A high-capacity prototype injection well was tested in the isthmus area of Maui, Hawaii. Pumping tests were made on April 14 and 15, 1978, and 10 injection tests were made between May 12 and June 30, 1978. Selected tests were monitored in order to obtain data which could be used to assess the effects of subsurface disposal on the ground water in the basal aquifer. Pumping and injection rates were measured. Basal-water head responses to pumping and injection were observed at the prototype well and at two observation wells located 435 and 6 ,100 feet from the prototype well. Water-quality samples were collected at the prototype well and the nearest observation well prior to testing. Samples of the injection water, as well as samples from the observation wells, were collected prior to and after the final test. The head data and water-quality data are presented in this report. (USGS)