Quick Calibration Method for Accurate TPH Analysis in Soil at Remote Sites without the need for Laboratory Analysis

Poster Presentation

Prepared by , R. Stewart, W. Lee, G. Webster

Contact Information: andrew.toop@ziltek.com; +61 8 8152 9390


Industry standard practice for measuring Total Petroleum Hydrocarbons (C10-C40) in soil involves sending soil samples to an off-site laboratory for analysis by GC-FID (US EPA Method 3510/8015). This process is time consuming (5-10 days) and costly (~100 USD/sample) and is not suitable for remote sites.
RemScan is a handheld infrared instrument that measures TPH in soil in 20 seconds, with a similar accuracy to laboratory analysis. The technology is ideal for remediation activities at remote sites where real-time decisions can lead to significant cost savings by being able to accelerate project site closure.
While RemScan is a proven technology (Webster et al., 2016; Forrester et al., 2013) and is operating at many sites worldwide (Stewart et al., 2017), a site-specific calibration needs to be built for optimal accuracy. This calibrates the instrument and reduces the influence of soil texture and interferences such as carbonates and organic matter.
In the past, the site-specific calibration process has involved sending representative soils from the project site to an off-site laboratory for scanning and validation of selected samples using the GC method. This process can take 1-2 weeks and may involve quarantine procedures which can lead to further delays. This time impost is not a problem for large project sites that have nearby laboratory facilities especially where the instrument is going to be dedicated to a single project over several years. However, this calibration requirement can restrict the application of the technology at remote sites, where getting soil samples out of the site in advance may be difficult or impossible.
This paper presents a new method that allows the site-specific calibration process to be completed onsite within 1-2 days with no requirement for GC analysis. The method involves spiking representative clean soils at site with the appropriate petroleum (e.g. diesel, crude oil) and building a dilution series from 0 to ~100,000 mg/kg TPH. This series is then scanned and the infrared spectra are used to build an accurate calibration model which is uploaded to the instrument for immediate use. The calibration model is based on “theoretical” TPH values, which avoids the need to send any samples to an off-site laboratory. For quality control and assurance, users still have the option of validating selected samples at a later date at an off-site laboratory.
This new calibration method opens up market opportunities for quick closure of remediation projects at remote sites worldwide. Recently, the method has been used successfully at many remote locations globally including in the arctic, SE Asia, Europe and the Middle East. Data from these sites will be presented using the Root Mean Square Error (RMSE) as an indicator of accuracy against laboratory data.

G.T. Webster, J.M. Soriano-Disla, J. Kirk, L.J. Janik, S.T. Forrester, M.J. McLaughlin, R.J. Stewart, Rapid prediction of total petroleum hydrocarbons in soil using a hand-held mid-infrared field instrument, Talanta, 160 (2016) 410-416.
S.T. Forrester, L.J. Janik, M.J. McLaughlin, J.M. Soriano-Disla, R. Stewart, B. Dearman, Total petroleum hydrocarbon concentration prediction in soils using diffuse reflectance infrared spectroscopy, Soil Sci. Soc. Am. J. 77 (2013) 450–460.
R. Stewart, A. Toop, G. Webster,T.T. Chin, G. Paulus, Reducing Site Liabilities – Rapid Measurement of Hydrocarbons in Soil, Paper No. 185255, SPE Asia Pacific Health, Safety, Security, Environment and Social Responsibility Conference, 4-6 April 2017, Kuala Lumpur, Malaysia.