Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 110
16 WATER SUPPLY
One specific task of the ESIA for Mt. Coffee HPP is to look at the situation of, and
potential positive or negative impacts of the Project on, the drinking water treatment
plant downstream of the dam.
16.1 Situation of White Plains Water Treatment Facility
White Plains Water Treatment Facility was inspected by the Consultant on January 19,
2012, together with a representative of the Liberia Electric Company (LEC) and
representatives from the Liberia Water and Sewage Company (LWSC).
The facility comprises two treatment plants, the former now derelict plant that received
its raw water supply from the Mount Coffee HPP, and the newer plant that draws raw
water directly from the St Paul River. The latter was first constructed in 1968 in a joint
project between the Republic of Liberia and the USA. The facility was latterly
augmented under “Monrovia Water System Phase II” in 1982 cited as a “Joint KL & O
Project” with the Republic of Liberia, World Bank and the Republic of Finland.
Although structurally sound, operated well, with a seemingly well-equipped analytical
laboratory on site, the plant is clearly suffering from broken or worn out ancillary
equipment. Negotiations with consultancy companies are on-going, with a view to
engage one of them for engineering services pursuant to rehabilitation of the facility.
Notwithstanding the above, the LWSC are keen to re-establish the raw water pipeline
between the Mount Coffee HPP and White Plains Water Treatment Facility. However,
the existing capacity of the Mount Coffee Pipeline may be insufficient in terms of
capacity and is in need of revision. Its take off may need to be relocated due to water
quality issues that may arise from the construction of new reservoirs above the Mount
Coffee HPP; this is an issue that will have to be addressed a carefully evaluated in the
EIAs that will have to be prepared for these projects.
As mentioned above, the raw water pipeline is presently connected to the Mount Coffee
HPP Turbine penstocks; the valve mechanisms are missing, some of the joint clamps are
missing, and one of the concrete supporting pedestals has been undermined, the exposed
section of the pipe [manifold] is seemingly full of silt. In addition to these issues an
approximate 50 metre length (approx. 10 sections) has been washed out of the river
embankment some 700 metres downstream of the HPP, reportedly at the same time as
the historic breach.
The previous report of saltwater intrusion being drawn into the water treatment facility
from the lower estuary has been averted by the construction of a river spanning rock
weir across the St Paul river some 200-300 metres downstream of the raw water intake,
which has resulted in the effect of creating an artificial pool, and effective barrier
against the afore mentioned intrusion due the difference in water levels.
An additional site visit was mad by the Consultant on April 25, 2012. At that day, high
tide was at 09.36 h. At that time, at the rock weir d/s of the intake structure a
conductivity of 40 µS/cm was measured, no difference between u/s and d/s of this
structure. Flow velocity was estimated at about 0.5 m/s. At 08.55 h, a measurement had
been taken approximately 10 km downstream. At that site, a conductivity of 170 µS/cm
was recorded, and 140 µS/cm at the same place at 16.10 h (low tide had been at 15.15 h).