Report No DWI0441

May 1992

Organic chemicals in contaminated land can permeate plastic drinking water pipes and adversely affect water quality. In a report on previous WRc work under contract to DOE (ECI 9268) target organic chemicals to be monitored were recommended and analytical methods suggested for the investigation of contaminated sites (Report DoE 2222-M/1, January 1990). The objectives of the work covered by this report were, essentially, to confirm the identity of target chemicals and recommend sampling and analytical techniques for the investigation of contaminated land.

Following a literature survey and exploratory laboratory and site experimental work (which is summarised in Appendix A), an approach to the investigation of contaminated sites in relation to effects on buried services is proposed. The main conclusions are as follows:

• Two groups of volatile organic chemicals (VOCs) are proposed for monitoring contaminated land in relation to potential effects on buried water pipes. These chemicals were selected on the basis of their ability to permeate plastic pipes, occurrence in contaminated soil and their scale of use. Nine commonly used and frequently detected chemicals in Group 1 should be monitored at virtually all sites (carbon tetrachloride, trichloroethene, tetrachloroethene, chlorobenzene, benzene, toluene, and o-, m-, and p-xylenes). Nine more compounds constitute Group 2 (dichloromethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,2-dichloropropane, vinyl chloride, methyl bromide, ethyl benzene and di- and tri-chlorobenzenes); it is advisable that these should be monitored, in addition to Group 1 chemicals, at sites where contamination with unknown chemicals is suspected. Other compounds of similar nature should be investigated when the site history suggests their use.
• Trigger concentrations with respect to protection of water supplies from permeation through pipe walls of buried services ('threshold' and 'action' levels) are proposed for the target chemicals selected, with appropriate values calculated for soil gas, pore water and soil samples. o The sampling and analysis of soil gas is recommended as the most appropriate approach in most circumstances (but not in water-logged ground or in the saturated zone) for predicting whether soil contaminants could permeate plastic water pipes and contaminate the drinking water supply.
• Where pipes are to be laid below the water table or where the site is subject to frequent waterlogging, it is recommended that the soil pore water is sampled and analysed. Only where neither soil gas nor soil water samples can be taken, should the analysis of soil samples be employed.
• A systematic approach has been proposed to the investigation of a site for possible contamination by VOCs. This approach should be adopted whenever the installation of vulnerable plastic pipes, such as polyethylene, is considered for the distribution of drinking water.
• At each site, the VOCs to be determined should be chosen in accordance with information on the site history and appropriate analytical methods should be selected and validated by an experienced analyst.
• In practice, contamination of water supplies by permeation into distribution pipework from redeveloped sites does not appear to pose a major problem at present. However, some compounds, such as benzene, vinyl chloride and dichloromethane, could reach unacceptable levels in drinking waters well before they would be detected by consumers as an objectionable taste or odour. Their presence would not be recognised unless appropriate monitoring was implemented. More information on the occurrence and levels of such compounds should be gathered. To be safe, Water companies tend to use metal pipes (for both mains and service pipes) laid in clean in-fill at any site where contamination is suspected (a list of sites where such measures were undertaken is given in Appendix B). Previous WRc reports to the DOE, as well as more recent papers from the USA, concluded that taste and odour problems resulting from permeation through pipe walls were usually caused by accidental spillage of chemicals in the vicinity of the pipe.
• For the sampling of soil gas, a grab sampling technique has been recommended. Passive sampling, a technique where a sampling device is buried for an extended time under similar conditions as those for the proposed pipes, may be a useful alternative or even more appropriate than grab sampling. However, a suitable passive sampling technique needs to be developed and tested in the field.
• It is possible to determine all the target compounds using a combination of analytical methods which have adequate limits of detection. It would, however, be beneficial to assess the most suitable analytical conditions and recommend an optimised method for on-site analysis.
• Laboratory and field studies have shown that a technique employing on-site soil gas sampling followed by analysis of the gas by a portable gas chromatograph, is potentially very useful for the investigation of contaminated sites. More work is needed to evaluate this technique and, in particular, the newer instruments now commercially available.
• The same (or similar) approach to that recommended for investigating sites with respect to effects on water pipes could also be useful for general survey work on contaminated sites. For example, when assessing possible effects of contaminated sites on the quality of underlying groundwater.

The objectives of the work covered by this report were:

• to test at contaminated land sites a range of the proposed target organic chemicals and associated analytical techniques;
• modify tests as appropriate, and then confirm the identity of suitable target chemicals;
• recommend sampling and analytical techniques for the investigation of contaminated land;
• evaluate the success of remedial measures that have already been carried out at redeveloped sites to protect buried services; and
• suggest changes to DOE policy, where appropriate, on advising on remedial measures.

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