PASSIVE TREATMENT SYSTEM FOR

ABANDONED MINE Sonya Daley

DRAINAGE – GLADDEN Andrew Timbrook MINE DISCHARGE INTO Hendrik van Hemmen Ted Mullen MILLERS RUN, SOUTH Cory Harris Alissa Petrik

FAYETTE, PA

Abandoned Mine Drainage (AMD) is a serious problem for Western Pennsylvania. One particularly polluted waterway, Millers Run, is examined in this report, and treatment options are considered. Since nearly all of the mass of pollutant comes from one discharge, Gladden Discharge, it is selected as the critical source for treatment. Various treatment methods are explored and a passive treatment system is described in detail. It consists of quicklime dosing to raise pH, cascade aerators to increase dissolved oxygen, a settling basin for sludge collection, and an aerobic wetland. Cost is estimated and some construction issues are considered. Table of Contents Visual Summary of Design ...... 3 Executive Summary ...... 4 Background Information ...... 5 Abandoned Mine Drainage ...... 5 Millers Run ...... 5 Gladden Discharge ...... 5 Other Discharges ...... 6 Project Origin ...... 6 Testing, Data, and Results ...... 7 Water Quality Tests ...... 7 Topographic Information ...... 8 Flow Quantification ...... 11 Settling Test ...... 12 Dosage Test ...... 12 Design Considerations ...... 13 General AMD Design Considerations ...... 13 Site-Specific Design Considerations ...... 14 Alternate Solutions ...... 15 Alternative 1: Two Settling Ponds Separated By a Rock-Lined Channel ...... 15 Alternative 2: Limestone Channels and an Aerobic Wetland ...... 16 Alternative 3: A Combination of VFP & Other Treatment Elements ...... 17 Final Design ...... 19 Summary ...... 19 Limestone Channels ...... 21 Doser ...... 23 Distribution Box ...... 24 Cascade Aeration Steps ...... 25 Settling Pond ...... 27 Weirs ...... 29 Wetland ...... 31 Effluent Calculations ...... 32

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Operations and Maintenance ...... 33 Refilling ...... 33 Dredging ...... 33 Testing ...... 33 Inspection ...... 33 Construction ...... 34 General ...... 34 Site Access ...... 34 Excavation ...... 35 Channel D ...... 36 Aerobic Wetland ...... 36 Possible Construction Order ...... 37 Cost ...... 38 Acknowledgements ...... 40 References ...... 40

2

Visual Summary of Design

Schematic

Plan

3

Executive Summary

Final Design This report describes the design of a passive system for treating abandoned mine drainage (AMD) in Millers Run.

The system will be located along the current run between Gladden discharge and Millers Run.

As shown in the figures on the previous page, the system’s main components are an Aquafix doser (to raise pH), cascade aerators (to raise dissolved oxygen), a settling pond (to remove the majority of the suspended iron), and an aerobic wetland (to remove remaining iron).

The settling pond is split in half to facilitate clean-out.

An overflow channel will protect the wetland from heavy rain events.

Cost The total cost for implementing the system will be $318,368.

Total annual O&M cost will be $30,040 in the first year, and $27,480 for subsequent years.

Test Results Testing showed that the majority of AMD in Millers Run can be treated by treating just the water from the Gladden discharge.

The Gladden water contains high levels of iron (74 ppm) and a low pH (5.25), which is typical of AMD.

Attempts were made to quantify the flow from the Gladden discharge by several methods. Although all of these methods returned similar average flow rates (1,000-1,500 GPM), the data was not comprehensive enough to confidently calculate the effect of large rain events. Therefore, a large factor of safety was built in.

Tests were also conducted to validate the final design, and were largely successful.

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Background Information

Abandoned Mine Drainage Abandoned mine drainage is formed when abandoned mines fill up with water and overflow or upwell to the surface.

The chemistry of the water draining from the mines in Western Pennsylvania depends on the type of coal, rock, and minerals that the water contacts as it flows in and out of the mine.1 While underground, water dissolves metals (aluminum, manganese, and iron) in the ground. When the mineral-laden water surfaces and comes in contact with the oxygen in air, the metals form solids that coat the bottom of the waterway.

This coating gives the waterways a distinctive orange color.

The coating of sediment AMD causes can affect the public water supply and disrupt the ecology of waterways.

Millers Run Millers Run is a creek located southwest of Pittsburgh. It flows into Chartiers Creek.

Millers Run is presently polluted by abandoned mine drainage and devoid of aquatic life in the four-mile stretch downstream from the Gladden Discharge.

Gladden Discharge The Gladden Discharge is located in South Fayette Township.

It is a mine seepage that emerges from underground and flows in a channel that runs for about six hundred (600) feet before its confluence with Millers Run.

The water is AMD and heavily polluted with iron.

The Gladden Discharge is the major contributor of AMD to Millers Run.

The Gladden discharge has the highest iron and second highest manganese content of the discharges to Millers Run, and, with its high flow accounts, it for the highest acid and iron loading.2

1 (What is Abandoned Mine Drainage (AMD)?) 2 (Gladden (Millers Run))

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Other Discharges There are several other discharges in the Millers Run watershed. None of these contribute as much AMD as the Gladden discharge does.

One discharge of particular interest was the Cuddy Discharge. However, Cuddy Discharge does not pollute nearly as much as the Gladden discharge does.

Project Origin This project came from the mind of Dr. John Oyler, who was aware of the discoloration of Millers Run and the discoloration that that water causes when it enters Chartiers Creek.

Knowing about a successful AMD remediation project is located at Wingfield Pines, this project is meant to imitate that success for Millers Run.

