Wireless Network Monitors Landfill Emissions
The Hidden Hollow Sanitary Landfill, located in Ada County, ID, is not hidden at all; in fact, it is located on top of a hill, and you can see it from the entire Boise Valley. Your trip to the landfill takes you through several scenic miles of dry, reddish-hued land, dotted with sagebrush. Ada County owns 2,655 acres of land in the foothills northwest of Boise, and the landfill sits on 110 acres near the center of that property. More than 200,000 customers pass through the landfills gates each year, bearing an estimated 850 million pounds of trash.
During a time when many counties (and states) are suffering debilitating budget crunches, Ada County demonstrates fiscal strength and responsibility. As an Enterprise Fund, the Solid Waste Management Department of the Ada County Landfill relies solely upon fees collected at the landfill gate, and no tax dollars are spent to operate the department. In addition to meeting its expenses, the department has managed to save enough money to meet closure and post-closure requirements as required by Federal law. Post-closure care is a minimum of 30 years after the landfill closes, and includes monitoring and remediation of environmental issues that may arise after closure.
Another example of fiscal responsibility involves staffing. While the landfill is an enormous project, the department employs only 13 people six of whom are part-time. Unlike many landfills around the United States, Ada County chooses to pursue public-private partnerships, and has done so for 30 years. The landfills Solid Waste Management Department provides the core management of the landfill, while the private sector provides all equipment and manpower to accomplish the landfill tasks. There are currently 6 contractors who manage landfill closure, final cover construction, landfill operations, organics recycling, hazardous waste management, waste screening and engineering. The landfill chose CH2M HILL as its engineering partner.
How a Landfill Works
This landfill began as a ravine a hundred feet deep in some places. Trash is brought in on a daily basis. Liquids that can leach into the soil and other hazardous materials such as tires, batteries, televisions, computer monitors, refrigeration units, motor oil, and paints that can contaminate the environment are not allowed in the landfill. As trash is added to the landfill, heavy machinery is used to flatten it out and soil is placed on top at the end of each day to eliminate blown litter. As the trash decomposes and pockets in the landfill collapse, earthmovers continue the smoothing and soil-layering process.
The Closure Process
At some point, landfills reach their capacity, and are essentially filled up. Roughly 40 acres of Hidden Hollow Sanitary Landfills 110 acres have reached designed capacity, meaning the County is no longer burying trash in that area. Ada County has begun a landfill closure process on that 40 acres. It will take an estimated five to seven additional years to completely fill and close this landfill. Closing a portion of a landfill is a complicated endeavor, involving a special cover called an evaparo-transpiration cap, as well as the addition of special soil and vegetation to prevent water from infiltrating the landfill. In this case, closure also involved installing gas extraction and irrigation systems.
Why Extract Gas?
One of the naturally occurring byproducts of trash decomposition is landfill gas. Landfill gas consists of methane (CH4) and carbon dioxide (CO2) in almost equal amounts. While both methane and carbon dioxide are truly colorless and odorless gases, there are a few other trace gases, such as hydrogen sulfide (H2S) that emit the sour smell we tend to associate with landfills. Understanding how much of a particular gas is present in landfill emissions is very important. The landfill staff exercises great care to minimize the amount of landfill gas found outside the landfill property.
Gases emitted from landfills are heavier than the surrounding air. Like water, they tend to flow down the side of a landfill, pooling in certain areas. By building dikes, Hidden Hollow Sanitary Landfill has been able to trap some of the gases, interrupting their flow into populated areas. Another strategy to prevent landfill gas odors from reaching Ada County residents involves sucking the gas out of the landfill in a controlled, proactive manner through a process called gas extraction. The lifecycle of landfill gas at Hidden Hollow looks like this:
1. As trash decomposes, gas is created underground in the landfill.
2. Large pumps suck the gas out of the landfill.
3. A small amount of the gas is sampled at various locations on the landfill surface, and this test data is sent wirelessly back to the departments computer network.
4. The gas is pumped through underground pipes to an area containing two enclosed flares (big, tall cylindrical ovens with flame).
