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Mr. Eric Charest <br />November 8, 2022 <br />Page 2 of 4 <br />Tetra Tech will review the available data and provide input to IRC on any data gaps that could <br />affect the model results. <br />Task 2. Develop ArcNLET Model and Conduct Modeling <br />Using the data gathered in Task 1, Tetra Tech will develop an ArcNLET model that encompasses <br />the entire IRL Basin within unincorporated IRC. The ArcGIS files will be incorporated into the <br />model and the available water quality data will be used to adjust the model parameters. The <br />model will then be run to determine the nitrogen loading impacts from the septic system to the <br />surface waterbodies within IRC. <br />Task 3. Conduct Sensitivity Analysis for Nitrogen Load Estimate <br />Tetra Tech will investigate the sensitivity in the nitrogen load estimates from the ArcNLET <br />model by providing probability density functions of the load estimates. This information will <br />help IRC to understand the minimum, maximum, and average nitrogen load estimates to help <br />with identification of future septic to sewer projects. <br />Task 4. Prepare Draft Report <br />Tetra Tech will prepare a draft report that summarizes the nitrogen loading from septic systems <br />to surface waterbodies for each area/basin of IRC and include a spreadsheet/database that shows <br />pollutant loading estimates per parcel. The report will also include the results of the sensitivity <br />analysis to help IRC understand the range of loading estimates. The draft report will be provided <br />as a Word document to IRC for review. <br />Task 5. Prepare Final Report <br />Tetra Tech will prepare a final report that incorporates the comments received from IRC on the <br />draft report in Task 4. The final report will be provided to IRC as both a Word document and <br />PDF. <br />Task 6. Communication and Meetings <br />Throughout the project, Tetra Tech will communicate with IRC to ensure the best data are <br />incorporated into the ArcNLET model and to keep IRC updated on the project status. An in- <br />person meeting will be held to review the draft report and model results with IRC to obtain input <br />for the final report. <br />PROJECT SCHEDULE <br />The approximate duration noted for each task is based on our current understanding and best <br />estimates of time required to perform the basic services and may be subject to change upon <br />agreement between IRC and Tetra Tech. <br />Task Timeline <br />Notice to Proceed TP November 10, 2022 <br />IRC Provides All Data November 18, 2022 <br />TETRA TECH 122 <br />