http://www.iflscience.org/missing-sc...-lsd-drug-lab/
from a reddit post:
"208 litres in 55 gallons (take that the barrels had approx 8 litres in each make it 200 litres or 200,000 ml)
200,000 x 3 = 600,000 ml
21 years x 364.25 days = 7649 days
600,000 ml / 7649 days = approx 78 ML of acid for 21 years"