A landfill in eastern Iowa is one of 12 national testing sites trying to find a cheaper way to seal off old garbage dumps. The Bluestem Solid Waste Agency in Marion is testing three types of caps used to cover landfills once they become full of garbage. Consultant Tim Hall says the study pits the traditional rubber cap against a clay cap. He says the program puts the two caps systems side by side in identical locations under identical conditions. They will be monitored to see if they perform the same way. The other alternative includes hybrid poplar trees and grass. He says lowering the cap cost is only one objective of the study. They’re also looking for a cap that keeps water from infiltrating the garbage and running into the groundwater. Hall says the Federal Environmental Protection Agency will monitor the three caps for five years to determine how each holds up in the elements. There are a number of devices buried in the caps to monitor the water flow. Hall says good results for the two alternative caps could prompt the E-P-A to adopt them for use over landfills across the country.