title: Time vs. Money: A Quantitative Evaluation of Monitoring Frequency vs. Monitoring Duration.
abstract: The National Research Council has estimated that over 126,000 contaminated groundwater sites are unlikely to achieve low ug/L clean-up goals in the foreseeable future. At these sites, cost-effective, long-term monitoring schemes are needed in order to understand the long-term changes in contaminant concentrations. Current monitoring optimization schemes rely on site-specific evaluations to optimize groundwater monitoring frequency. However, when using linear regression to estimate the long-term zero-order or first-order contaminant attenuation rate, the effect of monitoring frequency and monitoring duration on the accuracy and confidence for the estimated attenuation rate is not site-specific. For a fixed number of monitoring events, doubling the time between monitoring events (e.g., changing from quarterly monitoring to semi-annual monitoring) will double the accuracy of estimated attenuation rate. For a fixed monitoring frequency (e.g., semi-annual monitoring), increasing the number of monitoring events by 60% will double the accuracy of the estimated attenuation rate. Combining these two factors, doubling the time between monitoring events (e.g., quarterly monitoring to semi-annual monitoring) while decreasing the total number of monitoring events by 38% will result in no change in the accuracy of the estimated attenuation rate. However, the time required to collect this dataset will increase by 25%. Understanding that the trade-off between monitoring frequency and monitoring duration is not site-specific should simplify the process of optimizing groundwater monitoring frequency at contaminated groundwater sites.
authors: GSI Environmental Inc., 2211 Norfolk St., Suite 1000, Houston, TX 77098. temchugh@gsi-net.com.
authors: Thomas E
authors: TE
authors: McHugh
authors: GSI Environmental Inc., 2211 Norfolk St., Suite 1000, Houston, TX 77098.
authors: Poonam R
authors: PR
authors: Kulkarni
authors: GSI Environmental Inc., 2211 Norfolk St., Suite 1000, Houston, TX 77098.
authors: Charles J
authors: CJ
authors: Newell
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater; D014874:Water Pollutants, Chemical
chemical_list: D014874:Water Pollutants, Chemical