Public concern around the historical disposal of industrial wastes in New Plymouth has again been raised due to a recent event at Marfell Park.
This note covers the main points of the background, the nature of the event itself, and proposed actions going forward. There is no comment upon some of the material presented in the media.
The recent concerns arose when two remnants of drums and chemical residues were unearthed at Marfell Park during District Council excavations for a stormwater pipe. Consequent investigations unearthed another seven container remnants. A large volume of soil material was removed and appropriately disposed of by the District Council’s contractor, under the supervision of Regional and District Council staff, and the site has been reinstated.
The Taranaki Regional Council has been investigating and monitoring known and alleged rubbish dump sites in New Plymouth on an on-going basis for the last 15 years (since 1994).
Nine years ago (2001), the Council undertook a comprehensive investigation of 36 sites in response to public concern and intense media speculation over possible inappropriate disposal of agrichemical wastes. The investigation, conducted with the close participation of interest groups, concluded that there were no environmental risks from any of the sites.
Taranaki Regional Council investigations and sampling at Marfell Park following the recent discovery of container remnants, and the actions of the District Council, have confirmed that there is no reason to believe there is any environmental risk at Marfell Park.
When did the Council first begin monitoring the Marfell site?
In 1994 the Regional Council committed to identifying and assessing every known past or present rubbish dump in the region, to determine whether such sites posed an environmental risk. Approximately 120 sites were identified and assessed by the Council at this time. Marfell Park, a former city rubbish dump in the 1950s to early 1970s, was included in these investigations.
The New Plymouth District Council, as successor to the City Council, that had operated the site, was required to seek and did obtain a resource consent because of an ongoing discharge of leachate (flow of liquids containing dissolved material from the contents of the dump and rainfall) from the site.
In 1998 leachate from the site was diverted from discharging to the stream and piped to the municipal sewerage system for treatment.
The Regional Council has regularly inspected the site and sampled stormwater and residual leachate discharges from the site. The most recent inspection occurred in February 2009. At no time has any discharge or event of environmental concern been found.
Allegations of agrichemical waste disposal sites in New Plymouth
Around 1999/2000 public concern was raised by allegations of inappropriate disposal of agrichemical wastes which could contain dioxin, at a number of sites in New Plymouth.
In 2000, the Regional Council began a comprehensive compilation and investigation of these allegations. Marfell Park was one of the 36 sites where further investigations and sampling were carried out. The report on these investigations was released by this Council in August 2001.
See the table below for links to the full report, the executive summary, and the report's section concerning Marfell Park.
Events surrounding excavations at Marfell Park in May 2009
On 7 May, a contractor working for the New Plymouth District Council excavated two drum remnants during excavations of a trench across the bottom of Marfell Park. The excavations for a new stormwater pipe were dug through soil and, for approximately 30 metres, through landfill rubbish. The drums were at a depth of about 2 metres.
One drum remnant had a characteristic agrichemical smell. The contractor immediately stopped work and contacted both the District Council and the Regional Council.
The Regional Council collected 6 samples of the residues within the drums and of surrounding soil, over a distance of about 7 metres of the excavated soil. The volume of chemical residue was a few litres of caked crystalline material.
The District Council immediately removed the drum residues, the chemical residue and approximately 80 cubic metres of excavated soil and rubbish to the Colson Road land fill, a modern highly-engineered landfill. The site was secured while the samples were analysed.
One residue sample contained the chemicals tetrachlorobenzene (concentration of 17%) and trichlorophenol (concentration of 27%). A second sample had about 3% of each of these two chemicals. The other four samples, which were of the surrounding soil, had none.
The dioxin 2378 TCDD is a known contaminant of trichlorophenol. The analysis of the most concentrated chemical residue was found to contain 2.9 ppm dioxin, and the second chemical sample 0.45 ppm.
The levels in the other four soil samples were 1,000 to 10,000 times lower, and were therefore of far less significance.
Four of the samples had concentrations of the organophosphate pesticide dichlofenthion ranging from 3 to 6.9 mg/kg. Two of the samples were associated with residues within crushed drums. Samples of soil a few metres from the drums had low or no dichlofenthion (at a detection limit of 0.01 mg/kg).
Contaminated sites consultant Dr Graeme Proffitt says dichlofenthion has a moderate acute toxicity. Its LD50 (rat) is reported to be 270 mg/kg bw, about the same as another organophosphate, diazinon, which is freely available from garden centres as a lawn treatment for grass grub. Related organophosphate compounds have allowable daily intakes between about 0.01 and 0.001 mg/kg-bw/day (see International Programme on Chemical Safety Poisons Information Monograph (Group Monograph) G001). On that basis, a residential soil guideline would be tens to hundreds of mg/kg. At only a few mg/kg, the detected concentration would not be a risk in a residential setting. The park setting is less sensitive than a residential setting and the detected concentrations of dichlofenthion are of no concern for human health. Regardless, the drums/soil with the higher concentrations are no longer in the park. The lower concentrations that may remain in surrounding soil are also of no concern.
