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Geosynthetic containment beneath Stockholm-Arlanda Airport
Geotextih,sandGeomemhranes 14(1996~ 201 205 I 1996 Elsevier Science Limited Printed in Ireland. All rights reserved 0266-1144'96 $15.00 ELSEV[ER
P11:S0266-1144(96)00010-6
Geosynthetic Containment Beneath Stockholm-Arlanda Airport
J. Bystr6m," L. K. Overmann b & L. O. Ericsson ~ "Golder Associates AB, Uppsala, Sweden J'Golder Construction Services, Atlanta GA 30136, Georgia, USA 'The Swedish Civil Aviation Administration, Norrk6ping, Sweden
A BS TRA C T Arlanda International Airport in Stockholm, Sweden, is in the process g[ constructing a new, third runway. Through extensive siting studies and economic evaluation, the alignment of this runway and the associated taxiway has been located over an esker, a ridge-like glacio-fluvial formation common in Sweden. This esker is an aquifer and constitutes a water supply for the airport as well as a back-up water supply for more than 250,000 residents of the area. The use of approximately 100 tonnes (110 tons) of deicing products per runway each year, and the periodic use of solvents to remove rubber deposits from the pavement have resulted in the need for a protection system for this valuable water resource. As a result, design of a lining system was commissioned to minimize the impact of these constituents on the groundwater. Based on the preliminary design, select portions o[ the new runway and taxiway are to be lined with a geomembrane. Sensitive and critical areas will include the use of a geosynthetic clay liner (GCL) beneath the geomembrane to form a composite liner, and/or a geotextile above the geomembrane as a protective cushion. The geomembrane lined area totals approximately 330,000m 2 (3,550,000 ft2 ), making the project one of the largest installations of this nature in northern Europe. Copyright ~ 1996 Elsevier Science Ltd.
INTRODUCTION Arlanda International Airport (Arlanda) in Stockholm, Sweden, is one of the busiest airports in Europe. The heavy traffic volume is due to the fact 201
202
J. Bystr6m et al.
that Arlanda is recognized as the northern gate to the former eastern states and the orient. Arlanda is also the center of the star-shaped Scandinavian air traffic system. To accommodate this heavy volume of traffic, especially during peak travel hours, the Airport Authority decided to add a third runway. Construction of this runway and the associated taxiway began in October 1995, and is scheduled to be in operation in the year 2000. Several runway/taxiway alignments were considered by the Airport Authority during the preliminary siting stage of this project. The economics associated with locating the runway a greater distance from the existing airport facilities resulted in the design presently under construction. Some of the primary economic factors considered during the siting process included the additional fuel cost and time necessary for each aircraft to taxi a greater distance to the terminal facilities. Portions of the runway and taxiway are being constructed over the L~ngS_sen esker, a glacio-fluvial ridge deposit. The sand and gravel deposits of this esker range from 15 to 25 m (50-80 ft) in depth over an area of approximately 100 hectares (250 acres). As a result, it has been designated as a Swedish national potable water supply source. The existing pumping station is located at the edge of the planned runway and extracts groundwater at a rate of approximately 15-201/s (240 315 gpm). Because of the esker, the permit requirements stipulated stringent restrictions regarding the effect of the new runway and taxiway on the groundwater, i.e. the groundwater concentration of polyaromatic hydrocarbons (PAHs) must not exceed 0.2#g/1. Additionally, the concentration of nitrogen must not exceed 5mg/1. These conditions pose a significant technical challenge, particularly since Sweden's cold climate results in the use of up to 100 tonnes (110 tons) of deicing products per runway each year. In addition, solvents are used occasionally to remove rubber deposits from the landing section of the runways. If leakage into the esker occurs such that the specified concentrations are exceeded, the environmental permit conditions require ceasing operation of this 2600 million Swedish kronor ($350 million US) capital investment until groundwater conditions have been restored to background levels. The Swedish Civil Aviation Administration conducted preliminary studies to evaluate the effect of discharges from the runway on the esker groundwater. Environmental consultants were commissioned to manage the licensing process and identify means to minimize the potential impact on the groundwater from the runway.
Geosynthetic containment beneath Stockholm airport
203
P R E L I M I N A R Y STUDY Before commencing with the design, two preliminary studies were performed. These preliminary studies included a risk analysis and a lining system material evaluation. The risk analysis study examined the effects of the discharges of the different chemicals used on the runway on the esker groundwater. The results of this study indicated that a containment system would be necessary, and that the transport of urea and aromatic hydrocarbons into the groundwater would become the criteria for design. The lining system under the runway will potentially be exposed to a large range of chemicals including deicing products (urea, potassium acetate), solvents of different kinds, jet fuel and other hydrocarbons and fire fighting chemicals. Based on a preliminary study of the physical and chemical durability of various synthetic materials, the Airport Authority concluded that a geomembrane, specifically high density polyethylene (HDPE), is the most suitable for a lining system beneath the runway and taxiway. A desk study was initiated to assess the chemical resistance of this material in contact with the constituents expected from the runway and taxiway. The results indicated that an H D P E geomembrane has good resistance to the considered chemicals in the expected concentrations.
