Landfilling of Waste

5. Preliminary Investigations

5.1 Definition and strategy
5.2 Existing conditions
5.3 Geology
5.4 Hydrogeology
5.4.1 Groundwater monitoring
5.5 Surface water
5.5.1 Leachate
5.5.2 Paved areas and cut-off drains
5.6 Future situation
5.6.1 Traffic
5.6.2 Noise
5.6.3 Future land use
5.7 Draft design

5.1 Definition and strategy

Any location of sites for landfills is made in connection with the regional planning of the counties.

Preliminary investigations are carried out at the site designated for the contemplated landfill. Such preliminary investigations must include a detailed description and assessment of all factors at the planned landfill which may affect the surrounding environment. The result of investigations forms the final basis for the assessment as to whether the relevant site is environmentally suited for landfilling the expected types of waste.

The result of the preliminary investigations must provide the basis for determination of the nature and extent of necessary environmental protection measures. Thus, the preliminary investigations must provide a basis for the establishment of separate environmental protection measures for each unit at the landfill.

The preliminary investigations must become part of the background documentation for the application for environmental permit. The preliminary investigations must therefore be sufficiently detailed to ensure that unanswered questions will not arise at a later stage which may have an impact on the environment, including the possibilities of transition to the exclusive use of passive environmental protection systems 30 years after landfilling has stopped.

5.2 Existing conditions

Existing conditions at the selected site are described, including the importance of the site in terms of natural and cultural patrimony as well as present use of the site. A description must be made of the observed above-ground structures and culture-historical monuments in the area. All possible and necessary measures relating to above-ground structures and culture-historical monuments must be described and evaluated.

The history of the area should be surveyed - including earlier activities, previous pollution and underground installations - by examining existing archive material.

Any known groundwater pollution upstream from the landfill should be evaluated. The data should be included when drawing up the monitoring and control programme.

5.3 Geology

The purpose of the geological investigations is:

	to assess the bearing capacity of the soil;
	to provide a basis for the hydrogeological evaluation (see sect. 5.4);
	to evaluate the suitability of naturally occurring clay for the landfill;
	to assess the occurrence of raw material resources and their suitability for extraction.

Geological data may be obtained, for example, from the relevant county administration and are used for detailed planning of the preliminary investigations. Data exist in the form of geological basic data maps with selected bore holes, in the form of special soil type and thematic maps with or without cross sections, and as a computer database with various search facilities and presentations of data. Data are also available in the water abstraction plans drawn up by the regional authorities. As a basis for the selection of areas with special drinking water interests the regional authorities have drawn up groundwater protection maps. The maps are available in most counties via a geological information system (GIS). This information is used as basis for the assessment of the site and the need for additional investigations in the field.

Field investigations consist, primarily, of geophysical and drilling activities, including the drawing of soil type and groundwater samples, the extent of which depends on the local geological conditions.

Assuming that the selected site has a simple geological structure, the extent of geophysical investigations and drilling programme should be decided on the basis of available knowledge of the geology of the area.

At sites without interbedded clay strata or other low-permeable strata between the future landfill and the primary aquifer, the geology can be examined solely by means of a drilling programme.

At sites with interbedded clay strata or other low-permeable strata between the future landfill and the primary aquifer, geophysical - notably geoelectrical - measurements should be carried out to determine the extent and thickness of the low-permeable strata. This mapping should then be supplemented by a drilling programme designed on the basis of existing knowledge and the result of the geophysical investigations. The geophysical investigations are used for:

	description of the homogeneity/heterogeneity of the area;
	assessment of the extent of low-permeable strata;
	design of the subsequent drilling programme; and
	assessment as to whether the site is still considered suitable for a landfill.

For further details of the geophysics, see Note at the end of this chapter. Reference is also made to the soil and groundwater project from the Danish Environmental Protection Agency’s Guidelines No. 11/1995: "Monitoring of groundwater based on new geophysical measuring methods".

