There are no volunteer positions for the Baltimore-Washington Parkway.
There are many National Park volunteer opportunities throughout the Washington, D.C. area through Volunteer. Gov.

VIP Program Mission

The National Park Service Volunteers-In-Parks Program (VIP) was authorized by Public Law 91-357 enacted 1970.
The primary purpose of the VIP program is to provide a vehicle through which the National Park Service can accept and utilize voluntary help and services from the public. The major objective of the program is to utilize this voluntary help in such a way that is mutually beneficial to the National Park Service and the volunteer.

Volunteers are accepted from the public without regard to race, creed, religion, age, sex, sexual orientation, national origin, or disability.