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Home My WebLink About1.11 Drainge ReportExhibit K - Drainage Report ENERT/A • • • • CONSUL -MG • • • • s • • • GROUPLLC Mr. Patrick Waller, Sr. Planner Garfield County Community Development 108 8th Street, Suite 401 Glenwood Springs, CO 81601 RE: Drainage Letter Report and Weed Management Plan Ziegler Solar Garden 31154 State Highway 6, Garfield County 1529 Market Street, Suite 200 Denver, CO 80202 720.473.3131 sean.ohearn@enertiacg.com November 7, 2017 This drainage letter and weed management plan (included as Attachment A) is intended to provide Garfield County with drainage and land disturbance information related to the proposed 5.4 acre Ziegler Solar Garden located at 31154 State Highway 6, approximately 1.3 miles west of the Town of Silt. Project Specific Information Project Name and Location Ziegler Solar Garden, 31154 State Highway 6, Garfield County Developer/Owner Microgrid Energy, 1644 Platte Street, Denver, CO 80202 Site/Civil Engineer Enertia Consulting Group, LLC, 1529 Market Street, Suite 200, Denver, CO 80202 Project Description The Project is solar garden located on approximately 5.4 acres of undeveloped land (or Lease Area), located within the +/-42 acre Ziegler property, north of State Highway 6 approximately 1.3 miles west of the Town of Silt. This Project is located Section 5, Township 6 Range 92, County of Garfield, Colorado. Project components include: a solar garden with approximately 3,000 solar panels mounted on +/-1,000 steel I -beams; concrete equipment pads; access drive with emergency turn -around; and perimeter fence with gate. In order to construct the Project, approximately 0.5 acres of land will require clearing and grading. The project will be accessed via State Highway 6. Existing Ground Surface Conditions and Drainage Patterns The 5.4 acre Lease Area may be characterized as undeveloped land. Based on NRCS soils data, the site soils (Arvada Loam and Ildefonso Stony Loam) have been classified as Hydrologic Soil Group C. The site ground surface slopes from north to south toward State Highway 6 at an average slope of 3 percent. Site drainage ultimately flows toward existing culverts under State Highway 6 and ultimately toward the Colorado River. Land Disturbance Activities The site improvements include installation of: (i) solar garden components; and (ii) all-weather surface access drive. 1 Solar Garden Components - Installation of the 5.4 acre solar garden will include: 3,000 solar arrays placed on +/-1,000 steel I -beams (driven into the ground), an inverter and electric transformer placed on poured concrete slabs and a gated perimeter fence. Solar array installation will not require clearing or grading of the ground surface beneath the array footprint. Access Drive — All-weather gravel surface access drive will extend from the existing Ziegler property driveway, east to the solar array. The gravel surfaced access drive will be placed and compacted over the existing ground surface and will be capable of handling a load of 85,000 pounds. Land Disturbance Area A total of approximately 14,445 square feet (0.33 acres) of the Project site is anticipated to be disturbed installing the access drive (13,495 sf), I -beams (400 sf total) and equipment pads (550 sf). Since the land disturbance is less than 1 acre, a CDPS permit issued by CDPHE is not required for this project. Impervious Surface The Project will effectively change approximately 6,348 sf (0.15 ac.) of surface area from pervious to impervious (I-beam, concrete equipment pads, and the access drive). The access drive will be an all-weather gravel surface. The solar panels themselves are not included in the imperviousness calculations because the runoff from the solar panels will shed onto the undisturbed vegetated surface below. A summary of the impervious area calculations is as follows: gravel access drive: 5,398 sf (13,495 sf x 40% impervious factor for gravel); equipment pads: 550 sf concrete; solar array support system 400 sf (total footprint for 1,000 I -beams driven into the ground. The site runoff will follow existing drainage patterns and will not increase peak flows from the solar garden site. Water Quality and Detention Requirements Water quality and detention are not warranted due to the additional impervious surface and the minimal amount of site activity during solar garden construction and operations. Summary 1. The areas considered impervious (access drives, concrete equipment pads and steel !