Drillings are carried out as part of the geological mapping and as part of the hydrogeological mapping. If, at the individual drilling, the drill has penetrated low-permeable strata, the bore hole must be sealed - for example, with bentonite - at the level of the low-permeable strata to prevent leakage from the landfill via bore holes. If there are no low-permeable strata, the material which has been drilled out will be returned to the hole.

If a geophysical mapping has been carried out, one or two drillings should be performed for the purpose of checking the interpretation of the geophysical measurements. Thereupon, a drilling programme should be carried out in a grid covering the various types of stratigraphic sequence as they appear from the database information and the geophysical mapping.

Where no geophysical mapping has been carried out, a drilling programme should be performed in a grid with a spacing of some 100 metres - unless the geological data indicate that another grid spacing must be selected.

Regarding the carrying-out of drillings please refer to Statutory Order of the Ministry of Environment No. 4 of January 4, 1980, and the Danish Environmental Protection Agency’s Circular of February 28, 1980, on the carrying-out of drillings for groundwater. Reference is also made to DS 441 and DS 442 on non-common and common water supply systems. The Danish Environmental Protection Agency plans to publish a Statutory Order in 1997 on the carrying-out of onshore drillings.

5.4 Hydrogeology

The purposes of the hydrogeological investigations are:

	to describe aquifers that are being used or are suitable for water abstraction;
	to describe the routes of the groundwater between and within the individual aquifers and to wetlands;
	to describe the suitability of low-permeable strata as natural liners;
	to describe the water quality in each aquifer;
	to describe the possibility of remedial actions, if any; and
	to determine the location of groundwater monitoring bore holes.

Hydrogeological data are gathered from the geological databases, from the relevant county administration, as well as data from the regional water abstraction plans. Data are stored in the form of computer databases as geological database maps and as thematic maps describing the transmissivity and potential of selected aquifers.

In addition, there is a chemical database describing the chemical composition of the individual groundwater aquifers. For a number of areas these data are also presented in the form of groundwater-chemical maps.

Information on groundwater pollution deriving from landfills and contaminated sites is gathered from registers kept by regional and local authorities. This information is relevant to the assessment of the present chemical background level in aquifers associated with the landfill.

Existing knowledge and the result of the geological investigations are used as planning basis for the field investigations.

The field investigations may include the location of existing bore holes, new drillings, and various forms of hydraulic tests.

The extent and nature of drillings and hydraulic tests depend on existing data on the geological structure of the area and the occurrence of aquifers.

Investigations will normally be more comprehensive when the area holds several aquifers separated by low-permeable strata.

The main components of the investigation programme can be described as in Table 5.1 depending on the prevailing local conditions.

Extent of field investigations in relation to local conditions.

Cased bore holes are made to the secondary and primary aquifers in the area. After the drilling work is complete, each aquifer must have a minimum of three bore holes with screens. If there are existing bore holes in the immediate vicinity of the area under review, the drilling work can be reduced correspondingly - provided that the existing bore holes are well described. When installing screens in bore holes that penetrate low-permeable strata, the holes are sealed with bentonite (a minimum of 1 metre of bentonite) at the level of these strata. After completing the installation of screens, the hole should be pumped clean. During this procedure the drawdown and the output of water in the hole should be recorded. This registration may be used for a preliminary assessment of the hydraulic conductivity of each aquifer - and thus for the planning of longer-lasting, subsequent pumping tests.

Core samples from the drilling work should be drawn and described as specified under the geological drilling work in para. 5.3.1.

A minimum of three bore holes from each aquifer in the area should be included in simultaneous probing of the water table. A minimum of three bore holes in each aquifer is necessary to enable a determination of the direction of gradient of the water table - and thereby the direction of flow of the water under the landfill.

The results of the probing should be produced in the form of a potential map for each aquifer.

Water table/pressure differentials between the individual aquifers should be used for an assessment of the risk of leachate infiltration from the landfill to secondary as well as primary aquifers. If the aquifer just beneath the landfill has a higher water table/pressure level than the pressure level in deeper aquifers, there is an increased risk of downward leachate infiltration.

The knowledge of flow direction - combined with the knowledge of flow rates as determined by hydraulic tests - should be used for the location of groundwater monitoring and control wells upstream and downstream from the landfill.

