Via October Mr. William Neal, P.E. Technological Specialist DTE Electric Company One Energy Plaza Detroit, MI 48226

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1 134 N. La Salle Street, Suite 300 Chicago, Illinois PH FX Via Mr. William Neal, P.E. Technological Specialist DTE Electric Company One Energy Plaza Detroit, MI Subject: Hydrologic and Hydraulic Capacity ssessment Monroe Power Plant sh asin Facility Monroe, MI Dear Mr. Neal: This letter report presents the results of the Geosyntec Consultants (Geosyntec s) hydrologic and hydraulic capacity assessment for DTE Electric Company s (DTE s) Monroe Power Plant sh asin (sh asin). The hydrologic and hydraulic capacity assessments are required under the United States Environmental Protection gency (USEP) Coal Combustion Residual (CCR) Rule (CCR Rule) published on 17 pril CFR Parts 257 and 261). Under the CCR Rule, the sh asin is an existing surface impoundment and must meet hydrologic and hydraulic capacity assessment per and of the CCR Rule. EXECUTIVE SUMMRY hydraulic capacity of the facility was completed using the design storm specified under (a)(3). The results of the analyses indicate that the sh asin meets the hydraulic capacity requirements per Hydrologic and Hydraulic Capacity Requirements for CCR Surface Impoundments.

2 Mr. William Neal Page 2 HYDROLOGIC ND HYDRULIC CPCITY SSESSMENT Requirements of the CCR Rule hydraulic capacity analysis was conducted to assess whether the discharge structure, acting as the spillway, meets the requirements of of the CCR Rule. The CCR Rule requires that: (a)(1) The inflow design flood control system must adequately manage flow into the CCR unit during and following the peak discharge of the inflow design flood. (a)(2) The inflow design flood control system must adequately manage flow from the CCR unit to collect and control the peak discharge resulting from the inflow design flood. (c)(1) Inflow design flood control system plan. The owner or operator must prepare initial and periodic inflow design flood control system plans for the CCR unit according to the timeframes specified in paragraphs (c)(3) and (4) of this section. These plans must document how the inflow design flood control system has been designed and constructed to meet the requirements of this section... Hydraulic Models and Inputs The sh asin has received a Significant Hazard Potential classification per (a)(2) 2. Per the CCR Rule, the sh asin must adequately manage peak discharge from a 1,000yr flood event. However, the peak discharge was estimated based on the more conservative probable maximum flood (PMF). The combination of available storage volume within the sh asin and the hydraulic (flow) capacity of the discharge structure must be able to safely convey the expected peak flows during the PMF without overtopping the perimeter embankment. The assessment was conducted using the hydrologic model HECHMS (HECHMS, 2013) to simulate inflows into the sh asin, temporary runoff storage in the sh asin, and outflow from the sh asin via the discharge structure. HECHMS is hydrologic analysis software developed by the U.S. rmy Corps of Engineers that is in the public domain and widely used for hydrologic modeling related to flood 2 separate letter is provided for the hazard potential classification for the Monroe sh asin, which is considered to be a Significant Hazard Potential.

