methodology for site-specific risk assessment of
METHODOLOGY FOR SITE-SPECIFIC RISK ASSESSMENT OF LANDFILLING OF WASTE M. GODIKSEN*, J.B. HANSEN**, J. AABLING***, I. L. THERKILDSEN*** * DANISH WASTE ASSOCIATION, Vodroffsvej 59, 1, 1900 Frederiksberg C, Denmark
**SUSTAINABLE LANDFILL NETWORK, Vesterbrogade 149, 1620 Copenhagen, Denmark
***DANISH ENVIRONMENTAL PROTECTION AGENCY (EPA), Strandgade 29, 1401 Copenhagen, Denmark
SUMMARY: Currently, no acknowledged methodologies or tools for substantiating if and when a landfill site is converted to a state safe for the environment exist in Denmark. According to Danish waste legislation, the authorities are responsible for determining the extent of the aftercare period. However, no practices or techniques are available to ensure an accurate decision. Following paper covers a study applying the current best information to create a model, which will present the risk of landfilling waste in Denmark. The model includes a source strength model, the transportation of substances in soil and water, the impact in point of compliance, as well as the economic impact assessment of the model and its implementation.
1. INTRODUCTION It is unclear whether the current Danish Landfill Regulation assures an effective environmental protection. Present regulation is rather general and simply cover some parts of the waste landfilled. Therefore, the Danish waste industry seeks a qualified alternative to the regulation’s general requirements in order to implement an explicit and site-specific assessment of the environmental impacts concerning an individual landfill site. One of the biggest challenges the Danish landfill sites face is determining the extent of damage on the surroundings of each site. Especially, the prediction of the aftercare period is a difficult task. An essential part of the Danish legal requirements, i.e. the EPA act, states that all costs after a landfill site is full must be covered by the landfill rate, including closures and aftercare for 30 years (as a rule). Currently, no acknowledged methodologies or tools for substantiating when and whether a landfill site is converted to a state considered safe for the environment exist. According to the Danish waste regulation, the authorities are responsible for determining the extent of the aftercare period. However, no practices or techniques are available to ensure an accurate decision. In order to address the abovementioned technical challenges and economic uncertainties, an operational methodology is developed to complete a site-specific risk assessment of landfilling waste to meet the conditions of the surrounding soil, groundwater, and surface water. The methodology will be presented along with the preliminary results of the implementation, which are currently underway. The development of a methodology is divided into four sections: Source strength, transportation of contaminants, impact in point of compliance, i.e. POC, and economic impact assessment. All four sections have separate background reports and, moreover, none of the four sections are presently completed. The latter is the reason for which only the essence of the background reports Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
as well as preliminary methodologies and results will be addressed, since the project will in its natural form not fit the criteria of an article.
2. SOURCE STRENGTH Source strength includes developing an Excel-based model for estimating the flow of substances as a function of time based on site-specific parameters. It includes parameters and substances of interest, time schedule, and point of compliance (POC) on relevant substances, heterogeneous water flow in waste, formation of leachate, and release of contaminants into the environment. In case of a lack of site-specific parameters, a set of default values is modelled/estimated and can be used as a supplement. 2.1 Phase 1 − First-hand knowledge on the source strength First phase contains the collected knowledge and considerations forming the basis of following: § § § §
Set-up of conceptual models for source strength Set-up of the foundations for handling heterogeneous water flow in the waste Set-up of the foundations for determining e.g. the time frame in the model Set-up of the foundations for identifying relevant substances/groups of substances.
The objective is to collect existing knowledge on the different subjects for setting up a systematic overview of: § The operational situations, i.e. filling, aftercare and after aftercare period, which must be mod-
elled, and § Which concepts of water flowing at the landfill site are necessary. In addition, it is the objective to offer recommendations on: § § § §
If and possibly how heterogeneous water flow can be managed by applying the model The time frames relevant to consider in a risk assessment What substances possess a risk to soil, ground water, and surface water How to work with a site-specific choice of substances.
2.1.1 Suggestions for conceptual models The overall conceptual model for source strength is shown in Figure 1. Please see Table 2.1 for the description of different flows.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 1. Overall conceptual model for the source strength. Table 2.1: Short description of water flows Flow QI1
Type Rain
Comment Can be found via Danish Meteorological Institute or local weather stations. Estimation made based on historical data and geography. Typically uncontaminated.
