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HomeMy WebLinkAboutAIRPARK VILLAGE - ODP - 16-05A - SUBMITTAL DOCUMENTS - ROUND 1 - PLANNING OBJECTIVESPROFESSIONAL ASSOCIATION Licensed Professional Engineer registered in Colorado, USA Others working on this document Troy Jones — Planner working on land uses, buffers, ROWS and wetlands Martin/Martin — Civil Engineers for roads, drainage and utilities Eric Berg — Ecological and Wildlife consultant Gene Cappola — Traffic Consultant Ron Mills — ROW specialist v) Issues from Neighborhood Meeting A neighborhood meeting was conducted in May 2007. In a conversation with Ted Shepard on September 7, 2007, Ted stated that his summary notes were not as of yet completed, and that we should go ahead and submit without them. vi) Name of Project as Well as and Previous Names the Project may have been Know by The project has always been referred to as "Airpark Village." vii) Mitigation and Avoidance of Conflicts Between Land Uses • A helicopter flight path is being provided along the southern property boundary to accommodate the adjacent helipads. • Upon initial annexation, we voluntarily agreed to a zoning restriction for our residential component of the project to have mixed -use residential as the only type of residential allowed in the Employment zone portion of the project. • Residential is designed to be on upper floors of mixed use buildings, which are to be oriented toward the new boulevard, rather than toward adjacent properties. 35 about $12 million is required to fully improve all tracts. The Underwriter is D.A. Davidson & CO of Denver who has issued over $2.6 billion in bonds for 195 special districts.. Grimshaw - Harring of Denver is writing the service plan. Design Team RESUME BRIEFS Richard L. Husmann, P.E. 12245 E. 14'hAve., #204 Aurora, CO 80011 Voice 303-340-2967, FAX 303-340-2984, Cell 303-909-6089 Colorado Registered Professional Engineer #11120 - 1972 California Registered Professional Engineer #15907 - 1965 Forty plus years of involvement as a Professional Engineer in land development projects varying in size from 0.5 acre commercial sites to large residential and multi -use recreational projects as a Design Engineer, Project Engineer, Project Manager and as Engineer of Design in charge of the engineering on all projects in a 20 person office.. My experience also included serving as the engineering member of an advance planning team investigating new large and small properties. Responsibilities included researching zoning and master planning, flood plain, wet and dry utilities, existing & proposed transportation facilities, as well as preliminary design studies and final design. David T. Snow, Ph.D. Degrees from Harvard Univ. and Univ. of California, Berkeley Registered Geologist, California #2495, Engineering Geologist #730 Professional Engineer, Colorado # 10995, 1972, Hawaii, #11769, 2005 Professor of Geology, Colorado School of Mines, 1964-77 Consultant in Hydrogeology, 1963-present Hydro -Geological Engineer working on subsurface drainage, soils and water supply for mining, environmental, civil engineering, nuclear and industrial clients. Publications in groundwater hydrology. See www.davidtsnowphd.com James C.Y. Guo WORK Department Civil Engineering, University of Colorado at Denver 1200 Larimer Street, P.O. Box 173364, Campus Box 113, Denver, CO, 80217 Tel: 303-556-2849, Fax: 303-556-2368, EDUCATION Ph.D. Water Resources, University of Illinois at Champaign/Urbana, USA, 1978-82 M.S. Water Resources, National Taiwan University in ROC, 1974-76 B.S. Hydraulic Engineering, National Cheng-Kong University in ROC, 1970-74 PROFESSIONAL EXPERIENCE 1999-prsnt Professor 2003-2004 Director, Continuing Education Division. 1995-1997 Director, Science and Technology Education Program 34 Greeley engineers have asked to buy and occupy an alignment that extends the length of the development. Its size and depth, 12 feet to invert, would require a large dedicated easement that could prove tricky with many of the other utilities, such as subdrains and filters. The south -side alignment has intervals of about 50 ft along the alignment, where a drainpipe of small diameter should be laid between the bedding material and the low -flow channel so to maintain the water levels in the bedding distant from the slopes of the floodway. It will be necessary for us to collaborate with Greeley in the design of the bedding, which must be well -graded materials up the sides to the top of the pipe, for permanent effective operation. As with drains discharging to the low -flow channel, the Greeley bedding drains need to have flap -valves installed to prevent flood waters from invading the bedding. Metro District as the Implementation Tool We are proposing a $4 Million start-up program that prepares the site for infrastructure development.. This will be funded by an improvement district that spreads the costs over 5,300,000 sf of net salable land in 17 of our 19 tracts. Each square foot of land will then have a $2 psf lien. The funds will be used to pay for a road crossing at International Blvd, a dewatering system, grass on the channel and irrigation to water it, an extension of International Blvd to the traffic circle and across the site to the south boundary and 2 lanes of the parkway west for about 1,000 feet. The Metro District will provide the services and the governance for all properties. Expected services are to be filtered water, raw fire suppression water, irrigation water, sewer, storm drainage, refrigerated water, possible gray water recycling, telecom, tele-library, SmartSkyways, gas, alternative power, trash, incineration, security, lighting and roads. Additional funding will provide about $8 million to improve all the site with roads and utilities as needed How it will fund Metro District at Airpark Villag Even though there is insufficient tax base � i 11 to fund the District in a normal manner, _ - - - '""""" we think it can be privately guaranteed by p T investors during the early years when y � On" there is no assessment. The initial bond issue will be about $4 million to pay for 4 2 ;; o;,,hD, an entry at International with a culvert �Owk crossing to the new parkway, a subdrain system to regulate the water table, landscaping and irrigation for the buffers, detention and flood channel. This map a L_ shows the District boundary and the two main development areas. The initial -_-. M�;ht,,. w�Ld rt development area is shown inside the blue circle. The 11 acres parcel at the top is not included because it gets it's roads and utilities from the Dry Creek project to the east. The bonding capacity of the site over the first 15 years is about $22 million, although only 33 Maintenance Road (southl 31x 1 slope Lower Section International to Existing S = 0.23% Q = 1250 cfs Looking West x 120' Low Flow Channel 4.0" 1.5 Storm Water Management Model (SWMM) Offsite flows are being contributed according to the city's SWMM. This included undetained flow from Mobile Home Park, historic runoff from Ferguson, detained flow from Skurich site north of new blvd, undetained flow from industrial area and 19.4 acre of site at the NW end. Low Flow Channel From the Dry Creek Diversion to the exiting channel at Timberline, it is generally 18" deep x 10' wide and possibly lined with impervious soil. It may have to steadily convey as much as 50 cfs, so should be designed as an efficient channel. Moving High Pressure Gas Line There is an 8 to 10 inch gas line running north and south that crosses the flood channel and must be relocated or deepened under the channel. Diversion The ongoing flows of Dry Creek, up to the capacity of the present conduit under the airstrip, 37 cfs, is to utilize a turnout that City provides. Since the diversion channel is one foot higher than the flood channel, it will create some back water into the wetland. It will have to be lowered all the way to the Parkway and will require a siphon to go under the Parkway. It may be, in part, open channel and closed conduit. Greeley Water Line The City of Greeley is installing a 60-inch main the length of Airpark Village. It enters east of the floodway alignment, passing under Timberline Ave. and would go on the south side of the floodway. Greeley Water Lne Maint Road 32 Upper Section Vine to Diversion S = 0.2% Q = 950 cfs Looking West 130' 11.7 ! 106.6' 1 117 3 z 1 slope Road (surds) The middle section of flood channel is steeper at 0.4% slope, thus more narrow, 85 ft wide with a 10 ft by 1.5 ft low flow channel mainly along its south edge. Because the water table is to be controlled to levels below the flood channel surface, the low -flow channel must be impervious, lined with plastic covered with soil or with a compacted clay mix, in order to convey the under - drainage waters without recharge occurring in this reach. Middle Section Diversion to International S = 0.4% Q = 950 cfs Looking West 3 z 1 slope Rod{swo6) Low Flow Channel 1s � The lower reach, extending from International Blvd. to the Lincoln St. bridge, is to have slope of 0.23% and a bottom width of 96 feet, including its low -flow channel. The alignment may be made to avoid the wetland existing in the NE corner, or it may cut into the topographic embankment while relocating the limits of the wetland. The subdrain system is to discharge at various places via pipes daylighting in the south bank of the low -flow channel. Flap valves will prevent back -flows into the drains at times of flood. Other drains, on the north side, will vent the bedding of the Greeley pipeline to the low -flow channel. Surface flood drains from the site also will discharge to that channel, and at higher levels during floods. 