DESIGN The initial risk analysis made it clear that the areas of the runway and neighboring taxiway in contact with the esker material require a lining system to reduce the potential contamination of the esker groundwater. Studies of the hydrogeologic conditions around the runway indicated that in some areas the lining system should be extended outside the esker to cover adjacent permeable materials. Ultimately, it was concluded that the lining system is to cover an area of approximately 330,000m 2 (3,550,000 ft2), making it one of the largest geomembrane installations in northern Europe. A challenge in the design of the lining system was the varying ground conditions. Transition zones between rock and soft clay/peat areas had to be accommodated for in the design. Analyses of differential settlements were made to assess the risk of excessive strains in the geomembrane. The chosen solution is to minimize the potential for overall settlement of the soft soil zones and thereby reduce the magnitude of differential settlement. The potential for settlement will be minimized through the incorporation
204
J. Bystro'm et al.
of various methods into the design, including excavation and replacement of material, the installation of vertical drains and surcharge and the installation of lime-cement pillars. Another design challenge was that the lining system had to be integrated with the airport utilities (power, signals, etc.) and with the runway drainage system. To avoid penetrations of the geomembrane, the lining system was designed to extend under the utility systems and the stormwater pipe alongside the runway and taxiway. In the preliminary design it has been assumed that the permeability of the main runway and taxiway pavement will be relatively low such that the lining system can be excluded from these areas. The lateral extent of the geomembrane lined area was determined by the longest expected reach of the snow throwing equipment used to clear the runway. This was a design criterion because the snow cleared from the runway may contain both deicing liquids and one or more of the other various chemical constituents. This distance is approximately 50m (165ft) from the edge of the runway and taxiway pavement, and includes the entire width of the paved area adjacent to the runway and taxiway. The lining system will terminate with a 1 m (3 ft) width of material extending under the runway and taxiway pavement. The geomembrane will be installed on a m i n i m u m of a 2 0 0 m m (8in) thick layer of sand obtained from a local source. The sand in contact with the geomembrane is anticipated to have a gradation ranging from 0 to 4 m m (0 to 0.16 in). The geomembrane lined surface will slope 2% towards the runway. Contaminated stormwater infiltrating over the lined areas will be contained by the geomembrane and transported laterally to a drainage pipe situated below the stormwater pipe alongside the runway. This drainage pipe will be confined within a trench and therefore will also contain any leakage from the overlying stormwater pipe. At the edge of the lined area, the drainage pipes will be connected to the stormwater pipes, which will outlet through pre-fabricated penetrations in the geomembrane. Under the drainage pipe the geomembrane liner will be protected by a needle punched, nonwoven geotextile functioning as a cushion. In other areas, the geomembrane liner will be protected by a 4 0 0 m m (16 in) thick sand layer obtained from a local source. The liner will be a 1.5mm (60mil) thick H D P E geomembrane. The initial risk assessment indicated that additional containment is required in some areas of the runway where the use of deicing liquids and solvents is anticipated to be greater. In these areas a geosynthetic clay liner (GCL) will be added under the H D P E geomembrane. Thus, a composite liner will be utilized in the areas with the highest risk for leakage.
Geosynthetic containment beneath Stockholm airport
205
FIELD TEST To further evaluate the preliminary design and the proposed materials, a field test will be performed during the spring of 1996. The field test program will be conducted by the Swedish Civil Aviation Administration Technical Department. The objective of the field test is to verify, to the extent possible, that the design, materials, equipment and procedures will perform as intended. To this end, the cross-section of materials resulting from the preliminary design will be placed over a limited area and tested under the anticipated worst-case loading conditions. Since the geomembrane will not be placed beneath the runway and taxiway, it is anticipated that the worst-case loading condition will be that of the equipment during the construction process. Several material, equipment and procedure alternatives will be evaluated with the field test. Several gradations of sand will be employed adjacent to the geomembrane liner to evaluate the puncture compatibility of these materials. Additionally, the performance of both a 1.0mm (40 mil) and 1.5 mm (60 mil) thick H D P E geomembrane will be evaluated through inclusion into this program. The outcome of the field test is planned to be evaluated both through exhumation of the materials and through the use of a sophisticated defect detection system based on electrical resistivity principles. The results of the field test will be utilized to modify and finalize the design, materials, equipment and procedures to be employed during the actual construction process.
