Wow, I never heard of a ground squirrel before and would not have thought of a groundhog!

I did some quick checking and as I live in Maryland, this comes from the University of MD, College of Agriculture and Natural Resources:

Dealing with Nuisance Wildlife

WOODCHUCKS (GROUNDHOGS)
Groundhogs adapt well to suburban areas and sometimes their burrowing and feeding habits may be a problem for homeowners. The groundhog is a rodent and a large member of the squirrel family. Groundhogs live in burrows located along roadsides, fields, at the base of trees, and around building foundations. Burrows are used for mating, hiding from predators, and hibernation. Burrow systems are extensive and usually have two or more entrances. Main entrances are about a foot wide with a mound of soil around them. Secondary entrances are usually dug from below and are well hidden. Groundhogs hibernate during the winter until late February-early March. They breed in March-April and produce a single litter of two to six young. Young groundhogs leave their burrows by early July and search for their own home.

Groundhogs can present a challenge to gardeners. They are herbivores and feed on a variety of wild and cultivated flowers, grasses, weeds, and garden vegetables such as broccoli, beans, lettuce, and squash. Groundhogs feed primarily in the early morning and evening because they depend on dew and plant moisture for their water intake. They travel only 50 to 150 feet from their den in search of food. In late August and September, groundhogs have ravenous appetites as they prepare to hibernate. Groundhogs are good climbers and persistent diggers. Fencing can reduce damage to gardens, only, if you can prevent climbing and burrowing.

Groundhogs Under Structures
Sometimes a groundhog may burrow under porches, garden sheds, or other outdoor structures. In some cases, homeowners coexist with the groundhog. If the burrowing conflicts with human interests, then control options need to be considered to reduce conflict and prevent future reoccurrence. Attempts to discourage groundhogs from living under a building by using repellents or scare tactics are not effective. Groundhogs usually burrow elsewhere on the property. Live trapping is an option. You can hire a licensed nuisance wildlife control cooperator to live trap a groundhog. They have access to professional baits/lures and the equipment required to do the job. If you intend to live trap a groundhog, contact the NWIL at *** for more information. No permit is required to trap a groundhog. However, permission is required from the landowner before releasing into suitable habitat. Consideration should be given to relocating groundhogs during spring while the young are in the den or in the autumn immediately before hibernation when there may not be time to establish a winter den. After the animal is removed, cover the opening with heavy poultry wire or two-inch mesh woven wire to the bottom of the building and bury the bottom of the wire 10 to 12 inches below the ground. Bending the buried section at an L-shaped angle leading outward can help prevent burrowing and future access.