It doesn't tell you a lot other than you have a high water table. The big differentiator is if you have enough clay for a good seal on site and/or if the water table stays that high even in dry years. Around where you live you will want to dig several test holes around the area you plan to dig. Best to rent an auger or small backhoe to get them deep enough to get a good feel for where bedrock resides.

From what little I know of Maine, there is a lot of granite under normally shallow soils. You can go from a few inches of soil over some really hard rock to many feet all within a few acres. The good part is granite is not like shale, if you are lucky, you could have an impermeable rock-lined basin like my relatives do in Saco. Nothing really leaks from solid granite.