(A) All sewer trenches shall be backfilled immediately after the engineer has inspected and approved the work of laying pipe but in no case shall more than 400 feet of sewer trench be open ahead of the backfilling.
(B) (1) Backfill at the sides of the pipe and to a point 12 inches over the top of the pipe shall be carefully placed and compacted in not more than six inch layers. Backfill shall be compacted to 95% standard proctor density. Backfilling at the sides of the pipe shall be carried on simultaneously on both sides in such a manner as to prevent displacement of the pipe. Backfill material around the pipe shall not contain large clods or other foreign matter. No frozen material, debris or organic matter shall be placed within two inches of the top of pipe. Compaction should be delayed until 12 inches of backfill is placed above the pipe if a hoe-mounted plate compactor is to be used.
(2) Backfill above the pipe envelope shall be performed in accordance with the following.
(a) Backfill material. All backfill material shall be free from cinders, ashes or refuse, vegetable organic material, boulders, rocks or stones in excess of two-inch diameter, or other material that in the opinion of the engineer is unsuitable.
(b) Compaction. In any excavation directly under and within a 1:1 slope of existing or proposed streets, alleys, drives or sidewalk surfaces, sand or lime screenings material shall be compacted in nine inch lifts to 95% of standard proctor density until two and one-half feet below the bottom of pavement, at which point select native material shall be compacted in nine inch lifts to 95% of standard proctor density. In lieu of sand or lime screening backfill, select native material may be compacted in nine inch lifts to 95% of standard proctor density. Backfill materials in excavations in all other areas within the street right-of-way and easement areas shall be compacted in nine inch lifts to 95% of standard proctor density.
(c) Backfilling in freezing weather. Backfilling shall not be done in freezing weather except by permission of the engineer. Backfill shall not contain frozen material. No fill shall be made when the material already in the trench is frozen. Backfilling will not be allowed when disturbed ground temperature is below 35°F, unless approved by engineer.