Engineering Evaluation/Cost Analysis Big Bug Watershed: Money Metals and Providence Mines Bradshaw Mountains Prescott National Forest, Arizona Prepared for: USDA Forest Service 333 Broadway SE Albuquerque, NM 87102 Prepared by: Weston Solutions, Inc. 960 West Elliot Road, Suite 201 Tempe, Arizona 85284 Contract No. AG-8371-D-09-0191 December 2010 Final Engineering Evaluation/Cost Analysis Big Bug Watershed: Money Metals and Providence Mines Bradshaw Mountains, Prescott National Forest, Arizona December 2010 TABLE OF CONTENTS EXECUTIVE SUMMARY ......................................................................................................................E1 1.0 INTRODUCTION.......................................................................................................................... 1 1.1 SITE LOCATION AND DESCRIPTION ..................................................................................... 1 1.2 AREA POPULATION ............................................................................................................. 2 1.3 PHYSICAL CHARACTERISTICS ............................................................................................. 2 1.3.1 Geologic and Hydrologic Setting .......................................................................... 2 1.3.1.1 Hydrology ................................................................................................. 3 1.3.2 Regional Climate ................................................................................................... 4 1.4 SITE OPERATION HISTORY AND CURRENT SITE CONDITIONS ............................................ 4 1.4.1 Money Metals Mine ............................................................................................... 4 1.4.2 Current Conditions ................................................................................................. 5 1.4.3 Providence Mine .................................................................................................... 5 1.4.3.1 Current Conditions .................................................................................... 6 2.0 APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS ........................ 7 2.1 DEFINITION OF ARARS ....................................................................................................... 7 2.1.1 Applicable Requirements ....................................................................................... 8 2.1.2 Relevant and Appropriate Requirements ............................................................... 8 2.1.3 Other Requirements To Be Considered ................................................................. 9 2.1.4 Waiver of ARARs .................................................................................................. 9 2.2 DEVELOPMENT OF ARARS ................................................................................................. 9 2.3 SITE-SPECIFIC ARARS AND TBCS ................................................................................... 10 2.3.1 Surface Water ...................................................................................................... 11 2.3.1.1 Human Health Surface Water ARARs ................................................... 12 2.3.1.2 Human Health Surface Water TBCs ....................................................... 12 2.3.1.3 Ecological Surface Water ARARs .......................................................... 13 2.3.1.4 Ecological Surface Water TBCs ............................................................. 13 2.3.2 Groundwater ........................................................................................................ 13 2.3.2.1 Human Health Groundwater ARARs ..................................................... 13 2.3.2.2 Human Health Groundwater TBCs ......................................................... 14 2.3.2.3 Ecological Groundwater ARARs and TBCs........................................... 14 2.3.3 Soil and Waste Rock ............................................................................................ 14 2.3.3.1 Human Health Soil ARARs .................................................................... 14 2.3.3.2 Human Health Soil TBCs ....................................................................... 14 2.3.3.3 Ecological Soil ARARs .......................................................................... 15 2.3.3.4 Ecological Soil TBCs ............................................................................. 15 2.3.4 Sediment .............................................................................................................. 16 2.3.4.1 Human Health Sediment ARARs ........................................................... 16 2.3.4.2 Human Health Sediment TBCs ............................................................... 16 2.3.4.3 Ecological Sediment ARARs.................................................................. 16 2.3.4.4 Ecological Sediment TBCs ..................................................................... 16 3.0 SOURCE, NATURE, AND EXTENT OF CONTAMINATION ............................................. 17 3.1 PREVIOUS INVESTIGATIONS .............................................................................................. 17 3.1.1 Characterization of Big Bug Watershed .............................................................. 17 3.1.1.1 Money Metals Mine ................................................................................ 17 X:\projects\USFS Big Bug EECA\EECA Report\Final EECA\Final Big Bug EECA.doc i Final Engineering Evaluation/Cost Analysis Big Bug Watershed: Money Metals and Providence Mines Bradshaw Mountains, Prescott National Forest, Arizona December 2010 3.1.1.2 Providence Mine and Township ............................................................. 18 3.1.2 Preliminary Assessment/Site Inspection .............................................................. 19 3.2 CURRENT INVESTIGATION ................................................................................................ 19 3.2.1 Deviations from the Sampling Plan ..................................................................... 22 3.3 EVALUATION OF DISTRIBUTION OF CONTAMINANTS ....................................................... 22 3.3.1 Money Metals Site ............................................................................................... 23 3.3.1.1 Sediment ................................................................................................. 23 3.3.1.2 Waste Rock ............................................................................................. 23 3.3.1.3 Surface Water ......................................................................................... 23 3.3.2 Providence Mine .................................................................................................. 24 3.3.2.1 Sediment ................................................................................................. 24 3.3.2.2 Surface Water ......................................................................................... 25 3.3.2.3 Soil .......................................................................................................... 26 3.3.2.4 Waste Rock ............................................................................................. 26 3.3.2.5 Groundwater ........................................................................................... 26 4.0 EVALUATION OF RISK ........................................................................................................... 27 4.1 DATA REVIEW ................................................................................................................... 27 4.1.1 Initial Chemical Data Screening .......................................................................... 27 4.2 STREAMLINED HUMAN HEALTH RISK ASSESSMENT ........................................................ 29 4.2.1 Exposure Assessment .......................................................................................... 30 4.2.1.1 Contaminant Sources .............................................................................. 30 4.2.1.2 Release Mechanisms ............................................................................... 30 4.2.1.3 Potential Receptors ................................................................................. 30 4.2.1.4 Exposure Media ...................................................................................... 30 4.2.1.5 Exposure Route(s) .................................................................................. 31 4.2.2 Evaluation of Human Health Risk ....................................................................... 31 4.2.2.1 Money Metals Mine ................................................................................ 31 4.2.2.2 Providence Mine and Township ............................................................. 34 4.3 STREAMLINED ECOLOGICAL RISK ASSESSMENT .............................................................. 38 4.3.1 Ecological Setting ................................................................................................ 38 4.3.2 Ecological Exposure Model ................................................................................. 39 4.3.3 Evaluation of Ecological Risk ............................................................................. 39 4.3.3.1 Money Metals Mine ................................................................................ 40 4.3.3.2 Providence Mine