THE UNIVERSITY OF NAIROBI

SCHOOL OF PHYSICAL SCIENCES

DEPARTMENT OF GEOLOGY

SGL 413: PROJECT IN GEOLOGY

TOPIC: EVALUATION GROUNDWATER USING

ENVIRONMENTAL ISOTOPES: A CASE STUDY OF

MERTI AQUIFER.

BY:GEORGE IGUNZA MULUSA

REG. NO:I13/2536/05

ADVISOR:

PROF. E.O.ODADA

A dissertation submitted in accordance with the requirement for a partial fullfilment of the

Bachelor of Science degree in Geology.

DUE: 27TH FEBRUARY, 2009

ABSTRACT

The evaluation of ground water quality in Merti aquifer was studied using environmental isotope

data of approximately 130 locations collected during 1974 to 2002. The principal evaluation

methods included hydrogen, oxygen and carbon stable isotope ratio analysis, radiocarbon and

tritium dating. The main conclusions are as follows.

Significant differences are observed in the stable isotope compositions. The combined isotope

data suggest that deep groundwater east of the area was recharged during periods of between

12,000 and 19,000 years ago. At depths -:::200feet, ground waters east of the area range in 14C

ages from 2400 to 12,000 years due to shallow mixing of younger water with older groundwater

ascending under hydraulic head into the discharge area.

Only two groundwater sources were observed to contain tritium at concentrations above the

background level. Both of these sources are from the Long Valley area. The lack of tritium in

other groundwater samples indicates that modem recharge «45 years) is not present in

detectable amounts in many of the wells.

Previous studies have outlined the general distribution and characteristics of groundwater

resources in Eastern and Northeastern Provinces. Between 1969 and 1973 The Kenyan

government drilled boreholes, with assistance from external donors, to study the groundwater

dynamics of the area. This project established the existence of fresh water at Yamicha,,northwest of Habaswein, as well as the presence of fresh water in the central part of the Merti

aquifer along the Ewaso Ng'iro drainage. However, saline groundwater also occurs over broad

areas along the flanks of the fresh water zone of the Merti aquifer. Radiocarbon and tritium

samples analyzed by the US Geological Survey in the 1970s suggest that groundwater in the

Merti aquifer is recharged during major floods that may occur on a time scale of a few hundred

to a few thousand years, however the complex carbonate geochemistry of the aquifer made it

impossible for the USGS study to assign more ages to the recharge events. Evaluation of the

groundwater is essential for the development of civilization and to establish a database for

planning future water resources development strategies.

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