Call them cautious, conservative or just plain prudent, but until recently, state regulators have scrutinized and often rebuked the latest technology in landfill containment.
Despite the fact that the same successful methodologies and applications have been advancing U.S. companies in other industrial sectors to the top of their fields, the landfill industry's adoption of these technologies has been a painful-but-persistent process.
Although the U.S. Environmental Protection Agency (EPA) established parameters with the release of its Subtitle D regulations, individual state regulatory agencies' decision to adopt, modify or adhere to the rules are as varied as the geographic regions represented. And landfill owners and operators often are the unfortunate victims who feel like frustrated guinea pigs in an environmentally-fickle field.
With a few years of Subtitle D experience under their belts, some regulators now are conceding that the use of geocomposite liners (GCL) - sodium bentonite carpets used to strengthen the permeability of landfill liners and caps - and ingenious covers and caps are environmentally equal to the soils and clays in which they've historically put credence.
"It's a win-win situation," says Bob Trexler of National Seal Co. (NSC), Aurora, Ill., of GCLs. "It's beneficial to the regulators because it produces a higher permeability, and it's a benefit to the landfill owners because they get the added volume in landfill space."
Jim Kynor of In-Line Plastics Inc., Houston, whose product, Advantage Cover has been "around for some time in various applications," wonders what took regulators so long to accept this as a viable alternative. "We're just taking an application that was used in, say, agricultural and applying it to landfills."
Despite GCLs' growing acceptance, some critics are still wary about the consequences of liner punctures sans the clay liner foundation. However, according to Trexler, puncture should not be a concern "as long as you're using a protective cover of soil on top of the liner, and you're monitoring the wastes."
Not as new an innovation, but catching the attention of regulators is the use of geocomposite drainage mediums in the liner system, according to Trexler. "Some states are finally realizing that you can use these composites in the leachate collection system rather than sand or gravel. A geocomposite drainage layer reduces the 18-inch thickness of sand or gravel to a quarter inch, and you still hit the same transivity flow rates."
Considering Climate The Wyoming Department of Environmental Quality (WDEQ), Cheyenne, proposes to grant landfill operators flexibility in cap construction capitalizing on the region's mild climate and indigenous vegetation.
Currently in draft form, a proposed rule change would modify the standard clay cap design of two feet of clay with a permeability of 10-5 centimeters per second (cm/ sec) to one that achieves an equivalent reduction of moisture infiltration through an evapo transpiration (ET) capping system.
"[ET] is the ability of the climate to pull moisture out of the soil and transfer it to the atmosphere," explains Ken Schreuder, WDEQ's solid waste program manager.
Instead of attempting to achieve a tight, impermeable clay barrier, landfill owners will be permitted to construct thicker, more loosely-compacted caps that allow plants with deeper root systems to draw moisture through evapotranspiration. "The intent is to have a thicker column of soil to store precipitation so that it doesn't leak through the cap's bottom," Schreuder says.
Between four to 19 inches of precipitation falls in Wyoming - most of which occurs in the form of melting snow during the winter. "When the plants begin to grow in the spring, they naturally draw moisture from the cap and transfer it to the atmosphere," Schrueder explains.
WDEQ probably will establish standard cap designs based on soil types and geographic regions. "We're proposing the rule change because the problem with compacted clay caps is they're susceptible to failure," Schrueder says. "Moisture and extreme temperatures cause caps to swell and crack, and eventually compromise the caps' integrity.
"On the other hand, when we do a good job of compacting the clay, it's hard for vegetation to grow," he adds.
WDEQ's objective is not to create a barrier layer, but to build a storage layer that allows water - if there's enough - to move through quickly or get caught in the soil drains from which plants can pull moisture, Schrueder says.
Flexibility In Texas And Tennessee In the eyes of some, the Texas Natural Resource Conservation Commission (TNRCC), Austin, Texas, offers landfill owners maximum flexibility in landfill liner design.
As long as landfill owners can demonstrate or justify the performance of their proposed liner designs through HELP and MultiMed models, state regulators are willing to review each design on a site-specific basis.
"We've allowed the use of flexible membrane liners and GCLs under performance-based liner standards," notes Mark Dollins, team leader for the TNRCC municipal solid waste permit section.
"We've also granted in situ liners if the proposed landfill site is sitting on a good clay source," he says.
Although portions of Texas are arid, Dollins says the state's climate "goes from one extreme to the other," averaging between 10 inches to 60 inches of annual rainfall. "We've permitted in situs with and without leachate collection systems in areas that average 30 to 40 inches of rainfall," he says.
