Which test should be carried out to detect the type and extend of soil and ground water contamination ?

Dear friends, for our new construction site we need to know the soil and water contamination in detail for various safety reasons. Can anyone advise me which are the chemical and biological tests to be done to find the type and extend of contamination in soil and water?  We collected samples of soil and water from bore holes at different depths up to 20 m from our site located in a reclaimed area inside the bay (in Bahrain). We monitored gas levels in this location and it shows very high levels of hydrogen sulphide. Our client has asked us to conduct some more detailed chemical and biological analysis of samples collected. Please suggest which are the different tests to be done on these samples to prove that this area is highly contaminated? We are also looking for an expert who can write a report depending on the laboratory result and help us minimize the risk involve at this site. Your suggestions and responses much appreciated. Davis