Mountain Laurel Environmental | The Phase III Investigation: Degree and Extent of Contamination
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The Phase III Investigation: Degree and Extent of Contamination

The last time we dealt with the Phase II Investigation, which confirmed the presence or absence of contamination. The Phase II was, in many ways, the most difficult phase of the investigation process. The goal of the Phase III Investigation is to determine the degree and extent of the contamination. Putting that another way, the Phase III should tell us how bad the contamination is and how far it goes. But why do we need to do this? Isn’t it enough to know contamination is present? The answer to that last question, generally, is “No, knowing contamination is present is not enough.” Here’s why…

The mere presence of contamination does not mean that clean-up is required. The need for clean-up (or not) is determined by the degree (or severity) of the contamination present. Unfortunately, contaminated soil and “clean” soil generally look pretty much the same. Let’s look at an example. Let’s say the Phase II identified Total Petroleum Hydrocarbons (abbreviated TPH) in the soil at a concentration of 250 parts per million (ppm). TPH is, essentially, oil. In Connecticut, the Department of Environmental Protection (CTDEP) most stringent criteria only require the soil to be cleaned up if TPH exceeds 500 ppm. So in our example, the concentration of TPH would not trigger a clean-up. Here’s the problem: we don’t know if the sample with 250 ppm TPH represents the worst of the contamination. If we took a sample five feet away, the concentration of TPH could be 500 ppm, or 50,000 ppm, or 2 ppm. We don’t know. In the Phase III, additional soil samples would be collected to determine where the worst of the contamination. I should mention that we not only look at the horizontal extent of the contamination, but also at what depth the worst contamination is located. Remember, if an underground heating oil storage tank is leaking, the worst contamination will be found under the tank, say at a depth of six feet, but no contamination will be found on the ground surface or soil at shallow depths. Alright, let’s summarize this in a sentence or two: In order to determine if clean-up is required, we need to know the highest concentration of contamination. The Phase III Investigation tells us what the highest contaminant concentration is and, based on that, if clean-up is required.

There is another reason to determine the degree and extent of contamination. In order to estimate the cost of a clean-up (if needed) we need to know how much contaminated soil is present. Often, contaminated soil is dug up, loaded into trucks, and taken to a disposal facility. The disposal facility charges by the ton or cubic yard of soil, so the more soil you have to remove the more it costs to clean up. The quantity of contaminated soil also affects clean-up costs in less direct ways. The more contaminated soil, the longer it takes to physically dig up and load into trucks. That means the workers who get paid by the hour have to be on the site longer and the excavation equipment that is charged by the day is on the site longer. In addition, the more contaminated soil that must be removed, the more trucks are needed to carry it away. Again, summarizing this: the Phase III tells us how much contaminated soil must be removed and, based on this, helps us determine what the clean-up costs will be.

So far we’ve only talked about soil, but groundwater can be contaminated as well. Groundwater is water that resides in the spaces between soil grains. Groundwater moves generally downhill through the soil, carrying contaminants along with it. The contaminated groundwater is known as a “plume”. Just as with soil, we need to know the degree and extent of contamination in groundwater in order to determine if clean-up is needed and to determine the costs. Since groundwater moves, we also have the added concern that contamination can be carried to off-site drinking water wells or to streams and river. Contamination in groundwater can potentially affect people drinking water from downhill wells, people eating fish or shellfish from downhill streams and rivers, and the aquatic animals and plants themselves. Groundwater is investigated by installing monitoring wells and then collecting water samples. In order to determine if groundwater clean-up is required, we need to know the highest concentration of contamination. The Phase III Investigation tells us what the highest groundwater contaminant concentration is and, based on that, if clean-up is required.

The cost of groundwater clean-up, if needed, is also dependent on the quantity of contaminated groundwater. There are several ways groundwater can be cleaned up. Water can be pumped out of the ground from wells and run through a treatment system. The more contaminated groundwater present, the more wells are needed, the more pumps are needed, the larger the treatment system is needed, and the higher the cost. Groundwater can also be treated by injecting chemicals and/or bacteria into the wells to increase natural degradation of the contamination. The more contaminated groundwater present, the more wells are needed, the more chemical or bacteria medium is needed, and the higher the cost. The Phase III tells us how much contaminated groundwater must be cleaned up and, based on this, helps us determine what the clean-up costs will be.

There is one final reason for conducting a Phase III Investigation. If you recall, the Phase I Site Assessment described where contaminants may have been released, where it may have migrated, and, ultimately, what the distribution of contamination is likely to be. The Phase III determines the actual distribution of contamination, which should match the anticipated distribution from the Phase I (within reason). If these distributions differ significantly, it may indicate that an additional release occurred or that we don’t fully understand how the contamination was released and migrated. This, in turn, may mean that we missed some contamination. Stating this in a more understandable way: The data from the Phase III Investigation serves as confirmation (or not) that our original theory as to how contamination was released, where it travelled, and where it ultimately ended up. If the Phase III data supports the original theory we (and the regulatory agencies) are more confident that the property can be cleaned up.

Daniel White
Daniel White
Daniel.White@mountainlaurelenvironmental.com

Daniel White is a Connecticut Licensed Environmental Professional (LEP License #447) and holds a Bachelor of Science degree in Marine Science/Geology from Long Island University and a Master of Science degree in Earth Science/Hydrogeology from Adelphi University. He has been a member of the environmental consulting industry since 1991, including more than 5 years in the Remediation Division of the Connecticut Department of Energy and Environmental Protection. Daniel has been involved in a wide range of environmental investigation and remediation projects including leaking home heating oil tank, commercial properties, gasoline service stations, large industrial complexes, and Superfund sites.