The Tennessee Department of Environment and Conservation (TDEC) also grants landfill owners flexibility in the construction of bottom liners. Of the state's 35 permitted Subtitle D facilities, at least three were constructed with a GCL system including the Bradley County Landfill in Cleveland, Tenn.
"Bradley County was one of the first Subtitle D landfills in our state to incorporate a GCL component," says landfill designer Rob Burnette of Santek Environmental Inc., Cleveland, Tenn.
"Since on-site soils consistently didn't meet the 1 x 10-7 cm/sec permeabilities, a GCL was the most logical alternative," he notes. "If we'd been forced to transport soils from off-site, it would have resulted in a tremendous economic burden."
Tennessee regulators have required the use of clay liners since 1990. However, the use of a GCL with the two-foot compacted soil component is equivalent, says Glen Pugh, chief of permitting for TDEC's division of solid waste.
Since TDEC recognized the weakness of compacted clay liners early on, it already was familiar with GCLs by the time Subtitle D rolled around, he notes.
Ironically, though, TDEC's regulation for closure caps for unlined facilities are far more stringent than the federal requirements, but regulators have conceded to the use of GCLs as a complement.
"For many sites, the option of a GCL in a closure cap has been more widespread because by the time landfill owners are ready to close, they've used up all their soil and don't have enough materials to construct a cap," Pugh explains.
If It's Broke, Fix It Unlike their counterparts in other states, landfill owners and operators in North Carolina have found the regulations governing the design and construction of liners and caps frustrating and restrictive.
Following design engineers' unsuccessful attempts to submit alternate designs to state regulators, the state chapter of the Solid Wastes Association of North America, Silver Spring, Md., chose to take proactive steps to fix a system it considered to be broken.
By forming a subcomittee of the technical committee, the chapter is working with state regulators to allow for more flexibility and rationale in the future design and construction of landfill liners.
The North Carolina Department of Environment, Health and Natural Resources (NCDEHNR), Raleigh, N.C., requires a four-foot vertical separation between the liner foundation and the bedrock or the seasonal high water table, regardless of the geological composition.
"We felt we could prove that, with an adequately designed liner system and a sufficient hydrogeological evaluation upfront, the four-foot separation is essentially wasted airspace," reports Gayle Wilson, chairperson of the chapter's alternate liner design subcommittee. "The four-foot standard is an arbitrary requirement placed upon us by the state. It doesn't take into account engineering properties or permeabilities. It could be sand or marble. It's not based in sound science."
The subcommittee, consisting of Wilson and eight engineers, began the tedious process of evaluating the current rules and identifying the sections that required revision. For evaluation and analysis ease, the section was separated into three subsections: base liner design, leachate collection design and vertical separation. To substantiate its recommendations, subcommittee members prepared technical papers to submit to NCDEHNR.
"We want the ability to consider local conditions, hydrology, geology, on-site clay availability and local construction costs," Wilson says. "Even the federal Subtitle D regulations allow for alternate designs while North Carolina requires strict adherence to a single composite liner which is not always in the site's best interest."
Wilson admits he's unsure the reception NCDEHNR will give his group's efforts, but through open lines of communication and the gathering of valuable information and feedback from state regulators, he is confident the state will support some flexibility.
"We're not offering profound and innovative changes," he said. "We're simply offering recommendations based on what other states are doing."
"The surprising thing is that many of the states' regulatory agencies that people consider to be 'tough' already have approved the GCL use in the liner system," says Greg Richardson of G.N. Richardson and Associates, Raleigh, N.C., a noted authority on the use of geosynthetic materials in landfill construction who has served as an advisor to a group of professionals working on the evapotranspiration approach to caps.
"The biggest concern regulators have about GCLs is the thickness of the system," he explains. "There always was a desire from the beginning if the synthetic element failed with a composite liner, you'd still have a clay liner to support it with adequate thickness. The regulatory mindset has been one of 'Can you install and build it without many defects?'"
Remaining flexible is the key to landfill success, but Richardson says ignorance among designers and some state regulators can be damaging.
"The law clearly states that, as long as you can demonstrate equivalency, you're well within your right to propose an alternate," he says. "If design engineers are smart, they'll run the numbers. Unfortunately, many facilities are designed by people who won't run the numbers and aren't fully knowledgeable so they stick with the regulations as they're written. It's been my experience, the regulatory way is the lazy way."