State’s Largest

A high-pressure dosing system enables the construction of a changing facility for workers at a coal mine in central Illinois.
State’s Largest

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Officials at Arch Coal-Viper Mine in Williamsville, Ill., wanted to build a changing facility with showers and restrooms for 180 miners. Extending the city sewer to the site two miles away would cost $320,000.

Joe Olson, P.E., manager of technical services, asked Rick Maguire of Maguire Backhoe Co. in Virden, Ill., to design an onsite system that would work in a small area with a seasonal high water table. The state Department of Health had just accepted EZflow by Infiltrator geosynthetic media, enabling construction of a shallow drainfield.

"Dennis Hallahan, environmental engineer and product consultant at Infiltrator Systems, helped with the design," says Maguire. The system, with duplex pumps and high-pressure dosing, cost half as much as tying to the sewer and is the largest pressurized system in the state.

Site conditions

The site, a topsoil berm with 4:1 slope, has silty clay loam (6E) soils with a loading rate of 0.52 gallons per square foot per day. The water table is 29 inches below grade with seasonal high water at 12 inches.

System components

Hallahan and Maguire designed the system to handle 3,600 gpd. Major components are:

5,000-gallon single-compartment concrete septic tank. All tanks from Wieser Concrete, Maiden Rock, Wis.

5,000-gallon single-compartment dose tank with dual 1/2 hp turbine STEP (septic tank effluent pump) vaults from Clarus Environmental

4,200 feet of EZflow geosynthetic aggregate

Two distribution valves from K-Rain

Intelligent Pump Control duplex panel from Aquaworx by Infiltrator

System operation

Wastewater flows 180 feet through a 6-inch Schedule 40 PVC lateral to the septic tank, then to the dose tank. Alternating pumps send effluent to the 21- by 600-foot dripfield, which has six 100-foot zones divided by 30-inch strips of soil 12 inches high to contain effluent. An area the size of two zones is reserved for future expansion.

Every 90 minutes, the first pump sends 650 gallons 425 feet to zone 1; 150 gallons drain back to the pump vault to prevent water from freezing in the 3-inch line. The second pump, on an identical dosing schedule, sends 800 gallons almost 600 feet to zone 4; 300 gallons drain back.

The distribution valves automatically switch the zones. Each pair – zones 1 and 4, zones 2 and 5, and zones 3 and 6 – are separated by 200 feet, enabling the media to dry out before the next dose. "Pressure dosing brings oxygen from the pumps to the media, slowing the development of a biomat," says Maguire.

Installation

The Department of Mines and Minerals requires Illinois coal mines to strip and stockpile topsoil for reclamation. "Before we could excavate a portion of the berm to grade, we needed permission from the agency to cut into it," says Maguire.

Permission granted, workers used a Caterpillar 320 excavator to level an area, leaving a bank of soil 2 feet high on the low side and 4 feet high on the high side. "We had various compaction layers from 7 to 12 inches, so I bought a two-bottom plow and an adapter plate that I modified for the job," says Maguire.

After the dripfield was plowed with the plow mounted to the front of a Caterpillar 259B rubber-track multi-terrain loader, dump trucks deposited prewashed sand just inside the zones. "We leveled the sand to a foot deep with a skid-loader," says Maguire. "It has a ground pressure rating of 6 pounds per square inch for operating over sensitive surfaces, and it has a Bullseye laser receiver from Apache Technologies on the bucket."

It took six workers three days to install the dripfield. Maguire purchased titanium-tipped drill bits for boring 1/8-inch holes on 4-foot centers in 4,200 feet of 1.5-inch PVC pipe. "The diameter of the orifices achieves our squirt height and allows water to scour the holes to keep them open for as long as possible," says Maguire. Workers ran the smaller pipe through the distribution pipes, each with a 1.5-inch ball valve.

Zones have 10 rows of aggregate seven bundles laid side-by-side with a 3-foot-tall standpipe on the end of every row to confirm equal distribution of effluent. There also is access for cleaning the lines.

The two distribution valves, protected by 18-inch Tuf-Tite risers, have a length of clear 1.5-inch PVC piping running to the zones, enabling service providers to see what zone the valve is on by cycling the pump.

To help lower seasonal high groundwater, the crew dug a trench 10 feet from the dripfield and laid a 5-inch corrugated HDPE drain tile (Springfield Plastics) encased in filter fabric. They then backfilled the dripfield with topsoil – 24 inches on the low side and 48 inches on the high side.

The tanks were set on 6 inches of sand and plumbed. The pump vault cover has two 24- by 30-inch stainless steel service hatches. As a safety precaution, workers set six pipe bollards around the tanks to keep vehicles from driving over them. Maguire installed a RockWorks system from RockWare on the control panel to ensure that only his company could access information and make adjustments.

Throughout the installation, state health department officials and the team from the Sangamon County Health Department visited the site. "Pressure dosing is new to the state and we had plenty to show them," says Maguire.

Maintenance

Maguire Backhoe holds the annual maintenance contract. A technician services the system twice a year, cleaning the effluent filters in the pump vaults and pumping the septic tank as needed.



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