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DEQ Issues Final Environmental Assessment for Proposed Drinking Water and Wastewater Facilities for the Quarry Phase II Subdivision Near Big Sky

Department of Environmental Quality
  • April 29 2025
The Department of Environmental Quality (DEQ) has published a final Environmental Assessment (EA) regarding proposed drinking water, stormwater and wastewater facilities near Big Sky in Gallatin County, Montana.    
  
DEQ appreciates the time and consideration that went into the comments provided on the draft EA. DEQ prepared the EA in compliance with the Montana Environmental Policy Act and found there are no anticipated significant impacts to the surrounding environment from the proposed drinking water and wastewater facilities. The final EA includes DEQ’s responses to substantive comments received during the public comment period.  
The proposed Residential Quarry Phase II subdivision was approved by Gallatin County Platting and Planning on April 16, 2024. Big Sky Rock, LLC, applied to DEQ for a Certificate of Subdivision Approval (COSA) to install drinking water and wastewater facilities associated with the proposed “Quarry Phase II” development. Under state law, a COSA is required for the drinking water, storm water and wastewater facilities that would service the proposed development. DEQ also reviews the public water, storm water and subsurface wastewater treatment systems for nondegradation and cumulative impacts to groundwater and surface water.  
  
In its application, Big Sky Rock, LLC, proposed that water services would be provided by connection to the existing Lazy J Utility Association facilities. Water will be provided through water main extensions and service connections to the new lots. Each of the proposed four lots would have its own wastewater treatment system provided by a Level 2 wastewater treatment facility and drainfield. Level 2 treatment systems can significantly reduce the nitrogen from wastewater prior to treatment by the soils.   
  
Stormwater retention and treatment would be provided by one on-site retention pond, swales, roadside gutters, storm sewers and manholes. Stormwater for the lots would be treated, retained and infiltrated by on-site storm water ponds proposed by the developer in Phase II or in oversized ponds built during Phase I that was previously reviewed and approved by the Department.   
  
The final Environmental Assessment can be found on DEQ’s website. 
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