According to Wikipedia, dichlofenthion has a relatively short half-life of only a few minutes in both water and soils. While little research has been conducted over the environmental fate this compound, much is known about the compound class in which it resides.
Dichlofenthion is an organophosphate pesticide. Because most organophosphate pesticides biodegrade relatively quickly, they are generally regarded as safe for use. While this may be true for most compounds, bacteria still require time to adapt to break down new compounds introduced to the soil. It has been shown that degradation rates increase as the same compounds are introduced repeatedly into the soil.
Because the sorption to soil and sediment is considered high, dichlofenthion is not a highly mobile compound. The estimated half-life of dichlofenthion in water, soil, and sediment is less than a few minutes. The estimated half-life in the air is 2.78 hours, much higher than that in water, soil, and sediment.
Traces (at parts per billion levels) of four other organophosphorus and organochlorine compounds were detected in samples taken from the soil that was removed.
Neither of the acid herbicides 245-T and 24D were present in any sample.
The New Plymouth District and Taranaki Regional Councils decided to carry out further investigations of whether this was one of the historical drum dump sites that had raised public concern in 1999/2000.
A second round of investigations on Friday 29 May involved extensive probing of the wastes and soil in the immediate vicinity of where the drum remnants were recovered. During this process, the remains of a further seven chemical containers were recovered and removed to Colson Road landfill, along with approximately 100 cubic metres of rubbish and soil.
Further leachate and stormwater samples were taken from the Park on Wednesday 27 May, to determine whether there was any discharge from the site. Samples were taken from two separate stormwater discharges to the Mangatuku Stream and from the “excavation pond”, the collected stormwater ponded in the trench from which the drums were recovered.
On Tuesday 9 June the Regional Council received verbal confirmation of the results from the analytical laboratory which were confirmed on 11 June.
The results were referred to contaminated sites consultant Dr Graeme Proffitt and he sees them as positive, in that they indicate no environmental risk.
“For the discharges to the stream, dioxin was not detected. An extremely low laboratory detection limit was used – a limit that’s equivalent to less than one teaspoon in two million Olympic-sized swimming pools.
“These results are not environmentally significant. They are typical of natural water quality in New Zealand, based on the Ministry for the Environment’s work in 1998,” said Dr Proffitt.
The two agrichemicals identified in the drum residue, tetrachlorobenzene and trichlorophenol, were not found at all in any of the stormwater/leachate samples.
The highest concentration of TCDD dioxin detected, of 2.3 picogramme per litre, was found in the stormwater ponded in the trench, not in the discharges. This maximum concentration was barely above the limit of detection of 1 picogramme per litre. (This translates as 1 part per thousand million million). The two discharge samples had respectively, less than 1.9 picogramme per litre and none detectable.
For comparative purposes, the US EPA drinking water standard is 2.2 picogramme per litre. (reference: pg 23, Organochlorines in New Zealand: ambient concentrations of selected organochlorines in rivers, MfE 1998). It should be noted that the New Plymouth samples were of discharges to the stream. The in-stream concentration would be hundreds of times lower due to dilution.
These results are very reassuring for local residents and the Councils.
See the table below for results of analyses.
The site was reinstated by the District Council, including capping with a layer of clean clay to at least one metre deep.
The Regional Council will continue to monitor the site, as it has done for the last 15 years, and will continue to respond to any situations or concerns from the public, as and when the need arises, as it does as a matter of long-standing practice for any environmental incident.
The Regional Council views the discovery of the drums very seriously and the situation was investigated thoroughly. Council believes that appropriate action has been taken to ensure that there is no risk to the environment or to residents in the area surrounding Marfell Park.
The Taranaki Regional Council has asked Dr Proffitt to lead the development of a sampling and testing programme to reassure the residents around Marfell Park and to ensure that the park remains a safe environment. Dr Proffitt is working with dioxin researcher Andrew Gibbs and representatives of the Marfell community to design the programme. (Updated 24 June 2009)
| Investigation of alleged agrichemical waste disposal sites in New Plymouth (2001) | |
| Executive summary | 91kb |
| Information on Marfell Park | 23kb |
| Full Report | 371kb |
| Appendix I: Record of Interviews | 111kb |
| Appendix II: Map | 539kb |
| Appendix III: Sampling Protocols | 3.5mb |
| Appendix IV: GPR Report | 4.1mb |
| Appendix V: Record of Sampling Action | 205kb |
| Appendix VI: Record of Marine Sampling | 2.1mb |
| Appendix VII: Record of Detailed Site Inspections | 393kb |
| Appendix VIII: Record of Site Excavations | 82kb |
| Appendix IX (part 1): Analytical Results | 3.6mb |
| Appendix IX (part 2): Analytical Results | 3.8mb |
| Appendix IX (part 3): Analytical Results | 1.7mb |