Monitoring the processes of both land and water remediation were central to the development of the 2012 Olympic Park – and for its legacy. James Apted led the project across the entire site, and shares the many complex variables that had to be taken into account.
The Olympic Park has undergone a major transformation. One of the key features of the project was the remediation required to overcome the effects of past contamination. This was carried out as part of a large earthmoving operation, to provide the new landform in order to support the venues and infrastructure for the London 2012 Olympic and Paralympic Games. The site was located over a prime UK aquifer, and criss-crossed by more than 10 km of waterways, with both the aquifer and the waterways being key environmental receptors.
From the outset of the project it was clear that a fundamental and integral part of the remediation works, and all of the significant follow-on construction, would be the general environmental monitoring, of which the water monitoring would in itself be a key part.
The review of historical maps confirmed more than a century and a half of mixed industrial land use on the Olympic Park with a potential for generating contamination. Additionally, a significant importation of fill material had been carried out in several phases to reclaim the original marsh land. The initial filling was during the mid-to-late industrial revolution, which was further supplemented by disposal of demolition material from the clearance of World War Two bomb damaged buildings in the London area, and finally from Nineteenth and Twentieth Century rubbish tips.
Looking at the transformed park now it is hard to imagine its previous existence. The site was handed to the Olympic Delivery Authority (ODA), following the completion of the land procurement by the London Development Agency (LDA). The land use had previously included offices and warehouses, car breakers, servicing units and parts storage, chemical works, food processing, concrete plants, bus garages, railway sidings, residential and travellers’ sites, hard standing concrete, access roads and derelict areas. A land without future purpose stood ready for its new future.
Almost all water monitoring schemes are influenced in some way by the underlying geology and the Olympic Park is no different, with a typical geological profile beneath the site: • Made ground: this covers the whole site and varies from a few metres to 15 metres thick • Alluvium: one to three metres thick, consisting of soft, silty clay • River terrace deposits: around three to five metres thick deposits of sands and gravels, a secondary aquifer • Lambeth Group deposits: generally around 20 to 30 metres thick, made up of interbedded clays, silts and sands • Thanet sand: ten to 20 metres thickness of very dense, very silty fine sand, which is a secondary aquifer but is linked to the chalk • Chalk: a primary aquifer
There were two key factors to consider as part of the remediation strategy which would clean the underlying soils and groundwater, and become a key part of the legacy that now follows the London 2012 Olympic and Paralympic Games. The first was to protect human health of future site occupiers once the project was completed. The second was to prevent contamination of the environmental receptors, the water courses and the aquifers. The fundamental approach to human health protection was to establish a ‘separation layer’ of material at the ground surface, of suitable quality for the proposed use of the site, in order to isolate the occupants from any residual below ground contamination.
Deeper soils and contaminated groundwater posed a contamination risk to the underlying chalk groundwater aquifer and surface waters; as a result these were targeted and treated. Soils that were removed for treatment were generally reused as a deeper ‘general fill’ material across the Olympic Park after treatment.
The ODA took responsibility for remediation of the Olympic site in February 2007 in an agreement with the then LDA, who were the landowner. This agreement obligated the ODA to remediate the land for both the Games and the legacy that would follow, as set out in the masterplans approved in the site preparation planning applications in February 2007.
The ODA was also required to minimise residual maintenance and future environmental monitoring requirements on the site, while also reducing potential below ground constraints on future development. So that enabling works could start prior to the approval of the full planning application, a number of early planning permissions were granted for zones around the Park. These permissions were later superseded by the main site preparation application. As a major consultee, the Environmental Agency (EA) was involved from the start of the planning process. In view of the scale of the works and the need for timely responses in the planning process, the EA provided a dedicated and site based co-located team to work closely with not only the planning decisions team (PDT), but the designers and contractors involved in the development platform.
