Mohammad Sharif Environmental Engineer, EIT
CV
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Closed MSW landfill — final closure constructionComplete

Colton Sanitary Landfill — Final Cover & LFG System

Third-party construction quality assurance on the new landfill gas collection system built with the final closure of an 88-acre landfill in Colton: extraction wells drilled into the waste, and new headers and laterals.

Client / program
County of San Bernardino — Solid Waste Management Division
My role
Third-party CQA — landfill gas system; author of the final CQA completion report
Dates
Oct 2022 — Jul 2024
Location
Colton, CA
Status
Complete
Pacific
Ocean 40° N 35° N 120° W
Colton Sanitary Landfill Colton, CA 34.00° N 117.30° W
Fig. 1 Key map. Position shown to about 10 km; drag to turn the ground.
Fig. 2 The rig's auger lifted clear of a new extraction-well boring, with the waste cuttings piled at the hole.

Problem

Closing the landfill with a geosynthetic cover meant rebuilding the gas system under it: old wells abandoned, new ones drilled into the waste, and the piping replaced, all built to a design that would be buried for decades.

Approach

Independent CQA on the landfill gas work designed by Advanced Earth Sciences (AES): observing drilling into waste and well construction, and checking headers and laterals against the plans and specifications, then writing the final CQA completion report.

Outcome

The new collection system was built to design, beneath what the County describes as the largest ClosureTurf installation in Southern California, completed in July 2024. I wrote the final CQA completion report that documents the work.

Setting

The Colton Sanitary Landfill is a 113-acre site in the City of Colton, with 88 acres used for waste disposal. It took waste from 1964 until the end of 2014. For final closure, the County of San Bernardino replaced a planned four-foot soil cover, which would have needed about 600,000 cubic yards of imported soil, with ClosureTurf: a polyethylene geomembrane under a synthetic-grass layer with sand ballast. According to the County, it is the largest installation of its kind in Southern California, laid on steep, highly visible slopes. The County’s figures for the closure are about $39.8 million and 21 months of construction, completed in July 2024.

A new cover changes how gas moves in the waste beneath it, so the closure included rebuilding the landfill gas (LFG) collection system. Public project summaries describe 171 existing extraction wells abandoned, 56 new wells drilled and installed, and the headers and laterals removed and replaced.

Our role

The gas system was designed by Advanced Earth Sciences (AES). We were the independent third party providing construction quality assurance (CQA): confirming for the County that what went into the ground matched the design, and documenting it.

What the CQA covered

Extraction wells. Each new well starts as a boring drilled down through the waste. CQA meant being at the rig while the boreholes were drilled, then watching each well built in it: the casing and screened interval set at the design depths, the gravel pack placed around the screen, the seal placed above it, and the wellhead finished. Drilling into waste brings gas, heat and refuse up to the surface, so every hole is a site-safety task as well as a construction one.

Headers and laterals. The piping that carries gas from each well to the main headers has to slope as designed so condensate drains instead of blocking the line. CQA meant checking pipe, grade and connections against the plans and specifications as they were installed.

Records. The CQA record is daily field observations and the as-built details of what went in. Once the cover is on, those records are the only way to see the system.

The final cover around it. The gas work went in alongside the new cover: textured geomembrane unrolled down the slopes from spreader bars, seams welded with hot-wedge welders, and samples cut from the seams and pulled apart on a field tensiometer before each cut-out was patched.

The CQA completion report

I was the author of the final CQA completion report: the document that closes out construction. It brings the whole CQA record together (the daily observations, the testing, how each deviation from the plans was resolved, and the as-built record) to show that the work was built to the approved design and specifications. It is the record the owner and the regulators rely on to accept the closure, and the one anyone reading the site in decades to come will start from.

Skills demonstrated

Construction quality assurance on landfill gas systems; observing drilling and well construction in waste; field verification against design drawings and specifications; working as the independent party between the County, the designer and the contractor; and writing the final CQA completion report.

FiguresFrom the site

Fig. 3 A drill rig set up on the landfill slope for a new gas well, the closure earthwork and snow-capped mountains beyond.
Fig. 4 Scrapers working at the foot of the landfill, with a drill rig's mast on the crest above.
Fig. 5 A roll of geomembrane lifted on a spreader bar, ready to run down the slope.
Fig. 6 Unrolling textured geomembrane across the prepared slope.
Fig. 7 A cut-out at a geomembrane seam, where a test sample was removed before the hole is patched.
Fig. 8 Geomembrane panels going down along the slope bench, the next roll on the spreader bar.
Fig. 9 The Soilmec SR-60 drilling a landfill gas extraction well.
Fig. 10 Well pipe stockpiled on the slope beside the rig's support truck.
Fig. 11 The drill rig and its support truck on the access road up the slope.
Fig. 12 Drilling on the upper slope, with the valley spread out below.
Fig. 13 Welding a geomembrane seam with a hot-wedge welder.
Fig. 14 A water truck wetting the subgrade for compaction and dust control.
Fig. 15 The water truck working down the slope ahead of the cover.
Fig. 16 A field tensiometer for seam samples: each weld is pulled apart to check its strength.