5.0 Soil Remediation

5.1 Soil Acceptance Criteria

• the manganese criterion for residential site use was increased from 500 mg/kg to 1,500 mg/kg to take into account high naturally occurring concentrations of this element in the region;

• for similar reasons, the nickel criterion was increased from 60 mg/kg to 600 mg/kg for residential site use and from 21 mg/kg to 70 mg/kg for marine sediments (TDC letter to MfE of 13 April 2007); and

• an additional category of ‘topsoil’ was added for the final 0.15 m of the capping layer. The only difference between the residential criteria and the topsoil criteria is the nickel criterion: 60 mg/kg for the topsoil category versus the revised 600 mg/kg for the residential category.

The final SAC associated with the resource consent were issued by TDC on 13 April 2007 and are set out in Table 1 below.

An additional set of criteria were also specified for DDX and ADL where soil was to be placed close to the foreshore areas, with the intention of creating a buffer zone. The criteria as set out in Condition 10(j) of the resource consent are set out in Table 2:

5.1.1 Basis of the Site Acceptance Criteria

It is not the purpose of this audit to question the site acceptance criteria. The SACs were considered as part of the consenting process and deemed appropriate at that time. However, it is appropriate to give the background to derivation of soil guidelines in general, and the SACs in particular, as this affects later consideration of the long-term fitness for purpose of the land.

As noted earlier, risk arises through a receptor (e.g. a person, a marine organism, or a plant) being exposed to a contaminant through some exposure mechanism or pathway (e.g. direct contact or ingestion of soil, or through leaching of contaminants from soil and transport of that leachate to the marine environment). Different receptors have different susceptibility to effects of exposure and different exposure pathways have differing efficiencies in conveying the contaminant to where it may cause an effect. In selecting existing published values or deriving site-specific values to become the SACS, the most conservative combination of receptor and exposure pathway was chosen for what were considered to be relevant receptors (Egis, 2001).

This process is based on the site conceptual model, which is a summary of contaminants, receptors and mechanism of exposure. For Mapua, a number of receptors/exposure combinations were considered for soil, including (Egis, 2001):

• people using the site directly exposed to soil through dermal contact, inhalation of dust or vapour, soil ingestion and indirectly through consumption of produce grown in contaminated soil, where relevant. Exposure was considered for residential, commercial and parklands uses;

• transport of soil in stormwater runoff to the adjacent marine environment, with consideration of direct effects on marine organisms (principally mud snails), sensitive higher trophic groups within the estuarine food chain (birds) and people eating shell fish;

• leaching of soil contaminants to groundwater and subsequent exposure of marine organisms following discharge of the groundwater to the marine environment after dilution.

The SACs for the key OCP contaminants were derived specifically for the site (Egis, 2001). It should be noted that the “critical” or most sensitive exposure pathway/receptor combination for these SACs varies for DDX and ADL and between end use categories.

For DDX, the controlling pathway for the residential site use (SAC of 5 mg/kg) was determined to be sediment runoff effects on the marine aquatic ecosystem. The guideline value derived for protection of human health in a residential setting was over 20 times higher, at 110 mg/kg. It should be noted that a lower generic New Zealand guideline for DDX for the residential scenario use for DDX was derived some years after the site-specific derivation for Mapua (MfE, 2006). The value, 28 mg/kg, is about a quarter of the residential value derived by Egis (2001), but the value protecting marine sediments is lower again and therefore protective of human health even if the lower residential value is applied. The more recent generic guideline has been used in this audit when fitness for purpose needs to be considered.

The controlling pathway for DDX for a commercial use (SAC of 200 mg/kg) was determined to be effects on groundwater (noting that the 0.5 m of capping surface soil in the commercial area still had to meet residential criteria to guard against sediment runoff effects). Again, the value derived for protection of human health was much higher at 650 mg/kg.

For ADL for the residential site use (SAC of 3 mg/kg), the human health and sediment runoff exposure pathways had similar derived values, with the value protective of human health being slightly lower and therefore the critical value. Similarly, for the commercial site use (SAC of 60 mg/kg), the human health and groundwater discharge to the marine environment exposure pathways produced very similar target criteria for ADL.

It should also be noted that the DDX and ADL criteria were derived by making a number of assumptions about dilution, infiltration and other factors. The Egis (2201) report noted the potential uncertainty in these assumptions by selecting a range where appropriate. Consequently, the SACs themselves were selected from within a range of potential estimates. They should not be viewed as precise numbers.

It should also be remembered that soil guideline values, and the SACs are no exception, are intended to be protective for chronic or long-term exposure. Short-term, or occasional, exposure at several-fold greater concentrations will not normally be of concern.

5.1.2 SACs and their Relationship to Fitness for Purpose

The basic conceptual model used in the derivation of the SACs and the approach to the derivation is appropriate. Consequently, in general, if the relevant SACs are complied with for a particular part of the site, then that part of the site is fit for its intended purpose. However, compliance with the SACs will not necessarily be protective of all potential site receptors. 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); and

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

The groundwater aspects are discussed separately in Section 7.

SACs were not derived for all the potential contaminants arising from use of reagents in the MCD treatment process. A problem was that there was no appreciation at the time of consenting that large quantities of copper (as copper sulphate) and diammonium phosphate would be used in the MCD process. An SAC for copper was fortuitously included as part of a general heavy metal suite, but there were no SACs for nitrogenous compounds or phosphorus.

5.2 Chemical Analysis Requirements

The chemical analysis requirements for validation testing of soil were not specified in the resource consent, other than indirectly through defining the various SACs. It is normal that the RAP would specify the detail of analytical requirements, including analytical suites, sampling frequency/density and sampling methods. The analytical requirements in the original RAP (Thiess, 2004), and that set out in the Validation Report (SKM, 2008) were:

• 100% of samples for OCPs, including DDT and its derivatives and aldrin, dieldrin and lindane;

• 50% of samples for total petroleum hydrocarbons (TPH), volatile chlorinated hydrocarbons (VCH) and selected heavy metals (arsenic, cadmium, chromium, copper, cyanide, lead, manganese, mercury, nickel, selenium and zinc); and

• 10% of all samples for a suite specified in a New South Wales guideline (NSWEPA, 1998).

However, in late 2004 a revised analytical suite was agreed between TDC, the Site Auditor and MfE. The change was based on the results of an additional investigation (T&T, 2004) which provided greater confidence that the CoCs were DDT and its derivatives, aldrin, dieldrin and lindane. The altered suite was referred to in the monthly site report for December 2004 (MfE, 2004b) and it appears that it was implemented from this point forward. The suite was also confirmed in a memo from the Site Auditor to MfE in January 2005 (GHD, 2005a) and is referred to in the second version of the RAP (MfE, 2005a).

The remediation site managers (EMS) recognised the initial lack of clarity in specification of analytical suites and created a series of summary tables outlining the suites that were actually applied (EMS, 2007). The set of four tables summarise the testing requirements for commercial soil, residential soil, marine sediments and treated soil. The final analytical suites were:

• 100% of samples for OCPs;

• 50% of samples additionally analysed for total petroleum hydrocarbons (TPH), organophosphorous (OPP) and organonitrogen (ONP) pesticides;

• 50% of samples from selected areas, based on observations of hydrocarbon contamination, analysed for volatile organic compounds (VOC);

• 10% of samples analysed for VOC, a heavy metal suite (arsenic, cadmium, chromium (III and VI), copper, lead, manganese, mercury, nickel, selenium and zinc), hot water soluble boron, total cyanide, free cyanide, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and chlorobenzene.

A slightly different analytical suite was implemented for the treated soil in mid-2005 i.e. only applying to soil that had passed through the MCD treatment process. The suite was altered to take into account reagent use in the remediation process (as potential contaminants) and the processing rate. The suite was formally set out in an attachment to an email from the Site Auditor to MfE dated 25 July 2005 (GHD, 2005d). However, the suite was applied to the treated soil from 1 April 2005, as set out in a revised version of the RAP (MfE, 2005). The analytical suite for treated soil was then:

• a sample from every day’s production and at least every 25 m3 for DDX, aldrin, dieldrin and lindane;

• a sample from every third production day (or two per week) also analysed for copper, leachable nitrogen (using the synthetic precipitation leaching procedure – SPLP). This was reduced to a sample every second week after October 2006 (EMS, 2007);

• for every 200 m3 (or every second week) a sample analysed for manganese, selenium and TPH; and

• for every 1,000 m3 (or every 10 weeks) a sample analysed for VOCs, OPP, ONP, PCBs, PAHs and a suite of heavy metals (arsenic, cadmium, total chromium, copper, lead, manganese, mercury, nickel, selenium and zinc). PCBs were removed from this suite from 4 July 2005 onwards.

For some of the contaminants, the analytical method used does not directly match the corresponding SAC, and a direct comparison of the results against the criteria could not be made. In addition, analysis was not completed for a number of contaminants with SAC values. The following discrepancies were identified in the Validation Report (SKM, 2008):

• there are SACs for methyl mercury and inorganic mercury. However, the validation samples were tested for total mercury. This is not significant as almost all total mercury results were below both the individual methyl mercury and inorganic mercury SAC for the various end use categories. Thus, even if the ‘total’ result was made up entirely of either methyl mercury or inorganic mercury, it still would have complied with the relevant SAC. The only exception to this was a single result from the marine sediment excavation in the west. This is discussed separately in Section 5.4.6 below;

• there are SACs for free and complexed cyanide, the lower value being for complexed cyanide⁴. However, total cyanide was analysed rather than complexed cyanide. Comparison of the total value against the complexed guideline for residential use is conservative. In any case, the maximum total cyanide concentration detected in all samples of 6.4 mg/kg was well below the complexed cyanide SAC of 20 mg/kg;

• no validation samples were analysed for sulphur or phenol, both of which are included in the SAC list. This is not a significant information gap as the previous investigations indicate that neither of these contaminants are likely to be of concern on the site; and

• many of the marine sediment SAC are based on the ANZECC ‘ISQC-Low’ marine sediment values (ANZECC/ARMCANZ 2000). This document requires the analytical results to be normalised to 1% total organic carbon (TOC). However, this could not be completed as TOC was not included in the analytical suite. This is conservative as the likely high organic content of the marine sediment would result in higher target criteria.

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 remediation. The use of an analytical regime with a variable sampling frequency depending on how likely it is that a particular analyte will be encountered at elevated concentrations is appropriate.

There is no doubt that the OCPs were the primary contaminants of concern and warranted frequent analysis. However, the decision to reduce the frequency of heavy metal analysis warrants some scrutiny.

The site history prepared by Woodward-Clyde (1996) mentioned production of organo-mercury compounds and storage of lead arsenate. It is not known (or at least not recorded in the documents reviewed) where these activities occurred. The main concern for heavy metals is in near surface soils in a residential setting (i.e. FCC West). The less intense exposure in an open space setting and the ability to manage exposure in a commercial setting means heavy metals are less of a concern for those uses. While every site is different, heavy metals typically bind to soil and are frequently not of great concern for groundwater contamination and subsequent discharge to the marine environment.

Residential quality soil was sourced from both FCC East, where much of the former manufacturing and storage historically occurred, and from FCC West, where less intense manufacturing and storage occurred but still had potential for spillages to occur. As a manufacturing and bulk storage site for concentrated chemicals, spillage could result in very high localised contamination. The issue then is whether sufficient investigation was initially carried out to have a good chance of detecting heavy metal contamination and whether the subsequent follow-up validation was at a sufficient frequency to confirm the decisions made from the initial sampling. The following sampling was carried out:

• 65 samples were analysed in the Woodward-Clyde 1992/3 investigations (Woodward-Clyde; 1992, 1993), including six from the Mintech part of the site. The samples were collected as five sub-samples from each location, which were then composited and analysed. The samples represented a depth range of 0 to 500 mm.

The results generally showed an absence of high metal concentrations. However, the sampling was fairly limited at some of the locations where spills might be expected to occur, i.e. manufacturing and storage locations.

• 21 samples were analysed in the T&T baseline study (T&T). Again the results showed only low to moderate contamination from heavy metals.

The relatively sparse level of sampling means that hotspots could have been missed. If the hotspot had high enough concentrations it would not be guaranteed to receive sufficient mixing during material handling to ensure that it would be below residential guidelines⁵ after backfilling. However, mitigating factors are as follows:

• during the remediation, the majority of the surface around former process areas, which are the most likely areas for heavy metal contamination, was removed to or remained on FCC East, either as commercial quality soil or following treatment for OCP contamination. In many cases, this surface stripping was to a depth of 1 m;

• a relatively small proportion of the residential quality soil mined and then used as backfill was used as capping soil on FCC West. Most was either used as capping material on FCC East or buried more deeply in FCC West, reducing the likelihood of any excessive contamination being near the surface;

• the residential soil is capped with clean topsoil, reducing the exposure to deeper soil;

• the validation sampling (see Section 1.1.4), found at most only slightly elevated metal concentrations, although the sampling frequency was only 3% of the primary samples; and

• additional test data for 25 post-remediation samples of residential backfill on FCC West showed low concentrations of arsenic, lead and mercury (see Section 1.1.4.1). These samples increase the frequency for these contaminants (the most likely metals to be of concern) to 9% of the primary samples for the residential backfill.

In summary, the decision to reduce the frequency of heavy metal analyse to only 10% of all samples increased the risk of missing a hotspot. However, the subsequent execution suggests that the risk of excessive concentrations of heavy metals in near surface soil is low, although the absence of such a hotspot cannot be absolutely guaranteed. No further work is required.

The information reviewed otherwise confirms that the actual analyses are broadly in line with the intentions. Other exceptions are discussed further against individual material types in subsequent sections.

5.3 Confidence in Data Quality/Laboratory Analyses

5.3.1 Introduction

The reporting on data quality provided 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 conclude that the conclusions arrived at in the Validation Report are probably valid, there are specific instances where confidence in the data quality is reduced. Other information has been relied on to provide additional confidence. Instances where the methods employed have the potential to influence the quality of the specific datasets are discussed in Section . General aspects of the data quality are discussed below.

5.3.2 Sampling Techniques

Overall, we have confidence that the soil and marine sediment sampling was undertaken in a professional manner, using methods consistent with accepted industry practice. The RAP (regardless of version) and the EMS quality assurance document (EMS, 2007) specified appropriate sampling techniques. The RAP (regardless of version) required that the sampling be carried out in accordance with AS 4482.1-1997 Guide to the Sampling and Investigation of Potentially Contaminated Soil (SA, 1997). The EMS quality assurance document (EMS, 2007), confirms the methodical and consistent approach employed for the validation sampling. A review of a sample of site documents suggests the methods set out in the EMS document were in fact followed.

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. One had over 25 years experience with remediation projects, including eight years managing a field operations team at the United States Environmental Protection Agency (USEPA). This role included training staff in sampling techniques, field analysis, environmental monitoring and remediation technology. The other EMS principal had a similar length experience in environmental clean-up projects. Site Auditor notes and anecdotal reports suggest that the field practice typically exceeded the written requirements.

In terms of the number of samples taken, there seems to have been a philosophy on the part on the part of the EMS team of taking extra samples (at least for OCPs) to build confidence in the validation, rather than trying to keep sampling to a minimum. An example of this is the decision by EMS to validate the extent of the FCC East at a higher density than the original RAP intention. Thus, the general scope of sampling is adequate for the validation purposes. Any exceptions to this have been discussed in Section .

5.3.3 Laboratory Analyses

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. This is not discussed in the Validation Report. It appears that different detection limits were applied to different parts of the site for the DDX and ADL analyses as follows:

• for testing on FCC East a laboratory detection limit of 1 mg/kg for each individual OCP was typically employed;

• for FCC Landfill a mixture of 0.5 mg/kg and 1 mg/kg detection limits were employed; and

• for FCC West a detection limit of 0.5 mg/kg was employed.

The result of this is the effective detection limit for ADL is 2.1 mg/kg for the samples with a 1 mg/kg base detection limit (i.e. the sum of the detection limits for aldrin and dieldrin and 10% of the lindane detection limit). Similarly, an effective detection limit of 6 mg/kg results for the DDX summation (i.e. a sum of the 1 mg/kg detection limits for the six individual isomers). For the commercial SACs for ADL and DDX of 60 mg/kg and 200 mg/kg, this is acceptable as the detection limits are well below the target criteria. However, these effective detection limits are close to or slightly above the corresponding residential SACs for ADL and DDX of 3 mg/kg and 5 mg/kg respectively. Consequently, in some circumstances, there could be a significant uncertainty as to whether samples with ADL and DDX concentrations below the detection limit actually comply with the residential SAC.

This uncertainty applies when material remaining on FCC West has been classified using the coarser detection limit of 1 mg/kg for the DDX and ADL analyses. This appears to have occurred only for residential material that was sourced from FCC East and the FCC Landfill. Consequently, the only dataset affected by the high laboratory detection limits is that for the validation results for the residential backfill material. While the use of laboratory detection limits of a similar magnitude to the SAC is not good practice, there are the following mitigating factors in this case:

• Of the approximately 400 samples representing residential soil mined from FCC East and FCC Landfill, only about 15% were analysed at the 1 mg/kg detection limit. The remainder were analysed at a detection limit of 0.5 mg/kg or lower. A detection limit of 0.5 mg/kg is acceptable, although not ideal;

• for the samples analysed with the lower detection limit of 0.5 mg/kg, approximately only 5% of the samples had aldrin, dieldrin or lindane concentrations above the lower detection limit of 0.5 mg/kg. This gives greater confidence that samples that were analysed with the 1 mg/kg detection limit are also likely to be below the 0.5 mg/kg limit, resulting in ADL concentrations below the SAC of 3 mg/kg. This also gives reasonable confidence that the average concentration of this dataset will be below the SAC;

• there appears to be a reasonably consistent ratio between the six different isomers making up the DDX sum, for concentrations close to the residential SAC. The 4,4 DDT isomer consistently makes up the greatest proportion of the DDX total. The isomers 2,4 DDT, 4,4 DDE and 4,4 DDD are typically each a third or less of the 4,4 DDT concentration. The concentrations of the 2,4 DDE and 2,4 DDD isomers are consistently less than a tenth of the 4,4 DDT concentration. Consequently, if the concentration of the 4,4 DDT isomer is less than 1 mg/kg, there will be reasonable confidence that the DDX sum will also be below the residential SAC of 5 mg/kg;

• the residential SAC of 5 mg/kg for DDX is based on sediment runoff effects. However, this exposure pathway is less relevant for the residential soil with the expectation that the future site will be paved, covered in buildings or well vegetated, with the additional barrier of 0.15 m of imported topsoil. As discussed in Section , a potentially relevant human health value of 28 mg/kg (MfE, 2006) is much higher and the higher than desirable detection limit is of less concern.

Overall, while the use of detection limits close to the target criteria is not good practice, it is acceptable in this case.

5.3.4 Quality Assurance and Quality Control

The general level of quality assurance and quality control procedures implemented during the remediation is considered to be good, if not always well documented. The main exception to this relates to the analytical QA/QC. The level of documentation of the QA/QC procedures provided in the Validation Report is limited:

• no details are provided in the Validation Report on the compilation of the datasets and what checks were made to ensure they are both complete and do not have results that do not belong in the particular dataset. The latter is particularly important for sample results for excavated material, as at the time of sampling it was not known which dataset of various potential material types the results would belong to;

• no statement is made in the Validation Report that the data has been transcribed correctly into the tables and the spreadsheets or formulas used have been independently checked; and

• no comment is provided on the process to identify invalid data, or details of any data that have been rejected.

Additional documentation would have increased confidence in the conclusions.

5.3.4.1 General Site QA/QC

The Mapua remediation project was complex and involved generating and handling a large amount of data. Similarly, the project required accurate tracking of the various categories of material generated during the works. The general QA/QC procedures employed during the remediation are outlined in the EMS QA/QC document (EMS, 2007). A review of site documents indicates that the intended procedures appear to have been implemented as intended. The detailed and methodical approach gives confidence in quality of the remediation works.

5.3.4.2 Analytical QA/QC

The resource consent did not require soil samples to be analysed by an accredited laboratory but required all water samples to be analysed by an IANZ (International Accreditation New Zealand) accredited laboratory. All versions of the RAP required IANZ accreditation for all samples.

EMS (2007) reports that MfE initially planned to use the EDL site laboratory in Mapua to analyse the soil samples (and may have been used for early samples). However, following a comparison of split samples carried out by EMS in November/December 2004, Hill Laboratories, an IANZ accredited laboratory based in Hamilton, was engaged by MfE to analyse the soil samples (EMS, 2007).

The resource consents and the RAPS were silent on the analytical methods to be used. We have examined a sample of laboratory reports and are of the view that the analytical techniques employed by the laboratory were appropriate (subject to the comments on detection limits in Section ).

No summary of the internal laboratory QA/QC procedures is provided in the Validation Report. The Ministry for the Environment’s Guideline No 1 recommends reporting of these in a validation report, with an analysis of the data. However, the laboratory reports provide no information on internal laboratory QA/QC, such as results for laboratory duplicates, spikes and blanks, with associated percent recoveries, to allow such reporting. This is not unusual for New Zealand laboratories, which will often only provide internal QA/QC on specific request (at an additional cost). It is understood the laboratory followed the usual internal QA/QC for an IANZ accredited laboratory.

There is reference to QA/QC requirements for the laboratory analyses in Site Auditor correspondence during the remediation works. An early recommendation was made to analyse 10% of samples as split duplicates at a separate laboratory to check on data precision for the main laboratory. In the Thiess RAP (Thiess, 2004) QA/QC samples were to be taken in accordance with the AS 4482.1-1997. AS 4482.1-1997 recommends testing of split samples at a second laboratory at a rate of 5% of the primary samples. However, early versions of the MfE RAP (in Work Plan 13) refer to samples being taken at some unspecified rate less than 5%. This was not carried out.

To retrospectively address the lack of analytical QA/QC data, a set of soil samples was collected from the reinstated FCC East in April 2007 for testing for OCPs, TPH, various forms of nitrogen and a suite of ten heavy metals. This is presumably reflected in the April 2007 update of Work Plan 13 of the MfE RAP, which states:

QA/QC requirements under the standard AS4482.1, including duplicate laboratory comparisons, will be met through a dedicated sampling program designed and approved by the Site Auditor.

This type of single-event QA/QC sampling was not undertaken regularly during the project and no similar sampling has been undertaken for the residential soil on FCC West.

The sample splits for the inter-laboratory comparison were prepared in the field by EMS. This is not the recommended practice, with sample splits normally being prepared by the primary laboratory. EMS homogenised the samples in the field by mixing with a trowel on a board and then using the trowel to split the sample. Samples for TPH analysis were not mixed before splitting.

The samples were sent to the laboratory of MGT Environmental Consulting in Victoria, Australia, a NATA (National Association of Testing Authorities) accredited laboratory. NATA is the Australian equivalent of IANZ and there is mutual recognition between the two accreditation schemes.

The details of this sampling programme are set out in the Validation Report (SKM, 2008). The main aims of the additional sampling were to:

• the confirm that the contaminant concentrations in the different categories of material used as backfill in FCC East were in line with the expected concentrations i.e. based on the original validation data; and

• to check the reliability of Hill Laboratories by analysing a number of split duplicate samples at a separate laboratory.