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Testing, Data, and Results

Water Quality Tests In order to properly design a system to treat the acid mine drainage, a series of water quality tests were executed to determine the characteristics of the water entering Millers Run.

Preliminary testing consisted of on-site pH and Total Dissolved Solid (TDS) tests at all the tributaries entering Millers Run. This testing, along with the flow data from the tributaries, determined which discharges and tributaries were contributing the most to the deterioration of Millers Run.

More intensive onsite testing occurred at the Gladden Discharge. Tests were performed on Millers Run upstream and downstream of the discharge in order to determine the impact, if any, of the discharge on the stream. The results of the pH testing showed a significant drop in pH due to the loading from the Gladden Discharge.

Additional testing was required to determine the characteristics of the compounds present in the discharge and their concentrations. (This information is critical in establishing which treatment design option will be most effective in treating the discharge.)

Tests were performed on samples taken from the Gladden and Cuddy discharge to determine the concentrations of iron, aluminum, manganese, magnesium, zinc, and calcium. The samples were filtered and compared to standard solutions using a flame spectrophotometer to determine concentrations. This information, combined with the flow data for the discharges, allowed for the daily loading in kg/day for each of the metals. The results can be found in the following table:

Gladden Cuddy Gladden Cuddy Flow (GPM) 1350 284 Flow (L/min) 5110 1075 TDS (ppm) 945 652 TDS (ppm) 945.00 700.94 pH 5.25 5.21 pH N/A N/A Fe (ppm) 74.17 20.72 Fe (kg/day) 4284.47 251.86 Mn (ppm) 0.61 0.47 Mn (kg/day) 32.21 5.29 Mg (ppm) 24.01 24.24 Mg (kg/day) 307.11 65.22 Zn (ppm) <<5 <<5 Zn (kg/day) - - Al (ppm) <1 <1 Al (kg/day) - - Ca (ppm) 64.57 70.91 Ca (kg/day) 736.50 170.15

*Assuming 1 ppm = 1 mg/L *Assuming Specific gravity of Fe is 7.85 *Assuming Specific gravity of Mn is 7.21 *Assuming Specific gravity of Mg is 1.738

Factoring in dilution, the Cuddy Discharge only accounts for 1.16 ppm of Fe in Millers Run.

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Topographic Information An accurate stream profile provided an overview of the stream to help with selection and placement of the system components (in the final design: the limestone channel, settling pond and wetland). The total elevation change and elevation head at various points along the stream showed where it would be beneficial to use the existing stream reaches for the limestone channels.

To find the profile, a Jacob’s staff was made out of a meter stick and small hand level. By assigning the farthest point downstream (where the Gladden Discharge enters Millers Run) as zero elevation, the staff provided relative elevation increases by sighting a point upstream and recording the height difference.

The profile was later used to determine how feasible it would be to excavate the soil necessary to build the treatment system. By assuming a width at several points along the stream and taking the area between the existing and proposed levels on the graph, an estimate was formed for the volume of soil that needed to be removed.

Using satellite images from Google Maps3 and Bing Maps4, and from walking the site, it was possible to estimate the size of the watershed of the run formed by the Gladden Discharge. It was also simple to

3 (Google, 2010) 4 (Bing, 2010)

8 determine the size of the open area available for the system by importing the file to AutoCAD and scaling:

Our usable area for the treatment system is 1.2 acres and fills most of the watershed. The area is bordered by route 50, a parking lot, and steep hillsides.

By combining the profile data and satellite images, a drawing was created that mimics a contour map:

Values shown are feet of drop in elevation from the source

The land surrounding the discharge is very steep. One hillside is moderately forested and the other is covered in dense brush. Route 50 runs parallel to the discharge to the south, a parking lot and railroad tracks exist to the north and run parallel, eventually crossing Millers Run after the confluence.

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The seepage and resulting discharge is mainly fed not by immediate runoff, but by infiltration and delayed runoff. This is because of the small size of the drainage area.

The seepage has opened an underground drainage area that allows water to infiltrate to the discharge from other locations that would be impossible to predict or locate, making the storm flows very difficult to accurately predict.

These existing conditions provide the discharge with a quick, relatively low peak flow from runoff, followed by a longer, larger peak from infiltrated water.

The discharge has created very swampy and unstable conditions, with most of the soil and rocks in the channel covered in a layer of iron.

The Gladden Discharge run watershed is very small in area. Therefore, there is not much runoff to take into consideration when estimating stream flows from storm events.

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Flow Quantification Three methods were used to quantify the flow from the Gladden discharge: research (average = 1,500 GPM), flow meter readings in the field (1350 GPM), and historical weir readings (average = 1,080 GPM).

During research, multiple sources put the average flow rate of the Gladden discharge at around 1500 GPM before a restoration project, and 1000 GPM after. There is anecdotal evidence of flow reaching 5000 GPM in 2004, following hurricanes Francis and Ivan.5

A flow rate of 1350 GPM was measured in the field using equipment borrowed from Dr. Dan Budny. This equipment was also used to take readings at two other discharges into Millers Run.

The third set of flow data for Gladden was obtained from the Bureau of Abandoned Mine Reclamation. These flow data were measured at a weir located about halfway between the discharge and Millers Run. The data was not taken at regular intervals, but the average time between readings appears to be approximately two weeks. A quick comparison to historical daily rainfall data6 failed to show a relationship between the dates when measurements were taken and major rain events. The average flow rate from these readings was 1080 GPM.

