Having dealt with Japanese Knot Weed (JKW) in an archaeologically sensitive
area a few years ago – there is definitely scope for the archaeological
requirements and JKW requirements to be achieved satisfactorily.
The Environment Agency are the best body to provide the most appropriate
advice – however, doesn’t sound like they were too helpful in this case.
My experience was that in order for archaeological works to proceed,
firstly the area containing the JKW needed to be treated with an
appropriate herbicide (see Environment Agency Guides for the appropriate
herbicide). Between July and September is the best time to spray. The
area was then left for a period of two weeks, after which the weed was cut
and burnt on site. This must be formally notified to the Environment
Agency (by completion of an ‘Exemption Registration Form’).
The archaeology then began with great care be taken to keep the soil from
the contaminated area separate from any other soils. Storing the
contaminated soil on a heavy gauge polythene sheet sufficed here.
Following completion of the archaeological works, the ideal is for the
contaminated soil to be reburied on the site where it was produced (after
another treatment of herbicide). A big hole in an archaeologically sterile
area was a great help here – hopefully you have such an area. Depths of 5m
for re-burial are recommended. The re-buried soil should then be covered
by geo-textile membrane.
Alternatively, the contaminated soil can be taken off site to an
appropriate disposal facility (Env. Agency should be able to give advice on
where). However, with the off-site disposal great care must be taken to
not disperse the material en-route – and appropriate storage should be
used. I also think that another round of licenses/notifications are
required to do this.
Hope this helps. If you need a useful South Yorkshire Environment Agency
contact let me know.