EXECUTIVE SUMMARY

Chapter 1 – INTRODUCTION

The Project Team, lead by Sperling Hansen Associates (SHA) and including its subconsultants Earth FX and CH2M Hill, were retained by the City of Vancouver to undertake a Hydrogeological Review of the Vancouver Landfill (the site). The Hydrogeological Review is required to be updated every five years under the site’s Operational Certificate. This study follows on from the most recent Hydrogeological Review conducted by Gartner Lee Limited in 2000 (GLL, 2000).

Site Background: The Vancouver Landfill is located in Delta, on 225 Ha of low lying land on the southern edge of Burns . The Landfill has been operated continuously since 1966 as the primary solid waste disposal facility for the City of Vancouver, the Corporation of Delta and the western municipalities in Metro Vancouver. The remaining landfill air space capacity is 31.0 million tonnes (effective April, 2008). At a waste acceptance rate of 750,000 tonnes per year, the facility is currently projected to reach capacity around 2049.

In order to minimize the leachate impact on the surrounding environment, a twin ditch leachate collection system was installed in 1978 after the landfill had been in operation for 12 years. The inner ditch collects leachate which is pumped to the Waste Water Treatment Plant. The outer ditch collects and conveys surface water runoff to the natural drainage system. The system relies on the inward hydraulic gradient principle. Leachate containment in the surficial aquifer is realized by maintaining the water level in the outer “clean water” ditch at a higher level than the water level in the inner “leachate” ditch, creating an inward hydraulic gradient with clean water from the outer ditch having a tendency to seep into the leachate collection ditch. This system effectively contains leachate within the established perimeter ditch system as long as water levels in the outer ditch are maintained above those in the inner ditch. Following the recommendations of the 2000 GLL study, leachate collection ditches were regraded to enhance the inward hydraulic gradient and additional upgrade works were carried out.

Purpose: The focus of this hydrogeological review was directed to:

1. Review available monitoring data to ensure that the landfill continues to effectively contain leachate, taking all reasonable measures to provide the best possible containment. 2. Develop a better understanding of leachate flow through Phase 1, the first landfill phase to be developed to the full 39 m height. In particular, to gain a better understanding of the potential causes for elevated water levels and leachate breakouts. 3. Further the understanding of groundwater flow through the shallow and deep groundwater flow systems. 4. Better understand the significance of gradient reversals in the twin ditch systems, and to determine if the incidence of grade reversals has been reduced by the ditch network upgrades in 2002.

City of Vancouver i SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES 5. Examine the impact of the landfill on aquatic life in the perimeter ditch system and Burns Bog. 6. Examine the causes for upward trends in a number of leachate indicator parameters in groundwater monitoring well GWD 23. 7. Evaluate the impacts of capping with a highly impervious geomembrane system on the overall moisture management within the landfill and the storm water management systems.

Methodology: The objectives of the Hydrogeological Review were achieved through a comprehensive investigation that included a detailed field program, extensive data compilation and analysis, sophisticated modelling and focused reporting.

The field program included a topographic survey of the ditch network to establish gradients, drilling of two Sonic boreholes in Phase 1, monitoring of water levels in existing gas wells, monitoring wells and sand point piezometers, electrical conductivity surveys, continuous monitoring of leachate and clean water in the twin ditch network, settlement monitoring on and around the Landfill and an assessment of aquatic habitat and fish inventory, conducted by CH2M Hill and a volunteer from the Burns Bog preservation society.

The modelling efforts included the development of a Site FX Database that contained all historical topographic, borehole, water level and water quality data. The data was analyzed with a number of computer models including WATBUD (for water balance), HELP (for vertical leachate seepage through various cover system scenarios), Finite Element Modelling (to investigate the possible causes of elevated water levels in Phase 1), PCSWMM (to investigate the capacity of the ditch systems to contain run-off from the site during extreme precipitation events) MODFLOW groundwater flow modelling (to investigate the dynamics of groundwater flow between the landfill, shallow and deep groundwater flow systems) and settlement modelling (to forecast anticipated levels of settlement that are likely to occur with time).

Chapter 2 – PHYSICAL SETTING

Vancouver Landfill is located on two parcels of land in central Delta that together encompass 635 ha. The northern parcel, identified as Parcel 2 and not affected by landfilling operations, is currently in the process of being transferred to the Corporation of Delta. The rectangular landfill footprint, approximately 800 m north-south and 3 km east-west, occupies 225 Ha. The landfill has been in operation at this site since 1966.

Burns Bog: The Landfill is located on the southwest edge of Burns Bog, a large raised peat bog that is a unique and important ecological feature in Delta. The Bog has been evolving over the past 5,000 years to its present dominant heathland type dominated by Sphagnum mosses and pine woodlands. The heathland originally occupied 2,200 ha in the core of the bog while the pine woodland covered 1,140 ha around the Bog’s edges. Today the bog occupies 2,700 ha. A radial groundwater flow system exists in the Bog, draining water from the centre of the Bog to discharge to the Bog edges.

City of Vancouver ii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Burns Bog was first purchased from the Crown in 1882. In 1981 Western Delta Lands purchased 2,283 ha of Burns Bog. Their interest was subsequently sold to Delta Fraser Properties. In March 2004, the property was purchased by the Province of British Columbia, Greater Vancouver Regional District, the Corporation of Delta and the Government of Canada. The City of Vancouver currently owns a much smaller land parcel, totalling 635 Ha. In September, 2008 Vancouver City Council approved transfer of approximately 200 Ha of surplus lands to the Corporation of Delta. The Corporation of Delta also owns 148 ha that is protected as the Delta Nature Reserve. The rest of the Bog (about one-quarter) is owned by various public and private interests, including Delta School Board, Pineland Peat (160 Ha) and the Fraser Harbour Commission.

