SWM Facility Sequence of Construction

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Wet Pond

This is only a guide. The actual sequence on the plans needs to be customized for each wet pond.

Notify the CCR a minimum of 2 working days in advance of any construction so that the required facility construction checklist can be completed.

  1. Initial Construction:
    1. Install stabilized construction entrance(s) as needed and approved by the Engineer.
    2. Clear and grub for installation of perimeter erosion and sediment controls.
    3. Install perimeter controls as shown on the plans.
    4. Clear and grub remaining area for wet pond construction.
    5. Construct pond outlet and outfall as shown on the plans. Dewater foundation as needed in accordance with dewatering practices as shown in Division 900 of the Standard Specifications. Install skimmer dewatering device and/or other temporary modifications as shown in the plans.
    6. Complete basin excavation as per plan, while also installing the clay liner (if needed) and topsoil.
    7. All disturbed areas meeting final elevations and grades above the permanent bottom elevation (or the existing water surface elevation) as shown on the plans shall be seeded with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch.
  2. Maintenance of Sediment Basin:
    1. The Contractor shall inspect the basin the next workday following a rain event and make any repairs as needed.
    2. Any excess sediment around the outfall area shall be removed within two working days and disposed at a location approved by the engineer.
  3. Conversion to Permanent Wet Pond Facility:
    1. Convert the sediment basin after all areas draining to it have attained final stabilization and the Engineer has approved the conversion.
    2. Remove any excess sediment from the pond bottom above elevation ‘X’.
    3. Remove any excess sediment from the forebay(s) above elevation ‘X’.
    4. Complete stabilization of all bare areas with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch.
    5. After all surrounding areas draining to the wet pond have sufficient vegetation, as approved by the Engineer, E&S devices shall be removed.

*As-built drawings shall be completed by the Contractor and certified by a Delaware PLS before the DelDOT Initial Inspection date. These drawings shall be sent to the Stormwater Engineer for verification. As-built drawings will include, but not be limited to:

  1. General topography of the whole facility at 1-foot contours including forebays and top/toe of any embankment.
  2. Inverts of all pipes and swales that inflow to the pond.
  3. Outline of all riprap and obtain spot elevations on top of the riprap.
  4. Outlet structure (or weir wall) inverts of any and all orifices/weirs, top of structure, outlet pipe, etc.
  5. Primary outflow pipe or channel. For a pipe outfall, inverts at the entrance and exit. For a primary outflow channel/swale, show at minimum three (3) cross sections equal distance apart at 50’ downstream along with the slope.

Dry Pond

This is only a guide. The actual sequence on the plans needs to be customized for each dry pond.

Notify the CCR a minimum of 2 working days in advance of any construction so that the required facility construction checklist can be completed.

  1. Initial Construction:
    1. Install stabilized construction entrance(s) as needed.
    2. Clear and grub for installation of perimeter erosion and sediment controls.
    3. Install perimeter controls as shown on the plans.
    4. Clear and grub remaining area for dry pond construction.
    5. Construct pond outlet and outfall as shown on the plans. Dewater foundation as needed in accordance with dewatering practices as shown in Section 900 of the Standard Specifications. Install skimmer dewatering device and/or other temporary modifications as shown in the plans.
    6. Complete basin excavation to the lines and grades shown. Suggest over-excavating by 6” for sediment storage (if using as a sediment basin). The final dry pond bottom elevation can be ‘filled in’ with topsoil at final conversion.
    7. All disturbed areas meeting final elevations and grades shall be seeded with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch. Areas not meeting final elevations and grades can be seeded with Temporary Grass Seeding.
  2. Maintenance of Sediment Basin:
    1. The Contractor shall inspect the basin the next workday following a rain event and make any repairs as needed.
    2. Any excess sediment around the outfall area shall be removed within two working days and disposed at a location approved by the Engineer.
  3. Conversion to Permanent Dry Pond Facility:
    1. Convert the sediment basin after all areas draining to it have attained final stabilization and the Engineer has approved.
    2. Remove any excess sediment from the pond bottom above elevation ‘X’.
    3. Remove any excess sediment from the forebay(s) above elevation ‘X’.
    4. Place topsoil on pond bottom to elevation ‘X’ making sure to follow plan lines and grades.
    5. Complete stabilization of all bare areas with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch.
    6. After all surrounding areas draining to the pond have sufficient vegetation, as approved by the Engineer, E&S devices shall be removed.