3 Mr. William Neal Page 3 control and management, drainage, stormwater management, and dam and reservoir management. The inflow design flood for the sh asin was conservatively selected to be the PMF. The volume and peak flow of stormwater runoff during the PMF was calculated from a simulation of the Probable Maximum Precipitation (PMP) storm event. The PMP data was taken from the PMP Study for Wisconsin and Michigan (EPRI, 1993). 72hour duration rainfall period was analyzed. The EPRI study published PMP depths for a range of durations up to 72 hours. The PMP depths for 6hour and 24hour periods are nested within the 72hour PMP. The 72hour PMP depth is 23.2 inches of rainfall. Most of the rainfall will occur within the peak 24 hours of the rainfall event. It was assumed that all of the rainfall falling within the sh asin will become direct runoff into the sh asin meaning that no runoff reduction credit was taken for infiltration into the ground. It was also assumed that sluiced fly ash continues to be discharged to the sh asin during the PMP storm event at a constant rate of 15 million gallons per day, or 23 cubic feet per second (direct communication with DTE, 2015). In addition to the constant sluiced fly ash rate, a constant flow of six cubic feet per second was included in the simulation to represent the estimated maximum inflow from the stormwater pumping station. Therefore, the total constant inflow rate used per the simulation (in addition to variable stormwater runoff from the PMP) was 29 cfs, which includes a 23 cfs contribution from incoming fly ash slurry and 6 cfs from the stormwater pumping station. fter calculating the inflow, storage and outflow characteristics of the sh asin were entered in HECHMS. The storage characteristics of the sh asin are based on topographic and bathymetric data, at and above the normal pool water elevation of 609 ft 3. digital terrain model was constructed to calculate the storage data. Sources used in the creation of the digital terrain model include: Topographic mapping of existing abovewater areas, based on the most current base map. 4 athymetric mapping of existing belowwater areas, based on May 2015 bathymetry performed by DTE. 3 Elevations are in National Geodetic Vertical Datum of 1929 (NGVD29). 4 Contains various asbuilt surveys conducted from

4 Mr. William Neal Page 4 To simulate the hydraulic characteristics of the discharge structure, a rating curve or structure geometry must be entered into HECHMS. ecause of the complexity of the discharge structure, it could not be represented with one simple hydraulic element. The discharge structure hydraulics are evaluated using a combination of three different hydraulic controls: First, water must pass through openings cut into the sheet pile wall surrounding the discharge structure. These openings hydraulically function as submerged orifices. If the water level increases above.5 ft, it will flow through sheet pile weirs. Next, water passes through the stoplog/weir structures. There are three weir openings, with the bottom elevations controlled by raising or lowering the stoplogs. Finally, water enters three parallel 36inch diameter steel pipes encased in concrete and is discharged to the east beyond the sh asin. HECRS (HECRS, 2010) computer model was developed to simulate the hydraulic interactions and performance of this series of structures. HECRS is widely used to simulate steadystate flow through artificial and natural waterways and structures such as culverts, bridges, channels, spillways, rivers, and gates. series of different steadystate flows was simulated in HECRS, ranging from 2 cubic feet per second to 250 cubic feet per second, and the pond water elevations corresponding to these flow rates were calculated. The pond water elevation for a specific flow rate corresponds to the hydraulic head necessary to push a specified flow rate through the discharge structure. These data were used to develop a storagedischarge curve for the HECHMS routing. Following the construction of the HECHMS model, the model was used to simulate the hydraulic performance of the sh asin during the PMF. The discharge structure has been recently modified to operate more reliably during the PMF event. The drawing provided in ppendix provides more information on discharge structure construction and modified geometry. The analysis was conducted based on sh asin operating water level of 609 ft and the modified discharge structure geometry. nalysis considered that 42 linear feet of a section of the sheet pile wall is lowered to an elevation of.6 ft. It was assumed that the sheet pile underwater openings are 70% blocked and that the effective diameter of the outlet culverts is reduced by 1.5 inches, to account for the ¾ inch thick deposits in the culvert pipes that was observed during 2015 inspection. starting water surface elevation of ft was used, which is the normal operating elevation.

5 Mr. William Neal Page 5 nalysis Results The PMF results in a peak water surface elevation of ft, which leaves approximately 1.0 feet of freeboard relative to the lowest point on the proposed embankment crest spillway, elevation ft. This indicates that the PMF will be safety contained within the sh asin. The peak outflow from the sh asin would be approximately cfs. Figure 1 shows how the water level is changed within the sh asin during and after the PMP storm event. Inflow Design Flood Control System Plan The sh asin is encapsulated by an embankment that is up to 45 ft higher than the surrounding ground surface. The perimeter of the embankment defines the outer limits of the watershed, which is the plan area of rainfall. There is no outer watershed area that directly flows into the sh asin. Inflow values have been previously described in the earlier section of this letter under Hydraulic Models and Inputs. Stoplogs should be adjusted so that water level in the sh asin is kept around elevation 609 ft. Underwater sheet pile openings should be visually inspected for plugging on an as needed basis and cleaned if necessary. QULIFICTIONS OF LICENSED PROFESSIONL ENGINEER John Seymour is a qualified licensed professional engineer with over 30 years of experience in civil and geotechnical engineering associated with dams.