Although Burns Bog has been described as the largest undeveloped parcel of urban land in Canada, anthropogenic activity, primarily peat mining, ditch and road construction and agriculture have altered an estimated 80% of the natural Bog environment The current 225 ha area occupied by Vancouver Landfill represents approximately 8% of the Burns Bog ecosystem. Peat has been extracted from the Bog since 1940. Approximately 40% of the Bog has been excavated to depths of 0.5 to 2 m. Cranberry and blueberry farms have been developed on the perimeter of the Bog.

Site History: The City of Vancouver began operation of the Landfill in 1966. The twin ditch leachate collection system was added in 1978 to contain leachate produced at the site. In 1985 Vancouver Landfill was identified as a long term solid waste disposal site in the Regional Solid Waste Management Plan. In 1999 the City of Vancouver finalized an agreement with the Corporation of Delta to authorize placement of an additional 20 million tonnes of refuse as of Oct. 1st, 1997 within a vertical expansion at Vancouver Landfill and for the transfer of 230 ha of surplus lands within Parcel “D” to Delta.

Since 1966 the landfill has been expanded eastward in cells approximately 300 m wide and 10 to 12 m high. In 2000, the operational method was switched to expand the landfill vertically to a maximum height of 39 m, starting with Phase 1 on the east edge of the landfill. Phase 1 was completed in 2006, with additional grading fills placed in 2008. Phase 1 will be capped with final cover in 2009.

A landfill gas collection system was first added in 1990 to control odours. The system has been expanded several times since. In 2003, a major upgrade was undertaken to convey the landfill gas to the Village Farms greenhouse operation where it is used to produce electricity from four large generators owned and operated by Maxim and heat from boilers operated by Village Farms.

Chapter 3 – GEOLOGICAL SETTING

Regional Geological Setting: The City of Vancouver Landfill is sited within the Fraser River Delta, which is in turn located within the Fraser River Lowland. The landmass today referred to as the Fraser River Delta began to form at the end of the last Ice Age between 11,000 and 13,000 years ago when massive glaciers retreated from the Fraser Valley leaving behind a dense blanket of glacial deposits under glacial melt waters. During the glacial melt the flood plain of the Fraser River became overloaded, flooding the low-lying plains to the west and southwest in the area that is now Delta. Marine deposits of silt were laid down in shallow depressions within the flood plains. These City of Vancouver iii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES now form the excellent confining layer at the base of the peat bog that serves as a barrier layer for the landfill. The postglacial deltaic sediments have a maximum reported thickness of 305 m. Over the last 5,000 years sphagnum moss has accumulated on top of the silt to form the peat bog deposit up to 5 m thick. Burns Bog is the largest domed peat bog in North America and covers an area of almost 40 km2.

Local Geologic Setting: Four distinct soil strata are readily identifiable at the site. Peats overlie a layer of clayey silt, which is underlain by a sand aquifer, which is confined at its base by a lower extensive silt deposit to depth. The upper fibrous peat layer is typically 0.5 m thick and very permeable. It is underlain by a one metre zone of transition peat. Below this zone lies a type of peat referred to as amorphous peat that is more impervious, especially when subjected to large confining stresses, as are experienced when the landfill phases are brought up to the full 39 m height (3.8x10-9 cm/s). The depth of the amorphous peat layer varies from 0.5 to 3.0 m around the site. The peat is underlain by the organic silt layer, typically 2 m thick, with an average hydraulic conductivity value of 4.8x10-9 cm/s. Together, the amorphous peat and the organic silt provide an excellent natural barrier layer that surpasses the minimum requirements of a natural barrier layer soil (2m of 1x10-6 cm/s), as defined by the Landfill Criteria for Municipal Solid Waste (MOE, 1993), by several orders of magnitude.

Chapter 4 – HYDROGEOLOGICAL SETTING

Regional Hydrogeological Setting: Burns Bog is a regional groundwater recharge area. Water from the Bog drains radially, with flows ultimately discharging south towards Mud Bay and north towards the Fraser River via numerous interconnected drainage ditches. Crescent Slough is also an important drainage feature volumetrically. The Fraser River at is strongly tidal. Flood boxes and pump stations at the north and south ends of Crescent Slough are used to control water levels in the ditches and prevent flooding. In the summer, the ditches are converted to irrigation mode at which time water from the Fraser River is allowed to flood Crescent Slough and nearby ditches.

Local Hydrogeological Setting: In proximity to the City of Vancouver Landfill, surface water flows are controlled by a series of “twin” drainage ditches that surround the entire landfill site. The inner ditch collects leachate from the landfill footprint while the outer ditch intercepts clean run-off from the Bog and diverts it around the landfill site. Inputs to the flow system are derived from precipitation on the landfill surface, water contained in the incoming MSW (about 28% moisture) and water released from the underlying peat layer due to consolidation.

Hydrogeological Regime Within Landfill: A number of leachate breakouts have been noted, particularly on the east side of Phase 1. SHA suspects that leachate mounding may be occurring within the landfill. However, it is also possible that the elevated water levels observed in monitoring wells may be caused by perched water table conditions on internal intermediate cover layers. A series of field work tasks, including sounding of existing gas wells, mapping breakouts and a drilling program were initiated to investigate whether the breakouts are due to perched water tables or mounding. The initial results from the two drill holes completed suggest that leachate mounding is the more likely cause, but additional drilling is still required to verify initial observations. City of Vancouver iv SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Moisture content analysis within the Sonic boreholes revealed that the moisture content is highly variable, with the waste being driest nearest the surface (about 34 to 44% moisture), then becoming wetter with depth (53 to 77% moisture). The moisture content decreases around the internal DLC drainage layer to about 35% and then increases to 65 to 93% at the bottom of the landfill.

