Storing oil underground overcomes the detrimental environmental effects of tank storage at the ground surface. But due consideration must be given to other factors. Preventing disturbance to the original groundwater pattern requires a thorough survey of the water table before mining operations begin, arrangements for maintaining a high water table during construction, and monitoring of subsurface water levels and quality during operations. The danger of an accident enabling oil to escape from the top of the shaft must also be prevented, by providing safety valves which operate automatical1y when the oil pressure drops. Underground storage offers environmental benefits in connection with other substances such as industrial and nuclear wastes.

INTRODUCTION

Even if the prime advantage that led to the development of underground oil storage was not environmental protection, there can be no doubt that it has made an important contribution in this area. The excellent safety record of the steadily increasing number of underground facilities throughout the world demonstrates their advantages over the more conventional tank farm as regards safeguardmg the countryside. Today, environmental protection must be one of the developer's foremost preoccupations before, during and after commissioning of a new store, and the increasingly large place given to environmental impact studies is ample evidence of this. With this trend in mind, we have taken a hard look at the specific precautions needed in connection with underground storage, working towards increasingly sophisticated means of protecting groundwater so as to retain the original properties of the rock formation and prevent migration of the stored products, and avoid any danger of an oil burst at the ground surface as a result of wilful damage as well as under normal operating conditions. Because of its excellent environmental safety, underground storage must inevitably spread to embrace other substances, for which present-day techniques do not provide adequate protection, such as industrial wastes whose neutralization would present an over-arduous pollution problem and radioactive wastes, for which underground repositories are the most logical answer, and should become a reality within the next decade.

PROTECTION OF THE COUNTRYSIDE

The advantages of underground storage as regards protection of the countryside need no elaboration, because it has been in use for many decades. We shall merely illustrate the fact by describing the Manosque oil storage facility, which has a capacity of 7.5 million cubic metres in a salt dome underlying public forest land.

Most of the Land is Untouched by the Engineering Works

The topside site area needed for a storage cavity of several hundred thousand cubic metres only represents about fifteen square metres for the top end of the shaft, with the stand pipes and valves only rising to a height of less than three metres. Each shaft head is surrounded by a concrete slab covering about 1,500 square metres, which is fenced off. The control buildings and pump house are practically the only constructions visible in the landscape. And even these have been grouped together at Manosque, so that they only cover an area of three hectares.

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