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Low Impact Development and Bioretention Maintenance
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  1. Low Impact Development and Bioretention Maintenance Module 6: Maintenance Practices I Dennis Chestnut

  2. Contributors The Low Impact Development Center, Inc. John Shorb Landscaping, Inc. Logo Groundwork Anacostia River, D.C. Logo

  3. Outline • Routine maintenance of bioretention cells

  4. Expected Outcomes • Be able to perform routine maintenance of bioretention cells • Be able to perform minor repairs to bioretention cells

  5. Administrative Practices

  6. Routine Maintenance Practices

  7. Crew and Equipment Requirements

  8. Routine Maintenance • Maintenance needs vary depending on the season and how long the bioretention cell has been in operation • Recently constructed bioretention cells require more frequent maintenance than do more established bioretention cells • The Guidebook contains a recommended maintenance schedule

  9. Upon Establishment • After storms • Inspect the bioretention cell and its drainage area after storm events with more than ½ inch of rainfall. Inspect at least twice in the first six months of operation. Conduct any needed repairs or stabilization.

  10. Upon establishment • In the drainage area: • Watch for bare or eroding areas, and stabilize immediately

  11. Upon establishment • Bioretention plants: • May need one-time, spot fertilization • Water once per week for the first 2 months, then as needed during the first growing season • Remove and replace dead plants

  12. At least 4 times a year • Mow any turf in bioretention cell or pretreatment areas • Clear curb cuts and inlets of accumulated grit, leaves, and trash

  13. Twice during growing season • Spot weed • Remove trash • Rake mulch

  14. As needed • Add plantings to maintain desired vegetation density • Remove invasive plants • Remove dead or diseased plants • Stabilize drainage area to prevent erosion

  15. Annually • Conduct a full maintenance inspection • Add mulch to maintain a 3-inch layer • Prune trees and shrubs • Remove sediment in pre-treatment areas and at inflow points • Annual inspection is usually conducted in spring, at the beginning of the growing season

  16. Every 2-3 years • Remove and replace mulch layer

  17. Training • Bioretention cells differ from other landscaped areas in many important ways • Maintenance techniques are similar to other landscaped areas, but with additional procedures to maintain stormwater function • Proper training is important for maintenance of bioretention cells

  18. Facility Assessments • Module 8of this course will present a detailed methodology for assessing bioretention performance and maintenance needs • The Guidebook contains a maintenance inspection checklist

  19. Maintenance – Bioretention • Primary maintenance requirement - regular inspection and repair / replacement of damaged components • Can be incorporated into regular landscaping maintenance contract, as the routine periodic maintenance for bioretention areas is similar to what is required of any landscaped area

  20. Sediment and Erosion Assessment

  21. Maintenance – Bioretention • Soils • Visually inspect and repair erosion at inflow points once in the spring and once in the fall, at a minimum.  • Use small stones to stabilize erosion along drainage paths. • Check the soil’s pH once or twice a year. • Apply an alkaline product, such as limestone, if needed.

  22. Soils - Maintain Infiltration Rates Runoff from impervious surfaces is directed to bioretention cells to infiltrate through the soil medium Once the infiltration capacity of the soil medium is exceeded, storm water begins to pool at the soil’s surface Ponding should only last 4-6 hours Mosquitoes larva need 4+ days of standing water Maintenance – Bioretention

  23. Maintenance – Bioretention Soils – Corrective Action • Depending on pollutant loads, soils may need to be replaced within 5-30 years of construction. • If standing water consistently over 4-6 hrs: • Clear the underdrain of potential clogs • Check filter fabric above the underdrain • Remove mulch and rake surface to remove surface blockages • Last resort - remove the soil mixture • Before removing soil mixture, analyze for clay content and hazardous content • If greater than 15% clay content, then: • Temporarily block end of discharge pipe, install appropriate E&S controls • Carefully dig up plants so that root systems are maintained (and return to cell following soil replacement) • Remove soil and dispose appropriately as clean fill or in an approved landfill • Inspect pipe and gravel layer, if pipe is clogged, then wash the gravel layer with a high-pressure hose – this should clean the pipe • Place new soil in the cell and replant vegetation