QI2
Surface flow
Water from the surface of other areas that runs to the landfill. Calculated or estimated based on the catchment area and rain. Water from a creek/lake can make it difficult to estimate, since it may cause an over float of the landfill. Typically uncontaminated.
QI3
Inflow of clean water
The mass of water will typically be registered and is known. Uncontaminated.
QI4
Inflow of recirculated wa- The mass of water will typically be registered and is known. ter from the same unit Contains contaminated substances.
QI5
Inflow of recirculated wa- The mass of water will typically be registered and is known. ter from other units Contains contaminated substances.
QI6
Infiltration of ground water Will only happen if the bottom and the sides of the cell are sufficiently through the bottom and permeable and the hydraulic pressure of the ground water is sufficient. the sides Can be estimated based on a water balance. Typically uncontaminated but can be strained.
QI7
Infiltration of groundwater Can be estimated based on knowledge about the hydrogeological conthrough the bottom ditions and assumption about the waste’s permeability. Typically uncontaminated but can be strained.
QU 1
Leachate collected and re- The removed leachate is typically registered and is known. moved med drainage system from the cell/site
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
In Table 2.2, the different types of landfill in Denmark are presented: Scenario
1 1a
Description
Membraneand leachate collection system?
Phreatic surface
State
Above bottom
Aftercare
QU 2
No
Beneath bottom
Aftercare or after aftercare No activity, vertical infiltrated water flow
QU 2
Landfill unit or controlled dump site
Yes
Beneath or above bottom
After aftercare = No activity Bathtub-effect after the end of leachate collection
QU 2 + QU 4
Landfill unit or controlled dump site
Yes
Above bottom
Aftercare. Inwardpointing gradient
No outflow
Above bottom
Aftercare or after aftercare Primarily horizontal groundwater flow
QU 2 + QU 3
Landfill unit
Yes
Uncontrolled dump site or landfill unit with reduced standards
2
3 4
Source strength volume
Uncontrolled dump site or landfill unit with reduced standards
No
Following table shows the connection between a landfill site’s location and the Phreatic surface, State and Scenario.
Type of Landfill
Before activity: Planning and extensions Relevant scenarios
Activity: Filling and aftercare Relevant scenarios
After Activity: Relevant scenarios
Landfill with a bottom above the Phreatic surface
1, 2
1
2
Landfill with a bottom beneath the Phreatic surface
3, 2
3
2
Regarding leaching of substances, following models for flux of substances are given for each scenario: Scenario 1:
K(t) = QU2(t) x C(t) M(t) = ((QU1 – QI4) + QU2) x C(t)
Scenario 1a:
K(t) = QU2(t) x C(t) M(t) = K(t)
Scenario 2:
K(t) = (QU2(t) + QU4(t)) x C(t), idet QU1 = QI4 = QI5 = 0 M(t) = (QU2(t) + QU4(t)) x C(t)
Scenario 3:
K(t) = 0 x C(t) = 0 M(t) = (QU1 – QU4) x C(t)
Scenario 4:
K(t) = (QU2(t) + QU3(t)) x C(t) M(t) = K(t)
M(t) describes the mass of a given substance, which at time t is collected and removed with the
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
leachate. Further, the source strength K(t) in relation to a risk assessment is part of M(t), which release or potentially release the surroundings. Time t can be converted to a fluid-/solid substance ratio (L/S) for a given landfill unit. L/S = t x I/(d x H), in which: t is the time spend since the beginning of leachate production (years), L is the total volume of leachate produced at time t (cubic metres), S is total dry weight of landfilled waste (tonnes), d is the average dry weight filling of landfilled waste (tonnes), H is the height of landfill site (metres), I is infiltration of rain at the landfill unit (metre/year). Hereafter, the concentration of substances is given by C(t) in the produced leachate and is defined as exponentially decreasing by the following function: C(L/S) = C0 x exp(-(L/S) x κ), in which: C(L/S) is the concentration of a given substance in the leachate as a function of L/S (mg/l). C0 is the starting concentration, i.e. the highest introductory concentration of the substance in the leachate (mg/l). L/S is the accumulated fluid-/solid substance ratio that corresponds to the concentration C (l/kg). κ is the first order constant that describes the speed by which the concentration is decreasing as a function of L/S for a given material (kg/l). It is recommended to employ the abovementioned models in the overall model.
