Site Screening – Using On-Site Soil Testing To Reducing Uncertainty in Phase II ESAs

When completing a Phase II Environmental Site Assessment (ESA), proper site characterization is essential to the investigation. It is important to gain a clear understanding of site conditions in order for the Qualified Person (QP) to give an accurate report at the conclusion of the ESA.

On-site screening is one strategy that strengthens the investigation and allows for increased understanding without significant additional cost. By screening the soil samples on-site uncertainty is reduced and the property owner is equipped to confidently make decisions about the site.

Seeing the Whole Picture

Imagine this – you’re looking at a photo where 3% of the pixels are revealed. These pixels have exceptional resolution and are entirely accurate, but don’t provide the information needed to understand what the picture shows.

In contrast, imagine a photo where all the pixels are revealed, but at a lower resolution. The resolution is lower, the accuracy is good, and they provide enough clarity that you can see what the image is supposed to be.

Traditional environmental soil sampling is like a picture with a fraction of the pixels revealed. Samples are taken from a few select areas on site, based on the engineer’s research on areas that may show environmental issues, and are sent for testing at an accredited laboratory. These samples often show a very limited picture of the actual condition of the site.

What is On-Site Screening?

On-site screening uses advanced technology to analyze a soil sample for a number of contaminants with screening level accuracy within minutes. This means that up to one hundred samples can be processed in a day on site.

The results of the on-site soil testing can be imported into data visualization tools by a mapping specialist on the environmental site assessment team. The sampling results are analyzed and presented on a simple, clear map.

With this map, the engineer can direct further sampling in the area, or move on to another spot. Within hours, an entire site can be screened and the site owner can be confident that the whole picture is understood, not just a few pixels.

An On-Site Screening Approach

When the AEL team uses on-site testing as part of a Phase II ESA, the QP begins with a general sampling plan, often in a grid or clustered around areas of concern, and uses the initial results to choose areas for further sampling.

This technique is called adaptive clustering sampling (based on the Triad approach recommended by the US Environmental Protection Agency (EPA)), and provides the required thoroughness and flexibility to delineate metals contamination in a timely and cost effective manner. Essentially, adaptive sampling applies a fixed grid to the site and points on the grid can be chosen as initial sampling locations, either due to their position in an area of concern, or in areas with little historical data.

If no exceedance above a screening criterion is found, then the adjacent grid point in a direction of known contamination will be sampled. By the use of this iterative process the extent of contamination can be fully delineated in a shorter amount of time than through a set sampling methodology that does not adapt to real time on-site findings. By using a gridded sampling approach it will be possible to fully delineate remaining gaps in data on a site with fewer points. Adjustments to the grid size can be made where more/less delineation is required.

Upper Limits and Lower Limits

AEL uses statistical analysis to determine what screening level result is considered the cut off for considering an area “clean”. By establishing correlation charts for specific contaminants by comparing on-site testing results to CALA laboratory results in the same sample, AEL’s engineers can determine what limits to set.

If the MOE’s allowable limit for lead in residential soil, for example, is 120 µg/g of soil, and the correlation results show that the screening has a statistically significant accuracy of ±10 µg/g, the team will use the XRF and consider soil with readings above 110 µg/g to be impacted. The work can proceed efficiently and without the added delay of waiting for more laboratory sampling. AEL takes final closure samples and sends them to a CALA laboratory to confirm that the impacts have been delineated or removed, based on project objectives.

Because AEL carefully analyzes statistical correlation, the team has had a 98% success rate in reaching the limits of impact prior to closure using on-site testing. AEL is very proud of that level of success and credits that with saving time and money for clients.

In Canada’s Far North and other remote regions, this approach to site sampling is obviously beneficial and perhaps the most useful and efficient way to direct site work where lab access is limited and time consuming. For any Phase II ESA in Ontario, on-site screening can be a very efficient method to reduce uncertainty.