COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF TERENURE-RATHFARNHAM AREA COMMITTEE (2)

Tuesday, May 13, 2008

QUESTION NO. 13

QUESTION: Councillor J. Lahart

"To ask the Manager to have the following matter addressed:  In Idrone Park, Knocklyon the manhole covering the sewer in this laneway is continuously being lifted up during heavy rainfall. It is happening more and more frequently and has been reported to the Council 3 times between March 15-22nd. The path is sloped, so the sewage comes out and runs in all directions, creating a health hazard?"

REPLY:

The Senior Executive Engineer, Drainage, has reported that the sewer in question is a 225mm public foul drain which services an extremely large area (Delaford estate, Cremorne estate, Westbourne, Knocklyon Park, Mount Alton etc…)  A large number of the households serviced by this sewer have either,

(a)        old combined (foul & surface water) systems or

(b)        unauthorised misconnections (surface water into foul).

Where a large volume of water can enter a foul sewer during a storm event, the capacity for the wastewater is reduced. In this instance the problem is compounded by the changing direction of the sewer. During the foul drain’s course it comes to a series of 90⁰ turns which effectively reduces the flow, thus backing up the sewer. In heavy rainfall events, the sewer becomes overloaded with rainwater thus causing the surcharge. During dry weather  and normal wet conditions this foul drainage system works effectively.

The manhole in question is constructed over a 90 degrees bend which can lead to the pipe overflowing into the public pathway during heavy rainfall. The problem by its nature is not easily rectified. In order to reduce the risk of future surcharging the following courses of action would be required;

(a) A duplication of the system would have to be laid. It should be noted that these works would be prohibitively expensive and very disruptive.

(b) A survey of all houses in the area would have to be carried out to identify the surfacewater into foul sewer connections. Many of the houses were originally built as combined systems, therefore to divert the surfacewater from these houses into a separate surfacewater system could be quite difficult. Such works would be matter for the household owners and would have to be enforced by South Dublin County Council.

A survey of large hardstanding / impermeable areas will be carried out to ensure such areas are connected to the surfacewater system and not impacting on the foul sewer system