Incorporating the design features that were successful in the treatment capacity of the 1.2 acre wetland at the Flight 93 site for a typical flow = 775 gpm. The average percent removal was roughly 70% for iron and 50% for manganese within the wetland. This analysis allowed for a design foundation of the polishing aerobic wetland at the Clyde Mine Water Water Treatment Facility and the potential application at other mine water treatment locations where a relatively minor amount of polishing is needed to enhance iron and manganese removal for the final discharge.

1. Effective Aerobic Wetland Design for
Metals Polishing in Mine Water
Treatment
Brad Shultz, E.I.T., Hydrologist
U.S. Office of Surface Mining Reclamation and Enforcement
Presented at the 2015 PA AMR Conference, State College, PA
June 26, 2015

2. Purpose of Aerobic Wetlands
• Passive form of treatment for net alkaline mine water
– Raw water
– Following alkaline treatment of net acidic water
• Provide vegetation in a relatively shallow water
environment capable of removing iron and manganese
precipitates
• Natural mechanism for treatment
• Aesthetically regarded, provides habitat
• Provides reliable and proven form of metals removal with
minimal maintenance, potential for use at tail end of
active treatment facilities (e.g., H2O2)
• Reduced need for polymer?

3. Example Aerobic Wetland Systems
• PA DEP has had recent involvement in the
design and/or update of several passive
treatment systems involving aerobic wetlands
• Some examples of systems with functioning
wetlands evaluated as part of OSMRE
technical assistance were:
– Melcroft Passive Treatment System
– Flight 93 Memorial Site Water Treatment System
– Lion Mining Water Treatment System

4. Melcroft Passive Treatment System
Fayette County
• Passive treatment of Melcroft #3 underground
mine pool using two VFPs followed by settling
pond, two aerobic wetlands (in series), and
manganese removal bed
• No deep water forebay
• Flow distribution using perforated pipe into first
wetland
• Rock baffles (check dams) used in each wetland
• Fabricated stop log system installed in the
spillway as the outfall for each wetland

5. Melcroft System Design Plan

6. Melcroft Passive System
Influent to Wetland 1:
Total Fe = 2.15 mg/L
Fe2+ = 0.86 mg/L
Total Mn = 2.95 mg/L
pH = 7.10
Typical Flow = 87.3 gpm
Design Flow = 125 gpm
Two 0.75 acre Aerobic Wetlands

7. Melcroft Mine
Drainage Passive
Treatment
System:
Polishing
Wetlands

8. Melcroft Wetland Performance:
Total Iron Removal

9. Melcroft Wetland Performance:
Total Manganese Removal

10. Flight 93 Memorial Site Water Treatment System
Somerset County
• Approx. 1.25 acre Aerobic wetland added to the
existing treatment system to improve iron removal
(2013)
• Four large settling ponds in series first treat the
water pumped from mine pool prior to entering
wetland, followed by additional ponds
• Design flow = 775 gpm
• Influent Total Fe = 1 – 2 mg/L
• Influent Total Mn = 6 – 9 mg/L
• Influent pH = 8.0

11. Flight 93 Memorial Site Treatment System
Pre-Wetland
Future Wetland

12. Flight 93 Overall Improvements Site Plan

13. Wetland Area
1.25 acres
Flight 93 Wetland Design Plan

14. Flight 93 Wetland Performance:
Total Iron Removal

15. Flight 93 Wetland Performance:
Total Manganese Removal

16. Flight 93 Memorial Site Aerobic Wetland

17. Flight 93 Memorial Site Aerobic Wetland

18. Lion Mining Water Treatment System
Somerset County
• Passive treatment system constructed ~ 2010
• Multiple settling ponds with two venturi type
aeration systems in parallel at beginning for aeration
• Approx. 0.75 – 1.0 acre Aerobic Wetland constructed
at end of system for final polishing of any remaining
Fe and Mn
• Level lip spreaders (grouted rock-lined spillway) used
to distribute flow into wetland
• Forebay and deep water outlet zones

19. Lion Mining Treatment System Wetland
Influent to Wetland:
Total Fe = 0.86 mg/L
Total Mn = 0.75 mg/L
pH = 7.50
Typical Flow = 650 gpm

20. Lion Mining Passive Treatment System
0.75-1.0 acre Aerobic Wetland

21. Lion Wetland Performance:
Total Iron Removal

22. Lion Wetland Performance:
Total Manganese Removal

23. LTV Clyde Mine Water Treatment Facility
• Constructed pebble quicklime (CaO) treatment
plant in 1998 for the flooded underground mine
• Mine water was initially net acidic, but eventually
became net alkaline once target mine pool
elevation was maintained
• Typical operating flows range from 1,000 – 2,000
gpm
• Main parameters of concern for treatment:
– Ferrous Iron (Fe2+)
– TDS

