The Inčukalns acid tar ponds were operated as waste dumpsites from the 1950’s to the 1980’s. Waste containing a mixture of used lubricating oils and sulphuric acid tar (considered “acid tar”) was disposed of by Riga lubricating oil processing plant. Waste from medical and perfume oil production were also disposed of here. The waste was dumped into sand quarries without a bottom or side liner.