Groundwater Quality Monitoring at Active and Closed Landfills Less is More. Rob Burden and Nicola Livingston

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1 Groundwater Quality Monitoring at Active and Closed Landfills Less is More Rob Burden and Nicola Livingston

2 Rationale for Monitoring Comprehensive monitoring programme setup at landfill commissioning stage Tighter regulatory controls on historical landfill leads to comprehensive monitoring programme

3 Groundwater Monitoring Objectives 3 main reasons for groundwater monitoring programmes Establish baseline water quality Develop hydrogeological model Monitor leachate excursions

4 Typical Comprehensive Monitoring Programme Large number of monitoring wells (15 to 30) Extensive list of chemical parameters (30+) High frequency of monitoring (1-3 monthly) Often continued through life of landfill (10+ yrs)

5 Regulatory Review of Monitoring Generally annual review of results, and Comparison with consent trigger levels However Rationale and objectives often not reviewed Potential for over-monitoring of landfills

6 Common Groundwater Quality Monitoring Problems Monitoring wells poorly constructed or located Monitoring wells actually site investigation wells Tendency to monitor every possible chemical parameter Frequency of monitoring not dictated by groundwater flow rate

7 Landfill A: Closed Landfill Major Auckland landfill Closed after 40 year active life Old areas of landfill not lined Mainly domestic but some industrial refuse

8 Groundwater Monitoring Programme Established in late 1990s 18 monitoring wells (4 upgradient) 30 + Chemical parameters Wells monitored quarterly

9 Hydrogeological Model Established main down-valley groundwater flow direction and minor flow direction to south Estimated leachate would have reached monitoring wells in less than 3 to 5 years No leachate detected in down-gradient monitoring wells (quarterly monitoring for 10 years)

10 Reduce Monitoring Wells Three down-gradient monitoring wells in known flow paths (2 main valley, 1 minor flow path) No up-gradient monitoring, but Monitor up-gradient wells if down-gradient trigger levels exceeded

11 Reduce Monitoring Parameters 30 chemical parameters plus organics Select key parameters: - Significant conc. in leachate - Mobile in subsurface Ammonia and chloride (6 monthly monitoring)

12 Landfill B: New Landfill Consenting and pre-commissioning monitoring completed 34 monitoring wells including up to 3 to 5 monitoring depths at some locations 30 chemical parameters plus organics Monthly (key parameter) and quarterly groundwater monitoring

13 Reduce Monitoring Parameters and Frequency Key parameters (ammonia, chloride, and conductivity) monitored monthly at all monitoring locations 30+ parameters monitored 3-monthly at all monitoring locations Reduce key parameter monitoring to 3 to 6 months Select B list parameters of key metals (copper, zinc) and other potential sensitive parameters or parameters characteristic of particular leachate

14 Change Trigger Levels Trigger levels originally based on 3 standard deviations above mean Some maximum parameter concentrations > or = trigger levels Trigger levels based on 3 standard deviations above maximum

15 Reduce Monitoring Wells Groundwater samples collected at up to five different depths No hydrogeological analysis carried out to identify different aquifers and flow paths Number of sampling locations could be significantly reduced

16 Conclusion Intensive groundwater monitoring often necessary at commissioning to: establish baseline water quality develop conceptual model check for leachate excursions Monitoring can be progressively scaled back without increasing environmental risks when appropriate monitoring information is available Scaled back monitoring reduces compliance costs (monitoring and regulatory review) and allows resources to be re-prioritised