Chapter NR 504

NR 504.06(3)(k) (k) Anchor trenches shall be designed and constructed around the perimeter of the landfill to secure the permanent edges of the geomembrane. The geomembrane shall be seamed completely to the ends of all panels to minimize the potential of tear propagation along the seam.

NR 504.06(4) (4) Zone-of-saturation landfills. All landfills proposed with base grades beneath the groundwater table shall meet the following requirements:

NR 504.06(4)(a) (a) The landfill shall be located in a fine-grained soil environment.

NR 504.06 Note Note: Fine-grained soil environment is defined in s. NR 500.03 (86).

NR 504.06(4)(b) (b) The landfill shall meet the requirements in sub. (2) (a), (d), (e), (f), (g) and (h), and if the landfill will accept municipal solid waste, sub. (3).

NR 504.06(4)(c) (c) An analysis shall be performed of the effect which groundwater flow may have on uplift of the liner and the short and long-term stability of the geomembrane component of the composite liner. The analysis shall evaluate the effect of an underdrain or other dewatering system.

NR 504.06(4)(d) (d) Borings, backhoe pits or other means of exposing subsoils shall be performed on a 100-foot grid to a minimum depth of 5 feet below the gradient control layer, if part of the design, or a minimum depth of 5 feet below the subbase grades of the liner. All detected granular or silty soils within this 5 foot depth shall be removed and replaced with compacted, fine-grained soils.

NR 504.06(5) (5) Leachate collection systems. All leachate collection systems shall incorporate the following design features:

NR 504.06(5)(a) (a) A leachate collection system shall be included in each horizontal phase of the landfill. This system shall be designed to route leachate to the perimeter of the landfill in the most direct manner possible and limit the average leachate head level on the liner to one foot or less. The piping layout shall be such that leachate flows no more than 130 feet across the base of the liner before encountering a perforated leachate collection pipe. The department will consider greater flow distances for well designed composite landfills.

NR 504.06(5)(b) (b) The minimum slope on all leachate collection pipes at the base of the landfill shall be a constant 0.5%. The department recommends that greater pipe slopes be utilized whenever possible.

NR 504.06(5)(c) (c) The minimum diameter of all leachate collection or transfer pipes shall be 6 inches. Schedule 80 PVC pipe or an approved substitute shall be used.

NR 504.06(5)(cm) (cm) Pipe fittings selected for use with PVC and HDPE pipe shall be secured to the leachate collection pipe. PVC fittings and pipe shall be solvent-welded. HDPE fittings and pipe shall be fusion welded.

NR 504.06(5)(d) (d) Leachate collection trenches for clay liners shall be designed as rectangular trenches. Leachate collection trenches for composite liners shall be designed as vee-trenches, with a minimum depth of 18 inches and with sideslopes no steeper than 3 horizontal to one vertical. The clay component of vee-trenches shall be smooth-drum rolled such that the clay in the trenches is smooth prior to placement of the membrane.

NR 504.06(5)(dm) (dm) A geotextile shall be used to line the base and sidewalls of all leachate collection trenches and shall be placed directly over the geomembrane component of a composite liner or the clay component of a clay liner. The geotextile shall have a minimum weight of 12 oz/yd2, and may not be overlapped over the top of the trench. The geotextile specifications, including manufacturer’s data for grab and puncture strength, shall be used to demonstrate that the geotextile can resist damage due to impact and puncture when aggregate is placed over the geotextile.

NR 504.06(5)(e) (e) The bedding material utilized in backfilling the leachate collection pipe trenches shall have a uniformity coefficient of less than 4, a maximum particle diameter of 1½ inches, a maximum of 5% of the material which passes the number 4 sieve and consist of rounded to subangular gravel. A minimum depth of 4 inches of gravel shall be placed in the trenches prior to installation of the leachate pipes. The backfill shall also be placed such that a minimum of 6 inches of material exists above the top of the pipe and within the trenches. An additional 12 inches of material shall be mounded above the trench. In cases where the particle size of the drainage blanket is significantly less than the collection trench bedding, a properly designed graded soil filter or geotextile shall be utilized to minimize the migration of the drainage blanket material into the collection trenches. Limestone and dolomite may not be used in the leachate collection system unless no other suitable material is reasonably available.

