PRELIMINARY ENGINEERING REPORT FOR SANITARY SEWER COLLECTION SYSTEM OSKALOOSA, IOWA 2017

Transcription

1 PRELIMINARY ENGINEERING REPORT FOR SANITARY SEWER COLLECTION SYSTEM OSKALOOSA, IOWA 2017

2 PRELIMINARY ENGINEERING REPORT FOR SANITARY SEWER COLLECTION SYSTEM OSKALOOSA, IOWA 2017 I hereby certify that this engineering document was prepared by me or under my direct personal supervision and that I am a duly Licensed Professional Engineer under the laws of the State of Iowa. Jack Pope, P.E. Date License Number: My license renewal date is December 31, 2017 Pages or sheets covered by this seal: All Prepared by GARDEN & ASSOCIATES, LTD rd Ave. East, Suite 1 - P.O. Box 451 Oskaloosa, IA GARDEN & ASSOCIATES, LTD. 500 E. Taylor, Suite C - P.O. Box 631 Creston, IA G&A

3 TABLE OF CONTENTS PRELIMINARY ENGINEERING REPORT SANITARY SEWER COLLECTION SYSTEM OSKALOOSA, IOWA 2017 Description Page Part 1 Introduction Background Information... 1 Purpose and Scope... 1 Study and Service Area... 2 Cost Estimates... 2 Part 2 Field Studies and Rehabilitation Recommendation Field Work... 3 Infiltration/Inflow Investigation... 3 Plant and Lift Station Flows... 8 Part 3 Recommended Rehabilitation and Sewer Improvements Private Property Manhole and Sanitary Sewer Part 4 Summary of Recommendation Financing and Schedule G&A i

4 LIST OF TABLES AND GRAPHS No. Title Page Table 2-1 Oskaloosa Rainfall Data... 9 Graph 2-1 April 2013 Rainfall vs. Flow Graph Rainfall vs. Flows Graph 2-3 June 2014 Rainfall vs. Flow Graph 2-4 July 2015 Rainfall vs. Flow Table 3-1 Downspout/Footing Drain Connections Table 3-2 Uncapped/Broken Cleanout Caps Table 3-3 Private Sewer Rehabilitation LIST OF FIGURES Figure No. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Title Existing Sanitary Sewer Map Manhole Map Smoke Testing Setup Locations Areas Recommended for Televising and Flood & Dye Location of Recommended Improvements LIST OF APPENDICES Appendix Title A IDNR Inspection Report ( ), Notice of Violation ( ) B Plan of Action ( ) C Table C-1 Manholes Inspected/Deficiencies Noted Table C-2 Manholes with I/I Noted Table C-3 Smoke Testing Investigation Sightings Table C-4 Televising and Flood & Dye Testing Summary D Manhole Investigation Photographs, Smoke Sighting Photographs E Estimates of Probable Cost F Plant and Lift Station Data G&A ii

5 Part 1 - Introduction Background Information: The City of Oskaloosa wastewater system was inspected by Iowa Department of Natural Resources personnel on June 24, 2014 (Appendix A). At the time of the inspection the following problems were identified: Southwest Wastewater Treatment Plant: Raw wastewater was bypassed in a portion of the collection system, as well as at the treatment plant. Northeast Wastewater Treatment Plant: Discharge of wastewater from the equalization basin have occurred without treatment, and bypassing in the collection system, specifically at manhole N57, has also been identified. Subsequent to the inspection, the city received a Notice of Violation (Appendix A). The city submitted a Plan of Action (Appendix B) for identifying and eliminating some of the Inflow and Infiltration (I/I) by January 1, The city council authorized the preparation of this report to evaluate the collection system and determine improvements necessary to meet the goal of I/I reduction. Purpose & Scope: The purpose of this report is to perform an extensive study of the sanitary sewer system to identify sources and location of inflow and infiltration and prepare a list of recommended improvements to address the sources identified. A reduction in I/I throughout the system will delay the need to increase the size of the sanitary sewer, pumps, force main, and treatment plant facilities. The scope of the study is as follows: 1. Conduct a field inspection of the system manholes and identify deficiencies. 2. Smoke testing of the sanitary sewer collection system. 3. Evaluate flood and dye testing information collected by city staff at suspected cross connections identified during smoke testing. 4. Review treatment plant and lift station flow records. Compare to rainfall data. 5. Evaluate Inflow/Infiltration (I/I) impacting system. 6. Evaluate field data. Make recommendation regarding rehabilitation, repair, and replacement. 7. Prepare opinion of probable costs for alternatives evaluated and recommended improvements. 8. Prepare schedule for construction projects. G&A Page 1

