Mohammad Sharif Environmental Engineer, EIT
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Superfund mercury mine — pre-design investigation & remediationActive

Sulphur Bank Mercury Mine

A former mercury mine on the shore of Clear Lake, now a federal Superfund cleanup. I helped lead the 2025 pre-design test-pit, soil-boring and boulder XRF campaigns that fed the remedial design, and now lead the construction effort for Phase 1, the cleanup of residential yards.

Client / program
U.S. EPA Region 9 — Superfund
My role
Construction lead, Phase 1 remediation; co-lead, pre-design field campaigns
Dates
May 2025 — Present
Location
Clearlake Oaks, CA
Status
Active
Pacific
Ocean 40° N 35° N 120° W
Sulphur Bank Mercury Mine Clearlake Oaks, CA 39.00° N 122.66° W
Fig. 1 Key map. Position shown to about 1 km; drag to turn the ground.
Fig. 2 The Site Explorer, flown

Problem

A century of mining left about 2.5 to 3 million cubic yards of mercury-bearing waste on Clear Lake’s shore. EPA’s 2023 cleanup plan consolidates and caps it, and designing that means knowing what is where, and what can be reused.

Approach

A pre-design investigation run alongside the design: test pits and soil borings to map the waste and the ground beneath it, and handheld XRF on more than 146 boulders to show which could be reused, with data turned around fast enough to shape the design.

Outcome

Field data in the designers’ hands while the design took shape, and a characterized stock of boulders the remedy can build with instead of trucking rock in. The project now moves into construction, and I lead the Phase 1 effort: cleaning up residential yards beside the mine.

Setting

Sulphur Bank sits on the Oaks Arm of Clear Lake, California’s largest natural lake. Sulfur was dug here from 1865; mercury from 1873, first underground and, from 1927, from an open pit, until mining stopped in 1957. The pit then filled with water and became the Herman Impoundment: a pit lake of about 23 acres, some 90 feet deep, a few hundred feet from Clear Lake’s shore. Around it lie roughly 2.5 to 3 million cubic yards of waste rock, tailings and ore in nine piles across a 160-acre mine, including a waste rock dam built out into the lake.

Mercury from the mine has built up in the lake’s sediments and fish, and Clear Lake has carried a fish-consumption advisory since 1987. The site is directly next to the Elem Indian Colony, on land its people have lived on for thousands of years. EPA listed Sulphur Bank on the National Priorities List in 1990 and ran a series of removal actions over the next two decades, from regrading the shoreline to cleaning up yards on the Colony.

The cleanup

EPA’s Record of Decision for the mine (November 2023) sets out the cleanup: excavate, consolidate and cap the mine waste; take the waste rock dam back toward the 1888 shoreline; backfill the Northwest Pit; secure the pit lake and rebuild the pipelines that divert clean stormwater around it; clean up residential soils; and keep the whole system monitored and maintained, at an estimated cost of about $94.5 million. EPA plans the construction in stages from 2026 into the 2030s, and to use the site’s own soil and boulders wherever it can: about 8,000 fewer truck trips on the roads around the lake.

A remedy like that turns on questions only the ground can answer: how thick the waste is and where native ground begins, what each pile is made of, and which material is clean enough to build with. That is what the pre-design investigation was for.

My role

  • Pre-design investigation (2025). I helped lead the test-pitting and soil-boring campaigns, run while the remedial design was being drawn, so the field data fed the design as it developed.
  • Boulder characterization. I helped lead the handheld XRF campaign that characterized more than 146 boulders across the site to support their reuse in the remedy.
  • Phase 1 construction. I lead the construction effort for Phase 1 of the remediation: the cleanup of residential yards next to the mine.

Test pits and borings

Test pits show the ground in section. An excavator opens a trench through a waste pile and into what lies under it, and the wall tells the story: roots and dark soil over weathered rock, bleached and hydrothermally altered material near the base, the occasional cinnabar-red piece in the spoil. We logged each profile, sampled it, and screened it with XRF, working inside roped exclusion zones, with water sprays holding the dust down and the excavated material laid out on plastic sheeting before it went back in the hole.

Borings reach where a trench can’t: deeper waste, the contact with native ground, and material below the water table. Between the two, the campaigns built a picture of what is where, in the three dimensions a cap design needs.

The design was being drawn in parallel, so turnaround mattered. Data from the field had to be logged, checked and in the designers’ hands quickly enough to change what they drew next, and field plans shifted as the picture sharpened.

146 boulders, one at a time

The mine is strewn with large andesite boulders, and the remedy can use them: as armoring and riprap, and in place of rock that would otherwise be trucked in. But a boulder from a mercury mine can only be reused once it has been shown to be clean enough.

