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Home My WebLink AboutDRB140452_414179A ES & Mitigation Plan (10-10-14)_1413906360.pdf I-IHepvorrh-Pawlak Geotechnical,Inc. P.O. Drawer 1887 Geotech 5ilverthomoraee, 8olora-1989n 80498 Phone: , HEPWORTH-PAWLAK GEOTECHNICAL Fax: 970-468-5891 email:hpgeo4)hpgeotech.coin ENVIRONMENTAL ASSESSMENT AND WETLAND MITIGATION PLAN PROPOSED RESIDENCE 5087 MAIN GORE DRIVE LOT 2,BLOCK 1,BIGHORN 5TH ADDITION VAIL, COLORADO JOB NUMBER 414 179A OCTOBER 10,2014 PREPARED FOR: HAROLD "SKIP"LEEVER 1397 VAIL VALLEY DRIVE VAIL, COLORADO 81657 • Glenwood Springs 970-945-7988 • Parker 303-841-7119 • Colorado Springs 719-633-5562 TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY 1 PROPOSED CONSTRUCTION 1 SITE CONDITIONS 1 WETLAND DELINEATION 1 THREATENED AND ENDANGERED SPECIES 2 HISTORIC RESOURCES 3 PROPOSED WETLAND IMPACTS 3 AVOIDANCE AND MINIMIZATION 4 MITIGATION 4 BASIS FOR DESIGN 5 WETLAND PLANTING AND SEEDING- 5 MONITORING 7 MONITORING SCHEDULE 8 SUCCESS CRITERIA 9 POTENIAL CONTINGENCY MEASURES 9 ENVIRONMENTAL ASSESSMENT 9 LIMITATIONS 10 FIGURE 1 -WETLAND MITIGATION PLAN FIGURE 2-WETLAND DELINEATION MAP WETLAND MITIGATION MONITORING DATA SHEET PURPOSE AND SCOPE OF STUDY This report presents the results of a wetland delineation and subsequent environmental assessment and preparation of a mitigation plan for proposed impacts to wetlands from development of the property. We previously prepared an Isolated Wetland Evaluation which was submitted to the Army Corps of Engineers for the project in a report dated September 2, 2014. PROPOSED CONSTRUCTION A single family residence is proposed to be constructed on the property. Proposed development plans are shown on Figure 1. SITE CONDITIONS The site is located within a developed residential neighboring in the"East Vail"portion of the Town of Vail municipal limits. Initial development of the area appears to have taken place from the late 1960s to early 1970s. There is a man-made drainage feature that flows along the western property boundary and another along the northern property boundary. We performed a wetland delineation of the property in accordance with the Army Corps of Engineers 1987 Wetland Delineation Manual and Western Mountain Valleys and Coast Regional Supplement. The wetland boundary is shown on Figure 2. WETLAND DELINEATION A representative of Hepworth-Pawlak Geotechnical,Inc.performed a wetland delineation on the property on June 26,2014. The wetland boundary was flagged and numbers and subsequently surveyed by Peak Surveying. Wetlands were identified utilizing procedures outlined in the 1987 Army Corps of Engineers Wetland Delineation Manual and the Mountain West Regional Supplement. The wetland boundary is shown on Figure 1. Approximately 9,063 square feet(0.21 acres)of wetlands were identified on the site. The Job No.414 179A 1 GeStech wetlands are concentrated along two man-made drainage features on the property along the north and west property boundaries. The drainage features did not present obvious connectivity to Gore Creek and were thus determined to be isolated. The wetlands on the site were classified as palustrine, scrub-shrub, broad-leaved deciduous, saturated(PSS1B) and palustrine, emergent, non-persistent,saturated(PEM1B)as classified by the Cowardin classification system. As previously mentioned,wetlands at the site were concentrated along the two man-made drainage features on the property. Wetland quality and vitality was found to be strongest in the areas immediately adjacent to the drainage features then gradually decreased in quality away from their primary hydrology source. The wetlands on the upgradient margins were found to be of very low quality. This was found to be particularly true of the wetland complex along the western property boundary. Wetland hydrology and soil characteristics were present,however,were found to be very weak in these areas. Wetland vegetation was also estimated to be marginal in these areas with a mix of wetland and upland vegetation and only a slight preference toward wetland or border species. The scrub-shrub portions of the wetland complex were dominated by a tall overstory of mountain willow and speckled alder and a ground cover of shrubby cinquefoil, cow parsnip, California false hellebore and a variety of other less dominant species. The emergent portions of the wetland complex were dominated by California false hellebore, mountain timothy and shrubby cinquefoil. No fen wetlands or other specially protected areas were observed on the property. THREATENED AND ENDANGERED SPECIES Based on information available from the U.S. Fish and Wildlife Service,there are 13 species listed as threatened, endangered or as candidate species that have the potential to be located in Eagle County, Colorado. A species list is provided in Table 1 below. None of the species listed below were observed on the site. Due to the limited nature of the project scope and heavy development that has occurred in the area over the last 40 years, impacts to threatened and endangered species are unlikely. Job No.414 179A 2 Gtech Table 1: U.S.Fish and Wildlife Service List of Threatened and Endangered Species in Eagle County,CO. Birds Greater sage-grouse(Centrocercus urophasianus) Candidate Mexican Spotted owl(Strix occidentalis lucida) Threatened Yellow-Billed Cuckoo(Coccyzus americanus) Candidate Fishes Bonytail chub(Gila elegans) Endangered Colorado pikeminnow(Ptychocheilus lucius) Endangered Greenback Cutthroat trout(Oncorhynchus clarki ssp. Threatened stomias) Humpback chub(Gila cypha) Endangered Razorback sucker(Xyrauchen texanus) Endangered Flowering Plants Penland Alpine Fen mustard(Eutrema penlandii) Threatened Ute ladies'-tresses(Spiranthes diluvialis) Threatened Insects Uncompahgre Fritillary butterfly(Boloria acrocnema) Endangered Mammals Canada Lynx(Lynx canadensis) Threatened North American wolverine(Gulo gulo luscus) Candidate HISTORIC RESOURCES No signs of cultural or archeological resources were found to be present at the site, which would warrant a more detailed survey. PROPOSED WETLAND IMPACTS Based on our wetland delineation and the proposed development,permanent impacts to wetlands on the site will total 4,570 square feet. Impacts to wetlands were considered Job No.414 179A 3 Ge Ptech necessary for construction of the residence as well as ancillary features such as drainage, driveway and lawn space. AVOIDANCE AND MINIMIZATION Based on the site development plans it was not possible to avoid all wetland impacts on the project site;however, impacts have been minimized where practical. The wetlands within the project area are considered to be relatively low quality especially within the impact area. Measures take for avoidance and minimization are outlined below. • The house location was situated as far into the north and east portion of the property to minimize permanent impacts to wetlands while avoiding impacts to the wetland complex along the northern property completely. • The house location also avoids the high quality wetland areas. The impact areas are primarily located within the low quality marginal wetland areas. • Original development plans showed a larger yard and landscaping area with fill and grading well out into the higher quality wetland areas along the western property boundary. A boulder wall has been designed to minimize wetland impacts in this area by an estimated 2,000 square feet. MITIGATION To compensate for the proposed impact of approximately 4,570 square feet of wetlands,the owner will use a combination of site drainage improvement,wetland preservation,wetland creation and wetland enhancement. Mitigation will take place primarily along the western property boundary. The wetland mitigation plan for the site is shown on Figure 1 and outlined below. Wetland Impacts=4,570 square feet Wetland Creation= 1,300 square feet Wetland Enhancement=3,430 square feet Wetland Preservation= 1,030 square feet Job No.414 179A 4 Ge Ptech BASIS FOR DESIGN The observed local wetland ecosystem will be utilized for the basis of the mitigation design. Mitigation areas(creation and enhancement)will target the higher quality wetland areas located along the drainage features. Hydrology is currently limited in some of the existing wetland areas. We plan to enhance the hydrology within the wetland creation and enhancement areas with a combination of site grading to lower the site elevations to come in closer proximity to