CCR Rule Annual Inspection Report (cont.) 2

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2 The inspection findings consisted of maintenance items and items that were not observed to be signs or potential signs of significant structural weakness. No deficiencies or disrupting conditions that would require immediate measures to remedy were identified in the inspection. The operation and maintenance of the GSP is in accordance with generally accepted good engineering standards. Inspection Description An Arcadis team performed the Trimble County GSP 2016 annual inspection by a qualified professional engineer. The overall goal of the inspection was to ensure that the design, construction, operation, and maintenance of the GSP is consistent with recognized and generally accepted good engineering standards. The 2016 annual inspection is the second inspection in accordance with 40 CFR (b) Annual inspections by a qualified professional engineer. Prior to the field inspection, the team reviewed existing engineering data and past comprehensive and routine inspection reports for the impoundment. Engineering data included geotechnical engineering reports, design reports, construction reports, design drawings, as-built drawings, instrumentation data, and instrument installation reports. The overall inspection consisted of visual inspection of the embankments (upstream slope, crest, and downstream slope), visual inspection of appurtenant structures, and visual inspection of the emergency spillway interior by Remote Operated Vehicle (ROV). The visual inspection occurred on September 7, The inspection team included Peter Zimmerman, PE of Canary Systems and Matt Patton of Arcadis. An ROV team from Glenn Underwater Services inspected the emergency spillway on July 28, The GSP visual inspection was completed with the goal of identifying signs of distress or malfunction of the CCR unit. Any indications of distress, unusual or adverse behavior, or malfunction of the CCR unit and structures were noted. The hydraulic structure passing through the embankment (e.g. the emergency spillway) was visually inspected by camera-mounted ROV to verify its structural integrity and continued safe and reliable operation. (i) CCR Surface Impoundment Geometry The GSP is enclosed by a continuous embankment with pond elevation higher than the natural ground surface beyond the embankment toe. The embankment in plan is generally rectangular and can be described as having four sides (north, east, south, and west). The GSP crest is constructed at a lower elevation than the adjoining Bottom Ash Pond (BAP) located immediately to the south. Mechanically stabilized earth (MSE) access ramps connecting the GSP and BAP crest access roads CCR Rule Annual Inspection Report (cont.) 2

3 are located on the southeast and southwest corners of the GSP crest. The typical upstream and downstream embankment slopes are approximately 3H:1V. The GSP emergency spillway is a reinforced concrete box culvert six feet wide and four feet high located at the northeast embankment corner with the spillway outlet located at the downstream embankment toe. The spillway inlet is gated. Slope improvements completed since the 2015 inspection include riprap placement on a portion of the exterior west embankment slope. These improvements did not alter the geometry of the structure. (ii) CCR Surface Impoundment Instrumentation GSP instrumentation includes piezometers, survey monuments, and a pond level gage. Piezometers are open standpipe-type installations that are manually read using a water level indicator. Survey consists of a sign fastened to the MSE ramp wall and concrete monuments placed on the embankment. Pond water elevation is measured using a non-contact radar water level sensor. (ii) a Piezometers Notes: Name Northing Location (1) Easting Maximum Recorded Reading (2) PZ PZ PZ ) All coordinates and elevations are reported in Trimble Station s Plant Grid. 2) Maximum recorded reading since September 29, (ii) b Pond Level Gage Notes: Location (1) Maximum Name Recorded Northing Easting Reading (2) GSP ) All coordinates and elevations are reported in Trimble Station s Plant Grid. 2) Maximum recorded reading since September 29, CCR Rule Annual Inspection Report (cont.) 3

4 (ii) c Survey Monuments Name POSITION POSITION SIGN Notes: Location (1,2) Northing Easting Elevation (ft.) / (+/- 0.01) (0.03) (- 0.02) / / (+/- 0.01) (0.02) (+/- 0.01) (-0.04) (-0.03) (-0.02) 1) All coordinates and elevations are reported in Trimble Station s Plant Grid. 2) Readings associated with the maximum recorded change in Northing, Easting, and Elevation since September 30, The maximum change in readings when compared to the September 30, 2015 readings are shown in parentheses. Readings that have an equal amount of movement positive and negative in two or more months are shown with a +/- symbol. Maximum readings in one direction are either positive or negative. (iii) CCR Surface Impoundment Contents Elevations The GSP pond water level was Elevation ft. on September 7, CCR elevations range from Elevation 432 ft. to 467 ft. The water depth within the pond varied from 0.9 ft. to approximately 36 ft. CCR elevations were measured as part of the August 5-8, 2016 bathymetric survey and August 4, 2016 aerial survey of the GSP. (iv) CCR Surface Impoundment Storage Capacity The total storage capacity of the GSP is million cubic yards. The remaining GSP storage capacity at Elevation is million cubic yards (based on the August bathymetric and aerial surveys). (v) CCR Surface Impoundment Contents Volumes The total volume of stored CCR is estimated to be million cubic yards. The approximate volume of impounded water at the time of inspection was million cubic yards. (vi) CCR Surface Impoundment Structural, Operational, and Safety Items The preamble to the EPA CCR final rule identifies appearances of structural weaknesses that may include, but are not limited to, nine general item categories. These signs of structural weaknesses may range from minor items that will be added to the routine maintenance plan to deficiencies that could have the potential to disrupt the operation and safety of the structure. CCR Rule Annual Inspection Report (cont.) 4

5 The inspection findings consisted of maintenance items and items that were not observed to be signs or potential signs of significant structural weakness. No deficiencies or disrupting conditions that would require immediate measures to remedy were identified in the inspection. The operation and maintenance of the GSP is in accordance with generally accepted good engineering standards. Inspection findings are grouped by category and described below. Visual Inspection Category Observed? Comment No. 1. Excessive, turbid, or sediment-laden seepage No 2. Signs of piping and other internal erosion No 3. Transverse, longitudinal, and desiccation cracking No 4. Slides, bulges, boils, sloughs, scarps, sinkholes, or depressions Yes 1 5. Abnormally high or low pool levels No 6. Animal burrows No 7. Excessive or lacking vegetative cover Yes Slope erosion Yes 2, Debris No Comment No. Comment 1 The east exterior embankment slope had a shallow depression approximately midslope in one area. A small area of excess soil was located approximately 50 feet north of the depression. Both features appeared to be anomalies in the original grading. 2 Somewhat sparse vegetation was observed at two locations on the east exterior embankment. At one location, gravel and sand from the crest road had washed onto the slope and very minor erosion rills were observed. 3 Tall vegetation including some shrubs or small trees was observed along the emergency spillway discharge structure. 4 Two erosion gullies caused by crest access road runoff were observed on the west exterior slope. The erosion was from runoff near the pump electrical structure or from the access ramp. The gullies had not noticeably worsened in the past year. 5 An erosion gully along the south side of the ramp access road on the north exterior slope was observed. The gully was approximately 1 to 2 feet wide and 8 inches deep. CCR Rule Annual Inspection Report (cont.) 5

6 The inspection findings consisted of maintenance items and items that were not observed to be signs or potential signs of significant structural weakness. No deficiencies or disrupting conditions that would require immediate measures to remedy were identified in the inspection. The operation and maintenance of the GSP is in accordance with generally accepted good engineering standards. (vii) CCR Surface Impoundment Changes Improvements to the embankment since the 2015 inspection include placement of riprap protection on a portion of the west exterior embankment slope and in former erosion gullies. No changes that will negatively affect the stability or operation of the GSP have occurred since the 2015 initial annual inspection report. CCR Rule Annual Inspection Report (cont.) 6