Risk Assessment And Remediation Technology Screening Of A Typical Urban Chrome Residue Contaminated Site

The pollution of a typical urban chrome residue contaminated site in Zhejiang province was investigaed in the work.The contents of the main heavy metals in the samples from the soil,the groundwater,the surface water and the sediment were analyzed.Different risk assessment methods were used to evaluate the pollution.Also, the soil washing and solidification/stabilization technologies were applied to the remediation of heavy metal contaminated soil.The main conclusions are as follows:1 The investigation of the heavy metal pollution in the polluted siteThe surface water from River L was not contaminated by heavy metals,and the content of the heavy metals in the sediment was low,but the accumulation of metals Cr,Zn and As around the factory;the groundwater was polluted,especially,the concentration of Cr(â…¥) and Zn in the groundwater from the storage site greatly exceeded the limit for theâ…¤water according to Quality Standard of the Groundwater.The heavy metal in the site was accumulated on the saface of the soil,also,the content of the heavy metal decreased when the depth of the soil layer increased The deepest soil layer polluted was about 3 m.The storage site,the former storage site and the chromate production workshop were seriously polluted.The main contamination was Cr and Cr(â…¥),and in some place the Pb,Zn,Cd and As exceeded the limted values.The content of Cr(â…¥) and As,Cd in the leaching solution from the soils in the storage site,the former storage site and the chromate production workshop were exceed or partly exceed the identification standards limit(GB5085.3-2007).2,The risk Assesement of the sitesThe results from the Hakanson potential ecological risk harmness exponent method showed that 26.2%of the heavy metal polluted soil had strong rank of ecological risk, 11.9%of it had relatively strong rank of ecological risk,and 8.3%of it had middle rank of ecological risk.The results from Health Risk Assessment revealed that 100%,100%and 92.8%of the polluted soil have cancer risk for adult under residential,commercial site and park land exposure scenarios,respectively.3,The selection of remediation technologies for heavy metal contaminated soilBy comparing the H₂O,HCl,H₃PO₄ and oxalate,filter out HCl was more effective washing agents.The best leaching conditions were:HCl concentration 2 mol/L, soil/liquid=1:3,reaction time 60 min,washing number 2.The removal rate of Cr,Pb,Zn,Cu,Cd in the soil was up to 80.75%,88.69%,98.00%,79.33%and 95.52%, respectively.The cement(P.C.32.5) and the supplements:fly ash,sand,blast furnace slag and ferrous sulfate were investigated in the solidification/stabilization experiment.When the ratio of the cement to the soil was 3:7,the addition of 2%ferrous sulfate can get the best solidification result.The Cr(â…¥) content of the leaching solution from solidified body was lower that 0.5 mg/L.