2.1.2 Suggestions for managing heterogeneous water flow It is suggested that phase two describes the water-/leachate flow through the waste based on three parameters: total volume of the waste with a fast flow and flow speed/time constants for the matrices for the channels/”cracks”. Furthermore, it is suggested that the leaching of substances is described by a simplified exponentially decreasing concentration of substances in time, in which the dependence of L/S is decreasing over time.
2.1.3 Suggestions for handling time and POC Since risk assessment for landfilling of waste needs to be site-specific, it is suggested that POC is determined with a great amount of flexibility. As a result, local conditions as well as a time frame can be considered. By default, the time frame should be dependent on both the distance to POC and the size of the unsaturated zone. The following time frames are advised when modelling the risk assessment: Distance to POC 0 – 100 m More than 100 m
Size of unsaturated zone (m) 0-2 More than 2 500 years 1,000 years 1,000 years 1,000 years
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2.1.4 Suggestions for substances/groups of substances that should be included in a risk assessment A meticulous selection of a methodology has been made and the following table contains the general list of substances. The list is compiled as a result of a general knowledge about the appearance of substances in the waste landfilled in Denmark along with the appearance in the leachate collected. Besides, the mobility of the substances as well as the general environmental criteria are considered. All the substances ought to be assessed on the specific site, and it may be necessary to add additional substances that are found relevant. Substance
Closed or uncontrolled dump site
Ammonium
Controlled land- Units for inert fill and landfill waste units for mixed waste
Units for mineral waste
Units for shredder waste
X
X
X
a
X
X
X
X
Arsenic (As)
X
X
X
X
X
Atrazine
X
X
a
X
X
X
X
X
b
b
Antimony (Sb)
Barium (Ba)
X
Benz(a)pyrene
X
Benzene
X
X
X
X
X
b
X
Bisphenol A
X
Lead (Pb)
X
a,b
X
b
X
b
b
Boron
X
Cadmium (Cd)
X
a,b
b
b
X
COD
BI5/BOD
X
b
X
X
b
b
X
X
b
X
X
b
X
DOC/NVOC
X
X
X
X
X
Phenol
X
X
X
X
X
X
X
X
X
Fluoride (F )
X
a
X
X
X
X
Iron, dissolved
X
X
X
Potassium (K)
X
X
X
Chlorobenzene
X
X
Chloroprene
X
Fluoranthene -
X
b
b
-
Chloride (Cl )
X
a
X
X
X
X
Copper (Cu)
X
a
X
X
X
X
Chromium (Crtotal)
X
a
X
X
X
X
Mercury (Hg)
X
b
X
X
a,b
X
b
X
X
MCPP
X
X
Molybdenum (Mo)
X
a
X
X
X
X
Naphthalene
X
X
X
X
Sodium (Na)
X
X
X
Nickel (Ni)
a
X
X
X
X
X
Manganese (Mn)
Nonylphenol
X
b
X
b
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Substance
Closed or uncontrolled dump site
Controlled land- Units for inert fill and landfill waste units for mixed waste
Units for mineral waste
Units for shredder waste
Selenium (Se)
X
a
X
X
X
X
2Sulphate (SO4 )
X
X
X
X
X
Total-P
X
X
Trichloroethylene
X
X
Vanadium (V)
X
Zinc (Zn)
a,b
b
b
X
X
b
X
X
b
X
a: If the objective is to conduct a general risk assessment, the substances convey. However, it is not the case if the objective is to assess whether a short-term need for an effort exists. b: Solely if POC is surface water in a distance smaller than 50 m from the landfill site will the substances convey. Landfills receiving hazardous waste hold a slightly different list for which following substances must be included at all times: As, Ba, Cr, Cu, Mo, Ni, Sb, Se, Chloride, fluoride, sulphate, phenol, DOC/NVOC. If a landfill is located right next to the receptor, the list is expanded with Cd, Hg, Pb and Zn. Based on a site-specific knowledge about the waste − including knowledge about the leachate and other substances − an assessment about whether a set of different substances is necessary.
2.2 Phase 2 − Components to the source strength model The second phase presents primarily the following four parts: § § § §
Basic information and conditions Release of contaminated substances from the waste Leachate production Release of leachate into the surroundings
Thereby, the second phase is concerned with how to apply the source strength model and under what circumstances. The optimal use of the model includes having good reliable data for a large time period. However, it is a possibility to apply the model if only a small amount of data or even no data is available. A set of careful and conservative default values are estimated to make sure all landfills can employ the model to conduct a risk assessment analysis.
