Kaiaua Landfill Remediation: an Example of Council(S), Consultant and Contractor Co-Operation to Remove a Historic Blight on the Landscape
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Kaiaua Landfill Remediation: An example of Council(s), Consultant and Contractor co-operation to remove a historic blight on the landscape. The Kaiaua coastline on the Gulf of Thames is an area of scenic and natural beauty. However, a 205m stretch of the coastline was for 20yrs used as a landfill for disposal of domestic and demolition waste, including asbestos containing material (ACM). Buried in natural hollows and localised excavations, and compressed to less than 1m thick the wastes lay hidden and largely forgotten until coastal erosion and retreat of the shoreline started to expose and wash out the refuse. Hauraki District Council inherited this legacy and decided to do something about it. To achieve a cost effective and practical level of remediation required a pragmatic approach by Regional and District Councils through the consenting process, by the Consultant in planning, verification and oversight, and by the Contractor working within a tight time frame, tidal and environmental constraints. The work also attracted considerable public and press attention. Close liaison and co-operation between all parties was essential during the site works including shared supervision of the work and joint assessment of materials that could be retained. In this paper we describe the constraints affecting the project and approaches used to overcome these to achieve a successful and acceptable level of site remediation. Authors: Ken Read: Principal Engineering Geologist, Opus International Consultants, Hamilton Andre Tibshraeny: Project Manager Hauraki District Council, Paeroa Debbie Dewar: Senior Environmental Scientist, Opus International Consultants, Hamilton Key Words: Landfill, Consenting, Asbestos, Contaminated Land, Remediation Introduction with site materials where possible or imported shelly material from further north on the The former Kaiaua landfill, located shoreline. approximately 1km south of the Kaiaua township is on a narrow strip of land (approximately 15m to 20m wide) between East Coast Road and the shore of the Firth of Thames (Figure1). Landfilling with locally derived waste occurred historically on the site with wastes being placed in low lying areas and covered with locally sourced shelly materials and in places a ‘capping’ of brown rock. At that time the land between the East Coast Road and the shoreline was approximately twice the width of that now seen. Over the years coastal erosion had exposed the waste which was now outcropping on the shoreline and beach creating an environmental nuisance and eyesore (Figure 2). In 2015 Hauraki District Council (HDC) decided to remediate the site by removal of the waste material and reinstate the resulting void Figure 1: Site location Opus International Consultants Limited (Opus) https://rsis.ramsar.org/RISapp/files/RISrep/N was engaged by HDC to carry out a review of Z459RIS.pdf previous work on the site, undertake a contaminated land investigation, prepare a Site usage Remediation Action Plan (RAP) for the site It is unclear when filling of the site started and assist with obtaining the necessary however anecdotal evidence describes waste consents. This included resource consent being placed in old tidal channels or inlets from Waikato Regional Council (WRC), and an during the 1960’s and 1970’s. Records show ‘NES’ Consent from Hauraki District Council. that the refuse tip was closed in 1983 however In order to ensure objectivity the latter was it is likely that fly-tipping has continued in the outsourced to another Consultant (AECOM). area since that time. Between 1944 and 2006 the coast line is estimated to have eroded line by between 5 and 20m and was continuing to do so. This had resulted in the exposure of waste on the foreshore and beach, and transportation of waste materials southwards along the coast and presumably into the ocean itself. Site Investigations The site was previously in the jurisdiction of Franklin District Council who commissioned investigations of the site in 2001 and 2010. The first of these comprised a series of auger holes and test pits. The second comprised six trenches at regular spacing perpendicular to the foreshore. The conclusions of each phase of work were broadly similar in identifying a thin layer of Figure 2: Waste exposed on coast line waste under a poor ‘capping’ of what is known locally as ‘brown rock’, which is essentially a The project had considerable local support, clay rich gravel material. and attracted significant local and national media interest. Two zones of extensive filling were identified http://www.stuff.co.nz/environment/85446968/ within the site area, a northern and southern coastal-erosion-catches-up-with-buried- zone