7-10 7.4.4 Soils and Vegetation

Ambient air impacts from the Main Flare presen ted in Sections 7.1 – 7.3 could have potential effects on potentially sensitive soils and vegeta tion in the region surrounding the Main Flare. However, maximum modeled impacts of SO 2 , NO 2 and CO are insignificant and their effects on regional soils and vegetation ar e also insignificant. To de monstrate the insignificance of potential effects on regional soils and vegetation from modeled Ma in Flare emissions impacts, a quantitative assessment of these impacts is pres ented. This assessment is based on guidance presented in “A Screening Procedure for the Imp acts of Air Pollution Sour ce on Plants, Soils and Animals” (U. S. EPA, 1980). Mo deled ambient air impacts of NO 2 , SO 2 and CO are compared to minimum ambient air concentrations leading to a perceptible effect on sensitive vegetation in San Juan County, Utah. Because PM emissions (3.1 lb/hr and 13.8 tpy) from the Main Flare are
small and metals content in the emitted PM are minimal, effects on soils and vegetation are also insignificant. However, the very small increase in soil metal content potentially associated with
Main Flare combustion PM emissions are estim ated per Screening Procedure guidance to illustrate their insignificant impact.

Vegetation in San Juan County include woodlands , dominated by Pinyon Pine and Utah Juniper,
desert and semi-desert shrubs classified as saltbush because of the prevailing saline soils, sagebrush, blackbrush and scattered grassland areas. Specific vege tation designated as sensitive for San Juan County are presented in Table 7- 8. This list is based on Table 13.1a of the “Analysis of Management Situation”, prepared by the Monticello BLM Field Office in January
2005.

NO 2 , SO 2 and CO Impacts

A summary of maximum modeled NO 2 , SO 2 and CO impacts from the Main Flare from Sections 7.1 – 7.3 for various averaging periods corresponding to exposure periods for sensitive vegetation are presented below.

1-hour 3-hour 8-hour 24-hour Annual
Pollutant (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 )
NO 2 2.456 2.210 1.719 0.982 0.15
SO 2 11.63 10.47 8.14 4.65 0.93
CO 21.04 18.94 14.73 8.42 1.687-11 To assess whether these maximum ambient air impacts are significant when considering sensitive vegetation exposure, screening ambien t air concentrations from Table 3.1 of the Screening Procedure guidance document are presen ted in Table 7-9. A comparison by pollutant of maximum modeled ambient air impacts to scr eening concentrations for sensitive vegetation exposure is presented below.

NO 2 3-hour 8-hour Annual Max Screening Max Screening Max Screening Impact Conc. Impact Conc. Impact Conc. (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) 2.210 3,760 1.719 3,760 0.15 94

SO 2 1-hour 3-hour Annual Max Screening Max Screening Max Screening Impact Conc. Impact Conc. Impact Conc. (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) (μg/m 3 ) 11.63 917 10.47 786 0.93 18

CO
1-week Max Screening Impact Conc. (μg/m 3 ) (μg/m 3 ) 8.42* 1,800,000 * - Maximum 24-hour averaged impact used as conservative estimator of 1-week exposure period

Conclusions for potential effects of Main Flare NO 2 , SO 2 and CO emissions on sensitive vegetation are the following:

 Sensitive vegetation exposure to maximum NO 2 ambient air impacts from the Main Flare are nearly three orders of magnitude below respective screening concentrations

 Sensitive vegetation exposure to maximum SO 2 ambient air impacts from the Main Flare are approximately 1% of the short-term (1 and 3 hour) exposure screening concentration and approximately 5% of the long-term (annual) exposure screening concentration

 Sensitive vegetation exposure to maximum CO ambient air impacts from the Main Flare
is at least five orders of magnitude below the one-week e xposure screening concentration7-12 Section 3.2.3 of the Screening Pr ocedure guidance document discusse s the possible in teraction of
SO 2 and NO 2 ambient air concentrations on sensitive vegetation and provides coincident 1-hour
SO 2 and NO 2 screening concentrations that may presen t a “synergistic” effect. However, this discussion cautions using these screening concentr ations as conclusive evidence of an adverse synergistic effect on sensitive vegetation. The 1-hour exposure screening concentration presented in Table 3.3 of the Screeni ng Procedure guidance document for SO 2 and NO 2 is 5

ppm v or 131 and 94 μg/m 3 , respectively. The maximum 1-hour modeled impacts of SO 2 and
NO 2 are 11.63 and 2.456 μg/m 3 , respectively. These impacts are less than one percent of the synergistic screening concentrations.

In conclusion, there are no adverse effects on re gional sensitive vegetation from Main Flare NO x , SO 2 and CO emissions either indi vidually or in combination.

PM Impacts

Potentially adverse impacts to soils and vegetation from PM emissions are primarily due to the metals content of the emitted PM. Table 3.4 of the Screening Procedure guidance document presents screening soil concentrations, in ppm w , that would potentially have adverse impacts on sensitive vegetation located in the soil. E quation 5.1 of the Screening Procedure guidance
document estimates the resultant soil concen tration increase from ambient air metals concentration as presented below.

DC (ppm w ) = 21.5 (N/d) χ

where:

DC = deposited concentration (ppm w ) N = expected lifetime of source (yr. ); assume Main Flare lifetime of 70 yr. d = depth of soil which deposited material is distributed (cm.); 3 cm. is recommended value

χ

= maximum annual average ambient concentration from source (μg/m 3 )

Maximum ambient air PM impacts from the Main Flare are estimated by applying the ratio of estimated hourly emissions of PM and NOx to estimated maximum ambient air NO2
concentrations. The maximum PM and NOx emissi ons are 3.1 lb/hr and 27.1 lb /hr, respectively. Applying the ratio of 3.1/ 27.1 to the maximum annual NO 2 ambient air impact in Section 7.1 provides the following estimate of the maximum annual PM ambient air impact:7-13 Maximum Annual PM Impact = (3.1 lb/hr÷27.1 lb/hr) x 0.1965 μg/m 3 * = 0.02248 μg/m 3

* Annual NO 2 impact, uncorrected by the defau lt ozone-limiting ratio of 0.75

Estimated soil concentration increase for each meta l in the Main Flare PM emissions is estimated by the following steps:

1. Metals content of PM emissions from the Ma in Flare estimated from the ratio of each metal emission factor and the total PM emission factor in Tables 1.4-4 and 1.4-2 of AP42 for natural gas combustion, expressed as lb/10 6 SCF of natural gas (EPA, 1998).

2. Maximum annual impact for each metal estim ated by the product of the maximum annual PM impact and metal/total PM emissions ratio.

3. Maximum annual metal impact is input to Equation 5.1.

4. Resultant soil concentration increase is compared to the metal screening soil concentration.

Table 7-10 summarizes comparison of the screening soil concentration to the estimated soil
concentration increase from emissions of each me tal from the Main Flare. The estimated soil
concentration increase of each metal from Ma in Flare PM combustion emissions ranges from three to six orders of magnitude below the respective screening metal concentration. Therefore, Main Flare PM emissions do not affect sensitive regional vegetation because existing soil metal concentrations containing these vege tation are not perceptibly increased.Table 7-8. Sensitive Plant Species Pote ntially Occurring in San Juan County, Utah 1

Common Name Habitat
Navajo Sedge Seasaonlly wet, seeps, springs, hanging gardens in Navajo sandstone: 3,770 - 5,908 ft. elevation
Chatterly's Onion Moist pinyon-juniper and sagebrush sites

Culter Milkwood Sand dunes

Cronquist Milkvetch Cutler formation (Comb Wash), Morrison formation (Aneth)

Copper Canyon Milkvetch Warm desert shrub, 3,085 ft. elevation, Copper Canyon

Skull Valley Spring Parsley Deposits of wind-blown sand

Beck's Spring Parsley Sandy soil of Navajo sandstone origin, crevices and ledges of slickrock, higher elevations in Abajo Mountains
Hole-in-the Rock Prairie Clover Sandstone bedrock and sand in blackbrush and mixed desert shrub: 4,690 - 5,000 ft. elevation
Spineless Hedgehog Cactus Blackbrush, ephedra, sagebrush, pinyon-juniper mountain brush, aspen communities: 3,200 - 8,400 ft. elevation
Nevada Willowherb Talus slopes, crevices