3. TRANSPORTATION OF CONTAMINANTS The mixing and dilution of contaminant in streams was investigated for six representative configurations with a dedicated mixing/dilution model, ranging from small streams with low flows to large streams with high flows. For generalisation, the simulations and consequent observations were confronted to a more general Monte Carlo simulation and led to similar conclusions. Looking at landfill leachate plumes, the mixing distance, i.e. the point for which concentration is
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
fully mixed, is found beyond the administrative mixing zone almost every time. The concentration at the edge of such mixing zone is often lower than other important concentration indicators, e.g. the maximum concentration or fully mixed concentration, particularly for the narrow small streams. For aforementioned streams, the mixing zone is relatively small compared to the zone, where the contaminant is discharging a significant build-up of pollutant still occurring downstream. Arbitrarily defined from literature in present paper, the mixing distance is dependent on the stream geometry, flow rate and, at the same time, influenced by the location of the plume discharge into the stream as well as its dimension for a given contaminant mass discharge. For a plume approximately 200 m large, mixing distances up to 400-500 m from the upstream point of the plume can be expected.
Certain simulations carried out for the three tested landfills and substances indicated that the concentrations estimated in large and medium streams were generally complying with the relevant quality criteria indicators due to an important dilution factor. The observation cannot be generalised to all substances, since it is dependent on both the amount of contaminant discharging and the strictness of the associated requirement. In the matter of small streams, it appears problematic for several of the tested substances, e.g. iron in Hørløkke, nitrogen in Tandskov, due to the low dilution achieved in the streams. Thus, it can be anticipated that it will be dependent on their presence in leachates for other compounds. Undoubtedly, the discharge of ammonium / nitrogen from landfills appears as a major issue due to the quantity released (Christensen et al., 2001) combined to stringent requirements and contribution from other important sources such as agriculture and fishing operations.
4. IMPACT IN POINT OF COMPLIANCE (POC) The objective is to compile a guide regarding how to meet the guidelines of following: § Designation and determination of receptor. § Mixing of leachate or leachate contaminated ground water in surface water caused by leaking
through a contaminant front. § Assessment of the impact in the receptor and observance of requirements, criteria, and environmental targets. Receptors relevant to consider when making a risk assessment are defined as follows: § Ground water § Surface water § Natura 2000 areas
If within 250 metres of the lump site, uncontrolled dump sites may constitute a higher risk of bringing contaminant into the surface water. Even though soil is not defined as a receptor in present paper, it can be one due to the fact that the risk assessment focuses on the leaking of leachate and not the risk of using the area. POC for ground water is determined by following criteria: § Legislation
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
§ § § § § § §
Location of landfill units and the leachate collection wells Hydrogeological conditions Distance to closest receptor both vertically and horizontally Site-specific risk Purpose of ground water monitoring Purpose of avoiding contamination Necessary reaction time in case of a threatening contaminant
POC for surface water and Natura 2000 areas must not suffer a reduction in environmental standards, and different districts monitoring water standards and focus areas exist. According to the regulation, a leak from a landfill site is defined as a leak from a point in order for authorities to point out a mixing zone around the starting point of the leak.
5. ECONOMIC IMPACT ASSESSMENT The implementation of the model will induce an economic effect. Therefore, the financial section will focus on the operational economic impact on each specific landfill site based on the sitespecific risk assessment obtained from the previous described sections. Currently, the go-to aftercare period at Danish landfills are 30 years. However, present project strongly emphasises that the period of 30 years is simply too short, and the economic consequences are vast. After the project’s technical end, it will include an analysis of the economic impact the implementation of new knowledge will have. The focus is restricted to the landfills’ economies but will not be limited, since landfills in Denmark are owned by the municipalities. Thus, the national economy will face a negative challenge.
6. CONCLUSIONS Presently, no final conclusions from the study can be reached. The project’s steering group consists of agents from all three cooperative partners, who will reach the final conclusions at the end of the study. At the conference, a presentation of the preliminary conclusions will be presented. Nevertheless, it is certain that not all sections of the project will be finalised in time. Present paper will function as a small teaser for Sardinia 2019 Conference, in which a set of final conclusions have been reached and some of the tools have been implemented.
AKNOWLEDGEMENTS COWI A/S Danish Waste Solutions ApS DTU Environment Danish Environmental Protection Agency Rambøll Energy research Centre of the Netherlands Reno Djurs I/S Odense Renovation A/S
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
AV Miljø.