None of these data sets is large enough to correlate flow rates from the Gladden discharge to rainfall, and the fact that the watershed for Gladden Run is so small that almost all of the flow comes from the discharge itself makes it practically impossible to calculate flow rates with GIS.

In addition, since the aquifer that feeds the discharge could extend a great distance, there could be an unknown delay between rainfall and discharge from Gladden.

5 (South Fayette Conservation Group) 6 (KPABRIDG1 (Olde Orchard), 2010)

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Due to the uncertainty of the flow data, a design flow of 1500 GPM was selected for treatment, but it was decided to design the system to survive flows of up to 4000 GPM, which is five standard deviations from the average and significantly outside of the observed data.

Settling Test A settling test was performed to determine the settling velocity of the particles in AMD with conditions similar to those in the proposed treatment system.

First, a one liter sample was taken from the Gladden Discharge itself.

Next, hydrochloric acid (HCL) was added to the continuously stirred sample to drop the pH to around 3.0, allowing all metals to dissolve into the solution.

Once all the metals were dissolved, sodium hydroxide (NaOH) was added to the continuously stirred sample to quickly raise the pH up to 7.5. The sample was covered and shaken to recreate the aeration process and allow the metals to oxidize.

The sample was then poured into a large graduated cylinder and observations were made to determine a line of separation in particle size and concentration due to settling. Measurements were taken every two minutes, tracking the downward progress of the particles.

This method proved to be inaccurate, since it was difficult to see a clear line of separation. Therefore, the data recorded from this test was not factored into the final design of the system.

The test did give confirmation that the metals will flocculate and settle when exposed to the right conditions.

Dosage Test To determine the optimal addition rate (and therefore concentration) of lime to raise the pH of the influent above 7.5, a test was performed by manually adding calcium carbonate (CaCO3) to samples of AMD water from the Gladden site (where an initial pH reading of 5.17 was taken).

Lime was added and dissolved in the water while pH readings were periodically taken.

Unfortunately, the water had only reached a pH of about 5.6 before it became completely saturated.

This test used CaCO3 instead of CaO due to availability, but it appears that that substitution made this data unusable.

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Design Considerations

General AMD Design Considerations7 In order to design a successful passive treatment system for AMD, one must consider and define several parameters:

Flow Rates A properly designed treatment facility, whether active or passive, must be hydraulically sound and able to operate at a range of possible flows. This is not only to effectively treat the influent, but also to avoid damage to the facility as a result of high flows.

pH In order to properly precipitate dissolved metals (such as iron and aluminum) in water, the pH of the water must be above neutral (ideally above 7.5). Quantifying this at the point of treatment will allow proper measures to be designed to raise the pH to a level that is treatable, since different treatment methods to raise pH work better with water of different pHs.

Iron Concentration/Form Iron is the primary contaminant of AMD (especially in the southwestern Pennsylvania region), giving a characteristic “rusty” color to the water. Not only is iron aesthetically displeasing in water, it is unsuitable for human consumption, everyday use, and the development of aquatic life. Quantifying the amount and type of iron (ferric [Fe3+] or ferrous [Fe2+]) allows for proper selection and design of treatment methods.

Aluminum Content8 Aluminum is a second common metal found in AMD and is harmful in several ways. Similar to iron, aluminum is toxic to plants, affecting roots and decreasing phosphate intake. Fortunately, aluminum concentrations in Gladden were found to be low.

Total Acidity/Alkalinity These are important concepts when investigating mine drainage, although both not pollutants, they refer to the ability of water to act as a buffer. Alkalinity is a measure of how much acid can be added to a liquid without causing a large change in pH, and acidity is a measure of how much base can be added to a liquid without causing a large change in pH.9

Dissolved Oxygen Content Chemically removing heavy metals produces oxygen demand in the water, due to the oxidation- reduction reactions that result. Dissolved oxygen levels lower than three parts per million are stressful to most aquatic organisms, and dramatic events like fish kills can result when there is excessive demand

7 (Hedin Environmental) 8 (Lenntech) 9 (pH, Alkalinity, Acidity, Oh My!)

13 on dissolved oxygen in an ecosystem. Dissolved oxygen level is an additional parameter needed in order to successfully design a treatment system10.

Site Layout The site layout can be one of the most difficult parameters of a passive AMD facility design to accommodate. Many treatment methods for AMD require large surface areas and detention times, but AMD discharges often occur at locations that are developed, or have topographies that are not conducive to the placement of a large treatment facility.

Site-Specific Design Considerations Since the point of discharge is at a location with very limited land space of approximately 1.2-acres between Route 50 and residential development off of Millers Run Road, the facility design must consider the importance of certain treatment aspects, specifically raising the pH of the influent, aeration, and detention time in settling ponds.

pH As mentioned previously, dissolved metals in water effectively precipitate at a pH above 7.5. In order to achieve this in such a small land space, the pH must be raised almost immediately after the water is intercepted by the treatment facility. This will allow for more surface area to be allotted to other methods of treatment.

Aeration Not only is it vital to raise the pH of the influent, but precipitation occurs once oxygen is introduced to the water and reacts with the dissolved metals. Aerating the water to maximum saturation will allow for best possible precipitation and optimize the effectiveness of later treatment processes.

Detention Time In order to remove as much of the reacted metals as possible, there must be sufficient time for the contaminated water to stand and settle. For this to be done, a fine balance must be made between the design flow rate, proper detention time in a settling pond, pond volume, and available space for said settling pond.

Optimal detention times for passive treatment systems range between 12 and 24 hours.11

10 (PASCO, 2002) 11 (DOE/NETL)

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Alternate Solutions Several design alternatives were considered to passively treat the AMD of the Gladden discharge.

