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9.0 Recommendations

A variety of uncertainties or gaps in information have been described in this audit. In general, these uncertainties are not sufficient to greatly reduce confidence in the results of the remediation. However, carrying out the recommendations below will provide an additional measure of confidence or reduce the need to manage residual risks. Other recommendations are to provide a benchmark to assess future natural improvements in the site’s condition.

  1. Undertake a similar programme of QA/QC soil sampling in FCC West to that completed on FCC East. The sampling should target the residential backfill material and the primary laboratory should use the same analytical techniques (and detection limits) used for routine testing during the remediation. The sampling is to address a QA/QC information gap with respect to detection limits for DDX and inter-laboratory comparisons at concentrations close to the DDX residential SAC.

  2. A programme of soil gas sampling and analysis should be carried out for ammonia gas 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 and whether further testing at specific building locations may be required at the time of development. If a potential risk is found, the Site Management Plan should be updated to ensure adequate procedures are in place for excavation workers, including 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.

    The soil gas sampling could be carried out in the near future to eliminate the current uncertainty or, alternatively, the Site Management Plan could be updated on the assumption a risk exists and soil gas sampling carried out on a case-by-case basis prior to the design and construction of future building developments.

  3. Additional groundwater monitoring wells should be installed as follows:
    • at least one upgradient well in the vicinity of the northwest corner of the site to obtain background;
    • a well midway along the western boundary of FCC West;
    • a well in the south-east corner of FCC West;
    • a well in the former vicinity of the MCD plant;
    • a well roughly at the midpoint of the south-western quadrant of FCC West;
    • two wells spaced out along the western boundary of FCC East;
    • two wells spaced out along a line running north-south midway across FCC-East;
    • a well in the vicinity of the former surge chamber location where there is a gap in the clay bund; and
    • ideally, wells either side of the clay bund installed on the eastern boundary of the FCC Landfill site.

  4. The additional wells and the following current wells should be included in a groundwater monitoring programme: BH1A, BH2A, BH5A, BH9A, Old BH1, BHH, BHG, BHD and 13 Tahi Street. The wells should be monitored for the same set of parameters measured in the current TDC monitoring (including groundwater elevation). The wells should be monitored on a quarterly basis for one year, with the monitoring frequency and number of wells monitored reviewed after that time. It is expected that a subset of wells would continue to be monitored for water quality but that all wells should continue to be monitored for water level. The monitoring should include appropriate QA/QC procedures. A selection of wells should be tested for hydraulic conductivity, to represent a range of backfill materials across the site.

  5. The groundwater monitoring data should be used to update the hydrogeological model for the site, with a particular focus on groundwater flow direction and estimates of mass flux of contaminants discharging to the marine environment. As part of the assessment, a water balance should be developed for the site under existing and potential future conditions. A review of the Site Management Plan may be required following update of the hydrogeological model.

  6. Prior to undertaking the next sediment and snail monitoring round, an appropriately qualified person should review the monitoring programme to confirm that the current programme is sufficient and appropriate given the altered habitat and different species that have re-colonised FCC East. The review should assess the previous reports on the subject, including that by Landcare Research (2002) and take into account recent monitoring data and the likely site use. Consideration should be given to the need for confirmatory sampling of other biota and extending the programme to improve its statistical robustness. The review should also consider whether the sampling is properly representing the quality of the surface sediments.

  7. Sediment monitoring should be undertaken as follows (taking into account any recommendations from the review in Item 9):

    • the annual monitoring frequency should be continued, with the monitoring scope reviewed after two additional monitoring rounds;
    • in addition to the current monitoring locations the following sediment sampling locations should be considered:
      • three additional locations parallel to the western foreshore, approximately 20 m from the foreshore edge. The locations should be evenly spaced along the foreshore;
      • two additional locations parallel to the eastern foreshore, approximately 5 m from the base of the sea wall. The locations should be evenly spaced between the current sampling transect and either end of the foreshore; and
      • three surface samples of the creek-bed sediment, evenly spaced along the portion of the creek adjacent to the site boundary.
    • at each sediment sampling location, samples from 0 – 0.02 m and from 0.02 – 0.10 m should be collected. A sediment corer with a core extruder should be used to ensure accurate sample depths. Each sample should be analysed for DDX and ADL;
    • the snail sampling should continue as previously, unless otherwise indicated by the review on biota sampling outlined above;
    • total organic carbon (TOC) should be measured in each sediment sample in the first monitoring round;
    • a particle size distribution should be undertaken on 50% of the sediment samples in the first monitoring round;
    • detailed field and photographic records should be kept of all observations, e.g. sediment colour, number/size of snails; and
    • a written and photographic record should be maintained of areas of algal growth. The photos should be taken from the same perspective to enable comparison between monitoring events.

  8. A check should be made that flood flows in the creek are not likely to be so high as to cause significant erosion.

  9. Benchmarking of the health and diversity of the marine ecosystem on the foreshores should be carried out, comparing the foreshore against suitable control sites. There are a number of survey techniques which can be used to assess ecosystem health and bio-diversity.

Carrying out the above recommendations will enable decisions on whether the local foreshore effects are acceptable relative to the likely large cost and environmental disruption of attempting further remediation.

Consideration could also be given to the additional recommendations set out below to further benchmark conditions and provide a means of comparison with future monitoring:

  1. Sampling the groundwater seeps on both the western and eastern foreshores and testing for a similar set of parameters to the groundwater samples. Care would be required to ensure that the samples are representative of groundwater and not contaminated with beach sediment. An alternative to sampling the seeps directly could be installing standpipes on the foreshore to target shallow groundwater immediately before it discharges. Quarterly sampling for one year (at the same time as the groundwater sampling is completed) would be appropriate.

  2. Additional sampling of marine water, both close to the site and further afield, to assess the actual concentrations within the Mapua Channel and Waimea Inlet.

 

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