## 3 Results and Discussion
### Petroleum Hydrocarbon Composition of the Oily Sludges  
No BTEX, aromatic petroleum hydrocarbon fractions with a carbon chain shorter than C12 or aliphatic hydrocarbons with a carbon chain length <C16 were detected from the collected oily sludge samples. This suggests that the volatile petroleum hydrocarbons had already been completely emitted to the atmosphere prior to sample collection. The predominant aliphatic petroleum hydrocarbon fraction was C21-C35 (45,750 \(\pm\) 30,108 mg/kg, \(n\) = 16) for all the investigated samples. The distribution of the three major fractions is given in Table 1.  
No aromatic petroleum hydrocarbon fractions with carbon chains longer than C35 were detected from the 16 collected sludge samples. Fraction C21-C35 dominated the aromatic hydrocarbons. Fraction C12-C16 was present at a small amount or not detectable. The total aromatic hydrocarbon had a mean value of 12,461 mg/kg with a standard deviation of 7704 mg/kg (Table 2).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Location** & **C16–C21** & **C21–C35** & **C35–C40** \\ \hline
1 & 2400 & 35,000 & 4400 \\
2 & 2500 & 31,000 & 3000 \\
3 & 20,000 & 110,000 & 12,000 \\
4 & 3700 & 36,000 & 4100 \\
5 & 1400 & 28,000 & 3500 \\
6 & 1100 & 33,000 & 3600 \\
7 & 1200 & 23,000 & 2300 \\
8 & 6600 & 33,000 & 3500 \\
9 & 7200 & 45,000 & 3900 \\
10 & 870 & 27,000 & 330 \\
11 & 8100 & 56,000 & 4800 \\
12 & 4500 & 35,000 & 3400 \\
13 & 3500 & 27,000 & 2800 \\
14 & 15,000 & 100,000 & 11,000 \\
15 & 920 & 13,000 & 1400 \\
16 & 14,000 & 100,000 & 11,000 \\ Mean & 5812 & 45,750 & 4689 \\ SD & 5808 & 30,108 & 3481 \\ \hline \end{tabular}
\end{table}
Table 1: Concentrations (mg/kg) of aliphatic hydrocarbons in the oily sludge samples collected from the oilfield waste pit.  
Figure 1: Graph showing the thickness of oily sludge and the underlying contaminated soil at the 16 sampling locations within the investigated oilfield waste pit.  
There was a close relationship (R\({}^{2}\) = 0.9469) between the total aliphatic hydrocarbon and the total aromatic hydrocarbon in the only sludges (Figure 2). However, the ratio of total aromatic hydrocarbon to the total aliphatic hydrocarbon was around 0.2, indicating that over 80% of the total petroleum hydrocarbon was in aliphatic forms. [PERSON] and [PERSON] [23] determined petroleum hydrocarbon fractions in two petroleum hydrocarbon-contaminated sites and found that the aliphatic fraction C8-C16 and aromatic fraction C10-C21 were the major contributors to human health risk via all the exposure routes. The pre-dominant aliphatic fractions and aromatic fractions were all C21-C35 in the investigated sludges, suggesting that these sludge materials were unlikely to pose a high risk to human health.  
The total PAH in the sludge materials was only detected in 10 out of the 16 sampling locations with a very low value (<20 mg/kg). Only three PAH species were found in  
\begin{table}
\begin{tabular}{c c c c} \hline
**Location** & **C12–C16** & **C16–C21** & **C21–C35** \\ \hline
1 & 110 & 1500 & 7800 \\
2 & 130 & 1100 & 6400 \\
3 & 230 & 6200 & 24,000 \\
4 & 0 & 2000 & 9800 \\
5 & 0 & 850 & 6000 \\
6 & 0 & 1300 & 9200 \\
7 & 0 & 1100 & 7100 \\
8 & 0 & 2100 & 7500 \\
9 & 0 & 2400 & 9800 \\
10 & 0 & 790 & 7500 \\
11 & 0 & 2200 & 12,000 \\
12 & 0 & 1600 & 7700 \\
13 & 0 & 1400 & 6400 \\
14 & 270 & 4700 & 23,000 \\
15 & 0 & 510 & 2600 \\
16 & 180 & 3900 & 18,000 \\ Mean & 58 & 2103 & 10,300 \\ SD & 95 & 1559 & 6110 \\ \hline \end{tabular}
\end{table}
Table 2: Concentrations (mg/kg) of aromatic hydrocarbons in the oily sludge samples collected from the oilfield waste pit.  
Figure 2: Relationship between the total aliphatic hydrocarbon and the total aromatic hydrocarbon in the sludge samples.  
the sludge samples: chrysene, pyrene and phenanthrene (Table 3). Chrysene was the most common PAH species with its presence found in 8 out of the 16 sampling locations. Location 3 had the highest level of chrysene (10 mg/kg). Pyrene was only detected at Locations 1 and 6.