We monitor the environment to search for and document change.
This is the first question we have to address in improving the efficiency of a monitoring program. Yet, it is often a question that goes unexamined in the years after installation of a remedy.
Every statistics text book covers experimental design and setting objectives for data collection to some extent - but the memory of these guidelines fades with the age of the project and becomes crushed into a monotonous routine over time.
Getting to the point, monitoring objectives for the network should be fresh. Objectives should be well articulated and connected to observable metrics, statistical analyses and specific monitoring locations. Most importantly, objectives should be reviewed regularly to see if they still fit the management decisions that must be made.
Based on USEPA documents, monitoring objectives for a plume fall into four general categories (USEPA, 1994; USEPA, 2004a).
· Evaluate changes in ambient physical conditions of the resource;
· Evaluate the movement and monitor the fate of chemical constituents;
· Evaluate compliance with regulatory requirements;
· Evaluate the effectiveness of the response action or remedy
I might add:
¨ Demonstration of compliance at property boundaries or institutional controls
Sure, one of your objectives is to “evaluate the efficacy of your remedy”, but have you really considered what kind of data will show your remedy is working? Chances are the remedy will not completely eliminate constituents of concern immediately, so you need to have metrics that reflect the gradual move toward cleanup goals. What do these metrics looks like?
Specific monitoring objectives should be developed to address each of the applicable general objectives. Specific objectives for long-term monitoring (LTM) programs generally have temporal and spatial components. The most common temporal aspect of LTM objectives is the evaluation of changes in contaminant concentrations at specific locations over time. Temporal objectives can be addressed by identifying trends in contaminant concentrations, or by estimating long-term summary statistics (mean, standard deviation) for concentration values (Zhou, 1996). An important aspect of establishing temporal objectives includes determining the sampling frequency for wells. Monitoring wells should be sampled at a frequency that captures changes in constituent concentrations without unnecessary or redundant sampling events. However, the frequency of reporting and management decisions are also critical. Will you have a statistically significant dataset to write your next report?
Objectives for monitoring constituents spatially are often related to predicting movement of constituents within the currently plume area or toward downgradient receptors. Spatial optimization is based on minimizing the uncertainty of predicting concentrations at critical locations within the monitoring network while eliminating redundant information. Spatial objectives are first addressed by identifying these critical monitoring locations. All wells are not created equal!
Each well should provide valuable (not redundant) information and all areas of interest should be represented by sampling locations. Areas that require no action or decisions can be removed from consideration before beginning the optimization. Frequently, response action documents will identify concentration ‘action levels’ at specific locations that may signal risk for downgradient receptors and trigger contingent response actions. The monitoring objective corresponding to this situation would be to predict, with confidence, any exceedences of the ‘action level’ at locations within the plume or locations that are surrogates for potential receptors.
In any case, establishing, reviewing and articulating monitoring goals is a critical first step in optimizing your monitoring program.
