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 1.2 1.3
SITE LOCATION AND DESCRIPTION.....................................................................................1 AREA POPULATION .............................................................................................................2 PHYSICAL CHARACTERISTICS.............................................................................................2 1.3.1 Geologic and Hydrologic Setting ..........................................................................2
1.3.1.1 Hydrology.................................................................................................3
1.3.2 Regional Climate ...................................................................................................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
1.4

• 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 DEVELOPMENT OF ARARS .................................................................................................9 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
2.2 2.3

• 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

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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 CURRENT INVESTIGATION ................................................................................................19 3.2.1 Deviations from the Sampling Plan.....................................................................22 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
3.2 3.3

• 4.0
• EVALUATION OF RISK ........................................................................................................... 27

• 4.1
• DATA REVIEW...................................................................................................................27

4.1.1 Initial Chemical Data Screening..........................................................................27 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
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.....................................................................................44
UNCERTAINTY EVALUATION ............................................................................................49
4.2 4.3 4.4

5.0 6.0
IDENTIFICATION OF REMOVAL ACTION OBJECTIVES.............................................. 51

5.1 5.2 5.3 5.4
DETERMINATION OF REMOVAL ACTION SCOPE ...............................................................51 REMOVAL ACTION OBJECTIVES........................................................................................51 IDENTIFICATION OF CLEAN UP ACTION LEVELS ..............................................................51 ESTIMATE OF VOLUME OF CONTAMINATED MATERIAL...................................................52 5.4.1 Money Metals Mine.............................................................................................52 5.4.2 Providence Mine..................................................................................................52