Water Level / Leachate Mounding Analysis: Through a careful review of observations of water level data from Phase 1 and a full range of computer simulations, Chapter 4 examines in detail for the first time the issue of elevated water levels within Phase 1 of the landfill. Two hypotheses are presented to explain this observation: 1) perched water table conditions on low K intermediate covers and 2) leachate mounding due to a decrease in K of the deep seated refuse and DLC drainage layer at the base of the landfill. The field data indicates that elevated water levels of about 17 to 20 m have developed in the new wells as well as in existing gas wells.

Climate Review: Analysis of precipitation data plotted as isohyets (lines of common annual rainfall) established that Vancouver Landfill receives about 100 mm less rainfall than Vancouver International Airport. The 30 year average rainfall intensity at Vancouver Airport between 1971 and 2000 was 1,199 mm/year. This is up considerably from the 1961 to 1990 statistics which reported only 858 mm/year and the 1951 to 1980 statistics that reported 1,112 mm/year. Whether the increase in precipitation is due to global warming or other climatic factors remains to be determined.

For prediction of short term climatic events, the most recent Intensity Duration Frequency (IDF) curve from Environment Canada was adopted for SHA’s calculations. The curve is based on data from 1953 to 2005.

Water Balance: A detailed water balance analysis of water inputs and outputs has produced results that are consistent, with a mass balance error of less than 1%. The results indicate that 2.7 million m3 of precipitation falls on the landfill each year on average. In addition, 169,000 m3 of moisture is contained in incoming refuse (6.3% of precipitation), 42,000 m3 of moisture is produced by peat consolidation (1.6% of precipitation) and 7,000 m3 of moisture is produced by cross flow from the outer ditch (0.3% of precipitation), for total moisture inputs of 2.91 million m3. Of that total, about 1.7 million m3 (65.5% of precipitation) flows off site as captured leachate, 936,000 m3 (34.7% of precipitation) is lost to evapotranspiration, 249,000 m3 is absorbed by the landfilled waste to reach field capacity (9.2% of precipitation) and about 17,000 m3 seeps through the confining layers as vertical seepage to the sand aquifer (0.6% of precipitation). The outputs total 2.90 million m3, virtually the same as the inputs, indicating that the water balance at the landfill site is well understood.

Vertical Seepage to the Sand Aquifer: Estimates of vertical seepage of leachate through the underlying confining layer have been made by GLL in 1995 (18,355 m3/yr), by GLL in 2000 (8,277 m3/year) and most recently, in this study at 17,062 m3/year. In all cases, the leachate flux has been very small, less than 1% of total leachate produced. More importantly, the most recent leachate flux estimate, when converted to a flux per unit area, is 11.2 L/m2. This flux rate is well below the minimum acceptable flux rate of 94.6 L/m2 for a natural control landfill with a 2 m natural barrier layer with K<2.0x10-6 cm/s and a maximum of 300 mm of head. As a result, the landfill appears to be very effective at containing leachate.

City of Vancouver v SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Leachate Mounding in Phase 1: Through a careful review of observations of water level data from Phase 1 and a full range of computer simulations, the issue of elevated water levels within Phase 1 of the landfill was examined. Two hypotheses are presented to explain this observation: 1) perched water table conditions on low K intermediate covers and 2) leachate mounding due to a decrease in K of the deep seated refuse and DLC drainage layer at the base of the landfill. The field data indicates that elevated water levels to about 17 to 20 m have developed.

The computer modelling completed by the Project Team indicates that the leachate mounding in Phase 1 could be caused by a decrease in permeability of the deeply buried MSW. The saturated / unsaturated Finite Element Modelling in particular has demonstrated that head build up and leachate seepage across the underlying barrier layer is very sensitive to the hydraulic conductivity of the DLC drainage layer. Initially, this layer had a hydraulic conductivity of 5.0 to 8.0x10-2 cm/s. A modest reduction of the hydraulic conductivity of this layer to 1.0x10-2 cm/s is anticipated and may have already occurred. At this level of K, a modest increase in pore pressure within the DLC layer is going to lead to a modest increase in gradient driving flow downward. It is anticipated that the increase in gradient will be more than offset by a decrease in permeability of the barrier layers due to consolidation so there should be no net increase in seepage to the sand aquifer, however, this assumption needs to be validated by field observations.

Based on observations at other landfills in B.C. SHA is concerned about the possibility of a leachate mound developing. To establish conclusively whether or not a mound is present, SHA recommends that additional drilling be initiated within the Phase 1 fill and within the DLC drainage layer at the base of the landfill so that water table elevations and pore pressures can be verified. If the drilling establishes that the water elevations observed in the landfill are actually due to a perched water table, then it is recommended that the groundwater flow model be re-calibrated as the model currently makes the more conservative assumption that the observed heads are due to leachate mounding. Recalibration of the model to lower heads would likely result in a significant reduction in the overall vertical seepage estimate.

Chapter 5 – SURFACE WATER FLOW

Leachate Flows: Leachate and drainage water from the Bog is managed with a twin ditch system that runs along the perimeter of the landfill site. Leachate and surface water run-off from areas within the property drain into the inner leachate collection ditch and then flow by gravity to the pump station located in the southwest corner of the landfill. From there it is being pumped via the Ladner Trunk Forcemain to Annacis Island Waste Water Treatment Plant for treatment. The average annual leachate volume for the time period between 1995 to 2007 was 1,749,249 m3/year, and the total annual volume of precipitation that fell within the landfill footprint for the same period was 2,675,13 m3/year, resulting in an average precipitation capture ratio of 65.5% of precipitation.

