Appendix F: Worked examples

Landfill waste acceptance

Case study 1: contaminated soil

Soil has been excavated from a former timber treatment site, which is being redeveloped for low-density residential. The contaminant concentrations exceed the residential soil criteria in the timber treatment guidelines (Ministry for the Environment and Ministry of Health, 1997).

Step 1: Is the waste prohibited from landfill disposal? No

Step 2: Is the waste a solid? Yes

Step 3: Does the waste comply with the cleanfill definition? No

Step 4: Is the waste asterisked on the NZ Waste List? Yes: 17 05 03* soil and stones containing hazardous substances

Step 5: Total concentration and/or TCLP test

Existing contaminant concentrations from site investigation report:

Contaminant Contaminant
concentration
mg/kg
Timber treatment residential criteria
mg/kg
Screening
concentration
mg/kg

Copper

53.6

80

100

Chromium

45.2

9

100

Arsenic

15.4

30

100

Boron

259.7

3

400

The waste material meets the screening concentration for Class A landfills. No TCLP test is required prior to disposal at a Class A landfill.

Case study 2: waste treatment sludge

Wastewater treatment sludge has been obtained from a liquid and hazardous waste treatment operation. The operation accepts a variety of waste streams for treatment prior to disposal/re-use and treats all liquid residues on-site prior to discharge to trade waste and/or landfill.

Step 1: Is the waste prohibited from landfill disposal? No

Step 2: Is the waste a solid? Yes: the sludge is approximately 17 % solids but passes the US EPA Paint Filter test and liberates no free liquids on transport.

Step 3: Does the waste comply with the cleanfill definition? No

Step 4: Is the waste asterisked on the NZ Waste List? Yes: 19 08 13* sludges containing hazardous substances from other treatment of industrial waste water.

Step 5: Total concentration and/or TCLP test

Existing contaminant concentrations from waste treatment operational monitoring:

Contaminant Contaminant concentration
mg/kg
Screening concentration
mg/kg
 

TPH

500

NA

~

Naphthalene

263

200

X

Phenol

26.5

800

*

Styrene

59.8

120

*

Benzo(a)pyrene

12.5

300

*

TPH analysis indicates an elevated level of hydrocarbons (with reference to relevant contaminated site guideline criteria). Further analysis is required to determine suitability for disposal, including consideration of PAH (naphthalene and benzo(a)pyrene) and volatile organics, depending on the source of waste. Naphthalene exceeds screening criteria for Class A landfills, but a TCLP test may indicate that the naphthalene is immobilised in the sludge matrix. Consideration of the TPH results indicates that the hydrocarbons are in the semi-volatile range (i.e. BTEX is unlikely to be an issue).

Contaminant TCLP result
mg/L
TCLP criteria
mg/L
 

Naphthalene

5

10

*

The TCLP result for naphthalene is below the TCLP criteria for Class A landfills.

Landfill classification

Case study 1: historical landfill

ABC Grove Landfill was developed in the mid-1980s and has a design life of 50 years (80-100,000 tonnes per annum). The site was granted resource consent (discharge to air, land and water, divert ...) in 1995 for 25 years' operation. Existing waste acceptance criteria are set out in the consent conditions.

  Design feature Meets Class A criteria

Siting

Overlies silty clay (10 m, 10-6 m/s) and siltstone (> 25 m, 10-7 m/s)

*

100 m to XYZ River, above floodplain

*

Groundwater 1 m below base of refuse

*

1 km to nearest groundwater user (irrigation, siltstone aquifer)

*

Design

No engineered liner

X

Leachate cut-off drain (retrofit)

*

Surface/stormwater divert (retrofit)

*

Landfill gas management system (flaring/generation)

*

Operation

Staged filling, daily and intermediate cover

*

Final cover on completed cells 1 m clay (10-7 m/s)

*

Documented waste acceptance system incl. manifest

*

Licensing and random inspections

X

Monitoring of leachate, groundwater and stormwater

*

The site meets the criteria for a Class B landfill (existing resource consent) but does not meet the screening criteria for a Class A landfill (no engineered liner, no licensing system, no random inspections).

Determining equivalence with the Class A Landfill Screening Criteria (Appendix D):

  1. Use benzene and arsenic in leachate at TCLP criteria concentrations.
  2. No liner so modelling of leachate flow through liner not required.
  3. 100 m to adjoining river, receptor considered groundwater at 100 m downgradient of landfill boundary

Contaminant parameters:

Parameter Benzene Arsenic

Half-life

732 days

NA

Log Koc

1.7

NA

Kd (in silty clay)

NA

1.3

Density/effective porosity

NA

6

Model results:

Parameter ABC Grove
Benzene in leachate 0.62 mg/l
Benzene at receptor 0.05 mg/l
Arsenic in leachate 3.1 mg/l
Arsenic at receptor 0.013 mg/l

Note: leachate concentrations derived using MfE Model, US EPA TCLP criteria adopted for benzene and arsenic

Conclusion

Since benzene and arsenic concentrations exceed the criteria for Class A landfills at the receptor, ABC Grove Landfill should use landfill waste acceptance criteria for Class B landfills.