Lima, the capital city of Peru, was home to over 6.5 million inhabitants
as of 1992, some 30% of the total Peruvian population, and accounts for
approximately 80% of the national industrial production. Lima is divided
into 41 administrative districts and the conurbation extends to the coast
to include the port of Callao. The urbanized area of the city is constrained
by the Andes mountain chain which runs parallel to the coast and future
growth is likely to be along the coastal strip and into three adjacent
river valleys: Chillon, Rimac and Lurin. In the past 40 years Lima has
grown rapidly, due in part to immigration from other parts of the country.
Since 1971 the population is estimated to have doubled from 3.3 million
to almost 6.5 million in 1992 (City of the World, 1998). The increase in
population has led to increased numbers of people living in non-planned
settlements, many of which are not served by water, sanitation or power.
Peru has three different climatic zones: the desert, mountains and the
rainforest. But Lima has its own climate, it's generally hot during the
summer and grey during the winter when the fog (garua) comes in. It's chilly
to cold during these months. Lima is situated just 12 degrees below the
equator, but its temperatures, modified by the cold Peru (Humboldt) Current,
average 21.0 C in Jan and 15.0 C in July. It has an arid climate with low
precipitation; the average annual precipitation is 26 mm; sea mists and
occasional light drizzles and fog during the winter supply moisture (Britannica,
1998).
The Lima aquifer comprises unconsolidated alluvial sediments deposited
by the rivers Rimac and Chillon, occurring either as lenticular deposits
or as cross-linked beds. The aquifer is of variable width and is bounded
by Jurassic and Cretaceous sediments - limestones, marls, arenites, quartzites
and mudstones, as well as intrusive granites, granodiorites, diorites and
andesites. The aquifer extends from the coastal plains in 'fingers' up
to the highest parts of the Rimac and Chillon river valleys. The aquifer
is split into two principal formations. The upper part of the alluvial
sediments is mainly composed of gravels and other coarse-grained sediments,
such as cobble beds, and these reach a thickness of up to 100 m. The coarse-grained
sediments have a sand and clay matrix and are interspersed with fine-grained
layers, causing variations in the permeability of the aquifer. The primary
water-bearing sediment are deposits of old courses of the Rimac and Chillon
Rivers, these being coarse-grained and of high permeability. The lower
part of the unconsolidated sediments is much finer and is largely composed
of sands, silts and mud, which reach depths of up to 150 m. These deposits
become increasingly fine-grained with increasing depth, and their permeability
decreases. The greater part of the aquifer is unconfined as the material
is mostly unconsolidated alluvial deposits, but there are exceptions: e.g.
there is a localized confined aquifer in the Callao area where the upper
alluvial layers are fine-grained deposits laid down on low-lying land between
the Rimac and Chillon (Rojas et al, 1994).
Besides the fast growing population, the water is mainly used for industrial
and agricultural activities. A small portion is for urban uses such as
parks and hotels for tourists. Water and sewerage services in the metropolitan
Lima are managed by the Lima Water Authority (SEDAPAL), part of the national
Potable Water and Sewerage Service (SENAPA) (Binnie and Partners, 1987).
There is a substantial increase in demand for water due to the rapid population
growth and urbanization in Lima. The result is over-extraction of groundwater.
It is not sustainable as the water drops 1-2 m every year (Rojas et al,
1994). The quality of groundwater is the main issue in Lima. The aquifer
is heavily contaminated by industrial and domestic faecal pollution as
well as the polluted River Rimac that recharges it. The quality deterioration
continues up to the point of consumption due to the recontamination in
the distribution network (Rojas, 1993). The public health effect of groundwater
supply is not only related to quality which requires immediate remedial
actions, but also other factors such as continuity of supply, coverage,
quantity and accessibility.
It is evident that there is significant faecal contamination of Lima aquifer,
which represents a risk to public health. A majority of groundwater sources,
which supply the distribution network in Lima, are chlorinated to disinfect
the water and the goal is to provide a free chlorine residual to prevent
recontamination in the distribution network. But recent studies show that
only 36.6% of groundwater supplies achieved the goal, the remaining portion
did not maintain any free residual due to equipment breakdown, poor maintenance
or high chlorine demand and thus do not provide protection against introduction
of bacteria in the distribution network. The main sources of faecal contamination
of the Lima aquifer are: abandoned dug wells, especially those that are
in the industrial sites, that are not sealed; currently used dug wells
which do not have a complete sanitary system; inefficient and unlined waste
stabilization pond and effluent irrigation at Callao; and the River Rimac
that recharges the aquifer, is grossly contaminated with agricultural and
industrial pollution with high levels of nitrate and other organic compounds.
As in common in developing countries, there is a lack of reliable data,
which describe the groundwater quality in Lima that makes groundwater quality
assessment difficult (Rojas et al, 1994).
There is an urgent need for routine groundwater quality monitoring to be
established and a thorough hydrogeological survey of the Lima aquifer to
be undertaken to establish flow patterns and rates, areas of recharge and
increased aquifer vulnerability, the level, type and distribution of existing
pollution, and to assess migration rates of common contaminants. In order
to improve the groundwater quality, there are a number of immediate actions
that could be taken to ensure that the quality of the groundwater supplies
for drinking in Lima is improved. The sealing of all unused and unprotected
wells in the city with low-permeability material such as clay is a priority
to prevent continued contamination of groundwater. This would remove obvious
point sources of contamination of groundwater within the city, help to
reduce the vulnerability of the aquifer to contamination. Other remedial
and preventive measures include lining of the waste stabilization pond
to the south of Lima; improvement of effluent quality and modification
of irrigation techniques to make them more efficient; control of the quality
of domestic sewage and industrial discharges into rivers and near groundwater
sources; and introducing restrictions on the use of inorganic fertilizer
and pesticides in aquifer recharge area (Bartram, 1990). In order to reduce
the pressure on the groundwater supply, Pomacocha-Rio Blanco Water Resource
Transfer Project was proposed in 1998. The purpose of the project is to
stabilize the volume of water in the Limac River, which falls considerably
in the dry period. It also ensures sustainable supply of water to Lima
by transferring water resources as a new source of water supply to the
Blanco River, a branch of the Rimac River, which flows through Lima, from
the Pomacocha Dam (see electronic reference).
Bartram, J., 1990. Drinking Water Supply Surveillance. Robens Institute
and WHO. Guildford. pp. 14
Binnie and Partners, 1987. Management of Aquifer Resources in Metropolitan
Lima. Report to SEDAPAL, pp. 105
Foster, S., and Hirata, R., 1998. Groundwater Pollution - an executive
overview of the Latin American-Caribbean situation in relation to potable
water-supply/ WHO, PAHO and CEPIS. Lima, Peru. pp. 38
"Peru". 1998. Britannica, vol. 25, Encyclopedia Britannica Inc., Chicago,
US, pp. 506
"Peru". 1998. Cities of the World, vol. 2, Gale Research Inc., Detroit,
US, pp. 743
"Peru". 1999. The Europa World Year Book, vol. 2, Europa Publication Ltd.
London, UK, pp. 2818
Rojas, R., 1993. Bacteriological Groundwater Quality of Lima Water Supply.
pp. 9
Rojas, R., Howard, G. and Bastram, J. 1994. Groundwater quality and water
supply in Lima, Peru. Groundwater Quality. Chapman and Hall, London, UK.
pp. 159-167
