D.C. Code § 9-411.02
The total assessment levied hereunder against any abutting property shall not exceed the number of square feet of area of said property multiplied by 1 per centum of the linear front-foot assessment and shall not exceed 10 per centum of the value of the said abutting property, exclusive of improvements thereon, as assessed for the purpose of taxation at the time of the laying of the curb or gutter or curb and gutter for which said assessment is levied. In computing assessments hereunder against unsubdivided land according to the assessed valuation, there shall be excluded from the computation land lying back more than 100 feet from the street, avenue, or road being improved where the depth is even, and where the depth is uneven the average depth shall be taken in computation but not to exceed more than 100 feet.
D.C. Code § 9-411.02