Reservoir Management

The problems that utility managers encounter in drinking water reservoirs differ from those on recreational ponds and lakes. Problems are often more subtle and less visible than acres of unsightly aquatic weeds or massive algae blooms. Because they are public utilities, reservoirs are managed to more exacting standards, and must meet requirements for a variety of water quality parameters that are not typical concerns on recreational ponds and lakes. Utilities must also achieve consistent water quality year-round, and protect their water sources from seasonal extremes.

To make a reservoir suitable for public water supply, its quality must be consistent throughout the water column. It must have a proper balance of nutrients and dissolved oxygen, and these should be distributed correctly through the reservoir. High algae and weed levels in the upper water column and deoxygenated water in the lower column create numerous problems. In the upper column, excessive aquatic plants and algae clog plant intakes and filtration equipment. In the lower column, Geosmins, high levels of dissolved metals, high organic content, and hydrogen sulfide create taste and odor issues that lead to customer complaints. Conventional approaches to inconsistent water quality include the use of treatment chemicals and auxiliary treatment processes. These increase the cost of plant operation and, in the case of chemical usage, may generate potentially harmful byproducts.

Clean-Flo has a deep understanding of the exacting requirements utilities face, and has been delivering effective solutions for decades. Our approach makes use of natural, chemical-free processes. Rather than merely address symptoms, we address the root of the problem by correcting the reservoir’s balance of nutrients, organic matter, and dissolved oxygen, and by promoting desirable aquatic organisms that help maintain a natural balance in the reservoir’s ecosystem. Specifically, our methods improve reservoir restoration in the following ways:

Normalizing pH

Increasing DO

Reducing levels of Mn and Fe

Reducing algae

Reducing turbidity

Reducing TOC and DOC

Reducing nitrates and nitrites

Eliminating hydrogen sulfide and geosmins

More consistent water quality

Better risk management

Reduced chemical usage

Lower operating costs of treatment plants

Reduced disinfection byproducts such as trihalomethane.

Toa Vaca Reservoir, Puerto Rico

Toa Vaca reservoir in Puerto Rico is 836 acres in surface area and over 51m deep when full. Toa Vaca was built in 1972 with a life expectancy of three hundred years. By 1985 its capacity had been reduced by 13.5% due to the build-up in sediment reducing the effective volume of the reservoir.

In 1985, the lake showed the very first serious symptoms of worsening on the quality of the water available for treatment due to eutrophication.

The intake tower consists of six gates, numbered one to six from bottom to top. As early as 2009, due to the eutrophication process, it was only possible to use water from gates number six and five, that is the upper two abstraction points to draw water for purification treatment.

This was because water drawn from deeper gates was untreatable due to the 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 because algae levels were so high that they caused clogging of filters and the need to use high levels of flocculants and chlorine in the purification process which generated excessive levels of TTHMs, a carcinogenic by-product of chlorination.

By 2012 high levels of manganese and hydrogen sulphide in the water were creating taste and odor problems with the potable water produced by the purification plant. Furthermore, there were problems with high levels of toxic cyanobacteria in the upper levels of the water column.

It was becoming increasingly difficult to produce potable water from the reservoir that was compliant with regulated standards and the future prognosis for the reservoir was poor.

Fish kills had become so common that recreational fisherman had abandoned the reservoir. So too had birds of prey, down to a solitary pair of fish eagles and just five pelicans.

“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 manganese and cyanobacteria problems. We needed experienced engineering and specialized technology”.

Within the first year, cyanobacteria and algae blooms were reduced to such an extent that chemical treatments costs at the water purification plant were halved, as were the levels of Tri-Halo Methanes (THMs) which are carcinogenic disinfection-by products of chemical treatment.

“With more than 65% of the overall dam capacity reduced due to drought, the degradation of water quality at Toa Vaca had become an environmental problem, but more importantly, sustainable potable water supply in Puerto Rico was at risk.

The transformation has been phenomenal since the Clean-Flo solution was implemented. From a purely practical point of view, not only has water quality improved but also operational costs have reduced and with a more consistent water quality, compliance for THM’s is a lot easier task, which is a big bonus.

Over and above that, fish are back, as are the bird life and the fishermen. All in all, this has been a fantastic investment with an ROI less than 3 years.”

– Carlos Gonzalez

Reservoir Restoration & Management

Toa Vaca Reservoir, Puerto Rico

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