Analysis of the Hydrologic Response Associated With a Shutdown and Restart of the 200-ZP-1 Pump and Treat System

A number of programs have been implemented on the Hanford Site that utilize the pumping and treatment of contaminated groundwater as part of their remediation strategy. Often the treated water is reinjected into the aquifer at injection well sites. The implementation of remedial pump and treat systems, however, results in hydraulic pressure responses, both areally and vertically (i.e., with depth) within the pumped aquifer. The area within the aquifer affected by the pump and treat system (i.e., radius of influence) is commonly estimated based on detecting associated water-level responses within surrounding monitor wells. Natural external stresses, such as barometric pressure fluctuations, however, can have a discernible impact on well water-level measurements. These temporal barometric effects may significantly mask water-level responses within more distant wells that are only slightly affected (< 0.10 m) by the test system. External stress effects, therefore, can lead to erroneous indications of the radius of influence of the imposed pump and treat system remediation activities and can greatly diminish the ability to analyze the associated well responses for hydraulic property characterization. When these extraneous influences are significant, adjustments or removal of the barometric effects from the test-response record may be required for quantitative hydrologic assessment. This report examines possible hydrologic effects of pump and treat remediation actions and provides a detailed analysis of water-level measurements for selected 200-ZP-1 pump and treat system monitor wells during the recent Y2K shutdown (December 1999) and restart activity (January 2000). The general findings presented in this report have universal application for unconfined and confined aquifer systems