When the Watershed Protection Department went to renew the city’s permit to discharge under the Texas pollutant discharge elimination system this past year, it found new requirements. The Texas Commission on Environmental Quality recently changed its rules to require cities to keep a list of priority areas – hot spots that are high-potential areas for illicit discharge.

In addition to the list of hot spots, Watershed Protection chose to develop a more sophisticated spatial heat map to track those areas.

“This literally has all of the problems we’ve ever found on it,” said Thain Maurer, an environmental compliance supervisor with Watershed Protection. Each of the 30,000 candy-colored dots on the new department map marks an incident of an identified pollutant spill from the last 32 years.

With data coming from all over Austin, it is readily apparent where the city has more significant water quality issues. On the map, records indicate that transportation corridors, older neighborhoods and the urban core have higher instances of illegal discharge and spills.

“This (map) does not say this area is more contaminated or this area is more polluted,” cautioned Maurer. Instead, the heat map identifies, based on historical data, where a spill is more likely to occur. Viewers can see that even changing the time period, this correlation holds true.

Additionally, Maurer said that the map does not have much context built into it. There is no toxicity or overall volume information available on individual cases. However, individual spill records note how much volume of a spilled substance was recovered. The spills can also be separated into pollutant categories to indicate what sort of substance, such as sediment, soaps or petroleum products, entered the city’s waterways.

To offer more context and track trends, the Watershed Protection Department will continue to produce non-spatial analyses. These analyses review data such as the ratio of pollutant types by year, which show that sewage overflows have decreased while petroleum spills have gone up over the last eight years.

Maurer said he eventually wants to work toward correlating the environmental quality in particular areas with the rate of illegal discharge incidences. In the meantime, he said the tool will be used internally to provide a different view of spills as well as for educational outreach.

Photo by Martarano Steve, U.S. Fish and Wildlife Service/Public Domain.

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