Your ancestor's service file contains a number of useful documents, but doesn't say his left leg was amputated in Richmond VA. It says Surgeon W. F. Westmoreland amputated his left leg below the knee at Atlanta GA. We don't have other records prior to May 1, 1864, stating his actual location. On that date he was paid at Rome GA. He could have been at home on furlough and reported to the hospital there for further examinatin and treatment.
By May 1, 1864, Law's Alabama Brigade was in transit from East Tennessee to rejoin the Army of Northern Virginia. Since Reed had not been discharged and eventually became able to travel, he returned to Virginia where his regiment was stationed. After being admitted to a Richmond hospital, he was sent to another hospital at Staunton VA, but returned to Richond after Early's defeat at Winchester. Reed was retired to the Invalid Corps on Nov.5, 1864, Richmond VA, and assigned to the military post at Gadsden AL.
If you don't have Reed service file, copies can be ordered here.