  24. Maintenance – Bioretention Mulch Layer • Uniformly applied approximately 2 to 3 inches deep. Do not pile the mulch around trees or other plantings • Fresh bark mulch (either standard landscape fine shredded hardwood mulch or hardwood chips). Make sure it is free from weed seeds, soil, roots or any other substance not consisting of bole, branch wood, or bark Do not use grass clippings as mulch • Every 6 months, in the spring and fall, add a fresh mulch layer. Once every 2 to 3 years, in the spring, remove the old mulch layer before applying the new one

  25. Plant Identification and Assessments • Module 9 of this course concerns learning to identify common bioretention landscaping plants, weeds, and invasive species • For installations owned by the District, DDOT has certified arborists on staff, who can assist with identifying trees and other plants, and who can recommend maintenance and/or control methods

  26. Plant Care and Replacement

  27. Maintenance – Bioretention Planting Maintenance • Routine maintenance should include a biannual health evaluation of the plantings, and removal and replacement of any dead or diseased vegetation. • The use of native plant species in the bioretention cell will reduce fertilizer, pesticide, water, and overall maintenance requirements. • Level of pollutants in the soil can become toxic, impair plant growth

  28. Maintenance – Bioretention Planting maintenance • Immediately after installation, water plant material for 14 consecutive days (unless sufficient natural rainfall). • When trees have taken root, or at least by 6 months, remove stakes and wires • Visually inspect vegetation for disease or pest problems at least once in the spring, once in the fall, and more frequently in the summer. If treatment is warranted, use the least toxic approach • During extended drought, look for physical signs of stress (unrevived wilting; yellow, spotted or brown leaves; loss of leaves, etc.). Water in the early morning if needed • Prune excess growth annually in the spring and throughout the growing season if desired. Trimmed materials may be recycled back in with replenished mulch or landfilled if there is a concern of heavy metals accumulation. • Weed regularly, as necessary

  29. Control of Invasives • In general, it’s best to avoid using herbicides in bioretention cells whenever possible • Hand-pulling or cutting is preferable • May need to be repeated multiple times before seed banks and roots are exhausted

  30. Use of Herbicides • When dealing with large infestations of particularly pernicious invasives, herbicide use may be warranted • Spot treatment of specific plants is preferable to spraying • Must use only herbicides certified by the EPA as safe for use around water • Herbicide applicators must be trained and licensed

  31. Structure and Pipe Assessment

  32. Standing water • Bioretention cell should not have standing water more than 72 hours after a storm event • Prolonged standing water is a health hazard, and indicates a malfunction somewhere in the system

  33. Potential causes • Clogged underdrain • Accumulated sediment at bioretention surface • Excessive fines in bioretention media

  34. Checking underdrains • Check observation wells • Standing water in underdrain • Underdrain is clogged and must be cleaned out • No standing water in underdrain • Clog is somewhere in the bioretention soil

  35. Clearing clogged underdrains

  36. Soil Clogging • To determine where bioretention media is clogged, dig a test pit • Look for: • Sediment layer at surface • Accumulation of fines in gravel surrounding underdrain, or above geotextile filter fabric, if present • Excessive fines in soil media

  37. Sediment at Surface • Thin layers of sediment can be broken up by raking the mulch surface • For excessive sedimentation, remove sedimentand mulch, and till sand into upper 6-12 inches of soil media • Eliminate sources of sediment (e.g. erosion within drainage area)

  38. Fines in soil media • Usually caused by unapproved material substitutions during construction Sticks together = Too much clay Not cohesive = Good

  39. Fines in soil media • Sometimes can be corrected by installing sand wicks to the underdrain layer (vertical columns filled with sand) • In severe cases, the media must be replaced

  40. Minor repairs to structures

  41. Contamination/Pollution Assessment • Notification procedures

  42. Reporting

  43. Review

  44. Resources