NR 504.06(5)(f) (f) The sizing of sand, gravel, geotextiles and pipe openings shall be analyzed for control of piping of soil materials. The gradation of sand and gravel, the apparent opening size of geotextiles, and the pipe opening sizes shall be selected to achieve a stable and self-filtering structure under all conditions of leachate flow.

NR 504.06(5)(g) (g) All leachate collection lines shall have cleanout access points installed on both ends of each line and may not exceed 1,200 feet from the end of one cleanout to the toe of the opposite slope.

NR 504.06(5)(h) (h) Leachate lines, manholes and other engineering structures may not penetrate the liner in the vertical direction. For clay lined landfills, leachate transfer lines may penetrate the liner in the horizontal direction only. The number of liner penetrations shall be kept to a minimum. Composite lined landfills shall be designed without any perforations in the liner and in accordance with par. (j).

NR 504.06(5)(i) (i) Any leachate line that penetrates a clay liner shall have a 4 foot by 4 foot anti-seep collar placed around it. A minimum of 5 feet of compacted clay, as measured from the pipe, shall be placed around the collar in all directions.

NR 504.06(5)(j) (j) All composite lined landfills shall be designed and constructed with sumps and sideslope risers as part of their leachate removal system rather than utilizing systems which penetrate the composite liner sidewall. The leachate removal system shall meet the following requirements:

NR 504.06(5)(j)1. 1. The volume of the sump and the capacity of the pump shall be sized so that accumulation of leachate outside the sump does not occur based on an assumed annual leachate collection rate of 6 inches. The volume of the sump shall take into account the potential buildup of solids over time.

NR 504.06(5)(j)2. 2. The base of the leachate collection sumps shall be protected by the use of a thick polyethylene plate or other means acceptable to the department which is placed prior to the installation of the sideslope riser and backfill.

NR 504.06(5)(j)3. 3. The leachate discharge pipes between the sideslope risers and collection tank shall be equipped with valves to prevent backflow into the waste disposal area.

NR 504.06(5)(j)4. 4. The minimum diameter of the sideslope riser shall be 18 inches. The geometry of the sideslope riser at the junction of the sump and sidewall shall be selected to assure passage of the pump and associated hardware and to assure correct positioning of the intake of the pump.

NR 504.06(5)(j)5. 5. The area of the sump and depth of gravel fill shall be sized to allow remedial installation of access and hardware for removal of leachate in the event of failure of the sideslope riser and pump system. The base of the sump shall be protected by polyethylene plate.

NR 504.06(5)(k) (k) All leachate lines transporting leachate out of the landfill by gravity shall be constructed with valves so the flow of leachate can be controlled. The valves shall be compatible with the leachate and be capable of being operated from the ground surface.

NR 504.06(5)(L) (L) All leachate transfer lines located outside of the composite lined or clay lined area shall be designed to assure groundwater protection through the use of double-cased pipe or by using another approved secondary containment method. All leachate transfer line piping shall be pressure tested prior to use. Unless otherwise approved by the department, the upslope end of the secondary pipe shall be sealed and the downslope end shall be open to allow any collected liquid to flow into the manhole.

NR 504.06(5)(m) (m) All leachate transfer lines, manholes, lift stations and other structures which transfer or store leachate outside the limits of waste shall be designed as shallow as practical and located far enough from the limits of filling so that excavations associated with repair of these devices would not infringe on the landfill cover system or sidewall liner. Each of these devices shall be constructed above the seasonal high groundwater table unless it is not technically feasible to do so and the design meets the requirements of par. (L).

NR 504.06(5)(n) (n) Leachate collection tanks and manholes shall be designed with a secondary containment system to prevent the discharge of leachate to ground and surface waters in the event of a leak or spill. Means shall be provided to monitor the tank and manholes within the secondary containment system unless other means for leak detection are approved by the department.

NR 504.06(5)(o) (o) All leachate collection tanks shall be designed to contain the volume of leachate which is generated by the landfill over a 4 day period and to withstand the soil and liquid loads that will be encountered during installation and use. The installation of the tanks shall follow the recommendations of the consultant and manufacturer.