groundwater and drainage concentration. Site drainage will be redirected and concentrated within the mitigation areas. Drainage culvert gravity outlets should be protected from erosion by rip-rap or other approved methods. Appropriate erosion and sediment control measures (silt fencing, straw waddles) should be placed between the existing drainage features prior to any soil disturbance on the site to help prevent unintentional impacts to wetland preservation areas and to prevent soil loss off site. WETLAND PLANTING AND SEEDING The wetland mitigation areas(creation and enhancement)will be replanted with a combination of transplanted shrubs(willow,alder and shrubby cinquefoil), willow cuttings and a high alpine wetland seed mix. Details are provided below and on Figure 1. • During site grading within existing wetland areas,topsoil should be separated from underlying granular soil. The topsoil contains valuable nutrients and a seed bank for re-establishment of vegetation, especially ground cover species. A minimum of 12 inches of topsoil should be replaced within wetland areas following grading. Topsoil may be imported if necessary. • As many willows,alders and shrubby cinquefoil shrubs that are currently within the proposed grading areas should be harvested as transplants. Details on transplanting are provided below. > Willows should be trimmed of all branches with sharp cuts from clippers. Chain sawing of branches is not effective. Once branches are trimmed,the root ball should be excavated to width and depth of three times the diameter of the top of the trimmed branch area. Job No.414 179A 5 Gtech > Disturbed roots should be trimmed with sharp clippers prior to re-planting. A hole of sufficient width and depth to fully accept the root ball should be excavated for re-planting. The hole should be loosely backfilled with topsoil and saturated. D Alders and cinquefoil should be excavated in the same manner as willows; however trimming is not necessary. > Transplanting should be completed in the fall (after growing season)or late winter(before growing season)for greatest success. > Additional fertilizers are not recommended. • Each large transplanted willow or alder is estimated as a 10 feet diameter replanting as shown on Figure 1. Additional coverage, if necessary, can be provided by willow cuttings. Willow cutting details are provided below. > Green willow branch cuttings can be used to supplement wetland shrub coverage. A minimum of 10 cuttings per 10 feet diameter area shown on Figure 1 should be planted. > Willow cuttings should be harvested and planted in the late fall or late winter. ➢ Cuttings should be pliable"green"branches. Cut the base of the branches at 45°angles. All other branches should be trimmed from the cuttings. The cuttings should be approximately 2-3 feet long. The tops should be cut square and coated with a 50/50 mix of latex paint and water to help prevent drying. The angled bases should be soaked in water for at least 48 hours prior to planting. > Insert cuttings approximately 1/2 of their length into the soil after a probe hole • is created. Tamp soil around the cuttings. • The entire mitigation area should be seeded with a high altitude wetland seed mix. We recommend a wet meadow mix from Western Native Seed. The seed mix contents are shown below. • The seed mix can be purchased at www.westernnativeseed.com/WMmixes.html. Job No.414 179A 6 Gtech Species Common Name 12 Beckmannia syzigachne American Sloughgrass 12 Deschampsia cespitosa Tufted Hairgrass 12 Glyceria grandis Giant Mannagrass 12 Hordeum brachyantherum Meadow Barley 12 Poa palustris Fowl Bluegrass 8 Elymus canadensis Canada Wildrye 6 Carex rostrata Beaked Sedge 6 Carex simulata Slender Sedge 4 Carex nebrascencis Nebraska Sedge 4 Scirpus microcarpus Small Fruited Bulrush 3 Eleocharis palustris Creeping Spikerush 3 Juncus balticus Baltic Rush 2 Carex aquatilis Aquatic Sedge 1 Calamagrostis canadensis Blue Joint Reedgrass 1 Juncus ensifolius Dagger Leaf Rush • 1 Juncus longistylis Meadow Rush 1 Mimulus guttatus Yellow Monkey Flower • Prior to seeding the ground surface should be scarified to a depth of at least 6 inches. A seed rate of 8 ounces per 1,000 square feet is recommended or 2.5 pounds for the