East Cambridgeshire District Council Water Cycle Study Detailed ...

Stage 2 Water Cycle Study: Final Report
Sept 2011
37
Cambridgeshire Horizons
East Cambridgeshire – Detailed WCS
solutions if there is deemed to be no headroom) through a series of workshops . This would
allow some early phasing of allocated and Windfall development (191 dwellings) at a controlled
per annum completion rate, and as such an amber coding has been applied to the first 5 year
delivery timeframe for Burwell (as reflected in section 6.5); this controlled per annum rate would
need to reflect that there are 31 outstanding developments to be built that already have
planning permission in the Burwell WwTW catchment Until a solution is developed for the
allocated and windfall sites, a red category has been applied to growth between 2015 and
2031.
In summary:
• The remaining residual allocated and windfall development proposed for Burwell should be
limited to an annual completion rate agreeable with both AWS and the Environment Agency
up to 2015; It is likely that the 31 outstanding permissions will take any available headroom
that can be identified up to 2012 and hence growth from allocations and windfalls should not
be granted permission without confirmation from AWS and the Environment Agency that
capacity is available up to 2015;
• ECDC should meet monthly with AWS and the Environment Agency to determine a suitable
annual completion rate up to 2015 until a long term solution can be determined;
• ECDC should facilitate workshops with AWS and Environment Agency to develop a long
term solution to be developed in time to implement in the next Asset Management Plan
period (2015 to 2020) to allow all remaining residual growth to take place.
Bottisham WwTW - Solution
Ammoniacal-N standards within the Swaffham Bulbeck Lode will limit the total volume of
effluent that can be discharged at this location. RQP modelling has shown that no further
increases in flow from Bottisham WwTW will be possible without deteriorating from the current
High Status for ammoniacal-N, even when treating at the limits of conventional treatment; an
absolute requirement of the WFD is that there must not be deterioration from the current status.
The modelling has shown that to maintain High Status, only a total of 7m 3 of discharge at a
treatment level of 1mg/l of Amm-N would be possible at this location, equating to 22 homes.
This level is lower than the number of homes already being treated at the WwTW which
suggests that if the WwTW operated at the Ammonia limit set by the new consent recently
issued it would prevent ‘High’ status for ammoniacal-N from being maintained irrespective of
growth. This in turn suggests that either the WwTW currently treats Ammoniacal-N to levels
that are beyond that considered achievable by conventional treatment or that there is a greater
availability of flow and hence dilution in the Swaffham Bullbeck Lode than is calculated using
conventional tools used to determine flow statistics.
There are several options that can be considered as follows:
a) proposed development in Bottisham that has yet to be granted permission be allocated
elsewhere 26 ;
b) an agreement to be reached between the Environment Agency and AWS as to how much
additional growth would be feasible at the WwTW before it would be considered that the
growth would be having additional detrimental impact to that currently caused by existing
flows and flow consents. It has not been possible within this Detailed WCS (using the high
level RQP methodology agreed with the Environment Agency) to ascertain an additional
26 50 dwellings of the residual Bottisham target of 136 across the plan period have already been granted permission and hence
cannot be located elsewhere.