A cocaine level of 860ng/ml found in urine. how much is likely to have been ingested?

Difficult to say: Here is an article that explains in general terms how sampling can be affected by time of ingestion, time of sampling and method used. http://primarypsychiatry.com/clinical-interpretation-of-drug-testing/ So difficult to infer original ingestion dose from a urine level. Best to seek advice from a toxicologist licensed in your area for specifics.

Impossible to say: Cocaine levels vary with individual absorption rates, and time from use.