Shade balls are the chosen answer to several problems faced by the Los Angeles Department of Water and Power with their open air reservoirs in the area. The EPA has mandated that such reservoirs be covered. Sunlight has been causing a reaction turning bromide in the water into bromate. a suspected cancer causing chemical. And, in the wake of multiple years of severe drought, open air reservoirs lose millions of gallons of water to evaporation.
Shade balls are four inch diameter plastic balls. As used in LA, they will be partially filled with water to stabilize them as they float on the surface of the reservoir.
Long Term 2 Enhanced Surface Water Treatment Rule
The Environmental Protection Agency is implementing the Long Term 2 Enhanced Surface Water Treatment Rule, which affects open air water reservoirs such as those used by Los Angeles.
Uncovered Finished Water Reservoirs: Systems that store treated water in open reservoirs must either cover the reservoir or treat the reservoir discharge to inactivate 4-log virus, 3-log Giardia lamblia, and 2-log Cryptosporidium. These requirements are necessary to protect against the contamination of water that occurs in open reservoirs.
The shade balls, four inches in diameter, were added to the Los Angeles Reservoir earlier this month, the Los Angeles Time reported. At 175 acres, the coverage required amount to about 7.6 million square feet of surface.
Basic geometry suggests that the coverage is significantly imperfect. Every four inch shade ball covers 12.7 square inches of surface in a square of 16 square inches.
Only 79.4 percent of the surface of the reservoir will be effectively covered by the shade balls (setting aside any irregularities in the shape of the reservoir.).
Bromate is created by a chemical reaction in the treated reservoir water from the bromide that is naturally dissolved in the water before it arrives in the reservoir. The New York State Health Department states:
Bromate is formed when ozone used to disinfect drinking water reacts with naturally occurring bromide found in source water. Bromate formation in disinfected drinking water is influenced by factors such as bromide ion concentration, pH of the source water, the amount of ozone and the reaction time used to disinfect the water.
The basic chemical reaction between ozone and bromide is accelerated in sunlight, though there are studies that suggest that its degradation by chlorine in the water is also accelerated. The reaction occurs at a lower rate even in total darkness. The inability of the shade balls to cover the entire surface of the reservoir means that bromate production will be slowed but in now way halted.
The August LA Times piece suggests that the deployment of shade balls will reduce evaporation from this reservoir by 300 million gallons a year. In a report from Feb. 2015, the Times noted that the Water Department loses about 8 billion gallons of water each year to leaks, use in fire fighting and other causes.
…the lost water could supply almost 50,000 households for a year.
The average household uses, from these figures, about 160,000 gallons of water per year. If the evaporation savings that are projected are reached, the water saved would serve 1,875 households. That is a modest savings, at best. And, of course, just over 20 percent of the reservoir’s surface is covered to prevent evaporation.
Problems with the use of shade balls
Are there problems associated with the use of shade balls in reservoirs?
One expert in plastics suggest that the savings in evaporation is wildly overstated. Clay Stephens writes that the black color of the balls, in and of itself, makes them less efficient than white ones would be.
Los Angeles’ ‘Shade Balls’ will only prevent a maximum of 141 million gallons from evaporating each year but may only suppress as little as 70 million gallons from evaporating at higher temperatures.
An io9 article attempts to explain to non-scientists why black is better for this use. The shade balls will prevent a great deal of the production of bromate by shielding the reservoir water. While they may heat from the sun during the say, they will cool at night equally fast. They will act much like a solar cover does on a swimming pool, with only the top layer of water affected by their temperature. Direct sunlight heats far more of the volume of water. The black color will also allow the balls to resist damage from solar UV better than would white, and they will last longer.
The authorities note that the plastic in the balls is stable and no chemicals will leech into the water supply.
While the Water Department hunts leaks and repairs aged pipe in its system, the shade balls in the reservoir will save some water. They will fulfill the EPAs requirement for covering and reduce the production of bromate. Any other benefits or problems remain to be seen.