REFERENCES The Environmental Protection Act § 50 a. Christensen, T. H., Kjeldsen, P., Bjerg, P. L., Jensen, D. L., Christensen, J. B., Baun, A., … Heron, G. (2001): Biogeochemistry of landfill leachate plumes. Applied Geochemistry, 16(7-8), 659–718. doi:10.1016/S0883-2927(00)00082-2
SUMMARY: Currently, no acknowledged methodologies or tools for substantiating if and when a landfill site is converted to a state safe for the environment exist in Denmark. According to Danish waste legislation, the authorities are responsible for determining the extent of the aftercare period. However, no practices or techniques are available to ensure an accurate decision. Following paper covers a study applying the current best information to create a model, which will present the risk of landfilling waste in Denmark. The model includes a source strength model, the transportation of substances in soil and water, the impact in point of compliance, as well as the economic impact assessment of the model and its implementation.
1. INTRODUCTION It is unclear whether the current Danish Landfill Regulation assures an effective environmental protection. Present regulation is rather general and simply cover some parts of the waste landfilled. Therefore, the Danish waste industry seeks a qualified alternative to the regulation’s general requirements in order to implement an explicit and site-specific assessment of the environmental impacts concerning an individual landfill site. One of the biggest challenges the Danish landfill sites face is determining the extent of damage on the surroundings of each site. Especially, the prediction of the aftercare period is a difficult task. An essential part of the Danish legal requirements, i.e. the EPA act, states that all costs after a landfill site is full must be covered by the landfill rate, including closures and aftercare for 30 years (as a rule). Currently, no acknowledged methodologies or tools for substantiating when and whether a landfill site is converted to a state considered safe for the environment exist. According to the Danish waste regulation, the authorities are responsible for determining the extent of the aftercare period. However, no practices or techniques are available to ensure an accurate decision. In order to address the abovementioned technical challenges and economic uncertainties, an operational methodology is developed to complete a site-specific risk assessment of landfilling waste to meet the conditions of the surrounding soil, groundwater, and surface water. The methodology will be presented along with the preliminary results of the implementation, which are currently underway. The development of a methodology is divided into four sections: Source strength, transportation of contaminants, impact in point of compliance, i.e. POC, and economic impact assessment. All four sections have separate background reports and, moreover, none of the four sections are presently completed. The latter is the reason for which only the essence of the background reports Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
as well as preliminary methodologies and results will be addressed, since the project will in its natural form not fit the criteria of an article.
2. SOURCE STRENGTH Source strength includes developing an Excel-based model for estimating the flow of substances as a function of time based on site-specific parameters. It includes parameters and substances of interest, time schedule, and point of compliance (POC) on relevant substances, heterogeneous water flow in waste, formation of leachate, and release of contaminants into the environment. In case of a lack of site-specific parameters, a set of default values is modelled/estimated and can be used as a supplement. 2.1 Phase 1 − First-hand knowledge on the source strength First phase contains the collected knowledge and considerations forming the basis of following: § § § §
Set-up of conceptual models for source strength Set-up of the foundations for handling heterogeneous water flow in the waste Set-up of the foundations for determining e.g. the time frame in the model Set-up of the foundations for identifying relevant substances/groups of substances.
The objective is to collect existing knowledge on the different subjects for setting up a systematic overview of: § The operational situations, i.e. filling, aftercare and after aftercare period, which must be mod-
elled, and § Which concepts of water flowing at the landfill site are necessary. In addition, it is the objective to offer recommendations on: § § § §
If and possibly how heterogeneous water flow can be managed by applying the model The time frames relevant to consider in a risk assessment What substances possess a risk to soil, ground water, and surface water How to work with a site-specific choice of substances.
2.1.1 Suggestions for conceptual models The overall conceptual model for source strength is shown in Figure 1. Please see Table 2.1 for the description of different flows.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 1. Overall conceptual model for the source strength. Table 2.1: Short description of water flows Flow QI1
Type Rain
Comment Can be found via Danish Meteorological Institute or local weather stations. Estimation made based on historical data and geography. Typically uncontaminated.
QI2
Surface flow
Water from the surface of other areas that runs to the landfill. Calculated or estimated based on the catchment area and rain. Water from a creek/lake can make it difficult to estimate, since it may cause an over float of the landfill. Typically uncontaminated.
QI3
Inflow of clean water
The mass of water will typically be registered and is known. Uncontaminated.
QI4
Inflow of recirculated wa- The mass of water will typically be registered and is known. ter from the same unit Contains contaminated substances.
QI5
Inflow of recirculated wa- The mass of water will typically be registered and is known. ter from other units Contains contaminated substances.
QI6
Infiltration of ground water Will only happen if the bottom and the sides of the cell are sufficiently through the bottom and permeable and the hydraulic pressure of the ground water is sufficient. the sides Can be estimated based on a water balance. Typically uncontaminated but can be strained.
QI7
Infiltration of groundwater Can be estimated based on knowledge about the hydrogeological conthrough the bottom ditions and assumption about the waste’s permeability. Typically uncontaminated but can be strained.
QU 1
Leachate collected and re- The removed leachate is typically registered and is known. moved med drainage system from the cell/site
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
In Table 2.2, the different types of landfill in Denmark are presented: Scenario
1 1a
Description
Membraneand leachate collection system?
Phreatic surface
State
Above bottom
Aftercare
QU 2
No
Beneath bottom
Aftercare or after aftercare No activity, vertical infiltrated water flow
QU 2
Landfill unit or controlled dump site
Yes
Beneath or above bottom
After aftercare = No activity Bathtub-effect after the end of leachate collection
QU 2 + QU 4
Landfill unit or controlled dump site
Yes
Above bottom
Aftercare. Inwardpointing gradient
No outflow
Above bottom
Aftercare or after aftercare Primarily horizontal groundwater flow
QU 2 + QU 3
Landfill unit
Yes
Uncontrolled dump site or landfill unit with reduced standards
2
3 4
Source strength volume
Uncontrolled dump site or landfill unit with reduced standards
No
Following table shows the connection between a landfill site’s location and the Phreatic surface, State and Scenario.
Type of Landfill
Before activity: Planning and extensions Relevant scenarios
Activity: Filling and aftercare Relevant scenarios
After Activity: Relevant scenarios
Landfill with a bottom above the Phreatic surface
1, 2
1
2
Landfill with a bottom beneath the Phreatic surface
3, 2
3
2
Regarding leaching of substances, following models for flux of substances are given for each scenario: Scenario 1:
K(t) = QU2(t) x C(t) M(t) = ((QU1 – QI4) + QU2) x C(t)
Scenario 1a:
K(t) = QU2(t) x C(t) M(t) = K(t)
Scenario 2:
K(t) = (QU2(t) + QU4(t)) x C(t), idet QU1 = QI4 = QI5 = 0 M(t) = (QU2(t) + QU4(t)) x C(t)
Scenario 3:
K(t) = 0 x C(t) = 0 M(t) = (QU1 – QU4) x C(t)
Scenario 4:
K(t) = (QU2(t) + QU3(t)) x C(t) M(t) = K(t)
M(t) describes the mass of a given substance, which at time t is collected and removed with the
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
leachate. Further, the source strength K(t) in relation to a risk assessment is part of M(t), which release or potentially release the surroundings. Time t can be converted to a fluid-/solid substance ratio (L/S) for a given landfill unit. L/S = t x I/(d x H), in which: t is the time spend since the beginning of leachate production (years), L is the total volume of leachate produced at time t (cubic metres), S is total dry weight of landfilled waste (tonnes), d is the average dry weight filling of landfilled waste (tonnes), H is the height of landfill site (metres), I is infiltration of rain at the landfill unit (metre/year). Hereafter, the concentration of substances is given by C(t) in the produced leachate and is defined as exponentially decreasing by the following function: C(L/S) = C0 x exp(-(L/S) x κ), in which: C(L/S) is the concentration of a given substance in the leachate as a function of L/S (mg/l). C0 is the starting concentration, i.e. the highest introductory concentration of the substance in the leachate (mg/l). L/S is the accumulated fluid-/solid substance ratio that corresponds to the concentration C (l/kg). κ is the first order constant that describes the speed by which the concentration is decreasing as a function of L/S for a given material (kg/l). It is recommended to employ the abovementioned models in the overall model.
2.1.2 Suggestions for managing heterogeneous water flow It is suggested that phase two describes the water-/leachate flow through the waste based on three parameters: total volume of the waste with a fast flow and flow speed/time constants for the matrices for the channels/”cracks”. Furthermore, it is suggested that the leaching of substances is described by a simplified exponentially decreasing concentration of substances in time, in which the dependence of L/S is decreasing over time.
