## 1 Introduction  
Soil quality is a fundamental factor in plant growth and impacts the forests, wet-lands, jungles, prairies, and grasslands that support the planet's diverse vegetation. However, soil can become contaminated with biodiesel-diesel fuel, which can interfere with soil-forming processes [1]. When soil is contaminated with biodiesel-diesel, it is considered hazardous waste and can cause diffuse pollution in the environment. In order to properly treat contaminated soil through remediation methods, it is important to accurately measure the extent of the contamination. This helps to ensure that the soil can be restored to a healthy state and support the growth of plants and the overall health of the ecosystem. Conventional methods for observing the difference between contaminated soil with diesel fuel and uncontaminated soil can generally be divided into two categories. The first category is chemical analysis, which includes methods such as Gas Chromatography (GC) [2], Infrared spectroscopy (IR) [3], and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) [4]. These methods involve collecting a soil sample, extracting the contaminants of interest, and analyzing the extract using specialized equipment to determine the concentration of the contaminants present. The second category is physical analysis, which involves examining the physical properties of soil, rather than its chemical composition. Physical analysis is often preferred because it can be performed quickly and non-destructively, making it a cost-effective and efficient method for detecting contaminated sites. There have been a number of recent studies that propose various physical methods for measuring the dielectric properties of contaminated soil. For example, the authorsof [5; 6] introduced Time Domain Reflectometry (TDR). This method involves the use of a pulse generator and a reflectometer to measure the electrical properties of soil. TDR is a non-destructive method that can be used to measure the dielectric permittivity of soil. Dielectric Spectroscopy (DES) was proposed in [7; 8]. This method involves the measurement of the dielectric properties of soil over a range of frequencies. DES is typically performed using a network analyzer or a vector network analyzer. In [9; 10], Capacitance and Resistance Method (CRM) was introduced. This method involves the measurement of the capacitance and resistance of soil using a capacitor and a resistor. CRM is typically used to measure the dielectric permittivity of soil. The authors of [11] presented Frequency Domain Reflectometry (FDR). This method is similar to TDR, but it uses a continuous wave signal instead of a pulse signal. FDR is typically used to measure the dielectric permittivity of soil. Finally, Ground Penetrating Radar (GPR) methods were proposed in [12; 13]. This method involves the use of radar waves to measure the electrical properties of soil. GPR is a non-destructive method that can be used to measure the dielectric permittivity of soil. In this study, we will focus on using DES to measure contaminated soil because it has a wide frequency range [14], is non-destructive [15], can provide fast measurements [16], is versatile [17], and is easy to use. In this paper, we introduce to monitor of dielectric properties in contaminated soil with biodiesel-diesel blends. Specifically, we use the commercial grade diesel B7 (a mixture of 7% biodiesel and 93% diesel fuel, which is the main commercial diesel fuel in Thailand) to contaminate a sample of sand soil. We also study the measurement of dielectric properties in contaminated soil with the commercial grade diesel B7 heated by a dual electrode plate-based radio frequency heating system. This allows us to observe the behavior of the contaminated soil with biodiesel-diesel blends before and after Radio Frequency (RF) heating treatment. We expect the dual electrode plate-based radio frequency heating system provide greater penetration than microwave heating systems due to lower frequencies.