*As-built drawings will be completed by the Contractor and certified by a Delaware PLS before the DelDOT Initial Inspection date. These drawings shall be sent to the Stormwater Engineer for verification. As-built drawings will include, but not be limited to:

  1. General topography of the whole facility at 1-foot contours including forebays and top/toe of any embankment.
  2. Inverts of all pipes and swales that inflow to the pond.
  3. Outline of all riprap and obtain spot elevations on top of the riprap.
  4. Outlet structure (or weir wall) inverts of any and all orifices/weirs, top of structure, outlet pipe, etc.
  5. Primary outflow pipe or channel. For a pipe outfall, inverts at the entrance and exit. For a primary outflow channel/swale, show at minimum three (3) cross sections equal distance apart at 50’ downstream along with the slope.

Infiltration Basin

This is only a guide. The actual sequence on the plans needs to be customized for each infiltration basin. Also, language needs to be added concerning post-developed infiltration testing. Contact the Stormwater Engineer to help determine appropriate notes needed.

Notify the CCR a minimum of 2 working days in advance of any construction so that the required facility construction checklist can be completed.

(Note: if the infiltration basin is to be used as a sediment basin during construction, grading shall be completed to maintain a minimum of 2 feet of cover above the permanent bottom elevation at all times. Have to be very mindful of incoming and outflowing inverts as well as the amount of sediment storage needed during construction. If cannot meet the 2 feet of cover, then discuss with the Stormwater Engineer.)

  1. Initial Construction:
    1. Install stabilized construction entrance(s) as needed and approved by the Engineer.
    2. Clear and grub for installation of perimeter erosion and sediment controls.
    3. Install perimeter controls as shown on the plans.
    4. Clear and grub remaining area for infiltration basin construction making sure not to impede within 2 feet of the permanent bottom elevation.
    5. Construct basin outlet and outfall as shown on the plans. Dewater foundation as needed in accordance with dewatering practices as described in Division 900 of the Standard Specifications. Install skimmer dewatering device and/or other temporary modifications as shown in the plans.
    6. Complete basin excavation to maintain a minimum of 2 feet cover above the permanent bottom elevation. NO EQUIPMENT shall be used within 1-foot of the permanent bottom elevation. Side slopes, maintenance access road, and forebays shall be constructed as per final design elevation and configuration.
    7. All disturbed areas meeting final elevations and grades above the permanent bottom elevation shall be seeded with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch.
  2. Maintenance of Infiltration Basin:
    1. The Contractor shall inspect the basin the next workday following a rain event and make any repairs as needed.
    2. Any excess sediment around the outfall area will be removed within two working days and disposed at a location approved by the engineer.
  3. Conversion to Permanent Infiltration Basin:
    1. Convert the sediment basin after all areas draining to it have attained final stabilization as approved by the Engineer with concurrence from the Stormwater Engineer prior to any facility construction.
    2. During excavation, the CCR shall observe the soil type. If standing water or excessive clay/silt material is discovered at the proposed bottom elevation, the CCR shall notify the Engineer and Stormwater Engineer immediately.
    3. Remove any excess sediment from the forebay(s). NO EQUIPMENT shall be used within 1-foot of the permanent bottom elevation. The final 2 feet of material to be excavated shall be started at from one side of the basin and removed going across or started in the middle and worked towards the outsides. A minimum of ingress and egress points shall be utilized as well as these areas will be stabilized within one working day when no longer needed. Other than what is necessary to complete the bottom excavation, no disturbance of the side slopes shall be conducted at this time. The completion of the side slopes to the design bottom elevation shall be completed to the best of the Contractor’s ability to limit disturbance to the adjacent areas.
    4. All disturbed areas meeting final elevations and grades above the permanent bottom elevation shall be seeded with Item #908015, Permanent Grass Seeding, Stormwater and mulched with Item #908020, Erosion Control Blanket Mulch.
    5. Basin bottom elevation shall be seeded with Item #908015, Permanent Grass Seeding, Stormwater and mulched with a hydraulic mulch.
    6. After all surrounding areas draining to the infiltration basin have sufficient vegetation as approved by the Engineer, E&S devices shall be removed.

