Reconstructing the history of mining and remediation in the Coeur d’Alene, Idaho Mining District using lake sediments Matthew J. Morra a,⇑ , Meghan M. Carter a,1 , William C. Rember b , James M. Kaste c a Division of Soil & Land Resources, 875 Perimeter Drive, MS 2339, University of Idaho, Moscow, ID 83844-2339, USA b Department of Geological Sciences, 875 Perimeter Drive, MS 3022, University of Idaho, Moscow, ID 83844-3022, USA c Geology Department, 217 McGlothlin Street Hall, The College of William & Mary, Williamsburg, VA 23187, USA highlights Lake Coeur d’Alene sediments are a record of mining contamination and remediation. Metal(loid) loading decreased after installation of tailings ponds. Arsenic concentrations show evidence of diagenesis. Sedimentary Cr and Pb concentrations remain at mining era levels. Improved management of tailings containing toxic Pb concentrations is required. graphical abstract article info Article history: Received 3 December 2014 Received in revised form 9 April 2015 Accepted 19 April 2015 Available online 15 May 2015 Keywords: Lake sediments Mining Mine tailings Metals Metal contamination abstract Mining that began in the late 1800s intensified during World War II contaminating Lake Coeur d’Alene sediments with potentially toxic elements. We used 80 y of the sediment record to reconstruct metal(loid) loadings to the lake and quantitatively evaluate the effectiveness of tailings management. Sediment core analysis for pollen, chronological markers, and metal(loid)s permitted stratigraphic reconstruction showing that contaminant loading decreased after tailings pond construction, but that most metal(loid) concentrations exceed recommended limits. Arsenic concentrations (250–450 mg kg 1 ) at the sediment–water interface are potentially toxic; however, low P concentrations in recent sediments (1.0–1.4 mg kg 1 ) inhibit eutrophication and the concomitant release of soluble As. Zinc (3 g kg 1 ), Cd (10 mg kg 1 ), Ag (10 mg kg 1 ), and Cu (90 mg kg 1 ) concentrations are now lower than in sediments deposited during active mining, but remain an environmental concern. Sedimentary Cr and Pb concentra- tions have not changed in the last 50 y, because tailings continue to enter the lake. Although modern Cr concentrations (40 mg kg 1 ) are unlikely to cause toxicity, current Pb concentrations (4 g kg 1 ) exceed acceptable limits, creating challenges for remediation. Strategies to manage other mining-contaminated watersheds should include consideration of elemental differences when evaluating remediation effectiveness. Ó 2015 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2015.04.055 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 208 885 6315; fax: +1 208 885 7760. E-mail addresses: mmorra@uidaho.edu (M.J. Morra), meghan.carter@gmail.com (M.M. Carter), rember@uidaho.edu (W.C. Rember), jmkaste@wm.edu (J.M. Kaste). 1 Present address: Office of The Attorney General, PO Box 83720, Boise, ID 83720, USA. Chemosphere 134 (2015) 319–327 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere