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OTETRA TECH <br />November 8, 2022 <br />Eric Charest <br />Indian River County Public Works — Coastal Division <br />1801 27th Street <br />Vero Beach, FL 32960-3388 <br />Email: echarestAirc og v.com <br />Subject: Proposal to Indian River County for Development of ArcNLET Model <br />Dear Mr. Charest: <br />Tetra Tech, Inc. (Tetra Tech) is pleased to provide Indian River County (IRC) with this proposal <br />for services to provide an ArcGIS Nitrogen Load Estimation Tool (ArcNLET) model for the <br />unincorporated area of the Indian River Lagoon (IRL) basin in IRC. <br />BACKGROUND <br />IRC is located along the IRL, which is one of the nation's most ecologically diverse estuaries <br />and an important ecosystem in the state of Florida. The local governments and state agencies <br />have been working together to restore this system, which has been impaired by excessive <br />nutrient inputs that are causing algal blooms and low dissolved oxygen conditions. <br />One restoration element for the IRL is the basin management action plan (BMAP) that outlines <br />projects that have been or will be implemented in the near future. In February 2021, the Central <br />IRL BMAP was finalized and outlined requirements for IRC to fulfill nutrient reductions. Septic - <br />to -sewer projects account for a significant reduction in nitrogen load to the IRL. The Florida <br />Department of Environmental Protection (DEP) uses the ArcNLET model to quantify nitrogen <br />load reductions to the IRL from septic -to -sewer conversion projects. <br />SCOPE OF WORK <br />Task 1. Collect Data Needed for ArcNLET Modeling <br />Tetra Tech will work with IRC to gather the data needed for the ArcNLET model. The model is <br />an ArcGIS extension that is dependent on good, local data to provide the best estimates of the <br />nitrogen loading from each septic system within the County. These data include geographic <br />information system (GIS) coverages with the exact location (or parcel) of the septic systems; <br />detailed local waterbodies with streams, ditches, creeks, canals, and lakes; topography; and soils. <br />In addition, water quality data for IRC, specifically groundwater data, are helpful to adjust the <br />default model parameters to match local conditions. Tetra Tech will gather available water <br />quality data from IRC as well as the St. Johns River Water Management District (SJRWMD). <br />Tetra Tech, Inc. <br />1353 N Courtenay Pkwy, Suite S j Merritt Island, FL 32953 <br />Tel 321.636.6470 Fax 321.636.6473 www.tetratecln <br />