31 temporary pumping. Since the object of shallow drains placed to intercept pipe flows is to protect pavements from sinkhole formation when runoff events occur, they may be placed during construction of base courses, especially targeting the edge of each impervious area, including sidewalks. Utility trenches may double as drains if similarly designed. It would be prudent to avoid slab -on -grade construction, favoring raised floors above an airway, so that sinkholes remain harmless. Likewise, avoid footing walls that may concentrate runoff and have formed sinks in the past. Flood Channel Multi Use This huge easement thru the Airpark Village site needs to serve multiple uses: A flood channel capable of handling a 100 year storm, the drainage discharge for the Airpark Village site and a recreational path for the neighborhood for walking and bicycling. In addition, we would like to see it landscaped with irrigated grass and some natural vegetation in selected areas. Shrubbery may be used for bank protection, where needed. Dividing the _Flood Channel into 3 Sections For our planning purposes, the flood channel may be divided into three reaches, upper, middle and lower. The upper is from Vine to the diversion point at Dry Creek, the middle is from the diversion to International Blvd. and the lower is from International to the existing ditch near Timberline Ave. Flows The City has given us a flow of 860 cubic feet per second (efs) at Vine Street coming under the Railroad bridge from the north and a restriction of 1240 cfs to get under the Lincoln Street bridge. The subdrain system to be installed in the gravel aquifer may contribute from 4 to 40 cfs in that interval, but not during flooding because the seepage will stop because of equal pressure from the water in the channel. Runoff from the impervious surface in built -out Airpark Village will augment the flood waters. The final figure we calculate for flood flow at the Lincoln St Bridge is 1,170 cfs. Charnel ROW In the Upper Section, the flood channel will enlarge the existing Dry Creek channel and replace the trees according to city code. This reach will be an enlarged wetland over 100 feet wide with 0.2% slope, so will have no low -flow channel. Except during floods, all surface flows will be diverted into the Dry Creek diversion crossing the Parkway to flow through the industrial park and to New Cache la Poudre Ditch. A low dam spanning the width of the channel is to control the diversion. WE with non -tributary water from the Wellington Water Works, recharged through our floodway wetlands. Profile and Heads in Subdrains, Discharge Lines and Collector Wells S 0 ground surface 2'--------------- -____ top of gravel aquifer _ original watertable ------------------ flood channel floor 6' lined bottom of low flow channel a_ R de loeV ped water table — - - Perforated, filtered drain -- 3 next drain —' — 12' 0 14' l e bedrock surface � +rr•z r+r4 \ _ _ _ 20' The system of erosion pipes erratically disposed throughout the fine-grained soil profile will remain poorly defined until much excavation has exposed it. It can be likened to a limestone karst, evidently unconnected to the underlying gravels. Two known springs discharge from it. What I call Horse Spring lies just north of Vine and provides perennial flow to Dry Creek, gaged at 130 gpm in April, increasing to 500 gpm in August, probably responding to irrigation and canal seepage to the north. Another spring, emerging from an eroded natural pipe under the International Blvd. embankment, flows year-round, perhaps as much as 40 gpm. It then disappears into the pipes, whereas Dry Cr. flows on impervious clay that lines its bed. The pipe system is obviously recharged also by runoff collecting on -site, sometimes forming sinkholes where the pipes collapse. To protect pavements, this system should be intercepted and directed safely to the low -flow channel and the flood channel coursing the length of the central parkway. Because the height of each natural pipe may be anywhere in the section to 9 ft depth, the interceptors are conceived as gravel -filled slit trenches of 4 to 6 ft depth with a perforated drain pipe on bentonite at the bottom that discharges to an open flood channel. Collapse of pipes deeper than the controlled depth is deemed less likely. Inflows to excavations from the shallow system of eroded pipes is not as hazardous as inflows from cuts into the artesian gravel aquifer. Rates are uncertain, but probably can be handled by 3I ODP 3WM7 ~W . Sub Drain Schematic :;W% `" An equally important function of a subdrain system to be emplaced in the gravel aquifer is to provide reliable, high -quality water for domestic, irrigation and fire water from about five collector wells distributed along the length of the property, the needed amount pumped into a manifold and standpipe on site that will provide head and surge. Each collector well, to be permitted by the state, will be a large -diameter caison sunk to bedrock. About 20,700 feet of perforated, filtered drain pipe is to be drilled within the gravel at about 10-14 ft depth, mainly along the periphery of the property. Two or more such drainage galleries will lead down gradient to each collector well, into which they will discharge by gravity and controlled in head by weir gates inside the well, by the level of water spilling through a discharge pipe to the low -flow channel and by pumping. Each well serves a loop of the gallery system, and within the 1000-foot loops, the piezometric level will remain close to that in the drains. Recharge to the gravels at the river and at the wetlands in the floodway lying upstream of the Dry Creek diversion point will influence the rate of drainage through the galleries and collector wells to the low -flow channel. In essence, the subdrain system in the gravel aquifer is to form a bathtub -like hydraulic depression, short-circuited back to the river by the low -flow channel. The floor of the floodway is to remain unsaturated, thus useful for recreation. Because the wells produce from a tributary aquifer, permits will have to be based on an augmentation plan that replaces project consumption 28 Could be a pond Could be a parking lot Dewatering Plan The prior owners grew hay on the major part of the acreage, which flourished due to high water table conditions. Because sinkholes were evident and heavy equipment was sometimes mired in the fine wet soils, they considered the site unbuildable. We can meet the challenge of correcting these conditions by permanently altering the hydrology. Construction cannot proceed without dewatering, nor can the long -tern use be facilitated without controlling the groundwater. Whereas dewatering is usually implied to be temporary, our designed system is to operate by gravity in perpetuity. There are actually two aquifers. The lower one above bedrock is a confined gravel layer about 10 feet thick, presumably connected to the Cache la Poudre River southwest of the site. The second and upper aquifer is the sequence of fine-grained soils with its unconfined system of open pipes. 27 Median Drainage Schematic 19' median catch :`.. -.` catch Id be basin �� Could be 48" pipe or box basin nx�v `� 14 x 8 Culvert lI 4 x R Culvert Detention The Storm Water Management Model tell us that about 14.5 acre feet of detention is required. We think the mitigations techniques described on page 6 can reduce the imperviousness conditions down to even less. The exact amount will be determined by engineering, but we show where the detention can be located for now. Areas along the channel can accommodate about 10 acres and the median can store some. But along the southern border where a series of detention ponds cascading into each other for about 3000 feet in length times 30 feet wide and two feet deep will result in as much as 4 acre feet of storage. The area we can area use are some of the parking lots with one foot deep. At the bottom of the parkway, we will reserve a 200,000 sf site shown below for detention averaging about one foot deep. Engineering will determine the exact locations and sizes of detention. Here's the summary of detention pond sizes: Tract 18 pond = 28,961 s.f. Tract 1 pond = 196,377 s.f. Tract 16 pond = 18,943 s.f. Tract 15 pond = 47,951 s.f. Tract 14 pond = 63,221 s.f Tract 12/13 pond = 79,112 s.f. Tract 12 pond = 56,145 s.f. Tract 11/14 pond = 150,341 s.f. Tract 6 to 8 pond = 126.088 s.f Total = 767.139 s.f. = 17.6 acres Possible Locations for Detention 26 serves the entire site, almost all building will front on this parkway with parking to the rear. There