Daniels and Orndorff, 2003 ICARD Acid Rock Drainage

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W L DANIELS and Z W ORNDORFF early-1980s included capping of the waste rock pile with clay and topsoil, a water treatment facility, wetlands, and other experimental techniques. Initial remediation costs exceeded over two million dollars, with operation and maintenance costing about $US 240 000 annually since 1982. Nonetheless, acid drainage from the airport and associated sites continues to be a problem (Zentilli and Fox, 1997; Fox, Robinson and Zentilli, 1997; Hicks, 2003). Perhaps the most critical step in characterising and managing sulfidic materials is the development and testing of accurate techniques for screening the acid-forming potential of geologic materials. Extensive research has been conducted on this topic over the past 30 years in various mining environments (Sobek, Skousen and Fisher, 2000; Geidel and Caruccio, 2000), however, the application of these same procedures to the diverse range of sulfidic materials likely encountered in statewide road building programs has not been documented. METHODS AND MATERIALS In the fall of 1997, a questionnaire regarding occurrence and locations of acid roadcuts was distributed to all of the Virginia Department of Transportation (VDOT) districts. All sites reported (n = 27) as a result of this questionnaire were visited over the following year. Over 20 additional sites were reported later or discovered independently. Geologic materials and road drainage grab samples, where available, were collected from all sites. Both fresh and weathered representative samples of lithologies at each site were obtained. The geologic formations and specific rock types at all sites were determined through field observations, personal communications with state geologists, and geologic maps. All geologic samples were tested for potential peroxide acidity (PPA) using the H2O2 oxidation/titration method of Barnhisel and Harrison (1976) which is a variation of the method described by O’Shay, Hossner and Dixon, (1990). Total-S was determined with an Elementar Vario Max CNS analyser, and rated for presence of carbonates by the HCl ‘fizz test’ (Sobek et al, 1978), and pH in H2O and KCl using a combination electrode. Surface samples from rock exposures that contained a sufficient amount of soil-sized particles (0.2 per cent) were found at all locations indicating that S occurrence may be ubiquitous in the Chesapeake Group. Sediments containing carbonates have lower PPA values, generally ranging from 0 - 20 Mg CaCO3/1000 Mg material, and were found in only few samples from deep borings and not in acid road banks. This suggests one of the following: 1. carbonate-bearing layers in the Tertiary marine sediments tend to occur at greater depths; 2. excavation through carbonate-bearing sediments does not result in severe ARD; or 3. carbonates have been leached out of existing roadcuts by acid drainage. 480 Cairns, QLD, 12 - 18 July 2003 6th ICARD
ACID ROCK DRAINAGE FROM HIGHWAY AND CONSTRUCTION ACTIVITIES IN VIRGINIA, USA TABLE 1 Summary of potential peroxide acidity (PPA) and per cent total-S levels for geologic samples, and pH and metal content of a road drainage sample from representative sites. Note: The Appalachian Plateau Province was not specifically sampled by Orndorff (2001) and therefore data are not presented here. Geologic formation (Region) Sample size Geologic samples Representative surface water drainage samples PPA † %S pH Fe Al Mn Dissolved – mg/L Zn S Tabb Formation (Coastal Plain) n = 10 3.2 0.1 3.05 12.4 15.2 2.4 0.6 136 Tertiary Marine Sediments (Coastal Plain) n = 49 20.9 0.79 3.09 13.9 49.5 2.1
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Page 7 and 8: Location Date pH EC (uS/cm) SW 4 (A
Page 9: Daniels, W L and Stewart, B R, 2000

Daniels and Orndorff, 2003 ICARD Acid Rock Drainage

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