A study on microbial diversity in groundwater in an oil-contaminated site

There are some microorganism samples from oil-contaminated or non-contaminated groundwater, but the concentration of petroleum organic pollutants in oil-contaminated samples is not very high. Most of them are about 10µg/l or less than 1µg/l. The study wants to find out what are the characteristics of microbial community structure in such an environment