Salt River Pima-Maricopa Indian Community; Final Approval of an Alternative Liner System Design and Use of Alternative Daily Cover Material for the Salt River Municipal Solid Waste Landfill

A. Regulatory Background

Subtitle D of the Resource Conservation and Recovery Act (RCRA), as amended by the Hazardous and Solid Waste Amendments of 1984 (HSWA), 42 U.S.C. 6941-6949a, governs the disposal of nonhazardous solid waste and of small-quantity hazardous waste not regulated under Subtitle C of RCRA. Subtitle D prohibits ``open dumping'' and EPA established criteria for determining which solid waste facilities should be classified as ``municipal solid waste landfills'' and which as ``open dumps.'' Pursuant to HSWA, EPA added revised criteria to establish minimum federal standards to ensure that municipal solid waste landfills (MSWLF) are designed and operated in a manner that protects human health and the environment. The Federal revised criteria are codified at 40 CFR part 258. RCRA also requires states to implement permit programs to ensure that MSWLF facilities comply with the revised criteria (40 U.S.C. 6945(c)). EPA determines whether each state has developed an adequate solid waste permitting program and ``approves'' those states. In states that do not develop an adequate program, the regulations set forth in part 258 are self-implementing and apply to owners and

operators of MSWLF units without additional EPA approval or review (40 CFR 258.1). For many of the criteria, part 258 establishes a flexible performance standard as an alternative to the self-implementing regulation. The flexibility provided in the MSWLF criteria allows for the consideration of site-specific conditions in designing and operating a MSWLF at the lowest cost possible while ensuring protection of human health and the environment. The flexible standard is not self- implementing, and use of the alternative standard is generally approved by the Director of an approved state. Part 258 does not currently provide owners and operators of MSWLF units located in Indian Country with a mechanism for obtaining approval of the flexible performance standards. Indian tribes are defined as ``municipalities'' under RCRA section 1004(13), 42 U.S.C. 6903. As a ``municipality,'' the tribe would seek approval of design flexibility from the appropriate approved state. However, states are generally precluded from enforcing their civil regulatory programs in Indian Country absent an explicit Congressional authorization. California v. Cabazon Band of Mission Indians, 480 US 202 (1987). Including tribes as part of section 1004(13) was a definitional expedient, to avoid adding the phrase ``and Indian tribes or tribal organizations or Alaska Native villages or organizations'' wherever the term ``municipality'' appeared. By this definition, Congress did not intend to change the sovereign status of tribes for purposes of RCRA. In Backcountry Against Dumps v. EPA, 100 F.3d 147, 151 (D.C. Cir. 1996), the District of Columbia Circuit Court determined that the inclusion of Indian Tribes as ``municipalities'' ``does not strip the tribe of its sovereign authority to govern its own affairs * * * [the tribe has the authority] to create and enforce its own solid waste management plan.'' RCRA does not grant this kind of regulatory authority to municipalities. Owners and operators of MSWLF units in Indian Country are not subject to state authority and cannot obtain approval from the state for the performance standards included in part 258. Yet, the Federal revised criteria are silent as to the process by which MSWLF units in Indian Country can apply for the alternate standards. This site-specific provision allows the Salt River Pima-Maricopa Indian Community (``Community''), an owner/operator of an MSWLF in Indian Country, the same flexibility as owners and operators of MSWLF units in approved states. EPA derives its authority to promulgate this document from sections 4004, 4005, and 4010 of RCRA, 42 U.S.C. 6944, 6945, and 6949a. These sections provide the basis on which EPA developed the criteria distinguishing open dumps from landfills and the revised criteria in part 258. Nothing in these provisions limits EPA's ability to issue site-specific criteria. In this instance, where the existing part 258 regulations do not contain a process for approval of the flexible performance standards for MSWLF units in Indian Country, it is appropriate to issue a site-specific provision to supplement Part 258 and address this unique situation. The US District Court in the District of South Dakota reviewed this issue directly and upheld EPA's authority to issue a site-specific provision to provide design flexibility under subtitle D of RCRA. (Yankton Sioux Tribe v. US EPA), 950 F. Supp. 1471 (D.S.D. 1996). The Yankton court determined that EPA appropriately created an ``alternative mechanism'' to provide flexibility to the relevant MSWLF in Indian Country. The US Court of Appeals for the D.C. Circuit also supports EPA's authority to issue such a site-specific provision under RCRA Subtitle D. (See Backcountry Against Dumps v. EPA, 100 F.3d at 152 (1996)). For a description of the suggested process used to apply for and approve flexibility requests in Indian Country, see EPA draft guidance entitled ``Submitting Site- Specific Rulemaking Requests for 40 CFR part 258.'' Prior to making this Final Determination, EPA provided opportunity for public participation through a public comment period and a public hearing. A document was published on May 8, 1998, (amended on May 27, 1998) describing EPA's tentative determination to approve the two flexibility requests and announcing the public comment period and public hearing. Notice was also published in two newspapers of general circulation as well as the tribal newspaper. In addition, EPA sent information on the tentative determination and public participation opportunities directly to interested parties. August 5, 1998, was the final date to submit public comments. EPA has not received either written or verbal comments on the Tentative Determinations.