The Validation Report provided an analysis of the QA/QC sampling but did not arrive at a conclusion as to whether the results were satisfactory. Unfortunately, the Validation Report comparison of the results from the two laboratories for ADL was incorrect as an error was made by SKM in calculating aldrin+dieldrin+10% lindane for the primary samples (SKM, 2008). This error resulted in an apparent systematic under-reporting of ADL concentrations by Hill Laboratories i.e. non-conservative.

It is debatable whether in fact such a calculation should have been made for ADL and DDX, rather than comparing each compound separately, as the laboratories reported the individual compounds. Regardless, we have examined the DDX and ADL results from the two laboratories and are satisfied that for these particular samples the correspondence was satisfactory for soil samples.

An equivalent sampling programme has not been undertaken for the residential quality soil. This is not such a concern for the ADL compounds as many of the results in the FCC QA/QC samples were of a similar magnitude to the residential SAC for ADL. Consequently, the conclusions drawn are likely to also apply for residential quality soil. This is not the case for DDX where the concentrations in the split duplicate samples were much higher than the residential SAC of 5 mg/kg, thus there is limited data at lower concentrations.

There are five inter-laboratory data points in the range of 25 to 35 mg/kg, which is close to a relevant human health guideline of 28 mg/kg for DDX (MfE, 2006). These show a reasonable correlation between the laboratories for this concentration range, although the secondary laboratory returned a concentration twice the primary laboratory for one sample. This could be a result of less than ideal preparation of the split samples. The other four samples showed much closer correlation. Overall, the dataset at these concentrations is too limited to draw firm conclusions.

The laboratory results from the primary laboratory did not have any results below the detection limit. However, there are results for individual ADL components of less than 0.2 mg/kg (and non-detects of other than DDX or ADL compounds at <0.01 mg/kg). This suggests that the screening method used throughout the project (with a detection limit of either 0.5 or 1 mg/kg) was not used by the primary lab for the inter-laboratory comparison. The inter-laboratory comparison was therefore not a good test of the precision of the DDX analysis actually employed to assess compliance with the residential SAC.

Greater confidence would be gained by repeating the QA/QC sampling on residential soil, with the primary laboratory using the same method (and detection limits) used for the routine testing.

5.3.5 Data Handling and Statistical Analysis

The information provided by SKM in the Validation Report on methods used for data handling and statistical analysis is limited. The following general comments are made:

• how non-detect results have been dealt with in calculations has not been discussed. From the spreadsheets it is apparent that a value of half the detection limit has been substituted for non-detect results. This is common practice where the proportion of non-detects is not too large. However, for a number of the datasets presented in the Validation Report, the percentage of non-detects is high, sometimes over 90%. In this case, a 95% UCL using values of half the detection limit is statistically meaningless. However, this is unlikely to change the conclusion i.e. the ‘average’ for the dataset is still likely to be below the SAC (assuming the detection limit is low enough relative to the criterion);

• there is no discussion on the various laboratory detection limits applied and how these relate to the SACs (see Section above); and

• use of 95% UCL estimates for the mean is an accepted way of evaluating environmental data. However, SKM routinely assumed the datasets were log-normally distributed yet many, if not most, of the datasets are not log-normally distributed. The assumption of log-normal distribution is a common but often incorrect assumption for left-skewed environmental datasets. No attempt was made to check whether the data followed particular distributions, by plotting histograms Q-Q plots or carrying out statistical goodness of fit tests. In addition, no identification of outliers is reported. Reanalysing some of the datasets⁶ showed that nonparametric estimates for the 95% UCL was more appropriate than assuming a log-normal distribution, with the estimate being higher than if log-normality was assumed. However, the critical DDX and ADL datasets were often large and the differences in estimates are not so great as to arrive at a different conclusion. For example, goodness of fits test shows the 1798 member dataset for commercial soil does not follow normal, log-normal or gamma distributions and returned nonparametric 95% UCL estimates for ADL and DDX of 6 and 57 mg/kg, respectively. SKM calculated values of 5.4 and 79.3 mg/kg assuming log-normal distributions.

In considering the various datasets, the statistical analyses in the Validation Report are only referred to in some cases. Where data summaries from the Validation Report have been used, comment on the applicability of these is provided as required.

5.4 Management and Validation Sampling Procedures

There were two main types of sampling undertaken on the site:

• site management sampling; and

• validation sampling.

Site management soil samples were collected to enable decisions on how a particular batch of soil was to be handled e.g. if it required treatment or could be reused on site as commercial or residential soil.

The purpose of the validation samples was to demonstrate that the site/material complied with the SACs. In many cases samples originally taken as site management samples became validation samples. This was the case for all soil that was defined as either commercial or residential soil on the basis of the management samples. Soil placed in stockpiles was not generally tested again before being used as backfill unless there was concern about a particular batch of soil placed in a stockpile. Soil taken from stockpile and placed as backfill was also not generally tested in-situ after placement. Thus, the original site management samples taken during excavation of soil that was later placed as backfill without further treatment are, in effect, validation samples.

Because the stockpiles were large, it is not possible to track the soil that a particular sample represented to its final resting place. In the absence of post-placement testing, the stockpile being generally compliant must therefore be relied on. The best that is known is that soil of a particular type at a particular location should have concentrations somewhere in the range of concentrations of the samples representing the soil placed in the stockpile. This is an acceptable approach provided the frequency of sampling during excavation is adequate to properly represent the soil in the stockpiles. This was the case in general, as is described further below. Additional confidence arises because mixing of soil occurs during the process of original excavation, stockpiling, re-excavation from the stockpile and placing as backfill, resulting in an averaging of concentrations (and in theory a narrower range about the average, if good mixing has occurred). However, this incidental mixing will not be sufficient to average out extreme hotspots, but could result in up to two to three-fold reduction of high concentrations (and similarly raise the minimum concentrations towards the mean).

Where the sampling showed that the base or sides of the excavation complied with SACs, meaning that no further excavation was required at the location, then these samples also became validation samples for the base and sides of the excavation in the particular location.

Samples that showed the particular material could not be reused without treatment are not validation samples, but simply management samples. Such samples should not be part of the validation dataset.

For each different category of material, a different sampling strategy was employed to determine the frequency and type of sampling for that material. The results of that sampling generated a representative dataset for each material category. Those datasets were then compared by EMS with the SACs to determine compliance.

5.4.1 Sampling of Excavated Materials

In almost all cases soil was categorised by in-situ testing (site management sampling). As discussed earlier, the site was divided into 15 m by 15 m cells, which were further divided into vertical layers (Section ). Testing was carried out for each individual layer from each cell to enable categorisation. Testing of excavated stockpiles was generally only undertaken to confirm the in-situ testing or if there was some uncertainty about the classification of soil.

For FCC East and the Landfill, the original RAP intention was that at least one composite sample be taken from each 15 by 15 m cell layer. However, based on professional judgement, EMS typically took four composite samples per cell layer, i.e. the RAP requirement was exceeded. The cell was divided into four 7.5 x 7.5 m ‘quadrants’, with one composite sample collected per quadrant Each composite was made by further dividing the quadrant into four sub-quadrants and taking a sub-sample from the centre of the sub-quadrant (EMS, 2007). Where the cell also contained a wall, at least one composite sample was taken from each layer of each wall of the cell. Each wall composite sample consisted of four sub samples approximately equally distributed along the wall.

For the more sensitive residential end use of FCC West, a 7.5 m grid was applied from the start and a composite sample made up of four sub-samples collected from the base of each 7.5 by 7.5 m cell. For walls in FCC West the same general sampling philosophy as that adopted for FCC East and Landfill was applied to the decreased grid size.

Based on the in-situ results, a decision was then made on whether that cell layer required treatment or could be re-used on site as commercial or residential quality soil.

For various materials generated during the remediation and re-used on the site, the frequency of validation sampling was specified in the RAP on a volume basis. In almost every case, more samples were taken than the original intention. However, in some cases the sampling frequency that was actually applied is not clear.

The intended sampling frequencies for the various materials are understood to be:

• residential soil – to be sampled every 100 m3 for the main analytical suite and correspondingly greater volumes for the 50% and 10% suites. There was also a requirement in the original RAP (Thiess, 2004) that the soil be sampled every 25 m3 if sourced from a cell adjacent to a cell that exceeded residential criteria. The latter sampling frequency appears to have been implemented by default for residential soil sourced in FCC East and Landfill by the EMS decision to take four samples per cell layer (EMS, 2007);

• commercial soil – to be sampled every 100 m3 for the main analytical suite;

• crushed concrete – a ‘representative’ sample;

• oversize (>10 mm) – a representative sample of the fine material adhering to oversize material, analysed for OCPs.

5.4.2 Sampling of Treated Soil

The soil to be treated was screened prior to treatment to remove coarse fractions. An initial screening removed material above 10 mm, with a second screening to separate the 5 – 10 mm fraction after the soil had passed through a drier. The fraction less than 5 mm was then treated (EDL, 2007). The resultant treated fines (which were ground to dust during the treatment) were sampled on a daily basis and analysed for the suite of contaminants set out in Section 5.2 above. The daily production volumes were lower than anticipated so the sampling frequency was much greater than the minimum of 1 per 25 m3 specified in the analytical protocol. Average daily production was approximately 12 m3 (TDC, 2009a).

Nine samples were collected from the 5 – 10 mm component created during the treatment process, although no testing frequency was specified in the RAP documentation.

At the outset of the remediation, there was some difficulty in finding a suitable method to determine whether the treated soil complied with the SACs. Initially, the basis for acceptance was that the 95% upper confidence limit (UCL) of the mean for a particular analyte should be less than the relevant SAC, with no individual result being more than 2.5 times the SAC. However, there were not enough sample results initially to create a meaningful 95% UCL. Consequently, on the recommendation of the Site Auditor, the compliance assessment was altered to a rolling six day average, with no single result allowed to exceed 1.5 times the relevant SAC (GHD, 2005d). This was expected to result in a 95% UCL less than the SAC, whereas a rolling average with the 2.5 factor risked not achieving the necessary standard. The approach was a pragmatic solution and appears to have worked well. The compliance of the treated soil with the SACs is discussed further in Section 1.1.6.3.

5.4.3 Sampling of Imported Materials

During the course of the remediation, significant quantities of material were imported to site for use as backfill in different parts of the site. The following materials were imported (approximate volumes are taken from the volume balance diagram (MWH, 2008):

• 5,300 m3 of topsoil to complete the 0.15 m capping layer across the entire site;

• 5,800 m3 of residential quality soil to make up a shortfall of this material;

• 5,000 m3 of sand/gravel used as backfill for the marine sediment excavations;

• 1,000 m3 of clay for the bund and surge chamber backfill; and

• 430 m3 of sand/gravel that was imported as backfill for the marine excavations which was subsequently used as residential soil due to unacceptably high test results.

Overall, the test results that are available indicated that the various materials imported during the remediation are likely to comply with the relevant SAC. However, the level of information presented in the Validation Report (SKM, 2008) is limited, with sources and volumes from each source not generally given. Ideally the information for each source of imported material would include:

• a brief description of the source and type of material, and the historic potential for contamination at the source site;

• the total volume used;

• the type and number of validation samples taken for the material, with a summary of the results; and

• the final destination of the material.

A more detailed level of information on the imported soil would have enabled greater confidence to be placed on the conclusions that the material is suitable for its intended uses. The data presented in the Validation Report has been grouped into material categories and is not specific to each source. In this case the omission is not significant.

5.5 Test for Compliance with SACs

The resource consent does not state how compliance with the SACs is to be determined in a statistical sense. The different versions of the RAP and Work Plan 13 attempt to define compliance requirements. The original RAP (Thiess, 2004) stated that cell results comply if the cell mean is below the relevant SAC and no individual result exceeds the SAC by a factor of 2.5. It appears that the factor of 2.5 was also intended to apply to batches of commercial and residential material won on-site, although this is not clear. The subsequent MfE (2005) RAP reduced the exceedance factor to 1.5 and applied this to all material categories. It is unclear what was actually applied on site for cell results.

