Groundwater monitoring wells are necessary to determine water quality, flow characteristics, and flow direction. To accurately determine the direction of groundwater flow, water level measurements must be measured to a standard datum so elevation data collected at one site can be related to elevations of nearby features and to other release sites. For consistency, the measuring point on the top of the PVC casing should be marked on the inside northern rim at the top of the monitoring well casing. This is the point from which depth-to-water measurements are measured within the well. Per the New Jersey Department of Environmental Protection, the location of this measuring point must be accurately located in both the latitude and longitude plane as well as the vertical dimension. An initial survey of groundwater monitoring well elevations must be completed by a licensed surveyor.