The three alternatives below were considered as ways to treat the AMD, but were not selected due to a lack of space to construct the system, inability to treat the Gladden water, and/or prohibitive cost.

Alternative 1: Two Settling Ponds Separated By a Rock-Lined Channel

Overview In this alternative, the water from the discharge will flow into the first settling pond and collect there for a period of time. This allows suspended solids to precipitate out of the water. Solids such as iron (yellowboy or iron oxide) will settle to the bottom of the pond and collect there. The coarsest materials (heavy metals) within the water will be removed before it leaves to the next process.

Before the water goes to the next settling pond, a rock lined channel is used to help prevent erosion. This rock lined channel will lead to the second settling pond.

The second settling pond is used to precipitate metals out one more time before it leaves the passive treatment processes. This settling pond is used to remove the finer suspended solids that were missed in the first settling pond.

This design assumes that the water only contains iron and that the water has a high pH. This is not true of the Gladden Discharge.

Advantages This design is very simple.

Disadvantages Ferrous iron will only drop out of the water when the surface area is large enough so that the oxygen from the atmosphere is dissolved into the polluted water.

Gladden Discharge contains metals other than iron, so a settling pond in conjunction with other treatment elements would be more effective.

The solids collected on the bottom of the pond must be cleaned out periodically.

Rain or high amount of snow melt could cause the ponds to overflow. This would cause the polluted water to bypass the passive treatment system and pollute the stream.

The whole passive treatment system would need to be shutdown in order to clean one of the ponds or other elements.

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Alternative 2: Limestone Channels and an Aerobic Wetland

Overview In this design, the water from the discharge would first flow into a limestone channel, adding alkalinity and increasing pH.

After the limestone channel, water flows into an aerobic wetland. An aerobic wetland is a pond with a large surface area which collects AMD water and provides time for metals to precipitate out.12 The aerobic wetland also contains cattails and other vegetation to precipitate iron out of the water. The large surface area of the pond will help expose oxygen to water which allows metals to precipitate out.

From the aerobic wetland, water flows into the limestone channel and finally into the stream.

This design would not be effective for the water in Gladden Discharge. The Gladden Discharge contains high amounts of iron, which would necessitate constant maintenance on the passive treatment system.

Advantages Limestone channels are easy to construct.

Aerobic wetlands can precipitate out various metals (Fe, Al, and Mn hydroxides).

Aerobic wetlands are fairly inexpensive.

Disadvantages The design would require high maintenance of the limestone channel due to the high amount of metals in the water and the resulting armoring of the limestone.

High levels of iron would cause metals and sediment to build up at the bottom of the pond. Therefore, the pond would fill up quickly.

Aerobic wetlands are generally used after AMD has been treated in other ways.

This passive treatment process could get costly because of the high maintenance.

Rain or high amount of snow melt could cause the aerobic wetland to overflow. This would cause the polluted water to bypass the passive treatment system and pollute the stream.

The whole passive treatment process would have to be shutdown in order to clean it.

12 (WPCAMR)

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Alternative 3: A Combination of VFP & Other Treatment Elements

Overview In this design alternative, water from the discharge is first directed into a settling pond. The settling pond will collect the water for a set period of time. This allows the suspended solids to precipitate out of the water. Solids such as iron (yellowboy or iron oxide) will settle to the bottom of the pond and collect there.

The water would then flow into a vertical flow pond (VFP) which consists of a layer of organic compost, a layer of aggregate limestone, and a pipe underdrain system. This will precipitate out the iron and the aluminum.

The treated water is then sent through the piping system and discharged into subsequent treatment cells.

Finally, the treated water is sent into an aerobic wetland where the water collects and settles out any other metals that might be left. The treated water is then discharged back into the stream.

The limestone drain is designed for any overflow.

This passive treatment system will help treat the water from the Gladden discharge. However, there are many problems that are associated with the use of VFPs.

Advantages VFP’s take up a relatively small area.

VFP’s can treat very low quality water.

Aerobic wetlands are a simple system to design and are relatively inexpensive.

Disadvantages13 Operational life of a VFP can be reduced by the accumulation of precipitated metals.

Effective flushing of precipitated solids is essential to prevent clogging and to ensure long-term operation.

A buildup of precipitated solids reduces the permeability of the treatment media, resulting in the need for increased head to move water through the VFP.

13 (Lagnese, 2002)

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Localized clogging in the VFP can result in short-circuiting of flow through the media, potentially affecting performance.

VFP do not remove precipitated metals effectively.

VFP can leak if not taken care of properly.

VFP are fairly complex and costly in design due to the piping.

Noxious odors are produced in the vicinity of the VFP systems.

Aerobic wetlands take up a lot of space.

This process might take up too much space for the given area.

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Final Design

Summary

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The selected design consists mainly of a quicklime doser, a settling pond, and an aerobic wetland.

Limestone channels transport water from the source to the system, and between components in the system. Another limestone channel carries overflow past the wetland. These channels are not a part of treatment, but operate on the principle of: if it’s moving in a channel, it might as well be a limestone channel to treat as much as possible.

A limestone doser raises the pH to start the chemical process.

A distribution box splits flow into the two halves of the settling pond.

Aeration steps provide the necessary oxygen for the process.

A settling pond removes the bulk of the iron. It is split in two to facilitate easier clean-out.

Weirs measure and regulate flow.

A wetland removes more iron by different mechanisms. It is protected from high flows by an overflow channel.