are some low impact techniques for decreasing these impervious areas even more: • Porous Concrete • Porous Asphalt • Modular Block Pavement • "Green" Parking Lot • Porous Landscape Detention • Grass Buffer • Bin Swale • Green Roof • Level Spreader Over the build out period of 15 years, the goal is to reduce the runoff from the remaining impervious areas even more by generous use of the Low Impact Development techniques mentioned above as well as new, techniques as they emerge Discharging At the top of the site, the discharge flows are minor compared to the lower part There are two channel conditions to satisfy — 1) fully developed runoff from the total upstream watershed and the site, amounting to approximately1386 cfs at the Lincoln Ave. bridge (including 25 cfs of ground water flow into the channel), 2) as is right now - 200cfs. Standard policy is to restrict the 100 year developed flow to a 2 year historic, which is 0.2 cfs/acre, amounting to 30 cfs for the total site. Currently the site may not even develop any runoff. A big factor has been made out of the Lincoln Street bridge with it's drainage capacity for only 1240 cfs. Long range planning in the city has considered removing this bridge and tying Lincoln into out parkway to reduce the congestion. But if the bridge is still there when the 1240 cfs is realized, there are other measures that can solve this problem: 1) the sides of the channel can be widened to increase the capacity2) the bridge could be replaced. Median Drainage Approximately 50% of the site drainage will be carried inside the median with two 4 x 8 box culverts down to the main detention area just before the existing ditch. The median will accommodate 180 cfs in each culvert. The slope is .0015% Supply is on the outside which may mean that the catch basins could be located on the outside flow line. Engineering will determine the solution. 25 a vital function of the water supply system for Airpark Village, a costly part of which will be the augmentation water delivered via Water Supply and Storage Co. aqueducts to Dry Creek. Site Drainage Plan Red drains to channel Green drains to parkway Yellow drains to south boundary Conveyance -How the Flow Goes Thru Site The estimate for drainage discharging created on site in 10 to 15 years is 600 cfs without any of mitigation effects as described above. This on site flow will be divided into 3 discharge paths which are: flood channel, Parkway median and an open ditch on the southern boundary. Assuming- all the types of open space in the 152 acres: City Channel = 676,671 sq. ft. Dry Creek Channel = 18,425 sq. ft. (on Airpark property) Buffers = 484,933 sq. ft. The remainder of the site will be impervious areas such as buildings, walks, streets, plazas and parking lots. The zoning encourages three to four story densities. Because only a single parkway 24 We suggest spread footings in the high bearing capacity gravels for most structures, not footing walls which channel surface flows, sometimes to sinks that form at the wall. Heavy structures can be carried on concrete piles to bedrock. An immediate problem is the disposition of soils excavated from the flood channel. We would like to change grades by filling certain areas of the site, but do the fill areas need to be prepared in some way to minimize piping ? At least, we should protect the shallowest section in critical areas, since sinkholes probably do not form above deep pipes. Thus, any fill -site preparation may be neglected if means of drainage control can focus on the shallow parts. Flow through a system of shallow conduits, the pipes, can be controlled in two ways: If we knew the system geometry, such as the general direction (down -gradient ?), gravel -filled slit trenches could intersect them to collect the flows, perhaps into a drain pipe laid in the bottom. Or, slit trenches backfilled with non -erodible bentonite-soil mix could cut them off. If lateral drainage through these fine soils is impeded, it will cause the shallow water table to rise, at least occasionally, an undesirable consequence. In critical areas, the gravel drains may be worthwhile, protecting pavement areas. They could be part of the sub grade design of all roads, one under each sidewalk, graded to flow parallel to the road and thence to the flood channel. If unwanted pipes and sinks form, they will be confined mainly to landscaped areas where maintenance is affordable. The disposition of present and future wetlands is also tied to an understanding of the shallow soils and their hydrology. Each is a window into the water table. If the gravel aquifer is everywhere confined by a clay, the wetlands are best understood in terms of the fine soil profile. In the northeast corner of the property, there is an extensive wetland that everyone wants maintained. It spills on the surface down the face of the six-foot high bluff, then into sinkholes and pipes of the low-lying surface. I believe that wetland formed by borrow excavation in the past, that formed a depression on low -permeability soils not containing the same pipes as does the low-lying surface._ Surface drainage collects in the depression, and should do so after any development, such as roofs and pavements alter runoff characteristics. A bit west of there, where International Blvd. turns NW, there is another wetland but on adjacent land of the trailer park. It, too, probably drained on the surface to and down the bluff, but it has been obstructed by the fill of the International Blvd. embankment. Continued discharge has eroded a pipe through or under the fill, emerging at the face, where it cascades to the low-lying surface, enters a sink and disappears in a pipe. I conclude from these observed features that a wetland of any desired size or shape may be formed on the bench in the NE corner, simply by excavation. It is a good area for mitigating wetlands destroyed by flood -channel construction elsewhere. Construction of the flood channel in the NW reach upsteam of the Dry Creek diversion will remove most of the existing wetland features and trees. Restoration can be accomplished by retaining a high water table in that reach, so that the bottom of the channel grows cat -tails or other more desirable species and nurtures planted trees and shrubs. Yet, the flood channel floor will penetrate the gravel, so recharge may occur along that reach, depending upon the water table levels. A segment of one or more of the subdrain gallery loops should underlie the channel, in which heads are controlled by weirs in the collector wells. That is necessary because recharge is 23 below surface levels. Drainage to horizontal galleries is the method chosen for regional control, since vertical wells to do the same would be too numerous. It is likely that such sub -drainage is necessary but not certainly sufficient for eliminating water problems in excavations. The shallow soils are silty clays or clayey silts, or silt -sized sugar -beet wastes sometimes admixed with the native clay soils. These silty soils are easily eroded by flowing groundwater that has formed pipes, an inch to a foot in diameter from the surface to the depth of the gravels. They are fed by precipitation and perhaps also irrigation and canal seepage. Emergence of one pipe forms a major spring north of Vine St. to feed the perennial flow of Dry Creek. A smaller spring issues from a natural pipe under the International Blvd. embankment, flows a short distance on surface and disappears into the ground through a sinkhole and pipe. Sinks and pipes form at irregularities of asphalt pavements that concentrate runoff, such as the runway and parking areas. The regularity or pattern of the pipe system is unknown. Open pipes daylight at excavation walls and actively carry tens of gpm for long durations. New pipes may form during brief runoff events where water pools at the surface and sinkholes form above collapsing pipes. No one has fully understood the piping problem, in spite of several geotechnical investigations completed. Its relationship to the underlying gravel aquifer is uncertain. I believe that it is conservative to consider it a separate system of near surface drainage confined to the fine- grained soils less than 9 feet deep on site, a belief supported by the observations of artesian separation, probably signifying a clay aquiclude at or near the top of the gravel. Like a karst, the system of pipes has developed a very high transmissibility. in the fine-grained profile, so subsurface runoff occurs instead of recharge. No reasonable amount of reworking of the soil profile can be relied upon to eliminate the pipes, so they should be assumed to remain, posing a hazard to pavements. Even where recompaction has been done, the fine silty soils may be prone to pipe formation unless coarse materials, like gravels, have been blended with the fines. Since cracking of concrete and asphalt is a given, there will be some instances of pipe formation in spite of diligence in design and construction. But to minimize problems, gutters may be formed integrally with reinforcement, and transitions and joins should -be sealed with stop -water