Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 4/10)
Character Range: 155827–158499

m depth shortly after the depot was decommissioned. For the past 15 years the site has been used for storage of motor vehicles and agricultural equipment.
Response
A PSI was carried out and an initial CSM developed. The site has been investigated (including the 'clean' fill) according to an appropriate SAQP informed by the CSM. A source of contamination has been identified in the unsaturated zone which has an associated contaminated groundwater plume. Depth to groundwater is approximately 6 m. Soil and groundwater samples have been analysed for TRH fractions, BTEX, PAHs and lead.
It can be assumed for the purpose of this case study that the maximum slab width for the proposed residential dwellings is less than 15 m.
Summary of site contamination
    * A preliminary screening step (refer Section 9.2.1 of Schedule B2) has determined that an assessment of potential vapour intrusion risks is necessary as receptors (residents of houses) are to be located within 30 m of an identified volatile source.
    * The HSL assumptions and limitations were checked with the aid of the HSL checklist (ASC NEPM Toolbox) and the HSLs confirmed to be applicable for the site-specific conditions.
    * BTEX and naphthalene were subtracted from TRH fractions C6 – C10 and >C10 – C16 to obtain F1 and F2 respectively.
    * Fill layer 0–2 m below ground level – 95% UCL for all the identified contaminants of concern was less than the appropriate investigation and screening levels.
    * Soil Type: The borelogs indicate silt and silty clay,  predominant soil type determined to be silt (the HSLs for silt are more conservative than those for clay).
    * The geometric mean (GM) for TRH and BTEX in soil for 2–4 m is tabulated below.
    * All individual soil results are less than 2.5x the relevant investigation and screening levels; hotspots, if present, would need to be considered separately.
    * No contamination of concern was found below 4 m in soil.
    * Poor quality groundwater was found at 6 m in three wells MW1, MW2, MW3 (saline, TDS >5000 mg/L, low yield <2 L/sec)
    * The maximum concentrations (based on quarterly monitoring results carried out over one year) for TRH and BTEX in groundwater are listed below.
    * Soil vapour oxygen measurements of 910% were measured at 1 m depth at five locations above the soil source.

Step 1: Document results and select relevant soil and groundwater HSLs
Soil GM values mg/kg, refer Table 1A(3) for soil HSLs (silt, 2<4 m)
         F1   F2   F3    F4   B    T   E   X
Soil GM  130  160  1100  260  1.5  80  70  60
HSL A    100  NL   N/A   N/A  1.0  NL  NL  NL

Notes
   NL indicates the HSL is not limiting (see