The basic approach of using an average and maximum when assessing compliance with target criteria is common in contaminated site work and is appropriate. The average concentration is used to determine general compliance with the target, and the maximum concentration is imposed to ensure that localised hotspots of contamination are not likely to cause adverse effects. It appears that the original factor of 2.5 was taken from an Australian guideline (NEPC, 1999b) which requires that no single value exceeds 250% of the health-based target criteria. As discussed in the previous section, the factor of 1.5 was initially introduced as a means of ensuring the 95% UCL for treated fines complied with the treated fines SACs.

In most cases, no definition of ‘average’ was given and it is assumed that the average was to be the arithmetic mean of whatever dataset was being assessed e.g. individual cell or the six day average for treated fines.

The Validation Report (SKM, 2008) used the original Thiess (2004) RAP factor of 2.5 when assessing compliance of the maximum values of each dataset with the SAC and a 95% UCL to determine overall compliance. The use of a 95% UCL is accepted industry practice to provide a conservative estimate of the average concentration of a dataset.

For the purposes of this audit, while the SKM analysis using the 2.5 factor has been considered, the factors of 1.5 and/or 2.5 have not been rigorously applied when assessing compliance. These factors were originally intended for ‘site management’ purposes when assessing individual cells or other small datasets and do not necessarily apply when assessing the larger combined datasets. Instead a case-by-case judgement has been applied to SAC exceedance depending on the relevant receptors and exposure pathways. For example, the basis of the original 2.5 factor relates to human health effects and assumes direct exposure to the contamination. Many of the SAC are not based on human health exposure and individual exceedances are typically less critical for other exposure routes, as the exposure mechanism (transport in groundwater or runoff of sediment) has an averaging effect. Similarly, if human health is relevant, but the material is buried and not immediately available for contact, then occasional large exceedances may not be significant.

In auditing compliance, the data have been compared directly with the SAC to determine initial compliance. The significance of any exceedances is then discussed in the context of that particular dataset and relevant receptors. The statistical analyses of the datasets provided in the Validation Report have been used to assist in this assessment (SKM, 2008), taking into accounts the limitation of using log-normal distributions where relevant. Where most results are non-detects and the detection limit is suitably low, compliance can generally be judged by direct examination, rather than resorting to statistics (which may be meaningless if there are large number of non-detects) as compliance is obvious.

5.6 FCC West Remediation

5.6.1 Validation of FCC West Excavation

Soil within the FCC West area was required to comply with the residential/topsoil SACs. During the course of the remediation, all of the approximately 17,000 m2 of FCC West was excavated. The cell and subgrade arrangement is shown in Figure 3.

5.6.1.1 Frequency of Excavation Analyses

Overall, the density of sampling for the FCC West excavation validation is adequate. A total of 652 samples were taken from the extents of the FCC West excavation. This number of samples is enough to fulfil the RAP intention of one sample from each cell floor and wall layer, assuming the distribution of samples is even between cells. SKM undertook a check of records to ensure that at least one OCP sample had been collected from each cell floor and wall layer.

All 652 samples were analysed for DDX and ADL, with 264 of these (40%) also analysed for the full OCP suite. Approximately 286 samples (44%) were analysed for TPH and 270 (41%) for ONP, OPP and VOCs. A total of approximately 55 samples (8%) were analysed for heavy metals PAHs, and PCBs.

The frequency of analysis of secondary contaminants is less than required by the RAP. This is not significant in this case as sufficient confidence exists that the other contaminants are not generally of concern. The concern expressed in Section regarding sufficient numbers of metals analyses is less relevant for the base of excavations, as people do not typically have frequent exposure to sub-surface soil, particular for depths greater than 0.5 m.

5.6.1.2 Excavation Compliance with SACs

The Validation Report states that 56 of the 652 samples taken from the FCC West excavation extent had concentrations above the SAC (SKM, 2008). However, none of these exceedances are significant, as discussed below. The Validation Report also stated that 95% UCL values for all contaminant were below their respective SACs. As noted earlier, some of the 95% UCL calculations will be of dubious statistical validity. However, in this case the overall conclusions are not affected and it is accepted that mean values will be below the various SACs.

The highest DDX and ADL results were all from samples taken along the western edge of Tahi Street. This area is actually outside the proposed residential area and it is not appropriate to compare the results with the residential criteria as it will form the road verge. If the 17 samples elevated results from beneath the road verge are compared with the more appropriate commercial SAC, only one sample exceeds the criteria.

Sample 8474 was taken from the wall of cell L16 and had an ADL concentration of 137 mg/kg, above the SAC of 60 mg/kg. However, additional information from MWH indicates that six validation samples from the eastern wall in L16 all returned concentrations below the SAC, with a maximum ADL concentration of 14 mg/kg (MWH, 2009d). It appears likely that this sample represents material that was removed and should not be included in the validation dataset. TDC gave its approval to leave the soil beneath the road reserve in a letter dated 10 September 2007 (TDC, 2007b).

Removing the elevated results beneath the Tahi Street verge from the dataset for the FCC West excavation leaves 39 samples exceeding the SAC. Of these, 33 of the exceedances related to DDX failures, with a maximum concentration of 41 mg/kg. Most of the elevated concentrations were below 10 mg/kg DDX. Many of the exceedances relate to samples which were retested, returning different concentrations to the original test results. However, even assuming that all the peak results represent actual residual concentrations, the exceedances are not significant.

The DDX criterion of 5 mg/kg for residential site use relates to the sediment runoff exposure pathway. This pathway is not relevant for the excavation extents as the entire area is covered in at least 0.5 m of residential soil. The next most sensitive pathway is human health. All results comply with the SAC for human health and most results comply with the lower more recently derived generic value (MfE, 2006). Exceedances of the generic value at depths greater than 0.5 m are acceptable.

None of the remaining six SAC exceedances are significant. These were:

• a single cadmium result (22 mg/kg) exceeded the residential SAC of 3 mg/kg. However, this SAC is not significant as it is based on potential phytotoxic effects and the sample represents soil currently over 1 m bgl where effects on plant growth are unlikely. The criterion is based on the Australian National Environmental Protection Council values (NEPC, 1999a). The equivalent NEPC human health-based value for residential site use is 20 mg/kg⁷.

• two results exceeded the SAC for C10-C14 TPH of 510 mg/kg, with results ranging from 570 – 660 mg/kg. This criterion is from the Hydrocarbon Guidelines (MfE, 1999) and is a surrogate for PAH contamination associated with diesel. The directly measured PAH concentrations for both these samples were below the relevant criteria;

• the single ADL result (excluding the Tahi Street verge samples) above the SAC of 3 mg/kg is not significant (3.7 mg/kg); and

• two samples exceeded the hot-water soluble boron SAC of 3 mg/kg for a residential site use. The maximum concentration was 70 mg/kg, with the next highest result 5 mg/kg. The criterion is from the Timber Treatment Guidelines (MfE/MoH, 1997) and relates to phytotoxic effects. Both samples represent soil currently over 1 m bgl where significant effects on plant growth are unlikely. The equivalent human-health criterion from MfE/MoH (1997) is dominated by the home-grown produce consumption pathway, which is not relevant. Without produce consumption the guideline is several thousand mg/kg.

Overall, the FCC West excavation has been adequately validated.

5.6.2 FCC West Backfill Compliance with SACs

Backfill material used as residential soil on FCC West was derived from the following sources:

• soil excavated from FCC Landfill, FCC West and FCC East;

• excavated marine sediments from the West and East Marine remedial sites;

• a batch of soil imported as backfill for the marine remedial excavations that failed to meet the marine SAC;

• imported residential soil; and

• imported topsoil.

Each of these material categories is discussed separately below. The discussion is also relevant to residential soil and topsoil used to create the 0.5 m capping layer on FCC East and FCC Landfill.

5.6.2.1 Soil Excavated from Site

A total of approximately 18,200 m3 of residential soil was excavated from the site during the remediation, the breakdown in source locations being:

• FCC East – 13,900 m3

• FCC West – 2,150 m3

• FCC Landfill – 2,150

A total of 356 and 41 samples were taken from the FCC East and FCC Landfill material, respectively. For DDX and ADL this is the equivalent of one sample per 39 m3 and 52 m3, respectively. The sampling density and distribution is adequate for these two areas. An additional 32 samples were collected from the residential stockpile for quality assurance purposes.

Only 19 validation samples have been reported in the Validation Report (SKM, 2008) as representative of the material excavated from FCC West. It is apparent from the data spreadsheet that these samples were in fact from two separate stockpiles representing only two of the 21 subgrades making up that area. There are no data presented for any of the residential soil excavated from the remaining 19 subgrades. Additional information was sought and it appears that a summary spreadsheet was not completed for this material. However, as with other material categories, it is expected that a significant number of site management samples were collected and used to determine the destination of that material. There is no reason to suspect a different decision making process was applied for the residential material sourced from FCC West.

To test this supposition, five cells from FCC West with missing data were selected and individual test results sought from site data held by MfE. In each case, site management samples were found confirming the expected decision making process and compliance with the residential criteria for soil classified as such. A total of approximately 30 samples that were relevant as validation samples were found for the five cells that were randomly selected. It is expected that a similar level of data would be available for other cells with missing data. Based on the additional information obtained, the missing data for residential soil sourced from FCC West is not a significant gap. On average, it is expected that the residential soil excavated from FCC West will comply with the SAC.

The data presented in the Validation Report for site-derived residential soil is discussed below.

Of the 448 samples in the dataset, all were analysed for DDX and ADL, with 109 (24%) of these also analysed for the full OCP suite. Approximately 50 samples (11%) were analysed for TPH, ONP, OPP and VOCs. A total of approximately 15 samples (3%) were analysed for heavy metals, and five for PAHs and PCBs.

Individual batches of soil have not been tracked to their final resting places, as the soil was temporarily stored in stockpiles. Consequently, using the average concentration and assessing variability is the only way to assess compliance with the SACs. This relies on peak concentrations not being so high that localised effects become significant. Confidence in the soil complying with SACs and being suitable for its purpose must additionally be gained from:

• a sufficient number of samples being taken to assess variability

• the average of the results being well below the relevant SACs, with many non-detects giving greater confidence

• excursions above the SACs being few and small

• most of the residential soil being below 0.5 m depth meaning the likelihood of a result being close to the surface where it has the potential to be washed to the marine environment is reduced

• incidental mixing during excavation, stockpiling and backfilling tending to reduce the likelihood of localised hotspots remaining, although such mixing would not be sufficient if a batch had unidentified high concentrations of a contaminant (for example metals, which were only measured infrequently)

• the 0.15 m layer of clean topsoil provides and extra level of protection against non-complying residential soil being washed to the marine environment

In this case, the relatively large number of samples for DDX and ADL gives confidence that the material has been adequately characterised with respect to these contaminants. Of the 448 sample results, 43 exceeded the DDX SAC of 5 mg/kg, with two of those results also exceeding the SAC for ADL of 3 mg/kg. However, the majority of the samples were below laboratory detection limits and, despite the high laboratory detection limits employed (see Section ), the average concentrations for the DDX and ADL datasets are expected to be below the SACs.

The DDX exceedances are not of concern. The exceedances are spread across the west site and represent isolated areas. Averaging will have occurred during soil handling and the actual concentrations will be lower. The main concern is for the highest of the exceedances which, if they occurred within the capping layer, could present a minor risk.

The maximum DDX concentration detected was 23 mg/kg. Information presented by SKM in the Validation Report and also independently obtained from MWH indicates that most of the peak results do not belong in the residential stockpile dataset, and therefore do not require further consideration. Regardless, there is no human health concern as the maximum DDX concentration is below a generic New Zealand guideline for residential use of 28 mg/kg (MfE, 2006). There would be a minor risk for the runoff pathway if these samples were near the surface within the capping layer⁸, but the risk is reduced by the 0.15 m layer of topsoil.

