When you look at a piece of land, it’s easy to see only what’s on the surface-open fields, a nice parking lot, or maybe an old building that seems harmless. But the truth is, what’s happening beneath the soil and in the groundwater often tells a very different story.
As environmental scientists, we get asked all the time: “How does a site become contaminated?” It’s a fair question, especially if you’re thinking about buying, developing, or even selling property. Contamination can derail projects, scare away lenders, and in some cases, leave you with a very expensive cleanup bill.
The good news? Most of the causes are fairly predictable. After decades in land remediation and due diligence, we’ve identified some major red flags that explain how a site becomes contaminated and what you can do about it.
Here are the 7 red flags you should watch out for if you’re wondering how sites become contaminated-and what they mean for your property.
1. Legacy Industrial Activity
One of the biggest red flags is whether the site once hosted industrial operations-factories, chemical plants, rail yards, or even dry cleaners. Before modern environmental laws, many facilities handled solvents, heavy metals, and petroleum without proper safeguards.
Chemicals were stored in unlined pits, dumped in fields, or allowed to seep into the ground. Even if the buildings are long gone, the contamination often lingers underground for decades.
How does a site become contaminated in this case? Poor historical practices leave behind pollutants that don’t break down easily, meaning today’s property owners may inherit yesterday’s mistakes.
2. Underground Storage Tanks (USTs)
If the property once operated as a gas station, trucking yard, or auto shop, there’s a strong chance underground storage tanks were present. Steel tanks, especially those installed before the 1980s, are prone to corrosion and leaks.
When a UST leaks, gasoline, diesel, or other chemicals migrate into surrounding soils and groundwater, creating contamination plumes that can extend beyond the property boundary. Even tanks that were “removed” improperly can leave residual contamination.
How does a site become contaminated here? Hidden tanks slowly release petroleum hydrocarbons into the ground, often undetected for years.
3. Improper Waste Disposal and Dumping
Another common cause of contamination is illegal or careless dumping. In the past, companies often disposed of chemical drums, industrial byproducts, or even household waste on-site. These buried wastes eventually break down, leaching hazardous compounds into the soil and groundwater.
For example, a site we assessed looked like a harmless grassy field, but our borings revealed buried construction debris and oily sludge beneath the surface.
How does a site become contaminated in this way? Waste dumped on-site doesn’t stay isolated-it seeps, spreads, and impacts surrounding areas.
4. Agricultural or Pesticide Use
Contamination isn’t always industrial. Agricultural land may be impacted by years of heavy pesticide, herbicide, and fertilizer application. These chemicals can accumulate in soils and eventually migrate into aquifers.
Even if the property appears green and open, residues like nitrates or persistent pesticides can remain long after farming stops. Converting agricultural land into residential or commercial projects often reveals these hidden risks.
How does a site become contaminated in rural settings? Through long-term chemical use in farming practices that leave a toxic legacy in soil and groundwater.
5. Stormwater Runoff and Drainage Issues
Contamination doesn’t always come from what happens directly on your land-it can arrive through stormwater runoff. Parking lots, highways, and industrial sites release oils, heavy metals, and chemicals into runoff that flows into nearby low-lying areas or drainage ditches.
If a property doesn’t have proper drainage or a Stormwater Pollution Prevention Plan (SWPPP), these pollutants can concentrate in one area, creating hotspots of contamination.
How does a site become contaminated from runoff? Polluted stormwater acts as a delivery system, carrying contaminants onto your land where they build up over time.
6. Historic Landfills or Fill Material
Redeveloped properties often sit on or near historic dumpsites. In the mid-20th century, fill dirt was frequently sourced from questionable places-including contaminated soils.
These fill areas can contain lead, arsenic, asbestos, or even methane-producing waste. We’ve seen redevelopment projects halted when testing revealed landfill gases migrating through the soil into buildings.
How does a site become contaminated in this case? Contaminated fill material and decomposing waste release toxins into soil and gas into the surrounding environment.
7. Nearby Operations and Cross-Contamination
Finally, even if your land has a “clean” history, neighboring operations can impact it. Contamination migrates-through groundwater, soil vapor, or surface water.
For example, a property next to a dry cleaner may show chlorinated solvent contamination, even if no chemicals were ever used on-site. Similarly, fuel leaks from an adjacent gas station can spread beneath property lines, leaving the new landowner responsible.
How does a site become contaminated here? Pollution doesn’t respect boundaries. Nearby sources can migrate onto your land, creating liability for owners who had nothing to do with the original contamination.
What To Do if You Suspect Contamination
So, what happens if one of these red flags applies to your property? Here’s a step-by-step approach:
Step 1 – Start with a Phase I ESA
A Phase I Environmental Site Assessment reviews site history, records, and surrounding properties. It’s the industry standard first step.
Step 2 – Move to Phase II Testing if Needed
If red flags are identified, a Phase II ESA involves soil borings, groundwater sampling, or soil vapor testing to confirm contamination.
Step 3 – Remediation Options
If contamination is confirmed, don’t panic. There are proven remediation solutions:
- Excavation and disposal (removing contaminated soil).
- Soil vapor extraction (removing volatile compounds).
- Groundwater treatment (pump-and-treat or in-situ remedies).
Cleanup strategies depend on the type of contamination, extent, and regulatory requirements.
Final Thoughts
So, how does a site become contaminated? Often through legacy industry, hidden tanks, poor waste practices, or even neighboring operations. The important part is knowing what to look for-and having a professional team ready to step in when needed.
At CRG Texas Environmental Services Inc., we’ve spent more than 30 years helping property owners, buyers, and developers identify and resolve contamination issues. Whether you’re about to purchase land or you’ve discovered a problem on your property, we’re here to guide you every step of the way.
If you’re wondering how a site becomes contaminated and what it means for your land, reach out to our team today.