274-1 Given Sulfides, Expect the Expected.

Session: Advances in Ecohydrogeology

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Abstract:

Atmospheric deposition, orphan sulfide ore, clay and coal mine drainage legacies remain, all challenging and costly to mitigate. Much has been learned about depositional environments and abundance of reactive sulfides, water and mine drainage control and treatment technologies. Acid-base accounts, special handling of toxic spoil, AMD control and treatment measures are now routine. Years are required for full environmental impacts to be realized.

Surprises await at non-fossil fuel sites where sulphide encounters can be new to decision makers. I-99 construction across Skytop Mt., Centre Co., PA and its use were delayed more than 5 years and, $119 million added cost and still counting. Sulfides were encountered in 150 ft. deep, 350 ft. wide cuts. Nearly 3.6 million cu yd of spoil, 918.939 cu yd toxic, were placed for valley fill, abutments, base coarse, rock slide bolsters and stored at 12 sites. Sections had been paved and bridges under construction when acid breakouts led to a stop work order.  Seep, pHs ranged from 2.1 to 2.7, acidity from 2126 to 18,939 mg/L, Al 152 to 1,310 mg/L, Fe 283 to 4,950 mg/L, etc.

How much toxic spoil was generated, where is it located, where to place what's removable and how to isolate what is not were issues including leachate management during and following construction. Nearly 1 million cy of toxic spoil blended with lime-plant flue dust were placed in two 10 ac secure cells. In moveable spoil and outcrops were lined and covered with limestone aggregate to eliminate air and water.

A shallow nearly 40 ft. long cut along Route 322 on Skytop devoid of vegetation and a known sulphide mineral collection area might have guided the boring plan.

The Brimfield Schist contains pyrrhotite. Aggregates from a Northeast CT. Brimfield quarry were used for concrete structures. Delayed cracking and crumbling of structures have and continue to occur due to delayed sulphide oxidation. Repair costs range from$100k to $200k per home. Property values have fallen and property sales discouraged effecting tax bases needed for schools, roads and community services. Sulphide enrichments are indicated by high groundwater iron concentrations, active sluffing of acidic Brimfield Schist outcrops devoid of vegetation and associated Nipmuck soils. These sporadic Brimfield Schist occurrences demand further attention for all future landuse changes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11179

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