B. EPA's Final Determinations

1. Alternative Liner System Design (40 CFR 258.40)

The Salt River Landfill (Landfill) is located on 200 acres of property east of Phoenix, Arizona. It is operated by the Salt River Pima-Maricopa Indian Community and serves as a sanitary landfill for the tri-city area of Mesa, Tempe, and Scottsdale, Arizona. Landfill operations began in October 1993, and are expected to continue until at least the year 2003. The landfill currently consists of three lined cells and three undeveloped cells. The three operational cells are lined with the composite liner prescribed by 40 CFR 258.40(b). On May 23, 1997, the Community submitted an application to the EPA requesting approval to use a geosynthetic clay liner (GCL) in place of a composite liner for the undeveloped cells of the Landfill. The regulations at 40 CFR 258.40(b) require that the composite liner have the following components: (1) A two-foot thick soil layer with a maximum permeability of 1 x 10-7 cm/sec; (2) a geomembrane layer with a minimum thickness of 60-mil if constructed out of high density polyethylene, or 30-mil for other materials; and (3) ensure protection of ground water. The federal revised criteria do not specifically include a procedure for EPA's tentative determination. However, EPA relied on the requirements set forth in Sec. 258.40 as a guideline for analyzing the Community's application. Generally, Secs. 258.40(a)(1), (c), and (d) require the following: • The alternative liner design ensures that constituent concentrations of the chemicals listed in Table 1 of the criteria will not be exceeded in the uppermost aquifer at the relevant point of compliance; and • The alternative liner design addresses the hydrogeologic characteristics of the landfill site, climate, volume, and physical and chemical characteristics of the leachate, and models potential contaminant migration. The reinforced GCL to be used at the Landfill consists of a layer of pure sodium bentonite fixed between two layers of geotextiles. The GCL is used to replace the two-foot thick soil layer required by 40 CFR 258.40(b) and forms a composite liner using a geomembrane. A geomembrane is a polymeric material that cannot be penetrated by liquid as long as it maintains its integrity.The bentonite used in the GCL is an extremely absorbent, granular clay formed from volcanic ash. It rapidly hydrates when exposed to liquid, such as water or leachate. As the bentonite hydrates, it swells, providing a strong barrier layer. Hydration of the bentonite is critical. Laboratory tests demonstrate that dry, unconfined bentonite's