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Limestone Channels

The purpose of the limestone channels is to raise the pH of the water and precipitate out as much of the metals as possible before entering the rest of the treatment system. The channels are not intended to be an integral part of the treatment process, however, since they are relatively inefficient at raising pH.

Limestone channels A and B have identical cross sections. Limestone channel A carries water from the source to the doser, and limestone channel B carries it from the doser to the distribution box.

Limestone channel C consists of two identical channels that carry the flow from the distribution box to the cascade aeration steps.

Limestone channel D is an overflow channel for storm events larger than 1500 GPM, and is located at the downstream end of the settling pond.

A trapezoidal channel shape was selected for all channels to maximize the water’s contact with the limestone gravel.

The capacities of limestone channels A and B were designed for 4,000 GPM, based on estimates made from the site data and using a form of Manning’s Equation:

The k constant for English Units is 1.486, and since the channel will be lined with limestone gravel, an n value of 0.029 (gravel) was selected.

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The slope was calculated using the change in horizontal and vertical distance between the beginning and end of the channel length.

The side slopes of the channel (3:1) create a gentle slope and a shallow water depth. A smaller water depth (y) and larger bottom channel width (b) maximizes the wetted perimeter (Pw) which also maximizes the water’s contact time with the limestone.

The following equations were used to calculate the area and wetted perimeter:

( ) (√ √ )

Limestone channel C consists of two identical channels that carry the flow from the distribution box to the cascade aeration steps. Each channel needs to carry 2000 GPM and was designed accordingly, using the same side slope and water depth as channels A & B.

Limestone channel D was designed for a capacity of 2500 GPM, since a maximum of 4000 GPM can flow into the system from the first channels, but a maximum of 1500 GPM will flow into the wetland. A storm event causes a shorter detention time in the settling pond, so the overflow channel is designed to treat the excess water as much as possible before it discharges back into Millers Run.

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Doser A quicklime doser will provide the necessary rise in pH.

This doser will not use electricity. They rely on a water wheel to drive the system. As the water wheel turns, it drives an auger at the bottom of a gravity fed silo containing quicklime. This allows the lime pellets to be distributed into the stream at a rate that is appropriate for the stream flow.

This type of self-contained system will not require constant monitoring or adjustment for continued operation and will greatly reduce long-term labor and maintenance costs.

The size of the gravity fed storage silo was chosen to enable uninterrupted operation over long periods of time, without the need for continuous replenishing.

More information on refilling can be found in the operations and maintenance section of this report.

A picture of a large Aquafix Systems doser located on an open channel is shown below:14

14 (Aqua-Fix Systems Inc., 2005)

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Distribution Box

The flow distribution box splits the flow evenly between the two sides of the settling pond.

The box will be constructed at a depth of 1.5 feet on the upstream side where the flow enters, which allows the water to flow directly in without going over a weir. There will be no water ponding upstream of the distribution box.

The opening is 12 feet wide to match the width of limestone channel B.

The depth of water in the box will be one foot, resulting in 77 cubic feet (576 gallons) of storage. It is important to provide enough depth and length in the box to ensure that the water is not flowing unevenly.

The effluent discharges through two separate openings, six inches below the height of the influent opening, allowing water to pool up and discharge even amounts through each opening (providing the box is constructed level).

While dredging the settling pond, it is necessary to stop the flow to one side. This can be done by covering one effluent opening with any material that will temporarily stop the flow to one side and allow all the water to discharge to the other side.

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Cascade Aeration Steps

Before entrance into the settling pond, aeration is required.

With the available elevation head, it made sense to use cascade aeration. A weir was also considered, but cascade steps would be more efficient and would ensure the water is completely aerated. This also conforms to the plan to provide a passive system with all energy provided by gravity.

There are equations to approximate the oxygen transfer, but they can be very inaccurate for different aeration methods. Therefore, the design is based on a study done by Dr. Tamer Bagatur15 to find the optimal design parameters for efficient aeration by cascade steps. During the tests, Dr. Bagatur added

Na2SO3 and CoCl2 to change the dissolved oxygen concentrate to 0 mg/L. Therefore, his methods to completely aerate that water will be adequate for any level of dissolved oxygen. The study concludes with design considerations for discharge, efficiency, angle, step height and width, total cascade height and length and the number of steps.

The discharge does not matter here; the design parameters will be accurate for any flow.16

15 (Bagatur, 2009) 16 (Bagatur, 2009)

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The optimal angle is 22 degrees but anything between 20 and 25 is acceptable.17 Both sets of aeration steps are very close to 22 degrees.

The controlling factors for total cascade height and length are the efficiency desired, step height and width and number of steps.

An angle was selected (22 degrees) and the steps were designed to yield an aeration efficiency of 100%, using the following formula from Dr. Bagatur’s study:18

( ) ( )

The flow (q) is in m2/s and h is the step height in meters.

With the available space, three steps and a step height of 2.9 feet and 3.3 feet for the first and second aeration steps, respectively, was used.

The efficiency for the first set of steps is 33.3% per step and 100% total. The second set has an efficiency of 36.7% per step and 100% total.

Since this system is not treating wastewater, as Bagatur’s study did, the objective is to aerate the water as efficiently and completely as possible given the space and head available. We could not meet the criteria for critical water depth but should still sufficiently aerate the water for treatment.

The aeration steps located between the settling pond weir and the wetland were included to aerate and to help dissipate energy.

The widths are determined taking the width of the incoming channel and adding one foot on either side of the steps to account for water turbidity. A side wall along the stairway, with a height of one foot above the steps, acts to contain water that may be splashed around during aeration. It is the step height and desired efficiency that are critical to the design, however.