2.1.3 Suggestions for handling time and POC Since risk assessment for landfilling of waste needs to be site-specific, it is suggested that POC is determined with a great amount of flexibility. As a result, local conditions as well as a time frame can be considered. By default, the time frame should be dependent on both the distance to POC and the size of the unsaturated zone. The following time frames are advised when modelling the risk assessment: Distance to POC 0 – 100 m More than 100 m
Size of unsaturated zone (m) 0-2 More than 2 500 years 1,000 years 1,000 years 1,000 years
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
2.1.4 Suggestions for substances/groups of substances that should be included in a risk assessment A meticulous selection of a methodology has been made and the following table contains the general list of substances. The list is compiled as a result of a general knowledge about the appearance of substances in the waste landfilled in Denmark along with the appearance in the leachate collected. Besides, the mobility of the substances as well as the general environmental criteria are considered. All the substances ought to be assessed on the specific site, and it may be necessary to add additional substances that are found relevant. Substance
Closed or uncontrolled dump site
Ammonium
Controlled land- Units for inert fill and landfill waste units for mixed waste
Units for mineral waste
Units for shredder waste
X
X
X
a
X
X
X
X
Arsenic (As)
X
X
X
X
X
Atrazine
X
X
a
X
X
X
X
X
b
b
Antimony (Sb)
Barium (Ba)
X
Benz(a)pyrene
X
Benzene
X
X
X
X
X
b
X
Bisphenol A
X
Lead (Pb)
X
a,b
X
b
X
b
b
Boron
X
Cadmium (Cd)
X
a,b
b
b
X
COD
BI5/BOD
X
b
X
X
b
b
X
X
b
X
X
b
X
DOC/NVOC
X
X
X
X
X
Phenol
X
X
X
X
X
X
X
X
X
Fluoride (F )
X
a
X
X
X
X
Iron, dissolved
X
X
X
Potassium (K)
X
X
X
Chlorobenzene
X
X
Chloroprene
X
Fluoranthene -
X
b
b
-
Chloride (Cl )
X
a
X
X
X
X
Copper (Cu)
X
a
X
X
X
X
Chromium (Crtotal)
X
a
X
X
X
X
Mercury (Hg)
X
b
X
X
a,b
X
b
X
X
MCPP
X
X
Molybdenum (Mo)
X
a
X
X
X
X
Naphthalene
X
X
X
X
Sodium (Na)
X
X
X
Nickel (Ni)
a
X
X
X
X
X
Manganese (Mn)
Nonylphenol
X
b
X
b
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 Substance
Closed or uncontrolled dump site
Controlled land- Units for inert fill and landfill waste units for mixed waste
Units for mineral waste
Units for shredder waste
Selenium (Se)
X
a
X
X
X
X
2Sulphate (SO4 )
X
X
X
X
X
Total-P
X
X
Trichloroethylene
X
X
Vanadium (V)
X
Zinc (Zn)
a,b
b
b
X
X
b
X
X
b
X
a: If the objective is to conduct a general risk assessment, the substances convey. However, it is not the case if the objective is to assess whether a short-term need for an effort exists. b: Solely if POC is surface water in a distance smaller than 50 m from the landfill site will the substances convey. Landfills receiving hazardous waste hold a slightly different list for which following substances must be included at all times: As, Ba, Cr, Cu, Mo, Ni, Sb, Se, Chloride, fluoride, sulphate, phenol, DOC/NVOC. If a landfill is located right next to the receptor, the list is expanded with Cd, Hg, Pb and Zn. Based on a site-specific knowledge about the waste − including knowledge about the leachate and other substances − an assessment about whether a set of different substances is necessary.
2.2 Phase 2 − Components to the source strength model The second phase presents primarily the following four parts: § § § §
Basic information and conditions Release of contaminated substances from the waste Leachate production Release of leachate into the surroundings
Thereby, the second phase is concerned with how to apply the source strength model and under what circumstances. The optimal use of the model includes having good reliable data for a large time period. However, it is a possibility to apply the model if only a small amount of data or even no data is available. A set of careful and conservative default values are estimated to make sure all landfills can employ the model to conduct a risk assessment analysis.