Hydraulic tests should be performed in the screened bore holes to determine the hydraulic parameters of the aquifers. These parameters are: aquifer geometry, hydraulic conductivity, porosity, and aquifer coefficient. For further details of hydraulic tests, see Note at the end of this chapter.

Water quality in aquifer

In order to make a qualified assessment of any possibility of utilising the various aquifers under and around the landfill, the groundwater quality of each significant aquifer should be examined. Chemical parameters that should be included in this analysis are stated in the analysis programme for groundwater in Table 5.2.

If there is evidence of upstream groundwater pollution close by, the analysis programme should be adapted accordingly.

Existing and contemplated water abstractions should be mapped, normally within a distance of about 2 kilometres from the landfill. This distance should be increased in the groundwater downstream, and reduced upstream from the landfill. The mapping should include non-common supplies, common water supply facilities, and field watering systems. The result of the hydrogeological investigation forms the basis for the assessment of the risk of any impact on these water supply facilities.

The risk of affecting the groundwater (water supply) and/or recipients is assessed on the basis of the mapped flow directions , hydraulic conductivity in each aquifer, and the risk of leakage among the individual aquifers.

The risk assessment can be made in accordance with the guidelines described in the Danish Environmental Protection Agency’s Guidelines: "Cleaning Up Contaminated Sites", to be published shortly.

If it is estimated that there might be a risk, further investigations are called for. If these investigations continue to show an unacceptable risk - or if no supplementary investigations are made - no landfill should be located on the relevant site.

5.4.1 Groundwater monitoring

Purpose

The purpose of groundwater monitoring around a future landfill is to select bore holes for the subsequent groundwater control as well as to determine the background levels for the relevant parameters in relation to the groundwater control to be carried out after commissioning of the landfill.

Groundwater monitoring must thus be carried out before landfilling starts.

The number, location and development of monitoring wells depend, primarily, on the number of aquifers near the landfill.

The monitoring wells must be capable of monitoring:

	the groundwater flow (direction and rate) in the primary and secondary aquifers below and around the landfill; and
	the natural groundwater-chemical state upstream and downstream from and below the landfill.

Provided that the hydrogeology around the landfill is simple, the primary and secondary aquifers may be monitored by means of at least three screened bore holes in each aquifer. The flow direction in each aquifer has been determined by the preliminary hydrogeological investigations. The basis for the location of monitoring wells should be that at least one well is placed immediately upstream and at least two immediately downstream from the landfill depending on the hydrogeological conditions. If there are more aquifers, this procedure is repeated for the other aquifers.

The location of downstream wells in the aquifer just beneath the landfill is selected on the basis of an estimate of the prevailing flow-dynamics. Any impact on the deeper aquifers will not necessarily be evident immediately downstream from the landfill. Installing screens in the individual wells in more than one aquifer is not recommended; experience shows that this involves a high risk of leakage among the aquifers via the wells.

Increasing complexity of the hydrogeology around the landfill will increase the need for additional monitoring wells.

The wells for the primary as well as any secondary aquifers are normally provided with a 5-metre screen installed in the top part of each aquifer. The wells are to be carefully closed with a clay seal around the casing above the screened interval, so that pollution from above along the casing is avoided. If there are low-permeable strata above the screened section, these strata are provided with bentonite seals.

The wells are pumped clean after the installation of screens, so that they are ready for subsequent water sampling for chemical analyses. The pumping procedures should be the same as those for water supply bore holes.

Monitoring well are used for control wells after the landfill starts operation.

Regarding the carrying-out of bore holes please refer to Statutory Order of the Ministry of Environment No. 4 of January 4, 1980, and circular from the Danish Environmental Protection Agency of February 28, 1980, on the carrying-out of drilling for groundwater. Reference can also be made to DS 441 and DS 442 on non-common and common water supply systems. The Danish Environmental Protection Agency expects to publish a Statutory Order in 1997 on the carrying-out of onshore drillings.

