~ I~ ~»3a7~.~~ COMMISSIONERS' COURT AGENDA REQUEST PLEASE FURNISH ONE ORIGINAL AND NINE COPIES OF TffiS REQUEST AND DOCUMENTS TO BE REVIEWED BY THE COURT. MADE BY: Commissioner Williams OFFICE: Precinct 2 MEETING DATE: November 13, 2007 TIME PREFERRED: SUBJECT: (Please be specific). Receive report from Freese and Nichols are: Ingram Dam and Flatrock Lake Dam evaluation of concrete slab voids. EXECUTIVE SESSION REQUESTED: NAME OF PERSON(S) ADDRESSING THE COURT: Commissioner Williams, Stefan Schuster, Freese & Nichiols. ESTIMATED LENGTH OF PRESENTATION. 15 minutes IF PERSONNEL MATTER-NAME OF EMPLOYEE: Time for submitting this request for Court to assure that the matter is posted in accordance with Title 5, Chapter 551 and 552, Government Code, is as follows: Meeting scheduled for Mondays: 5:00 P.M. previous Tuesday THIS REQUEST RECEIVED BY: THIS REQUEST RECEIVED ON: All Agenda Requests will be screened by the County Judge's Office to determine if adequate information has been prepared for the Court's formal consideration and action at time of Court meetings. Your cooperation is appreciated and cotrtributes toward your request being addressed at the earliest opportunity. See Agenda Request Rule adopted by Commissioners Court. r~~se ~,~ IY~~~~~` It1C. Engineers 10814 3oltyvitle Road, Building 4, Suite 100 October 26, 2007 ~.r The Honorable Pat Tinley 700 E. Main Street Kerrville, Texas 78028 Dear Judge Tinley, Environmental Scientists Architects Austin, Texas 78759 512-451-7955 512-451-7956 fax www.freese.con The non-destructive testing of Ingram Dam and Flatrock Dam concrete slabs has been completed. The investigation was in response to an inspection from the Texas Commission on Environmental Quality (TCEQ) which pointed out to Kerr County that voids were noted in the slabs of both dams. Kerr County Commissioner's Court enlisted the professional services of Freese and Nichols, Inc. (FNI) to facilitate the evaluation of the dams. FNI then enlisted the services of Olson Engineering, Inc., a well respected nationwide non-destructive testing firm to perform the evaluations. FNI. assisted Olson Engineering with the investigations and reviewed their final report for the project. We respectfully submit herewith Olson Engineering's Report dated September 28, 2007, and revised on October 1~~', along with a brief summary report prepared by FNI dated October 26, 2007. The FNI report presents the results in a condensed format and makes recommendations on repair processes. We have prepared a visual presentation of the investigation and stand ready to present it to the Kerr County Commissioner's Court at your convenience. We sincerely appreciate the opportunity to assist Kerr County in these dam assessments and look forward to future opportunities to work with the County on resolving these critical water iss~_ae~ Wn are available to answer any questions related to this investigation or future repairs. Thank you far your continuing support. Sincerely, ~~--.. ~X..__ Stefan K. Schuster, P.G: IvI'~ICerr.CountylSubmittal lettee.doc ~~ Les: Boyd, P.E. SUMMARY REPORT for INGRAM DAM AND FLATROCK DAM EVALUATION OF CONCRETE SLAB VOIDS for KERR COUNTY COMMISSIONERS COURT OCTOBER 26, 2007 AUSTIN, TEXAS Presented by: _. Freese and Nichols Freese and Nichols, Inc. 10814 Jollyville Road, Building 4, Suite 100 Austin, Texas 78759 (512) 617-3100 FREESE AND NICHOLS, INC. LETTER REPORT Background: The Non Destructive Examination (NDE) contract with Olson Engineering was executed on June 5, 2007. Initial plans for performing the NDE testing of the slabs was originally scheduled for mid-June 2007. The rains in June and July resulted in overflows at both dams for a period of approximately 12 weeks. The NDE investigation started immediately upon the cessation of flows over both dams. Project Approach: Field investigations for NDE testing of Flatrock and Ingram Dams commenced on the morning of August 13, 2007 and concluded on the afternoon of August 16, 2007. Olson Engineering and FNI staff began evaluations at Flatrock Dam. The dam which is approximately 800 feet long by 20 feet tall was segmented into approximately 5 feet by 20 feet grid lines. Grid lines were not established in areas of wet surface conditions on the downstream slope. The investigation process is explained fully in the Olson Engineering report but essentially consisted of performing ground-penetrating radar (GPR) on the established