There Is a Well Under Central McAllen Showing Benzene at 1,988 Times the Federal Limit. The State Calls the Cleanup "Stable and Declining."
- Joshua Moroles
- Apr 19
- 5 min read
What TCEQ's own data actually says about the 23rd Street Groundwater Plume — 35 years in.
Walk west from Cine El Rey on 17th Street. Cross 21st. Cross 23rd. Somewhere under the pavement beneath your feet, there is a monitoring well labeled MW-LL.
On May 20, 2025 — the most recent sampling event the Texas Commission on Environmental Quality has publicly released — that well came back with a benzene reading of 9.94 milligrams per liter.
The EPA's Maximum Contaminant Level for benzene in drinking water is 0.005 milligrams per liter.
Do the math. MW-LL is sitting at 1,988 times the federal safety limit. It is the highest reading that well has ever produced in the eight years it has been monitored.
TCEQ's official public statement on the site, as of this writing, describes the plume as "stable and declining."
Both of those things cannot be true at the same time.
What the plume is
The 23rd Street Groundwater Plume is a 33-acre zone of hydrocarbon contamination sitting directly underneath central McAllen. Its footprint is roughly bounded by Cedar Avenue to the north, Fresno Avenue to the south, 21st Street to the east, and 25th Street to the west — residential blocks on either side of a working commercial corridor along Business 83.
The contamination was first discovered in 1990, when separate investigations at gas stations along Business 83 turned up hydrocarbons in the groundwater. Leaking underground fuel tanks — including a 37,000-gallon release from an old Coastal Mart — combined with deteriorating pipelines along the adjacent rail corridor to produce what is now one of the largest urban fuel plumes in the state.
The contaminants are BTEX compounds: benzene, toluene, ethylbenzene, and xylene. Plus MTBE, a fuel additive. Plus total petroleum hydrocarbons.
Benzene is a Group 1 carcinogen. Long-term exposure is causally linked to leukemia, including childhood leukemia. It is not something the human body processes safely at any dose.
TCEQ's Petroleum Storage Tank State Lead Program has been actively addressing the site since 2009. That is sixteen years of state-led remediation. Thirty-five years since the problem was discovered.
What the most recent data shows
TCEQ sampled the monitoring well network between May 19 and May 21, 2025. The data was released publicly. Anyone can download it.
Here is what it shows.
The network has 81 active monitoring wells. Only 67 could actually be sampled. The other 14 were dry, destroyed, paved over, obstructed, or could not be located. That is its own story — a monitoring network degrading faster than the contamination under it.
Of the 67 wells that could be sampled, 17 exceeded the federal benzene limit.
The top five readings:
Well | Benzene (mg/L) | Multiple of Federal Limit |
MW-LL | 9.940 | 1,988× |
MW-II | 1.920 | 384× |
MW-J | 1.210 | 242× |
MW-C | 1.150 | 230× |
EMW-3 | 0.912 | 182× |
Thirteen additional wells could not be sampled for benzene because they contained free-phase gasoline. That is not a technicality. That means when the TCEQ contractor lowered the sampling equipment into those wells, they encountered liquid petroleum product sitting on top of the groundwater. Up to 3.30 feet thick in MW-15. Over three feet of raw fuel, floating under the neighborhood, in 2025.
Add it up. Thirty of the 81 wells — 37% of the entire monitoring network — still show either federally unsafe benzene concentrations or free-phase fuel. Thirty-five years in.
About "stable and declining"
TCEQ's public language on this site is that the plume is stable and declining. The data does not support that claim uniformly. Several of the most contaminated wells are trending the opposite direction.
MW-LL's full recorded history:
2017: 3.10 mg/L
2020: 1.96 mg/L
2021: 6.28 mg/L
2022: 8.53 mg/L
2024: 9.00 mg/L
2025: 9.94 mg/L — the highest reading on record
MW-II went from 1.03 mg/L in December 2024 to 1.92 mg/L in May 2025. It nearly doubled in five months.
MW-MM went from 0.206 mg/L in 2022 to 0.829 mg/L in 2025. A roughly four-fold increase over three years.
There is more. From 2014 through 2025, every single year, 100% of the wells that produced a readable sample exceeded the federal benzene limit. Twelve consecutive years of total exceedance.
That is not a plume being remediated. That is a plume being monitored.
Why this matters even though nobody is drinking the water
The most common dismissal of this site is that the contamination is in the groundwater, and central McAllen is on city water, so nobody is drinking it.
That dismissal ignores the actual exposure pathway.
Benzene is volatile. It doesn't stay dissolved in groundwater. It rises as vapor — through soil, through cracks in concrete slab foundations, through utility conduits — and enters the indoor air of homes and businesses built over the plume. This is called vapor intrusion. It is the mechanism by which contaminated groundwater becomes contaminated air in somebody's kitchen.
Residents over this plume are not drinking benzene. They are, potentially, breathing it.
EPA's own vapor intrusion screening levels for benzene in indoor air are measured in micrograms per cubic meter. The groundwater concentrations documented at MW-LL are orders of magnitude above the levels that typically trigger indoor air testing at comparable sites in other states. Whether McAllen has seen systematic indoor air testing of homes inside the plume footprint is a question the state has not publicly answered.
The families
The University of Texas Rio Grande Valley maintains an archive called the Contaminación Collection. It documents 180 Mexican American families from the 23rd Street neighborhood who reported serious illness tied to the plume — cancers, autoimmune conditions, reproductive problems, and childhood leukemia cases.
The archive preserves more than 650 hours of audio-visual testimony, recorded from 1991 through 2004. Over 800 boxes of evidence and plaintiff documentation. More than 500 visual aids.
A public university took this seriously enough to build a research archive around it. The state of Texas takes the position that there is "no actual or potential contaminant exposure for the public."
Those two institutions cannot both be right.
Who is above it now
Roughly 500 to 1,500 residents and workers are above the contamination footprint on any given weekday. That includes the families still living in the blocks bounded by Cedar, Fresno, 21st, and 25th. The employees of the restaurants, auto shops, and small businesses along Business 83. The customers who stop for gas or lunch at a storefront sitting directly over a well that cannot be sampled because of the gasoline floating beneath it.
None of them receive a disclosure notice. There is no city ordinance requiring a seller or landlord to inform a buyer or tenant that the property they are moving into sits on top of a 33-acre federally monitored contamination site.
The accountability gap
This site has been under active state remediation for sixteen years. The contamination was discovered thirty-five years ago.
There is no binding cleanup deadline. There is no published target date for remediation completion. There is no public timeline that says by year X, benzene concentrations will be below federal limits at all monitoring wells.
There is only monitoring. And the monitoring, month after month and year after year, shows the same thing.
Central McAllen has one of the largest urban fuel plumes in Texas. The families who lived above it first were told, three decades ago, that somebody was handling it. Many of them are no longer alive to see whether that was true.
The question isn't whether the 23rd Street Plume is dangerous. The data answers that. The question is who, in 2026, is going to finally force it to end.
TCEQ Report here
Data source: Texas Commission on Environmental Quality, 23rd Street Groundwater Plume monitoring records, sampling event May 19–21, 2025, and cumulative groundwater analytical results, 2009–2025. Site number 108154.
Comments