2008-03-13_REPORT - C1981019 ‎(2)‎

• Permit No: C1981019
• IBM Index Class Name: REPORT
• Doc Date: 3/13/2008
• Doc Name: 2007 AHR 2007 Revegetation Monitoring Report
• From: Colowyo Coal Company
• To: DRMS
• Annual Report Year: 2007
• Permit Index Doc Type: Hydrology Report
• Email Name: SB1
• Media Type: D
• Archive: No

2.0 RESULTS
2.1 Overall Summa
Overall, a total of 55 plant species were observed within the 7 revegetated areas, whereas 78 plant
species were observed in the 2 established and 3 proposed reference areas evaluated in 2007. These
consisted of 23 grass taxa, 26 forbs, and 6 shrubs in the revegetation and 26 grass taxa, 37 forbs, and
15 shrubs in the reference areas (see Tables AB-1 and AB-2 in Appendix AB). Tables AB-1 and AB-2
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indicate all taxa observed during fieldwork and are the only tables that indicate 1) common names, 2)
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historic scientific nomenclature, and 3) most current taxonomic nomenclature. Remaining tables do not
indicate this latter category. On average, 32 unique plant species are observable in any given
revegetation unit and 22 in the references areas. Among these taxa are an occasional noxious or
invasive weed such as musk thistle or Japanese brome, with the latter occasionally existing as more
notable patches. Due to the average springtime moisture in comparison to spring 2006 precipitation;
both annual and perennial plant vigor and growth had noticeably increased from 2006 levels.
An analysis of the ground cover variable (Chart 3) indicated that both areas of older reclamation (7
years of age) substantially exceed the success criterion based on 2007 reference area values. Similarly,
Table 1 and Chart 4 indicate even greater success with regard to production on the revegetated units
that are 7 years of age. With regard to ground cover on areas exhibiting four years of growth, only 1 of
4 has exceeded the reference area based success criterion. There was only a single two year-old
reclamation unit evaluated in 2007, and as expected, it did not pass the success criterion for 2007.
Production data are not collected from younger areas, but eventual success is readily expected.
With regard to diversity, Colowyo's revegetation efforts appear to be reasonable as indicated on
Table 3 and Charts 8 and 9. As observable on these exhibits, diversity tends to increase with the age of
reclamation and in most cases should be sufficient for bond release testing by the time they are of
sufficient age for such testing (years 9 and 10 of the bond responsibility, period). As indicated on Chart
6, 50% of areas revegetated in 2000 would pass such testing; but none of 2003 or 2005 revegetation
efforts would currently pass diversity testing. Failures are mainly a result of reclamation not exhibiting a
dominant perennial forb. However, such failures may simply be due to random sampling error (i.e.
sample placement). This analysis suggests that Colowyo is in a reasonable position with regard to the
diversity variable.
Rio Tinto Energy America/Colowyo Mine Page 6 Revegetation Monitoring - 2007
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