3. SITE INVESTIGATION

3.3 Sampling Method

Samples can be taken using the following two methods in order of preference:

i) Boreholes

Boreholes are widely used when sampling to depths of greater than 3 metres or when disruption to a site must be minimised. Whenever possible, thin-walled volumetric (Shelby Tube) samplers or split-barrel drive samplers should be used to collect undisturbed soil samples. Surface samples may be taken using hand tools such as stainless steel scoops and hand cores.

ii) Trial pits

Trial pits may be used for depths of up to about 2-3 metres. The advantage of trial pits is that investigators can see the ground beneath the surface. A disadvantage is that cross-contamination can easily occur.

When sitting trial pits or boreholes, care should be taken to avoid underground services.

Groundwater can be sampled from boreholes or trial pits using a teflon bailer attached with rope. In addition to taking samples for analysis, the strata log should be recorded. This includes recording the general structure of the ground and the depth and thickness of each band of material. The depths at which samples are taken should be recorded with a description of each sample such as grain size, colour, wetness. Extreme care should be exercised when toxic gases or other hazardous materials are encountered. The presence of foreign materials such as metals, wood and plastics should also be recorded. If trial pits are used, photographic records should be taken.