The U.S. Environmental Protection Agency, a fierce critic of the Rosemont Mine for several years, recently wrote another round of critical comments on the U.S. Forest Service's latest report on the mine's impacts. The service's Supplemental Information Report was released in March.
Here is a sampling of both sides' views:
Wet-dry mapping of streams
Forest Service, Supplemental Information Report (SIR), page 38: "Wet/dry mapping has been conducted on Empire Gulch and Cienega Creek from 2006 through present. The past 2 years of mapping (2012 and 2013) have had the least amount of measured wetted stream length, suggesting a trend toward degrading aquatic habitat. However, when analyzed, there is no statistically significant trend."
EPA: ". . . the approach downplays the ongoing observed trend in wetted stream length, citing that there is not (a) significant statistical trend. This is misleading and may result in underestimating real impacts to aquatic organisms. For example, while a contracting wetted stream reach may show no significant statistical relationship, a contraction in a small linear distance can still have a large biological effect, especially when the available length of wetted channel is limited during the critical dry season."
Analysis of riparian area impacts
SIR, page 42: "The riparian analysis relied on the following basic assumptions:
-- That the flow observed at the USGS stream gage on upper Cienega Creek . . . from 2001 to 2013 (a period of severe drought) was a reasonable representation of flow conditions in the future.
-- That the cross-section at the gage location was similar in nature to elsewhere along Upper Cienega Creek, Empire Gulch and Gardner Canyon.
-- That predicted groundwater drawdown could be superimposed directly on the historic, observed stream hydrograph, and that the resulting new hydrograph could then be compared statistically with the historic observed hydrograph."
EPA: "All three assumptions have serious flaws/limitations that may render any conclusions of impacts unreliable or meaningless."
Climate change impacts on streams, riparian areas
SIR, page 46: Climate change has been incorporated into the analysis by analyzing trends over the past decade and incorporating additional groundwater drawdown due to expected future changes in temperature. Expected changes in precipitation have not been incorporated, since the trend analysis indicates that the hydrographs analyzed already reflect precipitation conditions similar to those expected to be experienced in the future. More detail on the climate change scenario is included later in this SIR."
EPA: "This logic seems flawed. Why wouldn’t the effects of climate change be additive. The above assumes that the current drought is the result of climate change and not natural drought cycle variation. The FEIS should at least present two scenarios: one with current precipitation trends and another with an additive effect of climate change."
SIR, page 46: "In the FEIS (Final Environmental Impact Statement), wetland areas adjacent to Cienega Creek were analyzed as part of the overall riparian corridor. The collaboration identified one wetland area of particular importance not only from a biological standpoint, but because of its closer proximity to Empire Gulch and higher levels of predicted mine drawdown, as well as the importance for species reintroductions. Cieneguita Wetlands, which are located within the Empire Gulch floodplain upstream from the confluence with Cienega Creek, have been identified as a key reach."
EPA: "While we support inclusion of Cieneguita Wetlands in the impact analysis, we question why other wetlands were not included in the analysis."
Refugia pools survey:
SIR, page 81: "It is recognized that this pool survey was not conducted during the same time of year that is of interest for the presence of refugia pools. Although the pool survey was conducted in November and December during a period that generally is not influenced by runoff, similar to the critical low-flow period in May and June, groundwater levels potentially sustaining the pools during May and June would likely be lower."
EPA: "This reflects a serious sampling problem. Pool surveys should be conducted during the May-June driest period to verify that the November-December samples are representative when adjusted to the seasonal correction factor."