A Three-Tiered Approach to Long Term Monitoring Program Optimization

ABSTRACT

Long term monitoring optimization (LTMO) has proved a valuable method for reducing costs, assuring proper remedial decisions are made, and streamlining data collection and management requirements over the life of a monitoring program. A three-tiered approach for LTMO has been developed that combines a qualitative evaluation with an evaluation of temporal trends in contaminant concentrations, and a spatial statistical analysis. The results of the three evaluations are combined to determine the degree to which a monitoring program addresses the monitoring program objectives, and a decision algorithm is applied to assess the optimal frequency of monitoring and spatial distribution of the components of the monitoring network. Ultimately, application of the three-tiered method can be used to identify potential modifications in sampling locations and sampling frequency that will optimally meet monitoring objectives. To date, the three-tiered approach has been applied to monitoring programs at 18 sites and has been used to identify a potential average reduction of over one-third of well sampling events per year. This paper discusses the three-tiered approach methodology, including data compilation and site screening, qualitative evaluation decision logic, temporal trend evaluation, and spatial statistical analysis, illustrated using the results of a case study site. Additionally, results of multiple applications of the three-tiered LTMO approach are summarized, and future work is discussed.

Keywords:

• long term monitoring network optimization
• Mann-Kendall temporal trends
• geostatistics
• kriging

Notes

^a COC = contaminant of concern.

^a Periodic water-level monitoring should be performed in dry wells to confirm that the upper boundary of the saturated zone remains below the well screen. If the well becomes re-wetted, then its inclusion in the monitoring program should be evaluated. A well that has been dry for more than two years should be replaced with a new well screened at a deeper interval if groundwater monitoring at that location is deemed to be required.

^a “Hot spots” are defined to be areas where contaminant concentrations exceed the cleanup level by a factor of 10 or more.

^a COC = Contaminant of Concern.

^b MCL = Maximum Contaminant Level.

^a Wells not sampled during the most recent sampling event were excluded from the analysis.

^b Ratio of the median “missing well” predicted standard error to median “base case” error.

^c 1 = least relative amount of information; 55 = most relative amount of information (55 wells included in the geostatistical zone analysis.)

^d Well in the “intermediate” range and received no recommendation.

^e Tie values receive the median ranking of the set.