After a multi-day contested hearing and in accordance with the administrative judge’s recommendation, TCEQ issued a wastewater discharge permit. The opponents appealed. They asserted the discharge would lower dissolved oxygen (DO) levels in the receiving stream below what was necessary for existing use. Moreover, the reduction in DO would be more than de minimis.

TCEQ’s “antidegradation” regulations require maintenance of water quality sufficient for existing uses. The regulations also forbid issuance of a permit that would lower water quality “by more than a de minimis extent,” even if existing uses are not impaired.

The Supreme Court of Texas (SCOTX) upheld TCEQ’s issuance of the permit.

TCEQ Can Choose between Competing Models.
While some models predicted the discharge would lower DO levels below the applicable standard of 5.0 mg/L, other models indicated DO levels would remain above 5.0. TCEQ provided reasonable explanations that the models predicting maintenance of the 5.0 standard were more credible. Courts must defer to agencies on such technical issues, and TCEQ’s assessment was affirmed.

Lowering a Single Parameter Is Not Degradation.
The opponents argued that the current DO level of the stream is 6.44 mg/L and that lowering that level to 5.0 “is degradation as a matter of law.” SCOTX disagreed, because TCEQ’s regulations “describe a qualitative assessment of degradation based on overall water quality, rather than a granulated parameter-by-parameter approach.” TCEQ has discretion to “make an informed judgment call as to whether any changes in the water body’s chemistry lower water quality by more than a de minimis extent.” TCEQ can issue a discharge permit if it analyzes degradation using “a qualitative assessment on a whole-water basis.”

To see SCOTX’s opinion https://txcourts.gov/media/1460291/230282.pdf