3. TRANSPORTATION OF CONTAMINANTS The mixing and dilution of contaminant in streams was investigated for six representative configurations with a dedicated mixing/dilution model, ranging from small streams with low flows to large streams with high flows. For generalisation, the simulations and consequent observations were confronted to a more general Monte Carlo simulation and led to similar conclusions. Looking at landfill leachate plumes, the mixing distance, i.e. the point for which concentration is
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
fully mixed, is found beyond the administrative mixing zone almost every time. The concentration at the edge of such mixing zone is often lower than other important concentration indicators, e.g. the maximum concentration or fully mixed concentration, particularly for the narrow small streams. For aforementioned streams, the mixing zone is relatively small compared to the zone, where the contaminant is discharging a significant build-up of pollutant still occurring downstream. Arbitrarily defined from literature in present paper, the mixing distance is dependent on the stream geometry, flow rate and, at the same time, influenced by the location of the plume discharge into the stream as well as its dimension for a given contaminant mass discharge. For a plume approximately 200 m large, mixing distances up to 400-500 m from the upstream point of the plume can be expected.
Certain simulations carried out for the three tested landfills and substances indicated that the concentrations estimated in large and medium streams were generally complying with the relevant quality criteria indicators due to an important dilution factor. The observation cannot be generalised to all substances, since it is dependent on both the amount of contaminant discharging and the strictness of the associated requirement. In the matter of small streams, it appears problematic for several of the tested substances, e.g. iron in Hørløkke, nitrogen in Tandskov, due to the low dilution achieved in the streams. Thus, it can be anticipated that it will be dependent on their presence in leachates for other compounds. Undoubtedly, the discharge of ammonium / nitrogen from landfills appears as a major issue due to the quantity released (Christensen et al., 2001) combined to stringent requirements and contribution from other important sources such as agriculture and fishing operations.
4. IMPACT IN POINT OF COMPLIANCE (POC) The objective is to compile a guide regarding how to meet the guidelines of following: § Designation and determination of receptor. § Mixing of leachate or leachate contaminated ground water in surface water caused by leaking
through a contaminant front. § Assessment of the impact in the receptor and observance of requirements, criteria, and environmental targets. Receptors relevant to consider when making a risk assessment are defined as follows: § Ground water § Surface water § Natura 2000 areas
If within 250 metres of the lump site, uncontrolled dump sites may constitute a higher risk of bringing contaminant into the surface water. Even though soil is not defined as a receptor in present paper, it can be one due to the fact that the risk assessment focuses on the leaking of leachate and not the risk of using the area. POC for ground water is determined by following criteria: § Legislation
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
§ § § § § § §
Location of landfill units and the leachate collection wells Hydrogeological conditions Distance to closest receptor both vertically and horizontally Site-specific risk Purpose of ground water monitoring Purpose of avoiding contamination Necessary reaction time in case of a threatening contaminant
POC for surface water and Natura 2000 areas must not suffer a reduction in environmental standards, and different districts monitoring water standards and focus areas exist. According to the regulation, a leak from a landfill site is defined as a leak from a point in order for authorities to point out a mixing zone around the starting point of the leak.
5. ECONOMIC IMPACT ASSESSMENT The implementation of the model will induce an economic effect. Therefore, the financial section will focus on the operational economic impact on each specific landfill site based on the sitespecific risk assessment obtained from the previous described sections. Currently, the go-to aftercare period at Danish landfills are 30 years. However, present project strongly emphasises that the period of 30 years is simply too short, and the economic consequences are vast. After the project’s technical end, it will include an analysis of the economic impact the implementation of new knowledge will have. The focus is restricted to the landfills’ economies but will not be limited, since landfills in Denmark are owned by the municipalities. Thus, the national economy will face a negative challenge.
6. CONCLUSIONS Presently, no final conclusions from the study can be reached. The project’s steering group consists of agents from all three cooperative partners, who will reach the final conclusions at the end of the study. At the conference, a presentation of the preliminary conclusions will be presented. Nevertheless, it is certain that not all sections of the project will be finalised in time. Present paper will function as a small teaser for Sardinia 2019 Conference, in which a set of final conclusions have been reached and some of the tools have been implemented.
AKNOWLEDGEMENTS COWI A/S Danish Waste Solutions ApS DTU Environment Danish Environmental Protection Agency Rambøll Energy research Centre of the Netherlands Reno Djurs I/S Odense Renovation A/S
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
AV Miljø.
REFERENCES The Environmental Protection Act § 50 a. Christensen, T. H., Kjeldsen, P., Bjerg, P. L., Jensen, D. L., Christensen, J. B., Baun, A., … Heron, G. (2001): Biogeochemistry of landfill leachate plumes. Applied Geochemistry, 16(7-8), 659–718. doi:10.1016/S0883-2927(00)00082-2
