How to Test Soil for Lead

How to test soil for lead in soil is easy following EPA Method 6200 (incorporated into SW486) guidelines, which validate the use of handheld XRF for soils analysis.  This method has been used for over a decade and continues to be useful in expediting soils remediation and monitoring.  Find out now how the Bruker S1 TITAN can expedite your remediation efforts using EPA Method 6200!

Below are the basic steps for how to test for lead:

  1. Determine Data Quality Objectives (DQOs) — figure out how “good your data has to be in order to meet the goals of the project. Do you need to do quantitative spot testing so you know exactly how much lead is in every survey spot, or will quantitative analysis only be necessary for certain areas? Or, will a pass/fail above or below a certain action level threshold be sufficient to guide your remediation process?
  2. Do not analyze moist soil — moisture effects XRF readings. Water attenuates x-rays, which means much of the information—in the form of fluorescent x-rays—available about the content of the soil sample is simply being “blocked” by water before making it back to the instrument’s detector. For quantitative analysis, dry your soil samples. For semi-quantitative analysis, soil may not contain more than 15-30% moisture.
  3. Do not analyze chunks of debris – sticks, shrapnel, rocks etc.
  4. Calibrate Instrument- this is referring to the calibration performed prior to use which involves a self-performing energy calibration to optimize the instrument for analysis.
  5. Analyze a blank standard — this will allow you to identify whether your instrument has any problems with false positives or if there might be some contamination on the analysis window or on the detector. The resulting data from a blank standard should contain none or trace amounts of the elements of interest.
  6. Verify calibration — analyze a known standard that includes targeted elements close to the range of your action level, and note the accuracy and precision of the result. Analyzing a “check standard” prior to beginning analysis for your project is essential, because it proves to you and to anyone else looking at your data that your instrument was functioning to-spec and producing accurate results.
  7. Analyze samples, and note the precision—precision tells you how “sure” the analyzer is of its calculations. Readings with low precision are not particularly meaningful, because low precision is an indicator of insufficient data for statistically certain quantitative analysis.
  8. Analyze blank standard – this provides proof that the instrument window has not picked up any contamination and that your calibration has not drifted.
  9. Analyze known standards, and note precision- this provides proof that the calibration has not drifted and you are able to obtain consistent results on the known standard you analyzed at the beginning of your analysis.
  10. Send 5% of samples to the lab for confirmation.

Recommendations for How to Test Soil for Lead Using Method 6200:

  • Sampling density—one of the chief advantages of not having to bring samples to the lab is the ability to take multiple readings on the spot, in any spot.  Methodically work a grid to determine the plume of contamination.
  • As you delineate the plume of contamination, your data quality objectives may change.  Adapt your data quality objectives to reflect your findings.                    

Quality Assurance:

  •  Verify your instrument is reading accurately by analyzing a blank and a known sample standard.
  • Choose a standard that is near your action level.  It is not useful to prove your instrument can analyze 5500 ppm lead (Pb) if your project has an action level of 20ppm lead.  Use a standard that is closer to that range i.e. 50ppm lead concentration.

 

 

Avoid the Pitfalls:

One of the major mistakes made with this method is not paying attention to precision on your readings.  XRF is one of the few instruments that actually shows reading uncertainty.  Use this to your advantage in 2 ways:  

Assume your target cleanup level is 100ppm:

  1. Analyze your sample until the error is satisfactory.  During initial sampling of your grid to determine the plume of contamination, continue measurement until your instrument provides reasonable certainty:
    100ppm + - 50ppm after 30 seconds is not reasonable certainty and requires a longer sampling time. Continue sampling until the precision on the instrument (+/- error) provides certainty well over the range of your action level. 100ppm + - 20ppm falls within the acceptable level of precision (20%) according to Method 6200.
  2. Stop sampling if certainty has been met.  Save time by doing the math as you go:
    2300ppm +- 500ppm after 20 seconds can be stopped since it is clearly over your action level even if you subtract the whole of the uncertainty: 2300 – 500 = 1800ppm.


Some sites are more naturally homogeneous than others when considering particle size of your sample.  Since XRF is affected by particle size, it is important to take steps to eliminate this affect.  By grinding your sample with a mortar and pestle and passing it through a sieve, you create particle sizes that are homogeneous and much more XRF friendly.

Don’t waste your time sieving down to the smallest µm sieve (i.e. 125 µm) if you obtain good data from sieving through a 250 µm sieve or if the improvement in data is less than 20%.  The Ziploc approach often saves time and delivers reasonable enough results depending on your DQOs.   Analyze directly into the bag once the large chunks are removed.

Avoiding the pitfalls:

 

  • Be certain to fill your XRF sample cup at least ¾ of the cup full.  XRF analyzers are calibrated for infinite thickness so if you do not have a thick enough sample to analyze, it will skew your results in an undesired manner.
  • Since XRF is nondestructive, send the same sample cup you analyzed with your XRF to the lab for analysis.  This ensures the closest possible corroboration of XRF results to lab results.


When used appropriately, Method 6200 can save time and money on sending all samples to the lab and waiting for the results.  Cut down sending 100 samples to 10 and enjoy the speed in which your project is completed.  Ask us any lingering questions you may have about Method 6200 now!

Precise XRF Soil Analysis with the Bruker S1 TITAN

The Bruker S1 TITAN boasts industry-leading precision in analysis of soil and soil samples, not to mention speed, accuracy, and ease of use. Contact us today to learn more about fully portable, ultra-fast S1 TITAN.

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