Here is evidence for the 20,000 recovered.
http://www.wtc7.net/articles/FEMA/WTC_ch5.htm
To date, the NY State Environmental Protection Agency (EPA) and DEC have recovered approximately 20,000 gallons from the other two intact 11,600-gallon underground fuel oil storage tanks at WTC 7.
It is worth emphasizing that 20,000 gallons (of a maximum of 23,200 gallons) where recovered intact from the two 12,000-gallon Silverstein tanks. So, it is probable that the 20,000 gallons recovered was all of the oil in the tanks at that time. Since the oil in the Silverstein tanks survived, we can surmise that there was no fire on the ground floor.