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Pre- and Post-Job Soil Sampling for Heavy Metals: What Do We Really Know?

TUESDAY, JUNE 26, 2018

By Kevin Guth


More items for Environmental Controls

Removing paint that contains heavy metals from a structure presents many risks to both the owner and the contractor performing abrasive blasting and painting. Contractors erect elaborate containment and ventilation systems to mitigate environmental impact. Air sampling and soil sampling are the key metrics used in the abrasive blasting and painting industry to evaluate the efficacy of a containment system.

If we are going to rely on environmental sampling to measure impact associated with abrasive blasting and painting, we should use an acceptable and defensible sampling method. Moreover, we should use a removal and sampling method that is compatible with the objectives of the sampling campaign. Failure to consider the limitations of the sampling and analysis method combined with the misuse of the intent of a given method can result in the generation of less-than-useful environmental data.

Soil Sampling and Project Specifications

Routinely, project specifications have adopted SSPC’s soil-sampling procedure in Technology Update No. 7 (Section 10 Ground (Soil) Sampling & Analysis) without appreciating the limitations of what has been specified. Similarly, contractors have in some cases adopted the SSPC soil-sampling procedure even when it is not specified.

Soil sampling
Courtesy of the author

Some specifications invoke TU7 to determine whether soil remediation will be required, but the document itself states that it "is not suitable for site characterization purposes."

More concerning is when the specification states that if the post-job soil sample is X percent above the geometric mean, soil remediation will be required. This is problematic because Technology Update 7 specifically states that it "is not suitable for site characterization purposes.”

If TU7 is not to be used to characterize a site, should it be used as a means to require remediation? The answer is clear: It should not be used in that fashion. The SSPC Technology Update No. 7 procedure should be viewed as a qualitative test.

TU7 advises sending in soil sample plugs to a lab for analysis, but the results reported by the lab can only reliably relay the presence or absence of a given analyte in the surface soil. A result (value in parts per million or milligrams per kilogram) will be generated by the lab, but does it represent the true concentration of the area it is purported to reflect? The answer is no.

This is not a knock on the SSPC soil-removal and analysis procedure. There is utility in the procedure being easy to use and easy to apply in the field to determine if metals are present or not. In fact, TU7 filled a much-needed knowledge gap in the industry when it was introduced. It is not SSPC’s fault the procedure has been adopted and used inappropriately.

Soil Sampling (Risk Characterization)

For risk-characterization purposes, providing defensible, quality environmental data will require a discrete soil sampling method that can reliably measure the accuracy, precision, completeness, representativeness and comparability for both the field sampling and the analysis of the samples. 

The objective of taking pre-job soil samples is presumably to generate data to quantify the presence or absence of lead (and other heavy metals). To meet this objective, samples removed during the collection stage must be defensible to meet this objective. Guide TU7’s soil sampling procedure is silent regarding these measurement quality objectives. 

Soil
© iStock.com / Pro2sound

For risk-characterization purposes, providing defensible, quality environmental data will require a discrete soil sampling method that can reliably measure the accuracy, precision, completeness, representativeness and comparability for both the field sampling and the analysis of the samples.

Even when using an accepted discrete soil sampling method that meets typical regulatory mandated measurement quality objectives, the error associated with field sampling of metals in the soil is concerning. Hadley & Petrisor (2013) found:

It has been clear for some time that the major sources of error in soil sampling for chemical contamination come not from laboratories but from field sampling and subsampling. This situation is—and should be—of concern to environmental forensic scientists.

In 2014, the Hawaii Department of Health issued a report entitled Decision Error Associated with the use of Discrete Soil Sample Data in Environmental Investigations in which it detailed the findings of a field study that was conducted to answer three questions posed by Brewer, Peard, Nakayama & Heskett (2014):

  • How different might the result be if the lab selected another random test portion of soil from the discrete sample submitted? 
     
  • How different might the result be if the discrete sample collection point was moved over a few inches or a few feet?
     
  • How many discrete sample points need to be collected and averaged to achieve a representative sample result for the area investigated?  

Brewer, Peard, Nakayama & Heskett (2014) found:

The results of the study indicate that the reported concentration of a contaminant for a sample point can indeed vary dramatically, due to random, small-scale variability of contaminant distribution in soil both at the scale of a traditional discrete sample lab test portion, and within a short distance of any given sample location point. 

The study also indicates that because of this small-scale variability, relatively large numbers of discrete samples (e.g. more than 24) would need to be collected and averaged to adequately characterize soil contaminants in selected decision units, and that for some contaminants or sites the number of discrete samples required for a representative average could be much higher.

It is apparent that the Ground (Soil) Sampling & Analysis procedures outlined by Technology Update No. 7 is not intended for risk-characterization purposes, and is clearly inadequate to determine if cleanup should be required on a project site after the completion of a project. As a result of the lack of measurement quality objectives, the interpretation of pre and post soil sampling results obtained using TU7 methodology should be taken with a grain of salt.

The TU7 soil-sampling procedure has served a very useful purpose in the industrial abrasive blasting and painting industry; however, recognize that using this document for risk characterization purposes will arguably yield scientifically indefensible environmental data.

References

Hadley, P. W. and Petrisor, I. G. (2013). Incremental sampling, challenges and opportunities for environmental forensics. Environ. Forensics 14, 109–120.

Brewer, R., Peard, J., Nakayama, J. & Keskett, M. (2014). Hazard Evaluation and Emergency Response. Hawaii Department of Health (HDOH).  Decision Error Associated with the Use of Discrete Soil Samples in Data in Environmental Investigations:  Part 1: Field Investigation of Discrete Sample Variability.

ABOUT THE BLOGGER

Kevin Guth

Kevin is serving as the Principal for KGC, where he oversees all aspects of business and technical operations. For the past 21 years he has provided senior oversight and management of KGC’s most complex industrial hygiene and hazardous waste management projects. Kevin holds a Master of Science in Public Health (Specialty: Industrial Hygiene) from the Tulane School of Public Health and Tropical Medicine and is currently pursuing his Doctorate in Public Health (Specialty: Occupational Health) from the University of South Florida. He is a Certified Industrial Hygienist (CIH) and certified Project Management Professional (PMP).

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Tagged categories: Abrasive blasting; Cleanup; Containment; Environmental Protection; Industrial Hygienists; Paint disposal; Surface preparation

Comment from Michael Halliwell, (6/28/2018, 12:05 PM)

Kevin, you are quite correct. due to the characteristics of heavy metals they can be extremely variable in soil. From my past work sampling bridge rehab jobs, we've done our sampling based on soil science and statistical probability rather than the fairly broad strokes from TU7. We've tried to incorporate the linear source of a bridge and local prevailing weather and environmental conditions to identify pre-disturbance soil sampling locations and likely "worst case" locations. We've also used substantial numbers of sampling points to get a good idea of the overall soil metals profile around the bridge before the work and used area samples rather than single discrete samples, at each sampling location. We end up with more of a surficial soil survey around the bridge before the work starts and can often see variations in metals content that are in general agreement with what you'd see from modelling the deposition from a linear source. After the work, we replicate the sampling program (i.e. within 1' / 30 cm). If there are substantive changes in a sample, we have the lab re-run the test from a different portion of the sample and evaluate both sample results for unacceptable duplicate variation. If not acceptable, additional sampling is done t that location. The assessment of impact (if any) and remediation area (if applicable) come only after substantial and defensible work has been carried out. It might cost a few more dollars to sample it this way, but it is far cheaper than what a needless remediation would cost.


Comment from Justin Beitzel, (6/28/2018, 4:00 PM)

Kevin, Great article. If limited soil sampling conducted on bridge rehabilitation projects according to SSPC-TU7 produces a qualitative result. Wouldn't pre-job visual soil inspection, visible accumulation inspection/remediation during construction and post-job visual soil inspection serve a useful function?


Comment from Thomas Van Hooser, (6/29/2018, 8:51 AM)

Very informative. Thank you!


Comment from Tom Schwerdt, (7/2/2018, 9:01 AM)

Michael, is there a published method you follow - or was this developed inhouse?


Comment from Michael Halliwell, (7/13/2018, 12:14 PM)

Tom, the technique was borrowed from an agrologist who specialized in topsoil assessments. When I am back in the office next week, I'll see if I can dig it up (I understand it is based on local standards).


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