Operation and maintenance of Infiltration trench Revision as of 15:58, 7 March 2013 by PLeegar (talk | contribs) (Created page with " ==Operation and Maintenance== ====Overview==== <p>Effective long-term performance of infiltration practices requires an infiltration management ...")
Contents
Operation and Maintenance
Overview
Effective long-term performance of infiltration practices requires an infiltration management plan (HIGHLY RECOMMENDED)and performance monitoring (HIGHLY RECOMMENDED).
The infiltration management plan (operation plan) should address the following items: periods of inundation, wet/dry cycling of soils, operating instructions for drawdown valves, gates and removable weirs.
The monitoring plan should address the following items: inspection and efficiency assessment, water quality monitoring, monitoring of ground-water elevations, long-term infiltration capacity and plant tolerances.
Elements to be considered for the development of a maintenance plan are broken into the following categories: Design Phase Maintenance Considerations; Construction Phase Maintenance Considerations; and Post-Construction Maintenance Considerations. In general terms, the most frequently cited maintenance concern for infiltration practices is clogging caused by organic matter and fine silts. Common operational problems include:
- Clogging and sediment deposition
- Erosion of contributing land or in channels leading to the practice
- Maintaining appropriate surface vegetation
The table below provides a summary of common problems for infiltration trenches and basins.
Summary of infiltration practices cost components.
Link to this table
| Implementation Stage | Primary Cost Components | Basic Cost Estimate | Other Considerations |
|---|---|---|---|
| Site Preparation | Tree & plant protection | Protection Cost ($/acre) * Affected Area (acre) | Removal of existing structures, topsoil removal and stockpiling |
| Infiltration area protection | Silt fence cost ($/’foot) * Perimeter of infiltration area | ||
| Clearing & grubbing | Clearing Cost ($/acre) * Affected Area (acre) | ||
| Topsoil salvage | Salvage Cost ($/acre) * Affected Area | ||
| Site Formation | Excavation / grading | X-ft Depth Excavation Cost ($/acre) * Area (acre) | Soil & rock fill material, tunneling |
| Hauling material offsite | Excavation Cost * (% of Material to be hauled away) | ||
| Structural Components | Vault structure (for underground infiltration) | ($/structure) | Pipes, catchbasins, manholes, valves, vaults |
| Media (for infiltration trenches) | Media cost ($/cubic yard) * filter volume (cubic yard) | ||
| Geotextile | Geotextile cost ($/cy) * area of trench, including walls | ||
| inlet structure | ($/structure) | ||
| Overflow structure | ($/structure) | ||
| Observation well | ($/structure) | ||
| Site Restoration | Soil preparation | Topsoil or amendment cost ($/acre) * Area (acre) | Tree protection, soil amendments, seed bed preparation, trails |
| Seeding | Seeding Cost ($/acre) * Seeded Area (acre) | ||
| Filter strip | Sod cost ($/square foot) * filter strip area | ||
| Planting / transplanting | Planting Cost ($/acre) * Planted Area (acre) | ||
| Annual Operation, Maintenance, and Inspection | Sediment removal | Removal Cost ($/acre) * Area (acre) * Frequency (1 time per 5 years) | Vegetation maintenance, cleaning of structures |
| Debris removal | Removal Cost ($/acre) * Area (acre) * Frequency (2 time per year) | ||
| Inspection | Inspection Cost ($) * Inspection Frequency (6 times per year) | ||
| Mowing (for some vegetative filters) | Mowing Cost ($) * Mowing Frequency (6 times per year) |
Design Phase Maintenance Considerations
Implicit in the design guidance in the previous sections is the fact that many design elements for infiltration systems can minimize the maintenance burden and maintain pollutant removal efficiency. Among them are:
- Open lawn areas are RECOMMENDED locations for infiltration practices because of their accessibility.
- It is HIGHLY RECOMMENDED that every dry well, infiltration trench and subsurface infiltration system design include an observation well consisting of an anchored six-inch diameter perforated PVC pipe fitted with a cap to facilitate periodic inspection and maintenance. It is also HIGHLY RECOMMENDED that infiltration basins include a draw down device that can be used for winter diversion and to conduct regular maintenance.
- It is HIGHLY RECOMMENDED that a mechanism such as a multi-stage outlet structure be incorporated into the design of the pre-treatment and infiltration practices to facilitate draining for maintenance purposes.
Construction Phase Maintenance Considerations
infiltration practices are particularly vulnerable during the construction phase for two reasons. First, if the construction sequence is not followed correctly, construction sediment can clog the practice. In addition, heavy construction can result in compaction of the soil, which can then reduce the soil’s infiltration rate. For this reason, a careful construction sequence needs to be followed. Critical construction elements for infiltration practices are as follows: