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	USDA Forest Service 1400 Independence Avenue SW Washington, D.C. 20250-0003 (202) 205-8333

Mission Mountains Wilderness

General Information

Image of Mission Mountains Wilderness

State(s): Montana

County(s): Missoula

Forest Service Administrative Unit(s):
Northern Region (Region 1) -- Flathead National Forest

Size: 73877 acres

Elevation Range: 4,500 - 9,360 feet

Data:

Wet Deposition (NADP)
Dry Deposition (CASTNET) - Glacier NP
Visibility (IMPROVE) - Monture, Visibility Summary

Resource Concern Thresholds

AQRV Type: VISIBILITY
Sensitive Receptor	Sensitive Receptor Indicator	Thresholds
Natural Visibilty		For sources generally further than 50 km from a Class I area, the visibility threshold for concern is not exceeded if the 98th %ile change in light extinction is <5% for each year modeled, when compared to the annual average natural condition value for that Class I area.
Plume Blight	Absolute Contrast	Higher level near-field screening and refined analysis: no further analysis will likely be requested if a new or modified source can show that impacts from a new or modified source will stay with the threshold of DeltaE <1.0 and \|C\| <0.02 modeled against natural conditions.
Plume Blight	Absolute Contrast	For near field sources (within 50 km of a Class I area), no additional analysis will be requested If screening analysis of a new or modified source can demonstrate that its emissions will not cause a plume with hourly estimates of DeltaE (color difference index) greater than or equal to 2.0 or the absolute value of the contrast greater than or equal to 0.05 when modeled against natural conditions.
Plume Blight	Color Difference Index	Plume blight near-field refined analysis: no further analysis will likely be requested if a new or modified source can show that impacts from a new or modified source will stay with the threshold of DeltaE <1.0 and \|C\| <0.02 when modeled against natural conditions.
Plume Blight	Color Difference Index	For near field sources (within 50 km of a Class I area), no additional analysis will be requested If screening analysis of a new or modified source can demonstrate that its emissions will not cause a plume with hourly estimates of DeltaE (color difference index) greater than or equal to 2.0 or the absolute value of the contrast greater than or equal to 0.05 when modeled against natural conditions.

AQRV Type: WATER
Sensitive Receptor	Sensitive Receptor Indicator	Thresholds
Water Chemistry	Acid Neutralizing Capacity	For waters that have a baseline Acid Neutralizing Capacity of 100-10 ueq/l, the limit of acceptable change is a cumulative change of no more than 10% from the baseline condition.
Water Chemistry	Acid Neutralizing Capacity	For waters that have a baseline Acid Neutralizing Capacity of <10 ueq/l, no change from the baseline condition is acceptable.
Water Chemistry	Aluminum	Water chemistry aluminum concentrations should not be elevated to > 50 ug/l.
Water Chemistry	Anions	For waters that have a baseline Acid Neutralizing Capacity of 10-100 ueq/l, the cumulative change in anions should be no more than 10% of the baseline concentration of total base cations and SO4+NO2 should not be elevated to >10% of total base cations in lakes with naturally low anion:cation ratios.
Water Chemistry	Water Clarity	For water clarity, the cumulative change should be no more than a 10% decrease from baseline.
Water Chemistry	pH	For waters with a pH baseline of < 6.0, no decrease in pH is acceptable.
Water Chemistry	pH	For waters with a pH baseline of 6.0-7.0, no more than a 10% change from baseline is acceptable.

Pollutant Exposure Concern Thresholds

Pollutant Exposures	Level Name	Thresholds
N	EXCEEDANCE	The Deposition Analysis Threshold for nitrogen deposition is 0.005 kg/ha/yr. Below this, estimated impacts from a source greater than 50km from a FLM Class I Area are considered negligible.
Q	QOverD	For new or modified sources locating greater than 50 km from a Class I area, its impacts will be considered negligible with respect to Class I AQRVs if its total SO2, NOx, PM25, PM10, and H2SO4 annual emissions in tons/yr, based on 24-hr maximum allowable emissions, divided by the distance (km ) from the Class I area (Q/D) is 10 or less. For sources operating less than a year, the emissions must be adjusted to reflect what the emissions would be if the source operated year-round.
S	EXCEEDANCE	The Deposition Analysis Threshold for sulfur deposition is 0.005 kg/ha/yr. Below this, estimated impacts from a source greater than 50km from a FLM Class I Area are considered negligible.

Natural Background Visibility

Site Specific Rayleigh scattering coefficient: 10	Clearest 20% Natural	Clearest 20% 2000-2004 Baseline	Haziest 20% Natural	Haziest 20% 2000-2004 Baseline	Average Annual Natural	Annual Average 2000-2004 Baseline
Standard Visual Range (km)	337	266	181	92	263	169
Haze Index (dv)	1.48	3.85	7.73	14.48	3.98	8.39
For more information on these numbers, click here.