Is Lined Landfill Leachate Really “Black Ooze”? How Will It Impact Your POW? David M. Heiser, P.E. Camp Dresser 62 McKee, Raleigh, North Carolina Presented at: 1996 Pretreatment Coordinators’ Workshop August 12,1996 - Asheville, NC ABSTRACT When precipitation passes through solid waste material, soluble, suspended, or miscible chemical compounds are removed from the decomposition process, producing an underflow called “leachate.” Past visual images of municipal solid waste landfill leachate have typically been on the order of toxic sludge - or “black ooze!” Earlier national studies have reported extremely wide ranges in leachate pollutant concerrtrations, with very high figures for both organic compounds/cmstitueats and metals, and low pH values. This data should be expected for older, screening programs. * unlined, undrained landfills where solid wastes were received with very little monitoring or However, recent data fiom numerous lined landfill fhcilities in North Carolina, constructed both before and after Subtitle D regulations were enforced, show that the constitueats in leachate more closely approximate moderate residential sewage. Wastes received at these landfills are more closely monitored and screened, keeping hazardous and/or toxic materials from entering the landfill and producing toxic leachate. Upon closure, a landfill cell must now be capped, allowing virtually no additional rainEdll infihtion into the waste (which aids in the decomposition process, as well). Thus, after closure a Subtitle D landfill will see everdecreasing leachate quantities, with pollutant concentrations slowly decreasing as well. Leachate quahty data from several North Carolina lined landtills - both municipal and private - are presented and evaluated in this paper, and compared to leachate fiom pre-Subtitle D fhcilities. Also discussed are the impacts of leachate to P O W s , as well as some example of pretreabnent requirements found in permits issued to various lined landfills in North Carolina. It has become quite apparent fiom this data that during the ht three or more years or operatian of a new lined landfill, leachate quallty is typically low enough in concentrations of metals and organic constituents that pretreatment has not been required to meet the sewer use ordinance requirements of most municipal wastewater treatment systems. This is hardly the “black ooze” of ye&ryear! Leachate quahty does, however, vary fiom landfill to landfill, and with time varies within the same fhcillty. Thus, “typical” leachate quahty cannot be generalized for all fhcilities, or over the life of the same fhchty. LANDFILL DESIGN In 1980, RCRA Subtitle C reguhans were promulgated, which regulated the disposal of hazardous, i n f d o u s , or radioactive wastes in municipal solid waste landfills, as well as in dedicated hazardous waste landfills. USEPA has coIlclucted studies to show that there has been a noticeable, but slight, improvement in landfill leab after Subtitle C was enforced. RCRA 1
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Is Lined Landfill Leachate Really “Black Ooze”? How Will It Impact Your P O W ?
David M. Heiser, P.E. Camp Dresser 62 McKee, Raleigh, North Carolina
When precipitation passes through solid waste material, soluble, suspended, or miscible chemical compounds are removed from the decomposition process, producing an underflow called “leachate.” Past visual images of municipal solid waste landfill leachate have typically been on the order of toxic sludge - or “black ooze!” Earlier national studies have reported extremely wide ranges in leachate pollutant concerrtrations, with very high figures for both organic compounds/cmstitueats and metals, and low pH values. This data should be expected for older,
screening programs. * unlined, undrained landfills where solid wastes were received with very little monitoring or
However, recent data fiom numerous lined landfill fhcilities in North Carolina, constructed both before and after Subtitle D regulations were enforced, show that the constitueats in leachate more closely approximate moderate residential sewage. Wastes received at these landfills are more closely monitored and screened, keeping hazardous and/or toxic materials from entering the landfill and producing toxic leachate. Upon closure, a landfill cell must now be capped, allowing virtually no additional rainEdll infihtion into the waste (which aids in the decomposition process, as well). Thus, after closure a Subtitle D landfill will see everdecreasing leachate quantities, with pollutant concentrations slowly decreasing as well.