24. Clyde Project Location
Clyde

25. Existing Clyde Mine Water Treatment
Facility
Proposed Wetland
Location ~ 2 acres

26. LTV Clyde Mine Water Treatment Facility
(cont.)
• In 2014, PA DEP and OSMRE personnel
conducted on-site pilot testing using 50%
hydrogen peroxide (H2O2) in place of CaO
• Tests revealed H2O2 capable of decreasing Fe2+
concentrations similar to CaO treatment
• Trade-off = Less Mn was removed with H2O2
• Considerable cost savings using 50% H2O2 in
place of CaO

27. LTV Clyde Mine Water Treatment Facility
(cont.)
• Upon conversion to H2O2 for treatment, the
operator, PA DEP, and OSMRE personnel discussed
idea of constructing a polishing (aerobic) wetland
following the clarifier to reduce or eliminate the
need to add polymer
• Technical assistance request from PA DEP to OSMRE
– Develop engineering design of Aerobic Wetland for
final outfall from clarifier
• Small amounts of iron particles and manganese
targeted for removal, typically less than 3.0 mg/L

28. Critical Design Features of Aerobic
Wetlands
• Evaluated several existing Aerobic Wetlands in PA
• Determined several critical factors that affect
efficiency of wetlands specifically for iron
precipitate removal
• Iron precipitates created through
aeration/oxidation do not readily floc, need
polymer or ‘surfaces’ for removal
– Particularly true for last few mg/L of iron

29. Flow Introduction
• Diffuse laminar flow introduction
• No concentrated flow outlet (end of pipe)
• Level lip spreaders, troughs, deeper water
forebay, etc
• Minimize potential for channelization
• Bypass available to divert flow
• Need to provide additional aeration (dissolved
Fe and Mn still present in the influent)

30. Forebay
• Deeper pool at upstream end of wetland (>2’)
• Retention time of concern?
• Encourage spreading of the incoming water
across width of wetland, reduce velocity of
water and help with precipitate settling,
increased storage for sludge
• Baffles needed?
• Length of forebay importance

31. Rock Baffles/Spreaders/Check Dams
• Provide a means of helping to distribute flow
• Allow for maintenance access
• Stone size
• CaCO3 content important?
• Height of baffle vs water level
• Important locations:
– Transition zones: Deep to shallow and shallow to
deep
– Throughout wetland (Melcroft & Flight 93)

32. Water Depth in Vegetated Zones
• Is 6 to 18 inches still ideal range for wetland
vegetation and function?
• Initial period at shallow depth (<6”) to allow
for wetland vegetation proliferation
• Importance of homogeneous vegetation
growth throughout wetland area to minimize
channelizing flow (short-circuiting)
• Wider and dense wetland = Low velocities

33. Outfall Structure
• Most important factor: Encourage
distribution/draw from entire width of wetland
• Deep pool similar to forebay
• Large perforated pipe along downstream bottom
end (pipe size and perforations based on design
flow)
• Ease of access for maintenance
• Hydraulically connected to allow water level control
of entire wetland
• Ability to measure flow and water quality

34. Clyde Mine Water Treatment Facility
Aerobic Wetland Design
• Design Flow = 2,000 gpm
• Typical Flow = 1,000 gpm
• Influent Maximum Total Fe & Mn = 3.5 mg/L
• Approximate 2.0 acre area available between
treatment facility and South Branch Tenmile Creek
• Challenges
– Sewer line, process water line, existing outfall pipe
– Potential for encountering spoil material during
excavation

35. Clyde Mine Water Treatment Facility
Aerobic Wetland Design
• Flow distribution trough at inflow to forebay
• Forebay
• Rock baffle/spreader at transition from forebay to
shallow wetland
• Three rock baffles/spreaders equally spaced within
the vegetated zone
• Rock baffle/spreader at transition from vegetated
zone to deep pool at outlet structure
• Perforated pipe along downstream bottom end
connected to a water level control structure

36. View from Clarifier of Area for Wetland

37. Existing Final Outlet Location

38. Clyde Mine Water Treatment Facility
Aerobic Wetland Preliminary Design

39. Acknowledgments
• PA DEP – Rich Beam and Malcolm Crittenden
• AMD Industries – Don Charleton
• Mountain Watershed Association