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HomeMy WebLinkAboutREPLAT OF EAST RIDGE - MAJOR AMENDMENT - MJA150005 - SUBMITTAL DOCUMENTS - ROUND 1 - ENVIRONMENTAL REPORT1 PROJECT SITE CHARACTERISTICS AND PERTINENT ENVIRONMENTAL REPORT HISTORY The East Ridge project site is typified by a nearly level to gently to moderately sloping topography. This site was farmed in the past with row crops and pastureland being the main agricultural pursuits. Farming and irrigation ceased more than four years ago and the current vegetation communities overlying the proposed development area are dominated by native and introduced grass and forb species. A few trees and shrubs have become established along abandoned irrigation ditches and the southern border of the existing wetland, while tree groves occur along Timberline Road. The subject wetland lies in a depression surrounded by moderately steep slopes leading to the nearly level upland fields described previously. The subject wetland was first delineated in 2009 and was deemed to be non-jurisdictional given a lack of hydrologic surface water connection to any Water of the U. S. As a part of the proposed development process, it was determined by East Ridge that the wetland should be delineated a second time to determine the current boundaries of the wetland for potential compensatory mitigation requirements. The second delineation was completed by Cedar Creek Associates, Inc. (Cedar Creek) on March 9, 2015. While on a site visit with representatives from East Ridge and the City on June 4, 2015, it was noted that a portion of the previously delineated wetland now supported Canada thistle (Cirsium arvense), classed by the Corps of Engineers as an upland species. The wetland was subsequently delineated a third time on June 24, 2015. As a result, the boundary of the wetland was revised as shown on the map entitled Wetland Area Exhibit. The revised delineation was accepted by the City and has been used as a baseline to complete the compensatory wetland mitigation and upland enhancement planning for this project. At the June 4 meeting, it was determined that a wetland functions and values analysis should be completed for the existing wetland. The analysis was completed in the field on June 16 by representatives from Cedar Creek and the City. The results of this analysis were used during meetings between East Ridge and the City to complete plans for the compensatory wetland mitigation and the upland enhancement activities that were to be applied on site to meet project objectives. A groundwater monitoring program was instituted to determine the depth to groundwater at four sites during the growing season from September 2015 through August 2016. The monitoring wells (piezometers) were sited in areas where it was believed that the required acreage of compensatory wetland mitigation could be successfully competed. The wells were drilled to a depth of _____feet according to the regulations promulgated by the Colorado Water Quality Control Division. The depth to groundwater in each well was measured and recorded every two 2 weeks during the month of September 2015. Monitoring will be renewed in April through August of 2016 to obtain a full growing season of groundwater depth data. COMPENSATORY WETLAND MITIGATION AND UPLAND ENHANCEMENT OBJECTIVES Open Water An open water body (pond) will be created as a part of the compensatory wetland mitigation approach. This pond will be created in lieu of a portion of the vegetated wetlands to be impacted. This is seen as a method of creating a wildlife project element that is not present across the undisturbed project area. The pond will be approximately .72 acre in size and be a maximum of 4 feet deep. This water body will be fed by groundwater as a result of area excavation and will also receive runoff from the surrounding area after passing through constructed forebays designed to treat runoff prior to entry into the pond. Shrub, tree, and willow cutting planting will be completed around portions of pond. Wetland Mitigation The objectives of compensatory wetland mitigation are to recreate vegetated wetlands that will provide wildlife habitat for species that were present prior to development. The planting of shrubs and trees will enhance the esthetic values of this site with respect to the surrounding development and add an additional wildlife habitat element. In addition, the planting of a minimum of 100 willow (Salix exigua) cuttings will further enhance the wildlife habitat value of this ecological feature. As noted above, representatives of the City and the project proponent completed a functions and values analysis in the field for the undisturbed, delineated wetlands on June 15, 2015. As a result of this analysis, the wetland functions of nutrient cycling, groundwater recharge, and soil stabilization were rated as “moderately high”. The wetlands also scored “moderately high” in terms of wildlife habitat, habitat diversity, cover availability, and roosting/nesting sites functions. These function scores, and the “medium” overall rating accorded this ecological feature, were deemed appropriate more for the location of the wetland than for the uniqueness of the site itself. While neither a large wetland, nor notably diverse or having an open water component, this feature lies somewhat isolated from other wetlands and open water bodies and therefore provides a vegetation community uncommon in the immediate area of existing croplands, pasturelands, residential and industrial developments. 