The maximum ADL concentration of 4 mg/kg is not significant relative to the SAC of 3 mg/kg.

A number of other SAC exceedances were indentified in the Validation Report (SKM, 2008) as follows:

• one of the 14 samples analysed for manganese (725 mg/kg) was identified as exceeding the corresponding SAC. However, SKM used the value of 500 mg/kg rather than the revised value of 1,500 mg/kg and the result actually complies;

• four of the 15 samples analysed for nickel were identified as exceeding the corresponding SAC. However, SKM used the value of 60 mg/kg rather than the revised value of 600 mg/kg. The maximum detected nickel concentration of 109 mg/kg is below the SAC.

The heavy metals analysis was well short of the RAP requirement at only 3 % of the primary analyses. The need for metals analysis and the mitigating factors is discussed in Section . The main metals of concern are mercury, arsenic and lead, from past manufacturing or storage of pesticides.

The 15 validation samples reported in SKM (2008) had mercury and lead concentrations typical of background. Arsenic for most samples also appears to be at background (around 1 – 5 mg/kg) although the maximum concentration of 17 mg/kg may be slightly elevated. The baseline pre-remediation testing (T&T, 2004) in which 21 surface samples were collected found arsenic generally at background concentrations, but one sample at 48 mg/kg (from a random location in FCC East that was in the vicinity of one of the original pesticide manufacturing buildings) is clearly elevated above background and three other samples showed a possible minor degree of contamination (11 – 16 mg/kg). Lead also showed minor elevation above background in some samples. Mercury was at concentrations typical of background. Early sampling by Woodward-Clyde (1993), while not reported in full, found significantly elevated lead in one sample (1290 mg/kg) in the vicinity of the same building at which elevated arsenic was found in the baseline sampling. Neither arsenic nor mercury was found to be elevated in the Woodward-Clyde sampling.

Additional sampling of the residential fill material for mercury was carried out by TDC in August 2008 (TDC, 2008b) in which 25 samples were collected on a grid, with clusters of four samples collected at each location. Subsequently, the laboratory provided arsenic and lead analysis results for these samples. This sampling found concentrations typical of background for all three metals. Including these as validation samples for the residential backfill on FCC West brings the number of samples analysed for these metals to approximately 9% of the total. The extra results have given sufficient additional assurance that significant undetected hotspots of arsenic, lead and mercury are unlikely to exist within the residential capping layer on FCC West.

5.6.2.2 Marine Sediments

The marine sediments used as residential backfill have not been well characterised by the data presented in the Validation Report (SKM, 2008) and there is therefore some uncertainty regarding strict compliance with the residential SAC. The majority of the potential exceedances were of the DDX criterion of 5 mg/kg. However, the average DDX concentration in the marine sediments is generally expected to be below the SAC (see further discussion below). In this case, the peak DDX concentrations detected were significantly above the SAC e.g. the two highest results were in the marine sediment samples were 125 and 82 mg/kg. Mixing during soil handling would be expected to reduce the significance of these peak exceedances to some extent. However, localised areas above 5 mg/kg are likely to remain given the initial concentrations. As noted above, the question then is whether such concentrations are likely to have ended up within the residential capping layer creating a minor risk for the sediment runoff pathway (noting the protection offered by the 0.15 m layer of topsoil) and a human health risk if the concentrations are above the residential criterion. More detailed comments are provided below.

A total of approximately 4,800 m3 of marine sediment was removed from the east and west marine remedial excavations. According to the volume balance diagram (MWH, 2008), approximately 850 m3 of the east marine sediments was mixed with commercial material and backfilled in FCC East. However, it is not known which of the samples represent the remainder of the marine east material which was used as residential material. For the purposes of assessing the portion of the material used for residential backfill, SKM included all the data for the east marine sediment (SKM, 2008). This is a reasonable approach.

However, for both east and west, SKM combined the pre-excavation and excavation base validation test results into single datasets that it considered representative of the excavated marine sediment. This assumes that the validation samples from the excavation base are representative of the material removed, presumably for the lower part of the excavated material. This is of dubious validity unless specifically tested and shown to be reasonable.

Examination of the pre-excavation and excavation base datasets by PDP indicates that that there are statistical outliers substantially biasing the 95% UCL estimates. When the outliers are excluded, the excavation base dataset is similar to the data from the removed material, and therefore could be treated as single combined datasets for each of east and west (but that similarity also means that insufficient material had been removed to effect adequate remediation).

Recalculating 95% UCL estimates without SKM’s assumption of log-normality, but using the complete datasets, found that both the east and west sediments had 95% UCL estimates substantially greater than the DDX residential criterion of 5 mg/kg. This would suggest the material should have been rejected as residential backfill. However, when one or two apparent statistical outliers were excluded from the datasets, the 95% UCL estimates complied with the DDX criterion for both the East and West sediments. The conclusion is that most of the sediment does in fact comply, but that there are isolated hotspots of many times the SAC within the sediment (up to 125 mg/kg for the east sediments and up to 82 mg/kg for the west sediments).

Such hotspots would not be completely eliminated by the incidental mixing during material handing and raises the possibility that some material within the residential capping layer could have DDX concentrations substantially above the SAC in isolated areas. The chance of this occurring can be roughly calculated.

The exact quantity of marine sediments used in FCC West as backfill is not known. Approximately 61% of the residential stockpile, of which the marine sediments made up 35%, was used in FCC West. If it assumed that the marine sediments were used in FCC West in the proportion in which they were in the stockpile, and knowing that the residential stockpile made up 84% of the 13,400 m3 of total residential quality backfill in FCC West, the marine sediments theoretically amount to 18% of the backfill. If it is further assumed that the marine sediments are evenly distributed through the 6000 m3 of residential capping, then a marine sediment hotspot has an 8% chance of being in the capping layer. This is acceptable when combined with the factors, discussed earlier, that further reduce risks to either the marine environment or human health.

A number of other SAC exceedances were indentified in the Validation Report (SKM, 2008) as follows:

• seven of 31 samples analysed for hot water soluble boron exceeded the SAC of 3 mg/kg, with a maximum concentration detected of 10.8 mg/kg. These exceedances are not significant as this criterion relates to phytotoxic effects and the maximum concentration is not significantly above the SAC. The 95% UCL concentration (SKM’s log-normal distribution assumption) was approximately 4 mg/kg;

• four of the 31 samples analysed for nickel were identified as exceeding the corresponding SAC. However, SKM used the value of 60 mg/kg rather than the revised value of 600 mg/kg. The maximum detected nickel concentration of 80 mg/kg is below the SAC.

In summary, while the various datasets for the marine sediments may not strictly represent the excavated material, the large number of samples analysed for the key OCP contaminants gives reasonable confidence that the actual concentrations fall somewhere within the overall dataset. Consequently, there is reasonable confidence that the material is suitable as residential backfill and the few DDX hotspots will not create an unacceptable risk.

5.6.2.3 Failed Imported Marine Backfill

A total of 430 m3 of material imported to site as backfill for the marine excavations was found to exceed the marine SAC of 0.01 mg/kg for DDX and used in FCC West as residential backfill⁹. However, the material complied with the less stringent residential SAC and was therefore appropriate for that purpose.

A total of 13 samples were taken to confirm the material was suitable as residential material. All 13 samples were analysed for the full OCP suite. Four samples were analysed for TPH, three samples were analysed for a metals suite and one sample was analysed for hot water soluble boron, total/free cyanide, PAHs and PCBs. The sampling rates are reasonable given the source of the material and the fact that OCPs were the reason the material could not be used in the marine environment.

The Validation Report identified minor exceedances of the nickel and manganese SACs in all three samples analysed for those contaminants. However, the SAC values used by SKM have been superseded and when the results are compared with the actual SACs, they easily comply. No other SAC exceedances were identified.

5.6.2.4 Imported Residential Soil

The test results for the approximately 5,830 m3 ¹⁰ of clean material imported as residential have been assessed as a whole in the Validation Report, rather than on a source by source basis. Whilst not ideal for the reasons outlined previously, conclusions can be drawn on the general quality of the material as a whole. It is difficult to determine exactly where the imported soil was used on the site and the dataset also represents soil used in the 0.15 m surface layer on FCC East and Landfill. Approximately 1,760 m3 or 30% of the total imported material was used on FCC West.

A total of 30 samples were analysed for DDX and ADL, with 23 of these also analysed for the full OCP suite. Approximately 16 samples were analysed for a metals suite, nine were analysed for TPH, and eight were analysed for PAHs and PCBs. The frequency of sampling was adequate.

The only result to exceed the SAC was a manganese concentration of 1,960 mg/kg, above the corresponding SAC of 1,500 mg/kg. This exceedance is not significant as the original data spreadsheet indicates that the destination of this material was subgrade 19A on FCC Landfill. The detected concentration is not significant for the recreational/open space site use for this part of the site.

Overall, the imported residential soil complies with the relevant SAC.

5.6.2.5 Imported Topsoil

A total of about 5,560 m3 of topsoil was reported to have been imported from several sources (SKM, 2008)¹¹. A total of 22 samples were taken at an average rate of one per 250 m3 for OCP analysis. This rate is satisfactory. The Validation Report statistically analysed the topsoil results together with imported residential material. The assumption is that results from the two types of imported materials and the various sources are from the same statistical populations, which is not necessarily the case (and was not reported as being tested). However, the generally low results makes this unimportant. Individual exceedances were identified against material types.

The topsoil SACs are identical to the residential SACs except for a lower nickel criterion of 60 mg/kg, compared with 600 mg/kg for the residential soil. Much of the soil in the Mapua area has naturally elevated nickel concentrations and there was some difficulty sourcing material that complied with the lower nickel value. As with the imported residential soil, it is difficult to determine exactly where the imported topsoil was used on the site. The dataset also represents soil used in FCC East, the Landfill and the private properties.

All test results were below the topsoil SAC except for a zinc concentration of 211 mg/kg in one of the samples which slightly exceeded the SAC of 200 mg/kg. The marginal exceedance is not significant, particularly as the criterion is based on plant health (NEPC, 1999a) and the equivalent human-health guideline value is several thousand mg/kg (NEPC, 1999b).

Overall, the imported topsoil complies with the relevant SAC.

5.6.3 The Remediation Treatment Area

The vicinity of the MCD plant and the locations of stockpiles of treated material have the potential for contamination by reagent chemicals, particularly copper, ammonia and nitrate (with consequent potential effects on groundwater). The Validation Report did not consider this possibility.

The MCD plant was decommissioned in August 2007. The slab was removed in the same month and the area beneath tested. This is Subgrade 40. Only the standard validation test were done, that is no testing was carried out for nutrients and only two metals test appear to have been done (both <10 mg/kg for copper). This subgrade was excavated to about 0.5 m and placed in the residential stockpile.

The area immediately to the south of the plant area (SG37) was tested around the same time as SG40. The top 0.25 – 0.5 m of this subgrade was sent to the commercial stockpile. The rest was excavated to about 1 m depth and placed in the residential stockpile. Again, only the standard validation suites were applied.

It is understood the treated material stockpiles were located in a variety of places. It is not known what testing was carried out post-decommissioning, but it is presumed that these areas were also stripped and tested in a manner typically of the rest of FCC-West.

In general, copper is not expected to penetrate much beyond the surface soil. Copper is not a health-concern but may be of concern for plant health. Copper may also be of concern for the aquatic environment but leaching of copper appears to be minimal (see Section 1.17.2). It is understood that most of the soil from the stockpile areas was used as commercial backfill on FCC East. If so, copper will not be of concern.

