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_ f; RECEIYEa Wetland Mitigation and ro~onitoring Plan ~ ~C~ ~ ~ 20 Puthfindcr Gravel Pit Applicant: Scott Smith/ Pathfinder L:c. INTRODUCTION The following plan is submitted as a wetland mitigation and monitoring plan for approximately .12 acre of wetland impact at the Pathfinder Gravel Pit road construction sits. The US Army Corps of Engineers under Nationwide Permit Number 14; case number 199975336 has authorized fill activities for the relocation of a roadway away from a historically unstable slope. The plan has been approved conceptually in the field by the US Army Corps and the San Miguel County Planning Department, and is submitted based on design and monitoring parameters discussed during site visits. MITIGATION DESIGN The existing wetland area is a seep-fed depression that is dominated by Carex sp. (sedge) with some Salix gyp. (willow) present. Mitigation for the approximately.l2 acre of impacted wetlands will be accomplished by developing a shallow Swale east of the existing wetlands, along the toe of slope. The Swale will be constructed in the native materials on site, which are a combination of colluvial deposits with many fines and will be lined with 3 feet of clay liner to reduce any infiltration to the substrate. Swale dimensions will be approximately 20 feet wide at top of bank and 12 feet wide at the Swale base, with a total length of approximately 570 feet on .5% grade. If the entire bottom of the Swale is converted to wetlands the total mitigation could be .1 b acre, however .12 is the target mitigation total. See Mitigation & Monitoring Figure 1 for Swale location. Once constructed, the existing wetland plants and soil substrate will be relocated to the Swale. Transplants will be moved by a small excavator that will remove sufficient below-surface materials to ensure root mass and soils are transferred with the excavated plant materials. Placement of the materials will be determined to maximize wetland plant coverage in the bottom of the Swale and to provide a solid matrix-of biomass for future wetland plant colonization. The slope east of the mitigation Swale will be graded at 1.5:1 to develop the area required for the Swale, and will be revegetated to minimize erosion into the Swale: Discharge during peak-flow periods will be from the north end of the Swale, and will follow the roadway bar ditch to a culvert approximately 150 feet north along the road. Once the discharge passes under the roadway, it enters an existing channel that drains into the Lake Fork of the San Miguel River. Due t0 the historically unstable nature of the slope to the west of the mitigation Swale, the design engineers for the project seek to eliminate infiltration from the Swale. The clay liner that wilt be installed in the Swale will serve to perch the water table through the mitigation site, ensuring that any moisture in the Swale is available to the wetland plants that will be growing in the Swale. MONITORING PROTOCOL Following construction, photos will be provided to the US Army Corps and San Miguel County for review of the constructed mitigation wetland. Long-term monitoring of the mitigation Swale will be accomplished from 4 permanently installed monitoring photo-points around the site. The established monitoring photo- points will provide perspective on the health, maturation and function of the mitigation wetland. Photos will be collected by June 15ih and August I S"' of 2003-2005 and submitted to the US Army Corps and San Miguel County for review by October 1 of 2003-2005 fur review. See Mitigation & Monitoring Figure f for photo-point locations. If failures in the mitigation wetland are noticed by owner/agent, they wilt be documented and the US Army Corps and San Miguel County will be notified of the failure and the proposed cortective measures for repairs.