17 (Bagatur, 2009) 18 (Bagatur, 2009)

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Settling Pond

To establish an order of magnitude of the size of the settling pond required for a design flow of 1000GPM (8,021cfh) and detention time between 12 and 24 hours, a table of detention time versus volume was generated:

Q = 1,000 GPM

td [h] V [cf] 12 96,250 14 112,292 16 128,333 18 144,375 20 160,417 22 176,458 24 192,500

Since the pond is intended to be earthen, the interior sides of the pond must be sloped.

The shape of the available land mass is narrow and irregular, so the pond is unable to have regular dimensions. With this in mind, a trial and error approach was used for the pond design, grading in an 8

27 feet deep pond (assuming 3 feet of iron storage at the bottom) with 2:1 interior side slopes in the available land area and comparing the resulting volume with its corresponding detention time.

Total Storage Volume = 178,785 cf Top Surface Area = 15,785 sf Total Depth = 9 ft Water Depth = 8 ft Maximum Storage Depth for Iron = 3 ft Interior Side Slope = 2H:1V Maximum Detention Time = 22.3 hr

[Fe] Q (75 mg/L)(1000 GPM)(3.785 L/gal)(525,600 min/yr) Vsludge = = 3 70% %solids ρ (454,000 mg/lb)(0.0125%solids)(42.98 lb/gal)(7.48 gal/ft ) =57,246 ft3 per year = 157 ft3 per day

3 Vstorage (54,099 ft )(365 days/year) tdredge = = 3 Vsludge/time 57,246 ft /year = 345 days = 49 weeks ≈ 11 months

The pond must be able to operate while the dredging of accumulated iron occurs. To account for this, a sheet pile wall will be placed along the pond centerline, creating two ponds of equal volume.

When dredging occurs, flow from the flow distribution box will be halted, diverting all flow to one side of the pond. The same will be done when the other side of the pond is being dredged. Each side of the pond has an outlet weir designed for similar flows, allowing each side to operate at the same rate.

To account for extreme wet weather events, the pond has an overflow weir (Weir C) that will activate once each of the other weirs (Weirs A & B) have reached their design capacity.

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Weirs

Three weirs will control and measure flow.

Weirs A and B are identical in size and each is located on one side of the settling pond. Each weir allows 750 GPM to enter the wetland, allowing a maximum total flow of 1500 GPM.

Weir C was designed to handle a flow into the overflow channel of 2500 GPM.

The dimensions for weirs A and B were designed using the following equations for square-opening weir flow:

√ ( )

The water depth Y was set at three inches and the design flow was 750 GPM. The larger the h value assigned, the less important Cd was as a variant in the equation.

After graphing the value of Cd and different h values, it was determined that Cd changed significantly with values less than two feet but insignificantly with values over two feet. A value of two feet was then

29 assigned to h, and the resulting width of the weir opening (b) was found to be four feet. (Changing h to ∞, the weir opening would only change by 1.7%).

Theses weirs were designed with a depth of four feet, to match the width of the earthwork around the settling pond, and with an arbitrary 1.5 feet on either side of the opening.

For Weir C, instead of setting the channel height and finding the width, it was necessary to select the channel width since the weir will be discharging into the overflow channel which has a set width. Weirs A and B could be designed by setting the water height since they discharge to the second set of aeration steps.

Based on a channel width of 3.9 feet, the channel height for Weir C is seven inches.

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Wetland

To effectively remove the remaining unsettled iron from the settling pond, an aerobic wetland was designed to act as secondary treatment. An aerobic wetland acts similarly to a settling pond in the sense that it relies on the oxidation of metals, but the removal process is quite different.

A wetland consists of one foot to three feet of soil and six to twelve inches of standing water with cattails planted throughout to bring oxygen to the soil. The soil acts as a filter for the water, trapping precipitate as water flows through. Additionally, it is important to consider the depth of the wetland during the design. Since this is an oxygen-driven process, a soil substrate thicker than three feet can result in anoxic conditions, and would therefore be ineffective in the removal process.

The design approach was similar to that of the settling pond; however, the main goal of the wetland design was simply to optimize the size in the remaining land space. Additionally, instead of all sides having a 2H:1V interior side slope, one side slopes 3% upward in the direction of flow.

The outlet of the wetland will tie into the existing streambed (elevation 14.00 ft), where the effluent is discharged into Millers Run.

Water Storage Volume = 55,837 cf Storage Surface Area = 20,697 sf Water Level = 4 ft Freeboard = 1 ft Depth of Soil = 3 ft Volume of Soil = 73,027 cf Porosity of Soil = 0.25 Interior Side Slope = 2H:1V Maximum Detention Time = 7.0 hr

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Effluent Calculations

SUMMARY-

Process Fein [mg/L] Feeff [mg/L] Reduction [%] (Influent) (Effluent)

Settling Pond 75 22.5 70

Aerobic Wetland 22.5 15.45 to 18.98 15.7 to 31.4%

Total 75 15.45 to 18.98 74.7 to 79.4%

Influent Loading

Fein [g/d] = 1,440 [min/day] x 0.001 [g/mg] x flow [L/min] x Fein [mg/L] = (1.44)(1000 GPM)(3.785 L/gal)(75 mg/L) = 408,780 g/day

Fein = 75mg/L = 408,780 g/day

pHin = 5.2

Aquafix Quicklime Doser At the predetermined rate of dosage, pH will be raised about 7.5.

pHeff = >7.5

Settling Pond Assumed max 70% removal with 23.2-hr detention time.

