Since 1979, forty-five passive Acid Mine Drainage (AMD) treatment systems have been constructed in the Six Mile, Sandy Run and Longs Run watersheds, located in Broad Top Township, Bedford County, Pennsylvania.

The first AMD treatment system was funded by the Rural Abandoned Mine Program (RAMP). The success of this project and a growing community interest in AMD abatement prompted a watershed study that was completed in 1981. This study identified illegal garbage dumping, sewage, and AMD as the major problems in the study area.

Broad Top Township has addressed the garbage and sewage by making garbage disposal affordable to all its residents and by taking ownership of the sewage management practices within the township.

By the mid-1990s, additional RAMP and Bureau of Abandoned Mine Reclamation (BAMR) projects were completed. In 2005, a Watershed Implementation Plan (WIP) was completed for Longs, Sandy, and Six Mile Runs. Since then, over $6.5 million of Clean Water Act’s Section 319 funds and over $0.5 million of Pennsylvania Department of Environmental Protection’s (DEP) Growing Greener Grant money has been spent on AMD abatement projects in the watersheds.

All the systems constructed since 2005 have been designed to treat the high flow discharges for a minimum of 20 years. These AMD discharges vary in quantity and quality from site to site. The design goal of all the AMD treatment systems is to remove 85% of the metal and acid loads entering the streams.

Challenging construction conditions were encountered at most of the treatment sites, including steep terrain, geology, and minimal land area availability due to some seeps close proximity to streams. The challenging conditions will be discussed.

A variety of passive treatment technologies have been employed. The technology chosen for each site is tailored for that site based on the chemistry and flow at that AMD seep location.

In 2014, after construction of 13 AMD treatment systems and intense biological studies by DEP, Longs Run was no longer considered biologically impaired, and was delisted in the Pennsylvania Integrated Water Quality Monitoring and Assessment Report (Integrated Report).

Funding and construction restraints and the importance of following an operation and maintenance (O&M) plan for the systems as well as chemical and biological improvements will be discussed.

Limestone (calcite) is the most common acid-neutralizing and alkalinity-generating material used in passive mine water treatment systems. Calcite’s solubility and dissolution kinetics can limit its utility in passive systems, especially for mine waters containing high concentrations of Fe²⁺ and Mn²⁺. Dissolved carbon dioxide is an important controller of calcite dissolution in natural and mine water treatment systems. The carbonation of mine water should increase the generation of alkalinity in limestone-based passive treatment systems. This project investigated the effects of mine water carbonation on alkalinity generation by passive limestone systems.

Mine waters were carbonated with varying amounts of CO₂ and incubated in limestone systems for varying amounts of time. Carbonation was provided with in-line nozzles commonly used in conventional environmental applications and a membrane system used in industrial bottling operations. Carbonated waters were exposed to limestone aggregate in pilot units containing 10 – 25 tonne aggregate and in operational passive systems containing 300 – 1000 tonne limestone.

Carbonation of mine water increased both the extent and rate of alkalinity generation. At the Orcutt site, mine water containing 103 mg/L Fe and 40 mg/L Mn was directed through experimental containers containing 25 tonnes limestone aggregate. Treatment without carbonation resulted in 250 mg/L alkalinity after 8-12 hours of theoretical retention time (TRT). Carbonation with a nozzle system resulted in 250 mg/L alkalinity after 3-4 hours of TRT and 350 mg/L alkalinity after 9 hours of TRT. Carbonation of operational limestone systems produced similar results. The Howe Bridge anoxic limestone drain (300 ton aggregate) received 75 L/min of water containing 130 mg/L Fe and 21 mg/L Mn. Without carbonation the limestone bed discharged water with 184 mg/L alkalinity and net acidity of 85 mg/L. Nozzle carbonation of the influent resulted in discharges from the bed containing on average 276 mg/L alkalinity and net acidity of -25 mg/L. Testing was also done at the Orcutt site using a membrane-based carbonator and a 10 tonne experimental system. The membrane carbonator produced 375 mg/L alkalinity after only 2 hour TRT. The membrane system also provided more efficient transfer of CO₂ than the nozzle-based system.

