The Canyon Tunnel, a Worker's Death, and San Joaquin County's Water Future
The Canyon Tunnel, a Worker's Death, and San Joaquin County's Water Future
LodiEye — April 2026
Summary
A 35-year-old engineer was killed inside an $84 million bypass tunnel being dug beneath the Stanislaus River canyon this week. The project she was working on — a joint effort of the South San Joaquin Irrigation District and Oakdale Irrigation District — is meant to secure water reliability for three San Joaquin County cities and 50,000 acres of farmland into the next century. Cal/OSHA has opened an inspection. Work is suspended. LodiEye examines what the project is, why the county has tens of millions of dollars riding on it, and what the incident means for the schedule ahead.
Twyla Capurro was about 200 feet inside a partially-bored tunnel in the Stanislaus River canyon when the rock above her gave way. It was 3:42 in the afternoon on Tuesday, April 14. Two of her colleagues made it out — one without a scratch, one with moderate injuries, pulled from the tunnel mouth by coworkers. Capurro, a mother from Coulterville and an employee of Provost & Pritchard Consulting Group, the engineering firm overseeing the Canyon Tunnel Project, did not. Modesto Fire's technical rescue crews worked the site for more than six hours. They recovered her body shortly after 10 p.m.
By Wednesday afternoon, the South San Joaquin Irrigation District had suspended all work at the site. Cal/OSHA's Mining and Tunneling Unit had opened a formal inspection. And a project that local officials had spent nearly a decade planning — one meant to insulate San Joaquin County's water supply from the very kind of rockfall that may have just killed Capurro — was indefinitely on hold.
The story has been covered adequately as breaking news by the Modesto and Manteca press. What has received less attention is the broader context: what the Canyon Tunnel Project actually is, why San Joaquin County has tens of millions of public dollars riding on it, and why a Lodi audience should care about a tunnel being dug an hour to the southeast.
What the project is
The Canyon Tunnel Project is a 12,106-foot bypass tunnel being constructed along the Lower Stanislaus River canyon, downstream of Goodwin Dam, near the Stanislaus-Calaveras county line. It is a joint effort between the South San Joaquin Irrigation District (SSJID), headquartered in Manteca, and the Oakdale Irrigation District (OID). When complete, it will replace a vulnerable, roughly two-mile stretch of the Joint Supply Canal — a century-old open canal system originally built in the early 1900s that clings to the steep northern wall of the canyon.
According to pre-award coverage by the Manteca Bulletin, the tunnel will be 18 to 20 feet in diameter, buried between 200 and 300 feet below the surface, and designed to carry a maximum flow of 1,263 cubic feet per second. The downstream portal discharges into a canal roughly 1.25 miles from the nearest home and a mile and a half from Knights Ferry. The terrain is unforgiving — the same canyon section contains a Class V whitewater rapid known to boaters as "Mr. Toad's Wild Ride."
Project at a Glance
Why San Joaquin County has the most to lose
This is not, in the strictest sense, a San Joaquin County construction project. The tunnel itself is being bored under a canyon wall at the Stanislaus-Calaveras line. But the water it will carry is SJC water — or, more precisely, it is water that becomes SJC water the moment it leaves the canal.
SSJID serves approximately 50,000 acres of farmland in San Joaquin County. More consequential for the urban reader: SSJID supplies treated drinking water to the cities of Manteca, Lathrop, and Tracy, and delivers raw water to Escalon. Several hundred thousand residents in the South County depend, in whole or in part, on water that flows through the Joint Supply Canal. Oakdale Irrigation District's portion of the JSC, meanwhile, irrigates an additional 26,000 acres and provides raw water to Knights Ferry in Stanislaus County.
This is the context in which the Canyon Tunnel was conceived. District planning documents going back to the 2020 design phase identify the existing JSC as sitting below an unstable rock slope that periodically drops rock onto the canal. A 2013 rockfall, SSJID officials have said publicly, nearly crippled the district's early-season water deliveries. The tunnel's stated purpose is twofold: to guarantee that water keeps moving regardless of what happens to the hillside above, and to protect the workers who currently have to maintain an exposed 1900s-era canal carved into a landslide-prone cliff.
