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Home My WebLink About20081280.tiff A P G RO • ■■ COMPLETE LAND & RESOURCE SOLUTIONS December 27, 2007 Hanna Hippely Weld County Planning 918 10 Street Greeley, CO 80631 RE: AgPro Job Number 1103-04, Weld County Amended USR#1405 Dear Hanna: Please find included the sketch plan drainage report for the Aurora Milk Plant amended USR#1405. This is the plan and the specific details of the proposed improvements will not be developed until this project is approved by Weld County Planning Department. I have also provided a copy to Don Dunker in Public Works for his review. As always if either of you have any questions or concerns please done hesitate to contact me • Sincerely, rT avis rtl#� nek�y, EIT Agricultural Engineer • ENGINEERING, SURVEYING, PLANNING & CONSULTING 4350 Highway 66 0 Longmont,CO 80504 970.535.9318/office 303.485.7838/metro 0970.535.9854/fax www.agpros.com AGPROfussiona4,LLC 2008-1280 • Sketch Plan Drainage Report Prepared for: Aurora Dairy Corporation Milk Plant Lot A of Pending RE - 4654 being part of the northeast 1/4 Section 30, Township 3 N, Range 67 W. Platteville, Colorado December 21, 2007 • Pre 8ared b AG PRO • ENGINEERING, SURVEYING, PLANNING & CONSULTING 4350 Highway 66 • Longmont, CO 80504 970.535.9318 /office • 303.485.7838 /metro.970.535.9854 / fax • www.agpros.com AGPROfcssmnals,LLC • Aurora Dairy Corporation Sketch Plan Drainage Report • TABLE OF CONTENTS CERTIFICATIONS 1 I. GENERAL LOCATION AND DESCRIPTION 2 A) PROJECT DESCRIPTION 2 B) LOCATION 2 C) DESCRIPTION OF PROPERTY 2 II. DRAINAGE BASINS AND SUB-BASINS 2 A) MAJOR BASIN DESCRIPTION 2 B) SUB-BASIN DESCRIPTION 3 III. DRAINAGE FACILITY DESIGN 3 A) GENERAL PROPOSED CONCEPT 3 B) SPECIFIC DETAILS 4 SKETCH PLAN DRAINAGE REPORT DRAWING, SP-1 4 • 12/27/2007 ACPROfessionals, LLC ii Aurora Dairy Corporation Sketch Plan Drainage Report • Certifications I herby certify that this report for the conceptual drainage design of Aurora Milk Plant was prepared under my direct supervision in accordance with the provisions of the Weld County storm drainage criteria for the owners thereof O REGIS O o 87-4.:•,. age 357iP Travis Hertneky, EIT Roger terling Registered Professional Engineer State Of Colorado No. j,r7ff • 12/27/2007 AGPROfessionals, LLC Aurora Dairy Corporation Sketch Plan Drainage Report • I. General Location and Description a) Project Description The Aurora Organic Dairy is expanding their current milk processing facility located west of Platteville Colorado. The facility currently consists of a milk processing plant surrounded by irrigated pasture. The proposed plan is to expand the cold storage capabilities of the existing plant. Overall changes to the site will be minimal including the impervious areas. Most recently, prior to the milk plant, the facility was a feedlot and all runoff from the site was collected in storm water retention ponds and land applied to crop ground. Prior to the feedlot, the site would have been irrigated row crops. b) Location The location of the Aurora Dairy Corporation Milk Plant is at 6788 Hwy. 66, Platteville, CO. The entrance to the facility sits between CR 13 and CR 15.5 on the South side of the road. The milk plant is located in the E% of the NE',4 of Section 30, Township 3 North, Range 67 West, of the 6th PM. The milk plant is approximately 1 mile north of the channel of the St. Vrain River. The plant is approximately 1.4 mile south east of the Grand View Estates Subdivision. The USGS topographic map is based upon the NGVD-29 datum. The 2006 topographic data collected at the Aurora Dairy site must be raised 2.2 ft. to match the NGVD-29 datum. • An existing irrigation ditch runs through the site and feeds existing private irrigation ponds. The first is a pond located east of the plant and has a surface area larger than the plant itself. The remaining ponds are under the control of Aurora Organic Dairy. c) Description of Property The milk plant property consists of approximately 19 acres and is located on the south side of highway 66. Highway 66 is located at the top of the hill and thus any run on to the site is not an issue. The general topography of the site and adjacent area drains directly to the St.Vrain River located approximately 1 mile south and at an elevation of approximately 50ft lower than the lowest point on the site. This site surfacing is currently and will continue to be gravel, asphalt paving, roofed area and pasture. II. Drainage Basins and Sub-Basins The primary Drainage basin of this project is that of the St. Vrain River. The St. Vrain is a tributary of the South Platte River. a) Major Basin Description 1) Weld Code, This site is a commercial development and all plans and designs will conform to the Weld County Addendum to the Urban Storm Drainage Criteria • Manuals. 12/27/2007 AGPROfessionals, LLC 2 Aurora Dairy Corporation Sketch Plan Drainage Report • 2) Major Basin Characteristics, The site is located in the major basin of the South Platte River and most directly the St. Vrain River. Both streams are mountain fed and typically have their highest flows during spring snowmelt. Peak rainfall events are usually of a short duration during the summer months. 