2-Beech Creek 105D Site Characterization.pdf

Beech Creek 105D Site Characterization (Beech Creek, Centre County)

Technical Report Provided by Hedin Environmental through the Trout Unlimited AMD

Technical Assistance Program

May 6, 2025

Background Trout Unlimited is reviving the effort to address pollution from abandoned mines in the Beech Creek watershed of Clinton and Centre counties. A watershed assessment conducted in 2006 identified the 105D discharge as the largest discrete source of pollution in the 171 square mile watershed. In 2024 Trout Unlimited contracted with Hedin Environmental to investigate the mines producing the 105D discharge through drilling and test pit excavation and prepare a conceptual reclamation plan. This report is the product of those efforts.

Mining History The Lehigh Valley Coal Company operated the No. 25 deep mine at this site before WWII.

Available mine maps show at least two drift entries at the 105D site. One entry was oriented to the west that worked the seam roughly along strike while the second entry was oriented toward the south and worked up dip. The total deep mine area shown in the available mapping is approximately 150 acres.

Surface mining of the shallow-cover coal between the outcrop and deep mine workings was conducted in the 1940s. The mining appears to have been haphazard with spoil piles arranged erratically around the site resulting in the formation of three flooded pits. The mining sequence may have been driven by the drainage challenges posed by the coal structure which dips either parallel to or into the highwall over much of the site. The site is also located within a surface drainage so runoff into the pit would have been unavoidable.

Surface mine disturbances are within AML inventory site PA 6795 (Poorman Side East) and include dry strip mines, flooded strip mines, and impacted water sources. All features are priority 3 with the exception of a small section of priority 2 highwall. The 105D discharge is likely represented by AML feature 6795-11 (impacted water source).

105D Discharge Water discharges from the site from the last of a series of three pit ponds and from toe of spoil seeps. The 105D discharge is a monitoring station situated below the confluence of these sources that combine to form an unnamed tributary to Sandy Run (Map 1). The water is acidic with elevated concentrations of iron, manganese and aluminum (Table 1). Water quality has improved since the 2006 assessment with acidity decreasing 22%. The decrease holds even after correction for flow conditions, which were considerably higher during the 2006 assessment monitoring.

Table 1. 105D average water quality and median flow from historical and recent monitoring.

Location Timeframe Flow pH Alk. Acidity Fe Mn Al SO4

105D 2004-2005 485 3.1 0 426 15.1 29.1 51.7 1,311

105D 2023-2024 186 3.1 0 372 6.5 18.6 43.0 905 Units: flow, gpm; pH, S.U., all others mg/L

The most environmentally damaging characteristic of the discharge is the large pollution loading produced during high flow events. This is due to a combination of unusually large peak flows and lack of dilution during the peak flow events. The maximum observed flow condition had half the acidity of the minimum flow measurement despite a 55-fold increase in flow (Figure 1).

Acidity loading during high flow events exceeds one ton per day.

Figure 1. Relationship between flow rate and acidity during recent and historical monitoring.

Site Investigation – Spoils and Overburden Test pits were excavated in the mine spoils to observe the composition of the material, measure the pit floor elevation, and determine the local groundwater level. Spoils were found to be highly variable in composition. Test pit locations are shown in Map 1. Photo 1 shows typical spoil material excavated. Random grab samples of spoil material were collected for analysis of acid generating capacity. Table 2 shows the results of the spoil analysis which reflects the heterogeneous nature of the material. Both samples were acidic but material from Test Pit #1 has a low potential for acid generation while material from Test Pit #2 is moderately acidic with more than four times the acidity generating potential of the Test Pit #1 sample.

Photo 1. Spoil material excavated from northern portion of site.

Table 2. Analysis of spoil grab samples

Location Total Sulfur Max Potential Acidity (ppt)

Neutralization Potential (ppt)

Net Neutralization Potential (ppt)

Test Pit #1 0.11% 3.44 1.78 1.66

Test Pit #2 0.43% 13.44 0.50 12.94

Drilling was conducted in the deep mined area to verify the presence of mine voids and determine if the mine is flooded. Photo 2 shows the drilling work. Samples of the overburden and coal were collected at one-foot intervals for analysis of acid generating capacity. Since the intact overburden over the deep mine is the source of the surface mine spoils but in an unweathered condition, it is considered representative of the maximum acidity generating capacity of the surface mine spoils and would thus be a conservative value for calculating alkaline addition rates. Results of the analysis are summarized in Table 3.

Photo 2. Drilling OB-2 hole.