The second purpose is where Tuesday's fatality becomes especially cruel. The project was meant to end, not perpetuate, the pattern of workers being endangered by loose rock in this canyon.
Where the money is coming from
Publicly reported cost figures have shifted as the design matured. At the August 4, 2025 ceremonial groundbreaking near Goodwin Dam, the districts framed the total project as $84 million. Earlier reporting from the Manteca Bulletin, covering the June 2025 contract award, put the Drill Tech Drilling & Shoring construction contract at $74,777,777, with all-in project costs — engineering, environmental review, permitting, contingency — projected at $94.3 million. The Oakdale Leader has more recently described it as an $80-plus million project on private property.
The cost-share arithmetic is stable: SSJID is paying 72 percent, OID 28 percent, a ratio drawn from each district's historical water usage through the shared canal. Applied to the higher $94.3 million figure, that is approximately $67.9 million from SSJID ratepayers and $26.4 million from OID. SSJID's share is being funded through the district's general rate base and Tri-Dam Project hydropower revenues; the two districts jointly own the Tri-Dam Project, a series of Stanislaus River watershed reservoirs that generate zero-carbon power.
Canyon Tunnel Project: Cost Share by District
Source: SSJID/OID joint funding agreement, August 2025 groundbreaking materials. Shares calculated on historical water usage from the Joint Supply Canal.
Drill Tech Drilling & Shoring, based in Antioch, is the tunneling contractor. Provost & Pritchard Consulting Group — Capurro's employer — is the engineering and design firm of record.
Safety history and the open investigation
Tuesday's incident appears to be the first fatality at the Canyon Tunnel construction site itself. There is no public record of prior Cal/OSHA citations against Drill Tech specific to this project. The broader canyon corridor, however, has a well-documented multi-decade history of landslide and rockfall events affecting the canal — which is precisely the reason the project exists.
The characterization of the incident is, at this point, disputed. First-responder accounts described a "collapse." A spokesperson for Drill Tech, cited by the Oakdale Leader and Modesto Today, pushed back on that framing, saying the event involved a portion of the tunnel coming loose rather than a full cave-in. Cal/OSHA's Mining and Tunneling Unit is the regulatory body that will ultimately determine cause, and its investigations in active tunneling incidents typically run several months.
The emergency response was substantial. Modesto Fire dispatched Engine 29, Quint 18, and Battalion 2 on the initial call, then upgraded to a technical rescue that pulled in Engines 1, 11, 21, and 23, Squad 32, Rescue 11, Trucks 1 and 5, Battalion 3, and Medic 1. Stanislaus Consolidated Fire, Cal Fire, Copperopolis Fire, and both the Stanislaus and Calaveras sheriff's departments assisted. One worker self-evacuated. A second was pulled to safety by coworkers and transported to a local hospital with moderate injuries, per the Oakdale Leader's reporting. Capurro was the third.
A grim piece of timing
Hours before the collapse, SSJID uploaded a Spring 2026 project update to its YouTube channel. The video shows workers inside the tunnel — footage captured before whatever happened Tuesday afternoon, posted to promote project progress, now serving as one of the last visual records of the site in its pre-incident state. The video remained live as of Thursday.
What happens next
Three processes are now unfolding in parallel. Cal/OSHA's inspection will proceed under its Mining and Tunneling Unit, which handles the small number of California workplaces that fall under federal MSHA-adjacent tunneling rules. SSJID and OID have said they will conduct their own review. And Drill Tech, as the contractor on the hook, will almost certainly mount an internal investigation of its own.
The broader question for San Joaquin County ratepayers and water users is schedule risk. The project's original target completion was spring 2029 per the Manteca Bulletin's contract-award coverage; the districts' public materials now cite 2028. Either way, every month the site sits idle is a month the existing JSC continues to carry the full operational load through a canyon section the districts themselves have characterized as dangerous. A sustained shutdown — whether driven by Cal/OSHA findings, contractor re-evaluation, or insurance considerations — pushes the moment of greater reliability further into the future and extends the window in which the old canal could fail.
