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Study on Ground Penetrating Radar Used in Monitoring Oil Leakage of Gas Stations

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Tutor: LiuZhenHong
School: Donghua University
Course: Environmental Engineering
Keywords: leakage of gas stations,pollution potential,ground penetrating radar,forwardsimu
CLC: X830.2
Type: Master's thesis
Year:  2013
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Abstract:
Nowadays,pollutants of petrochemical products has been widely detected in the groundwater under the urban area of our country.With a large number of gas stations decreasing since the1990s, if prevention and investigation measures were not taken before gas stations leakage,it would cause serious consequences of groundwater pollution.Therefore, to carry out the investigation of the leakage of the status quo of gas stations in our country and to study the monitoring technology of the gas station leakage contamination have significance about improving quality of the groundwa-ter environment.The most leakage pollutants of gas station is light fuel oil such as gasoline, diesel and and their additives. After permeating in the aquifer, they generally can not be mixed with water, and occupy part of the volume of the aqueous layer as a separate flow phase, resulting in pollution of the soil, the aqueous layer and groundwater. Dielectric constant and conductivity of the pollutants are certainly different from surrounding medium and water, so to use ground penetrating radar (GPR) detecte petroleum hydrocarbon pollution is based on this principle.Firstly survey on the status quo of gas stations in Shanghai was combined with the basic cha-racteristics about the underground storage tanks in gas stations and the Shanghai-specific hydro-geologic data. After it had been amended, the U.S. LPI index experience formula was tried to use to evaluate the permeability of each gas stationdrain pollution potential. According to the result, the gas stations with certain high risk of pollution were filtered out as the object of study.Then paper studied typical radar signatures of petroleum hydrocarbon contamination which is detected by GPR in theory through forward modeling about pollutants numerical model, and con-firmed the accuracy and sensitivity of the petroleum hydrocarbon contamination with GPR detec- tion. Study selected the software named GprMax to simulate freedom phase of pollutants and freedom phase and residual phase numerical model. The results of100MHz,250MHz and500MHz antennas showed that the three kinds of antennas can meet the detection requirements to a certain extent, but resolution of250MHz and500MHz antennas were higher than100MHz an-tenna, even the internal differences in the concentration of the contaminant plume can also be dis-played in profile.After that, the GPR was tried to be used in detecting petroleum hydrocarbon pollution in a known contaminated site. The main purpose is to explore of GPR operating method from the pre-paratory work to the latter part of the data processing and analysis and to understand the operating points for Shanghai gas station survey.100MHz non-shielded antenna and250MHz shielded an-tenna were used in study. The results showed that the250MHz shielded antenna was better, and initially confirmed the feasibility of GPR detecting petroleum hydrocarbon contamination.Finally, site investigations at the typical gas station were carried out. Using GPR as the pri-mary method, combined with other supplementary methods such as the sampling and analysis, high density resistivity method during the primary exploration and detailed investigation, deli-neated pollutants leak paths and pollution range and confirmed the feasibility of GPR. The re-search results showed that using GPR to detect petroleum hydrocarbon contamination in ground-water and soil achieved good results. High impedance characteristics of petroleum hydrocarbon contamination plume further increases the difference from the soil in survey area which presents a low impedance characteristics, so that despite the low resistance of the soil reducing the radar probing depth, it mproves the precision and accuracy of the radar detection. From the distribution of the contaminant plume, because of the shallow groundwater level of the study area, the petro-leum hydrocarbons lightweight pollutants exists in the vicinity of the water table as free-phase form in the long term, and fluctuating with groundwater level changing.Its vertical distribution ranges from3m to less. About diffusion in the horizontal direction due to slow groundwater veloc-ity, vadose zone soil permeability, most of the contaminant plume located inside the gas station.
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