Sampling

Monitoring wells are pre-pumped prior to sampling by pumping, as a minimum, a quantity of water corresponding to about ten times the volume of the bore hole and the gravel volume. The pump is placed at the centre of the screened interval, so that as far as possible the pumping represents the screened interval.

See also Guidelines from the Danish Environmental Protection Agency No. 3/1992: "General Sector Specific Guidelines for Contaminated Sites".

Analysis programme

The starting point for the selection of analysis parameters for groundwater monitoring in a future landfill should be:

	The results of the preliminary investigations; and
	the expected nature and composition of the waste to be landfilled.

Table 5.2 shows suggested analysis parameters for groundwater monitoring for future landfills intended for landfilling of, respectively, mixed wastes, mineral waste and inert waste.

In the case of mono-landfills the analysis programme should be more specifically oriented in terms of selection of measuring parameters based on leaching tests.

Frequency of analyses

It is proposed that groundwater monitoring be carried out at intervals of six to twelve months between analyses. As a minimum the monitoring should include three series of analyses. The monitoring period should be at least two years. The final monitoring analysis should be carried out within one year before commissioning of the landfill.

Analysis laboratory

Analyses must be carried out in laboratories that are accredited for the relevant analysis. Any use of non-accredited laboratories requires acceptance by the inspection authority.

Table 5.2

Analysis parameters, groundwater monitoring

NVOC = Non-Volatile Organic Carbon
AOX = Adsorbable Organically Bound Halogen
GC-FID screening = Screening by means of gas chromatography for contents of extractable,
organic substances, including solvents and oil products
* = Where the composition of leachate can be checked, cf. sect. 3.2.

5.5 Surface Water

The impact of the landfill on surface water is made up, partly, of an impact from treated leachate - no matter if the leachate is treated locally or is removed to another treatment plant - and partly of the impact from paved areas and cut-off drains, if any, around the landfill.

5.5.1 Leachate

Based on the quantity and composition of leachate possibilities of treatment, disposal and environmental impacts must be assessed.

The assessment should include:

	The capacity and suitability of nearby treatment plan for the treatment of leachate, including the sensitivity of the treatment plant to peak loads from the addition of leachate and the resulting content of heavy metals in the sludge produced.
	The prospects of disposal of leachate by tank lorry and/or sewer system.
	The treatment effect on leachate by treatment in a municipal treatment plant, and the effects of alternative treatment methods and/or direct discharge.
	Technico-economic assessment of the need for expansion of any treatment plant (such as the need for receiving and feeder tanks as well as adaptation of the treatment method).

If leachate is treated separately in an on-site facility, the treatment requirements should be determined along the lines of other wastewater treatment plants, having regard to the objective for the receiving wetland.

For landfill units established with reduced or exclusively passive environmental protection systems the expected impact from the leachate must be described. The description must specify where discharge takes place.

5.5.2 Paved areas and cut-off drains

Lakes, ditches and watercourses near the landfill must be mapped out.

The prospects of draining surface water from paved areas and cut-off drains around the landfill should be assessed, having regard to the objective for the receiving wetland.

The need for any technical measures (equalisation basins, oil separators, sand traps, etc.) should be assessed.

5.6 Future conditions

5.6.1 Traffic

The impact of the landfill on the traffic load and traffic safety of the area should be assessed in the light of the volume of waste likely to be transported to the landfill. Seasonal fluctuations (periods of peak load) as well as daily variations should be included in this assessment.

Access conditions to the landfill should be planned in such a manner that vehicles follow routes that provide the highest degree of traffic safety and the lowest degree of nuisance - especially in the form of noise and dust - for built-up areas in the vicinity (residential, commercial and industrial buildings).

5.6.2 Noise

In the light of initial considerations concerning the layout and operation of the landfill, cf. sect. 5.6, a calculation should be made of the expected noise level from the landfill. The calculated noise level should become part of the basis for an application for environmental permit. The noise calculation should be made on the basis of:

	The expected number of coming and going vehicles per day.
	The number of unloading operations per day.
	The expected number of stationary and rolling equipment on the site.
	The number of operating hours per day for each piece of equipment.

In the calculation, the topography around the landfill shall be taken into consideration.