Table 3. Analysis of overburden samples Geologic Unit

Thickness (ft)

Total Sulfur

Max Potential Acidity (ppt)

Neutralization Potential (ppt)

Net Neutralization Potential (ppt)

Brown sand 6 Inert -- -- -- Brown sandstone 26 <0.01 <1 1.80 -1.76

Gray sandstone 9 0.02 0.63 2.22 -1.60

Gray sandy shale 3 0.18 5.63 1.49 4.14

Coal 6 1.14 35.52 1.37 34.16 Gray sandy clay 3 0.43 13.33 0.99 12.3

Acid-base accounting results from the overburden show that most of the overburden is inert sandstone and what acid generating potential exists is concentrated in the shale above the coal and even this is only marginally acidic. The coal itself is strongly acidic but should not be present in significant quantities in the mine spoil. It is possible the acidic materials from offsite were disposed of in this mine pit but this project was not able to confirm this suspicion.

The volume of overburden produced by the mining activity and current spoil volume were estimated from lidar mapping, historical aerial photos, and geologic information (unit thicknesses and structure) based on the drilling. It was assumed that 100’ of crop coal was left in place due to the shallow slopes of the original ground. This coal and associated overburden were subtracted from the estimated spoil and overburden volumes as this material should still be in place. The estimated volume of overburden produced agrees well with the estimated volume of spoil on the site (Table 4). Due to the approximate nature of these estimates, it’s possible that a material was imported to the site but in a quantity that is within the error of these estimates.

Additional investigation is needed to confirm or deny this conclusion.

Material Area at base (ft2) Thickness (ft) Volume (yd3) Brown sandstone 428,403 22.0 174,535 Gray sandstone 623,358 9.0 175,294 Gray sandy shale 712,338 3 74,205 Total overburden above coal 424,033 Overburden on 100' crop coal still in place 88,980 6 9,887 Net overburden 414,147 Spoil 410,078

Site Investigation – Hydrology A site survey was conducted by a licensed surveyor from EADS Group to determine the surface elevation and location of test pits and drill holes. Benchmarks were set to facilitate future survey work. From the drilling data it was possible to determine that the coal is dipping 4.8° with a strike of 189°. Two monitoring wells were installed into deep mine voids. The monitoring well near the west entry (MW-1) is installed in workings flooded above the roof. The monitoring well near the south entry (MW-2) enter the deep mine workings updip where the coal is 23 feet higher than MW-1 and was dry.

Water elevation in MW-1 and the elevation of two of the pit ponds was measured on October 30, 2024. On that day, all three water elevations were within 0.1’ of one another which is within the error of measurement.

The source of three seepage zones was investigated. Three clay drainage pipes were discovered that produce AMD. The location and orientation of the pipes is inferred on Map 1 and suggests they were installed during the surface mining operation to convey water from the deep mine workings out of the open pit. All of the pipes were in poor condition and not functioning as intended (Photo 3).

Photo 3. Clogged and collapsed existing clay pipe.

Recommendations Water management is critical to the reclamation of the 105D site. The following tasks are recommended to fully develop the reclamation project.

1) Dewatering. The surface mine contains several flooded pits that appear to be connected to the deep mine workings which are partially flooded. A dewatering plan must be developed to release this water without causing environmental degradation. A holding pond and temporary treatment may be necessary. Excavation to connect and lower the existing pit ponds to the level of the lowest (northeast) pond is the easiest way to partially drain the site and possibly the deep mine.

A dewatering plan should be developed prior to any manipulation of the water levels at this site.

2) Regrading. Spoil should be regraded to discourage infiltration and promote surface water runoff from the site. Regrading alone will decrease pollution loading from the site by preventing the contamination of runoff from the 190 acres that drains to the surface mine. To accomplish approximate original contours, a total of 215,000 cubic yards of spoil material must be moved. A preliminary grading plan that reclaims the site to approximate original contours is show in Map 2

2) Re-establish deep mine drains. Existing drains that were originally installed to carry flow from the deep mine through the surface mine must be reconstructed to prevent both the accumulation of water within the deep mine workings and interactions of water with the mine spoils. The existing pipes are deeply buried under spoil so this work should coincide with regrading the site.

The grading plan shown in Map 2 was produced to align topographic lows with the locations of the existing drains. A total of about 1,400 feet of 12” pipe will be required to convey water from the three deep mine openings at the base of the highwall to the toe of the reclaimed slope. Each pipe should be equipped with a gas trap to prevent the ingress of air into the deep mine workings.

3) Alkaline addition. Pollution loading reductions can be achieved through the addition of alkaline materials to the spoils during regrading. Spoil sampling conducted as part of this project is not comprehensive enough to characterize all spoils on site and the overburden analysis showed insufficient acidity to provide a basis for determining an addition rate. Additional investigation is needed to identify buried coal refuse on the site. Once a more complete understanding of the spoil composition is acquired, an alkaline addition rate and placement plan can be developed.

MINE SPOIL

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105D

MONITORING

POINT

MINE SPOIL

BEAVER POND

Hole #4 Surface: 1459.47 Coal: 1418.5

MW-2

Dry Surface: 1460.95 Coal: 1415.0

OB-2

Surface: 1463.56

Coal: 141413.6

OB-2

Surface: 1463.56

Coal: 141413.6

MW-1

Water: 1407.5

Surface: 1442.28 Coal: 1392.3

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