Concern regarding the environmental implications of decommissioning major industrial facilities has been growing in recent years. Long term plant operations can lead to substantial on-site and off-site contamination problems and decommissioned sites must be left in an environmentally secure condition. Limited practical experience is currently available to assist in planning and completing environmentally acceptable clean-up and reclamation programs in association with a plant decommissioning exercise.

Gulf Canada Resources Inc. retained Monenco Consultants Limited to assist in the clean-up and reclamation of their major sour gas plant in Pincher Creek, Alberta, as part of the decommissioning activities. Monenco completed the following major activities:

  • reconnaissance field program to determine the extent, type and level of plant site contamination;

  • hydrogeological program to define the geology and hydrogeology of the area to determine on-site contaminant problems and probable pathways of contamination off-site; and

  • sampling program in the plant process area to determine existing conditions (location, type and level of contamination).

This paper summarizes the results of the above mentioned completed field programs. In addition, recommendations are made regarding the activities necessary to ensure that gas plant sites are decommissioned in an environmentally acceptable manner.


Decommissioning major oil, gas or chemical plants involves more than simply shutting down the process facilities and dismantling and removing equipment, buildings and storage facilities. In addition to the normal generation and accumulation of liquid and solid wastes such as sludge's and sediments, years of plant operation generally are accompanied by spills and leaks of process chemicals and products. As a result, normal plant operations may have inadvertently contaminated the environment in the area of the plant.

The General Decommissioning Scheme

Any decommissioning program for oil, gas, or chemical plants must include consideration of the possibility that contaminated soils, sludge's, sediments, surface waters and groundwater may exist on the plant site and may have influenced the environment outside the plant boundary.

In order to formulate a clean-up and reclamation plan for the plant site that is acceptable to the government regulatory agencies and the public, the decommissioning program must be based on a clear understanding of the nature and extent of possible plant site contamination as well as the geological and hydrogeological setting of the facilities location.

The activities associated with the clean-up and reclamation part of the decommissioning programs should be based on a progressive, step-wise approach to the problem, such as described in Figure 1. The first step in the process includes a plant site assessment (or operational history) based on:

  • plant waste management practices(past and present);

  • site inspections;

  • employee interviews;

  • operations history;

  • regulatory agency concerns;

  • literature data;

  • original plant setting;

  • plant site data;

  • process information; and

  • government information.

This initial assessment of the plant site, in turn, leads to the design of a reconnaissance level survey of the site. The objective of this survey is to identify the broad nature and extent of plant site contamination.

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