Incorporating HDD To Sewer Faster, Smarter, Cheaper
As thousands of aged and leaking septic tanks threatened wells and contaminated waterways with E. coli throughout the 33-sq mile service area of the Twin Lakes Regional Sewer District (TLRSD) in north-central Indiana, engineers calculated a septic-to-sewer conversion would require 219 miles of buried pipe — the equivalent of a conduit from Manhattan to Boston.
As designed, this spider web of approximately 1.16 million ft of pipe would network 7,000 sewer connections ranging from remote lakefront cottages to campgrounds, restaurants, tight clusters of homes on small lots and 5,000-sq-ft mansions with acres of privacy.
Terrain issues were equally daunting: Flat and hilly landscapes, high water tables, bedrock, utilities easements, major state and county roads, even five separate sewer passes under the Tippecanoe River.
“Because of the size of the lots, the nature of construction, the width of roads and easements, the terrain . . . by far and away horizontal directional drilling (HDD) for an All-Terrain Sewer (ATS) was the only way to sewer this area,” says Mike Darter, general manager of TLRSD. “It provided a timely installation with minimal disturbance to the property owners. From an operations point of view, this type of installation has fused joints, making it a continuous run of pipe, leaving out infiltration or exfiltration, which in turn allowed the wastewater treatment plant to be down-sized because of a smaller peaking factor.”
U.S. Wastewater Infrastructure Rated D+
An estimated 800,000 miles of public sewers and 500,000 miles of private lateral sewers connecting private property to public sewer lines lay hidden in the United States — and they are in vast need of an upgrade.
According to the American Society of Civil Engineers (ASCE), all are susceptible to structural failure, blockages and overflows. In some major urban areas, sewers are over 100 years old — and lined with bricks. Thirty-two states employ frequently overflowing combined sewers (collecting human waste, industrial waste and storm water run-off into a single pipe for treatment and disposal), which the Environmental Protection Agency (EPA) calls “the largest category of our nation’s wastewater infrastructure that still needs to be addressed.”
Simultaneously, tiny towns and even major metro areas realize cheap septic tanks proliferating since the 1950s have become ticking ecological time bombs. The U.S. flushes more than 1 trillion gallons of raw, untreated sewage (and soap, cleaning agents, pharmaceuticals and narcotics) annually into more than 25 million septic tanks, nearly half of which do not function properly. Yet more than 25 percent of all new home construction still employs septic to manage disposal even as failures multiply. The EPA calls them “the second greatest threat to groundwater quality.”
Add in the need for wastewater treatment plant upgrades and construction and it’s clear why the ASCE gave the United States’ wastewater collection and treatment system a D+ in its most recent Infrastructure Report Card.
Repair and new construction will be expensive. The EPA estimates $271 billion is needed for current and future wastewater infrastructure over the next 25 years, but “the federal government has provided on average $1.4 billion per year over the past five years to the 50 states through the Clean Water State Revolving Fund,” says ASCE.
Approximately 95 percent of spending on wastewater infrastructure is made at the local level, according to the U.S. Conference of Mayors.
HDD Empowers a ‘Sewer Anywhere’ Technology
Twin Lakes demonstrated that ATS and HDD is a formidable, affordable option applicable to other diverse locales like the fishing hamlet of Astor, Florida, the dense urban confines and archeologically rich coastline of Warwick, Rhode Island, and the historical integrity of Locke, California, the only town in the United States built exclusively by the Chinese for the Chinese.
Darter says the TLRSD considered “other types of sewer systems like vacuum assist or a combination of gravity and pressure, but after analyzing the alternatives, this district decided to utilize HDD and the ATS with grinder pumps for all phases of construction.”
The tandem solution was the only viable method for problematic soil conditions like clay, silt, sand and rock, as well as enabling directional capacities in order to cross waterways, roads and lake and river approaches. Costs were lowered, completion times abbreviated, dewatering and extensive open cut trenches avoided and environmental damage mitigated.
When the project ended, all but about 30 miles of pipe was installed by HDD. The contractor of one segment of the project, James Rothenberger, vice president of Rothenberger Company, Inc. of Concord, Michigan, says that in only 14 months his company utilized HDD for approximately 40 miles of ATS and 82,000 ft of electrical conduit to power the E/One grinder pumps.