Feeff = (75 mg/L)(1 – 0.70) = 22.5 mg/L

Feeff-pond = 22.5 mg/L

Wetland Using an area-adjusted removal rate as the measure of treatment performance, Hedin et al. (1994a) reported typical removal rates of 10 to 20 g/day/m2 for iron.19

Fein [g/d] = (22.5 mg/L)(1000 GPM)(3.785 L/gal) = 122,634 g/day Surface Area = 20,697 ft2 = 1,923 m2 10-20 g/m2/day = 19,228 - 38,456 g/day % Removal = 15.7 to 31.4%

Feeff = 22.5 mg/L – (0.157 to 0.314)(22.5 mg/L) = 15.45 to 18.98 mg/L

Feeff-wetland = 15.45 to 18.98 mg/L

19 (DOE/NETL)

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Operations and Maintenance

Refilling Each year, CaO will need to be brought to the site to refill the doser. The system will go through 20.35 tons/year.

Dredging Every eleven months, 54,100 cubic feet of sludge will need to be dredged from the settling pond.

It is important to dredge during low flow periods (at or below 750 GPM) since one side of the settling pond will not be handling any flow. During dredging, any flow in excess of 750 GPM through the treatment system will be directed into the overflow channel.

To dredge the settling pond, is it necessary to stop the flow to one side of the settling pond. This can be done by covering one effluent opening with any material that will temporarily stop the flow to one side and allow all the water to discharge to the other side.

Testing For the first year of operation, water samples should be taken every three weeks to quantify the effectiveness of the system.

After the first year, in order to ensure proper function of the treatment system, it is recommended that samples be taken and analyzed every 8 months during operation (at the same time that the doser is refilled).

These samples should be taken at three points: the influent of the system, after the primary settling pond, and after the wetland before discharging to Millers Run.

Samples should be tested to conclude if the system is properly removing the metals concentrations and raising the pH to an acceptable level above 7.0.

Inspection A visual inspection should be done periodically to see how the system has performed during a range of weather conditions.

If the visual inspection reveals evidence of a large amount of flow passing through the emergency channel adjacent to the pond, it may be necessary to further explore the option of increasing the pond size to ensure proper function.

The visual inspection should also look for evidence of vandalism, debris in the ponds, or water bypassing any step in the system.

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Construction

General This is not intended to be a comprehensive construction plan, but to point out issues that are likely to complicate this particular project.

Construction should be carried out in the mid to late summer and early fall. Construction should be during this period because it is when flows are typically lowest, temperatures will not interfere with earthwork or concrete placement, and re-vegetation and wetland plantings will have the greatest success.

Site Access Construction of this project will be challenging given that the site is small and constrained by the topography and existing built elements.

Currently there is a path that begins behind the parking lot seen in the South-West corner of the site plan and continues down until an area near the proposed placement area of aerator B. The full feasibility of modifying this path into a road that could accommodate heavy-equipment and trucks is not known but it would be a complex and expensive task.

Using full-sized equipment (excavators, loaders, backhoes, etc.) would lessen the time required to complete this project, particularly the excavation phase. However, the time and investment required to expand this path would be considerable.

In addition to access, the use of standard equipment may be difficult because of the small working space of the site.

Disturbance of the portions of the site that are to remain unchanged and potential inconveniences the people utilizing the space around the site may be considerable.

The more attractive and readily feasible alternative is to use compact construction equipment. This option allows the existing path to be utilized for site access with little to no modification. Though this option would result in construction times that are longer than in the first option it would be less costly overall, less disruptive and allow for more efficient and safe use of the working space available.

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Excavation

In order to build the treatment system proposed most of the 1.2 acre site will need to be cleared, grubbed, excavated, and re-vegetated.

Earth will need to be excavated in order to create desired profile and to build the channels, settling pond, and wetland. This is a total of 19720 cubic-yards of soil that will be removed from the site.

The soil that is excavated from the site will have to be removed as it will be of no use in the project or as fill elsewhere on the property. Excavated soil from this site is suitable for disposal at several local landfills and will be sent to the most appropriate one.

The excavation will probably need to be done in phases. First, the excavation should be aimed to remove the excess soil. The excavation for each portion of the system should follow in the order that they are to be built and taking care to pace the excavation in a way that maintains stability and does not create dangerous conditions (i.e., excavating settling pond long before the rest of it can be constructed.)

In addition to removing soil, there is a notable amount of debris on the site that will have to be taken out. When visiting the site in September and October 2010 empty, metal drums (about 55 gallon), rubber tires for heavy equipment (several feet in diameter), numerous pipes composed of a variety of materials (from 0.5 to 3 ft in diameter), and various other items were seen strewn around the site. These items are located in various places, such as: the stream bed, on top of enormous rocks surrounding the mine pool, on the path, and in the vegetation on either side of the stream bed. It is not known how many more large items are in the area to be excavated, but it is important to recognize this and be aware that it may impact the schedule and cost of the project.

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Channel D The first portion of the system that should be built is Channel D, which has been designed to operate as an overflow channel from just before the aerobic wetland until the confluence with Millers Run.

This should be done first because it is the only portion of the system that is not in the existing stream bed and once completed can be used to divert flow while the aerobic wetland is being built and will provide a small amount of treatment to the water shortly after the project begins.

Aerobic Wetland20 After channel D is built and can be put into service, construction on the aerobic wetland can begin.

The flow will need to be diverted from the stream bed at a point before the wetland and diverted into the overflow channel. The exact point where diversion will need to begin will determine whether a simple ditching system, piping systems, or other technique will be employed. It may be useful to divert the water directly from the mine pool, because as construction progresses the diversion point will need to be farther and farther upstream and eventually need to begin at the mine pool.

