What contaminants are most commonly found on industrial sites?

Stijn Boeren · 19 Sep 2026

The most commonly found contaminants on industrial sites are chlorinated solvents (VOCl), petroleum hydrocarbons, heavy metals, and polycyclic aromatic hydrocarbons (PAH). The specific mix depends on the industry that operated on the site and how long contamination has been present. Understanding what you are dealing with is the essential first step before any remediation decision can be made — and the sections below walk through the most important questions site managers face after contamination is discovered.

Which industries produce the most contaminated sites?

The industries most likely to leave behind heavily contaminated soil and groundwater are dry cleaning, metal degreasing, chemical manufacturing, petroleum refining, and wood treatment. These sectors have historically used large volumes of solvents, fuels, and heavy metal compounds that persist in the subsurface long after operations have ceased.

Former dry cleaners and industrial laundries are among the most problematic because they routinely used chlorinated solvents such as perchloroethylene (PCE) and trichloroethylene (TCE) for decades. Automotive workshops, machine shops, and electronics manufacturers also relied on these compounds as degreasers. Gasoline stations and fuel depots contribute petroleum hydrocarbons and BTEX compounds (benzene, toluene, ethylbenzene, xylene). Tanneries, electroplating facilities, and mining operations leave behind heavy metals including chromium, lead, zinc, and cadmium. Coking plants and former gasworks are strongly associated with PAH contamination.

In Belgium and the broader EU context, a significant proportion of brownfield sites carry contamination from multiple industrial eras, meaning the contaminant profile is rarely simple. A site that housed a garage in the 1960s and a dry cleaner in the 1980s may carry both petroleum hydrocarbons and chlorinated solvents simultaneously, complicating both the investigation and the remediation approach.

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What are chlorinated solvents and why are they so persistent?

Chlorinated solvents, also called volatile organochlorine compounds (VOCl), are synthetic chemicals in which chlorine atoms are bonded to a carbon backbone. Common examples include perchloroethylene (PCE), trichloroethylene (TCE), and their breakdown products dichloroethylene (DCE) and vinyl chloride (VC). They are persistent in soil and groundwater because they are dense, poorly soluble in water, and resist natural chemical degradation.

Their density is a key factor. Unlike petroleum products, which float on groundwater, chlorinated solvents are denser than water. This means they sink through the unsaturated zone and the water table, forming what specialists call Dense Non-Aqueous Phase Liquids (DNAPLs) at the base of the aquifer or trapped in low-permeability layers. From these source zones, they dissolve slowly into groundwater over years or decades, creating long contamination plumes that migrate far from the original release point.

The persistence of VOCl is compounded by the fact that natural microbial communities can only partially degrade them under certain conditions. Complete reductive dechlorination — the step-by-step removal of chlorine atoms down to harmless ethene — requires specific anaerobic bacteria, particularly members of the genus Dehalococcoides. These organisms are not always present in sufficient numbers at contaminated sites. When the microbial community is incomplete, degradation stalls at intermediate products such as vinyl chloride, which is more toxic than the parent compound. This is precisely why specialist assessment is needed before assuming natural attenuation is sufficient.

Avecom’s work in biological soil remediation focuses heavily on VOCl contamination for exactly this reason: it is one of the most technically demanding contamination types, and standard excavation is rarely a viable solution once solvents have migrated deep into the subsurface.

What other contaminants are commonly found alongside VOCl?

On industrial sites where chlorinated solvents are present, it is common to also find petroleum hydrocarbons, heavy metals, and in some cases cyanides or PAHs. Co-contamination is the rule rather than the exception on sites with long industrial histories, and each contaminant class behaves differently in the subsurface.

Petroleum hydrocarbons (mineral oils, BTEX compounds) are frequently found at sites that combined degreasing operations with fuel storage or vehicle maintenance. Heavy metals such as lead, chromium, nickel, and zinc accumulate in the soil matrix and are largely immobile, but they can leach into groundwater under certain pH conditions. PAHs from coal tar, creosote, or combustion residues bind strongly to soil particles and tend to concentrate near the surface or in former waste disposal areas.

The presence of co-contaminants matters enormously for remediation planning. Some biological degradation processes that work well for VOCl can be inhibited by high concentrations of heavy metals or by competing electron acceptors introduced by petroleum hydrocarbons. A thorough site investigation that maps all contaminant types — not just the primary target compound — is therefore essential before committing to any remediation strategy.

How do contaminants spread from the source zone to surrounding areas?

Contaminants spread from a source zone through three main pathways: dissolution into groundwater and subsequent plume migration, volatilization into soil gas, and physical transport via soil particles during excavation or flooding. The dominant pathway depends on the physical and chemical properties of the contaminant and the hydrogeological conditions of the site.