P11:S0266-1144(96)00010-6
Geosynthetic Containment Beneath Stockholm-Arlanda Airport
J. Bystr6m," L. K. Overmann b & L. O. Ericsson ~ "Golder Associates AB, Uppsala, Sweden J'Golder Construction Services, Atlanta GA 30136, Georgia, USA 'The Swedish Civil Aviation Administration, Norrk6ping, Sweden
A BS TRA C T Arlanda International Airport in Stockholm, Sweden, is in the process g[ constructing a new, third runway. Through extensive siting studies and economic evaluation, the alignment of this runway and the associated taxiway has been located over an esker, a ridge-like glacio-fluvial formation common in Sweden. This esker is an aquifer and constitutes a water supply for the airport as well as a back-up water supply for more than 250,000 residents of the area. The use of approximately 100 tonnes (110 tons) of deicing products per runway each year, and the periodic use of solvents to remove rubber deposits from the pavement have resulted in the need for a protection system for this valuable water resource. As a result, design of a lining system was commissioned to minimize the impact of these constituents on the groundwater. Based on the preliminary design, select portions o[ the new runway and taxiway are to be lined with a geomembrane. Sensitive and critical areas will include the use of a geosynthetic clay liner (GCL) beneath the geomembrane to form a composite liner, and/or a geotextile above the geomembrane as a protective cushion. The geomembrane lined area totals approximately 330,000m 2 (3,550,000 ft2 ), making the project one of the largest installations of this nature in northern Europe. Copyright ~ 1996 Elsevier Science Ltd.
INTRODUCTION Arlanda International Airport (Arlanda) in Stockholm, Sweden, is one of the busiest airports in Europe. The heavy traffic volume is due to the fact 201
202
J. Bystr6m et al.
that Arlanda is recognized as the northern gate to the former eastern states and the orient. Arlanda is also the center of the star-shaped Scandinavian air traffic system. To accommodate this heavy volume of traffic, especially during peak travel hours, the Airport Authority decided to add a third runway. Construction of this runway and the associated taxiway began in October 1995, and is scheduled to be in operation in the year 2000. Several runway/taxiway alignments were considered by the Airport Authority during the preliminary siting stage of this project. The economics associated with locating the runway a greater distance from the existing airport facilities resulted in the design presently under construction. Some of the primary economic factors considered during the siting process included the additional fuel cost and time necessary for each aircraft to taxi a greater distance to the terminal facilities. Portions of the runway and taxiway are being constructed over the L~ngS_sen esker, a glacio-fluvial ridge deposit. The sand and gravel deposits of this esker range from 15 to 25 m (50-80 ft) in depth over an area of approximately 100 hectares (250 acres). As a result, it has been designated as a Swedish national potable water supply source. The existing pumping station is located at the edge of the planned runway and extracts groundwater at a rate of approximately 15-201/s (240 315 gpm). Because of the esker, the permit requirements stipulated stringent restrictions regarding the effect of the new runway and taxiway on the groundwater, i.e. the groundwater concentration of polyaromatic hydrocarbons (PAHs) must not exceed 0.2#g/1. Additionally, the concentration of nitrogen must not exceed 5mg/1. These conditions pose a significant technical challenge, particularly since Sweden's cold climate results in the use of up to 100 tonnes (110 tons) of deicing products per runway each year. In addition, solvents are used occasionally to remove rubber deposits from the landing section of the runways. If leakage into the esker occurs such that the specified concentrations are exceeded, the environmental permit conditions require ceasing operation of this 2600 million Swedish kronor ($350 million US) capital investment until groundwater conditions have been restored to background levels. The Swedish Civil Aviation Administration conducted preliminary studies to evaluate the effect of discharges from the runway on the esker groundwater. Environmental consultants were commissioned to manage the licensing process and identify means to minimize the potential impact on the groundwater from the runway.
Geosynthetic containment beneath Stockholm airport
203
P R E L I M I N A R Y STUDY Before commencing with the design, two preliminary studies were performed. These preliminary studies included a risk analysis and a lining system material evaluation. The risk analysis study examined the effects of the discharges of the different chemicals used on the runway on the esker groundwater. The results of this study indicated that a containment system would be necessary, and that the transport of urea and aromatic hydrocarbons into the groundwater would become the criteria for design. The lining system under the runway will potentially be exposed to a large range of chemicals including deicing products (urea, potassium acetate), solvents of different kinds, jet fuel and other hydrocarbons and fire fighting chemicals. Based on a preliminary study of the physical and chemical durability of various synthetic materials, the Airport Authority concluded that a geomembrane, specifically high density polyethylene (HDPE), is the most suitable for a lining system beneath the runway and taxiway. A desk study was initiated to assess the chemical resistance of this material in contact with the constituents expected from the runway and taxiway. The results indicated that an H D P E geomembrane has good resistance to the considered chemicals in the expected concentrations.
