On 16/06/2019 19:06, Tim Lamb wrote:

Is the pond on level ground?

No it's half way up a fairly steep slope

I inherited a bit of arable land in Cambridgeshire. From time to time,
it *springs* according to the tenant at rent review time:-)

Rising land over some nice chalk. I suppose most years with normal
rainfall the problem is not seen but every 20 years or so water appears
part way up the hill and heads for the river via the roadside gardens.


Chris Hogg said the chalk would be free draining but I suspect much
the same happens here in that the rainfall from the hill above
percolates through the soil to the chalk but in winter some travels
down hill near the surface because the chalk underneath is saturated and
this fills the pond.

Either way if the pond didn't leak it would gradually fill anyway.

I suppose if the plastic liner is buried 6" under a covering of soil the
blistering wouldn't be an issue.

AJH