| Due to the progress of society and the rapid development of the economy,the demand for petroleum is increasing,but petroleum pollutants will be produced by exploration and gathering.Petroleum pollutants not only remain in the soil,but also may enter the vadose band or aquifer.Because some of them are hardly soluble in water and difficult to degrade naturally,only a small part is transferred,removed and absorbed through degradation,evaporation,etc.After entering environment,most of them may remain in the natural environment for several years to decades,it has polluted the soil and groundwater resources on which humans depend,destroyed local ecosystems and threatened human health.Therefore,it is of great practical significance to study and evaluate the water and soil environmental quality and pollution risks of abandoned petroleum sites,develop a scientific,rational recovery and utilization plan.This paper,taken the Qingcheng County as the research area in the east of Gansu and used the abandoned petroleum field and station as the object,conducted risk screening on 758 well sites in the area and identified 58 well sites and 5 stations as potential oil-contaminated sites for detailed pollution investigation.On the basis of the pollution investigation,the 37-well sites(stations)with excessive oil pollution were evaluated by the single factor pollution index method for the environmental quality.The human health risk assessment was carried out by combining HERA software with guidelines on 26 well sites located in sensitive areas,and the ecological risk assessment was carried out by using the potential ecological environmental risk index method.The suitability and effect of the restoration technology in the environment of the area were selected by contrast screening.According to the degree of pollution and risk,the management and classification of contaminated sites in the study area were proposed.The main results were as follows:1.Status of environmental quality of soil,groundwater and surface water(1)The soils from 63 well sites(stations)were sampled and analyzed,however,the total petroleum hydrocarbon concentration of the samples in 37 well sites(stations)exceeded the screening value.The concentrations of eight kinds of heavy metals(arsenic,copper,zinc,nickel,cadmium,lead,mercury and chromium)were lower than those of agricultural land(farmland/forest land),which indicated that the soil pollution in this area was dominated by petroleum hydrocarbon.(2)The 20 indicators were detected in six groundwater samples,and the contents of chloride,fluoride,total hardness,nitrate and total dissolved solids exceeded the groundwater quality standard Class III limits.This was because that the contents of these indicators in the study area were higher than in other areas,which determined by the geological and geomorphological and hydrogeological conditions of the area.There were not characteristic pollutants detecting in oil exploitation,such as petroleum,volatile phenol,indicating that oil pollution has not yet reached groundwater.(3)A total of 9 surface water samples were collected,and the 22 indicators were detected for each water sample.According to the Class IV standard for the surface water environmental quality,there were three indicators of total nitrogen,fluoride and chromium over the limiting value.Compared with the limiting value,the fluoride concentration of W-02 and W-03 samples was 0.28 times,the total nitrogen and the chromium of W-06 exceeded 12 and 0.16 times higher than that of the limiting value,respectively.The reason was that the sampling point of W-06 was located at the intersection of Huanjiang and Rouyuan River in Qingcheng Town,Qingcheng County.There were industrial enterprises and residential areas in the upper reaches of the Huanjiang River.Emissions of industrial and domestic sewage may result in excessive levels of nitrogen and chromium.Petroleum and volatile phenols were a feature of oil extraction and had not been discovered.At present,oil pollution has not affected surface water.2.Soil environmental quality assessment resultsThe single factor pollution index method was used to evaluate the quality of 37 sites contaminated in soil,of which,26 well sites(stations)were heavily polluted,6 well sites were moderately polluted,the rest were slightly polluted.3.Risk assessment resultsRisk assessment was carried out on 26 contaminated sites in sensitive areas(water source protection areas and farmland areas).The results of human health risk assessment indicated that the risk of 5 well sites in the water source protection zone was unacceptable,and the risk of 7 well sites in the farmland zone was unacceptable.The results of ecological risk assessment indicated that the 3 well sites located in the water source protection area were high risk,4 well sites were medium risk,and 6 well sites were low risk;Two well sites located in farmland areas were at higher risk,3 well sites were high risk,5 well sites were at middle risk,and 3 well sites were low risk.4.Suggestions for the treatment and restoration of contaminated sitesAccording to the present situation of petroleum hydrocarbon pollution and the results of quality assessment and risk assessment in 37 well sites(stations),the suggestions of treatment and remediation were put forward.The 11 well sites(stations)located in non-sensitive areas should be implemented risk management and control to prevent the spread of pollution;The 26 well sites located in sensitive areas should be implemented restoration: Two low contaminated well sites located at farmland area selected ?mixed screening,broken,thrown and one plant restoration? technology,and 4 contaminated sites located at water source protection area selected ?mixed screening,broken,thrown and multiple phytoremediation? technology.The 20 well sites with heavy pollution,heavier pollution,heaviest pollution and extremely heavy pollution selected ?mixed screening,broken,thrown,Bio-reactor and phytoremediation? technology for repair. |
PDF Full Text Request