# Geotechnical Evaluation of Diesel Contaminated Clayey Soil
## 2 Materials and Methods
### Test Methods
#### 2.2.1 Chemical Elements Analysis of the Soil  
The elemental chemical characterization of soils was performed with a total reflection X-ray fluorescence spectroscope (S2 PICOFOX TXRF, Bruker Nano), equipped with a molybdenum tube and silicon drift detector. The S2 PICOFOX is a portable benchtop spectrometer for multi-element analysis of liquids, suspensions, and solids.  
Before analysis of the samples, a gain correction was performed with a mono-element standard sample (1 \(\mu\)g As). Further, the spectroscopic resolution (1 \(\mu\)g Mn) and sensibility analysis (1 ng Ni) of the spectroscope were performed according to the manufacturer instructions.  
The standard solutions of H\({}_{3}\)AsO\({}_{4}\) (1000 mg/L); SiO\({}_{2}\) (10,000 mg/L), Ni(NO\({}_{3}\))\({}_{2}\) (1000 mg/L); Fe(NO\({}_{3}\))\({}_{3}\) (1000 mg/L); Al(NO\({}_{3}\))\({}_{3}\) (10,000 mg/L); Ca(NO\({}_{3}\))\({}_{2}\) (10,000 mg/L), NaNO\({}_{3}\) (10,000 mg/L), KNO\({}_{3}\) (10,000 mg/L), (NH\({}_{4}\))\({}_{2}\)Ti\({}_{6}\) (1000 mg/L), Mg(NO\({}_{3}\))\({}_{2}\) (10,000 mg/L), Mn(NO\({}_{3}\))\({}_{2}\) (10,000 mg/L), and Zn(NO\({}_{3}\))\({}_{2}\) (10,000 mg/L) were obtained from Merck, with a quality for Inductively Coupled Plasma (ICP) test, traceable to the Standard Reference Material (SRM) from NIST. The necessary dilutions have been made from the stock solutions in order to achieve the linearity of the standard curve.  
The soil samples for elemental analysis were prepared as follows: 20 mg of soil was ground in an agate mortar and then passed through a No. 230 (63 \(\mu\)m) sieve. Then, the powder was suspended in 1 mL of dispersant solution (1% Triton X-100 in distilled water).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Method Applied** \\ \hline Water content 1  & ASTM D2216 [18] \\ Unit weight & ASTM D7263 [19] \\ Soil mineralogy & X-ray diffraction analysis \\ Chemical elements analysis & Total reflection X-ray fluorescence spectroscopy \\ Specific gravity of soil solids & ASTM D854 [20] \\ pH & NOM-021-RECNAT-2000 [21] \\ Particle-size distribution of soil & ASTM D6913 [22], ASTM D1140 [23] \\ Liquid limit and plastic limit & BS EN ISO 17892-12 [24] \\ Soil classification & ASTM D2487 [25] \\ Modified free swell index & [PERSON] and Rao [26] \\ Direct shear & ASTM D3080 [27] \\ Soil suction & ASTM D5298 [28] \\ Soil texture & NOM-021-RECNAT-2000 [21] \\ Electrical conductivity & NOM-021-RECNAT-2000 [21] (by the saturated \\ paste extract, soil to water ratio of 1:2.5) \\ Organic content & AASHTO T 267 (by loss-on-ignition) [29] \\ Cation exchange capacity & NOM-021-RECNAT-2000 (Kjendahl method) [21] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Evaluated properties of both natural and diesel contaminated soils.  
The soil suspension was spiked with 10 uL of gallium (1000 mg/L, ICP standard traceable to SRM from NIST, Sigma Aldrich, St. Louis, MO, USA) as internal standard.  
The suspension was then sonicated for 15 min, after which it was homogenized in a vortex agitator. Then, 10 uL of a sample solution was transferred into a siliconized quartz glass sample carrier and dried at 50 \({}^{\circ}\)C on a hot plate. The prepared soil samples were analyzed with a live collection time of 1000 s. Spectra acquisition and data evaluation were done by using the software Spectra 7.8 (Bruker Nano GmbH, Berlin, Germany).