8.0 Audit Summary and Conclusions

8.1 Introduction

8.2 Soil Remediation

8.2.1 General

The basic conceptual model used in the derivation of the soil acceptance criteria (SAC) and the approach to the derivation is generally appropriate. Consequently, if the relevant SACs are complied with for a particular part of the site, then that part of the site is typically fit for its intended purpose. However, compliance with the SACs will not always necessarily be protective of site receptors. Potential exceptions are:

• direct ingestion of groundwater, as the derivation of the SACs for DDX and ADL do not appear to have taken this pathway into account (and effects on groundwater are greater than expected);

• effects of groundwater discharge on the marine ecosystem, again because of greater than expected effects on groundwater, and uncertainties with respect to the hydrogeology; and

• no criteria were derived for nitrogenous compounds or phosphorus, which were used in significant quantities as additives in the soil treatment process.

Based on the history of chemical usage on the site and the results of the various investigations undertaken to characterise the site, we consider that the analytical suites implemented were generally suitable for the purpose of validating the soil and sediment remediation. A lower frequency of testing for metals in residential backfill during the remediation resulted in some uncertainty in the compliance of this material. However, subsequent in-situ sampling of residential backfill for key metals has provided a reasonable confidence that heavy metals are not likely to be of concern.

The reporting on data quality in the Validation Report is limited. In addition, some of the procedures implemented during the project have not always been ideal. The aspect of the remediation that is most sensitive to this is the compliance of residential soil with the DDX and ADL criteria. While there is sufficient confidence in the data quality to confirm that the conclusions arrived at in the Validation Report are likely to be valid, there are specific instances where confidence in the data quality is reduced. Where this is the case, other information has been relied on to provide additional confidence. Specific comments are:

• Overall, confidence was gained that the soil and marine sediment sampling was undertaken in a professional manner, using methods consistent with accepted industry practice. A review of site documents gives confidence that the intended procedures were generally implemented in a detailed and methodical manner. A factor providing additional confidence were the people involved. The two principals of the company that supervised the remediation and carried out the sampling (EMS) were very experienced environmental professionals.

• In general, the analytical methods used during the remediation are suitable for characterising the site. The key exception to this relates to the detection limits for DDX and ADL analyses, which are relatively close to the residential SACs in some cases. While the use of detection limits close to the target criteria is not good practice, in this case other factors provided reasonable confidence that the analytical precision was, on the whole, adequate.

• The analytical QA/QC is not well documented. A retrospective sampling exercise on FCC East provided some additional QA/QC data for the materials on that part of the site. Split duplicate samples were analysed at separate laboratories to check on the consistency of the primary laboratory used during the remediation works. Greater confidence would be gained by repeating the QA/QC sampling on residential soil in FCC West, with the primary laboratory using the same method (and detection limits) used for the routine testing during the remediation.

8.2.2 FCC West Remediation

The validation sampling results show that FCC West is fit for its intended purpose with respect to soil quality, subject to the minor uncertainties outlined below. On average the soil quality complies with the SACs and in particular meets the ADL and DDX SACs. Probable isolated local exceedances are not so great as to be unacceptable..

The issue resulting in some uncertainty relates to detection limits for DDX and inter-laboratory comparisons at concentrations close to the DDX residential SAC. A programme of sampling (or reanalysis of archived samples) to evaluate this is recommended.

8.2.3 FCC East Remediation

With the exception the two uncertainties outlined below, the FCC East site is also fit for its intended purpose with respect to soil quality. This is in the context of a Site Management Plan being implemented to control excavation into commercial quality material, so that this material is not brought to the surface where it may migrate to the marine environment, or disposed of inappropriately off site (e.g. to a site with a more sensitive site use such as residential). The Validation Report concludes that FCC East meets the SAC for an open space and commercial use. Overall, we concur with this conclusion.

Issues that result in some uncertainty are:

• The potential for ammonia gas to be generated from treated fines material and possible effects on human health. A programme of soil gas testing is recommended, whether in the near future or at the time of building design and construction. Even if ammonia exists in the soil, the issue can be managed. The site management plan should be amended to manage the risk.

• The possibility of phytotoxic effects on deep-rooted plant species used in amenity planting. This is readily managed by soil replacement. The Site Management Plan should address this risk.

8.2.4 FCC Landfill Remediation

With the exception of the minor uncertainties discussed below, the FCC Landfill site is fit for its intended purpose with respect to the soil remediation. This is also in the context of a Site Management Plan being implemented to control excavation into commercial quality material, so that this material is not brought to the surface where it may migrate to the marine environment, or disposed of inappropriately off site. The Validation Report concludes that FCC Landfill meets the SAC for an open space use. Overall, we concur with this conclusion.

The uncertainties with respect to fitness for purpose relate to the possibility of ammonia generation and phytotoxicity of copper in treated fines. However, these are not significant human health issues for day to day use as open space. Carrying out further investigation to assess the risk from ammonia is not required on FCC Landfill. The potential risks from ammonia and copper during excavation or to plant health are readily managed by way of the Site Management Plan.

