.
Critical micronutrients can also be introduced to stimulate the growth of organisms that form the foundation of a productive food web.
The good news is that consistent use of these products over time reduces nutrient availability and helps maintain clean, healthy water.
In applications in the United States and in other countries, documented improvements in pH levels, increases in dissolved oxygen, reduced levels of manganese, iron, algae, turbidity, total organic carbon, dissolved organic carbon, nitrates, nitrites, hydrogen sulfide, and geosmins can occur within even a few months. The result is more consistent reservoir water quality, reduced chemical usage, and lower operating costs of treatment plants.
CASE STUDY: BOWLING GREEN, OHIO, DRINKING WATER RESERVOIR
The city of Bowling Green, Ohio, draws water from the Maumee River into its reservoir prior to treatment to supply safe potable water to its citizens. In summer, the Maumee River is typically overwhelmed by toxic cyanobacteria for several months. Because the reservoir only holds about 30 days’ supply, the city is forced to draw this cyanobacteria ladened water into the reservoir. For several years this became a problem as cyanobacteria began to dominate the phycological profile of the reservoir to the same degree as it does in the reservoir. To resolve the issue, in the late 2000’s a bottom based aeration system was installed in the reservoir, but this did not control the cyanobacteria and by 2016 it proved necessary to add the use of a peroxide-based algaecide to the reservoir. These two interventions combined were unable to control the situation. In late 2016 the proportional dominance of cyanobacteria in the river and in the reservoir were still about the same at approximately 68%. The absolute numbers in terms of cell count were slightly reduced in the reservoir due to the application of algaecide, but this did nothing to constrain the dominance of cyanobacteria. In April 2017, the City of Bowling Green decided to install Rapid Acting Dissolved Oxygen Restoration (RADOR) technology from Clean-Flo International. Numerous studies have demonstrated that high, stable oxygen levels reduce nutrients and minerals in the water column and can keep phosphorus locked into the organic sediments. “By increasing dissolved oxygen levels throughout the water column, the RADOR system initiates a sequence of events that bio-dredge mucky sediment, control aquatic weeds, improve water quality, reduce organic muck, nutrients, odor, harmful gases, and coliform bacteria. This helps to restore the nutrient clearing capacity of the food web by improving fish growth and health,” explains Shackleton.
Clean-Flo designs its RADOR systems using compressors of various sizes based on the lake and application, along with self-sinking airline and diffusers that maintain full oxygenation from the bottom to the surface of the water.
Data collected a year later showed that the total phycological cell count was reduced by around 75% and cyanobacteria were all but eliminated completely. By 2018, despite having to draw water from the river at a time when cyanobacteria levels were extremely high, total cell count, and cyanobacteria levels were well controlled in the reservoir.
“The implementation of the… RADOR system enhanced water quality and it is an important tool for its reservoir management.” Daryl Stockburger, Assistant Director of Utilities, City of Bowling Green.
CASE STUDY: TOA VACA, PUERTO RICO, DRINKING WATER RESERVOIR
Toa Vaca reservoir in Puerto Rico, built in 1972 and covers 836 acres and is over 51 meters deep when full. By 1985, the reservoir showed serious symptoms of water quality deterioration due to eutrophication.
The intake tower consists of six gates, numbered one to six from bottom to top. As early as 2009, due to eutrophication, only the upper two abstraction points (gates five and six) could be used to draw water for purification treatment.
Water from deeper gates was untreatable due to high levels of manganese and contaminants causing foul tastes and odors, such as geosmins and hydrogen sulfide. However, drawing water from the upper levels also presented problems, as high algae levels clogged filters and required the use of high levels of flocculants and chlorine in the purification process, generating excessive levels of trihalomethanes (TTHMs), a carcinogenic byproduct of chlorination.
By 2012, high levels of manganese, hydrogen sulfide, and toxic cyanobacteria in the upper water column made it increasingly difficult to produce potable water that met regulated standards.The future prognosis for the reservoir was poor, with fish kills becoming so common that recreational fishermen and birds of prey had abandoned the reservoir.
Recognizing that conventional aeration would not achieve the necessary improvements due to the reservoir’s size, depth, and chemical and biological problems, including severe manganese and cyanobacteria issues, the utility sought experienced engineering and specialized technology.
“In seeking a solution for the problems at Toa Vaca we knew that conventional aeration would not achieve the necessary improvements.
The problems were both chemical and biological with the severe algae and cyanobacteria problems. We needed experienced engineering and specialized technology,” says Carlos Gonzalez, GIT Puerto Rico.
Initial bathymetric analysis revealed that the reservoir is up to 51m deep, but drought can cause the water level to drop by over 20m. Ensuring full oxygenation across the scale and scope of these variations required RADOR oxygenation technology.
Several key parameters were closely monitored during the first 3 months and significant improvements almost immediately observed in the quality of potable water produced by the two purification plants drawing water from the reservoir.
Specifically, the goal to increase dissolved oxygen (DO) levels to at least 4mg/l at the surface was achieved within approximately a month and maintained thereafter. The target was also achieved and maintained at 70 feet or 21m depth within the first 3 months of operation.
Establishing adequate dissolved oxygen levels is a critical prerequisite to being able to address the other problems being encountered such as high levels of dissolved nutrients, and manganese and taste and odor issues. The ability to de-stratify and oxygenate the water column of a large deep body of water such as this rapidly is what distinguishes RADOR technology from conventional aeration and oxygenation.
A 75% reduction in total phosphorus levels to no more than 0.02mg/l at the surface was achieved within the first two weeks and the target limit was achieved after 3 months. The target was also achieved and maintained at 70 feet or 21m depth within the first three months of operation.
Excessive levels of metals such as iron and manganese are a common problem in reservoirs where dissolved oxygen levels are depleted. At Toa Vaca the problem was high manganese concentrations and a target level of no more than 0.05mg/l was achieved and maintained after approximately 2 months of operation. Initial manganese levels were higher at depth due to the deoxygenation of the water column, but the target was also achieved and maintained at 70 feet or 21m depth within the first three months of operation.
Within the first year of implementing the RADOR solution, cyanobacteria and algal blooms were reduced to such an extent that chemical treatment costs at the water purification plant were halved, as were the levels of TTHMs.
The deterioration of water quality in Toa Vaca reservoir not only affected the water supply but had resulted in frequent fish kills and a significant reduction in the fish-life in the dam. This resulted in a dramatic reduction in birds of prey; there was just a single remaining pair of fish eagles and only 5 pelicans remaining. Fishermen had abandoned Toa Vaca as a site for recreational fishing. Two years after implementing the RADOR system, there were 5 pairs of fish eagles and 28 pelicans at Toa Vaca, and the fishermen had returned too.
Addressing the complex challenges facing drinking water reservoirs requires a shift toward sustainable, chemical-free solutions that tackle the root causes of water quality degradation. Algae blooms and nutrient imbalances pose significant risks not only to public health but also to the long-term viability of these vital water sources. By implementing natural processes that restore the ecosystem’s balance, water management agencies can improve reservoir water quality and reduce the reliance on costly chemical treatments.
With proven results in improving reservoir health, these approaches offer a path forward to safeguard clean, potable water for communities while fostering healthier ecosystems. It’s time for water management agencies to prioritize these innovative and naturebased solutions to secure our nation’s future water supply.