So each boulder was located, tagged and read with handheld XRF: readings on its surface and at depth, with rock chips drilled and powdered for laboratory analysis to check the field instruments against the lab. Two XRF analyzers produced thousands of readings, which had to be tied back to the right boulder without error. I built the XRF Data App for exactly that: it reconciles every reading against the master tracker and shows each boulder’s surface, depth and lab results side by side.

Phase 1: the yards

The cleanup starts where people live. Phase 1 is the residential soil cleanup: yards on the Elem Indian Colony and in the neighborhood along Sulphur Bank Mine Road, closest to the old workings. EPA’s plan is to remove about 6,000 cubic yards of soil from around a dozen properties, starting in the fall of 2026, with Tribal Monitors on site alongside the crews.

I lead the construction effort for Phase 1. A residential cleanup is engineering at the scale of a garden: digging soil out to the depths and limits in the design, confirming by sampling that what stays behind meets the residential cleanup levels, bringing in clean soil, and putting each yard back together. And it is done around people’s homes, so dust control, access, scheduling and keeping residents informed matter as much as the excavation itself. It is the other half of the pre-design work: the same ground, now being rebuilt to the design it informed.

Tools I built for the site

  • The Site Explorer, in the film above: an in-browser terrain workbench on the site’s January 2024 aerial survey. It flies the lidar-derived 1-foot ground surface in 3D under the same flight’s orthophotography, relights the hillshade, reads slope and canopy height, and traces where a raindrop would run and how flow gathers, in one browser tab with nothing to install. The film shows only the terrain; the site’s data layers stay out of it.
  • A field-navigation tool that walks the crew to each planned sample point on a grid, and shows how close they really are.
  • A sampling planning map that puts current and historical samples together, finds the gaps, and places new points.
  • The Boring Data Explorer, for reading subsurface boring records on a map instead of one file at a time.
  • The XRF Data App, for the boulder campaign.

Skills demonstrated

Pre-design investigation planning and field leadership; test pitting and soil boring logging; handheld XRF screening with laboratory confirmation; characterizing material for reuse; leading construction on a federal Superfund cleanup; hazardous-site field safety; and building the software a field team needs.

Descriptions here stay at the level of the public record and contain no sample results or controlled site information.

FiguresFrom the site

Fig. 3 The mine's pit lake — iron-stained shoreline and pale mineral crust along the water's edge.
Fig. 4 Taking a handheld XRF reading directly on exposed rock.
Fig. 5 Drilling a rock chip to collect a sample in the field.
Fig. 6 A soil sample collected and sealed in a labeled jar.
Fig. 7 Historical view of the open-pit mercury mine and its terraced benches.
Fig. 8 An archival photograph — a figure overlooking the historic mine workings.
Fig. 9 The pit lake from the rim, with the hills beyond.
Fig. 10 Excavation at the edge of the brush.
Fig. 11 The excavator bucket at work in a pit.
Fig. 12 An excavator working among boulders.
Fig. 13 Excavation with a water spray to keep the dust down.
Fig. 14 Afternoon light on the pit lake.
Fig. 15 The pit lake and its shoreline from the slope above.
Fig. 16 An excavator digs while a crew member in protective coveralls sprays water to keep the dust down.
Fig. 17 On site above the pit lake: sun hat, hi-vis vest and radio.
Fig. 18 The pit lake's shore, with the bleached, terraced mine benches on the far side.
Fig. 19 Excavation behind the exclusion zone, with a water spray for dust and excavated material laid out on plastic sheeting.
Fig. 20 An excavator trenching through rocky ground under the oaks.
Fig. 21 A trench wall: roots and dark soil over weathered rock, with pale, altered material at the base.
Fig. 22 Cinnabar-red rock from the excavation, in a gloved hand.
Fig. 23 The excavator's bucket at rest above the pit lake.
Fig. 24 The graded mine yard, below outcrops of bleached, mineral-stained rock.
Fig. 25 A ridge of waste rock along the pit lake, with the pit wall beyond.
Fig. 26 Altered, mineral-stained ground running down to the pit lake.
Fig. 27 Waste rock on the pit lake's edge, looking along the shore.
Fig. 28 The pit lake, with the mine's terraced benches along the far shore.
Fig. 29 Stained waste rock and the benches of the old workings.
Fig. 30 Waste rock at the foot of the pit wall, with a rusted standpipe on the flat.
Fig. 31 A cinnabar-red rock among the mine waste.
Fig. 32 Red mineral crystals on a pale rock face.
Fig. 33 A handheld XRF analyzer in its field case.

NotesWritten about this project