Example 1An underground storage tank (UST) for petrol was suspected to have been present at the XYZ Enterprises Site. The UST was not able to be located from a visual inspection of the site (e.g. looking for old vents, old concrete, pump, pads etc.). A digger was used to excavate an area where the UST was thought to have been located. Test pits were logged. The UST was not located but the soil had a distinctive hydrocarbon odour. Soil samples XYZ-TP1/S1 and S2 were taken at a depth of 1.0m and 1.5m respectively and were analysed for total petroleum hydrocarbons (TPH) and BTEX. The results (mg/kg dry weight) were as follows:
The TPH analysis confirms a predominance of short-chain hydrocarbons consistent with petrol contamination. Human Health GuidelinesThe average concentration of benzene is 12mg/kg. This exceeds the Soil Acceptance Criteria for commercial/industrial uses compared to the MfE Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand (refer Table 4.11). At a first glance this assessment would indicate that this part of the site is unsuitable for commercial or industrial use. However, an analysis of the criteria indicates that the limiting exposure pathway (from which the criteria for benzene was derived) was for inhalation exposure indoors, through volatilisation of benzene in the soil. (refer to Table 4.17 of the guidelines - inhalation pathway for commercial uses, sandy silt soils). The guideline value for benzene indoors is 3.6mg/kg (at <1m depth) and 7.2mg/kg (from 1-4m depth). In contrast the relevant criteria for outdoor exposure through inhalation are 480 and 530 mg/kg respectively. The samples were taken from a site that does not contain a building and the site owner has no plans to construct on this part of the site. Therefore the limiting pathway at the time of the assessment is not complete and the indoor values are not necessarily appropriate in this particular instance. Knowing this information, the site owner may make different Risk Management Decisions regarding petroleum contamination of the site. In this example, there are few New Zealand guidelines that assess on-site ecological exposure to contaminants. The assessor may need to choose from a range of international guidelines and studies with little information on how accurately these values may reflect NZ conditions. A summary table has been prepared to assist identifying appropriate guideline values for soils. Example 2Soil samples XYZ-1 – XYZ-6 were taken for analysis of metals for an area suspected of metals contamination. Average results are presented below.
1 Guidelines for Timber Treatment Chemicals: 1997. The results show that ecological guideline values for soil are exceeded for copper, chromium and zinc. Further work analysing Cr VI specifically would be needed to check whether the concentrations measured are of concern, as Cr VI has a greater toxicity than Cr III. The assessment indicates that average concentrations of copper and zinc exceed guideline values only in the shallow soils. Example 3Many site investigations start by focussing on soil contamination for human health and safety reasons. However in New Zealand in particular, some of the key ecological receptors are likely to be found in nearby surface waters. In the absence of water quality data, one method that can be used to gauge the magnitude of exposure of surface water receptors to is to look at what dose could be delivered to surface water if some or all of the soil contaminants were routed to surface water. For example, soil contamination for copper, chrome, arsenic and boron at XYZ Enterprises was assessed as within guideline values for the protection of human health and safety at industrial sites. However, the migration of these contaminants to surface water may still present a risk to aquatic receptors. If we assume that 100% of each of these contaminants is routed to the river (i.e. all of the contaminant is dissolved in stormwater or groundwater and discharges to the river), would the concentration of each contaminant exceed water quality guidelines for the protection of aquatic organisms? To answer this question you need to establish several very arbitrary factors:
Cu = 400mg/kg = 576 kg Cu Cr = 251mg/kg = 361.4 kg Cr As = 217mg/kg = 312.5 kg As B = 1,900mg/kg = 2,736 kg The river has a mean flow of 2,400l/s, which equates to flow of 207,360m3/day. Therefore, the resulting concentration of each contaminant is:
These figures indicate that copper and chrome would exceed ANZECC and MfE/MoH guideline values for the protection of aquatic ecosystems. This calculation is obviously extremely simplistic and conservative, but it does indicate that there is the potential for contaminants to perhaps have effects on aquatic biota in the river and should serve as a trigger for additional investigation. These results also indicate that with the exception of boron, the source mass of the contamination is limited. Example 4Exposure to physical effectsThroughout the literature review for this site, and within this example, we have focussed almost exclusively to effects posed by toxicants. However, other factors should not be overlooked. For example, on-site workers could be exposed to significant levels of noise, or to other physical risks. Aquatic biota could be more greatly affected by elevated water temperature or physical conditions in the stream or river that are not associated with contaminants. These effects could mask, exacerbate or mitigate the effects of any exposure of identified receptors to the contaminants of concern. XYZ Enterprises had a dump located on the banks of the river, in an area of the site that is poorly fenced and allows access or direct exposure of workers or unauthorised visitors to sharp material on the surface of the dump. The magnitude and significance of these types of exposures should not be overlooked when considering Risk Management Decisions.
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