INSTALLING CONSTRUCTED WETLANDS

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NDWRCDP disclaimer This work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (WPA No. X ) with Water Environment Research Foundation (WERF) in Alexandria, Virginia. These materials have not been reviewed by the U.S. Environmental Protection Agency, NDWRCDP, or WERF. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, WERF, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.

Overview for Constructed Wetlands  Introduction  Types  Site preparation  Excavation  Liners  Borders  Media  Inlet & outlet devices  Vegetation  Startup

Constructed wetlands  Recreate treatment processes that occur in natural wetlands

Constructed wetland  Basin/cell containing microorganisms, media, and plants that treat effluent  Effluent flows horizontally through bed

Treatment in CW  Requires pretreatment Typically a septic tank Typically a septic tank  Pathogens and nutrients removed by microbes on surfaces of media & plant roots  Processes involved Sedimentation Sedimentation Nitrification Nitrification Denitrification Denitrification Adsorption Adsorption

Treatment

Hydraulic detention time  Amount of time effluent is in contact with and in the treatment media  The longer the wastewater is in the wetland… the better the quality of the exiting effluent! Typical warm weather design 3 days Typical warm weather design 3 days Typical cold weather design 10 days Typical cold weather design 10 days

Installation Form 10.5 installation checklist: constructed wetlands

1. Types  Identify flow regime Free water surface Free water surface Subsurface flow Subsurface flow Combination Combination

1. Type  Number of cells Single cell Single cell Multiple cell Multiple cell First cell linedFirst cell lined Second cellSecond cell May be unlined May be unlined May be lined with natural clay soil May be lined with natural clay soil compactedcompacted

1. Type  Dimensions Length, width, depth Length, width, depth Follow design Follow design Length to width (aspect) ratio, and depth are significant Length to width (aspect) ratio, and depth are significant

2. Site preparation  Stake out cell location Include area for berm or border Include area for berm or border  Check elevations Very important if gravity fed Very important if gravity fed  Remove excessive vegetation from footprint  Test soil moisture

3. Excavation  Record excavation equipment used  Walls typically vertical Consider using a trencher to cut walls before excavating Consider using a trencher to cut walls before excavating  Design may call for a more artistic form Gentle curves Gentle curves

3. Excavation  Bottom should be free of water, rocks, debris, roots, etc.  Grade according to design Slope is in correct direction Slope is in correct direction Level across width Level across width  Bedding material as cushion for liner Soil, geotextile fabric, bentonite clay Soil, geotextile fabric, bentonite clay

4. Liner  Liner keeps wastewater in cell Polyethylene Polyethylene Neoprene Neoprene Butyl rubber Butyl rubber Compacted native clay Compacted native clay Bentonite clay Bentonite clay PVC PVC Hypalon (HDPE) Hypalon (HDPE) Ethylene Propylene Diene Terpolymer (EPDM) rubber Ethylene Propylene Diene Terpolymer (EPDM) rubber

4. Rubber/poly liners  Smooth bottom & sides to remove creases  Tuck in corners and fold the liner  Liner can be purchased custom cut to fit

4. Bentonite liners  Spread bentonite clay on bottom of wetland Often about 1-2 pounds per sq foot Often about 1-2 pounds per sq foot  Plastic liner 4-6 mil over the bentonite to prevent expansion into media

4. Liner  Liner should extend higher than water and media level  Protect from sun  Orient correctly when unfolding  Watertight Single piece preferable Single piece preferable Seams must be sealed Seams must be sealed Test by ponding water over the liner Test by ponding water over the liner Check for holes or defects Check for holes or defects

5. Influent distribution  Types Perforated pipe Perforated pipe Leaching chamber Leaching chamber  Record length of device Should extend most of the width Should extend most of the width  If gravity fed, device must be level and stable  Elevation must match design  Accessible for O&M Cleanouts/inspection ports Cleanouts/inspection ports  Protected from clogging

5. Influent distribution  Penetrations must be watertight Boot Boot Concrete around pipe Concrete around pipe Mastic and pipe clamp Mastic and pipe clamp Bentonite clay Bentonite clay

6. Effluent collection  Often slotted pipe across wetland  Larger gravel placed around pipe  Liner penetration must be watertight  Cleanout/inspection port

6. Water level control  Controls water level  Rotational control Elbow can be rotated Elbow can be rotated  Vertical control Additional pipe length Additional pipe length Sleeved pipe Sleeved pipe

7. Media  Most commonly washed rock  Use what is designated in the design  Media must be Clean- if it is not, don’t use it Clean- if it is not, don’t use it Properly graded Properly graded Rounded so it won’t puncture the liner Rounded so it won’t puncture the liner  Do not contaminate the media with dirty equipment or by placing it on soil

7. Media  Document media depth  Do not damage liner as you add media Geotextile fabric over the liner Geotextile fabric over the liner May add water to the cell as a cushion May add water to the cell as a cushion  The top of the media should be level Add water to cell and temporarily adjust water level to be at the desired media level Add water to cell and temporarily adjust water level to be at the desired media level

8. Vegetation  Provide oxygen to bed  Removes a small percentage of nutrients  Must be able to survive in a saturated medium  Must survive in climate Design should call for plants that can overwinter in that area Design should call for plants that can overwinter in that area

8. Plants  Not all CW will have plants All free surface wetlands must have plants Design should specify plants  Clean roots to remove soil  Plant on a grid pattern Follow design Generally 2′ x 2′

9. Borders  Prevent surface water and soil from entering media  May provide wall support  Types: Stone Stone Concrete Concrete Treated wood Treated wood Earthen berm Earthen berm

9. Wood border  Frames wetland Landscape timber Landscape timber Railroad ties Railroad ties  Place liner over wood frame  Cut liner to fit  Place second wood layer over liner  Rebar for staking wood to ground  May deteriorate over time

9. Concrete borders  Trench border  Construct framing Inlet and outlet Inlet and outlet  Pour concrete border

9. Concrete borders  Excavate soil from within concrete border  Make sure to protect inlet and outlet structures  Generally bentonite liner with plastic cover

9. Rock borders  Rock slate around border to protect liner  Grass cover or protective berm around the wetland  Edging material can assist with maintenance

Startup Form 10.6 startup checklist: constructed wetlands

Startup  Verify all steps in the installation process were completed  Verify water level is at desired depth  If wetland is recirculating, note the recirculation ratio.

Summary  Types  Site preparation  Excavation  Liners  Borders  Inlet and outlet devices  Media  Vegetation  Startup