Experiment Study On Dielectric Properties Of LNAPL Contaminated Soil

Light Non-Aqueous Phase Liquid (Referred to as LNAPL)–Class of liquid thatthey are less dense than water and have low solubility in water. Petroleum productsare the most common of LNAPL, such as gasoline, diesel etc. More attention hasgradually been paid on the problem of LNAPL leakage contaminated soil andgroundwater. The LNAPL leak would directly flow into the underground mediumresulting in the contamination of groundwater and soil. The complex migration ofLNAPL in the subsurface media can not be obtained directly. At present，different-filed researchers used more and more methods to study the complexmovements and changes of LNAPL in the underground medium. Ground-penetratingradar (Referred to as GPR), which has some advantages, such as high sampling rate,easer data processing and anti-interference ability, has been widely used in study ofsoil and groundwater pollution. GPR is a high resolution and non-destructiveelectromagnetic method which used the reflection of high-frequency electromagneticwaves beam from medium to detect object. GPR can describe the degree ofcontamination of the medium through the establishment of speed and dielectric modelto obtain the dielectric constant. There are still some problems involving using theGPR to detect complex permittivity of contaminated medium, because of influence ofelectromagnetic wave band, the sampling range and environmental interference etc.The further study should be made in using the GPR to determine the dielectricproperties variation of LNAPL contamination of underground medium.In order to further study the dielectric properties of LNAPL contaminated soil, weused medium mixed with different proportion of diesel, water and quartz sand(particle size of0.106mm to0.212mm) to simulate the LNAPL contaminated soil,and used opening coaxial probe method to detect the complex permittivity in thefrequency rang from200MHz to8.5GHz.First of all, we compared the data calculated by the Topp empirical formula withthe actual data within the range of200MHz to3.0GHz to confirm the feasibility ofthe experimental method and reliability of experimental results. From the analysis ofthe relative dielectric constant of the quartz sand with the different volumetric watercontent and oil content, we can see that the relative dielectric constant increases withvolumetric water content and oil content increasing before the quartz sand saturated, but the increase of the volume oil content had no significant effect on the relativedielectric constant after quartz sand saturated. The relative permittivity of thecontaminated non-saturated sand increases first, and then tended to be stable later astime prolonged．We also did the Polynomial fitting by using the experimental results,and obtained a relational model about the volume of oil content, water content and therelative permittivity.Secondly, we studied the effect of oil content on the real part and the imaginarypart of the complex permittivity, the situation of the imaginary part of the complexpermittivity changes with time prolonged, and the relationship between the real partand imaginary part of the complex permittivity and frequency within the range of200MHz to8.5GHz.The experimental results show that the real and imaginary parts of complexpermittivity of sand sample increase with the oil content increasing when the quartzsand was non-saturated, whether the quartz sand containing water or not, theincreasing of the volumetric oil content can not significantly affect the complexpermittivity when the sand was saturated. The complex permittivity of thecontaminated non-saturated sand will be a series of changes within72hours andtended to be stable as time prolonged．Within the detection frequency range, the realpart of the complex permittivity deceases gradually with the electromagnetic wavefrequency increasing, but the change of the imaginary part of the complex permittivityis opposite, the amplitude increases with increasing volume fraction of water orLNAPL.In short, we obtained the regularity of the volumetric LNAPL content and thevolumetric water content impact on the soil dielectric properties through the study thechanges of the real and imaginary parts of the complex permittivity of thecontaminated soil in the frequency rang from200MHz to8.5GHz. The experimentalresults provide an important experimental basis for the further application ofElectromagnetic method (Such as “GPR”) in the LNAPL contaminated soilmonitoring.