Septic Systems.
Most homes around Evergreen and the foothills treat their own wastewater on site. Here’s how a septic system — an OWTS, in Colorado terms — actually works, what the county requires when the house changes hands, what a real septic inspection covers versus a home inspection, and the warning signs that mean trouble.
How a septic system works
An on-site wastewater treatment system has two jobs: separate solids in a tank, then let the soil finish treating the liquid.
✓ The tank
Wastewater enters a buried concrete or plastic tank — 1,000 gallons for a 2–3 bedroom home under Colorado’s rules, 1,250 for four. Solids sink to sludge, grease floats as scum, and the clearer middle layer flows on.
✓ Baffles, tees and filters
Inlet and outlet tees keep scum from escaping; newer systems add an effluent filter at the outlet that has to be cleaned periodically.
✓ The soil treatment area
Colorado calls the drainfield a soil treatment area (STA): trenches or chambers where effluent seeps into the soil and bacteria finish the job. This is the expensive part.
✓ Foothills alternatives
Shallow, rocky mountain lots often can’t host a conventional field. Mound systems, engineered beds, aerobic treatment units and pressure-dosed or drip systems are common up here — and need more maintenance.
✓ Pumps and alarms
When the field is uphill or the system is engineered, a pump chamber lifts the effluent. An alarm light or buzzer means a pump or float has failed — not something to ignore.
✓ Sized by bedrooms
Systems are designed for two people per bedroom. Adding a bedroom, a rental unit or an ADU can require a permit and a bigger system.
Regulation 43 and county use permits
The state sets the floor; your county issues the permits and usually adds a step at sale.
✓ Regulation 43
Colorado’s On-site Wastewater Treatment System Regulation (5 CCR 1002-43) governs siting, design, installation and repair. Counties adopt local rules at least as strict — Jefferson County’s newest version took effect in mid-2026.
✓ Jefferson County Use Permit
Before a septic-served home in Jeffco is sold, the owner needs an OWTS Use Permit: a certified inspector evaluates the whole system and the tank is pumped. Systems first used less than five years before closing are generally exempt. Check the county’s current fee, forms and lead time.
✓ Neighboring counties
Clear Creek, Gilpin, Park, Douglas, Boulder (SepticSmart), Larimer, Adams and Arapahoe run similar transfer-of-title programs, each with its own name, fee, exemption window and validity period. Confirm with the county before you set a closing date.
✓ Certified inspectors
Transfer inspections must be done by a NAWT-certified (or county-approved) inspector. Home inspectors generally aren’t one, and the pumper emptying the tank isn’t either.
✓ Permits for repairs and changes
Installing, altering or repairing a system requires a county permit — and so does expanding the house beyond what the system was sized for.
✓ Wells and setbacks
Regulation 43 keeps the tank at least 50 feet and the soil treatment area at least 100 feet from a well. Some foothills lots can’t meet that, which affects both the well and the septic.
Septic inspection vs. home inspection
A standard home inspection and a septic inspection look at very different things — you want both.
✓ What a home inspection does
We run water at every fixture, watch the drains, note visible risers, lids, alarms and the pump panel, and look for wet spots or odors outside. We don’t open the tank or dig.
✓ What a septic inspection does
Locates and opens the tank, pumps it, checks baffles, tees and the effluent filter, measures sludge and scum, inspects the distribution box, loads the field with water, and tests pumps, floats and alarms.
✓ The pumping matters
You can’t see the tank walls, baffles or liquid level through sewage. That’s why county transfer inspections require the tank be pumped, not just looked at.
✓ Records you should get
The county permit and as-built drawing, the inspection report with a sketch, the pumping receipt, and any maintenance contract for an aerobic or engineered system.
✓ Timing in a purchase
Book the septic inspection the day you go under contract. Inspectors and pumpers get busy, and the county needs working days to issue the permit before closing.
✓ Who orders, who pays
In Jefferson County the owner — the seller — must hold the use permit before closing; who pays for what it turns up is negotiable. Make sure your contract says who orders it and who fixes what it finds.
Warning signs of a failing system
✓ Surfacing effluent
Wet, spongy or smelly ground over the tank or field — especially in dry weather — means the field can no longer absorb what the house sends it.
✓ Lush green stripes
Grass that stays bright green over the drainfield while the rest of the yard browns is being fed by effluent that should be underground.