The 1995 average leachate production rate was 4,890 m3/ha/year, while the 1995-2007 average leachate production equals 7,774 m3/ha/year. This shows that the efficiency of the collection system has increased significantly over the past 13 years, potentially due to improved cover on the landfill, as well as regrading and deepening of the leachate collection system.

City of Vancouver vi SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Eight flow monitoring weirs have been established to continuously track leachate and clean water flows in the two ditches in April, 2007. Four are established on the leachate ditch network and four on the outer clean water ditch. The data collected from those weirs shows that the leachate system responds to storms much faster than the outer ditch network. During a major storm in December 2007, the leachate ditch network hydrograph peaked within 10 hours of the storm peak while the outer ditch hydrograph peaked in 36 hours. The response shows that the landfill surface, which has been designed to promote run-off and minimize infiltration, provides much less storm water attenuation than the surrounding bog.

The peak daily leachate flow rate, as determined by combining flow data from the S-Inner and NW- Inner weirs has been 638 L/s. The maximum pumping capacity of the P1 to P4 pumping array is on the order of 850 L/s. As the winter of 2007 to 2008 was not particularly wet, it is likely that the pumping capacity of the pump station array could be exceeded during particularly intense storm events. SHA has recently been retained to conduct a review of on-site leachate storage capacity and develop a contingency strategy to deal with such situations.

Clean Ditch Flows: Flows in the outer ditches are currently of a smaller volume and better attenuated than flows in the leachate ditches as a result of the attenuating characteristics of the fibrous peat layer and very low gradients that are present in the Bog. Based on this observation, it can be concluded that the characteristics of the flow in the outer ditch network will change considerably once a large portion of run-off is diverted from closed Landfill areas. The total volume of flow is also expected to increase by more than 300% as the catchment area is expanded and the final cover system will provide much less attenuation and greater run-off than the existing intermediate cover. Therefore, the impacts of progressive closure on downstream ditches need to be carefully evaluated and significant storm water retention may be required to maintain peak flows at or below present levels.

Gradient Reversals in Twin Ditch Network: Monitoring of water levels at five stations on the inner and outer ditch networks has established that the twin ditch collection system is working very effectively with very minimal occurrences of grade reversals, particularly since 2002 when a series of improvements were undertaken to improve the ditch system efficiency. These included straightening out, deepening and cleaning out the ditches in problem areas. In 2007 the ditch network maintained an inward gradient 96% of the time.

No additional upgrades are considered necessary at this time. It is recommended that monitoring location L5/D5 be evaluated to verify that the improvement expected from the recent raising of the discharge culvert in the northwest corner of the landfill by B.C. Hydro is in fact manifested.

Ditch Drying: The outer ditch has a tendency to go dry along the east side of the landfill during the summer as water drains from the peat and the water table elevation decreases below the ditch invert. It was believed that this could potentially lead to a loss of inward gradient if the water table drops below the invert elevation of the inner ditch.

A detailed analysis of the problem areas, particularly at monitoring locations L3/D3 and L4/D4 has revealed that despite the fact that the outer ditch goes dry, it appears that an inward gradient is still maintained by the subsurface water table, except perhaps, for very short periods of time at the very City of Vancouver vii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES apex of drought conditions. Therefore, the risk of leachate excursions as a result of gradient reversals is thought to be small in the summer months.

Providing check dams to raise water levels in the outer ditch was determined not to be a practical solution to this minor problem, as it would lead to increased rates of ditch cross flow in the summer months, estimated to be as high as 360,000 m3/yr (GLL, 1995). Another solution identified in this report would be to add additional flow to the outer ditches from an engineered wetland at the top of the flow system. It was determined that a flow of about 378 m3/day would be required. This flow could be maintained by constructing a wetland about 3.5 ha in size and 2 m deep. However, it is SHA’s opinion that the risk to the environment resulting from gradient reversals is very small and self correcting. Therefore, we conclude that guaranteeing 100% inward gradient is not a high priority upgrade.

Outer Ditch Flow Capacity: There are no instances of flooding observed for any of the simulated design storms for the Phase 1 Closure scenario using PC SWMM. The current outer ditch network appears to have the capacity to convey the additional runoff generated from the capped sections of the Phase 1 Landfill closure.

For Final Closure of the entire site, PC SWMM shows that flooding will occur at several points along each of the profiles for the 5, 25 and 100 year storm scenarios. This indicates that the ditch network does not have adequate capacity to manage the stormwater runoff generated from any of the design rainfall events.

Dredge Pond Connectivity: Managing storm water run-off from closed areas of Vancouver Landfill is an emerging challenge that will require additional consideration in years to come, particularly as the area of progressive closure is expanded. Based on preliminary analysis, SHA believes that the use of the existing dredge pond as a storm flow attenuation facility may provide an excellent solution to this emerging problem.

By directing storm flows from closed areas on the south side of the landfill into the pond and holding those to zero outflow during extreme storm events, it may be possible to maintain total storm flow discharges from the north side of the landfill to existing levels, thus meeting Delta’s requirements for storm water management.

Chapter 6 – GROUNDWATER FLOW

Regional Hydrogeology: The regional ground water flow system is primarily controlled by the peat bog and the hydraulic conductivity contrasts of the four primary hydrogeologic units that include:

Peat Active Layer Very permeable Aquifer Amorphous Peat Relatively impervious Aquitard Silt Horizon Relatively impervious Aquitard Sand Horizon Very permeable Aquifer

City of Vancouver viii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES The raised peat bog is a regional ground water recharge zone with water levels near or at surface. Water from the Bog flows radially outward, with most of the flow occurring in the uppermost peat active layer. The ground water flow pattern in the underlying sand aquifer exhibits the same radial pattern. Horizontal hydraulic gradients in the sand are very gentle. As a result, ground water in the sand typically flows at a velocity of about 1 m per year.

