Begin Main Content Area

Water Quality Models and Tools

DEP maintains several water quality models and tools used by the NPDES permitting program. These models and tools are generally used in NPDES permit development and/or utilized by permittees as a part of permit conditions.

Water Quality Models

PENTOXSD and WQM 7.0 - Water quality models used to aid in the development of water quality-based effluent limits (WQBELs). WQM 7.0 is a Wasteload Allocation Program (WLA) for Dissolved Oxygen and Ammonia-Nitrogen. PENTOXSD is a WLA program for toxics and other substances. Technical Reference Guides and Supplemental Information are available in the Documentation folder of the ZIP file. For download instructions open the ZIP file and review the Read Me file.

Toxics Management Spreadsheet (Macro-Enabled Excel) – The Toxics Management Spreadsheet is a macro-enabled Excel binary file that combines the functions of the PENTOXSD model and the Toxics Screening Analysis spreadsheet to evaluate the reasonable potential for discharges to cause excursions above water quality standards and to determine WQBELs.

Lake Model Spreadsheet (Macro-Enabled Excel) – A water quality model used to implement the requirements of § 96.5 Phosphorus Discharges to Lakes, Ponds, and Impoundments. It is applicable to discharges to watersheds and their tributaries that flow into lakes, ponds, and impoundments that have a hydraulic residence time of 14 days or more, based on average annual flow conditions.

NPDES Permit Tools

DEP has developed several tools to aid in NPDES program implementation. These tools are Excel based and do not require installation. Instructions for each tool are available on the first tab of the workbook.

For technical issues or questions, contact the Bureau of Clean Water's Division of NPDES Permitting at 717-787-5017 or