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HomeMy WebLinkAboutColorado Geololgical Survey GA-26-0002_1 Harvest Roaring Fork PUD .docx 3:17 PM, 09/17/2025 Page 1 of 2 Dear John and Glen: At your request (August 19, 2025), the Colorado Geological Survey has reviewed the Harvest Roaring Fork PUD referral. I understand the applicant proposes a new PUD (and revocation of the River Edge PUD) to accommodate single-family, multi-family, affordable housing, open space, and commercial uses on approximately 283 acres. The available referral documents include a Preliminary Geotechnical Investigation, Harvest Roaring Fork Subdivision, State Highway 82 and Cattle Creek Road, Garfield County, Colorado (CTL Thompson Project No. GS06896.001-115-R1 (Revised), June 5, 2025). The primary concern on this property is ground deformation-related damage to buildings and infrastructure caused by water-soluble evaporites/hydrocompactive/collapsible soils and bedrock. Sinkholes are visible in high-resolution LiDAR-derived hillshade imagery, and significant damage due to ground movement has occurred in nearby developments. The entire site, but especially the following areas delineated on the Harvest PD Illustrative Plan, are impacted by geologic hazards and will require additional investigation, analysis, and avoidance or mitigation: • North Frontage Neighborhood, northeastern corner: subsidence hazard and known sinkhole(s) • North Frontage Neighborhood, eastern edge, The Farm, northeastern corner, and Cattle Creek intersection area: Cattle Creek debris fan / possible debris inundation hazard (fan is bisected by Highway 82) and subsidence hazard • North Riverfront, western edge: subsidence hazard and known sinkhole(s) • South Riverfront, western edge: subsidence hazard and known sinkhole(s) • Creekside Neighborhood, interior area and southern portion: subsidence hazard and known sinkhole(s) • Sopris Neighborhood: subsidence hazard and known sinkhole(s) CTL/Thompson’s 6/5/2025 preliminary characterization of subsurface conditions and development constraints is valid. CGS agrees (page 6) that “it is good practice to avoid development in areas with potential for sinkholes and subsidence.” Additional investigation and analysis, possibly including geophysical methods, will be needed once development plans are better defined to identify subsurface voids and more accurately characterize subsidence hazard. The applicant should be made aware that some areas of the site may not be developable without ground modification or stabilization. COLORADO GEOLOGICAL SURVEY 1801 Moly Road Golden, Colorado 80401 September 17, 2025 John Leybourne, jleybourne@garfieldcountyco.gov and Glen Hartmann, ghartmann@garfieldcountyco.gov Garfield County Community Development Matthew L. Morgan State Geologist Location: 39.4587, -107.2667 Subject: Harvest Roaring Fork PUD Garfield County, CO; CGS Unique No. GA-26-0002 John Leybourne and Glen Hartmann September 17, 2025 Page 2 of 2 GA-26-0002_1 Harvest Roaring Fork PUD .docx 3:17 PM, 09/17/2025 Sopris Engineering’s summary of past geotechnical investigations and plan for additional investigation and analysis to mitigate risk of damage due to ground movement going forward (page 9, Harvest Roaring Fork Zoning Application, Engineering Narrative, Sopris Engineering Job # 34010, Revised April 14, 2025) is valid: 7. GEOTECHNICAL Sopris Engineering has reviewed 3 different preliminary geotechnical investigation reports for the subject property. Below is a list of those reports: YEH and Associates Inc Dated 12, 2014, 18 test holes HP Geotech dated November 15, 2010, 21 test holes CTL Thompson dated September 16, 2021, 12 test holes Each of these reports were prepared as part of different development plans in the past. Based upon the three previous investigations and SE’s experience in the area, the proposed form-based-zoning application can mitigate or/ or avoid Geotechnical Hazards outlined. Between the three studies, 51 borings and test pits have been completed throughout the subject site (see appendix 3 exhibit 2 for boring and test pit locations). SE’s opinion is that updated geotechnical investigation reports will be provided as part of the preliminary plan application for each phase of development… As the subject sites preliminary plan develops, we will continue to coordinate on the Geotechnical hazards and work to develop a site plan that avoids and mitigates hazards to the extent possible. If the county approves the Harvest Roaring Fork PD, CGS would like to review subsequent applications. Thank you for the opportunity to review and comment on this project. If you have questions or require further review, please call me at (303) 384-2643, or e-mail carlson@mines.edu. Sincerely, Jill Carlson, C.E.G. Engineering Geologist