Upper Tenmile Creek Mining Area Site Angela Frandsen PE Helena Montana Overview Tenmile Creek Superfund Background Adit Discharge Source C ontrol Program SusieUpper Valley Forge and Lee Mountain Source Control Findings ID: 1045036
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1. April 3, 2012Acid Mine Drainage Source Control Program Design InvestigationUpper Tenmile Creek Mining Area SiteAngela Frandsen, PEHelena, Montana
2. OverviewTenmile Creek Superfund BackgroundAdit Discharge Source Control ProgramSusie/Upper Valley Forge and Lee Mountain Source Control FindingsUpcoming Work
3. Site Background Over 150 abandoned minesAbout 40 discharging aditsPrimarily gold, lead, and zinc70-80 percent of the municipal water supply for HelenaEPA –Fund Lead – no PRPs
4. Tenmile Creek in RiminiLow flows due to city water diversionsElevated Arsenic Cadmium, Lead, and Zinc
5. Record of Decision (2002) Overall Goals of Selected Remedy:Protect watershed which serves City of HelenaRemove mine wastes from 70 abandoned sites to repositoryRemove contaminated residential yard soils to repositoryAdit discharge source control and treatment
6. Tenmile ROD Requirements for Adit Discharge“Four-Phase” Source Control Program to reduce contaminant loading from discharging adits to the watershed.Three adit discharges qualify as “Principle-Threat Wastes” Lee MountainSusieRed Water“…source materials considered to be highly toxic or highly mobile that generally cannot be contained in a reliable manner or that would present a significant risk to human health or the environment should exposure occur”Expectation of treatment under the NCP These three account for 70-80% of metals loading from adit discharge
7. City of Helena Water IntakeLee MtRed WaterSusieRimini
8. Site Wide Mass Load Ranking
9. Source Control ProgramPhase 1 – Initial Design Investigations Site PrioritizationFigure out the unique hydrology/geochemistry of the mineTracers, historic workings maps, flow measurementsPhase 2 – Source Control and Flow Reduction Design StudiesPilot scale - regrading, rerouting drainages, plugging, grouting, flooding, dewateringPhase 3 – Source Control and Flow Reduction ImplementationImplement full scale if successfulPhase 4 – Design and Construction of Treatment Facilities – Passive or Active
10. Phase I Design Investigations on the Susie and Lee Mountain AditsTwo discharging adits on opposite sides of the canyonWithin the Community of RiminiLess than 1,500 feet apartUnderstanding the internal workings is critical to reducing flows and contaminant loadingResults – these two adits require different source control strategies
11. Susie AditDrains Upper Valley Forge5-10 gpmpH 3.5-4.3As = 10-20 mg/LFe = 150-200 mg/LAl ~ 1 mg/LCd ~ 200 ug/LZn ~ 30 mg/LThese are several orders of magnitude above water quality standards Adit reopening in 2005
12. 2010 Susie Discharge No immediate response to precipitation
13. Historic Mine Workings Susie Adit Drains the Upper Valley Forge Mine Workings 1 mile!
14. Historic Mine Workings – Plan ViewCan we reduce infiltration from the surface to the workings?Susie Adit
15. 2010 Site ReconnaissanceIdentify possible areas of rechargePlan Tracer Study Dry ReachTwo Ponds
16. 2011 Tracer StudyDetermine if hydraulic connection between surface water bodies and the adit discharge.Presence/AbsenceThree injection points dosed with three different dyes:Two small pondsLosing reach of Moore’s Spring CreekFrom a remediation standpoint, the two ponds and the creek are the features that could most easily be altered to limit infiltration to the mine workings
17. 2011 Tracer Study5 pounds of Eosine introduced in Moore’s Spring Creek6 pounds of Fluorescein introduced into Pond 25 pounds Rhodamine WT introduced into BMP PondActivated carbon sample points:Susie Adit Two residential wells upgradient and downgradient of the aditMouth of Moore’s Spring Creek Residential springs upgradient and downgradient of Moore’s Spring Creek
18. Tracer Study
19. Tracer Study
20. Tracer ResultsDye tracer detected at mouth of Moore’s Spring CreekExpectedNo detections in Susie adit, springs, or groundwater wellsTravel time?Insufficient tracer mass?No connection?Still sampling once per month
21. Susie - Next StepsBulkhead evaluationWould the water discharge somewhere else?Any other unmapped connected workings?Stability and safety going undergroundSafety of Rimini residents Ceiling Void
22. Lee Mountain Adit2-8 gpmpH <3 (2.5-3)As ~ 25-30 mg/LFe ~ 250 mg/L (dissolved)Al ~ 20 mg/L (dissolved)Cd ~ 0.5-1 mg/LZn ~ 50-80 mg/LPb ~ 0.3-0.6 mg/LOrders of magnitude above standards Adit reopening in 2005
23. Lee Mountain – Waste Piles Adit
24. Lee MountainWaste removals occurred incrementally Waste Removals
25. 2010 Lee Mountain Discharge Increased flows after precipitation eventsUnusually high flow observed prior to regular monitoring
26. Lee Mountain Cross Section - 1918 Adit
27. 700-Level Workings and Reconnaissance
28. 2010 Reconnaissance Adits and shafts and waste rock farther up very steep hillPreviously unknown discharging adit – “Caplice” mineShaft with snow insideDeep exploration trenchesMinimal connection with nearest creek
29. 2011 Flow MeasurementsInstall continuous recorder prior to spring runoff to capture the peak and to determine flow variationTenmile Creek reached over 600 cfs on June 7, 2011
30. Cutthroat Flume and Stage Recorder
31. Lee Mountain Discharge - 2011Confirmed flows increase after precipitationDaily snowmelt signature
32. Lee Mountain - Next StepsBulkhead ruled out due to interconnected workings and adits higher on the mountainsideCan we drill horizontal wells to dewater the mountain away from the mine workings?
33. Upcoming Work and Tough QuestionsScoping for bulkhead feasibility (Susie) and horizontal drilling (Lee Mountain)Red Water adit investigationEvaluate further source control costs versus long-term water treatment costs – is it worth chasing these source control measures for these two adits?Good access and existing infrastructure Success of source control uncertain – if 75% reduction is achieved, are we still killing fish? Will we still need treatment?Each mine site is unique!!