Featured Video: Why Are 96,000,000 Black Balls on This Reservoir?

By Jill Wallitschek

In 2015 the Los Angeles Department of Water and Power went viral when it unleashed 96 million shade balls into the Los Angeles Reservoir. The 175 acre reservoir served to store 3.3 billion gallons of treated drinking water. Shade balls were previously introduced to three other reservoirs in the LA area between 2008 and 2012. Releasing the 96 million balls marked the end of a 8 year project.

The project was first instigated when the Department of Water and Power was notified of high bromate levels in their water. Bromate (BrO₃^- ) is a disinfection byproduct regulated at 0.01 mg/L. High levels can increase risk of cancer. The chemical forms when bromide (Br ^- ), an otherwise harmless ion, reacts with ozone (O₃). For this reason treatment plants that use ozone are required to monitor for bromate monthly. Qualifying plants can reduce their monitoring to quarterly.

The LA Department of Water and Power determined that while they were finding low levels at the treatment facility, levels were elevated at the reservoirs. Upon investigation the facility realized that bromate can form under chlorination as well. When chlorinated water containing bromide reacts with sunlight, it forms bromate at even higher concentrations than ozonation. This realization prompted the facility to look toward a solution.

Removing the naturally occurring bromide wasn’t an option. Chlorination residual was necessary to protect public health. Ultimately the Department determined that sunlight was the only variable left to control.

After brainstorming for affordable and effective covers that could block sunlight across 175 acres, the Department discovered a product called “bird balls”. At the time, bird balls were used to deter waterfowl from swimming in contaminated water bodies or ponds near airport runways. These balls were made from high density polyethylene, a floatable, food grade plastic. The addition of carbon black gives them a black color and increases their life expectancy to approximately 10 years without sun bleaching. After consulting the manufacture, the balls were put through a small-scale test to access their bromate reduction abilites. The shade balls passed with flying colors.

Shade balls not only reduce bromate formation in the reservoir, but they deter birds, control algae, and reduce evaporation by 80 to 90%. Having been implemented under historical drought conditions, the innovation was applauded for its water saving results. According to the Massachusetts Institute of Technology these shade balls will have to be used for roughly 2.5 years to compensate for the water required to produce them. Since less chlorine is required to control algae formation with the adoption of shade balls, the treatment facility is experiencing significant cost savings as well. Over the course of their life span the reduction in chlorine use and evaporation will have paid for roughly half the shade balls.

Shortly after their installation, one of the reservoirs was removed from service and two of the remaining reservoirs transitioned to floating covers. Federal law requires that all drinking water bodies open to the air be covered. Transitioning the final Los Angeles Reservoir would have been too cost prohibitive based on its size. So given the effectiveness of the shade balls in such a large area, they shall remain in the Los Angeles Reservoir to prevent bromate formation, evaporation, and algae for the Los Angeles people.