Leachate quahty data from several North Carolina lined landtills - both municipal and private - are presented and evaluated in this paper, and compared to leachate fiom pre-Subtitle D fhcilities. Also discussed are the impacts of leachate to P O W s , as well as some example of pretreabnent requirements found in permits issued to various lined landfills in North Carolina. It has become quite apparent fiom this data that during the ht three or more years or operatian of a new lined landfill, leachate quallty is typically low enough in concentrations of metals and organic constituents that pretreatment has not been required to meet the sewer use ordinance requirements of most municipal wastewater treatment s y s t e m s . This is hardly the “black ooze” of ye&ryear! Leachate quahty does, however, vary fiom landfill to landfill, and with time varies within the same fhcillty. Thus, “typical” leachate quahty cannot be generalized for all fhcilities, or over the life of the same fhchty.
LANDFILL DESIGN
In 1980, RCRA Subtitle C reguhans were promulgated, which regulated the disposal of hazardous, infdous, or radioactive wastes in municipal solid waste landfills, as well as in dedicated hazardous waste landfills. USEPA has coIlclucted studies to show that there has been a noticeable, but slight, improvement in landfill l e a b after Subtitle C was enforced. RCRA
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Subtitle D regulations were promulgated in October 1993, which stated the detailed requirements for composite liners, final cover caps, leachate collection and dlsposal systems, groundwater monitoring, and methane gas extraction, among other items for municipal solid waste facilities. The leachate from these newer lined landfills must be continuously withdrawn and has shown a considerable improvement over the quahty of leachate from the older unhed landfills.
Prior to Subtitle D, sanitary landfills were built without any bottom liners, or with clay liners alone - mostly without leachate extraction systems. Final cover systems were not designed to be impermeable to any great degree. Therefore, rainfall umtinues to saturate the waste materials, and simply gravitates to the bottom, where the leachate may remain for decades before eventual percolation into the ground (and groundwater table) below. Solids are concentrated in this leachate “pool”, and under very anaerobic conditions can only decompose to a small degree. If water percolates into the ground leaving solids behind, the leachate is concentrated to such a degree that if it were pumped out, it would surely fit the description of “black ooze”.
As of October 1993, all new landfills to be designed or constructed must follow Subtitle D requirements. There are numerous details for the design of solid waste landfills (and dedicated monofills) in these new regulations, the most noticeable of which include both the bottom
. composite liner and the final cover cap systems. Example of these two systems- are shorn in Figures 1 and 2, attached. In Figure 1, perforated leachate collection pipes in the upper sand layer collect leachate and transport it to submersible pumping stations andor gram sewers, that transport it to the equalization basin. It is understandable why, after being filtered by 2 feet of sand, a double filter fabric layer, crushed stone and an additional fabric layer around the perfi>rated pipe, the leachate from this system is noticeably lower in TSS concentrations than from unlined landfills. Likewise, Figure 2 shows how much more impermeable the cover cap system is now, which completely cuts off any additional rainwater infiltration after the landfill cell is capped and closed out.
PRE-SUBTITLE D LEACHATE QUALITY
The qualay of leachate from unlined landfills, both pre- and post- Subtitle C, has been documented in a few articles and reports by Federal, municipal, and private agencies. This data is assimilated from lab analyses from samples taken either at the outlets of a very few drainage systems, or from specially installed extraction wells. The characteristics of this leachate fiom hur of these sources is tabulated in Table 1, which shows the ranges and averages of parameter values recorded. Obviously, the leachate pollutants reported varied in extremely wide ranges, with upper values 100 to 500 times greater than typical domestic sewage. Such concentfated wastewater could hardly be discharged to municipal wastewater treatment plants without considerable pretreatment - most likely to a level of seumdary treatment, with chemical precipitation in addition! Some of the lower ends of the ranges do appear to be quite low, but these may be only isolated cases, from groundwater monitoring wells located some distance away from the associated landfills. However, this data is from landfills across the U.S., old and younger alike, large and small - with “average” leachate characteristics high enough to cause much concern to P O W operators.
