DWP Gets High-Tech Weapon in War on Slime

For years it has been an all too common sight in Los Angeles: water reservoirs covered by a thick layer of slimy, green algae. Less visible were the underlying risks of treating that algae with large amounts of chlorine.

But the culmination of more than a decade of research has minimized both the aesthetic and health issues, local officials say.

The city Department of Water and Power has created a state-of-the-art monitoring system that checks water quality and algae presence more frequently than in the past.

The Remote Electro Optical Sensor (REOS) is used in five reservoirs in Los Angeles. A study of the Los Angeles Reservoir completed in September showed that the system has led to significant chlorine use reductions, and the DWP plans to expand the monitoring system to three more reservoirs for raw, or untreated, water this year.

By catching algae growth earlier and therefore needing less chlorine to treat it, smaller amounts of a suspected carcinogenic byproduct are formed. Less chlorine use also saves taxpayer money and improves water taste and odor.

Open, or uncovered, reservoirs for treated water are uncommon--about 300 exist nationwide, and 10 of those are in Los Angeles. Subject to changing weather conditions, open reservoirs can provide an ideal breeding ground for algae, which thrives in warm, somewhat still, nutrient-rich water.

“These open reservoirs really are an Achilles’ heel,” said Gary Stolarik, DWP engineering manager. “A lot of attention has to be given to the reservoirs. . . . The No. 1 problem for someone with open reservoirs is algae growth.”

When growth conditions are at their peak, reservoirs can develop extreme algal blooms that turn the surface green. The Silver Lake Reservoir experienced such an extreme bloom in 1990, when water was diverted from entering the reservoir, leading to stagnation.

Each remote monitoring unit has two cylinders placed at different depths, said Brian White, the DWP biologist who created the system with John Morrow, president of San Diego-based Biospherical Instruments. Each cylinder has two sensors. The top sensor measures the amount of sunlight passing through the water, while the bottom sensor measures the natural fluorescence that algae emits.

By comparing the amount of light reaching each cylinder, scientists can determine how much algae is blocking the sunlight coming through the water.

The instruments transmit data every two seconds to controllers that post 15-minute average values. Scientists see a morning report of the past 24 hours, and can review algae levels in shorter time periods if a situation warrants.

Before the remote monitoring sensor, biologists collected water samples from each reservoir.

“Most water utilities that monitor their reservoirs for algae traditionally . . . go along the shore or take a boat out to get a sample,” said Elizabeth Kawczynski, senior project manager of the American Waterworks Assn. Research Foundation, in Denver. She said larger bodies of water need more sampling because different areas of the water can have different algae levels.

These samples have to be taken to a laboratory to be analyzed, which can take hours or days. By the time workers can get around to treating the problem, two weeks or more may have passed.

In Los Angeles, prior to remote monitoring, “field biologists would go around once a week--there was a huge data gap,” Stolarik said.

The more time algae has to grow unchecked, the more chlorine will be necessary to treat it. Chlorine reacts with organic material to form trihalomethanes, or THMs, which are a suspected carcinogen and were linked in a February 1998 study to an increased risk of miscarriage in the first trimester of pregnancy.

Using monitoring, “we can intercept an algal bloom and treat it within a few days,” Stolarik said.

“REOS has come in with a technological solution,” Stolarik said. “REOS has provided eyes and a data stream.”

Local health officials are encouraged by remote monitoring.

“They have been able to respond quicker to impending water quality problems in reservoirs,” said Gary Yamamoto, section chief of the Los Angeles office of the California Department of Health Services. “If it looks like water quality is deteriorating, they begin treatment sooner. [Previously], they would not know about it until they went to the reservoir, collected samples and brought them back to the lab. That’s labor intensive.”

The recent one-year study of the Los Angeles Reservoir found that using remote monitoring resulted in 42% fewer chlorine treatment days and a 40% decline in tons of chlorine used, compared to the previous three years.

The Environmental Protection Agency standard, which allows 80 parts of THM per billion parts of water, falls to 40 ppb in May 2002.

Although average THM levels in area reservoirs have consistently met EPA guidelines, there have been instances where reservoirs contained more than 100 ppb.

“Every day you can avoid turning the chlorine on, you can avoid making THMs,” White said. The reduced chlorine use also saved DWP about $140,000 in one year at Los Angeles Reservoir.

White added that the chlorine savings at each reservoir will eventually cover the cost and maintenance of the sensors.

Each reservoir’s instruments cost about $100,000. In addition to the Los Angeles Reservoir, remote monitoring has been installed in the Silver Lake, lower Hollywood, Stone Canyon and Encino reservoirs.

Some open reservoirs don’t need monitoring. For example, Ivanhoe Reservoir, which adjoins Silver Lake, does not have algae problems because its water is constantly moving.

Including research, development and installation of the five systems, the program has cost about $1 million. White and Morrow, who co-patented the method, began working on the project in 1988.

The inventors plan to market it to other municipalities or for offshore purposes by the end of the summer.

“One of our goals is to . . . simplify the approach, so it can be used for smaller, less high-tech applications,” Morrow said.

White also plans to test adaptations such as a probe that measures copper levels. Copper is used to treat algae in some reservoirs.

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Reducing Chlorine

In the years after the Remote Electro Optical Sensor (REOS) was installed in January 1995 in the Los Angeles Reservoir, the amount of algae and, consequently, chlorine use, dropped significantly.

Source: Los Angeles Department of Water and Power