To assist all project participants, the EA produced a guide for contractors on the Olympic Park, which provided guidance on the main licences and consents required, and detailed the processes to be followed. Monthly coordination meetings were undertaken with all regulators, consultants, contractors and the ODA, so that attendees were kept informed of progress and any issues that required early resolution could be targeted. The environmental regulation of the Olympic Park remediation works was carried out as part of the planning permission process. The works carried out to create the development platform on which the facilities were developed required detailed planning permission.
The planning permission, when granted, set a number of specific environmentally focused planning conditions, which dealt with the assessment and remediation of the contamination. Acknowledging the highly sensitive nature of the site, the planning conditions also set out obligations for establishing an environmental monitoring regime, including monitoring water quality. The formal regulator was the PDT, supported by the EA.
From the very outset of the project it was clear to us that water was a key environmental resource, and one that needed to be protected. The water resources fell into two distinct areas: the surface water and the groundwater.
The surface water is made up of various waterways from canals, river channels and ponds that run through the park and have an overall combined length just exceeding 11 km. The main channel is the River Lea, with subsidiary channels of the Waterworks River, the City Mill River and the Bowback River. These flow across the Olympic Park from north to south, and eventually the River Lea flows into the River Thames. While some of the water courses, such as the canals, were not considered key assets, the River Lea was thought to be a key resource and one that should be and was capable of supporting aquatic life.
Prior to the start of the Olympic Park project, the water quality of the River Lea as it passed through the site was granted an acceptable quality according to the Environment Agency. This status had been achieved by a long process of controlling and improving discharges to the River, particularly those from water treatment plants upstream of the Park. The water of the River Lea was used as a defined ‘receptor’ as part of the remediation strategy. While this did generate a requirement to treat some of the contaminated soils and groundwater throughout the site, the evidence indicated that there was no significant ongoing pollution of the existing surface water network from the Park.
The groundwater falls into two generally quite separate regimes. An upper groundwater table within the river terrace deposits separated from a lower groundwater in the chalk and Thanet sand by a clay rich stratum called the Lambeth Group deposits. The upper water table has some limited hydraulic connectivity with the river channels, and in any case, for the purposes of remediation assessment, it was assumed that at some point there would be a connection. This was generally taken to be to the south of the site. The lower water table with an elevation well below ground level was typically separate and uninfluenced by the upper water table, but there were some exceptions. These were either by geological features or artificial pathways such as wells. Historical deep foundations may also have created vertical pathways.
There were two parts to the strategy of water protection: dealing with sources of contamination that posed a threat to water resources, through a combination of treatment and removal which was part of the remediation process, and establishing a system of monitoring, to verify the remediation works, and to show no adverse impact to the water resource during the course of the works. The latter was part of a site-wide environmental monitoring regime, used throughout the project life to monitor potential impacts, provide qualitative information on environmental quality, and to help control operations.
Groundwater monitoring regime
Groundwater monitoring generally fell into two categories that were directly associated with the remediation process and general environmental protection.
Monitoring the remediation process
Monitoring associated with the remediation process was typically undertaken to show that the underlying river terrace deposit groundwater aquifer had not been impacted by the overlying earthworks and remediation operations. In this instance, the monitoring wells were typically installed within a groundwater body, usually within the river terrace deposits, as it represented the commencement of the waterborne portion of the contamination migration pathway that required it to be addressed.
In these cases the monitoring was based on sampling before, during and after treatment to the point that the monitoring could show – to the satisfaction of the regulator (the planning authority supported by the EA) – that the remediation treatment target, generally a concentration for particular contaminants of concern, had been reached.
Generally the regulator required a period of not less than a year of monitoring, typically at three-monthly intervals following completion of the remediation, to show that the treatment had been successful, and the remediation target had been achieved.
Given the varied history of the Park, there were a number of contaminants to consider: heavy metals such as arsenic, lead, copper, zinc, poly-aromatic hydrocarbons, chlorinated solvents, and ammonia. In cases where the contamination source was in the groundwater, rather than the overlying soil, and the groundwater itself was undergoing direct treatment, the monitoring was also targeted with the same water body. Thus achievement or otherwise of the remedial targets was clear cut.
