Water Quality Protection Charge Program

The Montgomery County, Maryland Department of Technology Services - Geographic Information Systems (DTS-GIS) team has developed an automated digital process to update two GIS data layers to support the Water Quality Protection Charge (WQPC) program administered by the County Department of Environmental Protection (DEP). The WQPC was initiated for the fiscal year 2003. To assess water quality protection charges equitably, the amount of impervious surface of each land ownership parcel needs to be determined. The existing County GIS data layers—property parcels, building footprints (BLDG), transportation features (parking lots and driveways, TRANS) and the assessment database, maintained by the State of Maryland,were identified as data sources to enable the calculation of the impervious areas for the ownership parcels.

A system of GIS data layer maintenance was designed to update the data layers so that as many parcels as possible will have the impervious areas correctly calculated. The system entails making use of the up-to-date digital ortho-photo imagery as the source for updating the BLDG and TRANS layers. Technician time was paid for by the WQPC operating budget. The cost for this type of GIS database maintenance is estimated to be about one third of what it would cost if a conventional photogrammetry contractor were used. Updated data layers also benefit other County programs such as the new Computer Assisted Dispatching (CAD) system of the County’s Public Safety 2000 program.

The data are served using the County GIS Intranet Map Server so that DEP customer service staff can use their web browsers to access the information within seconds.