Environmental due diligence is crucial for any commercial and industrial transaction or redevelopment project. A Phase II Environmental Site Assessment also known as a site investigation or subsurface investigation looks beneath the surface to identify potential contamination issues on a site following the findings of a Phase I ESA. Our commitment at AEI is to provide detailed and reliable environmental assessments, equipping property owners and stakeholders with the essential data to make informed decisions. At AEI, we’ve conducted thousands of environmental assessments across diverse property types and industries and our latest Phase II ESA research reveals some eye-opening insights into just how prevalent contamination can be.

How Often Does Environmental Contamination Get Detected?

The data speaks for itself – contamination is discovered at the majority of sites during a Phase II ESA. Our studies found that 70% of sites assessed in 2012 had contamination present. That percentage has only increased over the past decade, with 76% in 2015 and a staggering 80% in 2023 experiencing some level of contamination.

Perhaps more alarmingly, a significant portion of these sites exceeded regulatory action levels or standards. In 2023, over half (54%) had contamination levels that triggered a regulatory compliance concern. Our data indicates an upward trend in sites exceeding these safety thresholds, signaling potential health and legal risks that could impact property value and land usability. This data is crucial for understanding how environmental risks are evolving and stresses the importance of rigorous and regular environmental assessments.



Environmental Contamination Across Property Types

Certain property types and business operations are more prone to causing environmental contamination based on their activities and chemical/waste handling practices. Among these, we’ve identified several key property types:

  • Metal Fabrication: 72% contamination rate, with a significant focus on pollutants like heavy metals and solvents.
  • Off-Site Issues: This category, with an 85% contamination rate, often involves the migration of contaminants from adjacent properties, highlighting the complexity of source identification.
  • Historical Manufacturing: Sites previously utilized for manufacturing have a 72% rate, with common contaminants including PCBs and various organic compounds.
  • Dry Cleaners: With a 71% rate, these sites frequently contain chlorinated solvents, particularly problematic due to their persistence in the environment.
  • Plating: At an 82% contamination rate, electroplating facilities often have issues with heavy metals such as chromium and cadmium.

It’s clear that no property type is truly immune from potential contamination concerns. Each property type has its typical contaminants, primarily influenced by the industrial processes historically conducted on-site.

Have contamination concerns? Contact AEI to ensure your property meets regulatory standards.



Contamination in Environmental Media

In addition to evaluating the types of properties and operations, our research analyzed how frequently contamination was detected across different environmental media like soil, groundwater, soil vapor, and indoor air.

  • Soil: The majority of our Phase II assessments involve soil testing, where we’ve detected contamination in 73% of the sites. Soil contaminants typically include heavy metals and hydrocarbons, which can pose significant risks to groundwater quality and land use.
  • Groundwater: Groundwater assessments revealed contamination in 65% of the sites, highlighting the need for vigilant monitoring and protective measures against pollutants like VOCs and pesticides.
  • Soil Gas: Soil gas surveys, detecting vapors from volatile substances, showed a 77% contamination rate. These findings are crucial for assessing vapor intrusion risks into buildings.
  • Indoor Air: Often overlooked, indoor air quality was tested in various environments, revealing a 37% contamination rate, emphasizing the importance of air quality monitoring inside structures.

Contamination in different media reveals the diverse pathways through which environmental hazards can affect human health and ecological systems. These findings underscore how crucial comprehensive investigations are. Relying solely on limited soil sampling, for instance, could miss substantial contamination in other critical exposure media like groundwater or soil vapor. Understanding where contamination is most prevalent helps us prioritize remediation efforts and prevention strategies.



Common Remediation Solutions For Environmental Contamination

While uncovering contamination is the first step, AEI goes above and beyond with our comprehensive in-house site mitigation and remediation services. Our Site Mitigation Division collaborates closely with our environmental assessment teams to design and implement creative, lasting solutions to reduce environmental risks and liabilities at impacted sites. Common contamination solutions include:


Pump and Treat Method:

  • “Pump and Treat” is a classic method used to clean up contaminated groundwater. In this approach, groundwater is extracted through wells or trenches and brought to the surface. Once at the surface, the contaminated water is either immediately treated or temporarily stored in tanks. The core of this method involves treating the contaminated water using various technologies. Common treatment options include physical methods like activated carbon filters or air stripping, or more complex approaches such as oxidation, thermal oxidation, and ultraviolet treatment. This method is versatile and can be applied to various types of contaminants including organics, metals, and radionuclides. It is particularly useful where groundwater is accessible from the surface. However, because it involves above-ground treatment, facilities need to be constructed to house and secure the treatment systems. These facilities often require heating and constant security.

