Erico Bridge Abandoned Mine Restoration Project

BioMost was responsible for the design and installation of the Erico Bridge Restoration Area that addresses five abandoned mine discharges in Venango Township, Butler County, PA. 

Monitoring data and restoration recommendations for this area are presented in the PADEP, Knox District Mining Office, 9/1998, Slippery Rock Creek Watershed Comprehensive Mine Reclamation Strategy.  According to this report, these five discharges are responsible for more than 1/2 (57%) of the acid load and 84% of the iron load in Seaton Creek.  They are also responsible for almost 1/4 (24%) of the acid load and 41% of the iron load for the entire 27-sq. mile Slippery Rock Creek headwaters area.  The reference narrative further states: “The acid and iron loading from the discharges in this priority area are the main contributors of pollution to Seaton Creek.  Extensive amounts of iron deposition can be seen along the flood plain of Seaton Creek in proximity to the discharges.”  This highly-visible iron deposition is not only severely impacting aquatic life (essentially eliminating the macroinvertebrate community) but also significantly contributing to the severe sediment problem, causing flooding concerns to community residents downstream.


Water Quality of Site Drainage (Average Values)

Desc. Flow
pH Alk.

D. Fe

D. Mn

D. Al (mg/l)
Raw 320 5.7 50 60 30 <1
Final 500 7.0 110 2 3 <1


The raw water characteristics are pre-construction values while the final, treated, discharge characteristics are post-construction values.  During construction additional degraded drainage was encountered and directed into the passive treatment complex.  The passive complex is responsible for decreasing acidity loadings by ~100% (328,000 lbs/yr), iron loadings by ~97% (140,000 lbs/yr), and manganese loadings by ~81% (48,000 lbs/yr).  This system combined with other restoration efforts of the Slippery Rock Creek Watershed Coalition are responsible for improving the quality of Seaton Creek, one of two major tributaries in the Slippery Rock Creek headwaters, from a characteristic pH of 4.1 to 6.8 and from a total iron of ~2 to <1 mg/l, a total manganese of 14 to 3 mg/l, and a total aluminum of 1 to <1 mg/l.    

BioMost worked with a public-private partnership effort formed including a local mining company, local and county government agencies, local volunteers, and other environmental professionals, who have received awards specifically for innovations in passive treatment technology, abandoned mine reclamation, and watershed restoration.  By installing 17 piezometers and monitoring and manipulating the potentiometric surface of the confined abandoned underground mine pool and considering other hydrologic factors, most of the passive components were constructed above the mine workings or horizon of the coalbed.    

Construction work supervised by BioMost was completed in June 2003.  As part of the restoration effort, ~40,000 CY of abandoned coal refuse were removed, neutralized with circulating, fluidized-bed, coal ash and used to backfill a nearby abandoned surface mine.  The passive treatment complex with 16 components  includes Anoxic Collection Systems, Anoxic Limestone Drains (12,000 T limestone aggregate total, largest known in the United States), a ~5 ac Settling Pond/Aerobic Wetland Complex planted with native species to enhance wildlife habitat and function and to allow for settling of iron particulates, and a Horizontal Flow Limestone Bed (9,000 T limestone aggregate) to encourage manganese precipitation and generate additional alkalinity.

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View Final Report
(83MB file)

Datashed - Water Quality Data