R2026-136 Resolution Authorizing Lake Decatur Watershed Farmland Conservation Program Agreement With Lynn Clarkson for a Bioreactor Drainage Water Treatment Structure

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Drainage rationale and conservation opportunities The rationale for adding a denitrifying bioreactor to the existing subsurface drainage system is to improve water quality by reducing the concentration of nitrate nitrogen in drainage outflow. Based on the topography of the field and the existing drainage system, the field presents an opportunity for an 88 ft by 22 ft denitrifying bioreactor. With the use of two above ground control structures, and 403 cubic yards of woodchips, 99.0 acres of subsurface drainage can be treated. Preliminary design alternatives Two denitrifying bioreactor design alternatives were presented to the client(Table 2). A summary of the estimated costs and benefits for each alternative is provided in Tables 3 and 4. No construction permits are known to be required for this project. The client should contact the local Soil and Water Conservation District and/or NRCS field office to confirm. Table 2.Preliminary denitrifying bioreactor design alternatives Design Design Alternative Woodchip Total Estimated Total Estimated ID Volume Cost* Cost-Share** 1 Manual Bioreactor 403 cu.yd. $42,216.69 $29,733.34 One manual 12-inch,3-chamber,8-ft tall water control structure,and one manual 6- inch,2-chamber,8-ft tall water control structure. Denitrifying bioreactor footprint of 88 ft by 22 ft,with effective chamber height of 5.1 ft. 2 Automated Bioreactor 403 cu.yd. $49,937.49 $29,733.34 One automatic I2-inch,3-chamber,8-ft tall water control structure,and one manual 6- inch,2-chamber,8-ft tall water control structure. Denitrifying bioreactor footprint of 88 ft by 22 ft,with effective chamber height of 5.1 ft. *Based on engineering cost estimate in Tables 3 and 4 **Based on NRCS FY2026 EQIP payment schedule for CPS 605 Table 3.Design alternative 1-manual denitrifying bioreactor,engineering cost estimate No. Description Unit Qty Unit Price Subtotal 1 Clearing and grubbing LS 0 $500.00 $0.00 2 Tree removal LS 0 $3,000.00 $0.00 3 Seeding&fertilizing AC 0.5 $500.00 $250.00 4 Mobilization LS 1 $500.00 $500.00 5 Tile investigation HR 0 $165.00 $0.00 6 Earthwork&grading CY 617 $20.00 $12,333.02 7 Tile abandonment LS 0 $1,000.00 $0.00 8 Inlet WCS-8 ft x 12-inch w/6-inch side port EA 1 $3,143.36 $3,143.36 9 Outlet WCS-8 ft x 6-inch EA 1 $1,606.42 $1,606.42 10 12-inch non-perforated CPP dual wall LF 40 $15.00 $600.00 11 6-inch non-perforated CPP LF 125 $8.00 $1,000.00 12 6-inch perforated CPP LF 44 $8.00 $352.00 13 6-inch CPP tee EA 2 $50.00 $100.00 14 6-inch CPP elbow 45deg EA 0 $30.00 $0.00 15 6-inch CPP end cap EA 4 $10.00 $40.00 16 6-inch SDR35 backflow check valve EA 1 $150.00 $150.00 17 6-inch CPP to PVC flex coupler EA 2 $20.00 $40.00 18 3'x 3'gum rubber antiseep collar EA 0 $120.00 $0.00 19 Class 2 non-woven geotextile SY 216 $4.00 $864.00 20 4 mil plastic liner SY 400 $3.00 $1,200.00 Page 4 of 14