There is an emergency/storm overflow from the Pentewan pumping station, that discharges
to the St Austell River 250m from the beach.
Within the Pentewan bathing water catchment there are four emergency/storm overflows
that discharge into the St Austell River at least one and a half kilometres upstream
of the bathing water.
The operation of the overflows can lead to a temporary drop in water quality in the
St Austell River and Pentewan bathing water.
This bathing water is included in the Surfers Against Sewage “Safer Seas Service”.
This service can alert you to Combined Storm Sewer Overflow discharges via a phone
App and in addition, it includes the Environment Agency Pollution Risk Forecast warnings
where they are available. Further details of the service can be found at - http://www.sas.org.uk/safer-seas-service/
The South West Water scheme for Menagwins (St Austell) sewage treatment works (STW),
which provides secondary treatment and ultraviolet (UV) disinfection, was completed
in 1996, on a trial basis. The continuous untreated discharge at Mevagissey was transferred
to Menagwins STW in 1997, and following completion of the trials, the UV system was
permanently installed in early 1998.
Improvements were made to the sewerage network in Mevagissey in 1999 which have reduced
saline infiltration and flooding problems at both Mevagissey and Menagwins. Improvements
were made to the storm discharges Menagwins STW in early 2000.
Storm overflow event duration monitoring (EDM) was installed at Menagwins STW and
Pentewan pumping stations by April 2011.
The urban area of St Austell (six kilometres upstream from the bathing water) is served
by a combined (surface and sewer) system. There are no outfalls from the system onto
the beach.
For the four year (2015-2018) assessment period where data is available, seaweed (macroalgae)
was assessed as being sufficient to be objectionable for 1% of visits, with 86% of
visits noting the presence of seaweed (macroalgae). This bathing water does not have
a history of large amounts of seaweed (macro algae).
For the four year (2015-2018) assessment period where data is available, phytoplankton
(microscopic algae) was not assessed as being sufficient to be objectionable, but
was observed as being present on 1% of visits. Phytoplankton (microscopic algae) naturally
increase in number at certain times of the year. This process is known as a phytoplankton
bloom. This bathing water does not have a history of phytoplankton blooms.
The risks to human health from contact, ingestion or inhalation with marine algae
that currently occur in UK coastal waters are considered to be low. However, some
individuals may be more sensitive and display some reactions.
A common marine algae found in UK coastal waters is Phaeocystis, which is often mistaken
for sewage as it forms foam and a brown scum, but it is non-toxic.
Streams and rivers are typically affected by human sewage, animal slurry and runoff
from roads. The St Austell River flows onto this beach at the north end. The Environment
Agency have monitored the river at Pentewan Bridge between 1986 and 2008, and found
that water quality is temporarily worse during and after heavy rainfall.
The outfall from Menagwins (St Austell) STW discharges to the St Austell River approximately
4.6km upstream of the bathing water. This discharge is disinfected and designed to
protect bathing water quality.
Environment Agency samplers make observations of litter present on the beach at every
visit, this includes assessments of sewage debris, litter and tar. At Pentewan for
the four year (2015-2018) assessment period where data is available, sewage debris
was not noted at this site. Litter was not assessed as being sufficient to be objectionable,
but was observed as being present on 57% of visits. Tarry residue was not noted at
this site.
The catchment surrounding Pentewan is approximately 3,960 hectares and includes the
St Austell River which rises near Carthew. The river flows through areas of flood
plain for much of its course south of St Austell and enters the sea at Pentewan Beach.
In the past the St Austell River has been affected by the China clay industry. The
combined effects of clay mining, cross catchment transfers and the porous nature of
the catchment, have reduced runoff from the steep gradient of the St Austell River
resulting in reduced peak flows to the bathing water. Two much smaller streams also
flow across the beach just south of the Environment Agency monitoring point.
The catchment is mostly agricultural, with around 20 farms. The rural areas are mostly
improved grassland with pockets of arable land and woodland especially in the steeper
valleys. The upper third of the catchment is characterised by the china clay mining
landscape including the pits and associated spoil heaps. Urban areas include part
of St Austell and Pentewan and there are camping and holiday parks close to the coast.
Seaweed (macroalgae) and phytoplankton (microscopic algae) are a natural part of the
marine and freshwater environment. Below we note whether these have been recorded
in quantities sufficient to be a nuisance.
The majority of sewers in England are “combined sewers” and carry both sewage and
surface water from roofs and drains. A storm overflow operates during heavy rainfall
when the sewerage system becomes overwhelmed by the amount of surface water. The overflow
prevents sewage from backing up pipes and flooding properties and gardens. An emergency
overflow will only operate infrequently, for example due to pump failure or blockage
in the sewerage system.
Heavy rain falling on pavements and roads often flows into surface water drains or
highway drains, ending up in local rivers and ultimately the sea. The quality of bathing
water may be adversely affected as a result of such events.
It is the Environment Agency role to drive improvement of water quality at bathing
waters that are at risk of failing higher standards. It is natural for water to run
off the land to the sea. Water quality at a bathing water is dependent upon the type
and area of land (the catchment) draining to the water and the activities undertaken
in that catchment.