NR 504.06(5)(p) (p) Measures shall be proposed to prevent accidental discharges at the leachate loadout station from entering groundwater or surface water. Unless an alternate method is approved by the department, the leachate loading station shall be paved with a concrete or asphalt pad and sloped to a catch basin to direct all spills back into the leachate holding tank.

NR 504.06(5)(q) (q) All manholes and enclosed structures for leachate and gas control systems shall be designed to allow for proper venting and access control. For landfills designed with active gas recovery systems, these devices shall be designed to minimize air intrusion into the landfill.

NR 504.06(5)(r) (r) All control systems such as pumps, valves and meters shall be designed to be operated from the ground surface.

NR 504.06(5)(s) (s) All leachate and groundwater collection systems shall be designed to accurately monitor the volume of liquid removed by the system.

NR 504.06(5)(t) (t) A minimum one foot thick granular drainage blanket shall be placed on top of the geomembrane component of a composite liner and on top of the clay component of a clay liner. For composite lined landfills, if the drainage blanket contains gravel greater than 1/4 inch, then a nonwoven geotextile shall be installed below the drainage blanket. The geotextile shall have a minimum weight of 12 oz/yd2 and shall be certified to be needle-free. The granular drainage blanket shall contain no more than 5% material by weight which passes the number 200 sieve.

NR 504.06(5)(tm) (tm) Leachate collection blankets shall have a minimum hydraulic conductivity of 1 cm/sec for any site that accepts any amount of municipal solid waste and 1x10-2 cm/sec for landfills which do not accept municipal solid waste. The gradation of the granular drainage blanket and associated hydraulic conductivity shall be selected to maintain the maximum head in the drain within the drain thickness.

NR 504.06(5)(u) (u) All major horizontal clay lined phases above the saturated zone shall be designed with a collection basin lysimeter to monitor the unsaturated zone except for composite lined landfills.

NR 504.06(6) (6) Additional requirements for landfills with extended collection lines.

NR 504.06(6)(a) (a) Landfills shall meet the requirements of pars. (b) to (f) where they will accept municipal solid waste and contain leachate collection lines that exceed 1,200 feet from the end of each cleanout to the toe of the opposite slope. Where the requirements of this subsection differ from other requirements of this chapter, these requirements shall take precedence.

NR 504.06(6)(b) (b) The maximum length of leachate collection lines from the access point at one end to the toe of the opposite slope may not exceed 2,000 feet.

NR 504.06(6)(c) (c) The minimum slope on all leachate collection pipes and associated pipe trenches at the base of the landfill shall be designed and constructed to be 0.5% after accounting for primary and secondary settlement of the subgrade. The minimum design slope shall be selected following computation of 100% of the primary consolidation settlement and the secondary consolidation settlement of the compressible materials beneath the facility, which includes, as applicable, in-situ soil, added geologic material, structural fill material, and compacted clay liner. Secondary settlement shall be calculated using a 100-year time frame.

NR 504.06(6)(d) (d) Pipe bedding material shall be composed of coarse, uniform gravel with a hydraulic conductivity that is greater than or equal to the hydraulic conductivity of the leachate collection blanket specified in s. NR 504.06 (5) (tm), in addition to meeting the other requirements of s. NR 504.06 (5) (e).

NR 504.06(6)(e) (e) The maximum anticipated construction, operation and post-closure overburden loads over the leachate collection piping shall be calculated and utilized in selecting the pipe material and wall thickness, based on 6-inch pipe diameter and an appropriate in-field consolidated density.

NR 504.06(6)(f) (f) All components of the leachate collection system shall incorporate all of the following design features:

NR 504.06(6)(f)1. 1. Sweep bends at all changes of alignment, using a minimum radius of 10 pipe diameters, consisting of prefabricated PVC sweep bends or smooth pipe bends or prefabricated sweep bends for HDPE or other pipe materials.

NR 504.06(6)(f)2. 2. Pipe alignments that minimize horizontal and vertical alignment changes for the entire leachate collection pipe length.

NR 504.06(6)(f)3. 3. Elimination or minimization of obstructions or artifacts of construction which impose drag on pipe cleaning jetter hose or nozzles.

