This polygon dataset represents IWPA features in Massachusetts, which are generated by buffering PWS well point locations in the DEP Public Water Supply datalayer based on radius values determined from the best available pumping rate information. The IWPA features are relatable to the PWS source points by SOURCE_ID.
In the absence of an Approved Wellhead Protection Area (Zone II), the MA DEP has adopted the Interim Wellhead Protection Area (IWPA) as the primary, protected recharge area for public water supply (PWS) groundwater sources in Massachusetts. For PWS sources that pump less than 100,000 gallons per day (GPD), the IWPA radius is proportional to the pumping rate in gallons per minute (GPM). Pumping rate is based on of several methods including, DWP approved pumping rate, metered data, Title 5 flow rate. The formula used for calculating the PWS well point buffer radius in feet is:
Radius = ( 32 x pumping rate in GPM ) + 400
The minimum IWPA radius is 400 feet, the maximum (default) radius reached at 100,000 GPD (70 GPM) is 2,640 feet (1/2 mile). In instances where pumping rate information is unavailable default radius values are assigned based on the PWS well classification. The default radius for community class PWS groundwater sources (GW) is 2,640 feet (804.6 meters). The default radius for non-community sources is 750 feet (228.6 meters) for Non Transient (NTNC) wells and 500 feet (152.4 meters) for Transient (TNC) wells.
The IWPA layer contains variable width IWPAs for BOTH community and non community groundwater sources in the DEP PWS datalayer which do not have an approved Zone II.