LINED LANDFILL LEACHATE QUALITY
The quality of leachate from newer lined landfill facilities has been improving greatly over the past two decades - whether or not the landfills were designed under Subtitle D guidelines. The main reasons for this quahty improvement are as follows:
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1. Source Control Regulations - Federal (Subtitle C and others), state and individual authority regulations have been enacted which do not allow toxic andor hazardous wastes (whether fiom industrial, commercial, or residential sources) to be disposed in municipal solid waste landfills, which has greatly reduced the possibllrty of leachate containing high concentrations of these materials.
2. Recychg Efforts - State and local authorities have continued to mcmse &rts to recycle and recover more solid waste resources, which keeps these materials out of the landfills.
3. Subtitle D Design Requirements - Impermeable battom liners have kept grouudwater fiom hfiltrating into the leachate flow stream; the new composite liner system filters out so much material and keeps it in the landfill itselfthat suspended solids concentrations (and hence metals, as well) have decreased appreciably; and the final cap system is impermeable enough that the majonty of any additional rainwater is kept out of the landfill after the cells are closed.
4. Continuous Leachate Withdrawal - Since leachate is now required to be continuously withdrawn from the active and closed cells, alike, the leachate does nat “stagnate” in an
. anaerobic environment, and become more concentrated with time.
Leachate pollutant characteristics from three representative lined landfills m North Carolina are presented in Table 2. These are three dif€erent sized landfills, both private and municipally owned and operated, with one operated and capped before Subtitle D regulations were promulgated m 1993. The only constituents that appear to be higher than concentrations allowed by most P O W pretreatment programs are BOD, COD, ammonia, and zinc fiom the New h o v e r County landfill. However, the high BOD and COD readings only appeared between the 4th and 5th year of operation; the high zinc figure only occurred m year 4 of operation, with all other results below 1 .OO mg/l. The higher ammonia nttrogen levels only appeared a h r the 9th year of Operation; and this cell was closed after the 5th year of operation. m e ather two landfills have been discharging to nearby P O W s for over 4 years each, with little to no pretreatmeat. Also shown on Table 2 are typical raw wastewater and urban stomwater runoff pollutant cc3ncentration ranges. One can easily see that the leachate fiom more recent lined landfills in North Carolina more closely resembles “graywater” (raw municipal wastewater) than the “black ooze” of the older unlined landfills.
LEACHATE QUANTITY ESTIMATES
In amrdauce with Subtitle D regulations, leachate collection underdrains must be designed to hydraulically handle the flows generated by a 25-year, 24hour storm event. However, average daily flowrates fiom lined N.C. landfills, with equalization fhcilities, generally have not exceeded a range of 10-25,000 gallons per day on a monthly average. The quant&y of leachate geuerate by municipal solid waste landfills is highly variable and dependent on such fslctors as;
amount and intensay of precipitation temperature
a humidrty a type of vegetation and cover material characteristics
moisture content of solid waste landfilled landfill operations, especially stormwater management
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As the landfill ages, leachate quantities are expected to fluctuate with the variation in landfill depth and working fice area. Seasonal variation in leachate quantities are anticipated throughout the year. Leachate quantities generated are expected to decrease as areas of the landfill are filled to capacity with soils of low permeability and vegetation. Projected leachate quantities for the new landfills can be estimated using the Hydrologic Evaluation of Landfill Performance (HELP) computer model developed by the U.S. h y Corps of Engineers. The quantity of leachate generated during various stages of landfill development to determine average and peak flow rates is calculated using five year rainfall data from the nearest North Carolina gauging station. It was further assumed that very little surface water runoff from active areas would find its way into the leachate collection system, and that all penetrating rainfill will percolate through the various landfill layers. This assumption requires that adequate stormwater diversion berms be maintained throughout landfill operations.
In order to accommodate the fluctuation in flows depending on weather conditions and landfill operations, as well as to provide a uniform flow to the treatment plant, on-site leachate storage should be provided. The size of the storage pond will depend on the maximum allowable flowrate to the wastewater treatment facilities and collection system; pumping station capacrty; site
. limitations; and maximum period of time for emergency storage required by permit.