Ammonia and phosphorus derived from the MCD process reagents are very much more soluble than copper and could have leached into the underlying soil. This is primarily of concern for groundwater, but excessive quantities of ammonia may also generate ammonia gas in the soil, affecting plant health and, in the extreme, be of concern for human health if the gas should gather in confined spaces (e.g. excavations). The likelihood of this occurring at former stockpile locations is low and no further testing is recommended at this stage. However, if sampling recommended in FCC East (Section 1.1.7) shows that generation of ammonia is a significant issue in the treated fines, the need for testing on FCC West should be reassessed.

5.6.4 Acceptability of FCC West Soil Remediation and Fitness for Purpose

Overall, we consider that FCC West will be fit for its intended purpose, subject to the minor uncertainties discussed below.

The Validation Report does not provide conclusions as to whether the remediation of FCC West met the RAP requirements for soil quality. However, on balance we consider that the soil quality will generally meet the SACs and in particular meet the ADL and DDX SACs. Local exceedances are not so great as to be unacceptable. As discussed in Section , compliance with the SACs for FCC West also indicates that FCC West will generally be fit for its intended purpose with respect to soil quality. Potential effects associated with groundwater are discussed separately in Section 7.

Some uncertainty remains from:

• the detection limits for DDX being close to the residential SAC; and

• a lack of inter-laboratory comparisons for DDX results at concentrations close to the residential SAC.

A programme of sampling to evaluate this is recommended (Section 1.1.3.2).

5.7 FCC East Remediation

5.7.1 General

Soil within the FCC East area was required to comply with the commercial SACs below 0.5 m depth and with the residential/topsoil SACs for the 0.5 m capping layer. All of the approximately 13,000 m2 area of FCC East was excavated during the remediation works. The cell and subgrade arrangement is shown in Figure 2.

FCC East was backfilled with soil that was considered to have met the SACs when excavated and with treated material that was considered to have meet the SACs after treatment. Treated soil, was placed on its own, mixed with oversize material, commercial soil, or marine sediments from the East and West foreshores, or a combination of these.

5.7.2 Validation of FCC East Excavation

Overall, the density of sampling for the FCC East excavation validation is adequate. A total of 719 samples were taken from the extents of the FCC East excavation. This number of samples is enough to fulfil the RAP intention of one sample from each cell floor and wall layer, assuming the distribution of samples is even between cells. SKM undertook a check of records to ensure that at least one OCP sample had been collected from each cell floor and wall layer.

All 719 samples were analysed for DDX and ADL, with 499 (70%) of these also analysed for the full OCP suite. Approximately 280 samples (40%) were analysed for TPH, ONP, OPP and VOCs. A total of approximately 70 samples (10%) were analysed for heavy metals and approximately 50 samples were analysed for PAHs, PCBs.

The only results to exceed the SAC were four DDX concentrations ranging from 206 to 283 mg/kg. These exceedances are not significant relative to the SAC of 200 mg//kg. The isolated exceedances represent a small area of soil relative to the overall area of the FCC East excavation.

5.7.3 FCC East Backfill

5.7.3.1 Backfill Sources

Backfill material used on FCC East was derived from several sources:

• commercial soil excavated from FCC Landfill, FCC West and FCC East;

• treated soil;

• oversize material;

• crushed concrete;

• clay imported to repair the clay bund;

• marine sediments; and

• the 0.5 m capping layer consisting of site-derived and imported residential quality surface fill and imported topsoil¹²

Each of these material categories is discussed separately below.

5.7.3.2 Commercial Soil Excavated from Site

A total volume of approximately 27,500 m3 of commercial quality soil was excavated from FCC Landfill, FCC West and FCC East during the remediation. This soil was used as backfill below 0.5 m depth in FCC East and FCC Landfill.

A total of approximately 1,700 samples were taken from the excavated commercial material. All samples were analysed for DDX and ADL (an average of one sample per 16 m3, well within RAP requirements), with 73 also analysed for the full OCP suite (one sample per 380 m3). A total of approximately 20 samples (one sample per 1,375 m3, or 1% of all samples) were analysed for TPH, OPP, ONP and VOC. Approximately ten samples were also analysed for the metals suite, hot-water soluble boron and total/free cyanide (one sample per 2,750 m3 or only 0.5% of all samples).

The sampling density and distribution for DDX and ADL is adequate for characterising the material. Analysis for other compounds fell short of the RAP requirements (well short in the case of metals), although this is not a significant information gap given the proposed use of FCC East.

The Validation Report reported that the 95% UCL for DDX concentrations was 79 mg/kg, well below the SAC of 200 mg/kg. Approximately 26% and 10% of samples were non‑detects for ADL and DDX, respectively. Of the approximately 1,700 samples analysed, there were 53 exceedances of the DDX SAC (3% of the samples), with a maximum concentration of 765 mg/kg. Of the exceedances, most (43) were less than 1.5 times the DDX SAC. Given the large number of samples representing this material, there is a good degree of confidence that the peak results represent isolated SAC exceedances, noting that the mixing that will have occurred in the various excavation, stockpiling and backfilling processes will tend to “average out” exceedances in the final backfill.

The SAC of 200 mg/kg was based on leaching to groundwater and subsequent effects on the marine environment (via discharge of groundwater). Any remaining isolated SAC exceedances within the backfill are not significant in that context. Groundwater is an “integrating” medium meaning that effects of localised higher concentrations will be combined with effects from surrounding soil and averaged overall (but note the greater than expected effects on groundwater reported in Section 7).

The 95% UCL for ADL concentrations in the commercial soil reported in the Validation Report was 5 mg/kg (recalculated by PDP as 6 mg/kg), also well below the SAC of 60 mg/kg. Of the samples analysed, there were 6 exceedances of the ADL SAC, with a maximum concentration of 98 mg/kg. These individual exceedances are not significant for the reasons outlined above.

All other contaminant test results were below the respective SACs.

The commercial soil excavated from the site and used as backfill is compliant with the SACs. This also applies to the FCC Landfill backfill.

5.7.3.3 Treated Soil

Soil to be treated was initially screened to remove particle sizes greater than 10 mm (known as “oversize”). The 5 – 10 mm component was separated prior to treatment and stockpiled for later recombining with the treated soil during disposal. The validation of the 5 – 10 mm component is discussed separately below.

The less than 5 mm component, after treatment, became the “treated fines”. As noted in Section , the validation criteria for the treated fines evolved during the works. In July 2005, a 6-day rolling average assessment was implemented, with no single sample to exceed 1.5 times the SAC. Similarly, the analytical suite and frequency of testing varied slightly during the remediation works (see Section ), although the key changes were implemented early on in the project.

Overall, the scope and frequency of the validation testing for the treated fines is adequate to characterise the material and typically easily complied with various RAP requirements (SKM, 2008). The number of samples analysed for the various parameters is set out in tables 67 and 68 of the Validation Report (SKM, 2008). The approach in the Validation Report of analysing the pre and post-July 2005 datasets separately is reasonable.

Some of the early piles of treated fines went straight to stockpile without testing. Subsequent testing of these indicated slight exceedances of commercial SAC for DDX, with a maximum detected concentration of 231 mg/kg. These stockpiles were blended with other treated fines to reduce the concentrations and subsequently re-tested.

Pre-July 2005 Treated Fines

Approximately 1,400 m3 of soil was treated prior to July 2005. Of the 118 samples analysed (average one sample per 12 m3), 16 samples returned DDX concentrations above the SAC, with four of these samples also having ADL concentrations above the SAC. The two highest DDX results were just under 900 mg/kg, with the remainder of the exceedances only slightly over the SAC of 200 mg/kg. Although the two peak concentrations are significantly above the SAC, in the overall context, these exceedances are not significant.

The treated fines were handled several times and were either buried as treated fines or more commonly mixed with either commercial material or oversize before disposal (MWH, 2009e). The ratio of mixing was generally about one part treated fines to three parts commercial/oversize. The effect of this handling and mixing is to reduce the likelihood of significant hotspots remaining in the soil. The average concentration of DDX in the commercial soil was approximately 80 mg/kg. If a batch of treated fines is assumed to have the maximum detected DDX concentration of about 900 mg/kg, and this is combined with three parts commercial soil at the average concentration of 80 mg/kg, the average concentration for the combined material is about 285 mg/kg.

The 95% UCL calculated by SKM (2008) for DDX is 143 mg/kg for the pre-July 2005 treated fines, below the SAC of 200 mg/kg. This is acceptable.

For ADL, the Validation Report reported four exceedances (ranging from 70 to 84 mg/kg), only slightly above the SAC of 60 mg/kg. The exceedances are not significant. The 95% UCL calculated by SKM (2008) for ADL was approximately 16 mg/kg, well below the SAC of 60 mg/kg.

All other contaminant concentrations were below the corresponding SAC.

It should be noted that no SAC were derived for the various compounds containing nitrogen derived from the MCD process reagents. The significance of these results is discussed in the next section and with respect to groundwater in Section 1.12.

Post-July 2005 Treated Fines

Approximately 9,200 m3 of soil was treated post-July 2005. Of the approximately 470 samples analysed (average of one sample per 20 m3), 39 samples returned DDX concentrations above the SAC, with one of these samples also having ADL concentrations above the SAC.

The 95% UCL for DDX reported in the Validation Report was 114 mg/kg ¹³, well below the SAC of 200 mg/kg. The maximum DDX concentration of 300 mg/kg was 1.5 times the SAC and is not significant in the overall context, particular as mixing with commercial material is most likely to have reduced the concentration.

The 95% UCL for ADL was approximately 10 mg/kg, also well below the SAC of 60 mg/kg. The peak ADL concentration of 75 mg/kg was only 25% above the SAC.

Heavy metals were analysed on 136 occasions, or a frequency of 29% of the ADL and DDX analyses. This is greater than the required frequency of 10%. Two copper concentrations (out of 136 test results – one sample per 70 m3) exceeded the SAC of 5,000 mg/kg, with a maximum concentration of 5,250 mg/kg detected. The 95% UCL for copper was approximately 1,900 mg/kg. The elevated concentrations of copper relate to copper compounds used as reagents in the treatment process. The significance of the copper concentrations in the treated fines in terms of groundwater is discussed in Section 1.12.

Leachable nitrogen compounds were analysed on 99 occasions (not 49 as reported in the Validation Report), or 20% of the rate of ADL and DDX analyses. These were analysed as synthetic precipitation leaching procedure (SPLP) tests and are reported as concentrations (mg/L) in the leachate. The Validation Report combined these results with the soil results with no reference to the difference in units (in fact no units are given in the various tables appended to the Validation Report or in the analysis spreadsheets). The equivalent total concentrations in the soil were apparently not analysed, which is unfortunate.

Relationship between nitrogen soil concentrations and leaching test concentrations were later developed using the QA-QC samples (PDP, 2007). Using these relationships, the average Ammonia-N SPLP concentration from the treated fines validation sampling of 292 mg/L translates to a soil concentration of about 7300 mg/kg and the average Total-N SPLP concentration of 380 mg/L translates to a soil concentration of about 14,000 mg/kg (1.4%). While these relationships are based on a small number of samples, if they held true at the time of soil treatment they demonstrate that quite large quantities of potentially leachable nitrogenous compounds were being added to the treated fines. The significance of nitrogen in the groundwater is discussed further in Section 1.17.3.

Blended Stockpiles

Early batches of treated fines were found to have slightly exceeded the SAC for DDX (maximum DDX concentration of 231 mg/kg). Following discussions with the Site Auditor and MfE these were blended with other material under the supervision of EMS to bring the material into compliance, although the consent did not strictly allow treatment by dilution.

Eight samples were taken of the 1200 m3 of blended material, a rate of one sample per 150 m3. This rate is reasonable given the material was not far out of compliance in the first place. The Validation Report presents pre and post-mixing data which adequately demonstrates the material was brought into compliance.

5 – 10 mm component

Approximately 970 m3 of the 5 – 10 mm component of the soil was produced during the remediation works (SKM, 2008). Nine samples of this material (one sample per 110 m3, approximately) were analysed for DDX and ADL, and one sample was also analysed for the full OCP suite. The samples were analysed by using a solvent wash to remove fines adhered to the large particles (Graham Corban, Hill Laboratories, pers. comm.). The resultant contaminant weights were compared with the overall sample weight. The sampling scope and methods are reasonable.

