Preliminary Report
Natural Attenuation of Hydrocarbon Contamination by Denitrification in Nizwa Area

Table of Content
I Introduction
II Hydrocarbon Contamination
III Groundwater Condition in the ISS wells.
III.1 Total Petroleum Hydrocarbon
III.1.1 Biodegradation of the hydrocarbon contamination
III.2 Chemical analysis
III.2.1 Denitrification
III.3 Trace elements
IV Approach to solve the problem
V Summary
VI Recommendations
VII References

Groundwater contamination is one of the major problems facing the country and of great concern for the government. The contaminated groundwater is not only reducing the available water resources for use but also pose a threat to the human health. The groundwater has deteriorated in many locations due to various types of contamination and certain shallow aquifers their water status have shifted from fresh into brackish. In other words the groundwater shifted from good quality water fit for drinking purposes into contaminated completely unfit for human consumption and even for irrigation. The hydrocarbon contamination is the worse type. Such contamination had been documented at various locations throughout Sultanate of Oman. A detail study for four areas beside the potential contamination by hydrocarbon to the groundwater resources by the PDO wells had been described using the GIS techniques (Bajjali, 2000). Therefore, this report will focus only on Nizwa wells.

This research focusing on how the phenomenon of the denitrification is took place and how it can be used for eliminating naturally the hydrocarbon contamination.

A decline in the redox potential of the groundwater can, in some situations, cause DENITRIFICATION, a process in which nitrate (NO3) is reduced to N2O or N2.

This means that there is a hydrochemical process responsible for the reduction of nitrate level in groundwater. In literature the phenomenon of the denitrification is very well documented. The denitrification is a process that require a source of organic matter (hydrocarbon) and abundant NO3-, and bacterial systems that are capable of denitrifying large amount of NO3-. The NO3- concentration is considered to be the electron acceptor and in general it will be reduced and also consume the hydrocarbon as illustrated in general in equation 1.

CH2O + 0.8NO3- ® 0.4N2 + HCO3- + 0.4H2O + 0.2H+ Eq.1

For example the toluene (C6H5-CH3) will degraded as follow:

C6H5-CH3 + 7.2H+ + 7.2 NO3- ® 7CO2 + 7.6 H2O + 3.6 N2 Eq.2

It is obvious that the denitrification process is the only mechanism responsible for NO3- concentration reduction.

In 1980, a free oil layer has been detected floating on the top of the water table in some of the shallow groundwater wells located along Wadi Abyad. The groundwater contamination presumably caused by oil product leakage from three sources; Under Storage Tank (UST) of old Shell fuel station, Electric Power Station (EPS) and repair garages next to Shell station.........