David P. Ahlfeld
This study examines the effects of various environmental conditions on the behavior of a contaminant spill as it travels across the Wachusett Reservoir. The reservoir, located in central Massachusetts, is a 65 billion gallon water body that supplies drinking water to the Boston Metropolitan area and consists of numerous inflows and outflows. The Quabbin Reservoir, a 412 billion gallon system, accounts for close to half of the inflow. The Wachusett Reservoir receives Quabbin water through the Quabbin aqueduct located on its eastern side. CEQUAL W2, a two-dimensional, laterally averaged, hydrodynamic and water quality model was utilized to perform numerous simulations. The current version, version 3.6, was used due to its computational speed and ability to apply past years data without changing input files.
Four years were analyzed, 2003-2006, in order to examine similarities and differences from year to year. Simulations for years 2005 and 2006 were calibrated to measured temperature and conductivity profiles within the North Basin of the Wachusett Reservoir (Years 2003 and 2004 were completed prior to this research). Simulations were performed in order to better understand the behavior of the spill under three main scenarios: 1) seasonal change, 2) variation of spill temperature, and 3) turning the Quabbin transfer on or off. Spill characteristics and location were kept the same for each simulation to allow for comparison. The date of the spill was chosen based on similar wind conditions for each season of every year. The behavior of the spill was evaluated by analyzing conductivity versus time at the withdrawal of the reservoir, the Cosgrove intake. Profiles of conductivity versus water depth at some locations along the reservoir were observed in order to better understand spill behavior.
Model results demonstrated that similarities between years existed. The arrival time of the spill was affected by the seasonal change. Spring spills consistently arrived at the withdrawal within 2-3 days, fall spills within approximately 7-10 days, and summer spills took 10-15 days. The summer spills showed more variability, having larger peaks than the other seasons. Changing the temperature of the spill displayed minimal effect for the spring and fall seasons. The summer of 2004 showed a faster arrival time at the intake for a warm spill whereas the summers of 2003, 2005 and 2006 displayed negligible differences in spill behavior when changing the spill temperature. Altering the condition of the Quabbin transfer showed the most effect during the summer months for all four years. Turning the transfer off for a period of two weeks after the significantly. CEQUAL W2 V3.6 proved to be an effective tool in examining the behavior of a contaminant spill within the Wachusett Reservoir under various scenarios.