NR 504.06(7) (7) Composite-lined landfills using GCLs. Use of GCLs in construction of a composite liner may not be used except in landfills which do not accept municipal solid waste, unless the GCL is used as a pad for the upper surface of the 4 foot clay component of a composite liner for a municipal solid waste landfill. The GCL and soil barrier layer components of a barrier system shall meet all of the following requirements:

NR 504.06(7)(a) (a) The hydraulic performance of the GCL shall be assessed by the use of compatibility testing. The testing protocol shall be provided to the department for review and concurrence prior to the initiation of compatibility testing. The compatibility testing shall utilize percolation fluids that simulate the leachate that will be produced by the landfill.

NR 504.06(7)(b) (b) The GCL shall meet the specifications of s. NR 504.07 (4) (a) 1. to 11.

NR 504.06(7)(c) (c) The GCL shall be underlain by a soil barrier layer that is a minimum of 2 feet thick and that meets the specifications of s. NR 504.07 (4) (a) 12. to 17.

NR 504.06 History History: Cr. Register, January, 1988, No. 385, eff. 2-6-88; r. and recr., Register, June, 1996, No. 486, eff. 7-1-96; am. (5) (e) and (t), Register, August, 1997, No. 500; CR 04-077: cr. (5) (cm), (dm), (j) 4., 5., (tm) and (6), am. (5) (d), (e), and (t) Register November 2005 No. 599, eff. 12-1-05; CR 05-020: cr. (7) Register January 2006 No. 601, eff. 2-1-06; correction made under s. 13.93 (2m) (b) 1., Stats., Register January 2006 No. 601; CR 06-026: am. (5) (dm) and (e), Register December 2006 No. 612, eff. 1-1-07.

NR 504.07 NR 504.07 Minimum design and construction criteria for final cover systems.

NR 504.07(1) (1) General.

NR 504.07(1)(a) (a) All final cover systems shall be designed to minimize leachate generation by limiting the amount of percolation through the cap system, reduce landfill maintenance by stabilizing the final surface through design of compatible slopes and establishment of vegetation, account for differential settlement and other stresses on the capping layer, minimize the climatic effects of freeze-thaw and desiccation on the clay capping layer of the final cover system, and provide removal of leachate and venting of gas from those landfills which accept wastes with a high moisture content or which readily biodegrade.

NR 504.07(1)(b) (b) All new landfills and expansions of existing landfills shall be designed with a final cover system meeting the requirements in subs. (2) to (9) unless it is established to the satisfaction of the department that portions of the final cover system are not needed based on the proposed waste types and the proposed design. The geomembrane component in sub. (5) does not apply to landfills designed exclusively for the disposal of high volume industrial waste, or to other landfills which are not designed to accept municipal solid waste unless the landfill is composite lined.

NR 504.07(1)(c) (c) Any phases of an existing landfill which have been designed and constructed with a composite liner shall be designed and constructed with a final cover system meeting the requirements in subs. (2) to (9), except that the requirement for the geomembrane layer in sub. (5) does not apply to composite lined phases of existing landfills which have completed final cover placement by July 1, 1996.

NR 504.07(1)(d) (d) Landfills which accept papermill sludges or other industrial solid wastes with high water contents and low strength may propose alternate final cover systems if the strength of the waste mass will not allow for the construction of the cover system required in this section.

NR 504.07(2) (2) Grading layer. A minimum 6 inch thick grading layer shall be designed over the final waste elevation of landfills proposing to accept municipal solid waste to attain the required slope and provide for a stable base for subsequent system components. Daily and intermediate cover may be used for this purpose.

NR 504.07(3) (3) Support layer for low-strength wastes. A support layer shall be designed for stabilization, reinforcement and removal of leachate and gas over the final waste elevations for landfills which accept industrial solid wastes with high water contents and low strength.

