When a Colorado system failed right after the new homeowners moved in, Douglas County Septic switched out drainfields to save the day


Shortly after purchasing a five-bedroom home in Centennial, Colorado, the buyers received a shock. The Tri-County Health Department red-tagged the onsite system because the saturated drainfield had effluent surfacing in several areas.

The homeowner called pumper/installer Scott Kellogg, owner of Douglas County Septic in Franktown, Colorado, to pump the septic tank every 10 to 14 days during the replacement process. “We were surprised the system — installed in 1993 — had passed the recent title transfer inspection,” says Kellogg. “Groundwater and all the runoff from the property collected in a low area containing the drainfield.”

Kellogg referred the project to designer Kate Carney, P.E., of CHURCH Onsite Wastewater Consultants in Golden, Colorado, then worked with her to make the new sand filter fit in the existing drainfield’s footprint. “There wasn’t enough space in the backyard for the replacement field,” says Carney. “That left using the same location as the existing 4,600-square-foot nonpressurized drip disposal system.”

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Kellogg says his crew has installed many more challenging systems than this one, but the constricted workspace made it a seven on a difficulty scale of one to 10. The normal four- to five-day installation took 12 days.

SITE CONDITIONS

Soils are sandy clay loam with a blocky, weak structure and acceptance rate of 0.3 gallons/square foot/day. Groundwater is 74.5 to 82 inches below grade. The 2.2-acre lot is fronted on the south by a road and on all other sides by private developed parcels.

SYSTEM COMPONENTS

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Carney designed the system to handle 675 gpd. She doubled the size of the drainfield to prevent future failure. Major components are:

  • FLXX 2,000-gallon, three-compartment monolithic concrete tank (Front Range Precast Concrete)
  • Biotube FT Series 4-inch effluent filter (Orenco Systems) in second compartment
  • 1/2 hp PF5005 pump in flow inducer tower (Orenco) in third chamber
  • 300 Quick4 Plus low-profile chambers with drip dispersal (Infiltrator Water Technologies)
  • S Series demand-dose simplex control panel (Orenco)

SYSTEM OPERATION

Wastewater flows 54 feet from the house through a 4-inch Schedule 40 PVC sewer (with clean-out) to the tank. The on-demand pump in the third compartment sends 84 gallons per dose 23 feet through a 1.25-inch PVC supply pipe to the Orenco automatic distribution valve. An air vacuum relief valve just before the ADV facilitates drainage in both directions between pump cycles. The ADV alternates between six proprietary manifolds dosing six zones in the 3,672-square-foot mounded drainfield. Zones have two 102-foot-long rows of 25 chambers each. Suspended 1.25-inch PVC laterals in the chambers have 1/8-inch holes drilled on 36-inch centers, oriented at the 12 o’clock position.

INSTALLATION

Kellogg left the homeowners on the existing system until the new tank was ready. Site preparation and digging the tank hole took two days.

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Kellogg’s team of three removed the deck over the existing sewer pipe, then cut down trees and uprooted stumps using a Bobcat E55 track mini-excavator and T650 track skid-steer. They also grubbed out shrubs and bushes in the path of the new trench to the tank. “The owners were going to remove the deck anyway, and the trees were almost dead,” says Kellogg.

The sewer trench, supply trench and the tank hole were dug on the second day. “We hit groundwater while excavating the 18- by 6- by 7-foot-deep hole and had to stop until the tank arrived,” says Kellogg. “The muddy material was unsuitable for backfill, so we exported it and imported cleaner fill.” Sister company Kellogg Contracting made six trips hauling off debris, soil and vegetation using a PJ 7-cubic-yard dump trailer.

Front Range delivered the tank on day three. Kellogg’s team finished excavating the hole, then raced to stay ahead of incoming groundwater as they set the tank and backfilled around it. The tank required no anti-flotation anchors, but workers insulated the three risers with 2-inch-thick high-density INSULBoard (Higgins Insulation) before sealing them to the lid.

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Once workers connected the sewer pipe, they switched the family to the new system and demolished the existing tanks using a hydraulic concrete breaker attached to the excavator. “The corroded tanks were structurally unsound, and infiltration could have contributed to the system’s failure,” says Carney.

On the fourth and fifth days, Kellogg Contracting hauled in 705 cubic yards of common fill and built a berm around the entire system. “We basically created a bathtub to hold the imported sand,” says Kellogg. “My guys were stockpiling material everywhere they could to stay 10 feet away from the driveway and the neighbor’s property line on the opposite side.”

Next came 318 cubic yards of C33 concrete sand to fill the “bathtub” to a depth of 18 inches and build a 102- by 36-foot sand filter with 4-foot separation from groundwater. Over these two days, two Kenworth tandem-axle dump trucks with 15-cubic-yard Colt boxes each made 12 runs to the quarry 28 miles away.

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Kellogg brought in a fourth laborer to help install the chambers. “Working within those constrictive boundaries was difficult enough, but we also had to maneuver around four mature trees serving as a privacy barrier between properties,” he says. Setting the chambers took two days.

On day six, the crew plumbed the chambers and built the manifolds, flushing assemblies (Slip x FTP female adaptor, 10-inch HDPE hand-hold, 1.5-inch ball valve and PVC spool, and PVC long-sweep 90-degree bend pipe), and connections to the automatic distribution valve. To protect the ADV from freezing, the crew placed it in a riser, then insulated the outside of the structure and the lid with foam board.

The project’s second phase was backfilling and grading the site to divert runoff away from the drainfield. The crew constructed a swale along the east edge of the property and another around the west side of the system. Both drained to culverts near the road.

They installed four drainpipes in the east swale to collect roof runoff in the area of the sewer line and tank. “Doing the underground piping and making the connections was challenging,” says Kellogg. “We also graded against the foundation to achieve the proper slope away from the house. That was above and beyond the septic install.”

The crew then laid a 60-foot, 12-inch-diameter culvert lengthwise in the toe of the mound and parallel to the concrete driveway. This pipe spilled into an existing culvert that channeled drainage under the driveway and away from the mound. Including spreading topsoil, final grading and seeding, the work took another four days.

MAINTENANCE

There is no maintenance contract. Douglas County Septic technicians will monitor the septic tank yearly and pump it when the scum and sludge thickness reaches 18 inches. They will pull the effluent filter every six months for the first 18 months to establish a cleaning frequency, and check the effluent pump, ADV and float system twice a year. The surface area around the drainfield will be observed monthly.


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