Guidelines for Environmental Monitoring at Municipal Solid Waste Landfills
Surface water monitoring should only be a routine component of a landfill monitoring program where leachate and/or concern with groundwater is known to or suspected of impacting on nearby surface water. Otherwise, monitoring is normally necessary at the outset and only infrequently thereafter.
Surface water monitoring at landfills is intended to detect unacceptable surface water contamination resulting from landfill operations. Acceptable contaminant levels are specified by the Manager and will generally be in accordance with the Approved and Working Criteria for Water Quality - 1995 , (BC Environment, 1994).
Surface water monitoring locations should include (GLL, 1993):
- Upstream (Background) — to establish background water quality / bottom fauna conditions and flow;
- Immediately Downstream (Pathway, Receptor) — to determine leachate impacts on water quality and bottom fauna at and immediately downstream of the landfill; and
- Downstream Recovery (Receptor) — located further downstream to document the extent of the mixing zone and distance required for the surface water to assimilate leachate and for water quality to recover to background levels.
Surface water monitoring frequencies should be higher than groundwater sampling frequencies in order to account for the greater flow; in general, a faster velocity means impacts will spread more quickly. The suggested minimum sampling frequency for surface water is six to eight times per year. However, in most cases the sampling frequency will depend on the goals/objectives of the monitoring program. For example, the assessment of annual trends would require monthly to more frequent sampling whereas, the assessment of a specific event (e.g. low flow period) would require that sampling be conducted only during its occurrence. Measurements of surface water flow should be taken whenever surface water samples or bottom fauna are collected (GLL, 1993).
Water quality should be monitored in surface waters adjacent to landfill sites and compared with the ambient surface water background. Deterioration in water quality could indicate inadequate leachate containment or attenuation. Knowledge of surface water flow, quality and use, as well as aquatic biology information is valuable for assessing surface flow pathways and potential impacts on surface water receptors.
Surface water should be monitored for pH, redox potential, specific conductance, temperature and dissolved oxygen concentration. This range of parameters is usually sufficient to give an indication of any changes in inorganic water quality. Samples should always be collected on the same day as field measurements and during constant flow conditions (Environment Canada, 1994).
4.3.1 Bottom Fauna and Fish Surveys in Surface Waters
An indication of surface water quality can be obtained by carrying out a Biodiversity Index survey (e.g. fish and/or bottom fauna surveys). Studies indicate that certain bottom fauna and fish species (e.g. mayflies and stet) are very sensitive to contaminants in leachate and may not be present in normally anticipated species and numbers when under stress; conversely, there are other species (e.g. sludge worms and midge larvae) that may flourish in the stressed environment.
Surveys should be carried out by qualified individuals, in selected locations (i.e. upstream, adjacent and downstream of the landfill), and in areas of similar substrate and flow. Sampling methods include, but are not limited to, Surber sampler, seine net hauls, traps and electroseining.
The data collected from the bottom fauna survey can be used as direct measures of bottom receptors and represent the long-term surface water quality trends. Data collected from the fish survey provide the basis for correlating fish presence/absence with water quality information and allow meaningful interpretation of the significance of leachate impacts rather than inferred impacts based on fish toxicity literature (GLL, 1993).
4.3.2 Contaminant Loading Surveys
Contaminant loading surveys are best suited for sites where leachate is impacting on small- to medium-size streams. This type of survey attempts to identify background conditions and all upstream and downstream contaminant discharges. Measurements taken are: discharge flows, contaminant concentrations for parameters which are not attenuated or biodegraded (e.g. chloride) and background conditions. Sampling is usually carried out during a low flow period to assess the maximum impacts. Contaminant loading is calculated by multiplying the contaminant concentration by the flow rate. Due to conservation of mass, downstream loadings should equal the background loadings plus additional loadings from the contaminant source (GLL, 1993). Discrepancies could indicate an unidentified contaminant source, another diluting source (e.g.: a tributary stream) or sampling/analytical errors.
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