inserts. Unless preventive measures are taken to stop pipe formation, impervious channels may not be allowed to run out onto unpaved areas. Sidewalks should also have some side -slope and a channel on one side or the other. Downspouts and parking lots. need to be led to lined channels. Every facility should drain safely and not impede flow to the flood channel, where recharge may occur, since it will bottom on gravel but have an underdrain nearby that leads to the lined low -flow channel. Whenever water can move under high gradients through the fine soils, there is a potential for erosion to form damaging pipes and sinks. Because we cannot tolerate saturated conditions, the soils have to remain drained, therefore when ponding occurs at the surface during storms or snowmelt periods, there will always be short paths to low water levels, thus a tendency to form pipes. To prevent these from propagating and destroying pavements, filtered drains may be installed in the form of slit trenches backfilled with gravel graded according to the Terzaghi criteria, underlain by perforated drains. This system will conduct the water but prevent movement of the suspended silt. 22 Potential floods managed by various works upstream will eventually follow . this channel, diverted into a floodway to be excavated along the .NE edge of the property, exiting under Timberline and Mulberry, thus removing our developments from the designated 100-year floodplain. Fine-grained soils, consisting of silty to sandy clays and silts with some quantity of sugar beet processing wastes underlie the surface to a depth of 5 to 9 feet. Beneath these fines lie cobbly and sandy gravels to a depth of 17 to 19 feet, with firm shale bedrock beneath that. The gravel is an aquifer manageable as a water resource to serve all the project needs. With minor seasonal fluctuations, the heads in the artesian aquifer are 1 to 3 feet below surface, confined by some undisclosed clay strata, since any test pit can generally be excavated. without inflow until the gravel is penetrated, whereupon water fills the pit. A unique feature of the overburden fine soil profile is the prevalence of open conduits from an inch to a foot in diameter, formed top to bottom by water flowing generally southeasterly that have eroded the non -cohesive silty materials in a process called piping. We may find that the pipes forma connected system through the otherwise low -permeability soils, generally believed to be isolated from the gravel aquifer by the confining clay layer(s). In some places, particularly in the NE quadrant, small sinkholes have formed in the surface where concentrated surface runoff has entered the pipes, creating voids that have collapsed. Depressions in pavements where water has collected, such as on runways and parking areas, have also developed small sinks. Where excavations intersect water -bearing pipes, inflows can transform the fine soils to unmanageable conditions. If the gravel is cut into, water quickly rises to make it a quagmire. These conditions must be controlled by establishing a drain system in the gravel and aseparate system in the overburden before significant excavation is done for either the floodway, roads or utilities. Within the floodway is to be formed a low -flow channel, the principal and lowest drain for the site, to which all subdrains in the gravels are to be discharged and conducted to the river. It will be critically important to start the floodway excavation at the existing channel leading to a box culvert under Timberline, so that subdrains may be installed ahead of the floodway excavation, proceeding northwesterly. If a contractor were to dig the floodway in conventional top -down manner, he would soon be mired in slimey fine soils that cannot be moved or placed where needed. The lowest foot of soils excavated from the floodway will, in most places, include such select gravelly materials and mixtures that they can be recompacted as floodway banks or base courses. The cobbly gravel would make excellent stable fill, but should not be disturbed or borrowed because of the artesian conditions it would unleash. The gravel layer will serve well for spread footings of most structures, but footing walls are to be avoided. Heavy structures, such as a water tower, may be founded on piles driven or drilled into the shale. Soils Handling Five to nine feet of fine-grained soils overlie eight to twelve feet of gravels on shale bedrock. The gravel, an aquifer presumably connected and tributary to the Cache la Poudre River has artesian heads. Piezometric levels slope south- to southeasterly parallel to the terrain. Experience here has shown that an excavation not pre -drained is a quagmire. Lowering the piezometric levels in the gravel is essential, since it always rises into excavations, reaching one or two feet 21 iii) Estimate of Number of Employees for Commercial and Industrial Uses At build -out of the Airpark Village ODP, it is anticipated that the project will have approximately: • 3,140,631 square feet of "primary use" commercial square footage; and • 632,179 square feet of "secondary use" commercial square footage. Primary Commercial Uses: Offices, Financial Services, Clinics, Adult Day Care / Respite Care Center, Research Labs, Light Industrial Uses, Long -Term Care Facilities, Hospitals, Public & Private Schools. Secondary Commercial Uses: Clubs & Lodges, Child Care Centeres, Standard or Fast Food Resturants, Health & Membership Clubs, Lodging Establishments, Bed and Breakfast Establishments, Funeral Homes, Bars/Taverns, Workshops, Indoor Recreation Establishments, Personal & Business Services Shops, Artisan & Photo Studios & Galleries, Convience Shopping Centers ( which can include: Retail Stores, Convenience Retail Stores with Fuel Sales, Liquor Sales, Beauty or Barber Shops, Dry Cleaning, Equipment Rental without Outdoor Storage, Pet Shops), Food Catering, Veterinary Facilities and Small Animal Clinics, Convention and Conference Centers, Print Shops, Workshop & Custom Small Industry Uses, Places of Worship or Assembly. Assuming 3 employees per 1000 square feet of commercial area, Airpark Village will have approximately 11,318 employees. iv) Rationale Behind the Assumptions and Choices Made by the Applicant The Site and Soils Our 152 acres of grassy, undeveloped ground lies only 1 mile east of the center of Fort Collins. Formerly the Downtown Airport, the site is over 6000 feet long in the NW -SE orientation, and about 1000 feet wide, separated from the Cache la Poudre River and Mulberry Ave. by an industrial park. On the other side there is low -density housing and farmland. Access from Mulberry and Timberline Avenues will be via International Blvd. and Airpark Rd. Lying on an ancient floodplain, the gentle slope parallels the river, falling about 30 feet from NW to SE. A minor distributary of Dry Creek crosses Vine St. into the NW corner, snakes easterly 1500 feet, then crosses under the runway to exit the south edge of the property. Spring - fed perennial flows will continue to feed the New Cache la Poudre irrigation ditch via this route. 20 vegetation, Airpark Village will restore and replant native vegetation (implemented at PDP stage of review). vegetation, Airpark Village will restore and replant native vegetation (implemented at PDP stage of review). vegetation, Airpark Village will restore and replant native vegetation (implemented at PDP stage of review). Performance The Airpark Channel will not Channel will not The Airpark The Airpark Standard (h) Village design be a be a Village design Village design will minimize °naturalized" °naturalized' will minimize will minimize human access to Channel. Buffer Channel. Buffer human access to human access to wetland areas in not Required not Required wetland areas in wetland areas in order to strike a order to strike a order to strike a balance between balance between balance between human use, human use, human use, ecological ecological ecological character and character and character and wildlife use wildlife use wildlife use (implemented at (implemented at (implemented at PDP stage of PDP. stage of PDP stage of review . review). review). Performance Fencing on Channel will not Channel will not Fencing on Fencing on Standard (i) Airpark Village is be a be a Airpark Village is Airpark Village is intended to be °naturalized" °naturalized" intended to be intended to be compatible with Channel. Buffer Channel. Buffer compatible with compatible with the ecological not Required not Required the ecological the ecological character and character and character and wildlife use wildlife use wildlife use (implemented at (implemented at (implemented at PDP stage of PDP stage of PDP stage of review). review). review). 