As part of the UTBiome’s effort to paint a picture (with data, of course!) of Waller Creek running through campus, we carried out another sampling event this past February. This time, the graduate engineering microbiology class collected environmental and microbiological data from three spots near the Civil, Architectural, and Environmental Engineering building (called ECJ) at San Jacinto and Dean Keeton. Here’s a map below:
Figure 1. The balloon icons indicate where we sampled along the Creek. Even though it doesn’t looks like there’s water running through the top balloon icon, there is! Water flows from top to bottom.
We were particularly interested in looking at potential water quality impacts produced by the construction site within a dozen yards of the Creek. With the construction of a new engineering building (the yellow box on the map), large trucks are stationed near the Creek, where they are periodically rinsed down. We thought we might see an imprint from this truck washing show up in the Creek.
So we selected water quality parameters that might be directly impacted by rinse water, such as total suspended solids, turbidity, conductivity, and a few others. We also examined concentrations of fecal indicator bacteria, since Waller Creek has a history of violating the City of Austin’s bacterial standards. All of these we measured at three spots along the creek: two upstream (one in the western tributary leg, one in the eastern) and one downstream, just after the confluence of the two legs. The construction site lay between our upstream and downstream sites on the western leg.
And our results are in! We found good news with regard to the construction site’s impact, and some “not-so-news” with regard to the Creek’s fecal indicator bacteria levels.
From a physicochemical standpoint, the segment of Waller Creek running adjacent to ECJ appears to be in fine shape for an urban watershed stream, both historically and with the current sample values from this lab. Out of our measurements, conductivity was the only parameter that appeared higher than average, and was consistently high across all our samples. This means we cannot attribute the high conductivity to dissolved solids produced by the truck washing at the construction site, which would have generated conductivity levels downstream. One explanation may be lower flow values across the watershed, due to general drought conditions, which could concentrate ions in solution, thereby elevating conductivity. Flow measurements or examining the recent precipitation record at subsequent sampling events may help elucidate discrepancies such as these and others in water quality measurements.
At a minimum, we expected to see elevated turbidity and TSS levels after the sandy construction zone. However, the impacts of construction at the time of sampling were either negligible or not differentiable from impacts produced by mixing with the eastern fork. In addition to the TSS and turbidity data, none of the other physicochemical parameters vary greatly before and after the construction zone. It is possible, since we do not know the time of the most recent rinsing event, that little runoff had been generated prior to our sampling. Thus, it is important to remember that it is still possible that the construction site impacts Waller Creek; our data merely suggests that none of the parameters we measured were impacted that morning.
The not-so-news suggested by our data is that Waller Creek (next to campus) may still support levels of E. coli higher than those allowed by the Texas Commission on Environmental Quality (TCEQ). In two of our six samples (see Table 1), E. coli concentrations of 410 MPN/100 ml exceeded the maximum allowable level for any single sample, which is 399 CFU/100 ml. Note that there is some fudge factor thrown in here, as our units of MPN do not match the standard’s units of CFU. See the Technical Note post for more on this, as well as some background on why we care about E. coli.
Table 1. Waller Creek E. coli levels near ECJ
As I’ve hinted, TCEQ is well aware of Waller Creek’s elevated bacterial levels. In fact, they recently developed a total maximum daily load (TMDL) plan with five management measures aimed at reducing fecal inputs into Waller and a few other urban waterbodies. These measures focus on riparian zone restoration, wastewater infrastructure, domestic pet waste, resident outreach, and stormwater treatment strategies. Riparian buffer restoration is expected to reduce fecal pollution by several mechanisms, including seepage into soil, microorganism predation, adsorption to vegetation and soil surfaces, and environmental inactivation (e.g., dehydration or UV denaturation). The wastewater infrastructure focus includes installing more public toilets and creating incentives for onsite sewerage repair and improvements. The 1429C_02 segment of the Waller Creek watershed (part of which runs next to campus) has a sizeable pet population (greater than 5,000 cats and about 5,000 dogs (TCEQ 2015), so fortifying pet waste infrastructure by making pet waste bags and disposal containers available, along with education outreach on the issue, is expected to make a considerable impact as well.
It is interesting to consider the alternative to reducing Waller Creek’s fecal inputs: downgrade Waller Creek’s regulatory status to “secondary contact”. It would be interesting to gather more observational data on Waller Creek’s true usage patterns, since none of us has ever witnessed swimmers in the Creek near campus. More observation would be needed to determine if people are really swimming in the Creek, and thus if the current standard is overly conservative. Even if no one ever observed a swimmer in Waller Creek, however, supporting a waterbody with elevated fecal contamination running through the heart of a major city could run contrary to TCEQ’s mission to “protect our state's public health and natural resources consistent with sustainable economic development”. The risk that people might swim in Waller might just be too high.