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Well Data Sheet Instructions(Rev. 11/99) page 8 local knowledge or by using the value for a system or source of similar size. However, if it is likely that the pumping rate is low(less than 15 to 20 gpm),the DWSAP minimum distances for protection zones will apply, and it is not necessary to estimate the pumping capacity. If the pumping capacity is not known at the time the WDS is completed,the field can be left blank. In this case, staff will need to estimate the pumping rate when doing the delineation calculations for the DWSAP assessment. Screened Interval Screened interval is also used in the delineation calculations and in the PBE evaluation. The screened interval is that portion of the well casing that has screens or perforations through which water enters the well. The screen allows ground water to move freely from the aquifer into the well while stabilizing the aquifer material. The length of screened interval is used in the delineation calculations to represent the portion of the aquifer that the well can draw from. In general,the greater the screened interval,the more aquifer that the well can pull from,and the less horizontal distance away that a particular volume of water will travel within a given time period. Typically, several portions of the well casing are screened. The WDS asks for three pieces of information about the screened interval,which can generally be found in the well drillers' Iog.Each of the fields for screened interval is described below: Depth to the Highest Perforations/Screens—The depth to the first perforations should be entered in feet below ground surface. If the information is not available enter "Unknown". Screened Interval Beginning Depth/Ending Depth—The beginning depth of the first screened interval should be entered in feet below ground surface, followed by a slash(n then the ending depth of the interval should be entered. If there are more screened intervals they should be entered the same way separated by a semicolon from the previous one. The field length can accommodate several screened intervals. Total Length of Screened Interval—The length of all the screened intervals should be added and the value placed in this field. This value is used in the delineation and PBE calculations. Sometimes, information may be available on the length of screens, but not the specific beginning and ending depths. The total length should be entered here and the previous field should be left blank_ At other times,you may know the beginning and ending depths of all screens,but have no knowledge whether the entire interval is screened. In this case,the total length of screened interval can be determined as the distance between the beginning and ending of the perforations, but this may result in smaller protection zones. Judgment should be used to determine the appropriate length. The DWSAP program allows a default screened interval of 10% of the pumping capacity of the well in gallons per minute,with a minimum length of 10 feet. For example, the default screened interval for a well that has a pumping capacity of 400 gpm would be 40 feet. This is a conservative value for most wells. If the default method is used to determine screened interval this should be noted in the"Actual,Estimated or Default?" column.