respectively. The reports described the kaiaua-landfill main bodies of wastes as highly decomposed refuse and soil fill – with only steel, bottles and Background and Site History bricks still identifiable and containing plastic, rags, bottles, tyres and other refuse more Ecology and conservation typical of the 1970’s. The site is within an area of conservation significance. The Firth of Thames has been The southern area appeared to include more designated under the Ramsar Convention as bio-degradable refuse, suggesting that the site a wetland of international significance. Of was generally filled from north to south. particular importance are the intertidal mudflats between Miranda and Kaiaua, which No soil samples were obtained for analyses. during the summer can support up to 40,000 wading birds (average through the year of Two groundwater samples were obtained and 25,000), making it one of the three most tested for contaminants typically associated important habitats for wading birds in New with landfill leachate. The test results were all Zealand. below NZ guidelines for protecting marine ecosystems. In 2015 HDC appointed Opus to aid them with Landfill Gas preparation of a RAP to clear the site and with Due to the low volume of organic materials obtaining the necessary consents. As part of present, the age of the landfill and the open this work Opus carried out 12 hand auger porous nature of the overburden soils allowing boreholes within the two zones of waste venting of gases we considered the risk of materials previously identified and inspection hazardous levels of landfill gas being present of the foreshore exposures. to be very low. Samples of topsoil, overburden, ‘waste’ and Landfill leachate the underlying mud and sandy silt were ‘Classic’ landfill leachate is generated by the obtained. Forty four soil samples were taken decomposition of organic wastes and can be for laboratory analyses. rich in nitrates and nitrogen, and be discoloured. Wastes/refuse exposed on the foreshore was examined and samples obtained from one part The site was poorly capped with continual of the face. The nature of refuse/waste ‘flushing’ of the wastes by infiltration of surface observed was broadly in line with that water and possible occasional inundation by previously reported with the significant the sea. Seepages from the waste were addition of ACMs in the form of cementitious described as clear and odourless. Test results board and piping. from a ‘younger’ period were within acceptable limits. Key Findings and Conclusions The risk of hazardous leachate being present was considered to be very low. The following stratigraphy was determined: Contaminated Soil Pale/light A mix of natural and Samples of the overburden soils were shell/sand reworked beach deposits analysed to assess the likelihood of deposits highly variable in thickness contamination by mixing with wastes or and areal distribution. capillary action drawing contaminants in to the Locally intermixed with overlying soils. waste/refuse deposits. Samples of the soils surrounding the waste materials were tested for ‘source’ contaminant “Capping” of Localised imported ‘rotten levels. gravely rock’ type aggregate. silt/clay Samples of the underlying soils were tested to assess the likelihood of leaching of Dark brown Highly variable in thickness contaminants into the underlying silty/clay organic rich and distribution, locally muddy marine deposits. ‘mud’/clay/silt absent. Wastes include: Testing targeted contaminants typical of the with refuse plastic, metals, glass, materials observed on the site. This and waste wood, fabric, demolition comprised metals/metalloids associated with materials, bricks, concrete wood treatment, paints and the corrosion of and ACMs. metal, i.e. copper, lead, arsenic, chromium, lead, cadmium, nickel and zinc. Grey ‘mud’ Natural soils immediately and sandy below waste/refuse layer. In consultation with HDC, and with a view to silt/clay. Often with sandy surface the level of site observation and verification grading quickly to mud/clay testing procedures likely to be necessary with depth. during remediation, no asbestos testing was undertaken and the assumption made that all Landfills generally present three ‘sets’ of suspect ACMs were indeed ACMs. contamination risks; landfill gas generation The laboratory test results were assessed and migration, leachate generation and against recreational land use soil contaminant migration, and contamination of soils by standards (SCSs) for the protection of human migration of chemical constituents and health, published guidance for the protection physical mixing of the waste and soils. of groundwater for potable use, and sediment quality guidelines for aquatic protection based Results and Conclusions: Ecological on the sensitive environment of the site. protection As expected samples