STATE REGULATIONS
A guidance memorandum for landfill leachate disposal has been created by the North Carolina Division of Water Q u a l t t y . Several options for leachate disposal are discussed and prioritized according to preference by the State for implementation. The most desired option is to dispose of the leachate at the nearest POTW by connection to the nearest collection system with a dedicated pumping station and force main. Ifthe truck and haul alternative must by used in the early years of landfill operation, the State will permit this as a temporary alternative only. The least favorable option is a 111 tertiarytreatment plant with discharge to a surfsce water under a NPDES permit. The other alternatives discussed are recirculation, treatment with subsurface disposal, and treatment with spray irrigation.
However, recirculation (the practice of pumping the stored leachate back into the active landfill cell(s), by surface spraying, subsurface piping, or percolation ponds) has rarely proven to be effective as anything more than just a means of pretreatment - using the landfill itself as a large anaerobic reactor. There are cases within North Carolina, unfortunately, where recirculation was designed to be the ulthate disposal option; but due to weather conditions, reduced evapotranspiration capacities of new landfill cells, etc. large volumes of excess stored leachate must be regularly trucked away for ukimate disposal at nearby POTW’s. Sewndary treatment is usually required before spray irrigation or subsurface disposal. Advanced or tertiary treatment will most likely be required before discharge to a surfsce water.
Several other states have very similar regulations and/or guidelines which encourage discharge to a municipal sewage wllection/treatment system, if within feasible distance - with or without pretreatment. In order to obtain a permit to operate a new landfill in Pennsylvania, the Department of Environmental Resources waste management permitting requirements state that “Direct discharge to a POTW or other permitted treatment ficllay must be considered and proven “not practicable” before any other option can be selected.”
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EFFECT ON WWTP'S
Only a few studies have been made to determine the long-tern effects of leachate from older unlined landfills on typical municipal wastewater treatment hcilities. High strength pollutants in leachate can disrupt a plant's treatment processes, resulting in non-compliance with discharge permits, or can adversely impact sludge disposal. Some earlier studies of moderate to large sized POTW's which processed pre-Subtitle D landfill leachate stated that the only noticeable effect on typical P O W ' S using an activated sludge process was sludge bulking in the final clarifiers. No data was available on the effect on these plants' sludge dtsposal programs.
The impact of leachate from new lined landfills on typical POTW's has apparently been quite minor nationwide. In North Carolina, the concentrations of most pollutants, as seen from Table 2, are quite close to typical domestic wastewater. Some parameter concentrations may be relatively high; however, on a mass loadmg basis, these same leachate pollutants can be shown to be less than 2% to 5% of the average daily loading of the pollutant to the P O W from all other sources. If a specific pollutant is 10 times greater in the leachate flowstream of 15,000 gpd than the average influent concentration to a 15 mgd P O W , the mass loading of that pollutant from the leachate is only 1% of the total loading to the plant. The most likely impact to the P O W will be to its sludge
regulating authority must review its recent history of various parameters in its biosolids as well as in its plant influent when establishing pretreatment permit limits.
. disposal program, where solids (and metals) are collected and con-. Therefore, the
TYPICAL NC PRETREATMENT PERMIT LIMITS
As of the end-of 1995, there were approximately 20 landfills in North Carolina that were discharging their leachate into nearby municipal WWTP's. Almost all of these were issued a pretreatment permit prior to disposal, with parameter limits that varied fiom permit to permit. However, most of the limits established for each permit were similar in value for similar parameters, but varied widely on types of pollutants regulated andor the units of measurement. Some permit limitations were presented as maximum allowable concentrations (in mg/l), while others were listed as maximum daily loadings (in lbdday).
The pretreatment limitations for leachate from three municipal permits issued within the past two years are presented in Table 3. These three permits are for a low, moderate, and high flowrate condition; for one private and two wunty landfill hcilities; and for three diflkrent levels of required pretreatment. The three receiving POTW's are either moderate or large sized hcilities. The limits are very similar for organic constituents, but vary somewhat for metals - with the lower limits for the higher flowrate permit, where the leachate is a higher percentage of the POTW's average influ& flowrate.