Ground Water Flow in the Peat: Ground water flow patterns in the vicinity of the landfill are influenced by the presence of the fill, the perimeter drainage ditches and the dredge pond.

Ground water flow in the peat is generally toward the perimeter ditches. The ditches act as local ground water discharge zones that intercept most of the flow out of the Bog.

The primary source of recharge to the flow system is precipitation on the landfill surface. The average annual precipitation is about 1,199 mm per annum. Water budget modelling conducted during this study suggests that 416 mm (35% of precipitation) is lost through evapotranspiration annually. The remainder becomes leachate or runoff which are both collected in the inner leachate collection ditch.

Leakage into the Sand Aquifer: The piezometric surface in the demolition layer beneath the landfill is between 0 and 1.5 m higher than the piezometric surface in the underlying sand aquifer. The resulting downward gradient induces leachate flow through the silt toward the sand aquifer. A key objective of this study was to update the magnitude of the vertical leachate losses. As discussed in Chapter 4, it was estimated that the vertical seepage to the sand aquifer is on the order of 17,000 m3/year.

Contouring of piezometric levels in wells located around the landfill perimeter indicates that the flow system beneath the western most third of the Landfill appears to experience a very slight upward gradient, in which case it would be an active groundwater discharge area. However, water levels in the shallow peat aquifer may not be indicative of water levels within the DLC drainage layer beneath the Western 40 Ha fill area. As a result, slight downward gradients may also exist in the southwest portion of the landfill.

Ground Water Flow in the Sand Aquifer: In the vicinity of the landfill, the regional ground water flow pattern, southwest from the bog toward Crescent Slough, is strongly affected by the presence of the dredge pond, and to a lesser extent, the presence of the perimeter drainage ditches. Average flow velocities in the sand aquifer are in the order of 1 m per annum.

Chapter 7 – GROUNDWATER FLOW MODEL

A major update to the 1995 EarthFx groundwater flow model was undertaken as part of this project. In particular, the conceptual model was refined with more geological information, more detail on drainage ditches and additional detail concerning hydraulic conductivities. As well, for the first time the model investigated the potential impacts of increased leachate mounding within a 39 m high landfill.

City of Vancouver ix SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Model Input Parameters: As before, the computer model was extended to major hydrogeological boundaries that included the Fraser River, and the Surrey Newton uplands. The model was defined in six layers that included:

Layer 1 Solid Waste Layer 2 Demolition Drainage Layer (below Landfill) (aquifer) Layer 2 Fibrous Peat Layer (outside landfill) (aquifer) Layer 3 Amorphous Peat Layer (aquitard) Layer 4 Silt and Organic Silt (aquitard) Layer 5 Silty Sand and Sand (aquifer) Layer 6 Deltaic Silt and Clay (aquitard)

The model was discretized at a grid spacing of 12.5 x 12.5 m within the landfill and 250 x 250 m within the far regional system. In total, the model was constructed of 688,200 model cells.

Based on SHA’s detailed investigation of hydraulic conductivity within the refuse mass, the vertical conductance terms in the model were carefully adjusted to obtain a close match to water levels observed within the monitoring wells and gas wells on site.

For the first time, groundwater recharge was estimated using the U.S. Geological Survey Precipitation – Runoff Modelling System (PRMS) model that considers factors such daily rain intensity, temperature, ground cover conditions and slope aspect. The model determined that groundwater recharge rates ranged from 100 to 700 mm/year, with the highest recharge rates occurring on the landfill footprint. Recharge rates in the Bog averaged about 200 mm/year.

Model Calibration: The computer model was extensively calibrated with EarthFx trying to match both observed heads and flow rates. The final model reproduced observed both flow rates and heads (both within the shallow and the deep flow system) accurately. The mass balance error for water input vs. water output was 0.33% which is considered a very good result. Typically, mass balance errors up to 2% are acceptable. The mean error on predicted hydraulic heads was 0.158 m on the deep flow system and 0.052 m on the shallow system.

Model Results: The groundwater model indicates that the twin ditch system around the landfill perimeter has a strong influence on water levels in the peat layer and disrupts the natural flow system. Regional groundwater flow is intercepted by the ditch system on the north and east sides of the landfill and, to a lesser degree, on the west and south sides. Capture of some external water is necessary to ensure leachate confinement. Further lowering of the inner ditch levels would improve the certainty of leachate capture year-round and help lower leachate levels in the waste but at the cost of having to treat additional clean water captured from the peat. Deepening of the inner ditch could also lead to possibly adverse effects on the Bog ecosystem within the landfill vicinity. Alternatively, control of infiltration would reduce the volumes of leachate produced and thereby reduce the heads in the waste area. An active system in which inner drain levels are adjusted in response to Bog levels would provide the ability to optimize the leachate collection system performance.

City of Vancouver x SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES The computer model predicted that the total amount of leachate captured is 1,662,720 m3/year. This result compares favourably to observed leachate flows (1,749,249 m3/year average).

The groundwater model estimates vertical leachate flow through the peat and silt aquitard toward the sand aquifer to be at an area-averaged rate of 11.2 L/m2 per year, and to total 17,062 m3/year. The simulated leachate flux can be compared with the MoE requirements (based on the Landfill Criteria) that specify a maximum acceptable vertical leachate flow of 94.6 L/m2 per year. The estimated average flow rate at the landfill site is nearly one order of magnitude lower than the maximum accepted by MoE for a natural control site. As a result, the landfill appears to be very effective at containing the leachate. Nevertheless, efforts to lower the leachate levels through controlling infiltration, especially in the Phase 1 area, would further reduce leachate loadings to the sand layer as well as reduce the overall volume of leachate requiring treatment.

A particle tracking analysis determined that under current conditions the typical leachate breakthrough time to penetrate through the peat and silt barrier layers is on the order of 10 to 20 years.

