The degree of integration of geotechnical investigations with other studies (such as contamination or archaeological investigations) is based on the findings of the desk study and field reconnaissance.
It is important that appropriate expertise is applied to the design and execution of integrated investigations and that those involved do not go knowingly or otherwise beyond their expert capability.
Any integrated field investigation needs to be designed so that it does not compromise the requirements of any aspect of the integrated investigation.
Integrated geotechnical, contamination and ground gas investigations are the most common form of integrated investigations. However, linking the field investigation with other types of studies can also be appropriate in some circumstances. In particular, the ecological survey of a site and surrounding area could indicate contamination on the basis of observed impacts on flora.
Geotechnical, archaeological and contamination investigations can share information from geophysical survey work (see Section 5 and BS 10175).
Whilst the primary guidance on the investigation of potentially contaminated sites is provided in BS 10175, and on investigations for ground gas in BS 8576, it is important to recognize that these in turn refer to a number of standards in the BS ISO 10381 series (to be replaced by the BS ISO 18400 series, in preparation).
NOTE BS ISO 18400-102, which is to replace BS ISO 10381-2, is intended to provide guidance on the selection and application of sampling techniques for soil quality investigations (it covers agricultural and near-natural sites as well as potentially contaminated sites). It is intended to complement and be consistent with BS EN ISO 22475-1 as appropriate although the terminology and approach inevitably differ somewhat given the different contexts in which they are intended to be used.
G.2 Integrated contamination and geotechnical investigations
Integrated contamination and geotechnical investigations have the following advantages (which result in lower costs compared to undertaking separate field investigations):
- a) simplified project management;
- b) common use of equipment and procedures;
- c) exploratory holes can be used for more than one purpose;
- d) joint health and safety procedures can be established;
- e) joint environmental protection procedures can be established;
- f) integrated consideration of resultant data; and
- g) reduced project duration (compared to sequential contamination and geotechnical investigations).
As noted in G.1, any integrated field investigation needs to be designed so that it does not compromise the requirements of the various aspects of the investigation.
Geotechnical specialists involved in the design and execution of integrated contamination and geotechnical investigations need to be aware of both the different contexts in which contamination investigations often take place and the important differences in technical approaches, which, if not properly understood, could lead to poorly designed and executed investigations, intervention by regulators, and additional costs and liabilities for the client. Important differences include:
- whilst sharing many requirements, the two desk studies and site inspections do require different types of information and different expertise to be applied to the examination and synthesis of the information so as to form appropriate initial hypotheses about the nature and possible location of key physical, geotechnical and contamination features (i.e. conceptual site models and ground models);
- contamination investigations are often the subject of regulatory scrutiny and reports are often in the public domain; and
- the requirements for sampling (e.g. number of sampling locations, number of samples from each location and types of samples to be taken as well as sampling protocols) are usually markedly different from those for geotechnical investigations.
Both contamination and geotechnical investigations can be required in order to discharge conditions attached to Planning Permissions. Regarding geotechnical issues these usually relate to potential unacceptable risks from features such as: historical mining, karst and slope instability. In these cases, investigations for both contamination and geotechnical both follow similar procedures and discharging conditions often require staged written approvals by the local planning authority (LPA) as the work progresses. For example, approval of:
- a preliminary investigation (desk study, field reconnaissance and preliminary risk assessment) report;
- the design of a planned intrusive investigation;
- the report on the intrusive investigation and interpretation of results including a more detailed risk assessment;
- where risks are considered unacceptable, a proposed remediation scheme; and
- a verification report once remediation is completed.
Reports are consequently subject to careful scrutiny and are likely to be posted on the LPA's website or otherwise made available to the public. In many instances, the LPA consult the Environment Agency (or equivalents) before making a decision about the acceptability of a report or proposal. BS 10175 recommends that any conditions or similar formal requirements are provided in reports together with any key correspondence with regulators.
If, for any reason, a planning application is refused and the client appeals, any information or opinion regarding the contamination aspects of the site might have to be defended in public or at least before the Planning Inspector at an informal hearing. Those carrying out such work, therefore, need be confident that they can justify their claim to expertise.
