UAN and ASS storage tanks

Talking about liquid fertilizer nowadays, usually either UAN (urea and ammonium nitrate) or ASS (ammonium sulphate solution) are meant. Liquid fertilizer is classified as water contaminating and may not get into sewage plants, waters or in to the ground water. The handling of facilities for storage, bottling and turning water hazardous liquids is prescribed in the water resources act (WHG):

Storage facilities need to be constructed and operated so that no liquids can leak out
Single walled storage tanks below ground are inadmissible
Storage tanks either need to be equipped with a catchment tank or need to be double walled