5. The gases are cleaned, then processed through a de-mister that removes most of the entrained liquid.
6. The gas is pushed into the flares and burned, where 99.98% of the undesirable components of the landfill gas is destroyed.
The instrumentation and control system presented some unusual challenges to the design team:
1. Dealing with landfill gases generally is an unpleasant proposition, because their components can be flammable, corrosive, poisonousand downright smelly.
2. Landfills change over time in a process called differential settling. Using landfill director Dave Neals example, a pile of cabbages decomposes more quickly than a pile of clothing. Because the size, shape and depth of a landfill varies over time, physical connections required in a wired network would have been problematic; the length of cable needed to get from point A to point B might vary from day to day.
3. Ada Countys weather in the summer is very hot and arid, whereas the winters can be cold and snowy. The solution needed to withstand extreme temperature conditions.
4. Because Hidden Hollow Sanitary Landfill is within full-view of the Boise River Valley, it is susceptible to intentional and unintentional data interference or hacking. The communications system had to be inherently secure.
5. Because Hidden Hollow Sanitary Landfill is so visible, the system needed to be attractive, and preferably invisible.
6. Because the closure will be done in three phases, the system had to be easily expanded and remain fully functional during the expansions.
The Present-Day Locus Radio Network
Prior to installing the wireless network, monitoring at the site was done manually by taking core and gas samples. The Countys new wireless network allows constant, real-time monitoring of what is occurring beneath the surface of the landfill. The Locus network provides a continuous, reliable solution that will operate for years with little human intervention. The wireless network consists of a master radio communicating through a repeater radio, with one irrigation pump station and 14 metering stations located on the surface of the landfill. The network is designed to accomplish both irrigation and gas extraction monitoring.
A key consideration in the design of the communications system is that the 2.4-gigaHertz band used by the radios requires a line-of-sight path. The location of each of the metering stations was established by well layout and the piping design. The CH2M HILL team selected a site for a repeater to reach those metering stations that did not have a line-of-sight path to the master. They used a computer-based three-dimensional model to define line-of-sight paths for Phase I. They also projected the contours of the landfill through Phase II and Phase III closures. This allowed the team to be certain that there would be line-of-sight paths for future closure projects.
Because the landfill is so visible from the Boise River Valley it was critical that the landfill blend in with its surroundings as much as possible. To this end, CH2M HILL recommended to re-vegetate the landfill using soil, seed and indigenous plants. Soil sensors were placed beneath the surface of the landfill to measure the moisture in the ground. If the soil becomes too dry, adversely affecting the re-vegetation process, the sensors communicate the situation wirelessly through the Locus radio network back to the landfills control room where the irrigation system can be turned on for that area.
Gas Extraction Monitoring
This gas extraction process is monitored real-time using the Locus industrial radio network. Fourteen monitoring wells are located around the landfill for the purpose of monitoring, controlling and analyzing the flow and chemical composition of extracted gases. The system is designed to measure the flow, temperature, pressure and concentration of carbon dioxide (CO2), methane (CH4), and oxygen (O2). You may be wondering why a landfill would want to measure the levels of oxygen, a harmless gas. Its simple; when a landfill sees too much oxygen in the gas its extracting, it indicates a possible fire risk. The extraction system is pulling so hard that its bringing excess oxygen (needed for the burning process) from the atmosphere down into the landfill. If County workers detect unacceptably high levels of oxygen, they will reduce the amount of suction through the landfill layers to avoid a possible fire.
Cabinets, Panels and Equipment
The gas extraction well heads and piping system are all below ground. Gas from several wells is combined and sent to sub-surface vaults where the line-mounted instruments are located. Each metering vault has electronics that are evident by two back-to-back cabinets that are above ground and adjacent to the metering vault. One of the cabinets contains the analytical components of this system, and the other cabinet contains the telemetry. (The system must be housed in two separate cabinets because of the flammability of the methane gas.)
The analytical cabinet houses the various gas analyzers; the most interesting of which are the laser chambers. One laser measures the concentration of CO2, and the other measures CH4. The concentration readings are sent to the telemetry cabinet directly behind it.
