TURNER VALLEY GAS PLANT SITE PROTECTION AND REMEDIATION Mike McCrank, P.Eng. Project Engineer, Stantec Consulting Ltd., Calgary, Alberta, Canada

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1 TURNER VALLEY GAS PLANT SITE PROTECTION AND REMEDIATION Mike McCrank, P.Eng. Project Engineer, Stantec Consulting Ltd., Calgary, Alberta, Canada INTRODUCTION The Historic Turner Valley Gas Plant is located on the north bank of the Sheep River approximately 60 km southwest of Calgary, Alberta. The facility was used for petroleum production and refining from approximately 1914 to 1985 after which it was decommissioned. The plant became a historic site in 1989 and a national historic site in Independent environmental studies of the gas plant site identified the following four major contaminants: asbestos & biohazards, mercury, sulphur, and hydrocarbons. Prior to the commencement of this project, all of the contaminants had been remediated or safely managed, with the exception of the hydrocarbons. The objective of this project was to specifically address the potential migration of hydrocarbons from the gas plant site into the adjacent Sheep River. Figure 1. Turner Valley Gas Plant (photo circa 1914). Stantec Consulting Ltd. (Stantec) was the lead consultant of a design team that produced a conceptual design for the site protection and remediation of the hydrocarbon contaminated groundwater at the Turner Valley Gas Plant. The design team included several sub-consultants that provided specialized engineering design services for the different components for the project. The sub-consultants and their roles included:

2 MPE Engineering Ltd. - Design of erosion protection works and river isolation works, construction supervision of erosion protection works. Thurber Engineering Ltd. - Geotechnical design of slurry wall, QA/QC monitoring of slurry wall and clay berm construction. Waterline Resources Inc. - Hydrogeological study of the project area. Key to the project design was a plan to isolate and remediate the hydrocarbon contaminated groundwater prior to any release into the adjacent Sheep River. The design includes: a geotechnically designed bentonite slurry wall (cut-off wall) to isolate and divert the groundwater of the lower terrace; a weeping tile system to divert the groundwater of the middle and upper terraces; an erosion protection system to protect the site from periodic flooding events on the Sheep River; and a treatment corridor to remediate hydrocarbon impacts on the groundwater prior to its release into the river. The conceptual design was approved by Alberta Infrastructure and Transportation. Stantec was then retained to facilitate the completion of remedial work at the Gas Plant. Stantec s role was to prepare a scope of work, prepare contract specifications, aid in tendering the construction contract, provide consulting services during execution of the contract, inspect work completed and collect and analyze samples where required. Tendering of the construction contract was conducted on a public basis. Alberta Infrastructure awarded the contract to the successful bidder, Quantum Remediation, A Division of Quantum Murray LP. INNOVATION The intent of this project was to design a system which would contain and remediate hydrocarbon impacts in the groundwater at the Turner Valley Gas Plant. The concept of contaminant containment is not new or innovative, and neither is the concept of remediation. However, designing a containment and remediation system, especially for such a large area, is innovative and requires many innovative techniques and ideas. Some of the innovative concepts that were utilized in this project included the following: Develop a treatment system to remediate multiple hydrocarbon contaminants, including: BTEX, PAH s and F1 to F4 Hydrocarbons. Passive flow, the treatment corridor is gravity fed and under normal operating conditions, requires no energy to move water through the system. The system can operate in times of flood events on the adjacent Sheep River, despite negative head pressures. Automated treatment system components notify operators remotely of component failures. Expandable system, the treatment corridor was designed to accommodate new technologies as they may be developed. Monitoring wells for environmental sampling double as performance monitors for each component of the system.

3 BTEX F1 & F2 PAHs F1 & F2 BTEX & F1 PAHs Figure 2. Theory of design components. DESIGN Major components of the work include the design of a Containment System, a Treatment System, Erosion Protection Works and a Monitoring Network. Containment Structure Containment of hydrocarbons present in the soil and groundwater on site was accomplished through the construction of an impermeable bentonite slurry wall surrounding the eastern (riverbank) portion of the site. The wall averts groundwater from discharging into the adjacent Sheep River. The bentonite wall extends from the southernmost edge of the site along the river to the northern boundary and then to the west to tie into the slope of the middle terrace. The alignment of the bentonite slurry wall is dictated by the placement of the erosion protection works installed to control flooding and erosion from the river. The wall was aligned to be directly beneath the erosion protection berm and has been placed as close to the river as possible. The bentonite slurry wall generally consists of a trench excavated from ground surface to bedrock that is backfilled with a designed mixture of soils and bentonite. The slurry wall is approximately 1 m wide and depth varies depending on the depth of bedrock (generally between 2 m and 5 m below ground surface). Backfill material is designed such that the completed wall has a permeability no greater than 1 x 10-6 cm/s. The upper edge of the slurry wall ties into the clay erosion protection berm.