For Lodi readers, the direct connection is limited: the city of Lodi is not served by SSJID, and its surface water comes from a different watershed. But the regional framework matters. San Joaquin County has one cohesive agricultural economy, one labor market, and one set of cities whose municipal bond ratings and growth projections hinge on water reliability. What happens to water delivery in the South County eventually shapes the political and economic conditions under which Lodi operates. The Canyon Tunnel Project is, in that sense, infrastructure the entire county has a stake in — and Twyla Capurro is a worker whose death the entire county has reason to take seriously.
In memoriam
Twyla Capurro was 35. She lived in Coulterville. She was a mother. She worked for Provost & Pritchard, a California engineering consultancy active on water and infrastructure projects throughout the Central Valley. LodiEye extends its condolences to her family, her colleagues, and the crews who worked through Tuesday night to bring her home.
This LodiEye news analysis was produced using artificial intelligence tools under the direction and editorial review of Lodi411's human editor. Lodi411 uses multiple AI platforms in its research and publication workflow, including Anthropic's Claude (primarily Opus and Sonnet models) and Perplexity AI across a variety of large language models offered by each. These tools were used in the following capacities:
Source Discovery: AI-assisted search and retrieval identified breaking-news coverage and project background across approximately a dozen regional sources, including the Oakdale Leader, Manteca Bulletin, CBS Sacramento, ABC10, Modesto Today, myMotherLode.com, Smart Water Magazine, the Escalon Times, and the South San Joaquin Irrigation District's own canyontunnelproject.org and Spring 2020 newsletter archive. Perplexity AI was used for initial real-time retrieval of the April 14 incident reporting; Claude Opus was used for deeper synthesis of project background, funding history, and engineering specifications.
Credibility Validation: AI cross-referenced claims across multiple independent sources, prioritizing primary documents (SSJID/OID official project materials, Cal/OSHA statements, Calaveras County Coroner identification) followed by established regional newspapers and secondary news aggregators. Cost figures, cost-share ratios, tunnel dimensions, and the incident timeline were each confirmed against two or more independent sources. Conflicting figures (e.g., $84M vs. $94.3M total project cost) are presented to the reader rather than resolved by fiat.
Analysis and Synthesis: Claude Opus assisted in reconstructing the project's funding architecture, service-area footprint, and schedule risk, and in framing the San Joaquin County and Lodi-specific relevance of an incident that occurred outside the county line. The editor directed the analytical framing that the tunnel's worker-safety rationale is in painful tension with the fatality that has now suspended it.
Presentation: Claude assisted in drafting, structuring, and formatting the article for clarity and readability, including the project-at-a-glance fact grid, the cost-share donut chart, and the narrative sequencing from incident to context to consequence.
Final Review: Multiple AI models reviewed the completed draft for factual consistency, source attribution accuracy, logical coherence, and balanced presentation. All editorial judgments, analytical conclusions, and publication decisions were made by Lodi411's human editor.
Lodi411/LodiEye believes transparency about AI use in journalism serves both readers and the profession. We use multiple AI platforms — including Anthropic's Claude (Opus and Sonnet) and Perplexity AI — as research, analysis, and presentation tools, not as autonomous authors. All editorial judgments, analytical conclusions, and publication decisions are made by Lodi411's human editor, who directs and reviews all AI-assisted work.
References
- Oakdale Leader — Fatal victim identified in Canyon Tunnel incident (April 2026)
- Manteca Bulletin — Rock fall inside tunnel project for SSJID kills a consulting team member (April 2026)
- Manteca Bulletin — $77M, 2-mile long tunnel project before SSJID (June 2025)
- CBS Sacramento — Tunnel collapse near Knights Ferry kills 1, injures 1 (April 2026)
- ABC10 — Cal/OSHA opens inspection into fatal tunnel collapse near Knights Ferry (April 2026)
- Modesto Today — One Dead After Tunnel Collapse at Canyon Tunnel Project (April 2026)
- myMotherLode.com — One Dead After Tunnel Collapsed In Calaveras County (April 2026)
- Smart Water Magazine — $84 million Canyon Tunnel will secure water future for Central Valley communities (August 2025)
- Escalon Times — SSJID and OID launch Canyon Tunnel Project (August 2025)
- Canyon Tunnel Project — Official project website (SSJID/OID)
- South San Joaquin Irrigation District — Spring 2020 Irrigation Newsletter (PDF)