The analysis of and detection of coal tar has seen a significant increase in the last few years. This is linked, primarily, with an increased focus on thorough waste classification and some long running nationwide initiatives such as the Streetworks Project. It encompasses all the regional water companies and activities in line with the Regulatory Position Statement RPS211 relating to the excavated waste from utilities installation and repair, the withdrawal of which was delayed until April 2023 due to the scale of works underway and still requiring of completion.

One of the challenges facing laboratories is the lack of standardization in the specification of requirements from the clients and also the analysis itself. As an area not fully understood in terms of hazardous classification, it became beholden on the labs to put forward a range of approaches that would encapsulate the variety of client specifications while also providing what was hoped would be sufficient levels of detail to allow for the onward use of data for a range of purposes.

A recent review through the AGS Laboratories Working Group revealed a range of techniques, some common themes and a potentially confusing landscape for the industry to navigate in order to secure a fit for purpose and cost effective solution.

The two primary sources of information which influence the testing requirements, other than the labs individual clients are the EA WM3 (1^st Edition v1.2) Technical Guidance and the ADEPT Guide to Managing Reclaimed Asphalt (Version 2019 revision 1).

From section 3.2 of WM3, we have the following based on the knowledge that coal tar is present:

• Coal tar levels over 0.1% result in a hazardous classification to HP7,
• The total must be inclusive of all compounds, polycyclic aromatic hydrocarbons (PAH) concentration alone is not sufficient,
• If the concentration of Benzo(a)pyrene (B(a)P) is less than 0.005% of the coal tar then HP7 does not apply.

Looking specifically to Asphalt waste already classified  under 17 03 01* or 17 03 02 (bituminous mixtures that do/don’t contain coal tar respectively) then we also have to consider:

• If B(a)P is greater or equal to 50mg/kg in the Black top alone then the amount of coal tar should be considered to be sufficient (0.1%or more) to be considered hazardous and coded 17 03 01*.

The ADEPT guidance provides more specific focus on the managing of reclaimed asphalt and provides information in to the classification of waste. It reiterates and references WM3 and the 0.1% threshold for coal tar and also the use of the 50mg/kg level for measuring B(a)P should the total coal tar concentration not be available for measurement.

What the ADEPT guidance then gives, is a clear and defined protocol for sampling, sample preparation, sample volumes and data review with also indication of analytical requirements and basic principles.

The document gives details and refences to specific British Standards for the sampling and preparation of road plannings and road cores (BS 932 and BS 12697), and then recommends the following testing;

• PAH analysis in the laboratory by gas chromatography mass spectrometry (GCMS) for the USEPA16 suite of PAHs, though only B(a)P may be necessary. It is worth noting here that labs will test for the full suite in a single process so requesting B(a)P only will usually give no cost or speed benefit. Should further characterisation for landfill disposal be required then the USEPA17 suite inclusive of coronene should be used,
• Screening methods such as PAK marker sprays or Acrylic White sprays can be used but validated by the use of frequent ‘full’ analysis,
• Specifies the use of Monohydric Phenol (Phenol Index) testing, with a potential requirement to speciate the individual compounds (Phenol, Cresols and Xylenols) should the levels be sufficiently high.

In terms of data review the 3 potential outcomes are

1.Classed as Inert for the purposes of the Quality Protocol for Aggregates from Inert Waste if:

a. The guidance of sample numbers has been observed,
b. All the B(Aa)P results are below 25mg/kg,
c. There are ≥3 results.

2. Classed as Hazardous and treated accordingly is:

a. All the B(a)P results are above 50mg/kg

Note: If there are limited results and close to the threshold then further investigation is      required

3. Full statistical analysis required to make assessment if:

a. Some or all results are above 25mg/kg and below 50mg/kg

The incorporation of the Waste Acceptance Criteria (WAC) testing for characterization and landfill disposal is a good example of where labs adapt to meet the broader requirements of the customer. From the recent AGS LWG study, we can see a number of consistent elements:

• • Quantification of PAH compounds including B(a)P,
  • ‘Total’ extractable material/coal tar, usually by Dichloromethane (DCM) extraction and quantification either gravimetrically or by GCMS
  • ‘Forensic’ identification of coal tar

There is little to no consistency as to the how, but the principles all involve the selective identification of 1 or more marker compounds (Benzothiophene was common but arrange of other phenols, heterocyclics and aromatics were used) by GCMS

And then also often included in the suite we can see:

• A range of more traditional TPH tests, from a straightforward C10 – C40 extractable Hydrocarbons to a more thorough TPHCWG range from C5-C44 including Aliphatic and Aromatic breakdown,
• A Chromatographic interpretation of the hydrocarbon source
  • Usually taken from the TPH analysis, done either as a general identification against a library of standard chromatograms to identify exactly what fuel source is present, presumably should it not be Coal Tar. A specific determination of whether the hydrocarbon source can be identified as either diesel or weathered diesel. While neither of these are specifically relevant to Coal Tar, as part of the Classification process within WM3 when considering hydrocarbon contamination then should coal tar not be the issue, varying caveats can be applied to the hazardous threshold should the contamination be of a specific type and the laboratory identification of diesel as a source is one the most prevalently used.
• Phenolics
  • Either as a simple Monohydric Phenol (compounds containing one hydroxyl group) of a speciated output using HPLC or GCMS to identify specifically the Phenol, Cresol and Xylenol content amongst a range of other phenolic compounds.

The running of additional testing may seem extraneous based on the specific context of your project at that stage, but consideration of any subsequent stages may give rise to a more comprehensive suite. The relative costs of laboratory testing compared to the associated site costs in holding/transporting/disposing of waste materials are low, so a comprehensive approach may present a more cost effective solution.

It is also worth revisiting the question you are trying to answer, as the specific identification of coal tar may be of secondary importance to the quantified PAH, specifically the B(a)P results, in terms of onward management.

As with any project involving lab work, the overarching recommendation would always be to consult with your lab at the outset and throughout to discuss options and define a project specific set of requirements rather than looking for a default or ‘standard’ solution, especially in an area like waste and waste classification where standard solutions are a thing we can still only imagine.

References:

• Guidance on the classification and assessment of waste (1st Edition v1.2.GB) Technical Guidance WM3 (October 2021)
• ADEPT Guide to Managing Reclaimed Asphalt Version 2019 Revision 1 (August 2019)

Article provided by Will Fardon (Technical Director, Chemtech Environmental Limited) on behalf of the AGS Laboratories Working Group