permeability is only approximately 1 x 10-6 cm/sec. When saturated, the permeability of the GCL used at the Landfill is less than 5 x 10-9. The GCL approved for the Landfill is therefore less permeable than the prescriptive liner, provided that the bentonite is well hydrated when it is installed. While the GCL is thinner than a compacted soil liner at this level of permeability, the alternative liner design ensures that the performance standards are met. In addition to its low permeability, the GCL has many advantages over the composite liner. The GCL is rolled out like carpet and is quick and easy to install. It is cost effective, particularly in areas where clay is not available. Because bentonite swells readily when hydrated, it can repair itself if rips or holes occur. It is also more resistant to cracking than compacted clay. The GCL is thin, yet strong. It allows the Landfill to maximize its capacity while continuing to protect ground water, but can also absorb a large amount of stress without losing structural integrity. The Salt River Pima-Maricopa Indian Community submitted site- specific demonstration to the US EPA Solid Waste Program, showing that its alternative liner design proposal meets the environmental performance criteria set forth in 40 CFR part 258. 40. EPA staff reviewed the Community's site-specific demonstration to determine if the proposed alternative design meets the environmental performance requirements and does not allow for degredation of the groundwater. EPA's review determined that concentration values for parameters listed in Table 1 of 40 CFR 258.40(a)(1) will not be exceeded in the uppermost aquifer. EPA's review also determined that groundwater models used in the evaluation were appropriate and appropriately used and that results of the computer modelling presented in the evaluation likely provide a reasonable worst case estimate of the concentration of chemicals in the groundwater. EPA approves use of the GCL at the Landfill. Based on the information submitted by the Community and as discussed above, EPA determined that the alternative liner meets or exceeds the performance standards set forth in Sec. 258.40(a)(1), (c), and (d).

2. Alternative Daily Cover Material (40 CFR 258.21)

The federal revised criteria requires that MSWLF units must use six inches of earthen material to cover disposed solid waste each day. Section 258.21(b) provides flexibility by allowing use of alternative materials and an alternative thickness if control of disease carrying insects and animals, fires, odours, blowing litter, and scavenging is provided without presenting a threat to human health and the environment. On June 2, 1997, the Community submitted an application to the EPA requesting approval to use any alternative daily cover material that Arizona has approved for that state. These materials consist of tarps, foams, chipped green waste, drinking water treatment residues, and chipped tires. The Community subsequently restricted their current application to the use of tarps as an alternative daily cover material. The federal revised criteria does not specifically include a procedure for EPA's tentative determination. However, EPA relied on the requirements set forth in Sec. 258.21 as a guideline for analyzing the Community's application. The Community proposes to use the Tarpomatic tarping operation, consisting of a polypropylene tarp rolled over the landfill material at the end of each business day and retrieved at the beginning of the next business day. The Tarpomatic is a polypropylene tarp that is automatically deployed and retrieved by machine. It is fast, easy, and eliminates direct employee contact with waste. Field tests and industry usage show that tarps meet the requirements of Sec. 258.21. In addition, use of the tarping system rather than earthen material extends the life of the landfill, reduces labor in covering the waste, and saves landfill space. However, tarps cannot be used during wind storms as the winds will pick up the tarp and the landfill will not remain covered. EPA approves use of a tarp at the Landfill. Based on the information submitted by the Community and as discussed above, the proposed alternative daily cover meets or exceeds the performance standards set forth in Sec. 258.21(b).

Authority: This notice is issued under the authority of sections 2002, 4004, 4005, and 4010 of the Solid Waste Disposal Act as amended, 42 U.S.C. 6912, 6944, 6945, and 6949a. The Regional Administrator is making this decision in accordance with EPA Delegations Manual No. 8-47 (October 8, 1993).

EPA approves the applications by the Salt River Pima-Maricopa Indian Community to use an alternative liner system design and an alternative daily cover material for the Salt River Municipal Solid Waste Landfill.

Dated: November 20, 1998. Felicia Marcus, Regional Administrator, Region 9. [FR Doc. 98-32579 Filed 12-10-98; 8:45 am] BILLING CODE 6560-50-P