NR 504.07(4) (4) Clay capping layer. A minimum 2 foot thick clay cap shall be designed to provide a low hydraulic conductivity barrier to percolation. Clay used for this layer shall meet the specifications in s. NR 504.06 (2) (a). The clay capping layer shall be constructed according to s. NR 504.06 (2) (f). Final cover systems that are required to include a geomembrane layer may be designed with the following alternatives to the clay component of the composite capping layer:

NR 504.07(4)(a) (a) The clay component of the capping layer may be replaced by a GCL overlying a minimum of 2 feet of soil barrier layer. This GCL layer and the soil barrier layer shall meet the following material and construction specifications:

NR 504.07(4)(a)1. 1. The GCL shall consist of a layer of sodium bentonite clay encapsulated between 2 geotextiles.

NR 504.07(4)(a)2. 2. The GCL shall be covered with a geomembrane the same day that it is unpacked and placed in position. The GCL may not be installed in standing water or during rain. The GCL shall be dry when installed and covered. A GCL exhibiting unconfined swelling shall be removed and replaced.

NR 504.07(4)(a)3. 3. The GCL shall be installed in a relaxed condition and shall be free of tension or stress upon completion of the installation. The GCL may not be stretched to fit.

NR 504.07(4)(a)4. 4. Adjoining panels of a GCL shall be laid with a minimum of 6 inches of overlap on the longitudinal seams and a minimum 20 inches of overlap on the panel end seams.

NR 504.07(4)(a)5. 5. Irregular shapes, cuts or tears in the installed GCL shall be covered with a GCL patch that provides a minimum 12 inch overlap onto adjacent GCL surfaces.

NR 504.07(4)(a)6. 6. A seal of loose bentonite granules shall be placed in seam overlaps at a minimum rate of one quarter pound per linear foot of seam for all panel end seams and longitudinal seams. The seal of loose bentonite may be deleted, with concurrence by the department, for longitudinal seams where the manufacturer has processed the overlap area to enhance sealing. The seal may not be deleted for any longitudinal seams that are transitions between construction phases.

NR 504.07(4)(a)7. 7. Loose bentonite or bentonite amended soil shall be placed at all patches and penetrations.

NR 504.07(4)(a)8. 8. GCL panels shall be certified needle-free through magnetic and metal detection tests.

NR 504.07(4)(a)9. 9. The GCL shall be placed in direct contact with a soil barrier layer.

NR 504.07(4)(a)10. 10. Vehicle traffic on the subgrade of the GCL and on the GCL shall be restricted to the minimum weight and number of machines needed to deploy the GCL and geomembrane. Vehicles shall be operated to minimize the formation of ruts and surface deformations and to prevent damage to the GCL and geomembrane. Deployment methods shall be selected to prevent any tearing or combing out of fibers of the GCL.

NR 504.07(4)(a)11. 11. Soil cover placement over the geosynthetics shall be completed in the same construction season as the geosynthetic construction.

NR 504.07(4)(a)12. 12. The soil barrier layer shall consist of fine-grained soil or a well graded sandy soil with fines, meeting the USCS soil types ML, CL, CH, SM, or SC or dual-symbol classifications of these soils, with at least 25% by weight passing the P200 sieve size. The upper one foot shall have a maximum particle size of 2 inches or less. The lower one foot shall have a maximum particle size of 4 inches or less.

NR 504.07(4)(a)13. 13. The soil barrier layer shall be compacted in lift heights of no greater than 12 inches after compaction using footed compaction equipment with feet at least 6 inches long. Each lift shall be disked or otherwise mechanically processed prior to compaction to break up clods and allow for moisture content adjustment. Clod size shall be no greater than 4 inches.

NR 504.07(4)(a)14. 14. A sufficient number of passes of the compaction equipment shall be made over each lift to ensure complete remolding of the soil. All compaction equipment utilized shall have a minimum static weight of 30,000 pounds. Compaction equipment with static weight that exceeds 15,000 pounds may be utilized where it utilizes vibration to achieve dynamic compaction that exceeds 30,000 pounds of compaction energy. Lighter equipment may be used in small areas where it is not possible to use full size equipment. Alternative procedures or equipment may be proposed for approval by the department.

NR 504.07(4)(a)15. 15. All soil shall be compacted to 90% modified or 95% standard Proctor density or greater at a moisture content at or wet of optimum. As soil placement proceeds, the minimum density and moisture content targets shall be adjusted as necessary.

