Recommended Design Criteria for Artificial Wetland Systems...
Introduction...
The artificial wetland treatment system is a relatively new technology. Like other land application systems artificial wetlands are site specific, consequently, all proposals will be reviewed on a site-by-site basis. Plans and Specifications proposals shall contain the pertinent information as required in Chapter IV for Wastewater Stabilization Ponds.
Basis of Pond Design ( Pre - Treatment )...
1. The maximum design loading on the primary cell(s) shall be 30 lbs BOD₅ per acre per day.

2. The design average flow rate shall be used to determine the volume required to provide a minimum combined storage capacity of 180 days in the stabilization ponds (pre-treatment system) and the artificial wetland areas. The minimum recommended storage capacity in the stabilization pond system shall be 150 days. The storage in the pre-treatment system shall be provided above the two (2) foot level. The maximum normal liquid level should not exceed five (5) feet in the primary cell or six (6) feet in the secondary cell.

3. The seepage rate for the primary cell(s) shall not exceed 1/16 inch per day. Seepage of up to 1/8 inch per day may be allowed in secondary cells, considered on a case- by-case basis.

4. The minimum number of cells for the pre- treatment system shall be two when the system is designed to discharge.

5. The shape of the cells shall be such that there are no narrow, L-shaped or elongated portions. Round or rectangular ponds are most desirable. Rectangular ponds shall generally have a length not exceeding three times the width. Dikes shall be rounded at the corners to minimize accumulation of floating material.

6. Refer to Chapter IV Design Criteria for pond location, construction details, pond bottom details, influent lines, control structures and other miscellaneous criteria.
Basis of Wetland Design...
1. Design : ( a ) No discharge is recommended from the artificial wetland treatment system during the 180-day winter storage period unless it can be shown that the discharge meets NPDES permit limits. ( b ) The maximum hydraulic design loading flow through rate on the artificial wetland(s) shall be 25,000 gallons per acre per day. ( c ) The minimum recommended detention time for treatment in the artificial wetland system may be 7 days with 14 days being the most desirable. ( d ) The recommended depth of flow in the wetland system shall be between 6 and 24 inches, with nine (9) inches as the recommended optimum depth. ( e ) A rectangular configuration is recommended to enhance treatment efficiency in the system with a length to width ratio of between 5 and 10 to 1. However, irregular shorelines offer substantially better support for wildlife. ( f ) Seepage rates in the artificial wetland areas will be addressed on a site-by-site basis based upon in-situ material, groundwater depth and the groundwater use. Generally, no compaction will be required on wetland pond bottoms. The berms shall be compacted to at least 90 percent of Standard Proctor Density. ( g ) The bottom of the artificial wetland treatment units shall not have a slope greater than 0.2%. ( h ) Due consideration shall be given to multiple wetland cells and to possible future expansion on suitable land when the original land acquisition is made for flexibility and for maximum operational capability.

2. Construction : ( a ) The project site should be protected from surface inflow waters. The site should also be protected to one foot above the 100 year flood elevation. ( b ) In order to prevent erosion and channelization at the inlet of the wetland, a discharge header should be utilized. The header should be equipped with removable end-plugs so the line may be drained to prevent freeze-up. Uniform distribution of wastewater to prevent short-circuiting through the wetland shall be assured. It is recommended that the header outlet elevation be at or above the maximum design depth. ( c ) It is recommended that pipes and flumes located in or near inlet and discharge structures will not be in a completely submerged condition to maintain the integrity of the system and reduce freeze-up problems. ( d ) A suitable discharge structure from the wetland shall be utilized. The structure shall be adjustable so that the depth in the wetland may be modified as needed. It is recommended that the discharge or interconnecting structure outlet flow lines be 6 inches off the bottom to maintain the minimum depth. ( e ) Care should be taken to establish the vegetation as soon as possible after construction. The emergent vegetation, once established, should prevent the erosion of the berms of the system. Riprap may be required around the inlet and outlet structures of the wetland. A cover crop may be planted on the interior slopes to prevent erosion prior to the establishment of the emergent vegetation. Consideration may be given to the use of excelsior blanket over seeding. f. The exterior and interior slopes of the wetland berms surrounding the wetland basins shall not be steeper than 3H:1V. ( g ) The top width of the berms shall be a minimum of eight feet. ( h ) Following the final grade, the substrate should consist of a minimum of one foot of clean inorganic/organic material of which 80-90% will pass a number 10 sieve. ( i ) The dike elevation should be a minimum of two feet above the high water level in the wetland. ( j ) If groundwater contamination is a potential problem, the bottom of the wetland may be sealed with a suitable material. However, generally no liner will be necessary in the artificial wetland. ( k ) Aluminum, concrete, or PVC pipe or other material generally accepted for sewers shall be specified for the piping requirements in the wetland. Provisions may be required to prevent the settling of the piping structures under load. It is recommended where structures are partially or completely submerged in ice conditions that a flexible piece of pipe be installed to allow for some movement of structure. ( l ) The effluent discharge structure shall be equipped with a suitable flow monitoring device, such as a flume or V-Notch weir, to monitor flows leaving the treatment site. Staff gages for measuring depths in structures should be provided where flow monitoring is required. ( m ) In order to accurately monitor influent flows to the artificial wetland system, an influent measurement structure shall be included. ( n ) The entire wetland area shall be enclosed with a suitable fence to provide public safety, exclude livestock and to discourage trespassing. ( o ) Warning signs shall be provided along the fence around the treatment facility. There shall be at least one sign on each side of the facility, with a minimum spacing of 500 feet. ( p ) Removable screens should be provided on pipe ends to prevent entrance of trash and wildlife.