The research shows that calcite solubility limitations can be modified through the carbonation of mine water using existing carbonation technologies. Mine water carbonation can expand the potential applications for limestone-based mine water treatment systems while substantially decreasing the sizing of the limestone beds.

Manganese (Mn) is a common water contaminant at coal and metal mine sites. Its treatment by conventional methods involves strong oxidants or caustic chemicals which are hazardous, expensive, and produce copious amounts of sludge. Mn can be treated passively in oxic aggregate beds, but the design and reliability of these systems is uncertain. Pennsylvania’s Department of Environmental Protection recently reviewed its effluent standards for Mn and proposed to lower the in stream criterion from 1.0 mg/L Mn to 0.3 mg/L Mn. Public objections to the proposed changes included the high costs of meeting the standard with conventional chemical treatment. Passive treatment was not considered a practical option because of its large land requirements and unreliability.

In response to these concerns, a project was conducted that investigated Mn removal by existing, full scale passive treatment systems and two experimental oxic aggregate beds. The experimental beds were located at large conventional mine water treatment facilities and received Mn-containing effluent from the plants. The experimental units were constructed in open-top steel roll-off containers that contained 10-30 tonnes of limestone aggregate. Experiments were conducted by varying flow rates and measuring influent and effluent chemistry. The Hollywood unit received circumneutral water containing 0.6 mg/L Mn and 1.5 mg/L particulate Fe. The Brandy Camp unit received circumneutral water containing 5.8 mg/L Mn and 1.7 mg/L particulate Fe. The systems operated for 6-12 months. Both systems decreased Mn to less than 0.3 mg/L Mn. However, the kinetics of Mn removal, determined from changes in Mn concentration and theoretical retention times, differed substantially. The Hollywood system exhibited 1^st order Mn removal kinetics with a ½ reaction of 159 minutes. The performance suggested a heterogeneous abiotic Mn oxidation mechanism. The Brandy Camp system exhibited pseudo-zero order kinetics that, under the experimental conditions (Mnⁱⁿ 4-7 mg/L, theoretical retention time 1.2 – 3.5 hours) had a ½ reaction of 80 minutes. The Brandy Camp performance suggested a biological mechanism. The rapid removal of Mn by the Brandy Camp system was unexpected and shows the opportunity for efficient passive removal of Mn.

The presentation will describe the experimental results, suggest explanations for the differences between the two units, and discuss implications for the future sizing and design of passive Mn removal systems.

Acid mine drainage (AMD) discharging from abandoned coal mine facilities in the Midwestern U.S. are often highly acidic. The AMD in this region is typically characterized by iron, aluminum, manganese, and sulfate levels and is considerably higher than typical coal mine drainage in Appalachia and many international locations. Although active AMD treatment is a more secure, long-term solution, limitations in site conditions and the availability of long-term funding have prompted the use of passive treatment in the region. The poor AMD quality has required three types of treatment: 1) vertical flow ponds (VFP) often termed reducing and alkalinity-producing systems (RAPS) or vertical flow reactors (VFR), 2) anaerobic wetlands, and 3) sulfate-reducing bioreactors. Oxidation ponds and aerobic (surface-flow) wetlands support these alkalinity production cells. High aluminum in midwestern AMD requires increased limestone-amended compost as compared to more conventional VFPs used in Appalachia. This ultimately forms a hybrid between limestone-based VFP technologies and compost-based sulfate-reducing bioreactors. This paper will present the performance of five hybrid VFP-based treatment cells and compare the designs and results to both international VFP/VFR and several conventional bioreactors designs constructed in the Midwestern U.S. The design goal of these systems is to produce sufficient alkalinity to buffer pH in the following oxidation ponds and/or aerobic wetlands to stimulate precipitations of most of the remaining iron. Manganese removal in these systems is typically minimal. Conversely, limited sulfate removal can be expected. These midwestern systems are compared to results of earlier reviews of full-scale VFPs with the goal to increase the empirical dataset used in VFP design.