A land contamination expert at the Northern Ireland Environment Agency (NIEA) has advised that a risk assessment of the Mobuoy dump site has found "specific contaminant linkages that pose a potential future risk to water quality within the River Faughan".
But Dr. Theresa Kearney, a scientist at the NIEA, who briefed members of Derry City and Strabane District Council's Environment and Regeneration Committee on Wednesday, said the recent flooding in the city had had no adverse impact on water quality in the river.
Environmental campaigners mounted a protest outside the meeting at the Guildhall.
Inside, Dr. Kearney told councillors that the site was currently having no adverse impact on water quality in the River Faughan.
Site boreholes have not indicated "significant concentrations of contaminants close to the river", while the risk to Northern Ireland Water's tap water abstraction point is deemed to be "very low", she advised.
However, Dr. Kearney warned that a risk assessment had "identified specific contaminant linkages that pose a potential future risk to water quality within the River Faughan" and that NIEA's remediation approach has been informed by that view.
She advised that in the wake of the recent flooding enhanced monitoring of the river had been rolled out and that there had been close cooperation and data-sharing with Northern Ireland Water.
The flooding has had no detrimental impact on water quality, she told the committee.