entire creation and enhancement area. The seed should be broadcast spread evenly throughout the mitigation area. The seed should not be raked into the topsoil. SITE GRADING AND CONSTRUCTION OVERSIGHT A representative of HP Geotech should be on site during all site grading for consultation and to monitoring soil conditions. It may be necessary to alter site grades shown on Figure 1 based on variable soil conditions encountered. MONITORING Both quantitative and qualitative assessment methods will be used to evaluate the success of the wetland mitigation area. A general qualitative assessment of wetland health and viability will be performed at the outset of each monitoring event. Overall wetland health will be observed and evaluated including vegetation establishment and health, wildlife observed, and overall appearance of the wetland in relation to the targeted plant community. Job No.414 179A 7 Ge Ptech To perform the quantitative assessment two 10 foot diameter monitoring plots will be used. One plot will be placed in the creation area and one will be placed in the enhancement area. The center point of the monitoring plot will be marked with a permanent stake to ensure that each yearly monitoring takes place in the same location. A 5 foot length of rope will be tied to the marker stake. All planted/seeded species within the radius of the rope from the stake will be evaluated. Any additional identified woody or herbaceous species will also be noted. A relative percentage cover of ground cover species will be noted. One test hole will also be excavated within each monitoring plot. Soils and hydrology will be evaluated in accordance with the U.S.Army Corps of Engineers(ACOE) 1987 Wetland Delineation Manual and May 2010 Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Western Mountains,Valleys and Coast Region (Version 2.0). Information obtained during the quantitative monitoring will be recorded on Wetland Mitigation Monitoring Field Data Sheets. A sample Data Sheet is presented as an attachment. Both quantitative and qualitative assessment methods will be used to evaluate the success of the wetland restoration area. A general qualitative assessment of wetland health and viability will be performed at the outset of each monitoring event. Overall wetland health will be observed and evaluated including vegetation establishment and health,wildlife observed, and overall appearance of the wetland in relation to the targeted plant community. MONITORING SCHEDULE Following construction and planting, an initial monitoring will take place to attain a baseline sample within the monitoring plot. Actual monitoring will begin one growing season following completion of construction of the mitigation area. Monitoring should take place during the growing season typically between July 15th and September 15th. Three consecutive years of monitoring during this time period is recommended; however,this period may be lengthened based on the success and viability of the mitigation area. Annual monitoring reports will be submitted to the Town of Vail. Job No.414 179A 8 Ge< tech SUCCESS CRITERIA Vegetation: Ground cover species should be thriving after five years to 75%ground coverage Hydrology: Primary wetland hydrology indicators should be present during growing season. High water table surface water and saturation are those that will be targeted early in the restoration area's life. Soils: Wetland soil indicators can take many years to develop and may not be present during the monitoring period. Hydrology and vegetation will be the primary indicators utilized to determine wetland mitigation success. POTENIAL CONTINGENCY MEASURES If performance goals are not met or if final success criteria are not met, an analysis of failures will be performed and a remedial action proposal will be submitted to the Town of Vail. Since the property is a residential parcel and transfer of the property is a potential risk to mitigation success,a contingency funding mechanism will be necessary. Any sale of the property must disclose the mitigation permitting requirements and responsibilities as these requirements will follow the property and will be the responsibility of the new property owner. ENVIRONMENTAL ASSESSMENT