Guidance on desk studies and field reconnaissance is provided in Section 2 of this British Standard and in BS 10175.
Combining the desk studies and field reconnaissance for the two aspects of the investigation can provide significant savings in cost and help to provide a better informed initial conceptual model as a result of the two areas of expertise being brought to bear. It is essential if this work is carried out by a single person, that they have the requisite expertise and experience. If there is any doubt whether the person carrying out the field reconnaissance is properly able to address both contamination and geotechnical aspects then it would be better carried out by two appropriately experienced people, who can inform and consult each other.
A geotechnical investigation in which a few incidental samples have been taken does not form a sound basis for assessing contamination on a site although they might provide some useful information.
Guidance on sampling for contamination is provided in BS 10175. Particular attention is to be paid to the guidance regarding sampling depths and the need for a systematic approach. Failure to take enough samples of the right type in the various zones of the site and then to carry out appropriate analysis and testing can result in a report being rejected by a regulator.
Guidance is also given in BS 10175 on the proper choice of sampling containers for samples for chemical analysis and on such issues as packaging, preservation and transport. Failure to observe good practice could lead to loss of the integrity of the samples including, for example, chemical or microbial degradation of contaminants and loss of volatile organic compounds (VOCs).
Analytical strategies need to be developed with care, taking into account the history of the site. Failure to do so can not only lead to rejection of a report by the regulator because key potential contaminants have not been considered, but can also result in unnecessary additional cost and time. General suites of determinands embracing a wide range of possible contaminants cannot be specified unless this can be justified on technical grounds. It can mean that the analysis of each sample is unnecessarily expensive inducing pressure to reduce the number of samples analysed to contain costs. It is better to analyse more samples for a carefully chosen set of determinands than a few samples for a wide range of potential contaminants, some of which are highly unlikely to be present. However, where more than one phase of intrusive investigation is considered likely, a broader "screening" process might be beneficial in the initial stage so as to better inform the detailed design of the subsequent investigation and analytical stage. Proving a site "clean enough" for a specific purpose can demand much more sampling and analysis than that needed to show the converse situation.
NOTE 1 Characteristics of investigations for contamination carried out by poorly informed geotechnical specialists often include: too few sampling locations, insufficient samples being taken from each location with those taken appearing to have been taken at random depths from different holes, absence of data on surface and near-surface soil.
NOTE 2 The analytical methods employed in suites for wide ranges of contaminants might not be as accurate or precise as those employed for discrete determinands or types of determinands, e.g. determinations of speciated polycyclic aromatic hydrocarbons (PAHs) by GC MS tend to be more accurate than those determined as part of a SVOC (semi volatile organic compounds) suite.
G.3 Integrated geotechnical, groundwater and ground gas investigations
BS 10175 provides guidance on investigations of the water environment during investigations of potentially contaminated sites and BS 8576 provides guidance on ground gas (permanent gases and VOCs) investigations on all types of site.
The formation of boreholes for geotechnical purposes offers the opportunity to install gas, groundwater or combined ground gas and groundwater monitoring wells, with possible reductions in overall costs and possibly time savings for the overall investigations. However, whilst installation of monitoring wells on an ad-hoc basis can be simple, any detailed investigation might require the approval of regulators in advance and the results are often placed in the public domain. All the strictures regarding combined geotechnical and contamination investigations apply, e.g. the need for employment of appropriate expertise in the design and implementation of the integrated investigation and the need for the objectives of the two types of investigation not to be compromised.
Wells installed in geotechnical boreholes provide an opportunity to obtain data on groundwater quality but are not necessarily located where contamination is most likely. Also they might not be located so as to enable the direction of groundwater flow, and its gradient, to be determined. Thus, except when data is being collected on an ad-hoc basis, integrated investigations are likely to require formation of boreholes additional to those required for geotechnical purposes. Similarly, detailed investigations for ground gas are likely to require formation of additional boreholes.
NOTE Although it is frequently possible to use a single well for monitoring both groundwater quality and for ground gas, such wells are seldom suitable when carrying out detailed surveys for VOCs (see BS 8576).