✓ Slow drains and gurgling
Every fixture slow, or gurgling in one drain when another runs, is a system backing up — or a sewer-line problem. Either way, don’t close without knowing which.
✓ Odors
Sewage smell near the tank, the field or inside the house points to a failed seal, a blocked vent or a tank at capacity.
✓ Alarm lights on
A lit or silenced alarm on a pump system is a failed pump or float. We find them taped over more often than you’d think.
✓ No records, no risers
A tank nobody can find, lids buried under a deck or patio, and no pumping history in living memory: expect surprises.
What septic work typically costs
Every system and lot is different; treat these as typical ranges for the Denver and foothills area, not quotes.
✓ Pumping
Roughly $300–$600 for a routine pump-out; more if the lids are buried or the truck can’t get close.
✓ Transfer inspection with pumping
Commonly $400–$1,000 including the report and the pumping the county requires — plus the county’s permit fee.
✓ Small repairs
A new effluent filter, a riser and lid, or a baffle repair is often a few hundred dollars. A replacement pump or float assembly runs more.
✓ New conventional system
Roughly $15,000–$30,000 in this area for a conventional tank and field on a workable lot.
✓ Engineered systems
Mounds, aerobic units and drip systems for tight or rocky mountain lots commonly run $25,000–$50,000 or more, plus an annual service contract.
✓ Failed field on a small lot
The worst case: no room for a new field. Ask the county what replacement options the lot even allows before you buy.
Living with a septic system
✓ Pump on a schedule
Every 3–5 years for a full-time household; yearly for aerobic units and pump systems. Put the date on the calendar, not in memory.
✓ Watch what goes down
No wipes (even “flushable”), grease, coffee grounds, paint or harsh chemicals. A garbage disposal adds solids fast; use it sparingly.
✓ Spread out water use
Laundry all day Saturday floods the field. Space the loads, fix running toilets, and route softener backwash elsewhere if the county allows it.
✓ Protect the field
No driving, parking, building or deep-rooted trees over it. Keep roof and surface drainage away from it.
✓ Install risers
Bring the lids to grade with risers so the next pumping doesn’t need a shovel — and so an inspector can actually inspect.
✓ Keep the file
Permit, as-built sketch, pumping receipts, inspection reports. It shortens the next transfer and proves the system was cared for.
Common questions
Do I need a septic inspection when buying a home in Jefferson County?
Effectively yes. Jefferson County requires an OWTS Use Permit before a septic-served home is sold, which means a certified inspector evaluates the system and the tank is pumped — unless the system was first used less than five years before closing. Most neighboring foothills and metro counties run similar transfer programs with their own names and exemptions. Even where a county doesn’t require it, we recommend one: the field is the single most expensive hidden component on a mountain property.
How often should a septic tank be pumped in Colorado?
Every 3–5 years for a typical full-time household, sooner with a large family or a garbage disposal, and yearly for aerobic treatment units and systems with pumps. Part-time mountain cabins can stretch longer. The inspector’s sludge and scum measurements tell you where your household actually falls; set the interval from that, not from a rule of thumb.
What’s the difference between a septic inspection and a home inspection?
A home inspection is visual: we run fixtures, watch drains, and note visible septic components, alarms and wet areas. A septic inspection opens and pumps the tank, checks baffles and filters, tests pumps and floats, loads the field and reports on absorption. County use permits require the latter, by a NAWT-certified inspector. We’re happy to coordinate one alongside the home inspection.
Can I add a bedroom or an ADU on septic?
Only if the system is sized for it. Colorado designs systems by bedroom count (two people per bedroom), so adding bedrooms or a dwelling unit usually requires a county permit and often a larger tank or field. On a small or rocky lot that may not be possible at all — check with the county before you buy a property planning to expand it.
The grass over the drainfield is really green. Is that bad?
Usually, yes. A working field keeps effluent below the root zone; a bright green, spongy patch — especially in dry weather — means effluent is rising to the surface because the soil can no longer absorb it. Combined with slow drains or odor, that is a failing field. Get it inspected before you buy, or before it backs up into the house.
This guide is for general education. It reflects what we look for during a home inspection, not a substitute for a licensed professional. If you have a specific concern, please contact a NAWT-certified septic inspector or licensed OWTS contractor — and of course, we’re always happy to take a look during an inspection.
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