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Consent Item Indian River County, Florida Department of Utility Services Board Memorandum Date: November 15, 2022 To: Jason E. Brown, County Administrator Through: Sean C. Lieske, Director of Utility Services Prepared By: Richard Meckes, Operations Manager Subject: Unincorporated Indian River County Lagoon ArcGIS Nitrogen Load Estimation Tool (ArcNLET) Model, Tetra Tech, Inc., Work Order No. 12 Background/Analysis: On April 17, 2018, the Board of County Commissioners (BCC) approved the Continuing Contract Agreement for Continuing Engineering Services with Tetra Tech, Inc. for professional water resource engineering support services. The original contract was for three (3) years with an option for one (1) two- year extension at the County's discretion. This contract was renewed on May 18, 2021 for the two (2) year extension Indian River County (IRC) remains committed to its ongoing efforts focused at improving the health of the Indian River Lagoon (IRL), while continuingto pursue additional activities to further IRC's lagoon programs. A summary of IRC's programs related to water quality improvements for the lagoon is maintained and updated annually by the Florida Department of Environmental Protection (FDEP) and contained within the Central Indian River Lagoon Basin Management Action Plan (CTRL BMAP). This report is used to track Total Maximum Daily Load (TMDL) reductions of nitrogen and phosphorus as 'credits' for IRC's efforts against the required reductions for IRC contained in the CIRL EMAP. As IRC continues to provide annual updates to the FDEP in accordance with their reporting requirements, IRC's efforts at septic tank abandonment (septic to sewer (S2S) conversions) have yet to provide IRC with any FDEP-recognized TMDL 'credits'. Instead, these S2S projects are tabulated annually with 'credit' amounts that are to be determined (TBD). S2S projects within the CTRL BMAP are expected to account for significant reductions of nitrogen from reaching IRL. IRC continues to pursue opportunities for these types of projects, and now is seeking a way for these completed projects to account for TMDL 'credits' recognizable by the FDEP in their annual reports. FDEP has accepted the use of the ArcGIS Nitrogen Load Estimation Tool (ArcNLET) model to quantify nitrogen load reductions to the IRL from these S2S conversion projects. Tetra Tech, under Work Order No. 11, will be able to provide IRC with a calibrated ArcNLET model for the portion of unincorporated IRC that falls within the CIRL EMAP basin. With the calibrated model, IRC can then provide the FDEP with verifiable values for the current S2S projects that have been completed in order to receive TMDL 'credits', as well as use the model to potentially support future S2S projects. 118