grid lines and following up with impact echo and slab impulse tests where GPR indicated areas of suspected voids. The investigation of Flatrock Dam took 1.5 days to complete. Ingram Dam was evaluated next and again the grid lines were also 5 feet by 20 feet. There were more wet areas than at Flatrock, making some areas south of the spillway completely inaccessible. The investigation sequence was the same as at Flatrock beginning with GPR at 400 and 1500 MHz and followed by impact echo and slab analyses. The investigation at Ingram also took L~ days to complete. Difficulties experienced during the investigation included early morning boaters and daily recreational users of the dams sliding down its face at Ingram Dam. None of these distractions were encountered at Flatrock. The work at both dams concluded on August 16~'. Olson Engineering, Inc. submitted their final report to FNI on October 1 ~, 2007. The report provided the following conclusions: Summary of Findings: The full description of the results is contained in the Olson Engineering, Inc. report and is summarized below for convenience. • The investigation identified 12% of the concrete dam surfaces to have voids or have areas of concern, approximately 70% of the surface areas have no identified voids, and 18% of the dams' areas are considered to have questionable sub-grade support. • Therefore, approximately 30% of the concrete areas of the two dams are shown to be impacted by voids beneath the caps. • In general, Flatrock Dam has more identified voids than Ingram Dam. • In addition, there are areas on both dams that may have voids that were inaccessible during the field testing due to wetted surface conditions, including the spillways. Percentage Percentage percentage of concrete of concrete of good Location with an area with a of concern questionable concrete (%) area (%) (%) Flatrock Dam Crest - Long 15 30 55 Flatrock Dam Downstream -Long 10 25 65 Flatrock Dam Crest - Short 30 25 45 Flatrock Dam Downstream -Short 5 5 90 Ingram Dam Crest - North 10 15 75 Ingram Dam Downstream -North 5 15 80 Ingram Dam Crest - South 15 10 75 Ingram Dam Downstream -South 5 15 80 TOTAL 12 18 71 Table 1: Summary of Findings in terms of Dam Concrete Sub-grade Support. Recommendations: It is recommended that a repair program be initiated to re-establish proper foundation contact between the slabs and the earthen foundation. Failure to repair these voids could result in further erosion of the foundations and the formation of larger voids. Larger voids could result in failure of the concrete slabs and subsequent erosion of the embankments, leading to a break of the dam. The repair program would essentially consist of pressure grouting the voids to re-establish tlr~~t contact. The repair program would involve several of the recommendations set forth in the Olson Engineering report as follows: 1. Sound testing should be conducted to refine void areas and recommend repair procedures using grout to fill the identified voids. 2. Coring holes to confirm voids and have visual confirmation of NDE testing results. If a core confirms the void, selectively drill holes in adjacent aprons based on soundings and then grout core until filled. 3. Proceed with grouting in a manner which will reestablish contact between concrete and soil and avoid piping and associated problems with downstream aprons. 4. Follow up with core and destructive testing methods to determine extent of voids and properly assess repair recommendations. This investigation focused on the integrity of the contact between the concrete caps and the earthen foundation of the dams. The recommendations contained in this summary report are for re-establishing contact between the foundation and the concrete caps. This is important to reduce further loss of foundation materials beneath the concrete caps. The repairs are not presented as a cut-off for all seepage through the structures. The void grouting recommended herein will likely have little effect on deep seepage paths, if they presently exist. In the event a grouting program is not chosen by Kerr County, the voids could be repaired by physical destruction of the slabs in areas of the voids. This removal would be followed by replacement of the slabs. In conclusion, Freese and Nichols, Inc. concur with the assessments contained in the Olson Engineering, Inc. NDE report and recommend coring and subsequent grouting in areas of voids.