- beam array foundations) total 0.33 acres. The effective imperviousness is calculated to be 0.15 acres, or 3 percent of the 5.4 acre solar garden area. 2. Installation of the solar garden is not expected to impact existing drainage patterns or flow rates on or around the site. Runoff water quality will not be impacted by the solar garden components. We trust that the information provided is acceptable and complete. Please let me know if you have any questions or require additional information. Sincerely, ENERTIA CONSULTING GROUP, LLC Sean O'Hearn, PE Project Manager attachment 2 Attachment A WEED MANAGEMENT PLAN Introduction The Ziegler Solar Garden project is located on approximately 5.4 acres of undeveloped land within the +/-42 acre Ziegler property, north of State Highway 6 approximately 1.3 miles west of the Town of Silt. Once completed, this electric generation project will consist of a solar garden with +/-3,000 solar panels, transformer and other equipment on concrete pads, an access drive, and a perimeter fence. Clearing of existing vegetation will be required to construct the access drive and equipment pads. Minimal additional clearing of vegetation will be required. In order to control noxious weeds and soil erosion, disturbed areas around the access drive and equipment pads will be seeded and mulched. Seed will be certified noxious weed free and will be comprised of a Garfield County approved native grass mix, likely similar to the seed mix used by the Garfield County Department of Public Works. Survey/Inventory The 5.4 acre project area is currently undeveloped land with natural vegetation. Small areas may require seeding and mulching after solar garden construction. Microgrid will apply a native grass mix to minimize the spread of noxious weeds over any exposed area that requires revegetation. Management Goals and Control Methods Microgrid will consult with Garfield County personnel and/or a local weed mitigation consultant to identify all Table 1 species included below. Table 1 species will be either removed or sprayed. Microgrid plans to place an approved native seed mix once all solar garden installation activities have been completed. Representatives of Microgrid typically mow the grass within the solar garden several times each mowing season to reduce shade on solar arrays and to maintain a clean and orderly solar garden. Microgrid will take the following actions to manage weeds and keep a tidy project site. 1. Eradicate Garfield County noxious weed species before any ground disturbing activity begins with the assistance of the County and/or local weed mitigation consultant. Eradication will take place before construction begins. 2. Control the spread of Table 1 species within the 5.4 acre solar garden area. Make every attempt to keep any noxious weeds from leaving the sites by employing proper contain and control procedures. This can include mowing, trimming, removing, and spraying on an as needed basis. 3. Visually inspect equipment and personnel leaving the solar garden to ensure weed seeds or other plant parts are removed before leaving. When identified, clean seeds from tires, tracks and all other parts of machinery and personnel. 4. Microgrid has a routine operations and maintenance plan for all of its solar gardens. The O&M plan is a combination of electric performance diagnostic as well as onsite aesthetic maintenance. We routinely mow and trim our solar garden sites to maintain a neat appearance and to ensure our equipment is not shaded or interfered with. The frequency of our mowing and vegetation control depends on growth rates due to fluctuating moisture. Table 1 - Garfield County Noxious Weed List Common Name Scientific Name Leafy Spurge Euphorbia esula Russian Knapweed Acroptilon repens Yellow Starthistle Centaurea solstitalis Plumeless Thistle Carduus acanthoides Houndstongue Cynoglossum officinale Common Burdock Arctium minus Scotch Thistle Onopordum acanthium Canada Thistle Cirsium arvense Spotted Knapweed Centaurea maculosa Diffuse Knapweed Centaurea diffusa Dalmatian Toadflax Linaria dalmatica Yellow Toadflax Linaria vulgaris Hoary Cress Cardaria draba Salt Cedar Tamarix parviflora, Tamarix ramosissima Oxeye Daisy Chrysanthemum leucantheum Jointed Goatgrass Aegilops cylindrica Chicory Musk Cichorium intybus Thistle Carduus nutans Purple Loosestrife Lythrum salicaria Russian Olive Elaeagnus angustifolia