Air Sparging Method:

  • Air Sparging is an in-situ remediation technology that involves injecting air or other gases into the groundwater to clean up contaminated groundwater and soil. This method typically uses small diameter PVC wells, either vertical or horizontal, through which air is injected into the saturated soil layers beneath the groundwater level. The injected air moves through the soil, acting much like an underground air stripper. This process volatilizes (turns into vapor) the contaminants in the groundwater, allowing them to rise to the unsaturated zone above the water table. Once there, these vaporized contaminants can be captured and treated above ground. This technique is often used in conjunction with Soil Vapor Extraction (SVE), which helps capture and control the contaminated vapors released during the air sparging process. Besides volatilization, air sparging can also aid in aerobic bioremediation, which is the breakdown of contaminants by naturally occurring microorganisms that use oxygen. Sometimes, gases like ozone are used instead of air to enhance the effectiveness of the remediation. Air sparging is well-suited for sites contaminated with volatile organic compounds (VOCs), both chlorinated and non-chlorinated, and is particularly effective for treating concentrated areas of contamination. It also supports the natural cleanup processes in the environment (monitored natural attenuation) in areas downstream from the contamination.

Chemical Oxidation Method:

  • Chemical oxidation is a treatment process that uses strong chemical oxidants to degrade toxic organic chemicals found in contaminated sites. Common oxidants used include peroxide, ozone, and permanganate, each varying in strength and effectiveness. This method can completely destroy many harmful chemicals and make others more manageable for bioremediation. Chemical oxidants are highly efficient in degrading contaminants like aliphatics (TCE) and aromatic compounds (benzene), often achieving more than 90% destruction rapidly. The success of these treatments depends on properly matching the oxidant and delivery method to the specific contaminants and site conditions. Effective contact between the oxidant and the contaminants is critical, influenced by how the oxidant is introduced to the subsurface and the soil conditions present.

Multi-Phase Extraction Method:

  • Multi-Phase Extraction, also known as dual-phase extraction, vacuum-enhanced extraction, or bioslurping, is a versatile cleanup technology that simultaneously removes various forms of contamination from the subsurface, including contaminated groundwater, Non-Aqueous Phase Liquid (NAPL), and soil vapor. This is achieved through a high vacuum system that extracts these substances through recovery wells. Once extracted, the contaminated groundwater, NAPLs, and vapors are separated and treated using various technologies such as Granular Activated Carbon (GAC), thermal oxidation, and air stripping. These treatments depend on the type of contaminants present. MPE is particularly effective at sites contaminated with light and more viscous Non-Aqueous Phase Liquids such as gasoline, diesel, jet fuel, hydraulic fluids, and waste vehicle oils.

Slurry Walls:

  • Slurry walls are a containment technology primarily used to control the spread of contaminated groundwater and/or Non-Aqueous Phase Liquids (NAPLs). This method is effective in enhancing recovery systems and diverting contaminants away from sensitive areas such as drinking water sources or surface water bodies. The process involves excavating a vertical trench and filling it with a mixture primarily composed of soil, bentonite (a type of clay with low permeability), and water. This mixture is designed to stabilize the trench during excavation and to form a barrier that significantly reduces the flow of groundwater. Slurry walls are generally installed up to 100 feet deep and range from 2 to 4 feet in thickness. For optimal effectiveness, the base of the slurry wall is anchored into a low-permeability layer like clay or bedrock to minimize leakage. This anchoring, known as “keying-in,” enhances the wall’s foundation and sealing capabilities. This method is recognized for its durability and cost-effectiveness, making it a viable option for long-term containment of a wide variety of contaminants, although special considerations must be made for chemical compatibility.


Enhanced Bioremediation Method:

  • Enhanced Bioremediation is a natural and effective method for cleaning up contaminated soils and sediments by boosting the activity of naturally occurring microorganisms. These microorganisms are capable of degrading organic contaminants or immobilizing inorganic contaminants through the strategic addition of nutrients, oxygen, or other biological amendments. While effective in various climates, bioremediation requires temperatures above freezing to maintain microbial activity. In colder climates, engineering controls may be necessary to sustain appropriate temperatures. Enhanced bioremediation is particularly suited for degrading organic contaminants like petroleum products, including gasoline and diesel. It effectively breaks down compounds such as BTEX (benzene, toluene, ethylbenzene, xylene) and Polynuclear Aromatic Hydrocarbons (PAHs) under aerobic conditions.

Excavation and Off-site Disposal Method:

  • This method involves the physical removal of contaminated soil or sediment, which is then transported and disposed of or treated at an approved facility. It is a direct and often effective approach to address contaminated sites. Excavation and disposal can be used for most types of contaminants and is generally limited only by the practicality of accessing the contaminated material. Excavation may be infeasible if the contamination is under buildings, at great depths, within bedrock, or in other sensitive areas.

Soil Vapor Extraction (SVE) Method:

  • Soil Vapor Extraction is an in-situ remediation technology that uses a vacuum to extract volatile organic compounds (VOCs) and some semi-volatile organic compounds (semi-VOCs) from the soil. It’s primarily used to treat contamination above the groundwater table by inducing airflow through the soil to capture and remove contaminants. SVE is particularly effective for removing contaminants with high volatility or those that can easily transition to a gaseous state under ambient conditions, such as gasoline and chlorinated solvents. The technology works best in soils with good permeability. In soils like silts and clays, which have lower permeability, the radius of influence of the vacuum is reduced, and more wells may be necessary to adequately address the contamination. SVE is not suitable for remediation of heavy oils, metals, PCBs, and dioxins, as these contaminants do not volatilize easily.

Solidification/Stabilization (S/S) Method:

  • Solidification/Stabilization is a remediation technique that reduces the mobility of hazardous substances by physically and chemically trapping contaminants within the medium they inhabit, such as soil or building materials. This method does not remove contaminants but instead makes them less likely to leach into the environment. Common application techniques include using auger/caisson systems and injector head systems, which introduce S/S agents directly into the contaminated soil. For contaminants that pose a risk of vertical migration, bottom barriers (like grout injection barriers installed via directional drilling) are used to provide an impermeable floor beneath the waste. S/S can be employed as a standalone method or combined with other treatment and disposal techniques. Depending on the treatment, the stabilized material might be suitable for safe land disposal or even beneficial reuse.

Vapor Intrusion Mitigation (VI) Method:

  • Vapor intrusion refers to the movement of hazardous vapors from contaminated soil or groundwater into buildings. This is most common with volatile organic compounds (VOCs) from sources like dry cleaners, underground storage tanks or industrial processes. Effective mitigation strategies are crucial to prevent indoor exposure to these vapors. Common VOCs include chlorinated solvents like tetrachloroethene (PCE), trichloroethene (TCE), and benzene. While it does not remove the source of the contamination, it effectively prevents hazardous vapors from entering indoor environments, thus protecting building occupants. This method combines engineering controls and building modifications to provide both immediate and long-term protection against vapor intrusion.

Mitigation Techniques:

    • Sealing and Capping: Sealing floor defects, capping sumps, and using vapor barriers (EverCrete®) on concrete surfaces can effectively reduce vapor entry.
    • HVAC Modifications: Adjusting the HVAC system can mitigate stack effects, where heating systems create negative pressure that draws in vapors.
    • Sub-Slab Depressurization Systems (SSDS): Both passive and active SSDS are effective at mitigating vapor intrusion. These systems involve installing piping beneath the building slab to vent vapors outside, with active systems using a blower to create a vacuum.

Reach out to us to find out more about our remediation solutions and how they can benefit your site.

Final Thoughts

The data doesn’t lie – environmental contamination is alarmingly widespread across property types and environmental media. AEI’s latest Phase II ESA research found contamination at a staggering 80% of sites assessed in 2023, with over half exceeding regulatory limits.

From volatile compounds in soil vapor to persistent pollutants in groundwater, no area is immune. Identifying and addressing these issues through comprehensive site investigations is crucial for mitigating risks to human health and the environment.

At AEI, we provide rigorous environmental due diligence assessments backed by decades of experience. Our commitment extends beyond detection to delivering tailored, innovative remediation solutions that treat the source of contamination.

Don’t leave your property’s environmental safety to chance. Partner with AEI’s trusted experts to conduct a thorough Phase II ESA today. Safeguard your investment, ensure compliance, and pave the way for responsible site management by taking action now. Contact us to learn more about our environmental assessments and remediation solutions for your property.

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