Chiller Theater Seeps Acid Mine Drainage Passive Treatment System Design

Overview

This semester, we were given the task of redesigning the current passive acid mine drainage (AMD) treatment system at Chiller Theater Seeps. Chiller Theater Seeps is located outside Phillipsburg, Pennsylvania near historic coal mining sites, which are now sources of AMD. This mine drainage flows into Cold Stream, negatively impacting the health of the stream and killing off many native wildlife populations. Our objectives were to evaluate the current system, compare new viable methods for treating the AMD sources, and design a system that satisfies the effluent AMD standards set by the Office of Surface Mining Reclamation and Enforcement.

Based on the past 20 years of effluent data from Pennsylvania Datashed, we discovered that the existing system stopped effectively treating AMD within three years of initial construction. We visited the site in January 2023 and spoke with the current owners, who informed us that the vertical flow pond (VFP) used to treat the system was the main culprit. The high levels of aluminum entering the system were clogging the VFP, making it ineffective. Although a dosing siphon was designed to remove any clogs, it is now understood that dosing siphons break earlier than the design lives of these AMD systems and are no longer considered effective in creating the suction necessary.

Utilizing the same data, we found that the 50th percentile concentrations of the AMD source had a net acidity of 398 mg/L, iron concentrations of 16 mg/L, and aluminum concentrations of 39.6 mg/L. With minimal flow data on the site, we assumed that the average flow rate over the first three years of operation, 60 gallons per minute (gpm), would be the flow rate. After looking into alternatives, we found that a drainable limestone bed (DLB) could be a viable treatment route if iron concentrations were dropped to 10 mg/L before entry into the DLB. We researched low-pH iron oxidation, a method of utilizing terraces of hay to reduce iron loading prior to the DLB. This method could be installed along the current 900-foot path from the seeps to the treatment system. Bolstering already existing microbial activity along this path would then reduce iron concentrations to achieve the needed 6 mg/L drop, allowing us to utilize a DLB system at Chiller Theater Seeps. After designing an adequately sized DLB system for the site, we found that the site area could accommodate a treatment system for more than 60 gpm influent flow. Similar sites in the area have utilized oversized systems to better guarantee meeting effluent standards, as well as reducing system maintenance requirements. We then investigated maximizing the treatable flow based on the area and found that the site is able to accommodate a 115 gpm DLB system, nearly double the average flow rate.

Using AMDTreat to estimate cost and area needs for the system, we found that our design with a DLB capable of treating 115 gpm would cost $363,000, with an estimated annual cost of $36,300. However, we consider these costs to be quite conservative, as this system will mainly require a remodeling of the current site with the resizing of most of the existing site characteristics, as well as a decrease in maintenance costs due to the oversizing of the system to treat a much higher loading than anticipated. To counteract current breakdowns, we also added a computer-controlled water level control structure (WLCS) after the DLB in our design. A WLCS is the more modern version of a dosing siphon that will be able to create the required suction to remove clogs. We also designed an emergency spillway for the system to divert flows over 115 gpm, as the current system does not have an emergency spillway. This will cause the disturbance of an additional 0.32 acres outside of the site but will make the system effective.

Objectives

– Compare viable methods for acid mine drainage treatment at Chiller Theater Seeps

– Overcome previous problems with aluminum clogging in the Chiller Theater Seeps treatment system

– Satisfy effluent water quality standards for acid mine drainage at Chiller Theater Seeps

– Prioritize increased reliability and decreased maintenance requirements in final treatment system design

Approach

– Conducted Chiller Theater Seeps site analysis and gathered influent chemistry data

– Visited passive acid mine drainage treatment systems in central Pennsylvania and compared treatment options

– Used Office of Surface Mining Reclamation and Enforcement tool (AMDTreat) to model the cost and area required for different treatment options at Chiller Theater Seeps

– Prioritized treatment system reliability and minimization of maintenance in final treatment system design

Outcomes

– Determined failure points in the current Chiller Theater Seeps passive treatment system

– Designed passive treatment system options to meet effluent water quality standards at Chiller Theater Seeps

– Selected final design based on system reliability and decreased maintenance requirements

– Increased treatable flow at Chiller Theater Seeps from 60gpm to 115gpm