Understanding The E. coli Test Results
The Wimberley community has a lot at stake in maintaining the health and beauty of Cypress Creek. Through misunderstanding, misinterpretation or misrepresentation, the report of a recent small sample of bacterial sources along Cypress Creek is being used to try to convince the public that the pollution in the downtown section of the creek is not caused by leaking septic systems.
Wimberley has already approved a new downtown sewer system and plant, which should begin construction soon. Even so, Citizens Alliance for Responsible Development (CARD) thinks it is irresponsible to ignore implications that Wimberley does not need a modern, safe and decades-overdue sewer system. All indications, including this same report, make it clear that downtown water is NOT safe.
What these comments don't point out is that the test summary - which you can read at CypressCreekBSTReport.pdf (PDF Download) - states on page 5 that at the Cypress Creek testing Site #1, upstream of downtown, the water is safe. At Site #2 (just 0.10 mile downstream of the RR 12 bridge), however, in all of the samplings - including the two non-rain days - the water did not meet human-contact recreation standards.
From Page 5 of the report: "The data indicate Site #1 is achieving water quality protective of safe contact recreation during base flow conditions while E. coli concentrations at Site #2 exceeded contact recreation standards during each sampling event."
What is the difference between these two sites less than a half-mile apart? There are a lot fewer wild animals and a lot more septic systems in downtown. We already knew the water was polluted downtown, but we don't claim this test proves it because - again - the sample size is too small.
The test does show that in only 10 samples taken to date, one came from a human source, likely "raw sewage". It does show that E. coli from animal sources is present in the creek. The sample size is far too small to indicate anything significant about what percent of the E. coli present under dangerous conditions is from animal or human.
In addition, of those 10 samples, only four were taken on Aug. 7, the only day of testing during a rain event, when the number of coliform colonies was many times greater than on either of the two non-rain testing days. Of those, one of four was from human source. Does that prove a quarter of the E. coli in the creek is from human sources? No. Again, the sample size is far too small.
Stand outside Brookshire Brothers for one minute on three days and check out the first 10 people you see. If you see nine adults and one child, does that prove Wimberley has 10% children? No children?
The test was conducted and the report written for The Meadows Center for Water and the Environment at Texas State University by Nick Dornak - a well-known water-quality scientist in this area. On Jan. 11, CARD contacted Dornak and asked if the samplings proved that human waste from leaking septic systems is NOT a significant source of downtown Wimberley's Cypress Creek pollution problem.
"This study was not designed for making definitive conclusions of all bacteria sources in Cypress Creek," Dornak said. "Think of dipping a thimble in a bucket. If there were (for example) 60 E. coli colonies in our sample, we tested three of those, so you are only looking at 5 %."
"This testing was completed on a small budget to set the table for additional studies, so it would be an error to draw definitive conclusions in the positive or the negative regarding all sources of bacteria loading in the study area," Dornak said. "What did stand out to me was a substantial increase in E. coli concentrations between the upstream and the downstream sites during each sampling event."
Dornak went on to say, "Particularly during dry conditions Cypress Creek upstream was meeting its designated use for contact recreation, but once it flowed through downtown Wimberley (Site #2 in the study), bacteria levels were above the contact recreation standard. It would be unsafe on that day to be in Cypress Creek (at that location). In a half- mile we went from attainment level (of acceptable recreational standards), to non-attainment level after passing through downtown."
So, what has always and continues to be clear is that - despite having relatively easy access for animal sources, the water in Cypress Creek before getting to downtown is, thank goodness, clean and great for recreation. Right after it passes through downtown, where there are many very old septic systems, it is often too polluted for safe recreation. It is hard to believe that feral hogs, cattle and coyotes (the source of six of the other nine E. coli found in the 10 samples) are leaving relatively open spaces upstream to sneak downtown to poop.
It is disgraceful, and potentially harmful to the economy of a small tourist-focused town, to not clean up unsafe water, or to let kids and adults, tourists or locals, play in it.
- CARD Steering Committee
(Note: CARD publications are written and approved by CARD Steering Committee members. We are listed on our About page. Archives and more information are available on this website (hayscard.org)