MSHA: Signal Peak Silica did not inspect and maintain dam in 2025 collapse

In its final investigation report, the Mine Safety and Health Administration (MSHA) found Signal Peak Silica of Atascosa failed to properly construct, inspect, and maintain its waste tailing retaining pond dam at its Signal Peak sand pit.

On May 1, 2025, the dam ruptured, releasing material which pushed an excavator off its bench, causing it to overturn and become engulfed. Contract heavy equipment operator, 25-year-old Alan Josue Castillo Herrarte, was killed in the accident.

MSHA’s accident investigation team conducted an examination of the accident scene, interviewed miners, mine management, contractors, and contractor management, and reviewed conditions and work procedures relevant to the accident.

Five citations issued

MSHA found the accident occurred because the mine operator and contractor Stout Excavating Group LLC did not:

1. Substantially construct and inspect the retaining dam at regular intervals
2. Conduct a workplace examination in Pit 2C before miners began work
3. Use mining methods to maintain wall, bank, and slope stability

MSHA issued three citations to SP Silica of Atascosa, LLC and two citations to contract operator Stout Excavating Group LLC.

MSHA inspected mine within prior two months

SP Silica’s Signal Peak surface pit in Poteet, Texas supplies industrial sand to the oil and gas industry. SP Silica contracted Herrarte’s employer Stout to extract the sand using excavators and deliver it via haul truck to a processing plant.

MSHA completed its last regular safety and health inspection at the mine March 19, 2025.

Over two million gallons of material released

At 9:12 a.m., saturated material was seen progressing down the ramp from the retaining dam. Two minutes later, Herrarte announced over the CB radio that material from above his work location was moving towards the bench, describing it as pure mud.

At 9:18 a.m., another operator reported over the radio that material was being released in large clumps and water was coming out from the retaining dam in the same location.

Just as Herrarte instructed haul trucks to move up, material from the retaining dam surged forward, pushing the excavator off its eight-foot high bench. MSHA investigators later estimated the release ranged between 2.2 and 3.3 million gallons.

Second destabilization paused investigation efforts

Five minutes later, the Stout foreman arrived in the bulldozer he was operating and began using it to create a path to the excavator. At 9:40 a.m., Mike Harrison, Stout field safety specialist, notified the Atascosa County Sheriff’s office of the accident.

First responders found Herrarte unresponsive in the cab, and he was pronounced dead at the scene within an hour of the incident start.

At around 4:45 p.m., a secondary sloughing event occurred near the release location in the retaining dam, prompting MSHA investigators who had arrived on the scene to temporarily remove personnel.

Operator, contractor did not communicate location of pond

Pit 1 was developed near the south end of the mine property during 2018. After the pit was excavated completely, it was used for tailings disposal. Google Earth photos showed SP Silica initiated capping the pond sometime in 2021. Investigators found a portion of uncapped tailings in the center of the cap area.

MSHA determined SP Silica and Stout had knowledge of the location of the waste tailings pond, but this information was not conveyed to the miners working in the area.

Miners identified potential hazard days before failure

The retaining dam had visual indicators of a potential hazard, including water and mud present on multiple shifts identified by miners.

Indicators of seepage were present two days prior to the failure. The mine site had received rain in the prior week that collected in the uncapped portion of the waste tailings pond. Investigators could not determine if the recent rain contributed to the failure of the retaining dam.

Water was observed leaking out of the pond in the affected area on April 26 and 27, 2025, and water was observed running out of the pond in the affected area on April 30.

Stout management observed water coming out of the affected area but did not report it or document it on the workplace examination record.

Foreman completed examination from parking lot in his truck

Stout’s workplace examination records indicated that a record was created at 5:44 a.m. and completed at 5:45 a.m.

During interviews, the Stout Foreman said he arrived at the mine at 5:40 a.m. and performed the workplace examination from his truck while in the contractor parking area. The record did not indicate any hazards.

SP Silica and Stout did not withdraw the miners from the area, take prompt corrective actions, and document the conditions found. Investigators determined that the mine operator and the contractor did not conduct a workplace examination in Pit 2C before miners began work, which contributed to the accident.

Both SP Silica and Stout were cited under 30 CFR §56.18002 - Examination of Working Places, for not examining each working place at least once per shift before miners began work for conditions which may adversely affect safety and health.

Dam and cap not constructed or inspected sufficiently

SP Silica was mining the last remaining usable material in the accident area in preparation for creating a new tailings pond. The mining method used resulted in a retaining dam being constructed insufficient to support the contents of the adjacent tailings pond.

Both SP Silica and Stout were cited under 30 CFR §56.20010 - Retaining Dams, for not substantially constructing and inspecting the dam at regular intervals, which investigators found contributed to the accident.

SP Silica was also cited under 30 CFR §56.3130 - Wall, Bank, and Slope Stability, for not ensuring proper mining methods were used to maintain wall, bank, and slope stability, which investigators determined contributed to the accident.