River Almond valley water quality modelling strategic study for Scottish Water - Dr Vera Jones (Atkins) MIKE by DHI 15th UK User Group Meeting - Tuesday 19 March 2013

1. River Almond Valley Water Quality
Modelling Strategic Study
Client: Scottish Water
Context
Atkins was commissioned by Scottish
Water to produce a dynamic water
quality model of the River Almond,
using DHI MIKE-11 Ecolab.
The study, which is subject to
regulatory sign-off from the Scottish
Environmental Protection Agency
(SEPA), consisted of two key
elements:
 Assessing the impact of Scottish
Water wastewater treatment works
(WwTWs) and combined sewer
overflows (CSO) on the water
quality of the River Almond and its
tributaries.
 Identifying strategic options to
meet the requirements of the
Water Framework Directive (WFD)
and Urban Wastewater Treatment
Directive (UWWTD).
MWH was appointed as the lead
consultant for this study and also
undertook maintenance of the
drainage system hydraulic models for
the catchment during the first phase
of the work.
Understanding of
catchment issues
Review of background information
indicted that wastewater pollution is a
significant pressure on the water
quality of entire main stem of the
River Almond.
Additionally, there is limited storage
capacity at wastewater treatment
works (WwTWs) and untreated
discharges from combined sewer
overflows (CSOs). Pollution from
septic tanks and other private
discharges is also affecting certain
tributaries.
Finally, the area suffers from pollution
associated with historic mining and
surface water outfalls from industrial
estates; these two last issues are
being considered by separate studies
undertaken by SEPA and Scottish
Water (respectively), which Atkins is
also involved in.
Water quality
monitoring
It was recognised during the scoping
phase that a high frequency and
spatially extensive water quality data
set was needed to inform this work.
As a result, a 4-month-long water
quality survey of the River Almond
catchment was commissioned, with
site work being undertaken by Aspect
Survey and co-ordinated by Atkins.
26 monitoring locations were selected,
aiming to capture potential impacts of
Scottish Water assets. Monitoring
included automatic monitoring, spot
sampling and wet weather surveys.
Model development
The results of the monitoring
programme formed the basis for the
development of a Mike 11 Ecolab
(DHI) hydrodynamic water quality
model by Atkins, which also
incorporated inputs from the updated
River Almond sewer model, produced
by MWH.
A standard Ecolab template was used,
with some modifications to meet the
requirements of this project. The
water quality determinands modelled
were: temperature, dissolved oxygen
saturation, ammonia, nitrate, ortho-
phosphate, particulate phosphorus,
biochemical oxygen demand (BOD).
The model was calibrated against
observed data from several
monitoring locations. Simulated
results showed an overall very good
match with the observed data.
Review of the calibration and
verification was carried out and
deemed the model ‘fit for purpose’.
Study Outcomes
Once model development was
complete, 10-year stochastic model
runs were carried out, aiming to
identify the key sources of impacts on
water quality. The results of these
stochastic runs indicated that key
parameters of concern with regards
to WFD compliance are ortho-
phosphate, BOD and ammonia. The
most significant cause of WFD
failures appears to be continuous
discharges from WwTWs. However
WwTWs also have a beneficial effect
on water quality, by diluting the CSO
inputs. Operation of key WwTWs at
‘Best Available Technology’ treatment
levels, even when this was simulated
without any CSO spills, was not
sufficient to bring the whole system to
the required WFD Good/High status.
Conclusion
These results suggest that, assuming
the current amount of wastewater
load to the system, achieving the
requirements of the WFD through
investment in Scottish Water assets
alone will be challenging.
During the next phase of the work,
the model developed will be applied
to test different strategic options to
achieve the requirements of the WFD
and UWWTD in the River Almond
system
Contact: Dr Vera Jones
Senior Environmental Scientist
vera.jones@atkinsglobal.com