Crymlyn Bog (Cors Crymlyn) is an internationally important wetland with multiple nature conservation designations, part of which is owned by St Modwen, and is immediately adjacent to the site of the Coed Darcy Urban Village. It is designated as a Special Area for Conservation (SAC), a Wetland of International Importance (a Ramsar site), a nationally important National Nature Reserve (NNR) and Site of Special Scientific interest (SSSi).
Crymlyn Bog comprises a floodplain-valley mire located within a lowland coastal context and is the most extensive wetland of its type in Wales. The mire features a complex mosaic of vegetation types, supporting transition mires and quaking bogs, swamp, tall herb fen, fen meadow and wet woodland (carr) communities.
Surface water drainage from the Urban Village is expected to provide a high quality input to this internationally important wetland. The lagoons associated with the four surface water discharge points to Crymlyn Bog will be enhanced. A surface water drainage strategy is being developed and discharges to Crymlyn Bog will be attenuated and controlled to mimic as closely as possible the flow conditions existing when the refinery was operational. With closure of the refinery, the source of hydrocarbons has been removed and remediation of the Urban Village site will deal with contamination in the ground, thus improving the quality of the discharges to the Bog.