Millennium EMS Solutions Ltd.
April 2013
Executive Summary
Petroleum Technology Alliance Canada (PTAC) is investigating the feasibility of treating saline water from source water wells to criteria that would allow storage in unlined earthen reservoirs and transportation via overland pipelines. The objective of this study is to develop risk‐based guidelines that would dictate the level of treatment required to store saline water in this manner.
The scope of work included a comprehensive regulatory review, development of risk‐based criteria for the treatment of saline water, and an evaluation of potential liabilities.
PHASE I: Regulatory Review
Review of Existing Guidelines for Saline Water Storage and Transport
Guidelines related to saline water from regulatory agencies in North America were reviewed and summarized. For the purposes of the review it was assumed that the treated water would retain ion concentrations above natural background levels associated with groundwater and would be considered saline. Alberta defines groundwater with over 4,000 mg/L total dissolved solids (TDS) as saline and non‐potable, a definition which has also been adopted by British Columbia, Saskatchewan, and Manitoba.
Groundwater Quality Data in the Pipestone and Gordondale Areas
Groundwater quality data for the Pipestone and Gordondale areas of Alberta were compiled and evaluated. Sufficient data could not be found for the Gordondale area; therefore, data from the Pipestone area was considered to be representative of the entire study region. The waters analysed in the Pipestone area were found to have a mean TDS content less than 1,500 mg/L and were potentially potable.
Development of Risk Based Criteria
Two scenarios were developed: storage of 50,000 m3 of water with a pre‐treatment TDS of 20,000 ppm, and storage of 15,000 m3 of water with a pre‐treatment TDS of 2,000 ppm. These initial conditions were used as a starting point to derive risk based criteria, as the water will be treated before entering storage and will not include any other contaminants related to oil and gas processes.
Both human and ecological receptors were considered, exposed through ingestion and contact with impacted groundwater, respectively. Direct contact with saline water in the storage ponds is not considered a hazard to human or ecological receptors.
No existing models were identified that were directly applicable to the scenarios being modelled, and so existing models were adapted. Preliminary modeling was undertaken using the Subsoil Salinity and a modified version of the groundwater model used by Alberta Environment and Sustainable Resources Development (ESRD) to derive the Tier 1 and Tier 2 guidelines. The purpose of this preliminary modelling was to generate an expected range for salinity guidelines that would be applicable for unlined ponds. A sensitivity analysis was conducted by varying model input parameters within potential ranges.
Results
The 5th percentile value of all SST model runs from the sensitivity analysis, 5000 mg/L TDS, was selected as a representative guideline that would be protective of the vast majority of sites; no cases evaluated in the sensitivity analysis resulted in guidelines below this value.
Phase II: Risk and Potential Liability
Methodology
The liability assessment uses a fault tree/event tree approach that considers a number of release scenarios. The total liability associated with transporting and storing saline water would be the expected cost multiplied by the unit probability of failure aggregated over the number of kilometres of pipeline or number of storage facilities.
Scenarios and Probabilities of Failure
The expected costs for remediation of six release scenarios were calculated. These scenarios included both catastrophic and gradual releases from: pipelines, lined ponds, and unlined ponds. For each of the six scenarios, four possible spill types were considered, including: large volume of untreated saline water, small volume of untreated saline water, large volume of treated saline water, and small volume of treated saline water.
It was assumed that only treated water would be stored in unlined ponds, and that untreated water would be transported by pipeline or stored in lined ponds. The treated water would meet the derived criteria for storage, but the risk of impact would arise as a result of a greater rate of release than that assumed in the modelling.
Four common options for remedial action were included in the analysis:
Results
Liability was similar between unlined and lined ponds, with an expected cost of $1.131M for lined excavations and $1.607M for unlined excavation. Liability for pipelines was lower, at $0.265M per km of pipeline. Additional consideration of site placement, pipeline length, and design lifetime are required in order to accurately compare the expected costs of remediation between these methods.
# 09-9211-50