East Cambridgeshire District Council Water Cycle Study Detailed ...

17
Key
Stage 2 Water Cycle Study: Final Report
Sept 2011
28
Cambridgeshire Horizons
East Cambridgeshire – Detailed WCS
standard was calculated which will be needed as soon as the growth causes the WwTW flow
consent to be exceeded. This consent has been given in Table 3-3 below and is described as
what is required immediately. The results are presented geographically in Figure 3-1.
Table 3-3: Stage 2 modelling results for no deterioration
WwTW
Soham 12
Immediate consent requirement to
achieve no deterioration as soon as
flow consent is exceeded
BOD NH4 P
>current
consent
Is no deterioration
achievable?
1 Yes
Burwell 9 4 0.25 No (due to Phospate)
Bottisham 5 0.5 1
No (due to Ammoniacal
Nitrogen)
Haddenham 19 4 1.9 Yes
Witchford 18 11
No change
required
Yes
Littleport 12 4 1.7 Yes
Little
Downham
14 9
No change
required
Yes
Witcham 11 18 1.9 Yes
Green Value – no
change to current
consent required
Amber Value – consent
tightening required, but within
limits of conventionally applied
treatment processes
Red Value – not
achievable within limits of
conventionally applied
treatment processes
For Soham and Burwell, where ‘no deterioration’ could not be achieved, a new solution is
required for growth in these catchments as the absolute requirement of the WFD cannot be met
(see section 3.2.2- results discussion for further detail).
Step 2 – meeting future good status
For all WwTW where the current downstream quality of the receiving watercourse is less than
good, a calculation was undertaken to determine if the receiving watercourse could achieve
future Good status with the proposed growth within limits of conventional treatment technology
and what consent limits would be required to achieve this.
The assessment of attainment of future good status assumed that other measures will be put in
place to ensure good status upstream so the modelling assumed upstream water quality is at
the mid point of the Good status status for each element and set the downstream target as the
lower boundary of the Good status for each element.
If Good could be achieved with growth with consents achievable within the limits of
conventional treatment, then a proposed discharge consent standard which may be needed in
the future has been given in Table 3-4 below 17 .