Septic Tank Size Requirements in Colorado (CO)
Colorado septic system regulations are administered by the Colorado Department of Public Health and Environment. This page covers the minimum septic tank sizes required for each home size, drain field sizing requirements based on soil conditions, permit costs, and special rules that apply in Colorado. Whether you are building a new home, replacing a failed system, or purchasing property that requires septic, understanding Colorado's specific requirements will help you plan and budget accurately.
Key Colorado Septic Regulations
Colorado individual sewage disposal system regulations are administered by county health departments. High-altitude installations require freeze depth consideration for pipe and tank burial. Expansive clay soils in the Front Range require specialized drain field engineering.
Minimum Septic Tank Sizes in Colorado by Bedroom Count
The table below shows the minimum septic tank sizes required by Colorado regulations for each bedroom count, along with calculated drain field areas and cost estimates assuming sandy loam soil conditions and a concrete tank. Actual requirements may vary based on your specific soil type, site conditions, and local county regulations. Use the calculator to get a precise recommendation for your specific situation.
| Bedrooms | Min. Tank | Recommended Tank | Daily Flow | Drain Field | Est. Total Cost |
|---|---|---|---|---|---|
| 1 Bedroom | 750 gal | 750 gal | 150 gal | 250 sq ft | $4,275 |
| 2 Bedrooms | 750 gal | 750 gal | 300 gal | 500 sq ft | $7,400 |
| 3 Bedrooms | 1,000 gal | 1,000 gal | 450 gal | 750 sq ft | $10,725 |
| 4 Bedrooms | 1,200 gal | 1,250 gal | 600 gal | 1,000 sq ft | $14,050 |
| 5 Bedrooms | 1,500 gal | 1,500 gal | 750 gal | 1,250 sq ft | $17,375 |
Drain Field Sizing in Colorado by Soil Type
Soil type dramatically affects drain field sizing in Colorado. The table below shows how drain field area requirements change for a standard 3-bedroom home across different soil types while maintaining Colorado's minimum drain field requirement of 150 square feet per bedroom. Poor-draining soils require significantly larger drain fields or alternative system designs.
| Soil Type | Suitability | Drain Field Area | Trenches | Est. Field Cost |
|---|---|---|---|---|
| Gravel | excellent | 450 sq ft | 2 x 75 ft | $5,625 |
| Sandy Soil | excellent | 563 sq ft | 2 x 94 ft | $7,038 |
| Sandy Loam | good | 750 sq ft | 3 x 84 ft | $9,375 |
| Loam | good | 1,000 sq ft | 4 x 84 ft | $12,500 |
| Clay Loam | moderate | 1,500 sq ft | 5 x 100 ft | $18,750 |
| Silty Clay | poor | 2,250 sq ft | 8 x 94 ft | $28,125 |
| Clay | poor | 4,500 sq ft | 15 x 100 ft | $56,250 |
Septic System Installation in Colorado
Installing a septic system in Colorado involves several steps governed by the Colorado Department of Public Health and Environment. The process typically begins with a site evaluation, which includes a percolation test or soil morphological evaluation performed by a licensed professional. This evaluation determines whether your property can support a conventional septic system and identifies the best location for the drain field. The site evaluator will also assess setback distances from wells, property lines, water bodies, and structures.
After the site evaluation, a system design must be prepared by a licensed designer or engineer that meets Colorado's minimum standards. The design specifies the tank size, drain field dimensions, pipe layout, and all construction details. This design is submitted with a permit application to the local permitting authority along with the site evaluation report and applicable fees. Permit review times in Colorado range from two weeks to several months depending on the jurisdiction and complexity of the application.
Once the permit is issued, a licensed installer excavates the site, places the septic tank, constructs the drain field, and connects all piping. Inspections are required at various stages of construction, typically including a pre-cover inspection of the tank and drain field before backfilling. The inspector verifies that all components meet the approved design specifications and Colorado's code requirements. After passing final inspection, the system is approved for use and the permit is closed.
Ongoing maintenance in Colorado requires regular pumping of the septic tank every 3 to 5 years by a licensed pumper, with records kept of all service. Some Colorado jurisdictions require periodic inspections of the system components, particularly for advanced treatment units and systems near sensitive waterways. Proper maintenance is the single most important factor in achieving the full design lifespan of your septic system and avoiding costly emergency repairs or premature replacement.
Frequently Asked Questions
What size septic tank do I need in Colorado?
In Colorado, the minimum septic tank size depends on the number of bedrooms: 1 bedroom requires 750 gal, 2 bedrooms requires 750 gal, 3 bedrooms requires 1,000 gal, 4 bedrooms requires 1,200 gal, 5 bedrooms requires 1,500 gal. These are minimums set by the Colorado Department of Public Health and Environment. Your actual tank may need to be larger depending on the number of occupants and daily water usage. The calculator above factors in all these variables to give you a precise recommendation.
How much does a septic system cost in Colorado?
A complete septic system installation in Colorado typically costs between $8,000 and $25,000 depending on system type, tank material, drain field size, and site conditions. Permit fees in Colorado range from $300 to $800. Add $250 to $1,000 for the perc test, $800 to $3,000 for the tank, and $3,000 to $15,000 for the drain field. Difficult sites with poor soil, steep slopes, or high water tables can push total costs to $30,000 or more for alternative system designs.
Does Colorado require a perc test?
Yes, Colorado requires a percolation test before issuing a septic system permit. The perc test must be performed by a licensed professional and measures how fast water drains through the soil at your proposed drain field location. Results determine whether a conventional system is feasible and how large the drain field needs to be.