County outlines hydrogen sulfide monitoring, smoke testing and interim treatments in Monroe’s Airplane Park

County staff reported to the Orange County Sewer District No. 1 Advisory Committee that hydrogen sulfide complaints in the Village of Monroe’s Airplane Park area have prompted continuous monitoring, twice‑weekly ambient testing, interim chemical and oxygenation treatments at pump stations and a planned smoke‑testing program to find sewer‑to‑building connections.

Why it matters: hydrogen sulfide is both an odor nuisance and a health concern at elevated concentrations; the county said ambient monitoring averages are well below the number cited in the meeting but that odors remain unpleasant for residents.

Robert Gray, deputy commissioner, outlined the monitoring and mitigation steps underway. The county has had continuous hydrogen sulfide metering at two manholes in Airplane Park since January (identified in the monitoring report as manholes M‑7 and M‑1) and conducts twice‑weekly ambient surveys in the neighborhood. Each ambient survey collects about 180 samples, the county said; the two‑week report shows average ambient readings in the range 0.001 to 0.003 (reported in the meeting as 1%–3% of the cited allowable threshold).

Gray told the committee the county is sealing manhole vents where possible and pursuing source‑identification work. Two pump stations feeding the Airplane Park force mains use different interim treatments: the South Blooming Grove pump station is dosing sodium hypochlorite (liquid chlorine) and the Chester pump station uses a high‑pressure oxygenation/ozone system described in the meeting (the company name was transcribed in meeting materials as “Anu” or “Anew”). Gray said the Chester system was tested in a portable deployment in 2022 and that the pilot showed markedly improved hydrogen sulfide levels when the oxygenation system was applied; that pilot also produced a report the county has on file.

The county said the chlorine dosing at South Blooming Grove is currently about 60 gallons per day and that staff verify inventory and dosing several times per week. In response to resident complaints, staff visit the two pump stations two to three times weekly to confirm treatments are operating as intended.

To identify possible building exhausts or improper connections that could be allowing sewer gas into occupied spaces, the county plans smoke testing in the Airplane Park area along North Main Street (adjacent to the Heritage Trail) — likely to occur at the end of the week or the following week. Gray described the smoke test process: non‑toxic smoke is introduced into the sewer main and will exit where laterals or roof vents are improperly connected; where traps are present and functioning, the smoke should not exit into structures. County staff stressed they will notify property owners, local fire and EMS and post public notices before testing to reduce 911 calls and alarm responses.

Gray said the county will also pursue dissolved oxygen and hydrogen sulfide sampling upstream and downstream on the force mains to better isolate problem segments. Committee members asked for prompt testing of individual force‑main segments to separate where hydrogen sulfide is generated in the collection system versus in laterals or building plumbing.

On enforcement and remediation, staff said the county has enforcement authority under its sewer regulations to require corrective action if tests show exceedances of the cited standard. Gray emphasized the current ambient averages are low but that intermittent spikes and resident odor reports merit continued investigation and targeted fixes.

No vote was taken; committee members requested follow‑up reporting on test results and the smoke‑testing schedule.