3) Irrigation, As previously mentioned there is a single small irrigation ditch that bisects the facility. The irrigation ponds are privately owned and used solely for irrigation purposes. The first pond located to the east of the milk plant is used for irrigation on the north side of Hwy 66. The second two ponds are under the control of Aurora Dairy Corporation. The pond adjacent to Hwy 66 is a pond that must be pumped into, and is only used for short term storage to regulate flow from the ditch and facilitate sprinkler irrigation. The second pond is located below the milk plant and will be modified to create a single irrigation pond and a second storm water detention pond. The south end of this pond has a pump station that delivers water to side roll sprinklers for the dairy site. 4) FEMA Flood Plain, There is no mapped FEMA 100-yr floodplain that affects this site. B) Sub-Basin Description 1) Historical Drainage Patterns, This property has historically drained in numerous • different fashions. Currently the site drains to a irrigation pond or flows overland to the St. Vrain River. Prior to the milk plant the facility was a feedlot and flowed to retention ponds. Prior to the feedlot the site was farmed with irrigated row crops. Our intention is to return the drainage characteristics of the site to the original consisting of native rangeland and vegetative filtering. The small portion of the site above the irrigation ditch has historically drained into the ditch and to the east pond. 2) Off-site Drainage Flow Patterns, There are no off-site drainage issues that affect this property. Ill. Drainage Facility Design A) General Proposed Concept The property can be divided into two separate drainage boundaries. The first being the area located above the irrigation ditch and the second consisting of the rest of the site. The area above the irrigation ditch is very small, and is labeled the entrance area. It comprises less than 2 acres and storm water runoff will be controlled by creating a berm on the edge of the parking area and installing a flow control structure that will release • water at a slower rate then the peak runoff from the asphalted area. This area could be difficult to drain across the irrigation ditch, and thus we plan on releasing it into the 12/27/2007 AGPROfessionals, LLC 3 Aurora Dairy Corporation Sketch Plan Drainage Report • ditch as it historically has. If the ditch is ever decommissioned this entrance area will drain across the rest of this site and to the main detention pond. The main area is approximately 13 acres and does have some minor storm sewers installed to divert runoff to the existing pond. These storm sewers catch the roof runoff and a small area adjacent to the building itself. We plan on dividing the existing pond and berming off the southern most end of the trailer parking area. This area will create a detention pond that will now catch only stormwater. The detention pond will likely be much larger than would be required to catch the peak of a 100-yr rainfall simply due to construction constraints. This pond will discharge across the pasture area and flow to the St. Vrain River. A distribution device will be constructed to evenly apply the discharge across the pasture. This discharge across the pasture will allow for filtering of the runoff and will reduce not only the discharge volume, but also the potential pollutants. We do not anticipate the need to request any variances from the Weld county codes at this time. B) Specific Details This site lies within the Denver area urban flood control district and therefore the precipitation depth duration frequency maps from the Urban Storm Drainage Criteria Manual will be used to determine the appropriate runoff volumes and rates. It cannot be guaranteed that this adjacent property will remain as a pasture, and under the control of Aurora Organic Dairy. A drainage easement will be established along the western most property line that will extend to the St. Vrain River. If the current pasture gets developed, the discharge can either be piped along the easement, or an open channel drainage can be established, whichever suites the eventual development. Due to the excess capacity of the detention pond we will likely release the discharge at a rate less than the historic 5yr but will not release greater than that. An emergency spillway will be installed in this lower detention pond to protect against any potential storm overtopping and breaching the berm. The system will not have any functioning components that will need maintenance in order to ensure the system is safe and functioning. The only maintenance required will be the control of vegetation on the detention basin and to ensure that the flow control inlets are clean. Sketch Plan Drainage Report Drawing, SP-1 • 12/27/2007 AGPROfessionals, LLC 4 Hello