Abstract
The pipeline industry strives for continuous improvement and reaching zero incidents. The risks associated with below grade pipelines are typically assessed in detail as part of operators’ pipeline integrity management program. However, the level of risk associated with above grade facilities and equipment is often not investigated to the same level. As part of an effort, with an anonymous pipeline operator, to refine the calculated risks associated with these facilities and valve sites, a focus was made on enhancing the consequence calculations with more accurate site-specific information. An approach was developed to assess whether smaller volume releases from these locations may impact nearby waterways following a release.
The operator identified 150 sites throughout North America where releases had the potential to contaminate a waterbody. In order to confirm/disprove this potential impact to water, hypothetical releases of multiple hydrocarbon products were simulated using oil spill modeling tools to assess the potential overland and downstream transport and fates of the released products. Hypothetical release scenarios were simulated until all of the modeled oil had been released and had either adhered to the land surface, filled a depression in the land surface, and/or evaporated to the atmosphere; or when oil was predicted to enter a perennial waterbody (stream or lake). The goal was to assess the potential for each release to reach a waterbody. A single release was simulated for each site based on a historical maximum volume for a release associated with the specific equipment type (e.g. valves) that could be released over a 24-hour period. Releases were simulated using conditions selected to produce reasonable, conservative results to maximize the potential for the largest volume of oil to enter a waterbody. These conditions were based on the spring season, where rivers and streams would be under some of the highest flow conditions, intermittent streams and waterbodies would contain water feeding larger water bodies, cool air temperatures would reduce evaporative losses, and no snow cover maximize overland transport.
This screening level analysis allowed for identification of each location’s potential to reach a nearby waterbody under the conservative set of conditions and assumptions. By eliminating sites where oil would not reach a waterbody, the operator was able to focus efforts on the highest consequence areas in order to complete more detailed field-level analysis. In regard to spill modeling, more detailed analyses could be conducted in the future to predict the range of possible outcomes from other types of releases and using more site-specific and season-specific data. As an example, slower releases/leak rates, enhanced evaporative losses, a range of environmental conditions, and/or losses to infiltration could be assessed to bound the range of potential impacts.
