Rowlett: Liberty Grove odor investigation finds no ambient hydrogen‑sulfide hazard; city proposes $2M I&I program

Public Works staff and consultants briefed the Rowlett City Council Dec. 15 on the city’s wastewater system, recent odor complaints in Liberty Grove and a proposed in‑house inflow & infiltration (I&I) program intended to reduce long‑term treatment costs.

Munal, who led the wastewater portion of the presentation, reviewed system statistics: about 281 miles of sewer lines, roughly 3,816 manholes and 25 lift stations conveying approximately 4–8 million gallons per day to the Rowlett Creek Wastewater Treatment Plant in Garland under a contract that runs to 2041. He said odor events most often stem from sludge, fats/oils/grease buildup, infiltration and pressure changes when lift stations cycle.

On the Liberty Grove odor, staff said the city collected 38 ambient hydrogen‑sulfide (H2S) readings on Nov. 25 that returned 0.0 parts per million; a Friese & Nichols deployment of data loggers Nov. 26–Dec. 1 produced roughly 15,000 ambient records also showing 0.0 ppm H2S. TCEQ visited the site, smelled an odor but reported no ambient H2S detections and said it will issue a report within 60 days. Staff noted that H2S concentrations inside manholes and wet wells can spike during periods of heavy system use (thanksgiving week readings inside the manhole were higher), but those interior concentrations dissipate rapidly into the atmosphere and did not show hazardous ambient levels during the sampling events.

Munal cited Mead & Hunt’s engineer opinion: data do not show ambient H2S concentrations that would be considered a health or safety hazard for nearby residents, though high concentrations inside sewers have worker‑safety and corrosion implications. Staff said they have taken operational mitigation steps at affected lift stations — weekly chemical dosing (sodium percarbonate), installation of two aeration units (“WetWell Wizards”) and continued monitoring — and reported a 32.5% reduction in measured manhole H2S after combining aeration and dosing.

Deputy City Manager Christophe Bauer presented a separate but related proposal to address inflow and infiltration, which staff estimate accounted for roughly 10% of treated flow in 2023 and materially increased treatment costs. He recommended creating an in‑house investigation crew (CCTV, smoke testing and flow meters) and a repair crew to locate and fix leaks. Staff estimated a first‑year startup of roughly $2.0 million (equipment and one‑time costs) and five‑year program costs of about $8.9 million in‑house versus contractor estimates of roughly $13.4 million; staff projected approximately $7.8 million in savings over five years by building internal capacity. Funding options discussed included a combination of one‑time capital, reduced future debt issuance and modest rate increases (staff modeled scenarios with a 3–7% rate impact depending on structure).

Council asked for supplemental materials and for staff to provide clear documentation of proposed funding pathways; no final funding decision was made.