percolation
Hi Marianne,
First off rushes are usually a sign that the land is or can be quite boggy particularly after heavy rainfall. So you should be careful and find out as much as you can about the land and surrounding area. Have you visited the area after very heavy rainfall, is there any evidence of flooding around.
If the land tends to hold a lot of water, this could have implications for the house foundations which could require more a expensive type of foundation then standard. If the land is not serviced for sewage and you have to provide your own waste treatment setup, then poor drainage will affect this. Your treated water from your septic tank/waste treatment box may not drain away quick enough and if the ground is still logged after some rainfall then you have a sludgy mess to contend with.
However the good news is that if the site has outline permission a percolation test will have already been done. This basically indicates how well the land will drain water away. So it has been accepted by the local council as having suitable soil for drainage to support a residential development. You should be able to get these details from the original outline permission for the site. What you need to find out is the percolation test results. This will indicate a T-value. A low T-value (1-10) indicates fast drainage and a high value (50+) poor drainage. Generally a T-value in the range 1-50 is acceptable. Be careful of very high values and equally very low values and seek further advice.
Hope it helps.