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Public and External Expert Technical Review Summary

Purpose and Scope of Review

Through late 2018 and early 2019 EPA concurrently released the Subtask F/G Memos (Summary of Empirical Modeling & Nitrogen Endpoints) for public review and commissioned an independent technical review of the Subtask E (Summary of Hydrodynamic Modeling) and F/G Memos. For the Technical Review EPA’s external reviewers considered 15 specific questions, while also keeping in mind EPA’s objective for the review (to ensure scientifically-sound methodologies consistent with professional and relevant scientific practices). The external expert reviewers provided a variety of comments and questions on the analysis, as well as suggestions to improve its scientific defensibility.  While supportive of the multiple lines of evidence approach, the reviewers also provided general and specific suggestions that fit within the following three categories:

1. Clarity: Add additional clarity and further documentation of techniques used.
2. Near-term improvements: Revisit certain assumptions and conduct additional analyses that can be accomplished because there are available data to pursue the recommendations.
3. Future improvements: Conduct additional analyses that would further improve upon the defensible approaches used which, while valuable, EPA might not currently have the necessary data or resources to implement within the current project.

General Approach for Incorporating the Comments EPA will review the comments from both the public review and the technical review in detail and determine how best to incorporate them into the analyses, given available resources. Below is the general approach the team will use:

• Clarity: provide additional detail in the memo text by adding more explanation of the analyses conducted, justification for specific decisions or assumptions made, and additional figures to better explain concepts and steps taken. For example:

Elaborate on the assumption of conservative TN behavior for this analysis.

Add more detail on the stressor-response methods.

•  Near-term improvements: conduct additional analyses to test the influence of other factors on the analysis. For example:

Test a larger temporal period to examine the effect of the temporal scale used (i.e., July through September) on area of influence.

 Look into additional confounding factors to determine the influence of confounding factors on some models.

•  Future improvements: evaluate resource and time requirements for incorporating data/resource limited recommendations into the analyses; provide a detailed explanation for why EPA is able/unable to implement these and the extent to which such efforts would reduce uncertainty.

Response to Comments

As of October 2020 the analysis has been revised based on the public comments and the technical review recommendations. EPA will remain engaged with our partners and the public throughout this process.  Additionally, the team will develop a response to all the comments, which will be made available with the revised documents once it has been completed.