1 Comments Prepared by Maryland Depa rtment of the Environment (MDE) On Sierra Club’s May 4, 2015, “Evaluation of Compliance with the 1-hour NAAQS for SO 2 ” for C.P. Crane Generating Station and Fort Smallw ood Complex (Brandon Shores & H.A. Wagner), Maryland

On behalf of Sierra Club, Wingra Engineering conduc ted modeling of the Fort Smallwood Complex (Wagner & Brandon Shores Generating Stations) and Crane Generating Station with the mo st current (2012-14) meteorological data using U.S. EPA’s regulatory model, AERMOD Ver. 14134. The modeling used both allowable and maximum emissions rates limits from the permit application and actua l hourly emission rates (CEMS data) to conduct the 1-hour SO 2 NAAQS (196.2 ug/m 3 ) modeling.

MDE has taken this opportunity to review and prepare comments on the 1-hour SO 2 modeling conducted by Sierra Club. The comments are as follow:

1. Sierra Club has modeled 1-hour SO 2 using AERMOD and AERMET Ver. 14134. U.S. EPA’s latest version, 15181, of AERMOD and AERMET has been available since June 30, 2015. MDE would recommend designation modeling using latest versi on of AERMOD/AERMET for this modeling analysis. 2. Sierra Club has modeled the Wagner and Brandon S hores Generating Stations as a single complex, the Fort Smallwood Complex. MDE recommends m odeling Brandon Shores and Wagner separately. 3. Sierra Club’s modeling includes allowable emission rate limits and actual hourly emission rates. Sierra Club has also modeled the Crane, Wagner and Brand on Shores Generating Stations using the “maximum” emission rate. In MDE’s opinion, these “maximum” values do not reflect the accurate operating scenarios of the facilities or the probable conditions (startup, shutdown, maintenance, et c.) under which such higher emissions are released from the units. Since the 1-hour SO 2 NAAQS is statistical in nature, the predicted 1- hour SO 2 modeling results will have a higher degree of uncertainty. 4. Sierra Club’s modeling did not include the effects of building downwash (BPIP program) and GEP height of the stacks. It is a well known fact that inclusion of building dimensions and parameters in the modeling affects the downwind concentrations. MDE would r ecommend that building downwash be used in the modeling analysis. 5. In the modeling, Sierra Club has set the flag pole to receptors and placed th e receptors over the water bodies. However, EPA’s SO 2 NAAQS Designations Modeling Technical Assistance Document (TAD) recommends the designation modeling without receptors over water bodies, and predicted concentrations at the ground levels, i.e., wit hout flag pole receptor heights. 6. Background concentrations used in the modeling by Sierra Club are the Howard University (HU)- Beltsville monitoring site for years 2012-14. The background concentration of 26.2 μg/m 3 is based on Tier 1 analysis, based on EPA’s 1-hour SO 2 Modeling TAD. 7. Sierra Club’s modeling did not include the cause- and-contribute (MAXDCONT) analyses. MDE believes that such runs/files/analyses are he lpful in evaluating the impacts of affected sources in the area. These analyses are beneficial in sources interactive study, a nd quantifying the concentrations by sources/units at the receptors.