Environmental Mitigation Associated With the Installation of a Natural Gas Pipeline in the Vicinity of an Artesian Well

Abstract

In the fall of 2001, Enbridge Consumers Gas proposed to install a 190 mm extra-high pressure steel pipeline in proximity to an artesian well on the Oak Ridges Moraine in southern Ontario. This well is located within the Regional Municipality of Durham and it is used by over 300 persons per day as their drinking water source because of very high water quality. Potential impacts to drinking water quality have taken on greater importance because of the Walkerton tragedy, in which a number of people died from drinking contaminated municipal water. The Region of Durham was especially concerned because of the large number of people who use this artesian well as their drinking water source. The Region did not want to close the well during construction as this could be taken as an admission that construction might negatively impact water quality. At the same time, they wanted to ensure that water quantity and quality was maintained. SENES Consultants Limited (“SENES”) was retained to develop and implement an environmental management plan to ensure that no negative impacts would occur during construction. The plan involved characterization of the water-bearing zone in terms of depth, type of deposit and direction of flow, relative to the drinking water source. This was undertaken through the use of test pits, boreholes and piezometers. Potential construction impacts were identified. In this case, the natural gas pipeline was to be installed by a directional drill that injects bentonite (drilling mud) to provide lubrication and to keep the drill hole from collapsing. Mitigation measures related to containment of bentonite and fuel handling in the vicinity of the artesian well were prescribed. The rationale for directional drilling this section of the pipeline was to prevent erosion of the steep slopes and to undercross a watercourse. The water-bearing deposit consisted of a sandy-gravel layer that was found to occur at a depth of 3.65 meters. Every effort was made to maintain the drill hole for the pipeline above this depth. In addition to sampling the artesian well for chemical and bacterial parameters in advance of construction and upon completion of work in the vicinity, water from the artesian well and one of the piezometers was checked for turbidity every two hours. Other contingency plans included digging “burp-holes” to reduce the potential for bentonite frac-outs and having a water supply truck on stand-by should turbidity levels reach unacceptable levels. Construction proceeded smoothly. Minor frac-outs occurred and were appropriately contained. The turbidity readings and water quality samples taken before, during and post-construction confirmed that there were no negative impacts on the artesian well. The methods used on this project are directly applicable to other pipelines that may be constructed in the vicinity of artesian wells.