6 Study and Service Area: This report will address the conditions found throughout the system identified during the investigation. Figure 1 is a map showing the existing sanitary sewer system and shows the study area considered for this report. Existing Sanitary Sewer System: The existing sanitary sewer collection system consists of pipes ranging in size from 6 to 24. A portion of the sewers were originally a combined storm and sanitary sewer system. The combined portion has been separated. The pipes consist primarily of vitrified clay pipe and brick manholes. Newer sections of the system consist of polyvinyl chloride piping and precast concrete manholes. The collection system consists of 7 lift stations to transport wastewater via force main from low points in the system to either one of the treatment plants (Northeast or Southwest) or to a manhole to allow for gravity flow to the treatment plants. Pump capacity and lift station flow will be addressed hereinafter. Cost Estimates: The cost estimates presented in this report are estimates of probable cost based on present day conditions and construction environment. There have not been provisions made for future project costs. G&A Page 2

7 Field Work: General: Part 2 Field Studies and Rehabilitation Recommendation Field studies were conducted to gather data for analysis of existing condition and determine the basis for the recommended sanitary sewer improvements. The following paragraphs provide a general description of the field investigations conducted. Manhole Inspection: Manholes in the system were located and inspected. The manhole material, number of pipes entering the manhole, and pipe sizes were recorded. The condition of the manhole, frame and casting, and other defects were also recorded, as well as the presence of previously installed infiltration barriers. Smoke Testing: Smoke testing of manholes was performed to locate potential sources of I/I. Smoke testing is a cost effective method of identifying sources of surface water inflow. This procedure involved placing a smoke candle and blower on a manhole and forcing smoke through the sewer system. Smoke sightings were recorded and analyzed as potential I/I sources. Figure 3 shows the location of manholes that were used for smoke testing setups. Flood & Dye Testing: Selected sections of the system were further investigated after smoke testing. Flood and dye testing is used to verify that ground and/or surface water is entering the sanitary sewer system through the storm sewer. Potential I/I sources from the storm sewer were flooded with water containing dye. Sanitary sewer was then checked at manholes and via televising for indication of dye. Televised Internal Inspection: Televised internal inspection of sanitary sewer lines was done at specific locations of the sanitary sewer based on results of the smoke testing, and where manhole locations could not be determined. This procedure was performed by city staff using city equipment. Infiltration/Inflow Investigation: In order to determine the extent and type of inflow and infiltration problems existing in the sewer system, an inspection of the existing system manholes and smoke testing program was conducted. The investigation included the following: G&A Page 3

8 1. Existing system manholes were inspected, information was collected, and location was recorded by GPS coordinates between May 20, 2015 and December 3, Smoke testing of the system was conducted between October 20, 2015 and November 13, City crews have conducted televising of sewer and dye testing from the beginning of calendar year 2016, and their report included data gathered through December 29, Table C-1 contains the list of manholes with the type and number of deficiencies indicated. A sample of photographs showing deficiencies is provided in Appendix D. The following notes are a summary of observations made during the manhole inventory investigation: Summary: Approximately 160 manholes showed signs of I/I. 32 manholes have root growth. 31 manholes have damaged castings or covers. 40 manholes have damaged rings. Approximately 37 manholes have interior surface deterioration at the walls or invert. Approximately 84 manholes have deteriorated mortar or PCC barrel joints. Eight manholes have structural damage including vertical cracks, offset portions of the structure, and severely cracked inverts. 18 manholes have standing water or debris. Approximately 141 manholes have debris or sediment resting at the bottom. Approximately 32 manholes have loose or shifted rings or castings. Approximately 28 structures have holes or missing bricks from the walls. Two manholes have damaged chimney seals. Two manholes (N45.1 and N46.1) have holes eroded in the ground adjacent to the casting and rings allowing I/I. Water main was observed passing through four manholes (E105, M39.2, N74.4, and N74.5). A gas line was observed passing through manhole N31.1. Deficiencies of Note: Covers on several manholes of East interceptor (E6-E15) were ajar from surcharge during rain events. Most are bolt-down water-tight covers but no longer have bolts. Four manholes on 15" line north of the high school (N143, N145, N145A, N145C) have a fully or mostly deteriorated top ring with the casting resting on remaining wire mesh. G&A Page 4

