Abstract. Constructed wetlands for treating acid drainage are preferred, low-cost, alternatives to conventional treatment. Drainage with high Fe (e.g., >50 mg/1) and zero alkalinity has not been amenable to treatment with wetlands alone, primarily due to Fe hydrolysis and resultant low pH which requires chemical treatment. Anoxic limestone drains (ALDs) increase the alkalinity of seepage that is then routed to a constructed wetlands. Increased alkalinity buffers the wetlands system from pH decreases, and enhances the effectiveness of wetlands treatment. The Tennessee Valley Authority has modified two low-pH constructed wetlands with ALDs. Results indicate retrofitted wetlands· function at efficiencies meeting effluent limitations without chemical treatment. Designs of 'ALDs are site-specific, but generically consist of an excavated seepage-interception trench backfilled with crushed limestone covered with plastic and clay soil. Dissolution rates of limestone in operational and simulated ALDs were experimentally measured in attempts to estimate design parameters and longevity of an ALO. Potential problems with ALDs include structural and hydraulic stability, plugging due to reaction products within the ALO, and inadequate design and installation.

The authors describe two pedagogical strategies—rhetorical sentence combining and rhetorical pattern practice—that blend once-popular teaching techniques with rhetorical decision making. A literature review identified studies that associated linguistic and rhetorical knowledge with success in engineering writing; this information was used to create exercises teaching technical communication students to write Introduction, Methods, Results, and Discussion (IMRaD) reports. Two pilot studies report promising results: Preliminary findings suggest that students who were taught this method wrote essays that were perceived as significantly higher in quality than those written by students in a control section. At the same time, however, the pilot studies point to some challenges and shortcomings of exercise-oriented pedagogies.

At the Tennessee Valley Authority's Fabius Coal Mine, Alabama, manganese was more effectively removed from a pond containing an algae mat consortium and limestone substrate than from ponds containing only limestone or pea gravel substrates. The algae mat resulted from the integration of a microbial mat and volunteer filamentous green algae. The microbial mat consisted of blue-green algae (predominately Oscillatoria spp.) and bacteria isolated from the site, cultured in the laboratmy, and returned to the site. System operation ran from August 1992 through March 1993. Manganese and iron were consistently removed more efficiently in the algae mat pond (mean flow of 4.2 L/min) than through gravel-only ponds even as water temperatures dropped to less than 5° C in the winter.. Based on filtered water samples, during winter months, at 2 m from the influent point of each pond, the algae mat pond removed 2.59 g/d/m' manganese, compared with 0.80 in the limestone pond and 0.37 in the pea gravel pond. At 1 m from the influent pipe in the algae mat pond, 2.67 mg manganese and 34.25 mg iron were deposited in a gram of dried mat. In March 1993 two events likely caused the loss of much of the algae mat: (1) a 50-cm snowfall followed by a heavy runoff and (2) establishment of a snail population, as well as other possible invertebrate herbivores, which consumed the algae mat. The algae mat was reestablished in June 1993 and has persisted to date. A green algae and microbial mat consortium may be a cost-effective treatment technique for permanently removing metals from mine drainage.

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