Kachina Daisy Seasonally wet seeps, hanging gardens on sandstone outcrops

Redroot Buckwheat Sagebrush and pinyon-juniper: 5,000 ft. elevation

Cataract Canyon Gilia Mixed warm and cool desert shrub communities: 3,280 - 5,215 ft. elevation

Alcove Bog Orchid Moist streambanks, seeps, hanging gardens in mixed desert shrub, pinyon-juniper and oakbrush: 4,360 - 8,690 ft. elevation
Canyonlands Lomatium Slot canyons between Entrad a sandstone, sandy soil or crevices in sandstone, sheltered cool areas of slopes
Western Hophornbeam Small tree at bases of monoliths, hanging gardens of sandstone: 4,000 - 5,600 ft. elevation
Paradox Breadroot Pinyon-juniper and mixed desert shrub: 5,020 ft. elevation

Alcove Rock Daisy Drier crevices in seasonally wet hanging ga rdens, alcoves at 4,000 ft. elevation, Navajo & Windgate sandstone, Rico Formation
Howell Scorpionweed Salt and warm desert shrub, pinyon-juniper: 3,690 - 5,000 ft. elevation

Bluff Phacelia Salt desert shrub: 4,500 ft. elevation

Mancos Shadscale Salt desert shrub in Morrison Formation

Jane's Globemallow Sandy soils of weathered white rim and Or gan Rock areas of Cutler Formation, warm/salt desert shrub: 4,000 - 4,600 ft. elev.

1 Table 13.1a (Chapter 13) of “Analysis of the Manageme nt Situation”, Monticello BLM Field Office, January 2005.Table 7-9. Screening Ambient Air Concentrations for Sensitive Vegetation Exposure11-hour 3-hour 4-hour 8-hour1-week 1-month AnnualPollutant (μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3)SO2917 786 -- -- -- -- 18NO2-- -- 3760 3760 -- 564 94CO2-- -- -- -- 1800000 -- --1Based on Table 3.1 of "A Screening Procedure for the Impacts of Air Pollution Sources on Plants, Soils and Animals"2Reversible decreases in photosynthetic rate have occurred at significantly lower levels, but growth effects have not been demonstratedTable 7-10. Comparison of Screening Soil Concentration to Estimated Main Flare Concentration1AP-42 Emission Factor2Annual Avg. Estimated Soil Screening SoilTotal PM Pollutant Impact Concentration from Flare3ConcentrationMetal (lb/106SCF) (lb/106SCF) (μg/m3) (ppmw) (ppmw)Arsenic 2.0E-04 5.9E-07 3.0E-04 3Cadmium 1.1E-03 3.3E-06 1.6E-03 2.5Chromium 1.4E-03 4.1E-06 2.1E-03 8.4Copper 8.5E-04 2.5E-06 1.3E-03 40Manganese 3.8E-04 1.1E-06 5.6E-04 2.5Mercury 2.6E-04 7.7E-07 3.9E-04 455Nickel 2.1E-03 6.2E-06 3.1E-03 500Selenium 2.4E-05 7.1E-08 3.6E-05 13Vanadium7.62.3E-03 6.8E-06 3.4E-03 2.51Screening soil concentrations based on Table 3.4 of "A Screening Procedure for the Impacts of Air Pollution Sources on Plants, Soils and Animals" and are minimum concentrations wherevegetation in the soil could be adversely affected2Tables 1.4-2 and 1.4-4 of AP-42, Emission Factors forPM (Total) and Metals from Natural Gas Combustion (7/98)3Main Flare soil metals concentration based on Eqn. 5-1 of "AScreening Procedure for the Impacts of Air Pollution Sources onPlants, Soils and Animals" withflare lifetime of 70 yr. and ratioof metal to PM emissions multiplied by annual PM impact