The USGS constructed five new monitoring sites along the DMC to provide information on the geology, water levels, and water quality of the underlying aquifers. Data collected from these sites is being used to analyze vertical differences in water level and quality. In addition, these data are being used to help calibrate a groundwater-flow and land-subsidence model. The monitoring sites were constructed using the mud-rotary method and completed to a depth of about 500 feet below land surface (bls). During the drilling operation, cores were collected at strategic locations. Three to four 2-inch diameter PVC piezometers were installed in each borehole. One piezometer was installed at the water table, a second piezometer was installed in the aquifer system above the Corcoran Clay, and a third piezometer was installed in the aquifer system below the Corcoran Clay. Pressure transducers were installed in each piezometer to electronically measure water-level changes at each site. After well development was completed, each well was sampled and analyzed for major ions, nutrients, selected trace elements, and the stable isotopes of oxygen and hydrogen.