Zenah W. Orndorff

Reclamation of Acid Sulfate Soils Using Lime-Stabilized Biosolids

Excavation of sulfidic materials during construction has resulted in acid rock drainage (ARD) problems throughout Virginia. The most extensive documented uncontrolled disturbance at a single location is Stafford Regional Airport (SRAP) in Stafford, Virginia. Beginning in 1998, over 150 ha of sulfidic Coastal Plain sediments were disturbed, including steeply sloping cut surfaces and spoils placed into fills. Acid sulfate soils developed, and ARD generated on-site degraded metal and concrete structures and heavily damaged water quality with effects noted over 1 km downstream. The site was not recognized as sulfidic until 2001 when surface soil sampling revealed pH values ranging from 1.9 to 5.3 and peroxide potential acidity (PPA) values ranging from 1 to 42 Mg CaCO(3) per 1000 Mg material. In February 2002 a water quality program was established in and around the site to monitor baseline pH, EC, NO(3)-N, NH(4)-N, PO(4)-P, Fe, Al, Mn, and SO(4)-S, and initial pH values as low as 2.9 were noted in on-site receiving streams. In the spring and fall of 2002, the site was treated with variable rates of lime-stabilized biosolids, straw-mulch, and acid- and salt-tolerant legumes and grasses. By October 2002, the site was fully revegetated (> or = 90% living cover) with the exception of a few highly acidic outcrops and seepage areas. Surface soil sampling in 2003, 2004, and 2006 revealed pH values typically > 6.0. Water quality responded quickly to treatment, although short-term NH(4)(+) release occurred. Despite heavy loadings, no significant surface water P losses were observed.

Modeling Patterns of Total Dissolved Solids Release from Central Appalachia, USA, Mine Spoils

Surface mining in the central Appalachian coalfields (USA) influences water quality because the interaction of infiltrated waters and O with freshly exposed mine spoils releases elevated levels of total dissolved solids (TDS) to streams. Modeling and predicting the short- and long-term TDS release potentials of mine spoils can aid in the management of current and future mining-influenced watersheds and landscapes. In this study, the specific conductance (SC, a proxy variable for TDS) patterns of 39 mine spoils during a sequence of 40 leaching events were modeled using a five-parameter nonlinear regression. Estimated parameter values were compared to six rapid spoil assessment techniques (RSATs) to assess predictive relationships between model parameters and RSATs. Spoil leachates reached maximum values, 1108 ± 161 μS cm on average, within the first three leaching events, then declined exponentially to a breakpoint at the 16th leaching event on average. After the breakpoint, SC release remained linear, with most spoil samples exhibiting declines in SC release with successive leaching events. The SC asymptote averaged 276 ± 25 μS cm. Only three samples had SCs >500 μS cm at the end of the 40 leaching events. Model parameters varied with mine spoil rock and weathering type, and RSATs were predictive of four model parameters. Unweathered samples released higher SCs throughout the leaching period relative to weathered samples, and rock type influenced the rate of SC release. The RSATs for SC, total S, and neutralization potential may best predict certain phases of mine spoil TDS release.

REMEDIATION OF UPLAND ACTIVE ACID SULFATE SOILS WITH LIME-STABILIZED BIOSOLIDS, LIME AND YARDWASTE COMPOST

Excavation of sulfidic materials during construction has resulted in acid rock drainage (ARD) problems on disturbed lands throughout much of Virginia. In particular, exposure of sulfide-bearing Tertiary marine sediments in the Coastal Plain has become increasingly prevalent. Once exposed, these sediments rapidly produce acid sulfate soils which do not readily support vegetation. To date, the most extensive case of acid sulfate weathering problems in the Coastal Plain occurs at Stafford Regional Airport (SRAP) in Stafford, Virginia. Field plots were established at SRAP in 2002 to evaluate a variety of amendments for remediation and revegetation of acid sulfate soils. The plots were constructed in a completely randomized design with 5 treatments and 4 replications per treatment. Prior to treatment, surface (0–15cm) soil samples were collected from all plots to determine pH and peroxide potential acidity (PPA). Treatments included two rates of lime-stabilized biosolids (184 and 92 Mg ha -1 ) with small amounts of additional lime to achieve calcium carbonate equivalences (CCE) of 53 and 27 Mg ha -1 , two rates of lime (47 and 23 Mg ha -1 CCE) with N, P, and K fertilizers, yardwaste compost (101 Mg ha -1 ) with lime (24 Mg ha -1 CCE) and P and K fertilizers, and a control. The plots were seeded with a mix of acidand salt-tolerant grasses. Soil and vegetation samples were collected in duplicate from each plot after 1 and 2 years. No significant differences were observed among the amended treatments for surface soil pH, surface soil EC, or vegetation production for either of the sampling dates, indicating that all of the tested amendment combinations were effective in stabilizing these materials. Additional

PREDICTING DEPTH TO SULFIDIC SEDIMENTS IN THE COASTAL PLAIN OF VIRGINI

Construction through sulfidic materials in the Coastal Plain province of Virginia has resulted in localized acid sulfate drainage that threatens water quality, fill stability, integrity of building materials, and vegetation management. Information regarding the likelihood of encountering sulfide-bearing sediments in construction zones can help minimize the negative impacts that result from the exposure of these materials. The objectives of this study were to evaluate field relationships between depth to sulfide-bearing sediments and landscape parameters, and to test models for predicting depth to sulfides. A study area in Hanover County, Virginia was evaluated using landscape parameters including elevation, slope, distance to streams, and surficial geology to predict depth to reduced sediments (depth-rs). Actual depth-rs values were interpreted from stratigraphic data for 408 well logs obtained from the Hanover County Health Department. A regression model could not be developed to accurately predict depth to sulfidic sediments based on the landscape parameters. Similarly, interpolation using a random subset of the well log data was unsuccessful at predicting depth-rs for the remaining points. However, since excavation depths in the study area are typically less than 9 m a procedure was developed to evaluate the likelihood of encountering sulfidic sediments within this depth based on two risk factors elevation and soil type. This procedure accurately described the likelihood of encountering depth-rs within 9 m for 90% of 58 test points. Samples collected from twenty-three deep borings all had relatively high sulfur values and did not contain calcium carbonate, indicating that exposure of Tertiary sediments would always present a high risk of acid production. Additional