SEPA discharge consents
SEPA is responsible for the regulation of discharges
to controlled waters under Part II of the Control
of Pollution Act 1974 (as amended) and for the granting
of consents and service of instruments to discharge
under that Act. It inherited these functions under
the Environment Act 1995 from the river purification
Since its inception, SEPA has been formulating
policies to discharge these responsibilities, including
- Consenting policy for discharges to controlled
waters (SEPA Policy No. 3, Version 1, July 1996)
- Microbiological standards in marine waters (excluding
shellfish waters) in relation to design criteria
for discharges (SEPA Policy No. 27, Version 1,
- Initial dilution and mixing zones for discharges
from coastal and estuarine outfalls (SEPA Policy
No. 28, Version 1, September 1998).
Point source discharges for which consents are
required include sewage and industrial discharges
from non-prescribed processes (trade effluent).
Prescribed processes require an IPC authorisation
which is also issued by SEPA. Discharges from marine
fish farm installations are considered to be trade
effluent and require a discharge consent.
The procedure for the application for a discharge
consent and the form of consent conditions (95 percentiles,
upper tiers and absolute limits) is similar to that
in England and Wales.
There is a requirement for all existing discharges
to meet the following statutory requirements:
- EC Bathing Waters Directive and UK Regulations
(appropriate mandatory standards must be met at
designated bathing waters);
- EC Urban Waste Water Treatment Directive and
UK Regulations (the appropriate level of treatment
should be applied to the sewage, based on the
population equivalent of the agglomeration served
by the sewerage system);
- EC Dangerous Substances Directive and UK Regulations
(EQSs for List I and II substances in receiving
waters must be met, including standstill provisions);
- EC Shellfish Directive and UK Regulations (appropriate
standards must be met for designated shellfish
- North Sea Conference and OSPAR commitments (reduction
in loads of toxic substances in discharges to
the marine environment must be demonstrated).
policy on initial dilution and mixing zones (SEPA
Policy No 28) sets out requirements to be met in
the design of new or modified discharges.
For discharges with greater than 100 population
equivalent, outfalls should be designed and constructed
to provide the following minimum initial dilution
to reduce both the visibility of density slicks
and the occurrence of smell nuisance to acceptable
- minimum initial dilution of 100 times (95 percentile)
for primary treated effluent;
- minimum initial dilution of 50 times (95 percentile)
for secondary treated effluent, including septic
- minimum initial dilution of 50 times (95 percentile)
for significant new or modified industrial discharges
(to be judged on an individual basis).
Modelling studies are required to determine the
best location and design of the outfall and to demonstrate
achievement of the minimum initial dilution requirements.
SEPA specifies the requirements for modelling studies
and recommends the use of one of 3 models: ELSID,
PLUMES or CORMIX (see SEPA Policy No. 28).
Requirements for mixing zones are also specified
to inform the design of an outfall and the consent
conditions to be set to achieve compliance with
statutory requirements and to protect the environment.
These requirements include:
- a limitation on the size of a mixing zone to
100 m in any direction;
- UK or SEPA Environmental Quality Standards (EQSs)
should not be breached outwith the mixing zone;
- where toxicity-based criteria are used, there
should be no residual toxicity outwith the mixing
- neighbouring mixing zones should not merge and
ideally should be at least 100 m apart;
- no mixing zone should impinge on the Mean Low
Water Springs (MLWS) shoreline;
- no mixing zone should plug an estuary, sea loch
or small bay;
- the mixing zone will not be allowed to jeopardise
the integrity of any European marine site;
- the mixing zone should not give rise to significant
slicks or other aesthetic problems;
- accumulation of solids on the sea bed must not
threaten the achievement of standstill clauses
for List I substances outwith the mixing zone
and not cause acute toxic effects to sediment-dwelling
organisms within the mixing zone.
SEPA has developed a policy for microbiological
standards in marine waters (except shellfish waters)
in relation to design criteria for discharges (SEPA
policy No 27). This policy has some influence on
all marine waters in Scotland.
For all marine waters, no new or modified discharges
will be allowed to result in deterioration of the
class which is currently achieved under the coastal
classification scheme nor threaten progress in improving
class C and D marine waters identified in SEPA's corporate plans.
For identified bathing waters, existing discharges
must enable mandatory standards to be achieved and,
for new or modified discharges, the outfalls must
be designed so as to achieve guideline standards.
SEPA may also designate >recreational
where significant water contact activities are practised
outwith identified bathing waters. SEPA will require
mandatory microbiological standards to be achieved
at relevant times of year and promote the achievement
of guideline standards where appropriate.
SEPA will also adopt a strong presumption that
mandatory microbiological standards are achieved
waters' (i.e. those visited by the public).
As in England and Wales, the primary driver for
the derivation of consent conditions is compliance
with statutory requirements, in particular bathing
water, Urban Waste Water Treatment and shellfish
water standards. SEPA has supplemented these requirements
in Scotland to some extent with their policies.
These policies enable Scottish Natural Heritage
(SNH) to verify that consent conditions for new
or modified discharges in or close to European marine
sites have been set according to the procedures
outlined in these documents.
The approach to the regulation and monitoring of
cage fish farming in Scotland has been comprehensively
laid out in a manual of procedures (SEPA 1998).
This manual provides details of the application
process, the assessment of the application, setting
consent limits, process for granting and refusing
a consent, monitoring, data management and use of
information and review of consents. Conservation
agency staff should have access to this document
to ensure that all cage fish farming consents have
been set according to the process.