Encina Sewage Plant Tests Clean, but Fish Continue to Die in Its Output

No doubt about it--far too many fathead minnows are floating belly up.

It may not sound like a terribly pressing problem, but the deaths of these tiny fish have officials at the Encina sewage plant in Carlsbad mystified.

Like other facilities throughout the region, Encina periodically dumps the minnows into special tanks to test the toxicity of the 20 million gallons of treated sewage it pumps into the ocean each day.

Of late, the fish haven’t been doing so famously.

Eager to find out why, operators of the sprawling sewage plant, which serves about half of North County, agreed Wednesday to spend up to $74,000 for a private consultant to investigate what may be causing the toxicity problem at the plant.

Although plant officials insist that the higher-than-normal toxic readings do not pose a health threat or environmental danger in the ocean, they remain concerned, noting that Encina is now exceeding state limits.

No Help From Tests

Indeed, the Regional Water Quality Control Board when it meets on Monday is expected to slap the facility with an order requiring that the problem be corrected within a year.

Encina officials have been particularly puzzled because tests for more than 150 types of toxics and hazardous chemicals ranging from DDT to PCBs and heavy metals have come up below detectable limits, both for the raw sewage coming into the plant and for the treated effluent that flows into the ocean.

But minnows have all too often been dying off and turning keel up.

Rick Graff, Encina general manager, said, “It could be that some normal chemical, something that’s typically OK in the environment, is combining with something at the plant, and it’s reached a level that these little minnows can’t accept.”

The minnow test has been a staple at sewage plants for years. Researchers dump the minnows into test tanks filled with concentrations of effluent drawn from Encina. The 2 1/2-inch fresh-water fish are allowed to swim in the stuff--about 10 per tank--over a four-day period, then officials count the number that have survived.

A mathematical formula is used to determine the survival rate. Over a month, a limit of 1.5 is deemed acceptable under state standards, but Encina has exceeded that limit during seven of the last eight months, with a high of 2.16 in October. The lowest monthly reading, a 1.49 in November, just squeaked under the barrier.

Graff said the numbers are not particularly lofty, but he remains resolved to find out just what’s causing the plant to so regularly exceed the allowed limits. In the meantime, he argues, the ocean is not suffering.

Problem Believed in Plant

“In discussing this with the regional board and operators of other treatment plants, we don’t see any environmental problems at all,” Graff said.

If the regional board goes forward on Monday with an order for the plant to clean up the toxicity problem, Encina officials will be required to submit a report by mid-August recommending how the situation can be rectified. The plant must comply with the limits by the beginning of March, 1990, or it could face penalties.

Graff remains confident that the problem is inside the plant, and is not being caused by some business or private entity illegally dumping toxics that find a way to Encina.

For starters, there have been the negative readings on tests for heavy metals and other dangerous elements. Moreover, such hazardous materials typically wreak havoc with the normal treatment processes at a plant, an event that has not occurred at Encina.

“We’ve checked what comes in our front door and what goes out our back door, and there’s nothing there. We’ve also got a good handle on what industry is out there, and that doesn’t appear to be a problem,” Graff said. “There just may be some oddball chemical that we’ve not yet identified that’s causing the problem.”

After the high readings began to appear, Graff and other Encina officials expressed hope that a switch to a more intensive treatment process at the plant late last year would clean up the toxicity problem.

But instituting the treatment, which involves sending every gallon of sewage through a bubbling basin where a biological chain-reaction chews up germs, has had no effect on the toxicity.