If for any reason a herbicide treatment program cannot be carried out in situ, an alternative solution is to create a bund or stockpile elsewhere on location. For example, the proposed location for a new house build is in the area of infestation.
In this scenario, the area is excavated and the contaminated soil stockpiled to another area on site where it can be left undisturbed while monitored and treated with a herbicide treatment program. Excavation and bund creation is normally implemented after an initial herbicide treatment program to minimize the new growth in the bund area.
These bunds or stockpiles can often be worked into the proposed landscaping for developments e.g green areas or wind breaks. The advantages and disadvantages of a bund / stockpile solution are as follows.
- Cost effective
- Allows development works to be undertaken whilst treatment takes place elsewhere on the site
- Requires area on site for implementation of bund / stockpile
- Restrictions remain in stockpile area
- Soil from stockpile must remain on site
Soil screening is a technique by which the large biomass is removed from the excavated material. The large biomass can then be removed for incineration. It is important to remember that the screened soil will still contain viable plant material, and so is still considered contaminated. However this process greatly reduces the amount of future regrowth for bund and stockpile installations, and makes the subsequent herbicide treatment far more effective and short term.
A popular alternative to stockpiling is burial of plant materials and contaminated soil. Due to the ability of knotweed to regrow from very small pieces of stem and root, buried materials need to be encapsulated with an appropriate geosynthetic root membrane to stop the spread of root after burial.
Where appropriate, excavation and burial is normally implemented after an initial herbicide treatment program to reduce the amount of viable material being buried.
The advantages and disadvantages of a burial solution are as follows
Where it is required, the contaminated soil material can be removed from site to be disposed of at a suitably licensed landfill. Correct permits are required for the transportation and disposal of this material.
The advantages and disadvantages of a excavation and offsite removal are as follows
- Work can continue immediately after removal
- No restrictions remain on site