Chapter 8 – WATER QUALITY

The City of Vancouver has an extensive water sampling program in place to ensure that landfill leachate is not impacting the water quality in the aquifer and surrounding surface water bodies. This monitoring program consists of monthly sampling of the collected leachate prior to it being pumped to Metro Vancouver’s Annacis Island Waste Water Treatment Plant for treatment, and quarterly sampling of ten surface water locations as well as 28 groundwater wells.

Leachate Characteristics: Based on analysis of sample results, overall the leachate chemistry is remaining stable, with normal seasonal fluctuations, except for BOD and COD, which have been gradually increasing since 2000. Typically concentrations of most parameters are two to three times higher in the summer months than in the winter. This is clearly due to the dilution effects provided by clean surface run-off during winter months.

The leachate at Vancouver Landfill can be described as having near neutral pH with a range between 6.84 to 7.78, conductivity values ranging between 1,800 and 6,900 μS/cm, hardness between 155 and 1,000 mg/L, BOD ranging between 5 and 501 mg/L, COD between 184 and 1,370 mg/L, ammonia between 51 and 462 mg/L, chloride between 29 and 760 mg/L and total iron concentrations between 1.2 and 51.8 mg/L. Seasonal variations are clearly noticeable in nearly all leachate indicator parameters with concentrations typically three to five times higher during the summer months for ammonia, COD and chloride, and two to three times higher for conductivity and hardness. The leachate chemistry appears to be stable over time, subject to the significant seasonal fluctuations, with the exception of BOD and COD concentrations, which appear to be increasing slightly over time.

City of Vancouver xi SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Leachate Loading Analysis: An analysis comparing current leachate composition from the entire landfill vs. leachate composition from Phase 1, which is considered more typical of what leachate composition may be in the future, revealed that the Phase 1 leachate, typical of leachate from fresh garbage, has higher BOD and COD levels, as well as higher ammonia and slightly lower iron concentrations than leachate from the older landfill, but the increases do not appear to be significant (i.e. on the order of 10 to 20%). More important, the total amount of leachate flow is expected to decrease dramatically over the years as progressive closure is implemented, resulting in a reduction in contaminant loadings to the Annacis Island WWTP over time.

Burns Bog Water Quality Characteristics: The water draining from Burns Bog is atypical when compared to run-off encountered in most streams and ditches in the Lower Mainland. The run-off and near surface groundwater is strongly acidic (pH 3.0 to 5.0), with low concentrations of total dissolved solids, but strongly elevated tannins and lignins. The water also contains elevated concentrations of ammonia, iron and manganese.

A review of water quality monitoring data has established that there is no evidence that the Landfill is impacting the shallow groundwater in Burns Bog.

Significant soil deposition has taken place on the Pineland Peat Property 400 m to the east of the landfill site. Water sampling of three new sand point piezometers has established that there is no indication of groundwater pollution migrating from that facility toward Vancouver Landfill in the shallow aquifer system.

Electrical Conductivity Survey: An extensive electrical conductivity survey was undertaken, sampling conductivity in all accessible ditches on and around the Landfill. Electrical conductivity (EC) is generally an excellent indicator of leachate impact. Waters draining from the Bog typically have a conductivity of less than 100 μS/cm, whereas leachate at Vancouver Landfill that typically ranges between 1,500 and 5,000 μS/cm.

The conductivity survey of the inner ditches revealed that the most concentrated leachate is originating from Phase 1, and particularly the southeast corner of that phase. The east half of the north leachate collection ditch had lower conductivity, around 400 to 1,500 μS/cm, than the south side, which ranged from 2,000 to 6,500. This suggests more of the leachate from Phase 1 is draining to south than to the north. Conductivity levels increased in the western most third of the north ditch starting at Phase 2 (around 1,500 μS/cm), and continue to increase along the Western 40 Ha with conductivities up to 4,000 μS/cm.

The conductivity survey revealed that the north outer ditch is not being impacted by the Landfill. The three round EC survey showed that the highest EC readings were observed in west ditch, followed by the southwest and southeast corners of the landfill. Since even higher conductivity readings are observed down gradient, it is suspected that the ditches are being affected by salt water intrusion, agricultural run- off or discharge of higher conductivity groundwater from the deep aquifer.

EC values in the southeast corner were relatively high compared to other parts of the outer perimeter ditch during the April, 2008 monitoring event, but remained lower than readings further downstream. Although the EC data on its own suggests that landfill leachate may be the primary cause of the elevated EC levels, City of Vancouver xii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES detailed interpretation of other surface water chemistry data suggests that most of the observed EC impacts, particularly at the southwest corner and west side of the Landfill, may be due to other off-site causes such as upwelling groundwater from the deep aquifer, salt water intrusion or run-off from agricultural lands.

Surface Water Quality in Outer Ditches: Based on review of the analytical data from surface water monitoring stations in the outer ditch it appears from the data gathered to date that the twin ditch system is functioning well. There are indications that the water quality of the water leaving the site via the outer diversion ditches is mildly impacted by leachate from time to time as a result of gradient reversals and/or chemical diffusion, particularly during periods of little or no flow. The level of impact appears far less significant then suspected agricultural run-off impacts that are being detected further down stream.

The southwest corner of the Landfill may be slightly impacted by leachate. However, it is difficult to verify that measurable leachate excursions into the outer ditch are occurring in this area as there appear to be one or more non-landfill related sources (upwelling groundwater flow from deep aquifer, sea water intrusion, agricultural run-off) contributing to overall high levels of certain chemical parameters downstream of the Landfill where impacts seem to be the highest. Although the same parameters can also be linked to leachate, the levels are greater than would normally be associated with landfill leachate and concentrations of indicator parameters become progressively more concentrated further downstream and away from the Landfill site. This suggests that the Landfill is not the primary source of impact in the southwest corner of the Landfill.