9 Manholes N17, N54, and S28 have large elevation differences between incoming pipes and the inverts. Heavy flow from the incoming pipes is hitting and eroding the opposite wall of the barrels. Heavy efflorescence and surface deterioration was observed throughout cone and barrel in manholes N162 and M10. Manhole M64.1A has a vertical crack the full height of the barrel to the west. The casting at manhole S60.2 is offset from the cone by approximately half of its diameter. The top 1 of cone is also offset from the cone approximately 4. The chimney at manhole S60.1 is cracked in several locations and shifted out of the E curb line of S Market St. Manhole S3 is missing a cover. Manhole N48 has a locking-type cover resting upside-down in a non-locking casting. Manhole S52 has an extra loose casting resting on top of the existing casting above grade. Clay pipes to the north and east of E28 lay in a creek and are damaged allowing continuous infiltration. Manhole N69.1 sits in the south gutter line at 418 College Ave allowing I/I through pick holes during rain events. Manholes with heavy infiltration include E13, E15A.2B, E37, E60, E72.5, E79.2, E104, F9.6, L22.4, M40, M42, N54, N69.1, N79, N85.1, N139.1A, N139.4, N162, S6.8, S41.7, S46, and S54.5. Heavy root growth was observed in manholes E-22B, E104, N14, and N90. Old manhole covers and loose bricks are obstructing the inverts in two manholes: S74 and N138. An old sediment trap is resting on the invert at manhole L29. Manhole bases are severely cracked and deteriorated in N103.3 and N118D. The chimney in manhole E68 appears to have shifted away or was constructed to offset from the north curb line of A Ave E. Manhole N135.1 is in a driveway at 704 N 8 th St and does not have a casting (cover rests on top of cone). Manhole N101.3 is an old flush-type manhole. The outlet pipe at manhole M55.2 is elevated above the bottom causing a 0.7 thick collection of water and soft debris. Structure deterioration was observed at manholes E73.1A, E94.2, N30.3, S60.1, S60.2, and W12. Debris and water entering manholes through the bases of castings and rings is a common observation in 'A' Ave W and N Market St. Table C-2 is a listing of the manholes with noted I/I during the investigation along with the estimated I/I contributing to the sewer. Based on Table C-2, the I/I that will be removed from the system if the noted sources are removed will be GPM at the G&A Page 5

10 Northeast plant and GPM at the Southwest Plant. It is estimated these deficiencies contribute approximately 573,840 GPD to the sanitary sewer. Table C-3 contains the list of sightings during the smoke testing investigation and shows estimated I/I from flows for each source identified. A sample of photographs showing smoke sightings is provided in Appendix D. As shown in Table C-3, the estimated I/I identified is GPM at the Northeast plant and GPM at the Southwest Plant. It is estimated these deficiencies contribute approximately 1,048,320 GPD to the sanitary sewer. Figure 3 shows the location of smoke testing setups on manholes. Figure 4 shows the areas that were recommended for flood and dye testing. The following notes provide an overview of the results of the smoke testing: Summary: Approximately 65 intakes with smoke. Approximately 130 leaking manhole castings. Approximately 25 manhole structure leaks. Approximately 40 main leaks. Approximately 80 service line leaks. Approximately 8 buildings with direct downspout connections to sewer. Approximately 11 homes with possible footing drain connections. Approximately 50 residences and commercial properties that have cleanouts without caps or with broken caps. Approximately 3 manholes with holes eroded adjacent to casting and rings. Significant Notes: Broken VCP at S edge of creek with some infiltration to the north of Manhole (MH) E28. Broken VCP in creek with constant infiltration east of E High Ave E Smoke from MH cover at low point in driveway. Drainage area for roof downspouts. Top rings on MH s N143, N145, N145A, and N145C are partly to fully deteriorated and require replacement. Brick structures at the following manholes have deteriorated mortar joints and are leaking: W12, M60, N71, N30.3, N62, N63, N98.2, N118D, N139.1A, E94.1, E94.2, E73.1A. Vacant lot at 606 A Ave W does not have service cleanout cap. The casting on Manhole S3 is in good shape but does not have a cover. Smoke was observed in a Bell Systems manhole at the alley intersection south of A Ave E and west of S 2 nd St th Ave E Smoke was observed in an ADS tile line from the SE shed to the drainage ditch along 9 th Ave. G&A Page 6