3. Vegetation Establishment : ( a ) Specifications for the seeding of the artificial wetland shall as a minimum include : ( 1 ) Plant species and propagule type, ( 2 ) Plant distribution (vegetative zonation), ( 3 ) Planting (including time restraints), ( 4 ) Fertilization and ( 5 ) Water level control and site maintenance. ( b ) Topsoiling the graded wetland area is generally not required. Substrate properties generally do not limit the establishment of a wetland. ( c ) Only indigenous plant species shall be used, preferably collected within a 100 mile radius. Preferred species include, but are not limited to : ( 1 ) Typha Latifolia - Common cattail, ( 2 ) Typha Angustifolia - Narrow leaf cattail, ( 3 ) Scirpus spp. - Bullrush, and/or ( 4 ) Phragmites communis - Reed. ( d ) Seeding should generally be accomplished in the spring. Also, at least one fertilization should be required, preferably shortly after seed germination or at one month. The recommended fertilizer is the standard 10- 10-10 or 20-10-10 mixture at a rate of 600 lbs/ac or 300 lbs/ac, respectively. Where wastewater stabilization ponds exist, fertlilization may not be necessary, as the nutrients in wastewater may suffice. ( e ) For seeding, the following is recommended : The seed should be broadcast uniformly over the substrate at a rate of 10 viable seeds per square foot. The seeds should be cultivated to subsurface depths of 0 to 1 inch followed by lightly packing, rolling or dragging the tilled surface. Flood the site with 1-2 inches of water until the seeds germinate and become several inches tall. At this time, the area should be fertilized. ( f ) For transplanting (the recommended method of vegetation establishment) the propagule should be transplanted, as a minimum, on a two foot grid. The number of transplants required may be calculated from the equation :

N = [ ( L / D ) + 1 ] [ ( W / D ) + 1 ]

Where :

N = Number of transplants
D= Distance between transplants
L = Length of site (ft)
W = Width of site (ft)

Transplanting on a two foot grid should provide a uniform vegetative cover in one growing season. Transplants should be kept moist, but not flooded to submerged conditions. The transplants should also be fertilized, preferably with controlled release fertilizer such as Osmocote 18-5-11 for fall and winter planting, Osmocote 18-6-12 for spring planting, and Osmocote 19-6-12 for summer planting. Refer to suppliers instructions when transplanting.

4. Wildlife Enhancement (optional) : ( a ) Some method of detritus removal should be considered to prevent aging of the wetland. Harvesting or burning are two options available. ( b ) To provide the greatest potential for wildlife enhancement, 25 to 35% of the artificial wetland surface should be open water with a depth no greater than five feet. However, care should be taken to prevent a large open water area, which could influence treatment efficiency. Several small pools are most desirable. Of the 25 to 35% open water area, approximately 10% should be reserved for the construction of erosion protection bars. The emergent vegetation of the artificial wetland system should comprise 65 to 75% of the available surface area with a water depth of less than two feet deep. ( c ) In order to prevent mosquito-production problems, wetland systems should be designed so that the occurrence of hydraulically static areas is minimized. The majority of the natural predators of mosquitoe larvae are strictly aerobic, and as such, anaerobic conditions in wetlands should be avoided.

5. Water Quality Monitoring : ( a ) Surface Water - Refer NPDES permit limits and requirements. ( b ) Ground Water - Refer to Chapter XIII.

6. Deviations from Design Criteria : The Department may consider and allow deviations where adequate documentaiton is provided to prove the need for such deviation.