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7 Water Level In the Impoundment During and fter PMF Reservoir Water Level Probable Maximum Precipitation Days Change in sh asin Water Elevation During and fter PMF Monroe sh asin Hydraulic Figure Capacity ssessment September, G:\CWP\CHE8242Detroit Edison\500 Technical\502 sh Pond Stability\50213 Structural Stability & Hydraulics ssessment\task 2 Hydraulics ssessment\september 2016 Elevation (ft) Cumulative Precipitation (in)

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9 ' WLE #2 S30 S9 STOPLOG STRUCTURE S S27 9'' NORML OPERTING LEVEL 609 FT WLKWY STRUT #2 (W12 x 65) STRUT #6 STRUT #5 S2 STRUT #3 (W12 x 65) STRUT #4 (W8 x 35) STRUT #7 OPENING (SEE SECTION ) S WLE #1 S7 S S5 (NOTE 6) STIFFENERS PLN VIEW EXISTING CONDITION S3 S2 5' FLYSH SIN PIPING ND SUPPORTS STOPLOG STRUCTURE WLE #5 S5 STOPLOGS S25 PZ 38 STEEL S23 STRUT #1 (W8 x 35) S22 C S3 WLKWY STRUT #5 STRUT #2 (W12 x 65) STRUT #6 WLE #6 (W12 x 40) STRUT #7 NOTE 1 S2 STRUT #3 STRUT #4 (W12 x 65) (W8 x 35) NOTE 4 WLE #1 STRUT #8 C S21 S LEVE 6' +/ OF IN PLCE REMOVE 15' +/ OF S8 S9 S7 S5 S6 LEVE 6' +/ OF IN PLCE REMOVE 15' +/ OF PLN VIEW PROPOSED CONDITION S2 S3 REMOVE 12' +/ OF 0+72 SCLE IN FEET 7.5' DISTNCE (FEET) 0+40 WLE #1 (W24 X 94) S9 S8 S7 S6 S5 S3 S2 PPROXIMTE EXISTING GRDE NOTE 5 HOLE COVERED WITH RIPRP REMOVE 12' +/ OF 0.5' 0.5' S9 S8 S7 S6 S5 S3 S2 WLE #6 (W12 X 40) 7'' x 37'' 7'' x 36'' 9'' x 36'' 8'' x 35'' 9'' x 12'' 7'' x 37'' 8'' x 35'' REMOVE 15' +/ OF NOTE 5 HOLE COVERED WITH PLTE, 1.5'' X 3'' EXPOSED SEE SECTION FOR EXISTING CONDITIONS NOTE 4 DISTNCE (FEET) DISTNCE (FEET) OPENING NORML OPERTING LEVEL 609 FT WLE #6 (W12 x 40) REMOVE 15' +/ OF WLE #1 5' 0 WLKWY S6 S24 10' SCLE IN FEET S7 CONCRETE FLOOR CONCRETE WLL S26 PZ 38 STEEL 7.5' NOTE 4 FLYSH SIN PIPING ND SUPPORTS WLE #2 S27 STEEL 0 S28 7.5' 0+72 N S8 S9 13' WLE #6 (W12 x 40) ' 0 S8 PPROXIMTE EXISTING GRDE S21 DESIGN SLOPE 1.25' S35 1 N STRUT #8 STRUT #5, #6, #7 ND #8 CONCRETE S34 4 S29 10' STRUT #1 (W8 x 35) S22 S3 S33 5 S9 STRUT #2 ND #3 (W12 x 65) 2.05' S24 S23 WLE #6 (W12 x 40) S32 6 S30 STOPLOGS WLE #5 PZ 38 STEEL S5 S25 WLE #1 S6 CONCRETE FLOOR CONCRETE WLL PZ 38 STEEL S26 WLKWY S7 WLE #3 ND #4 (W24 x 117) 10.88' FLYSH SIN PIPING ND SUPPORTS (NOTE 4) 3' 6.93' S29 S28 S ' 7 S37 S36 WLE #3 (W24 x 17) 3 2 9'' FLYSH SIN PIPING ND SUPPORTS 2.95' 0 UNDERGROUND DISCHRGE PIPES WLE #4 (W24 x 17) 30' 4' ' S34 7 S37 S36 TOP OF EMNKMENT 7' S33 S35 WLE #3 (W24 x 17) ' S32 UNDERGROUND DISCHRGE PIPES WLE #4 (W24 x 17) S TOP OF EMNKMENT WLE #1 (EXISTING) (W24 X 94) EXISTING PZ 38 (NOTE 2) 1" Ø 36 GLVNIZED THREDED ROD, TOP & OTTOM WITH HEVY HEX NUTS & WSHERS GLVNIZED 3.5" X 3.5" X 0.5" PLTE WSHER ECH END (NOTE 2) tf WLE #1 (EXISTING) (W24 X 94) I GLVNIZED 3.5" X 3.5" X 0.5" PLTE WSHER ECH END J O N H 3.5" x 3.5" x 0.5" PLTE ERING SET (NOTE 3) K C d D E tw NOTE 4 D F M P G EXISTING PZ 38 (NOTE 2) NOTE 6 1" Ø 36 GLVNIZED THREDED ROD, TOP & OTTOM WITH HEVY HEX NUTS & WSHERS L GLVNIZED 3.5" X 3.5" X 0.5" PLTE WSHER ECH END (TYP.) WLE #6 (EXISTING) (W12 X 40) bf 3.5" x 3.5" x 0.5" PLTE ERING SET (NOTE 3) GLVNIZED 3.5" X 3.5" X 0.5" T OTTOM INSIDE POSITION (NOTE 3) NUMER WLE 1 WLE 2 WLE 3 WLE 4 WLE 5 WLE 6 STRUT 1 STRUT 2 STRUT 3 STRUT 4 STRUT 5 STRUT 6 STRUT 7 STRUT 8 STRUCTURE DESIGNTION (NOTE 8) W24 x 94 W24 x 94 W24 x 117 W24 x 117 W24 x 94 W12 x 40 W8 x 35 W12 x 65 W12 x 65 W8 x 35 W8 x 24 W8 x 24 W8 x 24 W8 x 24 1 bf d tf tw 12" 12" 81/ 1211/16" 121/4" 69/16" 69/16" 69/16" 69/16" / 241/4" 241/4" / 83/16" 121/4" 121/4" 83/16" 715/16" 7/ 7/ 7/ 7/ 7/ 3/ 7/16" 9/16" 5/ 7/16" 3/ 3/ 3/ 3/ 1" 1" 1/ 5/ 9/16" 3/4" 1/4" 5/16" 3/16" 7/16" 5/16" DETIL WLE/STRUT DIMENSIONS ( NOTE 7) NUMER S6 S0 S21 S22 S25 93/ 87/ 87/ 83/4" 8 93/4" 15 93/4" C 11" 113/ 113/ 113/ 11" 11" 113/ D 93/ 93/4" 97/ /4" 97/ 91/4" E 8 113/ 113/ / 11" 113/ F 0 93/4" 0 81/4" G 5/ 5/ 5/ 5/ 5/ 5/ 5/ 2 H 3/ 3/ 3/ 3/ 3/ 3/ I 5/ 3/4" 5/ 5/ 5/ 5/ 5/ J 5/ 5/ 5/ 5/ 5/ 5/ K 3/ 5/ 3/ 3/ 3/ 3/ 3/ DETIL DIMENSIONS (NOTE 9) L M NOTE 10 NOTE 10 5/ 5/ NOTE 10 NOTE 10 5/ 5/ 5/ N O P TO E REMOVED 3 DETIL ND WLE CONNECTION 10'