Home Water Quality Project Last minute letter to DC / WW
Last minute letter to DC / WW PDF Print E-mail
Written by Robbie M   
Monday, 07 February 2011 12:40

 

To whom it may concern

 

Proposed replacement sewerage works at

Y Cwm, Parrog, Newport, Pembrokeshire.

 

We write again on behalf of our Group, but through it with the benefit of our local knowledge and perspective, and of our appreciation of what is needed by our local community, to re-iterate our very strongly held view that, your proposed plan of works, regarding the above sited location, scheduled for a start in the near future now, needs a further modest element, in order to make it a real and optimal contribution to the improvement of the present arrangements and installations for the treatment and disposal of sewage effluent in this community.

 

That is to say that the evidence demonstrates to us very clearly that a significantly increased capacity to temporarily store so-called combined flows, carried in the present system during storm conditions, by means of an additional storm water storage tank, located next to the existing SPS @ ‘the Cwm’, would very greatly reduce the potential for/risk of the discharge of untreated sewage effluent, currently by-passing the Newport WWTW, through the SPS CSO during and after prolonged rainfall/storm periods, which exceed the pumping capacity of Cwm SPS to feed the Newport WWTW.

 

We remind you that the details provided us, through the agency of the local branch of the EA(W), regarding the telemetric reading of the SPS CSO spill events in 2008, revealed that :

 

 

Date & time Alarm Level     Status  Boolean FOR     Time to clear Time to clear

Secs Hrs         (days)

 

12/12/2008    22:53 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 80 426 22.34    (0.93 days)

09/11/2008    06:17 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 691 193 192.00    (8.0 days)

03/09/2008    19:04 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 812 176 225.6      (9.4 days)

02/09/2008    16:12 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 35 724 9.92    (0.41 days)

11/04/2008    04:55 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 87 028 24.17      (1.0 day)

10/03/2008    06:07 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 25 920 7.20     (0.3 days)

14/01/2008    06:19 NEWPORT CWM SPS

WET WELL SPILL EVENT 1 Clear B3988 42 12 959 3.60     (0.15 days)

 

Consequently we can see from this that according to the telemetric log readings presented by DCWW in total 7 storm water spill events occurred during 2008 down at the Cwm pumping Station, of which the two events on 09/11 and 03/09 respectively were the most prolonged by a considerable magnitude. Taken together all the spill events resulted in a total period of spill discharge from the station of untreated combined storm flow for 484.83 hrs or 20.20 days, which is the equivalent of approx 5.53% or 1/18th of the year.

 

 

In the view of NAEG, this represents a very significant period in operation and vastly exceeds the “one or two minor occasions” expectation which we had been previously led to believe was the anticipated character of the discharge frequency and duration through this CSO installation.

 

In our view the current storage capacity of the Cwm SPS storm storage tank (shown on your most recent plans as 140 m3) , is woefully inadequate given both the frequency and most especially the duration of actual over spill events as now revealed. Whilst the existing capacity may indeed exceed the required 6 hours storage at the designated Dry Weather Flow (DWF) rate of only (5.43 l/s), as per Condition 5 of the original Discharge Consent, this corresponds to only a storage capacity of 2.35 hrs at the Storm Flow Rate (SWR) of 13.7 l/s, which is now stated as flow rate triggering the CSO discharge.

 

We would expect that at a bare minimum a tank with at least 10 hrs storage capacity at the designated minimum or trigger storm flow rate, corresponding to at least 493m3 storage capacity is indicated. We note that such a storage capacity may well have been sufficient to fully store the demand which triggered the untreated discharge events on 14/01, 10/03 and 02/09 in 2008 and which lasted less than 10 hrs, and could have contributed to cutting the discharge events which occurred on 11/04 and 12/12 by something in the order of a half, naturally depending on the extent to which the actual storm flows which occurred during those events exceeded the determined CSO trigger rate.

 

Secondly, we do not share the assessment of the EA that the anticipated dilution effect of storm water run-off into the usual contents of a town sewer main is always of such a magnitude that one need not be sufficiently concerned about the concentration of bio-hazardous bacteria and other pathogens within the combined discharge. We feel contrariwise that the mere fact alone that this discharge is not subject to any scale of anti-pathogenic treatment whatever during a spill event, merits its extra special handling by means of adequate storage, sampling and testing rather than the converse.

 

Finally, we note with grave concern that time of the most prolonged storm spill event that year (during the period 03/09 through to 13/09 ie. the 9.4 day ‘event’) appears to correspond alarmingly with the recorded failure in the sample of bathing water taken off Traeth Mawr (so called Newport North designated sampling point)  at  11:40 on 11/09 with respect to the mandatory faecal coliform parameter  laid down in the European Bathing Waters Directive, and which in turn led to the failure of Newport Beach to secure a “Blue Flag” designation in that year.

 

The attached copy of your site plan “z2010-T02.” has been used by us to overlay where we suggest such a further additional storm storage tank could be sited, with a further ‘thumb nail’ impression of the relevant subterranean cross-sectional elevation, showing the proposal in comparison with the existing tank arrangement, added under the blue coloured title.

 

The tank we propose and which we find to have adequate space next to the existing Cwm SPS to be practically housed, is of the dimensions 16 x 9.6 x 2.5m = 384m3 which, when taken together with the existing smaller tank, produces a new total storm storage capacity of 524m3 (producing  10.63hrs of storage at the CSO trigger SWF rate) and which then not only meets but slightly exceeds our view of the minimal needs.

 

 

In conclusion, we would observe that whilst we naturally warmly welcome the prospect of the replacement so-called ‘long’ sea outfall which you are proposing to now shortly install, and the very positive effect that this is anticipated as having on the performance and capacity of the sewerage installation here in Newport ; nevertheless, this installation will have no effect whatever on the frequency and extent of spills occurring through the SPS CSO, which is determined instead by the pumping capacity of the SPS as against the anticipated storm flow rate demands, rather than by anything to do with the flow rate capacity of the discharge sea outfall.

 

Consequently, it seems to us that, given the relative minor additional expense involved in the installation of an additional storm storage tank, when taken in comparison to the scale of the current outfall replacement project , particularly when undertaken at a time when the requisite plant and workforce will be on-site in any event, the benefits to the overall optimal performance of the system is a further improvement of a self-evidently worthy nature.

 

 

 

 

 

 

 

For and on behalf of the

Newport Area Environment Group