The court heard that a member of the public alerted the Environment Agency to an incident in the Wyke beck in December 2003. Officers found a pipe discharging raw sewage into the stream.
An investigation found that the pipe was from a combined sewage overflow (CSO) designed to discharge into the stream during heavy rain when the sewers have insufficient capacity.
Gleeson was being employed by Yorkshire Water to excavate a new chamber for the CSO and had bypassed the overflow with a pipe which rejoined the sewer downstream. The company was also pumping silty water from the excavation into the sewer.
However, sandbags used by the company to stop water flowing backwards into the excavation had been dislodged and blocked the sewer. Raw sewage and silty water had built up and were discharging from the CSO.
A survey of the stream by the Agency found that the pollution had a severe impact on wildlife, killing rare and protected crayfish.
The magistrates said that because of the seriousness of the offence they had considered referring the case to crown court where fines are unlimited. However, Gleeson's statement in mitigation that it had spent some £50,000 cleaning up after the incident persuaded the magistrate to deal with the case. In addition to the £15,000 fine, the company was ordered to pay costs of £1,343.