The calculations should be carried out in accordance with the Danish Environmental Protection Agency’s Guidelines No. 5/1993: "Calculation of External Noise from Enterprises".

The need for and possibilities of noise-reducing measures, such as alternative technology, noise barriers, and the planning of operation, must be examined.

5.6.3 Future land use

The future land use for a landfill is laid down in a local plan for the area.

The landscape can affect the layout and filling rate of the landfill and must therefore already be part of the preliminary investigations for the landfill.

The factors outlined below should be incorporated, as a minimum, into the considerations regarding the future landscape.

Filling heights

The considerations regarding the maximum average filling height should include considerations regarding the leaching behaviour of the waste. This means that the filling height must be based on the demand that leachate from the waste must be acceptable in the environment when the active systems of the landfill must be abandoned.

In view of planning and the fact that there are limited possibilities for the location of new landfills, there should not be large areas of the landfill where the filling height is less than 5-7 metres.

Furthermore, when landscaping the site, the location of leachate collection wells on the landfill area should be given special consideration. Such wells should be placed where the filling height is lowest, because great filling heights can prevent the possibility of maintaining and inspecting the wells and/or their installations.

Stability

Future settlement of the landfilled waste must be allowed for, so that unintended depressions in the final landscape are avoided.

In order to avoid the risk of erosion no restored surfaces should have a gradient steeper than 1:3.

Drainage

The natural run-off of surface water must ensure that there will be no areas within the landfill with increased infiltration of water and a resulting increase in the production of leachate.

5.7 Draft Design

Draft Design

The draft design for a landfill should be based on the preliminary investigations performed as described in sects. 5.1-5.5 as well as the layout described in Chapter 6.

As a minimum the draft design must contain a description of the following subjects:

	The layout of the site;
	the need for active and passive environmental protection systems;
	the design of active and passive environmental protection components; and
	the total landfill capacity and the expected filling rate.

Environmental description and assessment

The draft design is used for an environmental description and assessment of the landfill and the site on which it is to be located. This description and assessment of the landfill will form the final basis for the application for environmental permit.

¹ A geophysical measuring programme can consist of a combination of vertical geoelectrical sounding and geoelectrical line profile measurements. The former should be made in a grid with a spacing of about 100 metres and a maximum current electrode spacing of four times the depth to the lower limit of the clay/low-permeable stratum.

One or two vertical geoelectrical soundings are made close to existing, geologically well-described bore holes for calibration and interpretation of the geophysical measurements.

The geoelectrical line profile measurements must be appropriately placed in relation to the soundings. The direction should be chosen so that it runs parallel, as far as possible, with the strike of the clay/low-permeable stratum. The distance between the current electrodes should be chosen as at least twice the depth to the centre of the low-permeable stratum. If a direction is chosen other than parallel with the gradient of the stratum, this will render the interpretation of measurements difficult - because the geophysical laws assume homogeneous and parallel strata.

The results of the measurements are produced as index maps and geophysical cross sections of the area investigated. The results should show the possible stratigraphic sequences and, as isoline and isopach maps, the extent and thickness of the low-permeable strata.

² Unconfined aquifers should be tested with brief pumping tests lasting from 3 to 5 hours. The pumping test is performed at maximum constant capacity as determined by the pumpings undertaken earlier (to clean the holes). Pumping tests are performed in two or three bore holes covering the area under review. If it is possible to include monitoring wells very close to the bore holes, any changes in the water table should be monitored to determine the specific capacity of the aquifer. If this is not possible, the geological test description must be used for an assessment of the specific capacity.

Confined aquifers should be investigated by means of longer-lasting pumping tests in a single hole, preferably in the centre of the area under review, with monitoring of the pressure impact in at least two monitoring wells located in different directions and at different distances from the bore hole. The pumping test should last from one to about three weeks, because the pumping test should continue until the data basis for the aquifer geometry and the assessment of aquifer and leakage coefficients is complete. The final hydraulic parameter, in particular, is important for the assessment of any active technical measures that should be included in the final design of the landfill.

In addition, the hydraulic parameters should be used for the design of the necessary monitoring programme.