8.2.5 Residential Property Remediation

Based on the results of the soil remediation, the four residential properties are suitable for their intended purpose. The Validation Report concludes that the soil quality in the four sites meets the SACs. We concur with this conclusion.

8.3 Marine Sediment Remediation

8.3.1 Eastern Foreshore

The remediation of the eastern foreshore was not successful in achieving the target SAC of 0.01 mg/kg for DDX and ADL. Post-remediation sampling has confirmed concentrations of DDX 100 times above the SAC remain at some locations in the vicinity of the remedial excavation. Elevated DDX concentrations are also present in adjacent un-remediated areas, including shallow sediment up to 100 m to the north of the site (including beneath the adjacent wharf), with concentrations of between 1 and 60 mg/kg detected.

The ADL concentrations on the eastern foreshore are much lower than the DDX concentrations, but still elevated. The post remediation sampling showed that most ADL concentrations were less than 100 times the SAC but concentrations 10 times the SAC were common.

Re-contamination of the remedial excavation occurred during the remediation works. The mechanism of this is unclear, but a significant proportion may have been due to site runoff. Reworking of the foreshore backfill by an excavator may also have brought underlying contaminated material to the surface. Recontamination by contaminated groundwater is not a credible mechanism. Since the remediation was completed, surface sediment quality appears to be improving, probably through deposition of cleaner sediment. This improvement will be limited by the quality of the surrounding sediment in the short to medium term, but will slowly improve by natural attenuation over the long term. The greatest benefit to the eastern foreshore is the removal of the land-based contaminant source. The removal of this source will now allow natural attenuation to play its part.

In a broad context, remediation to the extent practicable has been achieved for the marine sediments in the east. The additional benefits of further remediation are likely to be outweighed by the “costs” such as additional disruption to the current habitat, potential impacts on the wider environment and expense, for an outcome at the surface that will not be very different from the current outcome. Re-deposition of sediment with elevated contaminant concentrations from surrounding areas will reoccur until slower natural attenuation processes take over.

Apart from localised effects on the marine ecosystem, the effects of the residual sediment contamination on other potential receptors are not likely to be significant. This includes risks to human health via consumption of seafood, as indicated by monitoring of OCP concentrations in sea snails, although further monitoring is required to confirm this. Recreational users of the foreshore are not at risk from direct contact with soil or water.

8.3.2 Western Foreshore and Creek

The remediation of the western foreshore and creek was also not successful in achieving the target SAC of 0.01 mg/kg for DDX and ADL. Initial post-remediation sampling found DDX concentrations more than 100 times the SAC were present in the base of the remedial excavation. However, the majority of these were located in the creek discharging to the foreshore. On the foreshore itself, the initial post-remediation samples were typically well below 1 mg/kg and often below 0.1 mg/kg. Subsequent sampling in 2007 found higher DDX concentrations, almost certainly a result of site runoff during the remediation works. DDX concentrations measured in 2007 in the wider bay are typically well below 1 mg/kg, with an average in the order of 0.15 mg/kg. The residual ADL concentrations on the western foreshore are much lower than the DDX concentrations, but still elevated. As with the east, the most recent sediment monitoring on the western foreshore indicates the top 1-2 cm of sediment is improving in quality.

Remediation to the extent practicable of the marine sediments has broadly been achieved in the west, for the same basic reasons outlined for the east above; specifically that it is not possible to remediate the surface sediments to a higher standard than the surrounding surface sediments (assuming the wider bay is still as measured in 2007 and was not just reflecting temporary effects of runoff from the remediation site). It is not practical to remediate this entire area due to the cost, difficulties in handling and disposing of the large quantities of sediment, and the likely detrimental effects on the estuary ecosystem.

Some moderately elevated concentrations of DDX remaining in sediment adjacent to the creek could be remediated relatively easily. However, removal of these hotspots is not warranted as they present no particular risk as creek-bed gravel and vegetative cover prevents sediment mobilisation and hence a pathway to potential receptors. The Site Management Plan should ensure that measures are in place to control excavation in the area and to prevent the creek from being eroded.

As with the east, the removal of the site as a source of sediment contamination is a key aspect of the remediation. It is expected that the contaminant concentrations in the shallow sediment will reach approximate equilibrium with the concentrations in the wider bay and the elimination of the land-based source will allow natural attenuation processes to slowly reduce concentrations further.

In the case of risks to human health via seafood consumption, additional data is required to confirm the apparent low risk as the dataset is limited. Recreational users of the foreshore are not at risk from direct contact with soil or water.

