EPA request Ringsend Wastewater Treatment application withdrawn

12th Apr 2013

IWDG were informed today that the EPA have recommended that Dublin City Councils application for a Dumping at Sea licence in connection with the proposed wastewater treatment plant be withdrawn due to the late submission of an updated screening document for the Appropriate Assessment and Natura Impact Statement.

The letter to IWDG is in response to IWDG raising a number of issues regarding the proposed wastewater treatment plant and its potential impact on harbour porpoise.  Dublin Bay is a proposed candidate Special Area of Conservation for harbour porpoise and IWDG believes insufficient consideration was made on the impact of the development on this species.

IWDGs main concern was in connection with the proposed 9000m tunnel and associated vibrations and noise levels caused by the tunneling would degrade the local habitat for harbor porpoise. The EIA stated that the principal underwater noise generating elements of the construction phase is the construction of the tunnel, the diffuser shaft and the outfall diffuser. It stated that the loudest underwater noise was likely to come from pile driving, with typical values for Sound Exposure Level for pile driving large steel piles in the order of 190 dB re 1 uPa2.s @ 1m (SEL). The EIA estimated permanent hearing damage is caused to the animal within 2 metres for high frequency cetaceans and 8 metres for pinnipeds. We suggested that temporary threshold shift would have been a more appropriate measure to assess impact and also the objective should be to minimize disturbance. Recent studies have shown source levels for pile driving are in the order of 220dB-257dB re 1μPa peak-to-peak.

 

Brandt et al. (2011) showed harbor porpoise in the North Sea with a maximum peak source level of 196 dB re 1 uPa2.s @ 1m. This caused harbor porpoise to leave an area up to 2.6km from the sound source and activity remained below normal levels for between 24 and 72 hours after pile-driving ceased. At some sites with prolonged pile-driving harbor porpoise activity has not recovered some years later.

With respect to dumping at sea the IWDG noted that this required the use of a Marine Mammal Observer (MMO) to ensure no harbor porpoise, or other marine mammal, were close to the barge on release. This is consistent with best practice.

Dr Simon Berrow, IWDG Executive Officer