Kindly look in to the manual of WHO for the threshold limits in soil

Can you give a link?

Here is a journal article with some information for you.

http://www.ipublishing.co.in/jesvol1no12010/volumetwo/EIJES3038.pdf

This is an article on bioremediation of engine oil.

http://jeteas.scholarlinkresearch.org/articles/Bioremediation%20of%20Engine%20Oil%20Contaminated%20Site.pdf

This is a table of upper concentration limits (water and soil) for typical hydrocarbons in the state of Massachusetts (United States) that may be a guide for you.

http://www.mass.gov/eea/agencies/massdep/cleanup/regulations/mcp-method-3-upper-concentration-limits.html

This journal article should really be useful for you.

I think this question is not easy to answer because it very much depends on the legislation. Here in Germany values differ depending on the "pathway of action" of the contaminant, for example soil -> human, soil -> groundwater or soil -> plant. For total petroleum hydrocarbons (TPH) values range from 300 mg/kg to 1000 mg/kg. For soil -> groundwater they depend on protection zones, ranging from 200 mg/kg soil in highly protected areas to 1200 mg/kg for the vadoze zone and deep groundwater levels (>5 m). Another issue is the use of excavated contaminated soil, where unlimited use is permitted for

Thank you for you valuable answers. Can anyone suggest soil TPH limits pertaining to India?