The results were all below the SACs, with maximum DDX and ADL concentrations of 61 mg/kg and 14 mg/kg respectively.

5.7.3.4 Oversize Material

Approximately 3,800 m3 of material greater than 10 mm material was estimated to have been generated by screening the contaminated soil to be treated (SKM, 2008). The screened material retained a certain amount of fine material which adhered to the larger particles. This fine material contained contamination at similar levels to the remainder of the fine soil that was subsequently treated. One of the original RAP requirements was that the oversize material should have no greater than 5% fines attached. In practice, this was difficult to achieve and oversize with up to 10% fines attached was accepted in some circumstances.

To estimate the level of contamination in the oversize, the contaminant concentrations in the fines was estimated or measured and factored by the estimated percentage of fines, assuming the greater than 10 mm components to be ‘clean’. This is a reasonable approach.

In the first instance, the average DDX and ADL concentrations from the in-feed to the treatment plant were used as an estimate of the likely concentrations in the fines attached to the oversize. The DDX and ADL concentrations used were 1,012 mg/kg and 73 mg/kg respectively. However, the results of 24 samples of the oversize indicated that the actual concentration in the fines was likely to be somewhat lower, with average measured DDX and ADL concentrations of 457 mg/kg and 46 mg/kg.

Using the more conservative in-feed estimate, SKM estimated the DDX concentration of the total oversize to be approximately 40 mg/kg and the equivalent ADL concentration to be approximately 3 mg/kg. Both these values are well below the applicable SAC of 200 and 60 mg/kg for DDX and ADL respectively. The oversize material complies with the commercial SAC.

5.7.3.5 Crushed Concrete

A total of approximately 2,000 m3 of crushed concrete was generated during the remediation works. During that time, 53 samples of concrete were analysed for DDX and ADL. The RAP required a representative sample. The frequency of testing is adequate.

The concrete samples were ground at the laboratory before analysis (Graham Corban, Hill Laboratories, pers. comm.). Any contaminated fines attached to the concrete would then effectively be ‘diluted’ by the mass of concrete. For similar reasons outlined for the oversize material in Section 5.4.8.4, this is a reasonable approach.

All 53 test results were below the commercial SAC, with maximum DDX and ADL concentrations of 177 mg/kg and 1.5 mg/kg respectively, demonstrating compliance.

5.7.3.6 Imported Clay

Approximately 1,000 m3 of clay was imported to repair the bund and backfill the surge chamber excavation. A total of four samples of the imported clay were analysed for the full suite including OCPs, OPP, ONP, TPH, PAH, PCBs and a metals suite. All results were below the corresponding SAC, demonstrating compliance.

5.7.3.7 Marine Sediments

Approximately 850 m3 of marine sediments were mixed with commercial material and used as backfill in FCC East. The sediments are discussed in detail in Section 1.1.4.2. All results were below the corresponding SAC, demonstrating compliance.

5.7.3.8 Surface soil

FCC East was covered with a half metre layer of residential quality material, including 0.15 m of imported topsoil. The sources and testing of this soil is covered in the analysis of results for FCC West – see Section 1.1.4. The 0.5 m capping layer is expected to meet the quality requirements for residential soil, subject to minor uncertainties discussed in Section 1.1.7.

5.7.3.9 Diesel Contamination

Correspondence from the Site Auditor refers to ‘considerable diesel contamination’ in the north-west portion of FCC East which was land-farmed to reduce concentrations (GHD, 2005b). However, there is no mention of this in the Validation Report or any other correspondence reviewed during the audit.

It is assumed that the material was subsequently tested and the results are part of the commercial material dataset. If so, the material complied.

5.7.4 Acceptability of FCC East Remediation

The Validation Report concludes that FCC East meets the SAC for an open space¹⁴ and commercial use. We concur with this conclusion, subject to the comments below. As discussed in Section , compliance with the SACs for FCC East indicates that this part of the site will typically be fit for its intended purpose. However, we note six issues which are either potentially at variance with the SACs or may otherwise present a risk to the proposed site use:

1. the possibility of elevated concentrations of DDX within the residential soil in the 0.5 m capping layer;

2. the possibility of ammonia gas being generated from the nitrogen compounds in the treated fines;

3. the potential for the nitrogen compounds in the treated fines to cause adverse impacts on other receptors via groundwater;

4. the lack of buffer material adjacent to the marine environment of the Mapua Channel;

5. exceedance of the commercial copper guideline in treated fines material; and

6. the potential for copper concentrations in the mixed treated fine material to cause phytotoxic effects in some plant species.

Items 3, 4 and 5 are related to risks to groundwater and are discussed in Section 7. The exceedances of copper referred to in Item 5 are not so great as to be a risk to human health.

Considering Item 1, this has been discussed with respect to FCC West and is acceptable, assuming a site management plan is put in place control future excavation. The same conclusion applies here.

Considering Item 2, the treated fines contain nitrogen compounds that were added during the remediation process. Some of the treated fines were mixed with typically three volumes of commercial soil and/or oversize during the backfilling operations (MWH, 2009e), reducing the effective concentration of nitrogen compounds in this material. However, the QA-QC sampling showed concentration of several hundred up to 5000 mg/kg of ammoniacal-N in mixed and unmixed treated material. Greater concentration could exist on the basis of the SPLP testing carried out during the remediation. There is an unknown potential for ammonia gas to be generated, that increases if the pH of the soil is elevated (alkaline).

Cement-stabilised marine sediment material was placed in subgrades SG5C, SG3, SG7, SG9, SG11 and SG14 (SKM, 2008). Cement is strongly alkaline and is likely to have increased the alkalinity of the soil in which it has been mixed. Mixed treated fines was also placed in subgrades SG3, SG7 and SG14. The location of the cement-stabilised material relative to the mixed treated fines is not known. However, it may be that there is an increased potential for generation of ammonia if infiltration made more alkaline by passing through cement-stabilised sediments then passes through mixed treated fines.

The key human-health effects of ammonia are acute and relate to the corrosive effects on skin, eyes and internal respiratory membranes. Ammonia gas has a distinctive sharp odour and would typically be smelt before concentrations reached harmful levels. The most likely exposure route would be maintenance or construction workers working in confined spaces such as trenches near or within treated fines. Any exposure is likely to be short-term and the ability to smell the gas at low concentrations may give an effective warning mechanism for workers. The risk may be more one of aesthetics (unpleasant odours) than a health risk.

Ammonia gas is also phytotoxic and will cause burning of root tips and leaves at sufficient concentrations. No sign of distressed grass suggestive of such effects was observed during PDP’s site visit.

It is difficult to quantify the level of risk associated with ammonia gas given the available information. Additional information is required to better quantify the risk. It is recommended that a programme of soil gas sampling and analysis be carried out in locations where buried fines or mixed material exists. This should include subgrades SG3, SG7 and SG14 where cement- stabilised material and treated fines co-exist. If ammonia is found, interpretation should include consideration of migration to confined spaces.

If a potential risk is found, the risk can be managed by ensuring adequate procedures are in place for excavation workers. The site management plan should contain procedures for evaluating the atmosphere in confined spaces. If a significant risk is found by the sampling programme, the risk of gas penetration into future buildings will also need to be addressed in the Site Management Plan.

A buffer zone was required by Condition 10(j)(viii) of consent RM030521 to limit potential effects of leaching to groundwater and the adjacent marine ecosystem. The criteria are set out in Table 2. There is no information in either the Validation Report or other information reviewed to indicate that that a buffer zone was implemented adjacent to the Mapua Channel. However, the clay bund along the eastern foreshore provides a buffer of approximately 10 m between the commercial backfill and the shoreline (if the ‘shoreline’ is assumed to be the base of the sea-wall on the outside of the bund). The clay bund was tested and found to have low levels of contamination and imported clay to repair the bund complied with residential criteria. Additional information provided by MWH indicates that the majority of the fill immediately inside the clay bund is likely to generally comply with the ’10 m’ criteria of 120 mg/kg and 40 mg/kg for DDX and ADL respectively (MWH, 2009c). The as-built drawings (SKM, 2008) show the clay bund is underlain by clean gravel in subgrades SG10, SG11, SG13 and SG14 which will also comply with the buffer requirements. However, DDX concentrations of up to 174 mg/kg were present in backfill for subgrade SG14, but it is not known where in the subgrade the peak concentrations were placed.

In summary, the buffer zone requirements are likely to have been complied with to some extent on the eastern foreshore, but the full intent has probably not been realised. The potential implication is the effect on groundwater quality, which is discussed in greater detail in Section 7.

Considering Item 5, TDC intends using part of FCC East along the foreshore as open space (see Section ). This raises the issue of phytotoxicity. Phytotoxicity is not generally an issue for commercial use but it may become a concern for amenity planting in an open space context.

The average concentration of copper in treated fines (95 % UCL of 1,606 mg/kg for pre-July 2005 and 1,924 mg/kg for post-July 2005) suggests a potential for phytotoxic effects for some deeper-rooted shrubs and trees. Treated fines material was placed in subgrade SG 7. Shallow-rooted plants within the surface 0.5 m of residential/topsoil material should not be at risk. Whether the copper is plant available depends on such things as the form of the copper, the pH of the soil and the soil mineralogy.

The as-built drawings show that no treated fines were placed in subgrades close to the foreshore (subgrades SG7, SG9, SG10, SG11 and SG14) although mixed treated fines were placed in SG3 and SG 7 at depths of 0.5 and 1 m respectively. Whether the mixed treated fines have sufficiently high copper concentration is not known. The issue is readily managed by precautionary replacement of the soil to a sufficient depth if deeper-rooted plants are planted where mixed treated fines are buried close to the surface.

5.7.5 FCC East Fitness for Purpose

Overall, with the exception the two uncertainties outlined below, the FCC East site is fit for its intended purpose with respect to the soil remediation (but see separate discussion on groundwater in Section 7). 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 allowed to migrate to the marine environment or be disposed of inappropriately off site (e.g. to a site with a more sensitive site use such as residential).

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. The site management plan should be amended to manage any risk found.

• 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.

5.8 FCC Landfill Remediation

5.8.1 General

Soil within the FCC Landfill area was required to comply with the open space SACs below 0.5 m depth and with the residential/topsoil SAC for the 0.5 m capping layer. The intended end us is open space. The cell and subgrade arrangement is shown in Figure 3.

FCC Landfill was backfilled with soil that was considered to have met the SACs when excavated and with treated material that was considered to have meet the SACs after treatment.

5.8.2 Validation of FCC Landfill Excavation

The landfill covered an area of approximately 6000 m2. Subgrade SG 18 formed the majority of the excavation in FCC Landfill (Figure 3). The north-west, south-west and south edges of SG 18 were approximately coincident with the extent of the waste i.e. the excavation was extended to ‘clean soil’.

The south-west tip of the former landfill area, beyond SG 18, is shown as un-excavated on the remediation as-built drawings (SKM, 2008). However, the initial characterisation investigation indicates that a 400 mm layer of waste was present at a depth of 1.4 m bgl in cell M3 (GES, 2002). The Site Engineer has advised (Paul Russell, pers. comm.) that this area was excavated to approximately 3 m deep to bury koiwi (human bones) and that any waste would have been removed at that time (MWH, 2009e). No records to confirm this have been sighted. We consider that this is unlikely to be a significant information gap, as it appears unlikely that any significant quantity of waste remains. In addition, the area has been covered with at least 0.5 m of residential quality soil acting as a barrier to any waste that might remain.

