Construction specifications for Infiltration trench Revision as of 16:05, 7 March 2013 by PLeegar (talk | contribs)(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff) Construction specifications for Infiltration trench

Construction Details

CADD based details for pond systems are contained in the section on Computer-aided design and drafting (CAD/CADD) 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

Information: 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)

Construction Observation

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

Avoid excessive compaction

Warning: It is REQUIRED that in order to prevent soil compaction, the proposed infiltration area be staked off and marked during construction to prevent heavy equipment and traffic from traveling over it.

In addition, it is HIGHLY RECOMMENDED that the side walls of dry wells and infiltration trenches be roughened if they have been smeared by heavy equipment

Stabilize Vegetation Before and After Construction

Excessive sediment loadings can occur without the use of proper erosion and sediment control practices during the construction process.

Warning: It is REQUIRED that upland drainage areas be properly stabilized with a thick layer of vegetation, particularly immediately following construction, to reduce sediment loads.

Warning: If infiltration practices are in-place during construction activities, it is REQUIRED that sediment and runoff be kept away the infiltration area, such as with diversion berms and soil-stabilizing vegetation around the perimeter of the practice.

Correctly Install Filter Fabrics

Large tree roots should be trimmed flush with the sides of dry wells and infiltration trenches to prevent puncturing or tearing of the filter fabric during subsequent installation procedures. When laying out the geotextile, the width should include sufficient material to compensate for perimeter irregularities in the dry well or trench and for a 6-inch minimum top overlap. The filter fabric itself should be tucked under the sand layer on the bottom of the dry well of infiltration trench, and stones or other anchoring objects should be placed on the fabric at the trench sides to keep the excavation open during windy periods. Voids may occur between the fabric and the excavated sides of the practice. Natural soils should be placed in any voids to ensure fabric conformity to the excavation sides.

Carefully Finish Final Grading

Initial infiltration basin excavation should be carried to within 2 feet of the final elevation of the basin floor.

Warning: It is REQUIRED that infiltration systems not be excavated to final grade until the contributing drainage area has been constructed and fully stabilized.

The final phase excavation should remove all accumulated sediment and be done by light tracked equipment to avoid compaction of the basin floor and provide a well-aerated, highly porous surface texture.

Keep infiltration practices “Off-line” until construction Is complete

Warning: It is REQUIRED that Ssediment and runoff be kept completely away from the infiltration area during construction. Thus, infiltration practices should never serve as Ssediment control devices during site construction.

It is HIGHLY RECOMMENDED that construction of Ssediment practices be suspended during snowmelt or rainfall, in order to prevent soil smearing, clumping, or compaction.

Establish Permanent Vegetation

• Establishing dense vegetation on the basin side slopes is HIGHLY RECOMMENDED, to reduce erosion and sloughing and
• Provide a natural means of maintaining relatively high Iinfiltration rates. Vegetative cover at inflow points to the {Glossary#B|basin]] is also HIGHLY RECOMMENDED to provide erosion protection and reduce sediment accumulation. The use of native grasses is RECOMMENDED for seeding primarily due to their adaptability to local climates and soil conditions.
• Inspections during construction are needed to ensure that the Iinfiltration practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction to ensure that the contractor’s interpretation of the plan is acceptable to the designer.