The problem was revealed in spring 2007 during an inspection by the Scottish Environment Protection Agency.
The landfill site’s permit required five cells to be capped by the end of 2006, but the council failed to cap three. As a result odorous gases escaped, leading to 16 complaints being made to SEPA between August 2004 and March 2007.
SEPA "repeatedly told the council what the problem was and gave them plenty of opportunities to fix it", according to investigating officer Colin Morrow. However, the cells remained uncapped.
The council was issued with an enforcement notice requiring the works to be completed by May last year, but it missed the deadline.
The council was fined £5,500 on 24 September after pleading guilty before Hamilton sheriff court to failing to comply with an enforcement notice, contrary to Regulation 30(1)(d) of the Pollution Prevention and Control (Scotland) Regulations 2000.
In defence, the council said wet weather had prevented capping, which had to be done when waste was dry.
The council also pleaded guilty to a charge of allowing polluting liquids to enter a surface water drain, contrary to Regulation 40(1)(b) of the Water Environment (Controlled Activities) (Scotland) Regulations 2005. In November 2006, a street sweeping vehicle had discharged water into a drain at the landfill’s entrance, potentially polluting a tributary of the nearby Cocks Burn. The council was admonished for the incident.