*As-built drawings will be completed by the Contractor and certified by a Delaware PLS before the DelDOT Initial Inspection date. These drawings shall be sent to the Stormwater Engineer for verification. As-built drawings will include, but not be limited to:

  1. General topography of the whole facility at 1-foot contours including forebays and top/toe of any embankment.
  2. Inverts of all pipes and swales that inflow to the basin.
  3. Outline of all riprap and obtain spot elevations on top of the riprap.
  4. Outlet structure (or weir wall) inverts of any and all orifices/weirs, top of structure, outlet pipe, etc.
  5. Primary outflow pipe or channel. For a pipe outfall, inverts at the entrance and exit. For a primary outflow channel/swale, show at minimum three (3) cross sections equal distance apart at 50’ downstream along with the slope.

Bioretention

This is only a guide. The actual sequence on the plans needs to be customized for each bioretention area. If this is an infiltration facility, then discuss the language to be added concerning post-developed infiltration testing with the Stormwater Engineer.

Notify the CCR a minimum of 2 working days in advance of any construction so that the required facility construction checklist can be completed. Absolutely no wheeled or tracked equipment shall be allowed within 2 feet of the permanent bottom elevation. All #8 stone used in the bioretention area shall conform to the infiltration stone requirements of Section 910 of the Standard Specifications.

If the bioretention area is going to be used as a sediment trap during construction refer to some additional thoughts after the As-Built Notes that would need to be interspersed within these notes.

  1. Should bioretention area construction be necessary prior to vegetative stabilization of the contributing drainage area(s) as approved by the Engineer, the minimum shall be required:
    1. Inflow swales will have an 18” compost filter log placed 25 feet before the edge of the proposed bioretention area or closer if directed by the Engineer.
    2. Other inflow areas, including side slopes, will have silt fence or 18” compost filter log installed so that runoff is intercepted before entering the bioretention area.
    3. These items will remain in place until surrounding vegetation is established.
  2. Construct outlet and outfall as shown on the plans. Dewater foundation as needed in accordance with dewatering practices as stated in Section 900 of the Standard Specifications.
  3. Excavate the bioretention area to the dimensions shown on the plans and scarify the bottom a minimum of 6 inches.
    1. IF this is designed as an infiltration facility, i.e., no underdrain, then add “During excavation, the CCR shall observe the soil type. If standing water or excessive clay/silt material is discovered at the proposed bottom elevation, the CCR shall notify the Engineer and Stormwater Engineer immediately.”
  4. Place #8 infiltration stone up to the bottom invert of the underdrain orifice on the outlet structure. Do not compact the stone, just level.
  5. Place underdrain as shown on the plans.
  6. Place additional #8 infiltration stone so that there will be a minimum of 3 inches of stone covering the underdrain piping.
  7. Fill the rest of the area with biosoil mix to the elevation shown on the plans and do not compact. OPTION 1: Allow one storm event to take place or wait 3 calendar days to check for settlement and add additional biosoil mix, as needed, to achieve the design elevation. OPTION 2: Place biosoil mix in maximum 12” lifts, watering each lift until saturated.
  8. After final biosoil mix elevation achieved, apply and/or install the plantings as designated on the plans.
  9. Immediately after installing vegetation, place 4 inches of triple shredded, aged hardwood mulch over all of the biosoil mix.
  10. The same day that the bioretention area is completed, permanently stabilize the disturbed area around the bioretention area as shown on the plans.
  11. After all surrounding areas draining to the bioretention area have sufficient vegetation as approved by the Engineer, E&S devices shall be removed.

*As-built drawings shall be completed by the Contractor and certified by a Delaware PLS before the DelDOT Initial Inspection date. These drawings shall be sent to the Stormwater Engineer for verification. As-built drawings will include, but not be limited to:

  1. General topography of the whole facility at 1-foot contours including forebays and top/toe of any embankment.
  2. Inverts of all pipes and swales that inflow to the bioretention area.
  3. Outline of all riprap and obtain spot elevations on top of the riprap.
  4. Outlet structure (or weir wall) inverts of any and all orifices/weirs, top of structure, outlet pipe, etc.
  5. Primary outflow pipe or channel. For a pipe outfall, inverts at the entrance and exit. For a primary outflow channel/swale, show at minimum three (3) cross sections equal distance apart at 50’ downstream along with the slope.