Based on our analysis of the proposed impacts and mitigation, the proposed development will not pose a negative impact to water quality or the environment in the immediate vicinity. The wetlands on the site are considered marginal. Once mitigation is completed and established, a more viable aquatic ecosystem will be present at the site,which will provide greater value for water quality enhancement in the upper Colorado River basin. Job No.414 179A 9 HPtech LIMITATIONS This report has been prepared in accordance with generally accepted principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from our site reconnaissance,the proposed type of construction and our experience in the area. This report has been prepared for the exclusive use by our client for design purposes and permitting through the Town of Vail. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations,and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. Sincerely, HEPWORTH-PAWLAK GEOTECHNICAL, INC. Jason A. Deem Project Geologist • Reviewed by: JC Job No.414 179A 10 Gtech '4,':::•:,, (A1 _ Esq p ` iJf ` o> �> ' f• r Ar.•:• WETLAND 0,,ft,.. Z , \ --^ -- ` j i` 'ti;:, '....7;:7:\ '••••:jam►'•'•'•:•::0: ::::;i'•::•. PRESERVATION �s: LLJis \�'`,\` 1', I .♦y f�II �1'`, , `'ice •WETLAND•• ` i)r• 3 :•: ;••:',': ......-: _. •/ (aAll /k 5 O �� CREATION •-•-•-•--s4. ,�..:...:- �J •1 . AREA _ __ :•' :Ti :ii:;.. ET - F 0 •A o / 18!!T � •�sA '� _ F'/ ENHANCEMENT" - Y _ 1, ammo _ I , n . ` 1b AREA \, - 't \ ♦ ; ,, (3.430 SF) - _ ` PROTECT • =-+'.•': ••` rI ` ! CULVERT OUTLET \ ��`,; ` = 8Q `; . WITH RIP-RAP \, ` ' \`' 1• �' ;' ``\ 1 18"CULVERT PROTECT �` �. Q IMWETLMDPACT A ;, WITHRRP-'0 , , (4,570 SF) _ - S = O dt.: :. • ....._ , • air ---.!! ,. /.......s. l �� •.,�-• `� /` 18 CULVERT _O \.\-_ -. N. . ss i s ---#.- . a_ \ , A,. 4 \ -•,../: • • -..",.(-*I• ri-F 1,Th r..„,, s . ,, % ISSIII\ <<` .:::'N'N'N.N. ,, , '''-'1_4_,IrAttL '- ,,— Z 7 --Ps,... . ...,'-'''. .,:„.,...-Th.,,,,,_ . • , , . MIN ir \ ,,,�� x ,,, �� i _ �i terII :: W EL ' �� '� 11111 , „„ 0 c� +'i� • . • • "17-/W& I NM*IIII - —,yr nT �.v !411 1111/5.501111 ,==. MEI 11,111M I Legend '`� Wetland Enhancement Area Ail ,I` L.f L, 111 _ 'A, 4 Wetland Impact Area % ��;�� 1�' i I. �; 1 : : s^ - a �� Wetland Creation Area •�; '• ' ' 0111111 �� I,:-''1C MIIIIMMILIIIMP 040 Y ■ Wetland Preservation Area �\�'��' ��II mow`; .._ O .fir >�� r Aug —I �' r, - ` _,I , II I I I I isem,, Lu co Lu 10' Diameter Willow or Alder0 .a,wr1��/ a i !.,,i` ��,'��m� a� ` �� --- - .� Planting/Transplant/Cuttings �� 1li d► "_ I _11111111111111112 ..- s= .0000 ,0000'—000-4004w, Dasiphora Fruiticosa Transplant ` isp'��` �,J. i , I � o‘loss=1. • • •OA;, —»—Proposed Wetland Mitigation Grading Contours .. ie. ,,,‘,,„-,... -_______,,,..____ _____�. ;i �C-:.;':12 • ,\�••••,,,,,s„ � _,,i,...s __, •4 _l 1070,6.. ../..,::,,.- _1:--..._----:7-:-._.c.„. , *- Z �� diell � � / JOB NO. t---4/4110r---0.` '`-_-'` �I •• 414179A APPROXIMATE SCALE: v�� 1�� N -�� WETLAND 1 INCH = 20 FEET �� "-� �, �Z�3,- ,^,' PRESERVATION ...,:.- -,p,,...„.�;\; 7,.`�cop,, -:,' (475 SF) FIGURE 1 eo V, __—_ ,. Jteta. \ - %,, i • `, ` 9\ `s U +, , , .. .......... c... ° ,, , , `s WETLANDSU F— , , , ., , ,, .__, , , , , , , „ , , a) /�� „ ,, , N • `+ • s• 4 c,_ .„ , , , , , ss a •• ia .01 I M I a .. , , , UPLANDS • • • • • '• % 18 • • Q \ WETLANDS _ ,'''� WETLANDS I— • S. br w 1 • ' T • • • • • • • 0 • • ---___ UPLANDS �` �' • Q WETLANDS -- ;�``, , __ " LU UPLANDS 0 z O\ J i— _ ♦ " Wt , Jz`;� , N ,1--------------- - ------ - QJ; ' > in o. ' - • • 0 Z 0 I1 `_-_ - I I 11I I - W I CI CO H 0 ______ • _ UPLANDS JOB NO. APPROXIMATE SCALE: _ -- 414 179A 1 INCH = 20 FEET J, ��P�oS FIGURE 2 .4 WETLAND MITIGATION MONITORING FIELD SHEET Site Name: Location: Investigator: Plot ID: Plot Size: WOODY/SHRUB PLANTS #live #dead total %survival height volunteer (y/n) • OTHER PLANT SPECIES NOTED: HERBACEOUS PLANT COVERAGE%: INVASIVE SPECIES NOTED: SOILS Soil Texture: Munsell Soil Color: Mottles Munsell Soil Color: Mottle Abundance/Size/Contrast: Hydric Soil Indicators: Other: HYDROLOGY Depth to Surface Water(in.): Depth to Free Water(in.): Depth to Saturated Soil(in.): Primary Hydrology Indicators Present: Secondary Hydrology Indicators Present: