315 INFILTRATION TRENCHES
From MDOT Policy Manual
- Install infiltration trenches as specified.
Riprap 901.02, Class I Geotextile, Class as specified 919 Polyvinyl chloride profile wall drain pipe 905 Stone M 43, No. 2
- Do not place infiltration trenches in service until all of the contributing drainage area has been stabilized and approved. Restrict heavy equipment and traffic from the proposed infiltration trench location.
- 315.03.01 Excavation. Remove excavated material from the trench site. Ensure that trench walls and bottom are free of protruding objects that could damage the geotextile. When necessary, slope the trench walls. Ensure that the bottom dimensions and stone depth are as specified. Roughen the side walls of the trench. Grade the bottom of the trench flat. For excavated material, refer to 402.03.01.
- 315.03.02 Installation. Place geotextile on the sides of the trench and the top of the No. 2 stone. Do not cover the bottom of the trench. The geotextile for the sides of the trench shall overlap the top geotextile by 6 to 8 in. Extend the top geotextile the full width and length of the trench. All longitudinal joints in the top geotextile shall overlap at least 6 in. The upstream roll shall overlap the downstream roll by at least 2 ft, for a shingled effect.
- Place an observation well vertically in the longitudinal center of each infiltration trench. Use 6 in. diameter slotted perforated polyvinyl chloride profile wall drain pipe (PPWP). Place the pipe on a base plate at the bottom of the trench. Cap the well using a threaded PVC fitting and a vandal proof sewer cap. Set the cap 6 in. above ground, and mark the depth of the trench on the cap. Provide a plastic collar with ribs to prevent rotation of the well when removing the cap. When soil capping is used, construct the observation well using perforated PPWP within the No. 2 stone and non perforated pipe through the soil capping.
- All stone shall be clean and free of all soil and fines. Place the No. 2 stone in 12 in. lifts with no compaction. Avoid any intermixing of the soil and fines with the stone aggregate. Remove and replace contaminated aggregate. Cap the trench with at least 12 in. of stone or soil as specified.
315.04 MEASUREMENT AND PAYMENT.
- Infiltration Trenches will be measured and paid for at the Contract unit price per cubic yard. The payment will be full compensation for all excavation, stone, capping, riprap, geotextile, pipe, fittings, cap, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.