How impermeable are the surfaces of the moon? In the event that we want to dig into the surface of either face of the moon do we know yet if the surfaces of the moon are particularly difficult or particularly easy to dig in?
The moon's surface is made up of many layers.

The top few centimeters of the moon are generally composed of a layer of thin powder.  This is easy to dig into, and the Apollo astronauts easily scooped up this stuff.

Wikipedia - Lunar Soil

Below that layer is the bulk Regolith,  which contains a mixture of powder, grains, pebbles, and rocks - the remnants of billions of years of meteor collisions which have thoroughly mixed and distributed the material from collisions all over the surface.  The regolith ranges in depth around the Moon based on the age of the surface - the old highland and farside surface contains regolith up to 15 meters deep, while the mare regolith averages about 4 meters deep.

The regolith is not solid rock,  but it's very compacted and the grains are rough and billions of years of vibrations from impacts and quakes has caused the particles to interlock.  Therefore, it can be extremely difficult to dig into.  The Apollo 14 astronauts only managed to drive a heat probe 70cm into the regolith, using about 20 hard hammer blows to do so.  For later missions they had to use electric drills to get deeper, about 3 meters.

Lunar and Planetary Institute - Lunar Sourcebook, chapter 7

Apollo 14 - Soil Mechanics Investigation

Below the regolith is rock.  On the Mare, the rock is a very hard basalt (8 out of 10 on the hardness scale).  Getting through this is like cutting granite.  On the older highland regions, the most common material under the regolith will be anorthosite, which is less dense but it's still drilling through rock.

The mare basalts range in depth from 100m to about 3-4 km, with an average depth of .74 km.  Below that is old anorthositic crust.  The crust itself ranges from 10-70 km thick, with an average of about 35 km.  The crust on the near side is significantly thinner than on the far side.

Planetary Society - GRAIL maps of crustal thickness

If you want to drill deeper,  you're into the mantle, which is only partially melted near the core, and made up of roughly the same olivine basalt that makes up the floor of the mare, and goes down to a depth of about 1100 km.

The Moon - Internal Structure and Magma Ocean

Hope that helps.