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+ | Overview | ||
+ | Effective long-term performance of [[Glossary#I|infiltration]] practices requires an [[Glossary#I|infiltration]] management plan (''HIGHLY RECOMMENDED'')and performance monitoring (''HIGHLY RECOMMENDED''). | ||
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{{alert|Dedicated and routine maintenance schedule with clear guidelines and schedules are ''REQUIRED''|alert-danger}} | {{alert|Dedicated and routine maintenance schedule with clear guidelines and schedules are ''REQUIRED''|alert-danger}} | ||
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+ | The [[Glossary#I|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. | ||
<p>The monitoring plan should address the following items: inspection and efficiency assessment, water quality monitoring, monitoring of [[Glossary#G|ground-water]] elevations, long-term [[Glossary#I|infiltration]] capacity and plant tolerances.</p> | <p>The monitoring plan should address the following items: inspection and efficiency assessment, water quality monitoring, monitoring of [[Glossary#G|ground-water]] elevations, long-term [[Glossary#I|infiltration]] capacity and plant tolerances.</p> | ||
<p>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 [[Glossary#I|infiltration]] practices is clogging caused by organic matter and fine silts. Common operational problems include:</p> | <p>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 [[Glossary#I|infiltration]] practices is clogging caused by organic matter and fine silts. Common operational problems include:</p> | ||
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<p>[[Glossary#I|infiltration]] practices are particularly vulnerable during the construction phase for two reasons. First, if the construction sequence is not followed correctly, construction [[Glossary#S|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 [[Glossary#I|infiltration]] practices are as follows:</p> | <p>[[Glossary#I|infiltration]] practices are particularly vulnerable during the construction phase for two reasons. First, if the construction sequence is not followed correctly, construction [[Glossary#S|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 [[Glossary#I|infiltration]] practices are as follows:</p> | ||
<p>Example construction phase inspection checklist [[Infiltration basin - system construction inspection checklist|here]].</p> | <p>Example construction phase inspection checklist [[Infiltration basin - system construction inspection checklist|here]].</p> | ||
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+ | {{:Infiltration Trench - Construction inspection checklist}} | ||
====Post-Construction Operation and Maintenance==== | ====Post-Construction 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:
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) |
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:
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:
Example construction phase inspection checklist here.
Infiltration Trench and infiltration basin - Construction inspection checklists.
Link to this table
To access an Excel version of form (for field use), click here.
Project: | ||
Location: | ||
Site Status: | ||
Date: | ||
Time: | ||
Inspector: | ||
Construction Sequence | Satisfactory / Unsatisfactory | Comments |
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1. Pre-Construction | ||
Pre-construction meeting | ||
Runoff diverted | ||
Soil permeability verified | ||
Groundwater / bedrock verified | ||
Project benchmark established | ||
Facility location staked out | ||
Temporary erosion and sediment control established | ||
2. Excavation | ||
Size and location per plans | ||
Side slopes stable | ||
Depth adjusted to soil layer with specified soil type and permeability | ||
Sub-soil not adjacent to excavation area and stabilized with vegetation and/ or silt fence | ||
Stockpile location not adjacent to excavation area and stabilized with vegetation and/ or silt fence | ||
3. Filter Fabric Placement | ||
Fabric per specifications | ||
Fabric per specifications | ||
Placed per plan location | ||
4. Aggregate Material | ||
Size as specified | ||
Clean / washed material | ||
Placed properly | ||
5. Observation Well | ||
Pipe size per plans | ||
Under-drain installed per plans | ||
Inlet installed per plans | ||
Pre-treatment devices installed per plans | ||
6. Vegetation | ||
Complies with planting specifications | ||
Topsoil complies with composition and placement in specifications | ||
Permanent erosion control measures in place | ||
7. Final Inspection | ||
Dimensions per plans | ||
Check dams operational | ||
Inlet / outlet operational | ||
Effective stand of vegetation and stabilization | ||
Contributing watershed stabilized before flow is routed to the facility | ||
Comments: | ||
Actions to be taken: |
Effective long-term operation of infiltration practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Some important post-construction maintenance considerations are provided below.
Example operation and maintenance checklist here.
Typical maintenance problems for infiltration trenches and basins.
Link to this table
Problem | Practices Applied To | Comments |
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Clogging, sediment deposition | Both | Key issue for infiltration practice. Requires vigilant inspection and maintenance. |
Surface Vegetation | Both | Often important to maintain vigorous growth at the base of infiltration practices (basins). Important to restrict woody vegetation from the surface of infiltration trenches. |
Erosion of contributing land or in channels leading to practice | Both | In these practices, it is important to monitor not only the practice itself, but also upland infiltration to minimize the sediment load. |
Damage to filter fabric | Trench | Infrequent but important maintenance concern. |
Scouring at Inlet | Both | Similar issues to Ponds. Need to promote non-erosive flows that are evenly distributed |
Access Issues | Both | Similar issues to Ponds. Need access for inspection and maintenance. |
Concrete Failure | Basins, if they include a riser structure | Similar issues to ponds and wetlands. |
Problems with the Embankment | Basins | Similar issues to dry ponds. |
Typical maintenance activities for infiltration trenches and infiltration basins.
Link to this table
Activity | Schedule |
---|---|
Replace pea gravel/topsoil and top surface filter fabric (when clogged). | As needed |
Ensure that contributing area, practice and inlets are clear of debris. Ensure that the contributing area is stabilized. Remove sediment and oil/grease from pre-treatment devices, as well as overflow structures. Mow grass filter strips should be mowed as necessary. Remove grass clippings. Repair undercut and eroded areas at inflow and outflow structures |
Monthly |
Inspect pre-treatment devices and diversion structures for sediment build-up and structural damage. Remove trees that start to grow in the vicinity of the trench. | Semi-annual Inspection |
Disc or otherwise aerate basin bottom. De-thatch basin bottom. | Annually |
Scrape basin bottom and remove sediment. Restore original crosssection and infiltration rate. Seed or sod to restore ground cover. | Every 5 years |
Perform total rehabilitation of the trench to maintain design storage capacity. Excavate trench walls to expose clean soil | Upon Failure |