With funding provided by the Office of Electricity Delivery and Energy Reliability, Los Alamos National Laboratory (LANL) examined the approaches suggested in NERC Standard TPL‐007‐1for defining the geo‐electric field for the Benchmark Geomagnetic Disturbance (GMD) Event. Specifically,

1. Estimating 100‐year exceedance geo‐electric field magnitude,

2. The scaling of the GMD Benchmark Event to geomagnetic latitudes below 60 degrees north, and

3. The effect of uncertainties in earth conductivity data on the conversion from geomagnetic field to geo‐electric field.

This report summarizes the review and presents recommendations for consideration. The Appendix contains the comments from four independent reviewers of this work and LANL's responses to these comments, including a discussion of any changes made to the report's content.