19 themselves. times as large as the wetland area itself. Performance Although our Channel will not Channel will not Except for any Except for any Standard (d) ECS didn't be a be a key species that key species that identify any key "naturalized" "naturalized" the City will the City will species in this Channel. Buffer Channel. Buffer disturb with their disturb with their area, with an not Required not Required channel project, channel project, average we intend to we intend to combined leave any and all leave any and all channel & buffer key species key species width of 239.4 wetlands in wetlands in feet, any key place, place, species that my undisturbed, and undisturbed, and be in this area provide buffers provide a buffer are protected 4.4 & 3.2 times of the "aquafic from adverse as large as the resource" impacts. wetlands wetland 3.4 themselves. times as large as the wetland area itself. Performance With an average Channel will not Channel will not With buffer areas. With buffer of the Standard (e) combined be a be a 4.4 times and 3.2 "aquatic channel & buffer "naturalized" "naturalized" times as large as resource" width of 239.4 Channel. Buffer Channel. Buffer the wetland wetland 3.4 feet, the not Required not Required areas being times as large as degradation of buffered, the the wetland area ecological degradation of itself, the character & ecological degradation of wildlife use is character & ecological minimized. wildlife use is character & minimized. wildlife use is minimized. Performance Although the Channel will not Channel will not Although the Although the Standard (0 City's channel be a be a City's channel City's channel project "naturalized" "naturalized" project project necessarily will Channel. Buffer Channel. Buffer necessarily will necessarily will be disturbing not Required not Required be disturbing be disturbing much of the much of the much of the existing existing existing . topography, the topography, the topography, the Airpark Village Airpark Village Airpark Village design will design will design will minimize cut and minimize cut and minimize cut and fill on our grading fill on our grading fill on our grading plan to the plan to the plan to the maximum extent maximum extent maximum extent possible possible possible (implemented at (implemented at (implemented at PDP stage of PDP stage of PDP stage of review). review). review). Performance Although the Channel will not Channel will not Although the Although the Standard (g) City's channel be a be a City's channel City's channel project may °naturalized" "naturalized" project may project may disturb some Channel. Buffer Channel. Buffer disturb some disturb some trees and/or not Required not Required trees and/or trees and/or 18 purposes, provided that such access is compatible with the ecological character or wildlife use of the natural habitat or feature. (i) Fencing associated with the project shall be designed to be compatible with the ecological character and wildlife use of the natural habitat or feature. Please see our performance standard justification matrix below for a description of how each of our 5 buffer scenarios satisfies the performance standards, and therefore are providing adequate buffers per LUC criteria: Buffer Scenario Buffer Scenario Buffer Scenario Buffer Scenario Buffer Scenario 1) Buffers along 2) Buffers along 3) Buffers along 4) Buffers from 5) Buffers from the portion of the the one-sided the two-sided the portion of the the easterly City's channel portion of the portion of the existing "Dry isolated wetlands project that diversion diversion Creek" outside of qualify as "Dry channel channel the City's Creek" itself I channel project Performance With an average Channel will not Channel will not With buffer areas With buffer of the Standard (a) combined be a be a 4.4 times and 3.2 °aquatic channel & buffer "naturalized" naturalized" times as large as resource" width of 239.4 Channel. Buffer Channel. Buffer the wetland wetland 3.4 feet, the not Required not Required areas being times as large as ecological and buffered, the the wetland area wildlife uses are ecological and itself, the preserved. wildlife uses are ecological and preserved. wildlife uses are preserved. Performance With an average Channel will not Channel will not With buffer areas With buffer of the Standard (b) combined be a be a 4.4 times and 3.2 'aquatic channel & buffer "naturalized" "naturalized" times as large as resource" width of 239.4 Channel. Buffer Channel. Buffer the wetland wetland 3.4 feet, wildlife not Required not Required areas being times as large as movement buffered, wildlife the wetland area corridors are movement itself, wildlife preserved. corridors are movement preserved. corridors are reserved. Performance Although the Channel will not Channel will not Except for any Except for any Standard (c) City's channel be a be a trees and trees and project may "naturalized" "naturalized" vegetation that vegetation that disturb some Channel. Buffer Channel. Buffer the City will the City will trees and/or not Required not Required disturb with their disturb with their vegetation, we channel project, channel project, don't propose we intend to we intend to the disturbance leave existing leave existing of any. vegetation in and vegetation in and around existing around existing wetlands in wetlands in place, place, undisturbed, and undisturbed, and provide buffers provide a buffer 4.4 & 3.2 times of the "aquatic as large as the resource" wetlands wetland 3.4 17 (a) The project shall be designed to preserve or enhance the ecological character or function and wildlife use of the natural habitat or feature and to minimize or adequately mitigate the foreseeable impacts of development. (b) The project, including, by way of example and not by way of limitation, its fencing, pedestrian/bicycle paths and roadways, shall be designed to preserve or enhance the existence of wildlife movement corridors between natural features, both within and adjacent to the site. (c) The project shall be designed to preserve significant existing trees and other significant existing vegetation on the site. (d) The project shall be designed to protect from adverse impact species utilizing special habitat features such as key raptor habitat features, including nest sites, night roosts and key feeding areas as identified by the Colorado Division of Wildlife or in the Fort Collins Natural Areas Policy Plan (NAPP); key production areas, wintering areas and migratory feeding areas for waterfowl; key use areas for wading birds and shorebirds; key use areas for migrant songbirds; key nesting areas for grassland birds; fox and coyote dens; mule deer winter concentration areas as identified by the Colorado Division of Wildlife or NAPP; prairie dog colonies over fifty (50) acres in size as included on the Natural Habitats and Features Inventory Map; key areas for rare, migrant or resident butterflies as identified in the NAPP; areas of high terrestrial or aquatic insect diversity as identified in the NAPP; remnant native prairie habitat; mixed foothill shrub land; foothill ponderosa pine forest; plains cottonwood riparian woodlands; and any wetland greater than one -quarter ('/4) acre in size. (e) The project shall be designed so that the character of the proposed development in terms of use, density, traffic generation, quality of runoff water, noise, lighting and similar potential development impacts shall minimize the degradation of the ecological character or wildlife use of the affected natural habitats or features. (f) The project shall be designed to integrate with and otherwise preserve existing site topography, including but not limited to such characteristics as steepness of slopes, existing drainage features, rock outcroppings, river and stream terraces, valley walls, ridgelines and scenic topographic features. (g) The project shall be designed to enhance the natural ecological characteristics of the site. If existing landscaping within the buffer zone is determined by the decision maker to be incompatible with the purposes of the buffer zone; then the applicant shall undertake restoration and mitigation measures such as regrading and/or the replanting of native vegetation. (h) The project may be designed to provide appropriate human access to natural habitats and features and their associated buffer zones in order to serve recreation 16 Profile and Heads in Subdrains, Discharge Lines and Collector Wells 4 s � 2'--------- tw -o-- � ----------- 6m cl aquilcr 4' : j.. p flood channel floor 6_-___ lined bottom of low now channel 10' Perforated, filtered drain -� 12' 14' 16' 18'bedrock surface 20' original watenable next drain -- Therefore, it is hereby clarified that the channel, below where Dry Creek breaks away from the channel, will be a dry -bottom channel, which simply serves the purpose of performing a utility function. There is no existing natural feature. There's no future wetland associated therewith. Although it is certainly a storm drainage channel, it is not "naturalized." The buffer zone table in Section 3.4.1(E) of the LUC therefore does not apply to this section of channel. Fort Collins Buffer Standards. In accordance with the Fort Collins Land Use Code Section 3.4.1(E), buffer zones surrounding natural habitats and features shall be shown on the project development plan. This code section goes on to explain that the purpose of the buffer zones is to protect the ecological character of the natural habitat or natural feature from