GENERAL46848 - Laserfiche WebLink

Home Browse Search

The great majority of the wetlands on the project site are located topographically above the mining ce[Is and derive their waterfrom un-impacted sources (i.e. theponds or irrigation waters which are hypothesized as the source of the seep wetlahds). These wetlands cannot be impacted by the scope of the proposed project. Of the remaining wetlands, the oxbow wetland segment between cells 3 and 4 derives its water from the ponds above. Therefore, this wetland is not likely to be impacted by mining. The wetlands along the toe of the terrace scope have not been impacted, as determined by the empiricat conditions on-site to date (mining has already occurred downgradient). With reclamation of these cells, water table levels will rise topre-mining conditions. 5. There is a concern about the quantitative measure of wetland species for parts of the mitigation (which involves the transplant of existing wetland topsoils to another area). It is requested to have a quantitative and qualitative description with which to monitor the success of the mitigation. A special condition will be implemented involving success of greater Than 50% of wetlands species and 40% total vegetative cover to ensure success of the mitigated wetlands. See the specific explanation ofspecies in the comment responses letter dated October 17`", 2003. 6. Since the existing oxbow has a heterogeneous configuration, it is uncleaz how the mitigation oxbow will be configured and success criteria should be implemented. According to the applicant, the proposed mitigation oxbow configuration has greater sinuosity than that of the oxbow segments to be disturbed. While the design identifies the size parameters for the construction, it is common for actual "as-built" conditions to vary slightly from the design. If the concern is that the low jlow channel is too uniform, the applicant can ensure that some variability is built into the oxbow channel in the field. Of paramount concern is that the oxbow drains properly so as not to impound or artificially increase evaporative losses. The overall width of the proposed oxbow channels varies from 30 to 50 feet for the wetland portion of the channel, again providing variability. 7. Has the loss of lineaz feet of oxbow resource type have been completely compensated for? The length of the oxbow wetlands proposed for disturbance is 2150 feet. The preferred alternative proposes creating 2750 linear feet in the primary oxbow feature and 600 linear feet in the secondary oxbow feature. This plan is considered sufficient in functions and values to compensate for lost oxbow wetlands. 8. The Applicant proposes to install two piezometers at the proposed mitigation site. The Corps should determine if this is an adequate number of wells to monitor ground water to support successful wetland mitigation when the impacted site is so hydrologically diverse. The Corps has established that two piezometers are sufficient for monitoring ground water on the site at this time. If it is discovered that this is not su~cient, appropriate measures will be taken. 9. The wet meadow and drainage Swale seed mix contains introduced species such as Red Top. Only native species should be intentionally planted. The applicant proposes to substitute Redtop with Corps approved native species(such as prairie cordgrassJ, which are FAC or FACW A change will be made to the plant list attached with the mitigation plan. 10. The avoided wetland azeas and the mitigation wetland areas need to be placed in a conservation easement. The applicant has contacted the surrounding municipalities and private organizations that hodd conservations Project: Green & Croissant Aggregate Mining Applicane Lowland Ready Mix, lnc. Pg 14 of 53 Corps File No: 200180205 Waterway: Big Thompson Wetlands Weld County, CO