NR 504.07(4)(a)16. 16. Each lift shall be keyed into clay or soil barrier layer soils in adjacent phases to form a continuous seal. This shall be accomplished by excavating steps with a minimum width of 2 feet along the edge of the existing phase and overlapping them with lifts being placed for the new phase. A minimum of 2 steps shall be included.

NR 504.07(4)(a)17. 17. The surface of the top lift shall be graded or compacted to be smooth and firm and shall be inspected for removal of coarse gravel, cobbles and debris prior to placement of a GCL.

NR 504.07(4)(b) (b) For industrial solid waste landfills that predominantly accept compressible wastes or wastes with high water contents and low strength, the clay layer may be replaced by a GCL overlying a minimum of a one foot sand layer. The gradation of the sand layer shall be a uniform sand selected to vent gas, drain leachate and provide hydration water to the GCL.

NR 504.07(4)(c) (c) For industrial solid waste landfills that predominantly accept ash, the clay layer may be replaced by a GCL overlying a minimum of 2 feet of soil barrier layer. The soil barrier layer shall meet the requirements of par. (a) 13. to 17. The upper foot of soil barrier layer shall also meet the requirements of par. (a) 12. The lower foot shall be designed to provide a capillary break between the ash and the upper one foot of soil barrier layer.

NR 504.07(4)(d) (d) The lower one foot of the clay layer may be replaced with a minimum of one foot of foundry green sand system sand with a bentonite content of greater than 6%, a liquid limit of greater than 20, a plasticity index of greater than 6, and a hydraulic conductivity of less than 1x10-7 cm/sec. The green sand system sand shall be compacted to 90% modified or 95% standard Proctor density or greater at a moisture content at or wet of optimum.

NR 504.07(5) (5) Geomembrane layer. A geomembrane layer shall be designed to provide a low hydraulic conductivity barrier to percolation. The design and construction of the geomembrane component of the final cover system shall meet the requirements of s. NR 504.06 (3) (c) to (j) and the following:

NR 504.07(5)(a) (a) The nominal geomembrane thickness shall be 40 mils or greater, with no thickness measurements falling below industry accepted manufacturing tolerances.

NR 504.07(5)(b) (b) The geomembrane shall be installed in direct contact with the clay capping layer.

NR 504.07(5)(c) (c) Penetrations of the geomembrane, such as gas extraction wells, shall be fitted with prefabricated collars of pipe and membrane or plate and welded at the same angles which the penetrations make with the final cover slope. Methods of fixing membrane boots to vertical pipes extending above the geomembrane shall allow for differential settlement of the waste with respect to the piping without damage to the membrane seal.

NR 504.07(6) (6) Drainage and rooting zone layer. A minimum 2.5 foot thick drainage and rooting zone layer shall be designed above the geomembrane layer or clay capping layer. This layer shall include a rooting zone to provide additional rooting depth for vegetation and to protect the geomembrane layer or the clay capping layer from freeze-thaw damage and other environmental effects. It shall also include a drainage layer to allow for the drainage of liquid infiltrating through the cap. Soils available on or near the proposed landfill property may be proposed for the rooting zone portion of this layer. This layer may not be densely compacted.

NR 504.07(6)(a) (a) For all landfills, a drainage layer shall be designed immediately above the capping layer. The drainage layer shall consist of a minimum of one foot of sand with a minimum hydraulic conductivity of 1x10-3 cm/sec or a geosynthetic drain layer of equivalent or greater flow capacity. The design shall include an analysis which demonstrates whether the maximum head in the drain layer will be confined within the thickness of the drain. Drain calculations shall include infiltration rates based on saturated characteristics of the topsoil and rooting zone and a hydraulic gradient of one through the topsoil and rooting zone.

NR 504.07(6)(b) (b) A perimeter drain pipe shall be placed at the low end of all final cover sideslopes. The drain pipe shall be surrounded by a minimum of 6 inches of gravel or sand with a minimum hydraulic conductivity of 1x10-2 cm/sec. The drain pipe shall be sloped to a series of outlets at spacings no further than every 200 feet. Modeling may be submitted to the department which supports the proposal of a different spacing.