Once the water is diverted, excavation and construction of the wetland can start. When building the wetland, it is important to ensure that the gradients specified in the design are maintained so the proper flow and detention times are achieved.

The final step of construction for the aerobic wetland is to plant the vegetation. The plants for the wetland will be common reed (Phragmites australis), reedmace (Typha latifolia), and common rush (Juncus effuses). They should be distributed at a about one plant every 5 square feet.

20 (Younger, Banwart, & Hedin, 2002)

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Possible Construction Order Phase One 1. Establish adequate site access. 2. Remove large, obvious debris. 3. Clearing and grubbing. 4. Stage I excavation. Phase Two 1. Excavate channel D. 2. Place limestone in channel D. 3. Divert flow from mine pool into channel D. 4. Excavate channels A, B, C1, C2, and distribution box placement area. 5. Install flow distribution box (concrete poured in place). 6. Place limestone in channel A, B, C1, and C2. 7. Install Aquafix quick lime doser. 8. Move flow diversion point from mine pool to channel B. Phase Three 1. Excavate settling pond, cascade aerator A, B, and weir A, B, and C placement area. 2. Line settling pond. 3. Place sheet piling. 4. Install cascade aerator A, B, and weir A, B, and C (concrete poured in place). 5. Reroute flow through system but only allow water to exit settling pond via channel D. Phase Four 1. Excavate aerobic wetland. 2. Line aerobic wetland. 3. Place compost in wetland. 4. Plant vegetation in wetland. 5. Reroute flow through system as laid out in design. Phase Five 1. Remove any excess materials, equipment and debris. 2. Re-vegetate where necessary.

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Cost

Capital Costs Component Sub-Component Cost per Unit Units Component Cost Surveying1 $650.00 day 1.5 $975.00 Clearing & Grubbing2 $1,300.00 acre 1.8 $2,340.00 Site Activities Excavation $5.50 yd3 19720 $108,460.00 Re-Vegetation $1,500.00 acre 1.2 $1,800.00 Site Activities Total $113,575.00 Geo-Textile Liner $0.50 yd2 400.7 $200.35 Limestone Limestone $22.00 yd3 41.7 $917.40 Channels Limestone Placement $12.00 yd3 41.7 $500.40 Limestone Channels Total $1,618.15 Distribution Box $300.00 yd3 2 $600.00 Concrete Cascade Aerators3 $300.00 yd3 93 $27,900.00 Structures Weirs4 $300.00 yd3 7 $2,100.00 Concrete Structures Total $30,600.00 35-ton Bin Aquafix System $85,000 System 1 $85,000 Lime Doser Lime Doser Total $85,000 Synthetic Liner $5.50 yd2 650 $3,575.00 Settling Pond Sheetpile $6.00 ft2 2400 $14,400.00 Settling Pond Total $17,975.00 Clay Liner $5.00 yd3 414 $2,070.00 Organic Matter $20.00 yd3 2705 $54,100.00 Aerobic 3 Wetland Organic Matter Placement $4.50 yd 2705 $12,172.50 Wetland Planting $3,700.00 acre 0.34 $1,258.00 Aerobic Wetland Total $69,600.50 Total Capital Cost $318,368.65 1Surveying assumes that one acre can be surveyed per day and days may only in whole or half

2Clearing and grubbing requires a land multipliction factor of 1.5.

3This is for both cascase aerators. 4 This is for all three weirs.

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Annual Cost (Year One) Component Cost per Unit Units Component Cost Pebblized Quick Lime $0.055 pound 49600 $2,728.00 Sludge Removal $0.06 gallon 404000 $24,240.00 Sampling5 $70.00 visit 12 $840.00 Lab Testing $27.00 sample 36 $972.00 Maintenance6 $35.00 hour 36 $1,260.00 Total Year One Cost $30,040.00 5Sampling cost is based on taking three samples per visit at a rate of 3 samples per hour and one hour of travel time all at a cost of $35.00 per hour. 6Maintenance units are based off of 12 visits per year averaging two hours of work and one hour of travel per visit.

Annual Cost (After Year One) Component Cost per Unit Units Component Cost Pebblized Quick Lime $0.055 pound 49600 $2,728.00 Sludge Removal $0.06 gallon 404000 $24,240.00 Sampling7 $70.00 visit 2 $140.00 Lab Testing $27.00 sample 6 $162.00 Maintenance8 $35.00 hour 6 $210.00 Total Annual Cost $27,480.00 7Sampling cost is based on taking three samples per visit at a rate of 3 samples per hour and one hour of travel time all at a cost of $35.00 per hour. 8Maintenance units are based off of 2 visits per year averaging two hours of work and one hour of travel per visit.

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Acknowledgements Thanks to the following people:

 Dr. John Oyler for leading the class, providing us with referrals, and not putting up with us when we would try to cut corners.  Dr. Jason Monnell for a huge amount of help in the lab and for guidance when we had no idea what we were doing.  Dr. Ronald Neufeld for his indispensible advice on AMD remediation systems.  Dr. Dan Budny for letting us borrow his equipment.  Dr. Xu Liang for helping us dismiss bad data and for her numerous referrals.  Dr. Jorge Abad for putting up with our ridiculous questions.  Dr. J.S. Lin for his help with a geotechnical problem.  Tyler Davis for providing us with historical data on Millers Run and Gladden Discharge.  Mike Jenkins, of Aqua-Fix, for his information on dosing systems.

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