MEMORANDUM SUBJECT: Techni · cal Guidance Reviewed by US EPA for 40 CFR Parts 257 and 261, [EPAHQ-RCRA-2009-0640; FRL-9149-4], RIN -2 050
-AE81 , Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric Utilities. FROM: Patrick M. Kelly, P.E. Environmental Engineer Office of Solid Waste and Emergency Response TO: Docket DATE: Thursday , December 18 , 2014 Upon the in itia ti on of the CCR Surface Impoundment Assessment effort, EPA considered a number of regulation and guidance in developing a criteria to determine structura l adequacy and safety of CCR Surface Impoundments. EPA requested of its engineering contractor Dewberry and Davis to provide recommendations regarding what guidance or regulations would be appropriate in order to determine the overall structural and safety adequacy of the CCR surface impoundments. Attached is a memo sent from Dewberry and Davis personnel to EPA personnel offering recommendation for appropriate guidance and regulation for dam safety . EPA reviewed and in some instances based final regulatory text on these guidance and regulations , in addition to additional guidances which EPA reviewed, in the CCR Surface Impoundment Assessments and additionally in the finalization of the CCR final rule 40 CFR Parts 257 and 261, [EPA- H QRCRA-2009-0640; FRL-9149-4], RIN-2050-AE81, Hazardous and Solid Waste Management System; Disposal of Coal Combu stion Residuals from Electric Utilities.

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To: Jerry Strauss, PE CC: File From: Fred C . Tucker, PE Date: December 12, 20 II 8401 Arli ngto n Boulevard F airfax , Virginia 22031-4666 703 849 0100 703 206 0803 fax www .dewberry.com

Re: Appropriate Stability Analysis Guidance Documents for CC R Impoundment D ikes The U.S. Army Corps of E ngineers (USACE) is usually the best resource for engineering and techn ical guidance not dictated by other agencies such as the US Bureau of R eclamation , Natura l Resources Conservation Service, Federal Energ y Regulatory Commission, US Forest Servi ce , etc. Appropriate guidance on s lo pe st ab ility i s contained in the

**U_SACE~** Enginlli l EM 111 0-2- 1 902 " Slo e Stab ilit "dated 31 October 2003. The earlier version of EM 111 0-2-1902 , which wa s then titled " Stability ofEarth an ock-Fill Dam s," dated I April 1970, may also be useful , parti cu larl y wh en performin g screening

**asse ssm,~**  **nts** of dams or dike s constructed prior to abo u t 1 983 , when the USACE began to change policy and procedures in ana lys is of embankment dams under eart h quake loading. The later ve r sion of EM 1110-2-1902 does no t cover earthqu ake loading, but general guidance on earthquake desi gn is given in ngineer Re ulation E R 1110-2-1806, "Earthquake Desi nand Evaluatio n fi r Civ' ro·ect," dated 31 5. Interim gmdance is given in Engineer Technical Letter E TL 1110-2-301, " In terim Procedure for Specifying Earthquake Motions ,"

• . dated 26 August 1983. Guidance on dam s afety i s given in EC 111 0-2-60 61 , " Safety of 

# I Dams-Policy and Procedures," dated 30 April 2004. Comprehensi ve g uidance i s being . developed in Eng ineer Circular EC 1110
- 2- 6000, " Selection of De s ign Earthquakes and Assoc iated Ground Motions ," draft dated 10 July 2008 and in EC 11 1 0-2 -600 I , " Dynami c Stability of Emb ankment Dams," draft dated 4 February 2004. Alternative guidance may be found in the Engineering and Design Manual for Coal Refu se Dispo sal Facilities ( Manual) , o rigin a ll y publish ed by the Mining Enforcement and Safety Administration (MESA) in 1 975 and updated for the Mine Sa fety and Health Admini stration (MS HA ) in May 2009 , in particular Chapter 6 , " Geotechnical Exploration, Material Testing , Engineering Analy sis and De s ign ," and Chapter 7 , " Seismic Design: Stability and Deformatio n Analyses
. "

### The following federa l guidelines are used for seismic analyses of earthen dams: Analyses for earthq u ake loading begin with simplified procedures and evaluated by the pseudo - static met h od using the seismic coefficient to t h e seismic zone (developed by USACE) for the project. USACE ER 1110-2-1806 d. Est i mating OBE and MOE ground motions. 

### Estimates are usually made in two phases. The first estimates are used as a starti n g point for the study and are obtained from the Nationa l Earthquake H azard Reduction Program (NEHRP) spectra l acce l eration maps . The second p h ase is more site-specific, used for critical structures (eg
. , nuclear plants) and not usually used for impoundment dikes. National Earthquake Hazard Reduction Program (NEHRP) Spectral Acceleration Maps 

### The reference for seismic load i ng is USGS Seismic-Hazard Maps for the Conterminous United States, Horizontal Spectral Response Acceleration for 1. a-second Period (5 Percent of Critical Damping) with 

### 2 Percent Probability of Exceedance in SO Years. 

### (i.e. probable earthquake within 2 , 500 years).



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