the impacts of the ongoing activity associated with the development, and that he decision maker shall determine the buffer zones for each natural habitat or feature contained in the project site. The buffer zones may be multiple and noncontiguous. The general buffer zone distance is established according to the buffer zone table in LUC Section 3.4.1(E), the pertinent items of which can be summarized as follows: Natural Habitat or Feature Buffer Distance Naturalized storm drainage channels/detention ponds 50 feet Wetlands < 1/3 acre in size 50 feet Wetlands > 1/3 acre in size, without significant use by waterfowl and/or shorebirds 100 feet Dry Creek 100 feet LUC Section 3.4. l (E) goes on to clarify that the decision maker shall reduce or enlarge any portion of the general buffer zone distance, if necessary in order to ensure that the performance standards set forth below are achieved. The buffer zone performance standards are as follows: 15 wetland being buffered. It should also be noted that the channel is 120' feet wide adjacent to this wetland. Code Requirement: The buffer zone table in LUC Section 3.4.1(E), states that wetlands under a third of an acre shall have a 50 foot buffer and wetlands over 1 /3 of an acre shall have. a 100-foot buffer. A third of an acre is 14,520 square feet. In this case, the westerly wetland is required to have a 50-foot buffer, and the easterly wetland is required to have a 100-foot buffer. This section of the LUC goes on to clarify that the decision maker shall reduce or enlarge any portion of the general buffer zone distance, if necessary in order to ensure that the performance standards set forth in that section (and discussed in detail in the next section of this document) are achieved. The Buffer of the Break -Away portion of the Channel. It is important to acknowledge that there is a significant distinction between Dry Creek .and the lower portion of the City's flood channel project. Dry Creek is a naturalized stream channel with a perennial flow and historic wetlands associated therewith. The City's flood channel project does overlap with Dry Creek for a portion, but there is a location on the Airpark Village site where Dry Creek breaks away from the flood channel project. The portion of the flood channel below where Dry Creek breaks away is simply a proposed utility solution to dealing with disposal of flood waters during a 100-year storm, and is specifically not a "naturalized storm drainage channel." First of all, it doesn't currently exist. It will be a newly created channel, so the extent to which it will be "naturalized" is a function of what this new channel will physically become. The City's storm channel designers (consultants of the City, not Airpark Village) have stated that this portion of channel is specifically intended to NOT become a wetland. Additionally, David Snow, the Airpark Village hydrologist states the following: "It appears to be in the City's best interest to design a dry -bottom channel to prevent evapotranspiration losses that would require costly augmentation. As designed by the City's storm channel designers, the floor of the flood channel will be at a level below the top of the gravel aquifer and below its native water table. The low -flow channel, incised 18 inches into its bottom would further lower the water table to concentrate the run-off, so without an effective subdrain system, the 100 foot wide floor would otherwise potentially remain wet in places. However, Airpark Village proposes a subdrain system ofperforated pipes that will drain the water table to a level one to two feet below the low flow channel. That will be accomplished by conducting the water from each of five collector wells via a closed drain pipe lead 500 feet downstream to the low flow channel at a lower level than the subdrain it serves. Because the hydraulic gradient in the pipes will be flatter than the gradient of the flood channel, the water table can be maintained by gravity at levels sufficiently below the channel floor to keep it dry in most seasons. The cross-section below illustrates these designed levels. " 14 wide directly west of this wetland and 100 feet wide directly southeast of this wetland. • Southern Westerly Preserved Wetland Area: The southern wetland in this scenario is 18,367 sq. ft. in size and the surrounding buffers (including buffer areas 10 and 11) are 58,277 sq. ft. in size. Therefore the buffer area is 3.2 times as large as the wetland being buffered. It should also be noted that the channel is 130 feet wide directly northwest of this wetland and 100 feet wide directly east of this wetland. Code Requirement: The buffer zone table in LUC Section 3.4.1(E), states that wetlands under a third of an acre shall have a 50 foot buffer and wetlands over 1 /3 of an acre shall have a 100 foot buffer. A third of an acre is 14,520 square feet. In this case, the wetland north of the channel is required to have a 50 foot buffer, and the wetland south of the channel is required to have a 100 foot buffer. This section of the LUC goes on to clarify that the decision maker shall reduce or enlarge any portion of the general buffer zone distance, if necessary in order to ensure that the performance standards set forth in that section (and discussed in detail in the next section of this document) are achieved. Buffer Scenario #5. Buffers from the easterly isolated wetlands. . BUFFER Proposed Conditions: • Western Easterly Preserved Wetland Area: The western wetland in this scenario is rather linear and parallel to the channel, so a 50 foot wide buffer was applied. It should also be noted that the channel is 120' wide adjacent to this wetland. • Eastern Easterly Preserved Wetland Area: The eastern wetland in this scenario is 24,996 sq. ft. in size and the surrounding buffers (including buffer areas 6 & 7) are 83,936 sq. ft. in size. Therefore the buffer area is 3.4 times as large as the 13 • Total Channel/Buffer Width: With an average 85 feet on the north, a 120 foot wide channel, and 20 feet on the south, the average width of the combined channel and buffer in this section of channel is 225 feet. Code Requirement: We disagree with City staff's assessment that this portion of the channel would qualify as a "naturalized storm drainage channel." (See our justification as to why it isn't in the next section of this document). The buffer zone table in LUC Section 3.4.1(E), states that naturalized storm drainage channels shall have a 50 foot buffer. We contend that no buffer is required because the channel will not be "naturalized" in this segment, however, since City staff has requested a buffer here, we are providing some buffer in the spirit of cooperation. Buffer Scenario #4. Buffers from the portion of the existing "Dry Creek" outside of the City's channel project (i.e. existing on -site "Dry Creek" wetlands). . BUFFER - RESOURCE BEING BUFFERED FROM ADDrr1ONAL EFFECTIVE BUFFER Proposed Condition: • Northern Westerly Preserved Wetland Area: The northern wetland in this scenario is 7,370 sq. ft. in size and the surrounding buffers (including buffer areas 3 & 4) are 32,594 sq. ft. in size. Therefore the buffer area is 4.4 times as large as the wetland being buffered. It should also be noted that the channel is 130 feet 12 • Total Channel/Buffer Width: With an average 15 feet on the north, a 100 foot wide channel, and an average 31.3 feet on the south, the average width of the combined channel and buffer in this segment is 1463 feet. Code Requirement: We disagree with City staff s assessment that this portion of the channel would qualify as a "naturalized storm drainage channel." (See our justification as to why it isn't in the next section of this document). The buffer zone table in LUC Section 3.4.1(E), states that naturalized storm drainage channels shall have a 50 foot buffer. We contend that no buffer is required because the channel will not be "naturalized" in this segment, however, since City staff has requested a buffer here, we are providing some buffer in the spirit of cooperation. Buffer Scenario #3. Buffers along the two-sided portion of the diversion channel. . BUFFER RESOURCE BEING BUFFERED FROM ADDYnONAL EFFECTIVE BUFFER TRACT 17 NEW n�G DUFFMH m TRACT 18 Proposed Condition: • Channel Length: This section of channel is 1608 feet in length. • Channel Width: The channel is 120 feet across from the top of the bank of the 100-year bank on the north to top of the 100-year bank on the south. • North Buffer: We are proposing 136,625 square feet of buffer and effective buffer (including buffer areas 5, 6, 7 & the two easterly preserved wetlands) along the north side of this portion of channel which makes the average buffer width along the north side of the channel 85 feet wide in this portion of channel. • South Buffer: We are proposing 20 foot wide buffer in this portion of channel. 