3 Upland Enhancement Uplands currently surrounding the wetlands support an introduced grass community with little in the way of diversity in terms of species, growth form, and wildlife habitat. It is believed that the upland border that will surround the open water and wetland mitigation areas can be enhanced through native grass, forb, shrub and tree plantings following resoiling to provide, in concert with the vegetated wetland and open water to be developed, a wildlife habitat complex of greater value to a greater number of species that the ecological community mix currently supported on site. Wetland / Upland Transition Zone A transition zone between the constructed wetlands and open water and the upland enhancement area will develop as a result of water management requirements. This zone will be characterized by periodic, temporary soil saturation as a result of overflow from the constructed wetlands and open water features during times of high precipitation events. This zone will be planted to a mixture of grass species adapted to flooding conditions as describe above. Upland shrub and tree species may also be planted in this zone once the extent of saturated conditions is understood. MITIGATION PLAN AND UPLAND ENHANCEMENT PLAN ELEMENTS The plan to be prepared to guide the construction of the three features of the mitigation / enhancement project will contain the following elements. 1) A soil salvage, stockpiling and reapplication plan to be completed prior to excavation based on soil mass balance calculations and plant species establishment and growth needs. 2) Subsoil material preparation for soil reapplication 3) Soil seedbed preparation specifics 4) Seeding, willow cutting, and shrub and tree planting specifics 5) Adjunct disturbance stabilization techniques 6) A weed control plan summary 7) Fall and Spring revegetation and planting Schedules 8) Techniques for site management and maintenance 9) Proposed monitoring methods and performance standards 10) Revegetation methods, materials, and technique application specifics 11) Pertinent maps, figures, and cross-sections 4 GENERAL WETLAND SEED MIXTURE Preferred Rate Lbs./Acre PLS Species (Corps Designation) Varieties Planted (Broadcast) Seeded/Acre Alkali sacaton (FAC) NA 1.0 1,175,000 Sporobolus airoides Switchgrass (FAC) Nebraska-28 4.0 1,556,000 Panicum virgatum Alkali bulrush (assume OBL) NA 1.0 162,600 Boboschoenus maritimus Olney threesquare (OBL) NA 2.0 359,600 Schoenoplectus pungens Softstem bulrush (OBL) NA 1.0 550,000 Shoenoplectus tabernaemontani Totals = 9.0 3,803,200 (~87 seeds/ sq. ft.) WETLAND SHRUB PLANTING SPECIES AND RATES Species Total Planted in (Corps Designation) Mitigation Area Planting Site Considerations Chokecherry (FACU) 15 Upslope from dogwood plantings; Padus virginiana upland soil moisture regime Indigobush amorpha (OBL) 15 Upslope from the willow cuttings in Amorpha fruticosa saturated, not flooded soils Redosier dogwood (FACW) 15 Upslope from amorpha plantings or Swida (Cornus) stolonifera may be mixed with amorpha. Total planted = 45 WETLAND TREE PLANTING SPECIES AND RATES Total Planted in Planting Species Mitigation Area Site Considerations Narrowleaf cottonwood (FACW) 7 Upslope from willow cuttings in Populus angustifolia shrub planting voids Peachleaf willow (FACW) 7 Mixed with narrowleaf Salix amygdaloides cottonwoods Plains cottonwood (FAC) 7 Immediately upslope Populus deltoides from the narrowleaf cottonwoods in moist/wet but not saturated soils Total planted = 21 5 UPLAND ENHANCEMENT SEED MIXTURE Preferred Rate Lbs./Acre Species Variety(s) Planted (Drilled) PLS Seeded/Acre Slender wheatgrass Primar, Revenue 3.00 480,000 Elymus trachycaulus Thickspike wheatgrass Critana 4.00 774,000 Elymus lanceolatus Western wheatgrass Arriba, Barton 5.00 630,000 Pascopyrum smithii Lewis flax Appar 1.00 285,000 Adenolinum lewisii Upright prairie coneflower None 0.25 225,000 Ratibida columnifera Four-wing saltbush Wytana 4.00 208,000 Atriplex canescens Totals = 17.25 2,602,000 (~60 seeds/sq. ft.) NOTE: Shrub planting rate is based on a broadcast application. Note: This seed mixture will be planted at twice the rate shown when broadcast planting methods are used. UPLAND ENHANCEMENT DROUGHT-TOLERANT SHRUB PLANTING SPECIES AND RATES Species Total Planted Four-wing saltbush 40 Atriplex canescens Rubber rabbitbrush 40 Chrysothamnus nauseosus Skunkbush sumac 35 Rhus aromatic trilobata Woods Rose 30 Rosa Woodsii Total Planted= 145 UPLAND ENHANCEMENT TREE PLANTING SPECIES AND RATES Species Total Planted Ponderosa pine 20 Pinus ponderosa Rocky Mountain juniper 20 Juniperus scopulorum Total Planted = 40 6 UPLAND SOIL STABILIZATION SEED MIXTURE (LOAMY TO CLAYEY SOILS) Preferred Rate Lbs. PLS/Acre PLS Species Varieties Planted (Broadcast) Seeded/Acre Slender wheatgrass Pryor, Revenue 6.0 960,000 Elymus trachycaulus Thickspike wheatgrass Critana 4.0 744,000 Elymus lanceolatus Western wheatgrass Rosanna, Arriba, Barton 10.5 1,323,000 Pascopyrum smithii Blue flax Appar 2.0 570,000 Adenolinum lewisii Totals = 22.5 3,597,000 (~ 83 seeds/ sq. ft.) TRANSITION ZONE SEED MIXTURE Preferred Rate Lbs. PLS/Acre PLS Species Varieties Planted (Seed) Seeded/Acre Alkali sacaton (FAC) NA 0.5 587,500 Sporobolus airoides Switchgrass (FAC) Nebraska-28 2.0 778,000 Panicum virgatum Slender wheatgrass Pryor, Revenue 3.0 480,000 Elymus trachycaulus Thickspike wheatgrass Critana 1.0 186,000 Elymus lanceolatus Western wheatgrass Rosanna, Arriba, Barton 7.0 882,000 Pascopyrum smithii Totals = 13.5 3,099,500 (~ 67 seeds/ sq. ft.)