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The first of a series of reports on the health of the Santa Cruz River from the Nogales International Wastewater Treatment Plant in Rio Rico to Tubac cites pollution and a lack of river species as main concerns. Next report is expected to show better results from evaluation.

Photo/John Hays

However, report author Amy McCoy and co-investigator Sherry Sass of Friends of the Santa Cruz River (FOSCR), said the completed $63 million expansion of the wastewater treatment plant in June, 2009 has had a positive effect on the river.

That will become apparent in the next report planned for mid-2010 as part of the series, A Living River, funded largely by the Environmental Protection Agency.

McCoy said that although she considered evaluating the entire Santa Cruz River from where it flows in the San Rafael Valley south into Sonora and then back north across the border, there was not enough reliable information.

"We wanted to answer the overarching question of what is a healthy Santa Cruz as a whole and why is it healthy or not?" McCoy said. "We identified a bunch of indicators and selected 10 that we felt already had data. Given our budget, in the end we limited (the) study to north of the treatment plant along the effluent stretch where it is wet. Our question became, 'What makes a healthy effluent-dominated river?'"

Follow up:

Five of the 10 indicators were water quality constituents: Fish species and numbers; aquatic invertebrates; depth to groundwater (that could support trees); and variability of groundwater from year to year.

Riparian vegetation made up the remaining indicators. Birds were discussed but were not an indicator.

Monitors included FOSCR, National Park Service, Arizona Department of Environmental Quality, (ADEQ), Arizona Fish and Game, among others.

Ammonia, which is toxic to fish and a byproduct of sewage, showed up above ADEQ standards in eight samples at Rio Rico and Tubac. Pathogenic e-coli bacteria showed up in two-thirds of 94 samples at Tubac; two of three at Amado; and one of three at Rio Rico.

Seventy-five percent of the samples for phosphorous that removes dissolved oxygen from the water and kills animals, were high compared to historic levels, but dissolved oxygen in the river was within standards.

Among metals, cadmium levels in the river did not exceed ADEQ surface water standards but were close, said the report. Cadmium is toxic to humans and fish.

Fish surveys were disappointing, with one juvenile Longfin Dace and one adult caught at Tubac and Amado. Chironomidae, a form of fly-tolerant invertebrate, was found in Tubac. It was the sole invertebrate found in the river.

The depth-to-groundwater level to ensure cottonwood and willow forest growth was adequate at Rio Rico and Tubac, but not at Amado where levels historically have allowed the trees to survive.

During the monitoring period, 16 inches of rain augmented the sewage flows in the river. Groundwater variability during the 2008 period was considered within reason, although it had dropped below previous levels.

Riparian vegetation was not measured but a previous Sonoran Institute report for EPA published in 2007 established the vegetation along different sections of the river in 2006 as a baseline for future years.

"The next report will include data that spans treatment-plant expansion," McCoy said.

Clear water

"Anecdotal reports are that the river appears to be recovering very rapidly and is in much better condition with clear water. It smells good; it has fish in it where they weren't before. The story we'll be interested in is how quickly it appears to be recovering - within a couple of weeks of the treatment plant expansion coming on line, the water appeared to be clear. This might say something about the resiliency of the river, or that some scientific functions were in place that we can document that improved the Santa Cruz."

Co-investigator Sass said, I think it's a wonderful overview of the fundamentals of river health especially as it pertains to community conservation values FOSCR will continue to monitor as much as possible. But Amy's vegetation map and establishing these indicators is a huge accomplishment. Before that we were flying blind. The river looks great now since the plant expansion but we'll continue to be concerned about the pollutants entering the plant that it cannot clean up; for example, we have had spikes of cadmium."

The Living River report, although addressing a river of sewage effluent, does not include data on the contaminants in sewage flows coming into the plant, the majority from Nogales, Sonora, nor on the quality of the discharges. The data is available and could also allow river monitors such as FOSCR, ADEQ and the Sonoran Institute to understand how the Santa Cruz is responding to differing pollution levels.

Proposals by Sonora to divert sewage flows for agricultural or other usage could also have dramatic impacts on both the treatment plant and the river flow on the Arizona side.

By Dick Kamp, environmental liaison for Wick Communications