TYPICAL LEACHATE PRETREATMENT
Several of the roughly 20 landfills in North Carolina which discharge their leachate to POTW's have full secondary treatment plants after the equalimtion basins - but very few of these ever use the pretreatment plants on a regular, mandated basis. Many of the landfills that do have these pretreatment hcilities are privately owned and operated. Following is a tabulation of the major issues that should be considered by a municipahty when formulating a pretreatment permit for a neighboring landfill leachate;
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1 . Stormwater Management - The need for effective stormwater segregation using tarps or temporary earthen berms within the active landfill cells cannot be overemphasized. Leachate volumes can be 3 to 5 times the expected levels after a storm event without good stormwater management during normal landfill operations.
2. Equalization - Leachate storage basins are a must to equalize flowrates from the facillty to the POTW after storm events. However, these basins not only provide temporary storage, but can also provide the following added benefits:
a. Mixing - By induced currents from wind and influent velocities, or mechanical mixers. b. Constant Quallty - With a large enough basin, fluctuations in influent leachate quahty will
not be seen at the POTW. c. Reduced Odors - An open storage basin can provide some mixing and aeration to keep odors
to a minimum - both at the storage basin and within the sewage collection system receiving the leachate.
d. Aerobic Conditions - With some aeration provided to the basin, the leachate itself will tend to remain aerobic and stabilized.
. 3. Mechanical Aeration - Floating mechanical aerators can easily be added to open equalization basins, at minimum cost, low maintenance, and low power requirements. These aerators will provide the mixing and aeration required to keep the leachate at a fairly constant quallty, to reduce odors, and to maintain aerobic, stabilized conditions.
4. Flow Meters - Flow meters should be installed at the landfill site fbr record purposes, whether the leachate is pumped to a force main or a truck loading station.
5 . Sampler - A weatherproof, refiigeerated automatic sampler can easily be added at the site to monitor effluent qualrty, provided by either the landfill owner, or the POTW authonty on a periodic schedule.
6. Emergency pH Adjustment - There should be a manhole, pump or dedicated location m the leachate effluent path where specific chemicals could be added in an emergency situation to adjust pH before discharge to the P O W .
7. Future Pretreatment - A specific location should be identified and designed accordingly where a pretreatment plant could be added to the leachate f l o w s t m imen needed in the future.
8. Contingency Plans - Contingency plans should be identified for emergency conditions when discharge to the sewage collection system must be temporarily disrupted, which may include any of the following possible options;
a. Short-term on-site storage b. Temporary recirculation c. Pump and haul to an alternate WWTP d. Lease a non-discharge type treatment plant (such as an evaporation facillty, ifflowrates are
e. Lease a pretreatment plant (if quallty is the limiting factor) until a permanent facilrty can be low enough)
installed and made operational
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Leachate Collection Zone @ Dxainage Geocompoite (1)
60-mil Texwed HDPEGeomcmbrane
@ Compacted clay Liner Top Surface Must Be Smooth, Free of Rocks, Roots, or Debris
L60 MIL TEXTURED HDPE FML L24'' COMPACTED CLAY LINER
LEACHATE COLLECTION PIPE TRENCH DETAIL
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TABLE 1
LANDFILL LEACHATE CHARACTERISTICS FROM REPRESENTATIVE NATIONAL DATA
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TABLE 2 LEACHATE CHARACTERISTICS FROM
NORTH CAROLINA SUBTITLE D LINED LANDFILLS
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(1) Information provided by Rocky River WWTP, Concord. NC; Raw leachate quality for years 1 through 4 for the Charlotte Motor Speedway BFI Landfill
(2) Based on water quality data provided by New Hanover County Department of Environmental Management for samples collected from 1982 to 1991 from the raw leachate from Cell No. 1 : Cell No. 1 was opened in 1981 and capped in 1986.
(1) Buncombe County Sanitary landfill (Wc), north of Asheville, NC (Average Daily Limits)
(2) Charlotte Motor Speedway Development Corp. Sanitary landfill, in Cabarrus Co. (Average Daily Limits - calculated based on daily allowable loading limits)
(3) North Wake County Sanitary Landfill, north of Raleigh, NC (Maximum Daily Limits)
