Creating the right environment
Work undertaken by Biwater Treatment at Packington WwTW in Leicestershire played a significant part in the company gaining ISO 14001 accreditation. We look at what was entailed
Redevelopment of Severn Trent Water's Packington WwTW in Leicestershire helped Biwater Treatment to win ISO 14001 approval for its environmental management system. Situated close to the busy A42 trunk road that connects the M42 and M1, Packington WwTW treats domestic sewage from the 15,000 population of Ashby-de-la-Zouch and the village from which it takes its name, along with a proportion of trade effluent from a local food factory and a dairy.
Redevelopment was driven by the Environment Agency's (EA) River Quality Objectives, which set a tighter discharge consent of 15mg/l BOD, 30mg/l suspended solids and 5mg/l ammonia. Other benefits included the opportunity to reduce odour and fly nuisance, but probably the biggest influence on Severn Trent Water's (STW) choice of an appropriate process was the fact the existing facility - which used high-rate biological aerated filters (BAF) for secondary treatment - was close to the end of its asset life.
Taking into account the size of population and the variation in load caused by the fluctuating trade waste, STW identified an oxidation ditch process as the most robust and economically viable. The decision was in line with the company's policy of using oxidation ditches - usually for medium-sized population equivalents of 2,000-10,000, but sometimes outside of those limits where unusually variable loads are experienced. One consequence of this decision was the existing biological filters, humus tanks and inlet works would become redundant and the BAF plant would be mothballed.
The change to a different process (and the customary requirement to keep the plant in service throughout the redevelopment) meant the new plant had to be built on a substantial area of greenfield land, making appropriate environmental safeguards more than usually important. A survey of the site by an ecological expert before work began to locate areas that would need special consideration revealed a badger sett in one corner of the site. Like the animals themselves, badger setts have been legally protected since 1992, so it was decided to avoid any risk of disturbance by fencing off the area to a distance of 10m on all sides. The reason for the fencing was explained to site staff through induction training, and the integrity of the perimeter was checked at least weekly when completing the site environmental checklist.
Also considered to be of ecological value were the clusters of hedges surrounding the site. Although some had to be sacrificed for reasons of access, routes were positioned to retain as many as possible, and fencing was erected to prevent any accidental damage. All site water, both ground and surface, was pumped to a settling lagoon with an impermeable liner, where it was allowed to weir over naturally through a pipe and percolate through the surrounding grassland into a roadside drain en route to the river. The arrangement was covered by a temporary Consent to Discharge from the EA, and monitored from a dedicated sampling point. Excavations for the oxidation ditches and other below-ground structures gave rise to considerable volumes of spoil that, rather than being removed from the site, were put to good use as a means of shielding the works from the A42. When the project was completed, the spoil was landscaped to provide a permanent screening feature in accordance with the planning approval.
The waste materials generated during construction were also recycled as far as possible, with timber and steel being segregated and sent for recycling. Awareness of the potential environmental implications of construction activities was a central element of the induction training that everyone working on site received, complemented by 'toolbox talks' on the use of equipment. Special importance was attached to the appropriate way to respond to spillages of potentially hazardous or polluting materials, such as chemicals, oil and diesel.
The effectiveness of spill-kit equipment training was demonstrated by a successful spill drill overseen by Biwater's environmental advisor. All fuel and chemicals used on site were kept in a bunded area covered to prevent rainfall infiltration. The refuelling of mobile plant took place within this area, overseen on each occasion by a designated fuel controller. When the impact of construction beyond the site itself was assessed it was clear that noise and traffic movements would be the main concerns, especially for the residents of Packington village. Regular noise assessments were carried out, particularly during piling in the early stages of the work. In the event only one complaint about noise was received, but an investigation showed that this came from another source closer to the complainant. The impact of traffic movements was minimised by a clearly signposted alternative route that by-passed the village. Suppliers and sub-contractors were issued with maps showing the route to be used, and any deviations from this were noted by the gatekeeper and raised with the company concerned. One seasonal issue that had to be addressed was the effect of site traffic on the access roads - dust in summer and mud in winter. To guard against this, a road sweeping vehicle was called in as required, which at the height of the work meant a visit every evening during the working week.
To complete its strategy for maintaining good relations with the local community, Biwater arranged to give residents advance notice of occasions when work had to start early or finish late. Packington was one of the sites that were audited in connection with the company's application for approval of its environmental management system under ISO14001, which it secured during 2004. To complete the success story, environmental aspects of the running of the project also contributed to its bronze award in the 2005 Considerate Constructors National Awards.