Lime Amendment of Contaminated Soil and Acid-Producing Fluvial Tailing Deposits along the Upper Arkansas River, Colorado

 Deposition of mine wastes within the floodplain of the Upper Arkansas River near Leadville, Colorado has resulted from historic releases of tailings and associated product water with elevated levels of metals.  Fluvial deposits of acid-producing waste material are devoid of vegetation and frequently observed as point bar deposits along an 11 mile reach beginning at the confluence with California Gulch.  Eroding streambanks are frequently observed where contaminated materials are present adjacent to the active channel.  Irrigated meadows outside the floodplain, traditionally used for agricultural production, have been contaminated by metal-laden irrigation water resulting in large areas of sparse vegetation and bare ground.  Remediation of the contaminated areas is planned using in-situ soil treatment.  Permanent adjustment of soil pH is critical to establishment and survival of seeded species.  Modified acid-base account (ABA) analytical methods were used to characterize the deficit in neutralization potential found throughout the project area and to determine field lime rates necessary to account for both active and potential acidity.  Spatially variable ABA results were observed during sampling as well as variable depths of contamination.  Lime quality, particle size and moisture content were measured in candidate neutralizing amendments.  The resultant strategy for lime application was developed considering cost, effectiveness, permanence, and implementability.  A variable field lime application rate is prescribed using a multi-level decision logic.