Cindermoss Creek Mine Drainage: A Passive Treatment Design

Client: the fictional Cindermoss Watershed Association, working with the fictional Quarry Vale Borough. Site: a seep from an abandoned coal mine that flows into the fictional Cindermoss Creek. Every figure below is a hypothetical value written for this project.

Discharge characteristics, measured monthly for one year and steady across the seasons:

• Flow: 90 gpm, continuous.
• pH: 4.2.
• Acidity: 180 mg/L as calcium carbonate.
• Total iron: 42 mg/L, nearly all in the ferrous form.
• Dissolved oxygen: 1.1 mg/L.
• Aluminum: below 1 mg/L.

Design requirements:

• The treated discharge must reach a pH between 6.5 and 8.5 and a total iron concentration below 3.0 mg/L before it enters the creek.
• The system must run on gravity alone, since no electrical service reaches the site and none can be extended within the grant.
• The whole train must fit within the 1.8 acres the borough controls, which falls 9 feet from the seep to the creek.
• Construction cost must not exceed the $240,000 grant.
• Upkeep is limited to two volunteer work days per year, so any cell requiring frequent attention is unsuitable.

Design rules adopted for this project: size aerobic wetland cells at 10 grams of iron removed per square meter per day; give any settling pond at least 24 hours of detention at the design flow; and treat an anoxic limestone drain as suitable only where dissolved oxygen and aluminum are both below 1 mg/L, because iron and aluminum solids otherwise coat the limestone and stop it from dissolving.

The final report must contain a chemistry brief with the daily iron and acidity loads, a justified sequence of treatment cells, sizing calculations with units shown, a scaled plan of the site, a hydraulic profile showing the fall used by each cell, a line-item cost estimate, a two-visit maintenance schedule, and a sampling plan naming what is measured, where, and how often.

1. Session 1, chemistry brief. Teams convert the flow and concentrations into a daily iron load and a daily acidity load, describe what the low pH and the low dissolved oxygen together imply about the form the iron is in, and list the criteria and constraints in ranked order. Output: a two-page brief with the load calculations shown.
2. Session 2, process selection. Teams decide the order of alkalinity addition, oxidation, settling, and polishing, and write a paragraph justifying whether an anoxic limestone drain passes the project's screening rule at this site. Output: a labeled block diagram of the train with a written justification for each block.
3. Session 3, sizing. Teams size the wetland cells from the iron loading rate, size the settling pond from the detention requirement, total the footprint, and compare it with the land available. Output: a sizing sheet with units shown and a footprint total in acres.
4. Session 4, site layout and hydraulics. Teams arrange the cells on a scaled plan and draw a hydraulic profile assigning part of the available fall to each cell and to the piping between them, confirming the train runs without pumping. Output: a scaled plan and a hydraulic profile.
5. Session 5, cost, upkeep, and monitoring. Teams build a line-item cost estimate against the grant, write the two annual work-day tasks, and draft a sampling plan with locations, parameters, and frequency. Output: an estimate, a maintenance schedule, and a sampling plan.
6. Session 6, association presentation. Each team presents for seven minutes to the fictional association board, played by classmates and the teacher, and answers three questions, one of which must concern what happens if the flow doubles after a wet spring. Output: the presentation and the completed design report.