4 Figure 3. Typical cross section of the slurry wall and erosion protection works. Although the containment wall restricts water from passing through it s alignment, the groundwater would flow around or over a containment structure without a discharge point. By placing a discharge point in the lowest corner of the containment structure (northeast corner) the groundwater flow is controlled to pass through a treatment system where it is remediated prior to release into the Sheep River. In addition to the cut-off wall, a weeping tile system (perforated PVC pipe) extends west along the northern boundary of the site to collect groundwater from the upper terrace and drain into the containment area of the cut-off wall. The linear length of the weeping tile system is 400 m, including approximately 250 m that was placed below the Town of Turner Valley s existing sanitary sewer line. Treatment System The treatment system designed to address the hydrocarbons and PAHs found in the soils and groundwater is a subsurface corridor through which groundwater must flow before leaving the site. In conjunction with the cut-off wall, overall contaminant treatment system forms a funnel and gate system whereby the contaminated groundwater is directed through a single point release from the site. A treatment corridor was constructed in the northeast corner of the site (most downgradient corner) through which groundwater passively flows, is treated to meet the Canadian Water Quality Guidelines for the Protection of Aquatic Life (CCME 2001, freshwater), and is released at a single point into the Sheep River. The treatment corridor generally consists of a subsurface concrete vault into which treatment media and systems were installed. Groundwater enters the vault through the western (open) end, travels through the vault across the treatment components, and is discharged through a pipe at the eastern end of the system. Three main treatment components were installed within the treatment corridor, an oil / water separator (or skimmer), an air sparging unit, and activated carbon cells. Through the use of these three treatment components the discharge criteria will be met prior to release of groundwater into the adjacent Sheep River. The oil water separator is designed as a vertically orientated T-joint constructed of 300mm pipe in a manhole, which confines all free phase hydrocarbons to the upgradient side of the separator. In conjunction with the oil / water separator the free phase hydrocarbons isolated to the upgradient side of the separator are collected into an

5 independently floating passive hydrocarbon skimmer. The floating skimmer can contain 2 liters of hydrocarbon and can be easily replaced and / or drained during routine inspection / operation of the system. Figure 4. Conceptual model of treatment corridor. The sparging unit consists of a 5 hp blower motor attached to a series of perforated pipes located across the floor of the vault, downstream of the oil / water separator. This provides a curtain of air through which the groundwater will flow. Aeration of the water aids in volatilizing the dissolved light-end hydrocarbons (such as BTEX, F1 and F2) as well as increasing the dissolved oxygen content. The increase in dissolved oxygen serves to facilitate microbial growth to break down any remaining dissolved hydrocarbons. Downstream from the aeration curtain, sheets of geotextile were loosely hung to provide a media on which a microbial community is anticipated to develop. The effectiveness of the microbial community with respect to hydrocarbon degradation is not concretely known, nor relied upon, however some further hydrocarbon degradation is expected. Pelletized activated carbon serves as the final treatment for any residual dissolved hydrocarbons and dissolved PAHs. Water passing through the vault is forced (using only the natural gravity driven head available) through activated carbon cells. Over time the activated carbon will become less effective as it s available bonding sites become occupied with PAHs and other materials. A series of two cells were installed in order to

6 provide redundancy in the treatment system. Only one cell will be utilized at any given time as the limited head available precludes passing water through both cells simultaneously. Following the activated carbon, groundwater is then suitable for discharge to the Sheep River. The discharge level of the water will be controlled in order to convey greater water level control to the upgradient treatment components. Water will normally be passively discharged (gravity flow) into the adjacent river. However, in order to prevent backflow through the system in times of flood in the Sheep River, a one-way valve was installed in the discharge pipe. During flood conditions, when this one-way valve is closed, a water level activated pump will maintain the water levels at the discharge point in the treatment corridor. Utilizing this discharge control, groundwater treatment can continue even during flood conditions. In conjunction with the discharge control, a knife valve was installed such that the entire system can be stopped manually and all discharge to the river prevented. The pump that controls the water level in the discharge system can also be redirected to load tanks or trucks rather than pumping to the river. Guidelines to be met for the release of groundwater into the adjacent Sheep River are the CCME guidelines for the protection of freshwater aquatic life. Discharge water quality is monitored monthly for these specific parameters to ensure compliance with the discharge criteria. Erosion Protection Works The construction of the erosion protection works, as designed by MPE Engineering Ltd. (MPE), consists of a compacted clay berm and rip rap bank protection. The berm and riprap bank protection extends the entire length of the property boundary along the edge of the Sheep River. The berm height was designed to provide a minimum 0.5 meters of freeboard above the water levels experienced during the June 2005 flood event. The portion of the berm above the original river bank elevation was constructed using compacted impervious clay material. Average height of the berm varies from 1.0 m to 2.5 m. Average channel velocities (during a flood event) vary from 2.5 m/s to 4.5 m/s, therefore the rock riprap placed was blasted limestone. The average height of the riprap is approximately 5.5 m. The riprap extends from the top of the berm and is keyed into the underlying bedrock. Monitoring Network A monitoring network of shallow groundwater wells is established along the cut-off wall, the weeping tile system and within the treatment corridor.

