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Commitments and Contingencies Environmental Requirements - Water and Waste (Details) - Federal Coal Ash Regulation $ in Millions | 3 Months Ended
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Sep. 30, 2021 USD ($)
Site Contingency [Line Items] |
Number of sites where regulated ash units will still be in operation at a specified date | 8
NSP-Minnesota |
Site Contingency [Line Items] |
Number of sites where statistically significant increases over established groundwater standards exist | 0
Cost of construction of a new impoundment | $ 9
Estimated cost of closure of an impoundment | $ 4
Time period of existing ash pond closure completion in accordance with the CCR rule | 5 years
PSCo |
Site Contingency [Line Items] |
Number of sites where statistically significant increases over established groundwater standards exist | 4
Number of sites where corrective action options are being evaluated for locations with statistically significant increases above background concentrations | 2
Number of sites where monitoring results indicate potential offsite impacts to groundwater | 1
Estimated cost to remediate groundwater sampling results | $ 35
Estimated cost of construction of an alternative collection and treatment system | 25
Estimated cost to close Comanche station bottom ash pond | $ 3
NSP-Minnesota and PSCo |
Site Contingency [Line Items] |
Number of impoundments where closure plans will be expedited | 2

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