DESIGN The initial risk analysis made it clear that the areas of the runway and neighboring taxiway in contact with the esker material require a lining system to reduce the potential contamination of the esker groundwater. Studies of the hydrogeologic conditions around the runway indicated that in some areas the lining system should be extended outside the esker to cover adjacent permeable materials. Ultimately, it was concluded that the lining system is to cover an area of approximately 330,000m 2 (3,550,000 ft2), making it one of the largest geomembrane installations in northern Europe. A challenge in the design of the lining system was the varying ground conditions. Transition zones between rock and soft clay/peat areas had to be accommodated for in the design. Analyses of differential settlements were made to assess the risk of excessive strains in the geomembrane. The chosen solution is to minimize the potential for overall settlement of the soft soil zones and thereby reduce the magnitude of differential settlement. The potential for settlement will be minimized through the incorporation
204
J. Bystro'm et al.
of various methods into the design, including excavation and replacement of material, the installation of vertical drains and surcharge and the installation of lime-cement pillars. Another design challenge was that the lining system had to be integrated with the airport utilities (power, signals, etc.) and with the runway drainage system. To avoid penetrations of the geomembrane, the lining system was designed to extend under the utility systems and the stormwater pipe alongside the runway and taxiway. In the preliminary design it has been assumed that the permeability of the main runway and taxiway pavement will be relatively low such that the lining system can be excluded from these areas. The lateral extent of the geomembrane lined area was determined by the longest expected reach of the snow throwing equipment used to clear the runway. This was a design criterion because the snow cleared from the runway may contain both deicing liquids and one or more of the other various chemical constituents. This distance is approximately 50m (165ft) from the edge of the runway and taxiway pavement, and includes the entire width of the paved area adjacent to the runway and taxiway. The lining system will terminate with a 1 m (3 ft) width of material extending under the runway and taxiway pavement. The geomembrane will be installed on a m i n i m u m of a 2 0 0 m m (8in) thick layer of sand obtained from a local source. The sand in contact with the geomembrane is anticipated to have a gradation ranging from 0 to 4 m m (0 to 0.16 in). The geomembrane lined surface will slope 2% towards the runway. Contaminated stormwater infiltrating over the lined areas will be contained by the geomembrane and transported laterally to a drainage pipe situated below the stormwater pipe alongside the runway. This drainage pipe will be confined within a trench and therefore will also contain any leakage from the overlying stormwater pipe. At the edge of the lined area, the drainage pipes will be connected to the stormwater pipes, which will outlet through pre-fabricated penetrations in the geomembrane. Under the drainage pipe the geomembrane liner will be protected by a needle punched, nonwoven geotextile functioning as a cushion. In other areas, the geomembrane liner will be protected by a 4 0 0 m m (16 in) thick sand layer obtained from a local source. The liner will be a 1.5mm (60mil) thick H D P E geomembrane. The initial risk assessment indicated that additional containment is required in some areas of the runway where the use of deicing liquids and solvents is anticipated to be greater. In these areas a geosynthetic clay liner (GCL) will be added under the H D P E geomembrane. Thus, a composite liner will be utilized in the areas with the highest risk for leakage.
Geosynthetic containment beneath Stockholm airport
205
FIELD TEST To further evaluate the preliminary design and the proposed materials, a field test will be performed during the spring of 1996. The field test program will be conducted by the Swedish Civil Aviation Administration Technical Department. The objective of the field test is to verify, to the extent possible, that the design, materials, equipment and procedures will perform as intended. To this end, the cross-section of materials resulting from the preliminary design will be placed over a limited area and tested under the anticipated worst-case loading conditions. Since the geomembrane will not be placed beneath the runway and taxiway, it is anticipated that the worst-case loading condition will be that of the equipment during the construction process. Several material, equipment and procedure alternatives will be evaluated with the field test. Several gradations of sand will be employed adjacent to the geomembrane liner to evaluate the puncture compatibility of these materials. Additionally, the performance of both a 1.0mm (40 mil) and 1.5 mm (60 mil) thick H D P E geomembrane will be evaluated through inclusion into this program. The outcome of the field test is planned to be evaluated both through exhumation of the materials and through the use of a sophisticated defect detection system based on electrical resistivity principles. The results of the field test will be utilized to modify and finalize the design, materials, equipment and procedures to be employed during the actual construction process.