11 Setups with difficulty pushing smoke (televising may be required): L22.5 No smoke was visible at buildings or manholes N or S of setup. L38.1 Very little smoke visible from setup. L42.2 No smoke between L42.5 and L42.6. S54.5 Several leaks for approximately 50 starting 75 W of S54.5 and for approximately 25 starting 50 S of S54.4. S58 No smoke for ½ block S of S57. N74.2 & N74.5 Smoke could not get to N74 from the north or south. N29.2 Water is over pipe to south in MH. N139.1A & N139.4 Possible blockage at 460 N 9 th St, smoke not getting past this point from either north or south. N56A Smoke not pushing E of N56. N57 & N57.1 No smoke observed between these two manholes. E102 & E105 Smoke barely passing between E103 & E104 from setups. E56 & E59 Smoke could not get past E58 from either setup to north or south. E61.1, E61.2, & E63.1 Difficulty pushing smoke throughout Terrace Dr. subdivision. E80.1, E81, E81.1, E92A Difficulty pushing smoke along 3 rd, 4 th, and 5 th Ave E, W of S 11 th St. Table C-4 is a list of pipe segments where deficiencies were observed during televising by the city. Some of these areas were also flood and dye tested. Notes where roots were observed at pipe joints and where dye was observed, indicating I/I, are highlighted in the table. As shown in Table C-4, the estimated I/I identified is 84.5 GPM at the Northeast plant and 51.0 GPM at the Southwest Plant. It is estimated these deficiencies contribute approximately 195,120 GPD to the sanitary sewer. I/I Identified: The estimated total I/I identified during the field study is 1,262 GPM (or 1,817,280 GPD). This is further defined as follow: Manholes & Sewer Cleanouts Footing Drains/Downspouts Private Sewer Total 1,595,520 GPD 39,600 GPD 58,320 GPD 123,840 GPD 1,817,280 GPD The recommended rehabilitation projects will remove a total of 1,030 GPM (or 1,483,200 GPD). The private sewer line I/I was not included in this total. It should be noted that an estimated 78 GPM (or 112,320 GPD) will be removed by projects currently planned for the 2017 construction season. G&A Page 7

12 Plant and Lift Station Flows: The records for the flow rate to each plant and the pump records were evaluated to determine the impact on system flows during rainfall events. Data was received for a portion of 2012, all of 2013 and 2014, and a portion of The current design capacities (in MGD) as shown in the NPDES permit for each plant area as follows: Southwest Plant Northeast Plant Average Dry Weather (ADW) Average Wet Weather (AWW) Maximum Wet Weather (MWW) Table 2-1, at the end of Part 2, shows the rainfall data for the period from 2012 to As shown, the average annual rainfall in this area is 38.2 inches. This was exceeded by approximately 6 inches in 2014 and The maximum rainfall month and maximum day are also highlighted. Based on the plant flow records for the timeframe indicated, the recorded flows to each plant (in MGD) are as follows: Southwest Plant Northeast Plant Average Dry Weather (ADW) Average Wet Weather (AWW) Maximum Wet Weather (MWW) Based on a population of 11,463 people and assuming a 50/50 distribution of population to each plant the estimated flow per capita (in GPD) is as follow: Southwest Plant Northeast Plant 86 Average Dry Weather (ADW) Average Wet Weather (AWW) Maximum Wet Weather (MWW) 521 As shown, the ADW flows are less than 100 gallons per capita per day are acceptable, but the wet weather conditions dramatically increase the per capita flows. The following graphs show the relationship to rainfall not only at the treatment plants but also the impact on the lift stations in the system. Graph 2-1 shows the rainfall and plant flow for April 2013; as shown a 4 rainfall on the 17th generated flow in excess of 6.0 MGD at the Southwest Plant and nearly 2.0 MGD at the Northeast Plant. Graphs 2-2, 2-3, and 2-4 are additional examples of the increased flows experienced during rainfall events in 2014, June 2014, and July Beside the spikes at the treatment plant, the M Street Lift Station and the Southwest Plant Lift Station are significantly impacted by rainfall events. Appendix F contains the raw data used in the preparation of the graphs. The purpose of improvements recommended hereinafter will be to reduce these spikes in flow. G&A Page 8

13 Table 2-1 Oskaloosa Rainfall Data Normal Rainfall, in. M D M D M D M D J F M A M J J A S O N D Totals Maximum M = Monthly Total D = Maximum Day All data is in inches G&A Page 9

14 Graph 2-1 G&A Page 10

15 Graph 2-2 G&A Page 11

16 Graph 2-3 G&A Page 12

17 Graph 2-4 G&A Page 13