You could try the recent Ecological Risk Assessment publications the
Env Ag have put out, they allow use of other country's assessment
criteria if appropriate.
The last DQRA I did for groundwater required me to use 10ug/l for TPH
and I had to derive individual SSAC for each banding based on their
proportional concentration in my contaminant, obviously this led to
some very low SSAC. (This requirement came from the local EA officer
who had taken advice from his think tank at Solihull).
The Env Ag was less impressed with my thinking that I could use the
EQS (30ug/l for benzene, 50ug/l for toluene and 20ug/l for xylenes,
with 10ug/l for naphthalene) giving me a nice round 100ug/l for TPH.
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