A total of 361 samples were taken from the extents of the FCC Landfill excavation. This number of samples is enough to fulfil the RAP intention of one sample from each cell floor and wall layer, assuming the distribution of samples is even between cells. SKM undertook a check of records to ensure that at least one OCP sample had been collected from each cell floor and wall layer. The frequency of sampling for OCPs is acceptable.

All 361 samples were analysed for DDX and ADL, with 62 of these also analysed for the full OCP suite. This frequency is acceptable. Approximately 102 samples were analysed for TPH, ONP, OPP and VOCs, or only 28% of the primary analyses compared with the RAP requirement of 50%. A total of approximately 20 samples were analysed for heavy metals and approximately 19 samples were analysed for PAHs and PCBs. This is only 5.5% of the primary analyses compared with the requirement of 10%

The only results to exceed the SAC of the 361 samples taken were three ADL concentrations above the SAC of 60 mg/kg in samples taken from the floor of three separate cells (K7, K8 and N6). The concentrations ranged from 124 mg/kg (K8) to 170 mg/kg (N6). These exceedances are not significant as they appear to represent very localised hotspots and the average ADL concentrations in each of the cells with elevated results were all low. In each case, at least three other samples were taken from the cell floors, all returning concentrations well below the SAC of 60 mg/kg.

Examination of the secondary analytes (Table 77 of the Validation report) shows concentrations were at generally low levels. Examination of the validation spreadsheet showed many non-detects. Despite the less than required level of sampling, the results are sufficient to have confidence that the base of the excavation has been adequately validated. The lower than required testing frequency is therefore not significant.

5.8.3 FCC Landfill Backfill

The backfill for FCC Landfill was from the same sources as FCC East discussed in Section 1.1.6 above, that is:

• commercial soil excavated from FCC Landfill, FCC West and FCC East;

• treated fines;

• oversize material;

• crushed concrete; and

• the 0.5 m capping layer consisting of site-derived and imported residential quality surface fill and imported topsoil.

The as-built drawings show that, apart from layers of oversize or crushed concrete placed in the base of the excavation, all the commercial quality material was placed as treated fines alone or mixed treated fines. The commercial soil was always placed mixed with other material such as treated fines and oversize.

The discussion presented for FCC East and these sources (Section 1.1.6) also applies for FCC Landfill and is therefore not repeated.

5.8.4 Acceptability of FCC Landfill Remediation

The Validation Report concludes that FCC Landfill meets the SAC for an open space¹⁵ use. Overall, we concur with this conclusion, with similar uncertainties to that discussed above for FCC East (see Section 1.1.7). Risks to groundwater are discussed in Section 1.19. The uncertainties with respect to soil quality are:

• Treated fines material was placed at depth in subgrades SG19A, SG19B and SH19C, while mixed treated fines material was placed in these and subgrade SG18 up to 0.5 m from the surface. There is an unknown potential for generation of ammonia gas. Currently the grass cover appears healthy. The potential for generation of ammonia in this area is not expected to create a particular human health risk for day-to-day use as open space. No buildings are planned for this area and excavation is expected to be infrequent. Testing for ammonia in soil gas is not required in this area, but confined space precautions should be taken if any excavation does take place in the area.

• The treated fines also have elevated concentrations of copper, which could cause phytotoxic effects for some deeper-rooted shrubs and trees. Shallow-rooted plants within the surface 0.5 m of residential / topsoil material should not be affected. The issue is readily managed by replacement of soil around deeper rooted plants where treated fines or mixed treated fines were buried close to the surface.

• There is only limited information on placement of backfill in the buffer zone on the western foreshore. There is a clay bund along the foreshore which will provide a natural buffer between the backfill and the shoreline. However, there is no information on the width of this bund. It appears probable that the buffer zone requirements were not complied with on the western foreshore. The significance of this is commented on in Section 1.12.

5.8.5 FCC Landfill Fitness for Purpose

Given the compliance with the SACs, with the exception of some uncertainty with respect to the possibility of ammonia generation and phytotoxicity of copper in treated fines, the FCC Landfill site is fit for its intended purpose with respect to the soil remediation (but see separate discussion on groundwater in Section 7). 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 allowed to migrate to the marine environment or be disposed of inappropriately off site.

The uncertainty with respect to ammonia and copper are not human health issues for day to day use as open space. Carrying out further investigation to assess the risk from ammonia is not required. The potential risks from ammonia and copper during excavation or to plant health are readily managed by way of the Site Management Plan.

5.9 Residential Property Remediation

5.9.1 General

Four residential properties were remediated; 13, 15, 18 and 20 Tahi Street. The validation of the four residential properties was partly based on soil samples collected during the original characterisation investigation (GES, 2002). These soil samples were collected as vertical composites from the surface to 0.3 m depth and analysed for OCPs. The results were then compared directly with the SAC for compliance. Sampling over such a large depth range at the surface is not ideal as the peak concentrations are often found at the surface and the results could be ‘diluted’ by cleaner underlying soil. When assessing direct human exposure, a depth range of 0 – 0.075 is more commonly used in New Zealand (MfE, 2004a). For example, if it is conservatively assumed that all the contamination resided in the top 0.075 m of the characterisation (GES, 2002) samples, the actual surface samples could be up to 4 times higher than those reported i.e. by being diluted by the clean soil from 0.075 to 0.03 m depth. However, this potential flaw in sampling technique is not significant in terms of risk human health. Even if the reported concentrations are actually four times higher, the results will not be significantly elevated relative to human health criteria.

The SAC is based on potential effects on the local marine ecosystems via sediment runoff. However, even if the actual surface concentrations were slightly higher than indicated by the characterisation data, the overall effects are not likely to be significant. The potential for significant sediment runoff from the sites is relatively low as the properties make up a small proportion of the overall sediment ‘catchment’ for the local marine ecosystem.

5.9.2 13 Tahi Street

An area of DDX contamination along the northern boundary of 13 Tahi Street, adjacent to FCC East, was remediated and validated.

During the original characterisation (GES, 2002), 24 surface soil samples were collected from areas on this property not covered in building or hard-standing and analysed for OCPs. A further 13 samples were collected by TDC. Of the 37 samples, 17 had DDX concentrations exceeding the SAC of 5 mg/kg, ranging from just over 5 mg/kg up to 134 mg/kg. A single sample (6 mg/kg) had an ADL concentration above the SAC of 3 mg/kg. All other results were below the SACs.

The soil around the location with elevated OCP concentrations was excavated and the extents validated in line with the ‘residential’ protocol set out in Section 5.3. The excavation extended approximately 100 m along the northern boundary of the property and varied in width from about 12 m to 3 m. The depth of the excavation varied between about 1 and 1.5 m. A total of 48 validation samples were collected from the base and walls of the remedial excavation and analysed for OCPs. All samples returned OCP concentrations below the SACs.

A total of 22 samples were also analysed for TPH, ONP, OPP and VOCs. Four samples were analysed for 10% suite set out in Section 5.2 which included heavy metals, PAHs and PCBs. All non-OCP results were below the corresponding SAC. The only potential exceptions to this were two hot-water soluble boron results which that were unable to be interpreted due to a mistakenly high laboratory detection limit. The detection limit for these two samples was 30 mg/kg, ten times above the SAC of 3 mg/kg. The two other samples analysed for hot-water soluble boron had concentrations below 0.5 mg/kg. The potential information gap due to the high laboratory detection limit is not significant and the remaining two samples analysed for hot-water boron are considered representative.

The excavation was backfilled up to 0.15 m below surface with material from the residential stockpile and from 0.15 m depth to the surface with imported topsoil. The validation of these materials is discussed in Section 1.1.4.

Based on the information audited, we consider that the remediation has achieved compliance with the SACs at 13 Tahi Street.

5.9.3 15 Tahi Street

No remediation was required at 15 Tahi Street.

The validation of 15 Tahi Street is not reported in the Validation Report (SKM, 2008) as the characterisation sampling was completed in 2001, before the main remediation contract was awarded. The validation information relating to this property is contained in the characterisation report (GSE, 2002) and a report supplied by TDC (2002).

A total of seven surface soil samples were collected from areas not covered in building or hard-standing and analysed for OCPs. All samples complied with the relevant SAC. The DDX concentrations ranged from approximately 0.2 mg/kg to 4.3 mg/kg. No concentrations of ADL were measured above the laboratory detection limit of 0.1 mg/kg.

5.9.4 18 Tahi Street

A small area of DDX contamination was remediated and validated at the western end of 18 Tahi Street.

During the original characterisation (GSE, 2002), 18 surface soil samples were collected from areas not covered in building or hard-standing and analysed for OCPs. A sample close to the western property boundary returned a DDX concentration of 24 mg/kg, above the SAC of 5 mg/kg, but below the current human-health guideline of 28 mg/kg (MfE, 2006). All other results were below the relevant SACs.

According to the Validation Report (SKM, 2008), a total of nine validation samples were collected from the base and walls of the remedial excavation and analysed for OCPs. However, the extent of the excavation is not indicated in the report. The raw data in the validation spreadsheet indicates that the samples were from cells O9 and P9, in the south-west corner of property, that is adjacent to the initial exceedance. All samples returned concentrations below the SAC except for a single sample which returned a DDX concentration of 5.45 mg/kg, slightly above the SAC of 5 mg/kg. The ADL concentrations ranged from below laboratory detection limits up to 0.5 mg/kg. The slight exceedance of the 5 mg/kg SAC for DDX is not significant.

The EMS site records were also reviewed and these show that further sampling was undertaken across the western end of 18 Tahi Street. The data show two additional samples with DDX concentrations above the SAC of 5 mg/kg, up to 10 m away from the area of original contamination in the south-west corner. Both samples recorded DDX concentrations of 8 mg/kg and were located towards the northern property boundary in cells O9 and O10. The results are not discussed in the Validation Report. A diagram in the EMS site file appears to indicate that the area encompassing the two elevated results was excavated, although this could not be confirmed and no validation data for any such excavation could be found.

No samples were analysed for any of the contaminants in the 50% and 10% suites. However, this lack of information is not significant as there is no reason to suspect contamination of this type at the base of the excavations on this site.

It is assumed that the excavations were backfilled according to the protocol used elsewhere on the site i.e. up to 0.15 m below surface with material from the residential stockpile and from 0.15 m depth to the surface with imported topsoil. The validation of these materials is discussed in Section 1.1.4.

Based on the information reviewed there is some uncertainty with respect to the extent of the remediation. It is possible that soil with DDX concentrations of up to 8 mg/kg remains on the property. These potential exceedances are not significant as the DDX criterion of 5 mg/kg for residential site use relates to the sediment runoff exposure pathway and the average concentration in the surface soil is likely to be below the 5 mg/kg target. The possible SAC exceedances are not relevant to the human-health pathway.

5.9.4.1 20 Tahi Street

A small area of DDX contamination was remediated and validated near the centre of 20 Tahi Street¹⁶.

During the original characterisation (GSE, 2002), 10 surface soil samples were collected from areas not covered in building or hard-standing and analysed for OCPs. Three samples returned concentrations above the DDX SAC of 5 mg/kg, with concentrations of 5.1, 5.9 and 16.9 mg/kg. All other results were below the relevant SAC.

Additional sampling by TDC confirmed that the elevated concentrations were localised and an area of 5m by 2.3 m by 0.3 m depth was excavated to remove the contamination (TDC, 2002). Samples collected from the base and each wall of the remedial excavation had DDX concentrations ranging from 0.67 to 5.3 mg/kg. The slight exceedance of the 5 mg/kg SAC for DDX is not significant.

No samples were analysed for any of the contaminants in the 50% and 10% suites set out in Section 5.2. However, this lack of information is not significant as there is no reason to suspect a source for these contaminants on 20 Tahi Street.

Based on the information reviewed, we consider that the remediation has achieved compliance with the SACs at 20 Tahi Street.

5.9.5 Acceptability of Residential Property Remediation

The Validation Report concludes that the soil quality in the residential property sites meets the SACs. We concur with this conclusion.