“Find me a project on a large river or lake where you can install 40 miles of open-cut gravity sewer to over 1,100 locations without once having to set up an overnight detour for traffic. We literally never had to do that once with our method,” Rothenberger says.
Upon completion, the $65 million TLRSD project became the largest pressure sewer system in the Western Hemisphere.
The All-Terrain Sewer, Explained
The ATS was pioneered in 1969 by Environment One Corporation (E/One) of Niskayuna, New York. This wastewater infrastructure begins with a grinder pump station which has a buried tank about the size of a dishwasher. Inside, the primary component is a 1-hp, semi-positive displacement pump.
The pump’s robust torque can propel wastewater through small-diameter, inflow-and-infiltration-free pressurized pipe buried just below the frost line for a distance of more than two miles – or even straight up 186 ft – to a force main or treatment plant. The total dynamic head provides a nearly identical flow rate regardless of the network’s contours and fluctuating elevations, making the adaptable ATS compliant with any project’s physical traits.
Because continuous coils of small-diameter HDPE can be positioned with automatic trenching and HDD machines, the ATS has low initial costs due to easier installation, smaller diameter pipe, shallow and narrow trenches and non-critical variable grade which can be adjusted for specific site conditions. The number of costly lift stations (consuming electricity in 24/7 operations), manholes and clean-outs can be reduced, or even eliminated.
“Some of the geotechnical challenges we’ve had, being on the coast and being on an island, everything is sand here; we don’t have any clay; and you run into all kinds of problems with the sand and the high water tables, especially in the spring and fall with the high tides and storms,” says Jim Hewitt, field services superintendent of the Hilton Head (Island) Public Service District. “It’s nice with the ATS because everything’s bored; it’s about two to three feet deep; it’s very easy access to do any repair work if we have to.”
For municipalities, system expansion can be accomplished on a one house at a time basis without the need to install large collector lines based on future expansion projects. Builders see upfront costs for sewer infrastructure greatly reduced as wastewater connections are provided when a lot is sold. By “inventing” the land with HDD, the ATS gives developers a tool to construct expensive homes on remote lots once deemed unreachable.
Preserving Landscapes and Oyster Beds
The world’s biggest ATS project will count 15,000 E/One grinder pumps in Mornington Peninsula, a septic-to-sewer conversion which marked the first time HDD had drilled an Australian pressure sewer network of that scale.
“HDD is well-suited to the sandy soils of the peninsula. The pipe sizes are relatively small compared to conventional gravity systems and constructing in this manner means that our surface disturbance and environmental footprint is minimal,” said Charlie Littlefair, South East Water General Manager of Asset Creation.
The technique barely left a scar on the boot-shaped promontory — home to nearly a dozen national and state parks and wildlife preserves — and caused minimal disruption to its beach towns’ residential neighborhoods and urban commercial areas, golf courses, riding schools, fishing and boating facilities and campgrounds.
“The capital investment savings — made possible by utilizing pioneering technology to allow for downsizing of reticulation networks and transfer mains — are significant,” says Phil Thompson, former CEO of iota, a telemetry device enabling the ATS to function as a “smart sewer.”
Port Orchard — along the Sinclair Inlet in Washington state — faced an urgent problem when septic tanks began failing, creating a serious health issue and impacting its oyster and clam beds. A survey along a 5-mile stretch of coastline called Beach Drive revealed 21 percent of the existing 215 homes had contaminating septic systems. Their average age was approximately 50 years. In some cases, a septic tank or drain field did not even exist.
The homes with failing systems were located along the beach against a very steep hillside that contributed copious run-off. Besides high ground water, the soil conditions ranged from clay to solid rock.
An engineer evaluated four systems for the area. A gravity system with three pump stations carried construction expenditures of $8.4 million and an annual operations and maintenance (O&M) outlay of $25,000. The HDD-enabled ATS — with 26,900 ft of 3- to 8-in. force main, 22,400 ft of 1.25- to 2-in. pressurized discharge piping on private property and 210 grinder pumps — was the least expensive at $1.9 million with annual O&M of $10,710.
Joseph Harmes is a freelance feature writer who has covered the water/wastewater sector, notably the evolution and acceptance curve of low-pressure sewer systems, for two decades.