The southeast corner of the landfill may be slightly impacted by leachate due to leachate crossing from the inner to the outer ditch along sections of the southern boundary, particularly in areas where hydraulic trap grade reversals occur when the ditch network goes dry. The water quality remains typical of bog water (low salt content, elevated iron and manganese) and with conductivity readings at levels well below considered to be significantly impacted (above 500 μS/cm).

Shallow Groundwater Quality: The water quality data for the shallow groundwater wells show a gradient across the site with acidic Bog water with low mineral content on the north, east and parts of the south side of the landfill to near neutral pH and high mineral content towards the southwest corner. The parameters that frequently have exceeded either of the two applicable guidelines (B.C. Water Quality Guidelines – Drinking Water, and B.C. Water Quality Guidelines - Irrigation Water) have been pH, iron, manganese, aluminum. The evaluation of the results for background monitoring well GWS-1 suggest that this shallow well is being influenced by deep groundwater as there is an upward gradient at this location and the characteristics of the water have gradually shifted from typical Bog water to that of the deep groundwater system.

The results from the investigation of why the southwest area has been experiencing elevated chloride levels suggest that intrusion of saline water is most likely the cause. The hypothesis that the elevated concentrations of chloride in this area originated from leachate released during the force main failure in 1999 proved wrong as there was no concentrations gradient towards the area where the failure had occurred. Also, there was no conclusive gradient between the failure site and the landfill which could have indicated that the chloride originated from a leachate plume from the landfill.

City of Vancouver xiii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES Even though the shallow groundwater downgradient of the landfill has had elevated concentrations of leachate indicator parameters such as dissolved iron, manganese, conductivity, chloride and ammonia, the shift in chemical composition is interpreted to originate from the gradual change in subsoil conditions across the site with the peat upgradient and mineral soil downgradient. The evaluation of the concentrations vs. time does not show signs that the water quality at the property boundary is degrading over time in the shallow groundwater flow system.

Deep Groundwater Quality: The deep groundwater down gradient (south and west) of the Landfill has approximately the same characteristics as the background deep groundwater. There appears to be a gradient across the site in the same direction as the groundwater flow with lower hardness and conductivity values towards the northeast corner and higher values towards the southwest corner. Also, starting in 2006 an off-site source, either salt water intrusion or agricultural impacts are starting to affect chloride, ammonia, hardness and manganese concentrations at GWD-74 near Crescent Slough (the extreme west boundary of the study area).

The majority of leachate indicator parameters in the down gradient wells have had concentrations in the same range as that of the background wells with only down gradient wells GWD-23 and to a lesser extent, GWD-24 showing possible signs of minor impact by landfill leachate with slight increases in conductivity, hardness, chloride, dissolved manganese and dissolved iron over time. Concentrations of ammonia do not appear to increase, suggesting that ammonia is a reactive parameter that is somehow being attenuated along the flow path. This is common in natural flow systems as ammonia is an organic substance that can be attenuated by microbes and adsorbed onto organic matter along the flow path.

Statistical Analysis of Groundwater Data: A Mann-Kendall trend analysis of the groundwater data was completed in an attempt to identify trends in the data set that would indicate which monitoring wells could be removed from the monitoring program. No conclusive trends could be identified with the analysis. It is recommended that trends in iron, nitrate, nitrite, ammonia, sulphate and alkalinity be correlated with the groundwater reduction-oxidation potential (REDOX) due to their relationship. It is also recommended that conservative contaminants like chloride and anthropogenic compounds such as chlorinated VOCs be evaluated as specific indicators of leachate impacts.

Chapter 9 – IMPACTS ON BURNS BOG

Overall, the perimeter ditches are lowering water levels, specifically in the dry season. The zone of influence of the ditches extends about 100 m into the Bog. About 90% of the drainage impacts occur within 70 m from the outer ditch. In each of the water table sections created from the standpipe monitoring program, inward gradients towards the Landfill site were confirmed by the monitoring network.

Based on the review of historic aerial photos, the vegetation surrounding the landfill has changed from native sphagnum moss to pine and birch woodland in areas. This may be due, in part to the drainage ditches that have been established between 1966 and the present. However, the process may also be due to natural succession of species and other climatic factors. City of Vancouver xiv SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES

Based on the aquatic assessment completed by CH2M Hill, it was concluded that the ditches associated with the Vancouver Landfill generally appear to be characterized by relatively low aquatic habitat values, with absence of salmonids or listed fish species. The inner leachate ditches do not support fish, as expected. The outer ditches support a population of three spine sticklebacks. redside shiners and goldfish. Amphibian species that inhabit the outer ditch network include the American bullfrog and the Northwestern salamander. The dredge pond supports populations of prickly sculpin and American bullfrog.

Summertime temperatures and low dissolved oxygen contents appear to be the primary factors that limit use of this habitat by fish in the summer months.

Chapter 10 – SETTLEMENT ANALYSIS

Settlement of the landfill is an important consideration at Vancouver Landfill, not only for the impact it has on air space, but also from a hydrogeological perspective. Settlement can impact on the grading of leachate collectors and cover system ditches, the head build-up in the basal DLC drainage layer, and accumulation of condensate in gas laterals. Large differential settlements could potentially impact on the integrity of the compressed peat and organic silt barrier layers.

Previous studies by Gartner Lee (1995), SHA (2001), Golder (1998) estimated that significant settlement would occur in the soil strata beneath the Landfill as a result of increasing the Landfill height to 40 m., including 0.5 to 0.9 m of settlement in the peat, 0.1 to 0.2 m of settlement in the organic silt and about 5.5 m of settlement in the clayey silt strata at depth.

