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Home My WebLink About016 Canyon Gate Wetland Investigation Report 3530 Centennial Drive, Helena, MT 59601 | phone: 406-442-8594 851 Bridger Drive, Suite 1, Bozeman, MT 59715 | phone: 406-522-8594 2223 Montana Avenue, Suite 201, Billings, MT 59101 | phone: 406- 601-4055 www.seaeng.com Engineers and Land Surveyors June 7, 2023 Shawn Kohtz City Engineer City of Bozeman 20 East Olive Bozeman, MT 59715 (delivered via email) RE: Canyon Gate Wetland Investigation Shawn: Here is some more information supporting the absence of wetlands at Canyon Gate. The following statements were provided with the Preliminary Plat submittal. Surface Water The existing conditions are shown on plan sheet C0.3. There are no streams, irrigation ditches, wetlands, or delineated floodplains on the property. There are no alterations to water bodies proposed or required for the project. Due to concerns about the accuracy and age of the existing floodplain mapping of nearby Bridger Creek, the City of Bozeman Floodplain Administrator recommended that a Flood Hazard Evaluation be conducted. The evaluation found that a 100-year flood of Bridger Creek inundates portions of the adjacent Legends Subdivision and Canyon Gate Subdivision, even though it is not identified by existing floodplain mapping. The historical flood path is shown on plan sheet C0.3. Reference the Flood Hazard Evaluation. Groundwater Groundwater monitoring was conducted as part of the geotechnical investigation. The results of the groundwater monitoring are provided in the Geotechnical Report. Groundwater monitoring was conducted at 8 monitoring wells from March 2022 to the present. The seasonal high groundwater was found in early June and ranged in depth from 6.44’ to greater than 13 feet. Groundwater is flowing to the west and is assumed to discharged to the East Gallatin River about ½ mile to the west. The range of groundwater depth encountered was largely due to the rolling topography of the site with some wells located at lower or higher relative locations. After site grading, high groundwater will more consistently be about 10’ below the surface. The submitted information is accurate and describes the site conditions and results of on-site investigations. The following paragraphs describe the work to determine that there are “no wetlands on the property”. Page | 2 Wetland Investigation First, the lack of surface water indicates a low potential for significant wetland features. Secondly, the Gallatin Local Water Quality District and Natural Resources and Conservation Service databases were queried, and no published potential wetland areas or hydric soil groups were located on the property. This first level of reconnaissance typically identifies the potential for large, expansive, jurisdictional wetlands on a property, but does not rule out the presence of isolated smaller wetlands. Next, with the absence of surface water hydrology on the site, the groundwater hydrology was explored in depth. The on-site groundwater monitoring wells were monitored for the duration of the 2022 high groundwater season. The wells were surveyed, and seasonal high ground water elevations were mapped to create a seasonal high groundwater table contour map. This water table was then compared to existing grades. The water table was consistent and uniform and can then be used to predict depths to groundwater at all locations on the site. An exhibit showing the results of this comparison is provided. Note that only 20,434 sf (about 2%) of the site has a depth to groundwater of less than 4’. The shallowest groundwater identified is 2.63’ at three small locations. These three locations are located in isolated topographic depressions where the ground surface is nearest to the water table. To be classified as a wetland the depth to groundwater must be within 12” of the surface within the growing season. Field investigations were then conducted at these three locations to determine if wetlands were present. None of the low areas identified had wetland indicators (hydric soils, wetland hydrology, hydrophytic vegetation) present, so in accordance with BMC 88.220.060, a wetland delineation was not conducted. I hope this additional information helps you feel assured that the information provided with the Canyon Gate subdivision submittal is factual. Sincerely, Cordell D. Pool, PE, Certified Wetland Delineator LEGEND2.63' to 3'>4'3' to 4'DEPTH TO SEASONAL HIGH GROUNDWATER FROM EX. GRADEWeeping Rock Ln Boylan RoadStory Mill Road Northview Street Maiden Star Ln Spirit Crossing Ln Maiden Spirit St.Boylan RoadMAIDEN SPIRIT ST.CANYON GATE BLVD.LUCY LANE CANYON GATE BLVD.Bridger Canyon Road (AKAHWY 86 - 144' ROW)SEASONAL HIGHGROUNDWATERCONTOUR (TYP)AREAS OF SHALLOWESTSEASONAL HIGHGROUNDWATER - NOWETLANDS PRESENTEXHIBIT ASUBDIVISIONGROUNDWATEREXHIBIT1 6/7/2023 GROUNDWATER EXHIBIT CDP ZWL PROFESSIONALENGINEERS &SURVEYORSSTAHLYENGINEERING& ASSOCIATESCANYON GATE CANYON GATE INVESTORS, LLCBOZEMAN, MONTANANOTE: SHADING REPRESENTS COMPARISON OF EXISTING GRADE TO SEASONALHIGH GROUNDWATER ELEVATIONSNOTES1.Existing Grade Contours shown were generated from City of Bozeman 2018 LiDAR data.2.Groundwater Monitoring took place from March 2022 to July 2022, performed by TD&H Engineering.