As presented in Section 2, the potential risk for soil
and groundwater contamination at the project area is considered low. The potential contaminants associated
with oil storage and oil separation facilities are hydrocarbons. The soil and groundwater sampling under
this CAP aims to determine the present and/or extent of soil and groundwater
contamination within and around the oil storage and oil separation facilities.
The sampling locations
and depths are recommended based on the findings of the site appraisal and have
made reference to the guidelines on sampling and analysis recommended in the Guidance Notes.
The proposed site
investigation programme is described in the following and in Table 3.1a.
·
Six (6) boreholes (BH1 to BH6) shall be drilled to 2 m below the
groundwater level;
·
Sampling of soil for on-site investigation and screening using
photo-ionisation detector (PID) from sub-surface (around 0.5m) and every 1.0m
till end of drilling;
·
Three soil
samples shall be collected from each borehole to ascertain the vertical
distribution of any detected contamination ([1]).
It is proposed that samples be taken at from the unsaturated zone to
below the groundwater level (eg at between 0.5m to 1m bgl, at soil and
groundwater interface, at 1m below groundwater level) or where visual evidence
of contamination was observed;
·
All boreholes will be converted into six (6) temporary groundwater
monitoring wells to facilitate groundwater sampling;
·
One (1)
groundwater (GW) sample shall be collected from each monitoring well; and
·
Free-floating products in groundwater, if observed, will also be
collected for laboratory analysis.
Table 3.1a Proposed
Site Investigation Programme
|
Location |
Rationale |
Depth |
Monitoring
Well |
# Soil
Samples |
# GW
Samples |
|
Borehole/Monitoring
Well |
|
|
|
|
|
|
BH1 |
Located
up-gradient from the No. 4 oil tank |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
BH2 |
Located
down-gradient from the No. 4 oil tank |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
BH3 |
Located
up-gradient from the No. 5 oil tank |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
BH4 |
Located
down-gradient from the No. 5 oil tank |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
BH5 |
Located
up-gradient from the oil separator |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
BH6 |
Located
down-gradient from the oil separator |
2 m below Groundwater Level. |
1 |
3 |
1 |
|
(To be selected on Site) |
|
|
1
Duplicate Soil Sample |
1
Duplicate GW Sample |
|
|
Trip blank |
|
|
|
2 (water
samples) |
|
|
Equipment rinsate |
|
|
|
1 (water
sample) |
|
|
|
|
|
Total |
19 |
10 |
Figures 3.1a shows the proposed soil and groundwater
sampling locations.
With respect to the nature of the substance stored
and used at the project area (diesel oil) it is proposed that the soil and
groundwater samples collected will be analysed for BTEX (benzene, toluene,
ethylbenzene and xylene), TPH (total petroleum hydrocarbon) and polycyclic
aromatic hydrocarbon (PAHs).
Extra soil
samples will be collected during the site investigation and stored in the
laboratory for possible Toxic Characteristic Leaching
Procedure (TCLP) testing. The TCLP
tests will be conducted for the samples with pollutant concentrations exceeding
Dutch “B” guideline values.
A site utility
scan will be conducted prior to the commencement of any excavation/drilling. At each of the sampling locations, a
trial pit will be excavated to 1.2 m bgl.
Trial pits will be dug manually using hand tools and necessary concrete
breaking hand operated mechanical tools to ensure no interference with
underground utilities. Sampling
below trial pit levels, will be conducted using drilling rig. Drilling rigs, drilling equipment that
do not come in contact with samples and hand breakers will be steam cleaned
prior to mobilisation to the Site.
Prior to sampling, all sampling equipment and well materials will be
steam cleaned, scrubbed with a non-phosphate soap solution, washed with tap
water and rinsed with distilled water.
This procedure will be repeated after use at each sampling location to
avoid potential cross contamination, and between samples to ensure that any
contamination from the surface of the Site does not affect deeper substrata or
the groundwater.
In addition to
taking samples for analysis, the strata log will 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
will be recorded with a description of each sample such as grain size, colour,
and wetness. Extreme care will be
exercised when toxic gases or hazardous materials are suspected. Photographs will be taken during the
site investigation and for each sample.
The soil or
groundwater sampling will be undertaken following appropriate protocols so as
to minimise the potential for cross-contamination between sampling locations
and depths. The soil sampling
methodologies are based on methods developed by US Environmental Protection
Agency (US EPA), as outlined below.
Sampling
equipment used during the course of the site investigation programme will be
decontaminated using the following procedures:
·
Manual
washing and scrubbing with non-phosphate detergent;
·
Tap water
and distilled water rinse; and
·
Air drying.
Where available,
a steam cleaner or pressure washer will be used.
During the
sampling and decontamination activities, disposable latex gloves will be worn
to prevent transfer of contaminants from other sources. Any disposable equipment such as latex
gloves will be disposed of as general waste after each use. Provisions will be made to containerise
any decontamination fluids, although the volume of fluids to be produced is
expected to be low.
Soil samples will
be taken by ERM staff and placed into appropriate clean glass bottles or
sampling containers (provided by the laboratory) immediately after
collection. Before sampling
commences, the laboratory will be consulted on the particular sample size and
preservation procedures that are necessary for each chemical analyses. The sample containers will be
laboratory cleaned, made of glass or other suitable materials with aluminium or
teflon-lined lids, so that the container surface will not react with the sample
or adsorb contaminants. The
containers will be labelled with the sampling location codes and the depths at
which the samples are taken. They
will then be transferred to an icebox or cooler container. Samples will be kept between 0 to 4°C but not frozen.
Groundwater, if
encountered, will be sampled from the monitoring wells using disposable teflon
bailers.
Samples will be
dispatched to the analytical laboratory for analysis as soon as practicable
following sampling. All samples
will be handled under chain of custody protocols and relinquished to the laboratory
representative at the Site or at a location specified by the laboratory.
The parameters as
described in Section 3.2 will be
analysed using the methods stated in Table
3.4a.
Table 3.4a Analytical
Methods for Contaminants in Soil and Groundwater Samples
|
Contaminant |
Analytical Methods |
|
BTEX
(benzene, toluene, ethylbenzene, xylene) |
·
US EPA Method 8260 |
|
TPH PAH |
·
US EPA 8260 & 8015 ·
US EPA Method 8260 |
|
TCLP |
·
EPA SW-846 (Method 1311) |
Samples collected
should be representative of field conditions. At each sampling location, soil (and groundwater, if
encountered) samples will be collected using pre-cleaned sampling equipment. All sample containers will be provided
by the contracted laboratory who guarantees their sterilisation and
preservative contents.
Appropriate QC/QA
samples will also be collected during the field investigation, including:
·
Equipment
(rinsate) blank for the full suit of target parameters, in order to assess the
adequacy of the decontamination procedures;
·
Trip blank
for the full suit of target parameters in order to assess the potential
contamination of the sample handling and transportation processes; and
·
Groundwater
and soil duplicates for the full suite of analyses to assess the precision of
the procedures.
Precision will be
calculated as the relative percent difference (RPD) between the original sample
and the blind duplicate. For water
and soil, the acceptance criteria for precision are 20% RPD and 30% RPD, respectively. Accuracy will be assessed by analysis
of blank samples to ensure that no bias is present in the analytical data.
Analysis of
samples will be carried out by an appropriate, HOKLAS-certified (or other
equivalent scheme approved by the EPD) analytical laboratory. The laboratory should maintain high
standards of analytical and technical services for the detection of trace
organic contaminants. All analysis
will be conducted according to standard procedures set by the US EPA, along
with internal QC/QA procedures.