Fenceline monitoring under the HON Rule is no longer something facilities can plan for down the road. For most SOCMI facilities, monitoring for benzene, 1,3-butadiene, ethylene dichloride, vinyl chloride, ethylene oxide, and chloroprene came online this month. Passive tubes are in the field. Quarterly CEDRI reporting is on the horizon. And for the first time, facilities are getting a steady stream of real fenceline data instead of a projection or a modeled estimate. With real data comes something else: real spikes.
When a fenceline concentration crosses the action level, most teams respond the same way. They assume it’s related to their LDAR program, which is not an unreasonable first move. LDAR programs are mature and well understood, and they’ve been the default fenceline suspect since the 2018 Refinery Sector Rule first introduced benzene monitoring. However, for facilities with uncontrolled wastewater streams, there is something else to consider.
Why Wastewater Gets Overlooked
Wastewater systems don’t draw much attention. Most root cause investigations move past a sump without a second look. Wastewater simply isn’t part of the mental model most facilities use when a fenceline exceedance shows up.
That blind spot carries more weight now than it used to. Several of the six HON-regulated pollutants, including benzene and 1,3-butadiene, show up regularly in process wastewater streams. If a facility’s wastewater emission characterization hasn’t been revisited recently, the numbers on file may reflect an old stream composition, outdated information, or a sampling program that never caught up with process changes on the unit. Without a current baseline, there’s nothing solid to compare fenceline data against. A batch discharge, a treatment upset, or a flow surge can register at the fenceline and get attributed to LDAR by default, simply because there isn’t a current wastewater number available to rule it out.
The timeline leaves little room to look in the wrong place. Once a rolling average crosses the threshold, facilities have five days to identify a root cause and thirty days to implement corrective action before real-time monitoring requirements kick in. That’s a tight window to spend on an LDAR investigation, only to discover weeks later that the real source was in the wastewater system all along.
What to Check Before You Rule Out Wastewater
Wastewater doesn’t need to be the last stop after an LDAR investigation comes up empty. It can be part of the first pass. A few questions worth asking early:
- Does the timing line up? Spikes that track with batch discharges, treatment upsets, or flow events point somewhere different than spikes that track with process unit operating hours.
- How current is the stream data? Find out when benzene or butadiene concentrations in wastewater streams were last actually sampled, not just assumed from an old report.
- Is coverage complete? Drains, sumps, and separators near fenceline monitoring locations should be reflected in current emission calculations. Sometimes they simply aren’t.
- Is mechanical integrity current? Leaks from conservation vents, aging relief systems, or other covered equipment can also reach the fenceline. Confirm required inspections are up to date and consider whether additional checks, such as FLIR camera surveys, are warranted.
Working through these questions alongside an LDAR investigation, rather than after it stalls, tends to get facilities to the right answer faster and preserves more of that thirty-day corrective action window.
One pattern worth calling out specifically: if your facility has wastewater streams that don’t meet Group 1 status or require control under the Benzene Waste Operations NESHAP (BWON), meaning it’s uncontrolled rather than routed through covered collection and treatment, then these streams provide the greatest potential for fluctuations at the fenceline. Uncontrolled streams don’t have the same consistent capture and treatment that Group 1 systems do, so variability in flow, composition, or loading has a much more direct path to the fenceline. If your wastewater falls into this category, it’s worth moving it toward the top of the list rather than the bottom.
How Trinity Can Help
Fenceline monitoring is designed to catch emissions no matter where they originate, and wastewater has always been one of the least examined pathways at a chemical facility. That combination is exactly why it keeps showing up as the unexpected answer.
Trinity’s Chemical Sector Services group works with facilities across the country on exactly this kind of investigation. We help characterize wastewater streams, update emissions calculations so they reflect current operations, and run integrated root cause assessments that look at LDAR and wastewater together instead of treating them as separate problems. If your facility has already logged a fenceline exceedance and the LDAR review didn’t turn up an answer, or if you simply can’t remember the last time your wastewater emission calculations were updated, that’s a good sign it’s time for a closer look.
The sooner that review happens, the more of your response window stays intact. Reach out to Inaas Darrat to talk through how a wastewater assessment could impact your facility.