8.4 Groundwater

Prior to the remediation, site investigations identified the primary contaminants of concern to be organochlorine pesticides associated with the site’s original use i.e. DDX and ADL. These remain as contaminants of concern for groundwater. During the remediation several other contaminants became of concern as a result of the remediation, specifically:

• the nutrients ammonium, nitrate and phosphorus associated with the use of diammonium phosphate (DAP) and urea as reagents in the MCD soil remediation process; and

• copper associated with copper sulphate, and iron in an unknown form, also used as reagents in the MCD soil remediation process.

The groundwater under the site has residual contamination which will remain for an extended period unless some form of groundwater remediation is carried out. However, it is by no means clear that the groundwater contamination is creating an unacceptable risk, or risks that cannot be managed. The main potentially significant contaminants are DDX, dieldrin and nutrients. Copper does not appear to be presenting unacceptable risks.

It is not possible to fully quantify the risks presented by DDX, dieldrin and nutrients as the hydrogeological model for the site has significant uncertainties relating to:

• the detail of groundwater flow directions, particularly in relation to whether off-site flows occur to the south towards private irrigation bores in Tahi Street;

• the detail of groundwater quality over much of the site, with routine sampling currently being carried out in a relatively few perimeter monitoring wells; and

• a consequent uncertainty in the volume flux of water discharging to the Mapua Chanel and Waimea Inlet and the mass flux of contaminants discharging to these water bodies.

Additional data is required to address these uncertainties.

There is apparently discharge of DDX and dieldrin to the marine environment in excess of the PETCs and discharge of nutrients causing algal growth on the foreshores. However, given the uncertainties, contemplating groundwater remediation is premature. Remediation should only be considered when unacceptable effects are confirmed and cannot be managed in some other way. Remediation of groundwater would be expensive, potentially uncertain and have to continue for many years.

The potential risks from the residual groundwater contamination are to:

• existing and potential groundwater users;

• the local effects to the foreshore ecosystem; and

• the wider effects on the aquatic ecosystem.

8.4.1 Groundwater use

Abstraction of water in small quantities is currently a permitted use. Potential risks arise for two groups of people: current bore owners south of the site; and potential future bore owners within FCC West or south of the site. It is assumed that industrial use of groundwater on FCC East will be prohibited through the use of a management plan.

The lack of groundwater quality information on most of FCC West means that the risk cannot be properly assessed. While the presence of a reticulated water supply means that there is little incentive to construct a bore for a private supply, this will not guarantee that a private bore will not be constructed. Given this, and in the absence of good information, it must be assumed that the water is unsuitable for human consumption until such time as it is demonstrated otherwise. Some form of management of groundwater use on FCC West is recommended until that time.

In reality, the groundwater is probably suitable for irrigation use and, given the reduction in soil contamination, may be suitable for potable use. The quality is expected to improve with time as effects from past soil contamination reduce.

Management plans are not an effective tool in a residential setting. Greater certainty would require either a plan change or TDC placing restrictions on property titles before it sells the properties. However, it is recommended that the actual groundwater quality be determined and the risks assessed, before stronger controls are contemplated. Informal controls such as resident education and the disincentive provided by the reticulated supply are sufficient until the water quality is better known.

If the water quality proves to be adequate then no further controls are required. Otherwise, TDC must determine the best statutory instrument to exercise stronger control.

Existing bores to the south of the site are used for irrigation, for which the water is of an adequate quality. Apart from monitoring, no further action is required.

8.4.2 Foreshore effects

Discharge of nutrients is causing some local foreshore effects in the form of algal growth. Concentrations of DDX and ADL in wells closest to the foreshore and in seeps suggest that there will be local toxic effects at seep discharge points and where seepage discharge runs on the surface at low tide.

With respect to nutrients, the effects are greater than the pre-remediation situation, as nutrient enrichment was a direct result of the additives used in the MCD process. For DDX and ADL compounds the situation is less clear, with some wells showing small increases and other wells showing small decreases compared with the pre-remediation situation.

The question is now whether local effects are acceptable. To meet water guideline values at the points of discharge would require orders of magnitude improvement for the DDX and ADL compounds. This will not be achieved in the short to medium term without groundwater treatment. Such treatment would be relatively expensive, of uncertain effectiveness and required for an extended period of time, potentially decades.

It is not clear that the effects are unacceptable. Anecdotal reports are that similar algae effects are present elsewhere in the estuary. In addition, residual OCP contamination of the foreshore sediments is possibly outweighing any local effects of contaminated groundwater discharges. It has been recommended elsewhere that the health of the local ecosystem be better assessed. If this assessment shows that effects on the ecosystem are acceptable, then it can be reasonably concluded that the groundwater discharges are acceptable in this regard.

8.4.3 Effects after dilution

Groundwater discharging to both the Mapua Channel and Waimea Inlet is subject to large dilution. Effects to the wider estuary are therefore unlikely to be significant at the concentrations currently being measured in the groundwater. Further groundwater monitoring and better definition of the mass flux discharging to estuary should be undertaken to confirm this. Consideration could also be given to more seawater sampling, both close to the site and further afield, to directly measure actual concentrations.