Molehills along white lines?

Northrepps Playing Field school lane moles hillsThese group of molehills (mole hills) were photographed on the Northrepps playing field over a couple of days (Northrepps, Norfolk, England).

The Northrepps village playing has a 100 meter running strip marked into the ground - slightly dug out and marked with the white lines.

The moles seem to like digging up the soil below those lines and at some of the intersections of the lines.

Why?

Or is it just a fluke as there are other mole hills to the side of the running track and not all are on the lines?

Northrepps playing field molehills - Friday 12th June 2015

Northrepps playing field molehills - Sunday 14th June 2015