Detailed Site Investigation – Complex Industrial Site, Christchurch
A contaminated site investigation of the majority of the site, including areas proposed for future development and the accessway/carpark area confirmed the occurrence of historical fellmongery, rubber products storage, transport operations depot and warehousing activity on the site.
It also confirmed:
- The presence of up to 1m of fill material in the SW corner of the site, including some waste materials (e.g. wood, steel, rubber, plastic, etc.) and subsoils with elevated TPH (hydrocarbon) concentrations.
- The presence of a 4,500L underground fuel storage tank (UST), containing about 800L of weathered diesel. Fraser Thomas subsequently observed the removal of this UST and associated soil sampling, with these results being included in the contamination report.
- The location of historical short term oil re-refining operations, with soil sampling confirming that any contamination associated with this area appears to have been remediated.
- The location of a small historic coal bunker behind building E.
Soil sampling from around the site confirmed that concentrations of heavy metals and mercury are all within relevant guidelines for commercial/industrial sites and also comply with the Burwood disposal site waste acceptance criteria, except for an isolated elevated lead reading in testpit 18 at 200-600mm depth. If soil in this area was excavated and mixed together, the lead concentration would be reduced to acceptable levels for disposal off-site to Burwood.
Soil sampling did detect TPHs present in many locations around the site, particularly in the SW corner of the site (testpits 5, 8, 11 and 23). Additional analysis for PAHs were conducted on these samples but no exceedances were found.
Groundwater is considered unlikely to be impacted by the contaminants found in site soils. A minor rainbow sheen was noted in the shallow groundwater in the UST pit during its removal. However, this sheen is considered to be localised and no signs of any similar sheen or hydrocarbon contamination were observed in the downgradient testpit 18, where groundwater was also encountered.
Prior to undertaking the proposed development works, it is recommended that some additional geotechnical testpits should be undertaken of the identified fill area in the SW corner, in order to determine appropriate parameters for pavement design for the proposed turning circle area which will cater for heavy vehicles. This testpitting should also check the presence and abundance of waste material in this area.
- Preliminary site investigation
- Detailed site investigation
- UST removal and validation