Deleterious Materials – Good Practice in Use and Specification

Article Contaminated Land Loss Prevention by

Written by Hugh Mallett, Chair of the AGS Loss Prevention Working Group

Introduction
Despite the publication of the British Council of Offices “Good Practice Guidance in the selection of construction materials (Ref 1) we are still seeing some contracts in which clauses prohibit the use of “deleterious materials”. Typically, these clauses will then provide a list of prohibited materials, which usually includes asbestos.

This can cause particular issues when the earthworks on a site include the re-use of Made Ground (Fill). Typically analysis of this material on most sites in the UK will indicate that some samples of that material include asbestos containing materials. With an improved screening test (since about 2010) asbestos is often being detected in a proportion of samples of Made Ground at a large majority of sites. Typically the analyst reports that for samples subject to screening, whether or not any of the three main types of asbestos (amosite, chrysotile and crocidolite) are “detected” or “not detected”. Further testing to quantify the amount of asbestos in the soil sample may often then reveal that a proportion of samples where asbestos was detected, the quantity of is <0.001% (the limit of quantification). Such a material would now fail to comply with a clause that prohibits the presence of “any deleterious materials”.

Good Practice
As long ago as 1997, the BRE (Ref 2) and the BCO (Ref 3) published advice promoting a change in the practice of including lists of excluded materials in contract documentation. Those documents encouraged a change in emphasis from the exclusion of materials to ensuring good practice in their selection. Accordingly it became more common for contract documents to refrain from including exhaustive lists of prohibited materials, instead referring to the BCO and BRE reports, such as that presented below.

Prohibited Materials means any materials:
(a) which by their nature or application contravene any relevant British Standard or EU equivalent
(b) which contravene the recommendations of the British Council for Offices’ publication Good Practice in the Selection of Construction Materials (2011) or
(c) which are generally considered to be deleterious within the building design professions in the UK at the time of specification or approval;

And

The Consultant further warrants to the Client that it has not specified for use and will use the standard of skill and care provided for in clause 3.1 not to specify for use and will use such reasonable skill and care consistent with the supervisory and inspection responsibilities to be undertaken as part of the Services to see that there shall not be used in the Works any materials which at the time of specification or use (as the case may be):
are known to be deleterious when used in the manner in which they are to be used (either to health and safety or to the durability of the Works); or
contravene any relevant standard or code of practice issued from time to time by the BSI Group or under a European directive relating to standards; or good building practice; or
do not accord with the guidelines contained in the edition of the publication Good Practice in the Selection of Construction Materials (British Council for Offices (BCO)), current at the date of specification or use.

Current difficulties
However, notwithstanding this good advice and the ready availability of relatively standard clauses of the type presented above, it is still not uncommon for some contracts to prohibit materials in a way that is not helpful. For example;

Contracts which attempt to indemnify the Client from “any proper costs claims damages losses penalties fines liabilities encumbrances liens costs or expenses which might be incurred or suffered by the owner or occupier of the Premises as a result of the existence of Hazardous Materials upon about above or beneath the Premises” and then defines “Hazardous Materials” as any substance which contains asbestos. From the discussion above, this would include almost all Made Ground where some asbestos (even if only present in trace amounts) is likely to be present.

Furthermore, clauses can require that “Works shall not include retention of asbestos or asbestos containing material (ACM) within made ground on the Premises where any Survey discloses ACM content greater than 0.1% w/w. In that event, Remediation Works must achieve a reduction of overall ACM within the made ground through controlled screening and picking below 0.1% w/w.”

Firstly, it is difficult to demonstrate conclusively that ACM in Made Ground are above or below this threshold [due to sampling/ testing issues] and to define any areas where such contamination was present would be problematic and could become contentious. Secondly (and more importantly) – this requirement is contrary to the risk based approach to remediation that is current policy and which is promoted in the Good Practice guidance. Essentially, the provision requires that if there is Made Ground with ACMs in it at > 0.1% but that this soil is at depth (say >1m) and which will then be covered by a building or car parking and therefore presents no risk to anybody or the environment, nonetheless, it would have to be excavated, screened and the ACMs removed until you could conclusively demonstrate that the ACMs in the whole mass of soil were <0.1%. On a risk based remediation, all that would be required is that a record of the presence of the ACMs buried beneath the buildings/ car park was retained (e.g. in the Verification Report and recorded in the Health and Safety file) such that if in the future someone was to excavate into this material, the potential risks could be appropriately mitigated.

Recommendations

AGS Members are recommended to scrutinise clauses which refer to the selection / retention of materials which may be considered hazardous in particular circumstances. They should not agree to the inclusion of clauses which are contrary to the advice in the BCO document but should seek to include clauses which refer to and accord with the guidelines contained in the BCO “Good Practice in the Selection of Construction Materials” and /or include a qualifying phrase about the particular use of materials which may or may not be deleterious dependent upon specific use(s).

References
1. British Council for Offices. Good practice in the selection of construction materials 2011.
2. BRE. List of excluded materials – a change in practice. Digest 425. Sept 1997
3. British Council for Offices. Good practice in the selection of construction materials. 1997