11 • Total Channel/Buffer Width: With an average 84 feet on the north, a 130 foot wide channel, and an average 25.4 feet on the south, the average width of the combined channel and buffer in this segment is 239.4 feet. Code Requirement: The buffer zone table in LUC Section 3.4.1(E), states that Dry Creek shall have a 100 foot buffer. This section of the LUC goes on to clarify that the decision maker shall reduce or enlarge any portion of the general buffer zone distance, if necessary in order to ensure that the performance standards set forth in that section (and discussed in detail in the next section of this document) are achieved. Buffer Scenario #2. Buffers along the one-sided portion of the diversion channel. . BUFFER RESOURCE BEING BUFFERED FROM tm TRACT 15 Proposed Condition: CFA,1T/n %Vnym 1W TRACT 16 • Channel Length: This section of channel is 1887 feet in length. • Channel Width: The channel is 100 feet across from top of the 100-year bank on the north to the top of the 100-year bank on the south. North Buffer: There is no Airpark Village property on the north side of this portion of channel. International Boulevard abuts roughly the eastern half of this segment of channel and the Dry Creek Mobile Home Park abuts roughly the western half of this segment of channel. Dry Creek Mobile Home Park is providing a 30 foot wide buffer on the portion of this channel on which it abuts. A 30-foot wide buffer on approximately 50% of the frontage of this section of channel translates into an average buffer width of 15 feet wide. South Buffer: We are proposing 59,055 square feet of buffer (including buffer area 9) along the south side of this portion of channel which makes the average buffer width along the south side of the channel 31.3 feet wide in this portion of channel. 10 • Buffer Area 2 = 68,349 sq. ft. • Buffer Area 3 = 27,817 sq. ft. • Buffer Area 4 = 4,777 sq. ft. • Buffer Areas 5 = 15,338 sq. ft. • Buffer Area 6 = 6,286 sq. ft. • Buffer Area 7 = 77,650 sq. ft. • Buffer Area 8 = 31,499 sq. ft. • Buffer Area 9 = 59,055 sq. ft. • Buffer Area 10 = 27,821 sq. ft. • Buffer Area 11 = 30,456 sq. ft. • Buffer Area 12 = 49,817 sq. ft. Buffer Scenario R. Buffers along the portion of the City's channel project that qualify as "Dry Creek" itself. . BUFFER - RESOURCE BEING BUFFERED FROM Proposed Condition: • Channel Length: This section of channel is 1960 feet in length. • Channel Width: The channel is 130 feet across from top of the top of 100-year bank on the north to the top of 100-year bank on the south. • North Buffer: We are proposing 164,729 square feet of buffer along the north side of this portion of channel (including buffer areas 1, 2 & 3) which makes the average buffer width along the north side of the channel 84 feet from the top of the 100-year bank in this portion of channel. • South Buffer: We are proposing 49,817 square feet of buffer along the north south side of this portion of channel (Buffer Area 12) which makes the average buffer width along the south side of the channel 25.4 feet wide in this portion of channel. 7 at the collector well. Recharge to the gravel aquifer will be controlled by varying the head in the subdrain under the wetland reach, a function required by augmentation plan. Water purchased from Wellington Water Works, delivered to Dry Creek above Vine by Water Supply and Storage Co., will enter the wetland and the gravel aquifer to replace consumed water pumped from the aquifer via the subdrains and collector wells. Thus, the flood channel wetland is to be controlled, the through -flow naturally supplied by discharge from Horse Spring N. of Vine preserved by varying the recharge to the gravel whenever seasonal delivery of augmentation water is made. Any reductions of wetland area caused by floodway construction may be added to the existing wetland that now lies on the bench in the NE corner of the site. That wetland is isolated from the lower flat surface of the site, and its through -flow currently spills down the face of the bench and recharges the natural pipe system in the fine-grained surficial unit. That wetland, probably supplied by interflow from the Allen irrigation ditch and developed by someone who borrowed fill from the bench area, owes its existence to the low permeability of the soils underlying the depression. It can be enlarged at will, and its spill -point should be re-established at the head of an impervious channel leading it to the low -flow channel in the floodway. A small spring that emerges through a natural pipe from beneath the International Blvd. embankment should likewise be directed in conduit to the low -flow channel. No other wetlands are planned. Buffers The wetlands within the Airpark Village site, combined with the traditional Dry Creek streambed, and the City's proposed flood channel alignment going right through all these features, makes this project quite possibly the most complicated application of the City's buffer standards that has ever come through development review. Keeping that in mind, it is important to analyze the buffers not only as a whole concept throughout the site, but segment by segment within the site. There are 12 distinct areas of buffers that are used in 5 different usage scenarios, as described below. 12 Buffer Areas. They are numbered starting with buffer area 1 on the west end of the north side of the channel, and going around the channel clockwise. This diagram shows them small and not to scale, but please refer to the 24" x 36" ODP submittal drawings to see better detail of these buffer areas at 1" = 200'. The buffer area sizes are as follows: • Buffer Area I = 68,563 sq. ft. 8 Two Main Wetland Areas Westerly On -Site Wetlands T TRACT 17 Easterly On -Site Wetlands There are 4 wetlands being preserved in two main areas. The northern wetland on the westerly diagram is 7,370 sq. ft. in size. The southern wetland on the westerly diagram is 18,367 sq. ft. in size. The western wetland on the easterly diagram is 12,355 sq. ft. in size. The eastern wetland on the easterly diagram is 24,996 sq. ft. in size. On the diagram depicting the westerly on -site wetlands, the small tip of wetland disturbance at the main boulevard is 251 sq. ft., and the bulge of wetland disturbance that goes out of the channel alignment is 2795 sq. ft. (both depicted in red). The easterly on -site wetlands are proposed to remain undisturbed. Dry Creek is currently incised about 5 to 6 feet into the fine-grained upper unit, but accumulated clay lining its bed isolates the stream from the formation. That will change when the floodway is excavated a foot or more deeper, and in most reaches, the channel will cut into the gravel, breaching its confinement. If not drained downstream, the water levels would rise to within about two feet of the surface, manifesting the artesian heads revealed by piezometers that have been placed at many locations across the site. In time, such heads would fall due to the drainage, and gradients in the gravel aquifer would slope towards Dry Creek, probably augmenting the extent of the wetlands there and increasing the flow rates. Downstream of the convergence point, a low -flow channel 18 inches deep will be excavated into the 50-foot wide floor of the floodway, and it would become the main drain, dropping the water table beneath the floor and largely dewatering its surface. There might be some growth of cat- tails, but the floodway floor surface could probably be maintained for some recreational use. A further motivation for drying up the floor is to avoid having to buy augmentation water to replace evapotranspiration consequent to daylighting the water table. Further lowering of the water table is to be accomplished by installing a subdrain system consisting of five loops stepping down in altitude from NW to SE along the site, each of which will drain to lower positions via a closed pipe to the low -flow channel. Without pumping the five collector wells (the system is described elsewhere), the water table should drop about two feet below the floor. The only reach not so affected will be the wetland segment upstream of the diversion point, where no low -flow channel is intended to be made. However, a branch of the subdrain system will underlie that reach, and as with all the loops, to be controlled by a weir gate 7 ii) Existing and Proposed Open Space, Buffering, Landscaping, Circulation, Transition Areas, Wetlands and Natural Areas Wetlands ■ BUFFERS ■ vas- NG wETLANDs AIRPARK VILLAGE DEVELOPABLE PROPERTY Wetlands on the on and through the Airpark Village project fall into two categories. The first type are those wetlands that are within the City's Dry Creek Stormwater Channel. The City Stormwater staff is dealing with the disturbance of those wetlands and the associated 404 permit application with the Army Corps of Engineers. The second type are those wetlands on the site that fall outside of the Stormwater Channel right-of-way and within the Airpark Village property. Of those wetlands that fall within the Airpark Village property, are shown in the diagrams below. The areas depicted in blue are wetlands that will remain in place, and those shown in red are those that Airpark Village proposed to disturb. These minor disturbances will be replaced by equal areas that augment the two permanent wetlands. The existing wetlands are features of the upper aquifer, disposed on fine-grained silts and clays that sometimes display erosion pipes as the main conduits. There is no evidence that the wetlands are influenced by heads or flows in the underlying aquifer, the gravel unit that extends to bedrock beneath the fine strata. In all likelihood, there is a clay aquiclude that separates the two and is responsible for the artesian conditions in the gravel. Achieved: The Airpark Village ODP proposes a main spine boulevard going through the project designed with buildings fronting and opening directly onto the street sidewalk. The sidewalk is proposed to mimic the character of the sidewalks in Downtown Fort Collins, including shade trees, landscaped medians, street furniture, and on -street parking. Parking lots intended to serve these street fronting buildings are intended to be located behind the buildings. 