Additional Sediment Trap Thoughts to Consider:

  1. Excavating bioretention area to elevation “X”. This should be 2 feet above the permanent bottom elevation. Anything less than the 2 feet minimum would need to be discussed with the Stormwater Engineer.
  2. If the bioretention area has an outfall such as a catch basin, need to consider what type of sediment control device would be placed at the inlet.
  3. Facilities with underdrains could have a skimmer dewatering device installed in the underdrain orifice if elevations allow. Remember, sediment traps require a storage volume of 3600cf per 1ac of runoff coming to the facility. If elevations would not allow a skimmer to be attached, then it needs to be temporarily plugged.
  4. Interim stabilization around the bioretention area until “final” construction begins.
  5. The Contractor shall inspect the bioretention area the next workday following a rain event and make any repairs as needed.
  6. Remove any excess sediment from the forebay(s).

Infiltration Trench

This is only a guide. The actual sequence on the plans needs to be customized for each infiltration trench. Also, language needs to be added concerning post-developed infiltration testing. Contact the Stormwater Engineer to help determine appropriate notes needed.

Notify the CCR a minimum of 2 working days in advance of any construction so that the required facility construction checklist can be completed. No wheeled or tracked equipment shall be allowed within 2 feet of the permanent bottom elevation. All #3 stone used in the trench shall conform to the infiltration stone requirements of Section 910 of the Standard Specifications.

If the trench is going to be used as a sediment trap during construction refer to some additional thoughts after the As-Built Notes that would need to be interspersed within these notes.

  1. Should trench construction be necessary prior to vegetative stabilization of the contributing drainage area(s) as approved by the Engineer, the minimum shall be required:
    1. Inflow swales will have an 18” compost filter log placed 25 feet before the edge of the proposed trench or closer if directed by the Engineer.
    2. Other inflow areas, including side slopes, will have silt fence or 18” compost filter log installed so that runoff is intercepted before entering the trench area.
    3. These items will remain in place until surrounding vegetation is established.
  2. Excavate the trench to the dimensions shown on the plans and scarify the bottom a minimum of 6 inches. During excavation, the CCR shall observe the soil type. If standing water or excessive clay/silt material is discovered at the proposed bottom elevation, the CCR shall notify the Engineer and Stormwater Engineer immediately.
  3. Install geotextile on all trench sides making sure to have enough extra to cover the top of the trench completely after stone is placed and having at least 1 foot of overlap of the geotextile. The only area that is not covered with geotextile is the bottom.
  4. Place the inspection port(s) as shown in the plans.
  5. Place #3 infiltration stone and other specified storage devices (if any).
  6. After stone placement, immediately cover the entire top of the trench with the excess geotextile and secure with #3 stone, so geotextile does not move.
  7. The same day that the trench is completed, permanently stabilize the disturbed area around the trench as shown on the plans.
  8. Inspect the trench and remove loose sediment on top of geotextile after every rain event. Ensure E&S controls are properly functioning.
  9. After all surrounding areas draining to the trench are permanently stabilized, as approved by the Engineer, E&S devices shall be removed and the excess geotextile removed from the top.

*As-built drawings will be completed by the Contractor and certified by a Delaware PLS before the DelDOT Initial Inspection date. These drawings shall be sent to the Stormwater Engineer for verification. As-built drawings will include, but not be limited to:

  1. General topography of the whole facility at 1-foot contours.
  2. Inverts of all pipes and swales that inflow to the trench.
  3. Outlet structure (or weir wall) inverts of any and all orifices/weirs, top of structure, outlet pipe, etc.
  4. Primary outflow pipe or channel. For a pipe outfall, inverts at the entrance and exit. For a primary outflow channel/swale, show at minimum three (3) cross sections equal distance apart at 50’ downstream along with the slope.

Additional Sediment Trap Thoughts to Consider:

  1. Excavating trench to elevation “X”. This should be 2 feet above the permanent bottom elevation. Anything less than the 2 feet minimum would need to be discussed with the Stormwater Engineer.
  2. If the trench has an outfall such as a catch basin, need to consider what type of sediment control device would be placed at the inlet.
  3. Interim stabilization around trench area until “final” construction begins.
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