Your location: Home » Resources » White Papers » Investigating Metals

INVESTIGATING METALS

Due diligence investigations designed to confirm the presence or absence of potential contaminants at industrial properties often include sampling and analysis for metals. The evaluation of such data can be complex due to the natural presence of metals in soil and groundwater. In contrast, many chemically engineered organic compounds such as chlorinated solvents, gasoline additives and polychlorinated biphenyls are not naturally occurring and when encountered in the environment they are readily identified as anthropogenic.

There are numerous industrial processes that historically and/or currently use metals and generate metal containing wastes. Some of the more common uses of metals are in coatings and platings, pigments, dyes and paints, wood treatment, explosives and ammunition, metal refining and fabrication, plastics, and in technical equipment. In simplest terms, metals are widely used in industrial processes.

There are several waste streams in which metals enter the environment. The three basic mechanisms are through incineration, wastewater effluent, and landfilling. These waste streams can create large areas affected by anthropogenic levels of metals. Incinerators produce fall out “shadows” that impact surface soils. Landfilling of materials such as foundry sand, slags and ash and the use of concentrated fertilizers have been historically uncontrolled and can impact soils and groundwater in a seemingly random pattern. Untreated effluent has historically impacted biota, sediments and water of the Great Lakes and many of the major rivers of the country.

Metals are also found at naturally occurring concentrations throughout the country. The concentrations can differ significantly from one region to another and are influenced by their source soil and rock materials. Several studies have been conducted by the United States Geological Survey (USGS), United States Department of Agriculture (USDA), state conservation programs, and academic programs to map the range of naturally occurring metals concentrations across the country. Third-party sources of naturally occurring metals concentrations should be referenced whenever conducting investigations that include metals analysis.

Many of the state’s brownfields and/or voluntary cleanup programs incorporate methodology to evaluate metals concentrations in reference to background concentrations. Several states, including Ohio, even have generic background levels established through a statistical evaluation of statewide soil concentrations. Most programs also provide methodology to establish site-specific background concentrations. These programs have risk based evaluation tools to assess exposure risks to metals concentrations that exceed reasonable background. Typically, the risk based evaluation focuses on the solubility of the metal, soil matrix, soil pH, and depth to groundwater.

Several metals, arsenic in particular, often occur at natural concentrations that exceed protective risk based concentrations. In several states, the published generic background levels of arsenic are higher than the generic risk based value when evaluated as a carcinogen.

Acceptable arsenic concentrations in potable water have been a high profile debate for the past several years between potable water suppliers and the U.S. EPA in a battle over cost versus health effects, respectively. Based on numerous medical research findings we’ve known for several generations that high arsenic concentrations in potable water has a detrimental health effect.

The laboratory analysis of metals can be conducted for a single metal or a group of metals using a number of approved methods. Typically if there is not a particular metal of concern or there are several metals of concern, due diligence investigations will be designed to evaluate a particular group of metals. Several states have unique target metals lists. Common nationally used lists include the RCRA 8, Priority Pollutant List 13 and the Target Compound List 23. Grouping the analysis of two or more metals typically reduces the overall analytical cost on a per metal basis.

The sampling and analysis of metals in soils is typically conducted using analytical methodologies that evaluate total or leachable concentrations. The leachable result is a sub-concentration of the total that is most commonly used for waste classification purposes. However, leachable concentration in soil also provides quantitative information regarding the solubility and therefore potential to impact groundwater. The additional analysis of pH and valance state will also provide useful insight on the solubility of the metal.

Similarly, the analysis of groundwater samples for metals concentrations uses methods that evaluate total or dissolved concentrations. The sample collection and preservation techniques can have a significant impact on the analysis, and therefore, should be chosen based on the design and intent of the sampling plan. For typical due diligence investigations where the collection of groundwater is from a temporary well, it is preferred to submit samples for both total and dissolved analysis.

The remediation of elevated metals concentrations is difficult. In deeper impacted soils, stabilization techniques and engineering controls are used to control solubility. Developing technology such as electrokinetics suggests that metals in soil may be mobilized and collected. Impacted groundwater also requires an innovative cleanup strategy. Several methods can be used depending on environment. Reactive barriers work well in simpler groundwater flow regimes while pump and treat techniques work better where groundwater flow needs to be controlled.