5 Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another thereby reducing need for excessive vehicle miles to be traveled. PRINCIPLE GM-8: The City will promote compatible infili and redevelopment in areas within the Growth Management Area boundary. Achieved: The Airpark Village project is actually the redevelopment of a former use (airport), and is entirely surrounded by existing development. PRINCIPLE GM-11: The City will amend City Plan and elements thereof as necessary to respond to new and/or changing conditions, notable events, significant trends, and periodic review, as described in Appendix C of City Plan. Achieved: Because the Airpark Village ODP proposed a more intensive land use than was originally anticipated in the East Mulberry Corridor Plan, the Master Street Plan is in need of being amended. Our application includes a request to amend the Master Street Plan using the process set forth in Appendix C of City Plan. PRINCIPLE ED-1: Employment Districts will be major employment centers in the community. These districts will also include a variety of complementary uses to meet the needs of employees, such as business services, convenience retail, lodging, child care, recreation, housing and restaurants. By design, they will encourage non -auto travel, car and van pooling, telecommuting and transit use. Their attractive appearance should allow them to locate adjacent to residential neighborhoods and along primary entryways into the community. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another thereby encouraging non -auto travel. Policy ED-1.5 Walkable Destinations. Secondary and supporting uses in an Employment District will be accessible to and located within easy walking distance of major employment concentrations. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another. Policy ED-2.2 Parking. Parking and other vehicle use areas will be located in the interior of blocks, or in other secondary areas, so that they do not interfere with pedestrian connections. Trees and other landscaping will be provided within parking lots, along with pedestrian paths connecting buildings. Parking areas will be screened from adjacent streets with berming and landscape planting. n Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another. Policy T-9.1 Vehicle Miles Traveled (VMT). The City will continually strive to reduce the growth rate in vehicle miles traveled (VMT) by implementing a VMT reduction program that strives to meet or exceed the performance of similar programs in comparable cities. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another thereby reducing need for excessive vehicle miles to be traveled. Policy CAD-1.3 Streetscape Design. All new streets will be functional, safe and visually appealing. Shade trees, landscaped medians and parkways, public art, and other amenities will be included in the streetscape. Achieved: The Airpark Village ODP proposes a main spine boulevard going through the project designed with buildings fronting and opening directly onto the street sidewalk. The sidewalk is proposed to mimic the character of the sidewalks in Downtown Fort Collins, including shade trees, landscaped medians, street furniture, and on -street parking. Policy HSG-1.1 Land Use Patterns. The City will encourage a variety of housing types and densities, including mixed -used developments that are well -served by public transportation and close to employment centers, services, and amenities. In particular, the City will promote the siting of higher density housing near public transportation, shopping, and in designated neighborhoods and districts. Achieved: Upon build -out, Airpark Village is intended to integrate a large quantity of mixed -use residential units located on upper stories of mixed -use buildings, with employment, restaurant and retail uses on upper floors. This mixture of jobs, shopping and housing it a dense development pattern will be conducive to being served by transit. Policy ENV-2.1 Actions on Vehicle Miles Traveled. The City will slow the growth of vehicle -miles of travel by employing strategies that reduce vehicle trip rates, reduce vehicle trip length, and increase vehicle occupancy. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another thereby reducing need for excessive vehicle miles to be traveled. Policy ENV-2.1 Actions on Vehicle Miles Traveled. The City will slow the growth of vehicle -miles of travel by employing strategies that reduce vehicle trip rates, reduce vehicle trip length, and increase vehicle occupancy. 3 i) City Plan Principles and Policies Achieved by the ODP PRINCIPLE LU-1: Growth within the City will promote a compact development pattern within a well-defined boundary. Achieved: The Airpark Village ODP proposed a compact development pattern. LU-1.1 Compact Urban Form. The desired urban form will be achieved by directing . future development to mixed -use neighborhoods and districts while reducing the potential for dispersed growth not conducive to pedestrian and transit use and cohesive community development. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another. Policy T-1.1 Land Use Patterns. The City will implement land use patterns, parking policies, and demand management plans that support effective transit, an efficient roadway system, and alternative transportation modes. Appropriate residential densities and non-residential land uses should be within walking distance of transit stops, permitting public transit to become a viable alternative to the. automobile. Achieved: The Airpark Village ODP proposes a mix of uses (jobs, housing, services) within a single neighborhood, all within walking distance from one another. The proposed land use intensities of Airpark Village ODP would be concentrated along a new boulevard, which would be conducive to the future integration of a transit route. Policy T-4.2 System Design. The City will design a city-wide system of on- and off -road bicycle transportation facilities according to adopted standards while maximizing safety, convenience and comfort for bicyclists. of all ages and skill levels in conformance with accepted design criteria. Bicycle facility design will also include retrofitting older, existing streets with bike lanes in conjunction with capital improvement and maintenance projects, where feasible. System design will also provide for enjoyable and scenic bicycling routes. Off-street multi -use trails will be implemented to complement the on - street network and improve transportation mobility, while mitigating impacts on wildlife and plant communities. Achieved: The East Mulberry Corridor Plan identifies a bicycle path/trail to be located along the future dry creek flood channel. The Airpark Village ODP provides land for this trail. Policy T-5.1 Land Use. The City will promote a mix of land uses and activities that will maximize the potential for pedestrian mobility throughout the community. 2 Planning Objectives Airpark Village ODP 9/10/2007 Contents i) City Plan Principles and Policies Achieved by the ODP ............ 2 ii) Existing and Proposed Open Space, Buffering, Landscaping, Circulation, Transition Areas, Wetlands and Natural Areas ......................... 6 • Wetlands • Buffers iii) Estimate of Number of Employees for Commercial and Industrial Uses .... 20 iv) Rationale Behind the Assumptions and Choices Made by the Applicant ... 20 Site and Soils Conditions .............. :............................. 20 Site Drainage Plan ................................................... 24 Conveyance........................................................... 24 Detention............................................................. 26 Dewatering........................................................... 27 Flood Channel......................................................... 30 Channel ROW Low Flow Channel Diversion Greeley Water Line Metro District......................................................... 33 Resumes................................................................ 34 v) Issues from Neighborhood Meeting ................................ 35 vi) Name of Project as Well as and Previous Names the Project may have been Knowby ....................................................... 35 vii) Mitigation and Avoidance of Conflicts Between Land Uses ............ 35 1