Report No DWI0441
EFFECTS OF ORGANIC CHEMICALS IN CONTAMINATED LAND ON BURIED SERVICES
Final Report to the Department of the Environment
DWI0441
May 1992
SUMMARY
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.
OBJECTIVES
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.
Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.