7 A total of 13 monitoring wells were installed along the alignment of the cut-off wall. Five pairs of wells were installed along the cut-off wall of the lower terrace and three wells were installed along the weeping tile of the upper terrace. One well in the upper terrace could not be paired due to the density and location of utilities in the area. One well from each pair is located just inside of the cut-off wall and the other is on the riverside of the cut-off wall. Three of the paired monitoring wells along the cut-off wall are monitored for water level elevations on an ongoing basis through the use of pressure transducers installed in each well. A difference in water levels between each pair of wells will establish the effectiveness of the cut-off wall in isolating the groundwater from the river. A total of four monitoring wells were installed along the walls of the treatment corridor. One is situated in the oil / water separator, and one downstream of each of the treatment systems (oil / water separator, air sparger system and the activated carbon cells). This arrangement allows for the collection of detailed operational information of the treatment system to facilitate fine-tuning of the treatment as well as to confirm that discharge criteria is being met. Chemical parameters are monitored in all of the wells as part of the containment system monitoring. Samples collected will be analyzed to detection levels sufficiently low for comparison against the applicable guidelines for the protection of freshwater aquatic life (CCME 2001). Monitoring wells located on the river-side of the cut-off wall are available for risk management of the soils and groundwater that will remain outside of the containment structure. DEGREE OF DIFFICULTY Many design and construction challenges were encountered while working in Hell s Half Acre. The history of the site, both natural and anthropogenic, provided numerous issues to contend with throughout the life of the project. The natural site conditions found on-site that influenced the overall design of the project included the following: Natural Gas Seeps and Flares in the area provide a continual source of contaminants and are an environmental health and safety concern to the workers on site. Multiple River Terraces and associated groundwater regimes resulted in the requirement for the weeping tile system and an extension to the slurry wall.; The proximity to the Sheep River and the associated Spring flooding events that have historically flooded the site; Coarse granular material, causing difficulties with the trenching operations and cut-off wall construction; Weather, the majority of the project operations were conducted during the winter months;

8 Ice flows resulting from southwest Alberta s constant freezing and thawing temperature patterns were constantly threatening the river isolation works. The anthropogenic history of the site also caused numerous issues with the design and construction of the project, including: Burried Debris and Pipelines, unknown construction history and a lack of asbuilt drawings resulted in many finds. Active Pipelines and Utilities in the area meant many line locates, crossing agreements and safe work practices. National Historic Site Designation meant all structures required protection as much as possible. Multiple Contaminants required constant monitoring of environment, health and safety issues. In addition to the complications listed above, the scale of the project and the relatively short time frame required to finish the construction meant that the Project Team had to work together to ensure the project could be completed to the project specifications. Approximately 60,000 tonnes of material were imported to the site. Construction began in early September, 2006 and Substantial Completion was attained in May, MANAGEMENT OF RISK Contaminated Soils Outside of Containment Area Alignment of the containment wall was located as close to the river as possible, however there were impacted soils by the former use of the site that remain outside of the containment structure. During excavation associated with the erosion protection works all soils handled were screened, analytically and aesthetically, during handling. All impacted soils were segregated and stockpiled within the contained area. Potentially impacted soils remaining outside of the containment structure are to be risk managed as a whole under a separate scope of work. The characteristics and extent of the soil and groundwater impacts were documented and assessed during the construction activities. Using this data as well as data collected from the adjacent Sheep River, a risk management plan is currently being developed such that residual impacts will be managed. River Protection During Construction Works relating to construction of the cut-off wall were at no time within the banks of the river. However, during construction of the cut-off wall significant amounts of bentonite mud and slurry were present on site adjacent to the Sheep River. Accidental releases into the river were prevented through the construction and maintenance of the river isolation works, established prior to the start of construction of the cut-off wall and maintained as necessary throughout the life of the project. This ensured that, in case of a spill or failure,

9 all sediment would be isolated from the river, and could be remediated before it could impact the adjacent river. Additional erosion control measures were implemented for any stockpiled soil located on site. Primarily, all spoil material was placed inside of the cut-off wall and drainage was managed to remain within the containment area. Results The treatment system at the Turner Valley Gas Plant has only been in operation for a few months, however, preliminary results are showing that the containment system and the treatment system are operating as expected. Groundwater levels inside of the containment system are elevated above those outside of the cut-off wall, indicating that the groundwater is effectively being diverted through the funnel and gate design. Also, environmental analytical trends are indicating that the treatment system is effectively removing hydrocarbon contaminants from the groundwater prior to release to the Sheep River. As monitoring continues over the next few years, the treatment system will be adjusted so that it can perform at optimal conditions.