Either the targets had been achieved, with monitoring showing this to be the case, or they had not, in which case there were a number of further options. These included continued monitoring to see if there was any further improvement in groundwater quality, carrying out more treatment to ascertain whether a reduction in groundwater contamination was achievable, or demonstrating to the regulator that sufficient remediation had been achieved and that no more action was required.
In most cases the remediation removed a soil source, or treated an isolated pocket of contamination within the water body. Where a significant plume had developed, however, which itself had chemical contamination at concentrations that were unacceptable, the focus on remediation was to demonstrate that the contamination source had been removed, and that a trend of declining contaminant concentration in the plume could be discerned. In all these cases the common thread was to have a comprehensive system of groundwater monitoring in place.
The regime of observation wells, small diameter wells drilled into the groundwater bodies, depended very much on the hydraulic characteristics of the water body being monitored, permeability and thickness being key, and also depended on the spread and character of contamination.
The wells were installed in normal 150 mm boreholes, with the sampling zone lined with slotted well screens in turn isolated by appropriate bentonite cement grout seals. Thus groundwater was sampled from a clearly defined elevation.
The frequency of monitoring was related to the nature of the remediation process. Both during and after the remediation works, however, the monitoring was typically undertaken on a monthly basis.
The main reporting of the monitoring was in the validation reports used to demonstrate the successful completion of remediation. Interim reporting was undertaken as agreed with the regulator.
The establishment of a Park-wide system of groundwater monitoring was a very early activity of the project, initiated as part of the early site investigation works. As well as establishing a baseline position for groundwater quality, it was also used to calibrate the groundwater model of the site.
The model allowed an understanding of groundwater movement across the site to be developed, principally within the river terrace deposits but also within the chalk. The model aided in identifying pollution pathways, and the nature of the connectivity between the groundwater and surface water features.
As the project progressed and more of the site became available, the extent of the groundwater monitoring regime also grew. The regime allowed the groundwater quality and profile to be monitored across the Park, in both the river terrace deposits and the chalk groundwater bodies, and in turn significant value was added to the overall transformation of the Park both for the London 2012 Olympic and Paralympic Games and the legacy that follows.
The aims of the environmental groundwater monitoring were to:
• Provide a record of groundwater quality from the beginning into the construction phase and into the legacy • Identify any adverse impact that occurs to the two aquifers • Assist in determining any remedial actions • Provide an overall framework of groundwater monitoring across the Park • Provide a Park-wide basis to show any improvement to the ground water quality • Provide backup and support to the remediation monitoring Reporting against these objectives was carried out on a monthly basis for the main data, with a more detailed report given on a half yearly basis.
The surface water monitoring regime
As with the groundwater regime, the surface water regime was set up at the outset of the Olympic Park project. It also provided the basis for monitoring the quality of the surface water features across the Olympic Park, but with particular reference to the River Lea. The regime consisted of real-time automatic monitoring, regular direct manual sampling, direct manual testing with a hand held meter and visual inspections. The automated real-time system reported on pH, turbidity, dissolved oxygen, conductivity and temperature. The full sampling and laboratory testing as well as the above also included heavy metals, Biological Oxygen Demand (BOD), and Chemical Oxygen Demand (COD) ammonia and hydrocarbons.
A key part of the remediation and regeneration of the Olympic Park was the environmental monitoring, of which the water monitoring was a central feature. This was used to underpin the remediation process, and ensure that the critical water receptors were protected. The monitoring regime has been able to show that both the surface waters and the chalk aquifer have remained protected during the development of the Olympic Park. In addition, the water monitoring has provided critical data to support the assessment and validation of the remediation process and helped to refine and update the detailed understanding of the groundwater conditions beneath the site, and the interaction of the site and the surface water features.
Published: 01st Sep 2012 in AWE International