CADD based details for pond systems are contained in the section on drawings. The following details, with specifications, have been created for infiltration systems:

  • infiltration basin
  • infiltration trench
  • subsurface infiltration system
  • inlet/outlet structures

Construction specifications

Given that the construction of infiltration practices incorporates techniques or steps which may be considered non-standard, it is RECOMMENDED that the construction specifications include the following format and information.

Temporary erosion control

  • Installation prior to site disturbance
  • Catch basin/inlet protection
  • Use of BMP as temporary sedimentation basin

Excavation, backfill and grading

  • Timing of grading of infiltration practices (relative to total site development)
  • Use of low-impact, earth moving equipment
  • Controls to ensure site is not over-excavated
  • Restoration in the event of sediment accumulation during construction of practice
  • Gravel backfill specifications
  • Gravel filter specifications
  • Filter fabric specifications
  • Observation well specifications

Native plants, planting and transplanting

  • Site preparation of planting areas
  • Timing of native seeding and native planting
  • Weed control
  • Watering of plant material
Warning: It is REQUIRED that infiltration systems not be excavated to final grade until the contributing drainage area has been constructed and fully stabilized.

Construction sequence scheduling

  • Temporary construction access
  • Location of silt fence installation to protect BMPs and downgradient receiving waters
  • Removal and storage of excavated material
  • Installation of underground utilities
  • Rough grading
  • Seeding and mulching disturbed areas
  • Road construction
  • Final grading
  • Site stabilization
  • Installation of semi-permanent and permanent erosion control measures
  • Silt fence removal (often forgotten but an essential step)

The Construction Stormwater General Permit requires that infiltration systems not be excavated to final grade until the contributing drainage area has been constructed and fully stabilized unless rigorous erosion prevention and sediment controls are provided (Part III.D.1.c). The permit also requires when an infiltration system is excavated to final grade (or within 3 feet of final grade), the Permittee(s) must employ rigorous erosion prevention and sediment controls (e.g. diversion berms) to keep sediment and runoff completely away from the infiltration area. The area must be staked off and marked so that heavy construction vehicles or equipment will not compact the soil in the proposed infiltration area. It is Recommended that infiltration systems be installed or put online after final stabilization of the site.

Construction observation

  • Adherence to construction documents
  • Verification of physical site conditions
  • Erosion control measures installed appropriately

Related pages

This page was last edited on 25 August 2016, at 20:58.

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