Measurement of settlement at the landfill crest between May, 2006 and December, 2007 has revealed that the Landfill is settling rapidly, with about 3.6 m of settlement observed at the crest of Phase 1. The toe of the landfill has settled only 0.18 m in the same time period.

Soils outside the landfill are also settling as a result of the vertical stress induced by the landfill. Interpretation of aerial photogrammetry between April, 1999 and April, 2007 has shown that ground has settled about 0.5 m over eight years. Because the grades of the ditch collection system are very small (0.063 to 0.075%), the ditches are susceptible to settlement. Further maintenance may be required to re-establish grades as the Landfill settles.

Based on settlement modelling it is predicted about 0.05 m of additional settlement is expected in the ditches as a result of Phase 1. A grade change this small will not result in flow reversal of the ditches or loss of the hydraulic trap. It may, however, cause more ponding of water in the ditch system as there are already a number of very flat areas along both ditch profiles.

The base of the Landfill in the core area of Phase 1 has settled by about 6.0 m to -4.0 m elevation while the perimeter has settled only 0.2 m. As a result, significant differential settlement has taken place, on the order 3.7%. The possible effects of the large differential strain to which the barrier layers have been subjected should be investigated. City of Vancouver xv SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES

KEY RECOMMENDATIONS

Based on the findings from this study, the Project Team makes the following recommendations for follow up and further investigation at the Vancouver Landfill:

Chapter 4 Hydrogeological Setting • To investigate whether or not a leachate mound is present in Phase 1, SHA recommends that a drilling program be initiated within the Phase 1 fill and within the DLC drainage layer at the base of the landfill so that water table elevations and pore pressures can be verified. • If the results from the drilling program indicate that elevated water levels are due to perched conditions and leachate mounding is not occurring, then the groundwater flow model should be reanalyzed as it currently makes the worst case assumption that a significant leachate mound is present in the landfill.

Chapter 5 Surface Water Flow • The impacts of progressive closure on downstream ditches needs to be carefully evaluated and significant storm water retention may be required to maintain peak flows at or below present levels. • Although excessive storm flows are not expected to cause a problem after closure of Phase 1, they are expected to overwhelm ditches on closure of the entire landfill. More detailed analysis is required to determine at which point during progressive closure will the ditch capacity become exceeded. • In case the run-off from the cover system needs to be diverted to the inner leachate collection ditches as a result of water quality issues (due to the placement of Iona Biosolids), the flow rates to the leachate collection system could increase during storm events. The implications of increased flows on the leachate conveyance infrastructure should be assessed. • It is recommended that monitoring location L5/D5 be evaluated to verify that the expected improvement expected from raising the discharge culvert is in fact manifested. • In order to properly assess the impact of phased closure of the landfill on the capacity of the outer ditch network the following should be undertaken:

- Perform a survey of the current inner leachate and outer ditch networks including ditch inverts and cross-sections at regular intervals, culvert inverts, size and material, and cross sections of the weirs around the site.

- Determine site specific soil parameters. - Create a simulation of the existing landfill site to be used for calibration and verification of parameters.

- Update the Phase 1 Closure and Final Landfill Closure models with the calibrated parameters.

City of Vancouver xvi SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES - Run simulations for both design storms and long-term rainfall scenarios to determine ancillary effects that may not be apparent by simulation of design scenarios alone, such as multi-day storm events.

Chapter 8 Water Quality • From the data collated from the SHA EC survey as well as the historic water quality monitoring data, it appears that additional monitoring and analysis is required to establish whether observed anomalies occurring in the southwest corner of the landfill are due to leachate excursions or the result from interferences posed by backflows of saline or agriculture run-off impacted water from further down stream. • It is recommended that shallow aquifer monitoring well GWS-1 should not be relied upon as a reference point for typical background shallow groundwater quality because it appears to be impacted by upwelling groundwater from the deep system. It is noted that GSW-1 is a required monitoring site per the current Operational Certificate monitoring requirements. • SHA recommends that the BC Approved and Working Quality Guidelines for aquatic life be used in future water quality assessments for surface water and BC Approved and Working Quality Guidelines for aquatic life, drinking water and irrigation be considered when evaluating groundwater. In each case, the strictest applicable guideline should be selected. • Leachate indicator parameters should continue to be used to track if landfill leachate is impacting the water quality, and close attention should be given to tracking long term trends and localized variations. Tracking whether seasonal fluctuations do or do not occur is an excellent indicator of hydraulic connection between the deep and shallow flow systems, and should continue to be examined. • It is recommended that trends in iron, nitrate, nitrite, ammonia, sulphate and alkalinity be correlated with the groundwater reduction-oxidation potential (REDOX). It is also recommended that conservative contaminants like chloride and anthropogenic compounds such as chlorinated VOCs be evaluated as specific indicators of leachate impacts. • It is recommended that the site’s existing Field Sampling and Quality Control Manual be replaced with Standard Operating Procedures (SOPs) for: Sample Collection, Sample Preservation, Chain-of-Custody Records, Quality Assurance / Quality Control, Equipment Decontamination Procedures and for Purge Water Management.

Chapter 10 Settlement Analysis

• It is recommended that the inner and outer ditching network be surveyed on an annual basis to monitor settlement, with focus on areas receiving new fill. This data will be useful in assessing the rate of settlement and can be used to predict any potential loss of hydraulic trap or flow reversal in the ditching system. • Laboratory testing of the peat and underlying organic silt layers is recommended to verify that the strain rates being observed are not resulting in the formation of cracks in the compressed peat and silt barrier layers.

City of Vancouver xvii SPERLING Vancouver Landfill Hydrogeological Review HANSEN PRJ07009 FINAL REPORT ASSOCIATES