It will be at 801 New Jersey Ave, which is just down H street.
What may surprise you is that this Walmart is expected to have an urban architecture:
“D.C. residents want more convenient access to quality jobs and affordable groceries,” said Henry Jordan, Senior Vice President, Walmart U.S. “We want to be part of the solution and look forward to building even more support for what our brand can deliver.”
Walmart has also set up a webpage just for residents of Washington: http://www.walmartwashingtondc.com/
Walmart expects to open 4 stores in the District in the next 2 years, creating 1,200 new jobs and 400 construction jobs as well as an estimated $10 million in tax revenue.
Update: Although it's in the comments section, we thought we'd pull up the most accessible ways of getting to this new Walmart by public transportation. The site is four tenths of a mile from Union Station and four tenths of a mile from Judiciary Square, though the latter a harder route because of the bridge going over I-395. There is also the X2 bus, which stops right there at 1st and H, and the 80 bus, which stops at Massachusetts and New Jersey Ave.