Minnesota Department of Transportation example construction protocols
Contents
Preliminary analysis and selection
Recommended number of soil borings, pits or permeameter tests for bioretention design. Designers select one of these methods.
Link to this table
| Surface area of stormwater control measure (BMP)(ft2) | Borings | Pits | Permeameter tests |
|---|---|---|---|
| < 1000 | 1 | 1 | 5 |
| 1000 to 5000 | 2 | 2 | 10 |
| 5000 to 10000 | 3 | 3 | 15 |
| >10000 | 41 | 41 | 202 |
1an additional soil boring or pit should be completed for each additional 2,500 ft2 above 12,500 ft2
2an additional five permeameter tests should be completed for each additional 5,000 ft2 above 15,000 ft2
Field verification testing prior to pond construction
- Soil hydraulic group represent what is stated in SWPPP (Stormwater Pollution Prevention Plan)
- Seasonally high water table not discovered within 3 feet of the excavated pond base within a test pit
- Commonly will test bottom of proposed pond for soil compaction (subsequent subsoil ripping) prior to media placement
- Commonly will test bottom of proposed pond for insitu infiltration rate by test pit or water filled barrel placed on pond base surface
Filter media and material testing
- Existing soil (option 1 below) or Washed sand (option 2 below), and compost certification
- Washed course aggregate choker certification
- Other treatment material certification of iron filings, activated charcoal, pH buffers, minerals, etc.
- Geotextile separation fabric certification
- Drain-tile certification (if filtration is specified)
- Seed source certification
- Barrel test verification of infiltration rate using 2.5 feet of imported 3877 Type G media
Field verification testing/inspection/verification during construction
- Water drains away in 48 hours
- Infiltration drainage rate does not exceed 8.3 inches per hour
- No tracking/equipment in pond bottom
- No sediment deposits from ongoing construction activity, media perimeter controls kept functional
- Forebay is trapping settleable solids, floating materials, and oil/grease
- Area staked off
Notice of Termination (NOT) verification
- Option 1. Amending existing HSG soils with compost or other treatment material. Test the infiltration rate of each infiltration basin using a double ring infiltrometer prior to completion of the basin. Conduct the test at the finished grade of the basin bottom, prior to blending the compost with the in-situ soils or sand. Ensure infiltration rates meet or exceed greater of two times the designed infiltration rate or 2 inches per hour. Conduct a minimum of five tests per representative acre of basin area and a minimum of five tests per basin. Conduct double ring infiltrometer tests in accordance with ASTM standards. Thoroughly wet test areas prior to conducting infiltrometer tests.
- Option 2. Importing 3877 Type G Filter Topsoil Borrow (may be amended with other treatment material). Ensure infiltration rates meet or exceed greater of two times the designed infiltration rate or 2 inches per hour, or rate specified in the plan. Conduct a minimum of five tests per representative acre of basin area and a minimum of five tests per basin. Conduct double ring infiltrometer tests in accordance with ASTM standards. Thoroughly wet test areas prior to conducting infiltrometer tests. Amend soils with additional washed sand if rates less than specified in the contract, or compost if rates exceed 8.3 inches per hour.
The permanent stormwater management system must meet all requirements in sections 15, 16, and 17 of the CSW permit and must operate as designed. Temporary or permanent sedimentation basins that are to be used as permanent water quality management basins have been cleaned of any accumulated sediment. All sediment has been removed from conveyance systems and ditches are stabilized with permanent cover.