Published: June 26, 2009 10:02 am      

No low flow woes: San Marcos River water quality is good

San Marcos — San Marcos residents might be praying for rain to feed the pristine San Marcos River, but they may not consider the immediate effect.

“As soon as we get a little rain, guess what washes off from all of our streets,” said Mark Brinkley, Environmental Health Director for the city of San Marcos.

Representatives from two city departments and Texas State University collect samples and analyze the level of fecal coliform, or bacteria found in the colon, in the river three times every month at a dozen locations in the river.

Most of the readings at Spring Lake, where the river originates, are less than 10 colonies per 100 ml, which is “pretty good,” said Brinkley.

The highest level in the latest group of samples taken on June 17 came out to 130 colonies per 100 ml downstream of the waste water treatment plant.

“That’s still good as far as river water goes,” Brinkley said.

The city uses a threshold of 400 colonies per 100 ml to determine a health threat for recreational uses.

The river was flowing at 81 cfs when the last sample was taken, but what happens after it rains?

On Feb. 11, 2009, Texas State recorded a level of 1582 colonies per 100 ml, the highest so far this year. The river was flowing at 118 cfs and 1.02 inches of accumulated rain fall was recorded.

Brinkley said in September of 2000, the fecal coliform rate was so high in the river that the city posted warning signs along the banks.

“It doesn’t stop them from swimming, but it lets them know. If you have a weak immune system then you may not want to get in the river that day,” he said.

Protocol states when test results show a rate greater than 400 fecal coliforms per one 100 ml in more than ten percent of all samples taken during any 30 day period, notification procedures are triggered.

Fecal coliform can cause a potential health risk to humans and animals who ingest it.

Brinkley said the system can also prevent contamination in the case of a utility pipe leak. If the sanitary sewer system failed or if flooding caused extremely high bacteria levels, the health department may recommend the closing of the river for recreational use.

Samples for the study are taken with a “dipper extension” to collect river water from eight to ten feet from the bank, or as close to the center of stream flow as possible, said protocol released by the city. Each sample is filled, capped and labeled in dedicated, laboratory provided, sterile bottles and are delivered to a lab on ice.

The samples are analyzed by Edwards Aquifer and Research Data Center at a state certified lab on the Texas States campus.