Harron Homes Ltd admitted one charge of causing illegal discharges from its Farriers Croft estate in 2015.
The Environment Agency prosecuted the firm after investigating reports of contaminated run-off which was entering a tributary of Grimescar Dyke.
An Environment Agency officer visited the site on 20th November 2015 and saw polluted water flowing out of the entrance of the construction site. The company was also pumping silt contaminated water from site excavations, which also entered the watercourse.
Following the intervention, Harron Homes attempted to control the silt run-off by setting up settlement tanks. However, further incidents of pollution were reported in November and December 2015 and subsequent inspections revealed that this system was inadequate. Silty water was found to be discharging, resulting in further pollution.
Samples taken from the discharges showed that they were having a significant impact on the water quality in the watercourse up to 3km downstream. Some samples showed there to be nearly 35,000 milligrams of suspended solids per litre of water – more than a thousand times the 30 milligrams per litre concentration that a healthy watercourse is expected to have.
Mark West, environment management team leader at the Environment Agency, said: “These pollution incidents had a significant impact on the water environment over a number of weeks, and were entirely avoidable. In West Yorkshire there has been a worrying increase in the number of pollutions incidents reported to us that on investigation are attributable to the construction sector.
“Construction companies should consider the potential environmental impact of developments they undertake at the initial planning stage and must adhere to environmental permitting rules and invest in appropriate management systems to prevent their activities from affecting the local environment.”
In mitigation, Harron Homes told the court that it had now put procedures in place to prevent future pollution incidents.
In addition to the fine, the company was ordered to pay £8,706.71 in legal costs and a £120 victim surcharge.