Agenda item

Barbara Parsons gave a presentation on the results of the odour survey carried out.  The full report was circulated to members of the Group.

24 monitors were located in various sites to monitor ammonia and hydrogen sulphide concentrations.  12 were located within the works boundary and 12 located in residential areas (map attached).

The first month of the survey showed very low values of hydrogen sulphide, with the highest reading in Admiral Way.  May and June saw higher values around residential properties than on the SWW site but these were still low.  Sites that were high with hydrogen sulphide were not high with ammonia and vice versa.

Within the works site, the sludge reception tank demonstrated higher readings. After chemical dosing, the odours had cleared quite well for a month until a blockage had occurred.  Once this had cleared and the dosing had increased, the levels dropped again.

The tankers discharge area also had consistent higher readings.

The SW14 site in Wear Barton Road showed higher levels of ammonia than all other residential sites.  The highest reading up to June was from the sludge reception area within the works.  The SWW25 monitor in the sludge storage area showed a high level of ammonia, but it was difficult to detect any odour.

The customer complaints list was cross referenced with data (attached).

There are times where the wind was very strong from the west, which would suggest that odours were from another source due to the wind direction.  The report had flagged up other areas on the site where odours were not expected – this could be a possible tidal effect of the Exe Estuary.

Higher values were recorded between April and July before remedial measures were introduced, and also in September when an operational failure occurred.

Of the residential sites, SWW13 (Wear Barton Road) gave a higher reading of hydrogen sulphide particularly during June to September.

Hydrogen sulphide readings were higher at SWW26 on the site.  SWW25 was situated by the sludge tanks which cannot be covered.  One possible option for this area was screening by trees.  However, the flood defence works will have an impact on the site and it was unlikely any screening would take place until these works had been completed.

Hydrogen sulphide readings in SWW 20, 21 and 22 identified a possible localised odour source as they are situated relatively close together.

Odours could also be lifted, dragged and dropped, and it was questioned how the technique used can pick up on that.  It was noted that the tubes were only positioned at head height for this survey – ammonia was lighter than air and hydrogen sulphide heavier.

Jay advised that there are lower flows during the summer months which leads to less dilution in any period of dry weather.

Members were asked to read the report and to come back with any comments.

Some work would be undertaken with Charlotte and the team to provide residents with a copy of the report together with a summary to identify key points.