The telemetry cabinet contains various components, including Allen-Bradley I/O blocks, a Locus high-speed Ethernet radio (OS2400-HSE), a surge suppressor, and a power supply. Gas extraction and soil moisture data is received, processed and sent via wireless Ethernet back to the control room. From the landfills control room, staff have wireless access to the 14 transmitter cabinets and the data they are gathering, with future plans to include the enclosed flare and its controls in the network. Staff view the data through Rockwells RSView32 SCADA software. Because the Locus radio acts as an access point, the landfill can be managed from any location in the Boise Valley, provided the computer, laptop or PDA he is using has line-of-sight to the landfills repeater radio perched high on the hill.
The Locus high-speed Ethernet radios that the design team chose are Direct Sequence Spread Spectrum radios, and he has enabled encryption. The Hidden Hollow Sanitary Landfill radio network is extremely secure, and only the design team knows the password. Consistent with the Locus high-speed Ethernet radios performance, the Ada County landfill data is moving at a respectable 10 Mb/second!
Each of the 14 transmitter cabinets has an exterior 8dB omni antenna. The repeater site, located at the landfills Hazardous Materials Building, also uses an 8dB omni antenna fixed to a 60-foot pole.
The Benefits of Wireless to Ada County and its Residents
The Locus radio network provides several benefits to the Hidden Hollow Sanitary Landfill team and Ada County residents:
The Locus radio network is invisible, yet accessible, from the Boise Valley. All power lines and water lines are buried underground, and the wireless network complements the Countys desire to make this area as visually pleasing as possible.
The Locus radio network provides the County with real-time access to landfill data. This information helps the County make informed decisions affecting the safety and health of Ada County residents and landfill employees.
The Locus radio network controls and monitors the landfill with cost-effective technology that can change over time with the landfills shape and size; if the County desires monitoring in a new part of the landfill, CH2M HILL simply adds a Locus radio to the network in a matter of minutes.
The Locus radio network will require little human intervention in the years to come, and uses the license-free 2.4 GHz frequency. Both of these features translate into reduced costs for the County and its residents who use the landfill.
The County has discovered that its radio network has provided unexpected benefits. Antonio Serio of the Ada County IT Department realized that the repeater for the control system offered a clear line-of-sight path to a County building at the fairgrounds. Doug Heikkila agreed, and they teamed with the design team to design a fiberoptic connection from the landfill offices to the repeater, and a 5.8 GHz radio to the County’s network. This provides a high-quality data connection that was not available previously because of the limitations of the copper cables serving the landfill area. They also eliminated the monthly charges for the telephone service to the landfill offices by the use of VoIP (voice over IP).
By controlling the irrigation valves, the Locus radio network will allow the County to complete one of its most important initiatives — the re-vegetation of the landfill — with speed and precision.
A Shining Example, up on a Hill
Like many other western states, an air of self-sufficiency and independence pervades the state of Idaho. People out here have a pioneering spirit, and the Hidden Hollow Sanitary Landfill is an example of how citizens have taken personal responsibility for the health of their environment.
Ada County has gone out of its way to do things the right way and it shows:
1. The mile-long left-turn lane leading up to the landfill minimizes traffic difficulties for the residents beyond the landfill area.
2. The buried power and water lines preserve the beauty of the area.
3. The gas extraction system spares Ada County a whiff of those landfill gases.
4. The landscaping of the landfill area makes it beautiful to the eye.
5. The attractive, user-friendly (and fee-free) Household Hazardous Material Collection Facility encourages proper disposal of hazardous items.
6. The revolutionary use of litter screens keeps trash in its place and out of the Boise River Valley once it has been brought up for disposal.
7. The Hidden Hollow Sanitary Landfill team plans to create walking trails and a mountain bike area up near the landfill, to take advantage of the regions tremendous scenery.
Ada County Hidden Hollow Sanitary LandfillDave Neal, Director, Solid Waste Management Department200 West Front StreetBoise, ID 83702(208) 853-1297
CH2M HILLGary Koppelmann, Engineering Specialist700 Clearwater LaneBoise, ID 83712(208) 345-5310