Compiled Reference Documents - OPW25/0053 (As Published)

    About this Report
                                                                                           November 2023



Introduction                                               the time of construction as are indicated
These notes have been provided to amplify                  in the report; and
DP's report in regard to classification methods,
field procedures and the comments section.            •    The use of water or mud as a drilling fluid
Not all are necessarily relevant to all reports.           will mask any groundwater inflow. Water
DP's reports are based on information gained               has to be blown out of the hole and
from limited subsurface excavations and                    drilling mud must first be washed out of
sampling, supplemented by knowledge of                     the hole if water measurements are to be
local geology and experience. For this reason,             made.
they must be regarded as interpretive rather
than factual documents, limited to some               More reliable measurements can be made by
extent by the scope of information on which           installing standpipes which are read at
they rely.                                            intervals over several days, or perhaps weeks
                                                      for low permeability soils. Piezometers, sealed
Copyright                                             in a particular stratum, may be advisable in low
This report is the property of Douglas Partners       permeability soils or where there may be
Pty Ltd. The report may only be used for the          interference from a perched water table.
purpose for which it was commissioned and in
accordance       with   the     Conditions   of       Reports
Engagement for the commission supplied at             The report has been prepared by qualified
the time of proposal. Unauthorised use of this        personnel, is based on the information
report in any form whatsoever is prohibited.          obtained from field and laboratory testing, and
                                                      has been undertaken to current engineering
Borehole and Test Pit Logs                            standards of interpretation and analysis.
The borehole and test pit logs presented in this      Where the report has been prepared for a
report are an engineering and/or geological           specific design proposal, the information and
interpretation of the subsurface conditions,          interpretation may not be relevant if the
and their reliability will depend to some extent      design proposal is changed. If this happens,
on frequency of sampling and the method of            DP will be pleased to review the report and the
drilling or excavation.       Ideally, continuous     sufficiency of the investigation work.
undisturbed sampling or core drilling will
provide the most reliable assessment, but this        Every care is taken with the report as it relates
is not always practicable or possible to justify      to interpretation of subsurface conditions,
on economic grounds.            In any case the       discussion of geotechnical and environmental
boreholes and test pits represent only a very         aspects,     and     recommendations           or
small sample of the total subsurface profile.         suggestions for design and construction.
                                                      However, DP cannot always anticipate or
Interpretation of the information and its             assume responsibility for:
application to design and construction should
therefore take into account the spacing of            •    Unexpected     variations  in    ground
boreholes or pits, the frequency of sampling,              conditions. The potential for this will
and the possibility of other than 'straight line'          depend partly on borehole or pit spacing
variations between the test locations.                     and sampling frequency;
Groundwater                                           •    Changes in policy or interpretations of
Where groundwater levels are measured in
boreholes there are several potential                      policy by statutory authorities; or
problems, namely:                                     •    The actions of contractors responding to
•       In low permeability soils groundwater              commercial pressures.
        may enter the hole very slowly or perhaps     If these occur, DP will be pleased to assist with
        not at all during the time the hole is left   investigations or advice to resolve the matter.
        open;

•       A localised, perched water table may lead
        to an erroneous indication of the true
        water table;                                               continued next page

•       Water table levels will vary from time to
        time with seasons or recent weather
        changes. They may not be the same at


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