For chlorinated solvents, groundwater transport is the primary concern. Once a DNAPL source zone is established, dissolved-phase contamination migrates downgradient with the natural groundwater flow. Plumes can extend hundreds of meters from the source over time, affecting drinking water wells, surface water bodies, and neighboring properties. The rate of migration depends on groundwater velocity, soil permeability, and the sorption capacity of the aquifer material.

Volatilization is a secondary but important pathway for compounds with high vapor pressure, including many chlorinated solvents and BTEX compounds. Vapors migrate upward through the unsaturated zone and can accumulate in basements or enclosed structures, creating both health risks and regulatory obligations for building owners. This is sometimes called vapor intrusion and is increasingly scrutinized in urban brownfield redevelopment projects.

Understanding the spread of contamination is not only a technical question — it directly affects which neighboring parcels need to be investigated, what the legal liability picture looks like, and how urgently remediation needs to begin. If you are asking how to test if soil is contaminated on an adjacent property, the answer starts with understanding the plume geometry of the source site.

What site investigation methods identify and map industrial contaminants?

Site investigation for industrial contamination typically combines historical desk research, soil and groundwater sampling, chemical analysis, and increasingly, molecular biological tools. The goal is to determine what contaminants are present, at what concentrations, and how far they have spread — both in the soil matrix and in groundwater.

Phase 1: desk research and preliminary assessment

The first step in any contaminated soil assessment is a historical review of the site: land registry records, aerial photographs, former permits, and interviews with long-term users. This phase identifies likely source zones and contaminant types before a single sample is taken. It is the most cost-efficient way to scope the investigation and avoid unnecessary drilling.

Phase 2: physical sampling and chemical analysis

Soil borings and groundwater monitoring wells are installed to collect representative samples from different depths and locations. Samples are analyzed in accredited laboratories for the suspected contaminant classes. For VOCl, this means measuring PCE, TCE, DCE isomers, and vinyl chloride. For petroleum sites, the analysis covers mineral oils, BTEX, and PAH. The results are compared against regulatory threshold values — in Flanders, these are defined under VLAREBO.

Phase 3: molecular and biological characterization

For sites where biological remediation is being considered, chemical data alone is not sufficient. Molecular tools such as quantitative PCR (qPCR) and amplicon sequencing can determine whether the specific microorganisms capable of degrading the target contaminants are present in the soil, and at what activity levels. This type of analysis, which Avecom has specialized in for over 30 years, provides a direct answer to the question of whether natural attenuation is occurring and whether it can be enhanced through bioaugmentation.

Knowing how to test if soil is contaminated goes beyond sending a sample to a lab. A complete investigation maps the three-dimensional extent of contamination, characterizes the microbial community, and provides the data needed to evaluate remediation options — including whether biological treatment is feasible for the specific site conditions.

Which contamination types are suitable for biological remediation?

Biological remediation is most effective for organic contaminants that microorganisms can use as an energy source or degrade through co-metabolic pathways. Chlorinated solvents (VOCl), petroleum hydrocarbons (BTEX, mineral oils), and certain PAHs are the primary candidates. Heavy metals are generally not suitable for biological degradation, though biological processes can sometimes immobilize them.

For chlorinated solvents specifically, biological reductive dechlorination is a well-established approach when the right microbial conditions can be created or introduced. The key question is not whether the process works in principle — it does, and the scientific evidence is extensive — but whether it will work at a specific site given the local soil matrix, groundwater chemistry, and existing microbial community. This is why a microcosm test is a standard first step: it uses actual soil and groundwater from the site to determine, under controlled laboratory conditions, whether complete dechlorination to ethene is achievable.

Petroleum hydrocarbons are generally more amenable to aerobic biodegradation, which is faster and less condition-dependent than anaerobic dechlorination. Many sites with BTEX or mineral oil contamination show measurable natural attenuation, and biostimulation — adding electron acceptors such as oxygen or nutrients — can accelerate the process significantly.

The suitability of biological remediation also depends on practical site factors: contaminant concentration, depth, heterogeneity of the subsurface, and the presence of co-contaminants that might inhibit microbial activity. For sites where excavation is not feasible due to existing structures, groundwater levels, or cost, in-situ biological treatment is often the most realistic path forward. Avecom’s soil remediation services are specifically designed for these difficult cases — where standard approaches have failed or are not applicable, and where a science-based biological strategy is needed.

If contamination has been discovered on an industrial site and the question is what to do next, the practical steps are: complete a thorough site investigation, characterize both the chemical and biological conditions, assess which contaminant types are present, and evaluate whether biological remediation is feasible before committing to a more disruptive approach. For complex VOCl contamination in particular, early engagement with a specialist who can perform microcosm testing and molecular monitoring will save both time and cost over the course of the project. Avecom offers exactly that kind of preliminary screening as a starting point for sites where the right remediation path is still unclear.