Cutting oil was discharged to the stormwater pond of an aerospace plant. Iridescent colours could be seen on the pond’s surface. The valve used to discharge the water from the pond to the canal was closed and a containment boom was placed around the valve’s inlet. Due to the weather, there was a risk that the pond would overflow and pollute the adjacent area. The operator transferred the water in the pond to another pond. Water sprays and a containment boom were used to herd the oil into a single slick, which was then pumped up by a vacuum tanker.

The oil came from the stormwater drain pipe leading from the roof of a parts machining workshop. An extraction system in the workshop draws in oil-laden air produced by machine tools, filters it, and expels it onto the roof. Oil condensate is collected in a column fitted with a drain valve. Employees are instructed to drain these pipes regularly. According to the operator, this was supposed to be done several times a day. However, the pipes had not been drained for several days prior to the discharge event. As a result, oil had filled the column all the way up to the filter and clogged it. The high extraction rates pulled the oil all the way up to the roof outlet. This continued for several days of fair weather until a rainy period began. Oil was washed off the roof by the rain and drained into the plant’s stormwater network, which did not have a hydrocarbon separator.

The operator has since fitted a hydrocarbon separator on the pond’s inlet. It now carries out regular visual checks of the pond.