asked the Minister for the Environment the studies that have been carried out to reassure authorities that a step up of the sewage volumes going through the treatment plants will not increase contamination in Dublin Bay.
468.
Written Answers. - Dublin Bay Contamination.
466.
asked the Minister for the Environment if he is satisfied that the sewage plants discharging into Dublin Bay are only undertaking primary treatment that does little more than screen out solids from the effluent before discharging them into the bay, and whether he envisages further treatment that would minimise the danger of excessive contamination.
I propose to take Questions Nos. 466 and 468 together.
I am satisfied that primary treatment of sewage discharging into Dublin Bay is adequate. This form of treatment does more than screening — it reduces the solids content by settlement and lessens the oxygen demand in the receiving waters. The decision to provide primary treatment is based on the conclusions of Professor Crisp's Report on Dublin Bay which shows that the assimilative capacity of the receiving waters of Dublin Bay is adequate to take the discharge of effluent which has received primary treatment.
467.
asked the Minister for the Environment if in light of the evidence presented at the An Taisce seminar on Dublin Bay: (a) he is satisfied that so many samples should be in excess of the EEC mandatory standards, (b) he will order that monitoring of water quality occur outside of the bathing months May to September in view of the wide use of the bay for boating and surfing, (c) he will consider a hydrographic survey of the currents in the bay so that effectiveness of the break up of sewage effluent would not be left to chance, and (d) he will consider increasing the frequency of monitoring water quality as well as the duration of monitoring.
While a number of monitoring results at certain locations have on occasion exceeded the mandatory standards set out in the EEC Directive on the Quality of Bathing Waters, the coastal waters in Dublin Bay do not, in the opinion of the health authorities, constitute a threat to public health. Some of the monitoring data which was supplied at the seminar referred to in the question related to areas where little bathing occurs. In addition, samples taken outside the bathing season were included. Monitoring for the purposes of the EEC directive is carried out at two locations on Dollymount beach during the bathing season. Since 1978, full compliance with the requirements of the directive has been achieved, and analysis of the monitoring shows that results are well within the EEC parameters.
As regards other locations, the position is as follows:
Seapoint
The source of pollution is the Dún Laoghaire outfall off the west pier and, with easterly winds, pollution would tend to increase at Seapoint. Local authority proposals to alter this outfall are at early planning stage.
Dollymount
The Dublin city outfalls (which discharge into the river Liffey upstream of the Poolbeg generating station and carry sewage from the city centre and from Pembroke-Rathmines) affect the Bull Wall significantly with lesser effects on the south Dollymount strand. A programme for improvement in sewage treatment is being carried out and a new sewage treatment works at Ringsend is operational since February 1982. When the Ringsend pumping station is commissioned in Autumn 1984 a major improvement in the existing position should occur.
Coliemore Harbour, Dalkey
This is not a bathing area of any significance and the cause of pollution is a small sewage outfall at the pier.
Corbawn Lane, Shankill
The information given at the seminar related to the period to 1981. However, a new sewage disposal scheme has since been completed at a cost of £7 million and this includes a 1.4 km marine outfall at Shanganagh. This scheme, which came into operation in Autumn 1983, should resolve problems in this area.
Blackrock, North and South Beach
Occasional high readings have been mainly attributable to a malfunction in the Tobernea drainage pump. The beach is not used for bathing and chlorination is carried out on the water in the baths.
I understand that the Eastern Health Board, who carry out analysis for the local authorities concerned, have extended monitoring programmes beyond the traditional bathing months and that monitoring commenced this year on 1 March. The EEC directive on the quality of bathing water only requires monitoring of designated bathing areas on a fortnightly basis during the bathing season (i.e. the period during which a large number of bathers can be expected) and this is, in fact, being done at present for Dollymount and other undesignated areas in the bay. It is a matter for the local authorities concerned, in conjunction with the health board, to determine whether any further extension of the duration or frequency of the monitoring programme should be arranged. However, given the information available from monitoring results over the past few years, it is unlikely that more frequent monitoring would produce major variations in the general pattern.
The commissioning of a hydrographic survey on the currents in the bay is a matter for the local authorities. The 1971 Crisp study on Dublin Bay reported that hydrographic conditions in the bay are satisfactory for dispersal of effluent and found that "there is a strong clockwise circulation continually flushing the bay and maintaining high water quality standards". I am advised that the sewage solids from the centre city area are removed before effluent is discharged from the treatment works at Ringsend and that the effluent contains only very fine particulate matter. On discharge to the sea and admixture, the sewage is quickly dispersed in the water body.