3. SITE INVESTIGATION

3.2 Sampling Strategy

3.2.1 Choice of Parameters

The first step in planning for a site investigation is to determine the parameters for chemical analysis. The site history assessment and the 'walkabout' conducted during the initial site appraisal stage would have identified those activities likely to cause contamination at the site. The checklist given in Annex B is designed to assist the reader to identify possible contaminants and their respective waste disposal practices. This information should be taken into account in designing the site investigation.

Reference should be made to Table 3.1 and 3.2 on the parameters to be analysed. Additional parameters may be required, if there is any suspected presence of unlisted contaminants. On the other hand, some of the contaminant groups may be excluded from the testing regime if justified by the characteristics and history of individual sites.

The analyses should be conducted in accordance with international standard methods wherever practicable. It is necessary to employ an accredited laboratory to undertake the analyses. Where the potentially contaminated site area is large, suitable on-site screening tests could be conducted initially to identify the parameters of major concern for subsequent laboratory analyses.

Table 3.1 Petrol Filling Stations and Vehicle Repairing/Dismantling Workshops :
Main Groups of Contaminants and their Probable Locations

Contaminants		Locations
Main Group	Individual Contaminants	Fuelling Areas	Servicing Areas	Paint Shop
Metal Contaminants	Iead
	chromium	-		-
	zinc	-	-
	copper	-		-
Organic Contaminants	simple aromatics e.g. benzene, toluene, ethylbenzene, xylene			-
	non-halogenated solvents	-
	halogenated solvents	-
	polyaromatic hydrocarbons	-		-
	fuels/oils (Total petroleum hydrocarbons)			-
Asbestos	-	-		-

Table 3.2 Boat Building, Repairing and Breaking Activities and their Associated Contaminants

Site Feature/ Activity	Process Areas			Temporary Chemicals or Waste Storage	Waste Disposal
Chemical Group/ Material	Coating/ Steel Treatment	Fitting Out/ Repair	Breaking
Metals
Cyanides		-	-
Organic solvents/ thinners			-
Biocides
PCBs	-	-	-	-	-
Oily sludges
Fuel/ lubricating oils	-
Asbestos	-

Site Feature/ Activity	Process Pipework/ Pump	Drainage System and Soakaway System	Fuel Storage/ Pipework	Electrical Transformer Area
Chemical Group/ Material
Metals	-	-	-	-
Cyanides	-		-	-
Organic solvents/ thinners			-	-
Biocides	-		-	-
PCBs	-	-	-
Oily sludges				-
Fuel/ lubricating oils				-
Asbestos		-	-	-

3.2.2 Sampling Point Location

The sampling points should be located in a grid pattern to provide a good representation of the extent and nature of contamination. Extra sampling points should be located at or near potential source of contamination e.g. underneath storage tanks or near the underground pipelines. Where there are more than one storage tank present in a sampling grid, one sampling point per tank (at a minimum of 2 to 3 depths) should be taken within the grid. The sampling point for each tank should be placed at a groundwater downgradient position of the tank so that any floating product may be detected. It may be necessary to locate additional sampling points in areas suspected to be or identified as heavily contaminated during the preliminary site assessment.

3.2.3 Number of Sampling Points

The number of sampling points will depend on the size of the site and the number of potential sources of contamination. The minimum number of sampling points necessary for a site investigation is shown in Table 3.3. The greater the number of sampling points, the greater the degree of confidence for all contaminant 'hot spots' to be identified.

Table 3.3 Minimum Number of Sampling Points

* Subject to agreement with EPD.(see Table 2.3)
** To be agreed with EPD.

3.2.4 Depth of Sampling

In general, the concentration of contaminants varies both horizontally and vertically. A minimum of 3 samples per sampling point should be taken to ascertain the vertical distribution of contaminants. Groundwater sample should also be taken for analysis if it is encountered during sampling. For the contaminants which are relatively mobile, e.g. petroleum hydrocarbons or solvents, it is advisable to take soil samples at various depths from the unsaturated zone to below the groundwater level. Furthermore, samples should be taken to the full depth of excavations or structures that will be required during redevelopment of the site. If underground storage facilities are located at the site, samples should be taken at a minimum of 2 to 3 depths from the bottom of the tank or the storage device.

3.2.5 Contamination Assessment Plan

Before commencement of a land contamination investigation, the project proponent will need to submit a Contamination Assessment Plan (CAP) to EPD for endorsement. A CAP generally includes an introduction, description of site history such as the activities engaged, length of operation, inventory of chemicals and hazardous substances handled, proposed sampling plan and parameters to be analysed.