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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.

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

WQM 7.0 (Access) - WQM 7.0 is a Wasteload Allocation Program (WLA) used to developed WQBELs for Dissolved Oxygen and Ammonia-Nitrogen. A Technical Reference Guide 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.

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.

Total Residual Chlorine Spreadsheet (Excel) - May be used by DEP to evaluate effluent limitations and monitoring requirements for Total Residual Chlorine (TRC) in NPDES permits.

WET Analysis Spreadsheet (Excel) - May be used by DEP to evaluate reasonable potential to exceed water quality standards for Whole Effluent Toxicity (WET) and by NPDES permittees and/or laboratories to evaluate whether WET tests are considered "pass" or "fail".

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