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Home My WebLink About07/19/1994, 9 - WASTEWATER DRAINAGE BASIN B INFILTRATION AND INFLOW INVESTIGATION IHNII�N�I��IIIIIIIIII�Iull� / or r MEETING[]ATE: city san -LUis oBispo Jul 19 '. 1994 do COUNCIL AGENDA REPORT ITEM NUMBER: Q From: John Moss Prepared by: Dan Boyd Utilities D for Wastewater Collection Supervisor SUBJECT: Wastewater Drainage Basin B Infiltration and Inflow Investigation CAO RECOMMENDATION By motion, receive report concerning Wastewater Drainage Basin B Infiltration and Inflow investigation results and direct staff to develop and return to Council with a service lateral investigation and rehabilitation program. DISCUSSION The City's wastewater collection system and water reclamation facility has long been experiencing problems with excessive wet weather Infiltration and Inflow (I/I). The UI has caused problems with the water reclamation and treatment processes, surcharging, overflows, effluent violations and the release of partially treated wastewater to the creek due to hydraulic overloading. I In July 1989, Council directed staff to work towards elimination of I/I rather than designing and constructing the phase H relief sewer project. The collection system is divided into fourteen I/I drainage basins (A-N). An I/I study, performed by Brown and Caldwell Engineers in 1987, indicated that the more significant contribution of UI was coming from drainage basins B,D,E,F and H. Subsequently, drainage basin "B" was selected as the first target basin to be investigated. The investigation consisted of smoke testing, video inspection, dry and wet weather flow monitoring, physical inspection and dye testing. I I/I INVESTIGATION COMPONENTS AND RESULTS • Smoke Testing Smoke testing shows pipe leaks that are located under permeable surface materials such as open fields and lawn areas, inflow sources such as storm drains, roof drains etc. connected directly to the sewer system, and waste and vent systems that are not working properly. The majority of the privately owned upper service lateral system (building to property line) is located under permeable surface material. The majority of the lower service lateral system (property line to City sewer main) and public sewer system is located under impermeable surface material (asphalt and/or concrete). Subsequently the smoke test works well for identifying leaks in the upper service laterals and those few public sewers located under permeable material (mostly easement areas), but does not work well for the lower service laterals and the majority of the public sewer that is located under impermeable surfaces. 9_ city of San Luis OBISPO COUNCIL AGENDA REPORT 1/I Investigation Components and Results Page 2 • Smoke Testing Results The smoke testing performed in drainage basin B tested 601 service laterals and 32,731' feet of public sewer. The smoke testing is accomplished by isolating a section of pipe (manhole to manhole) and pressurizing the pipe with air and smoke. The smoke is forced through the sewer mains, service laterals, service lateral vent pipes and any cracks, offset joints etc. located in the collection system. The results of smoke testing the service laterals indicated that 10.1% of the service laterals leaked and 15.1% displayed no smoke through the vent system. No smoke through the vent pipes indicates other problems, such as, improperly vented waste pipes, a p-trap in the primary service lateral, and/or the primary service lateral not being installed at the proper grade. The smoke testing results thus indicate 25.2% of the service laterals tested had some problems. The public sewer system not covered by impermeable material also showed some deficiencies. A less significant number of leaks were identified in the public sewer system. A majority of the manholes tested leaked because of age and design but appear to be a less significant source of I/I because of their location in the drainage area. Only a few inflow sources, a roof drain, floor drain and storm drain, were identified. These inflow sources have been corrected. • Video Inspection Video inspection identifies pipe defects such as offset joints, root intrusion, cracks, broken pipe, etc. The video inspection also identifies tap.locations (point of service lateral connection to the City mainline), infiltration of water from defects, pipe material, pipe length, and many other important factors related to the inspection. Video inspection was only performed on sewer main lines. Additional specialized equipment will be required to perform video inspection on private service laterals. • Video Inspection Results The video inspection consisted of inspecting 36,442' feet of public sewer. Root intrusion was the most significant problem identified but does not appear to create a significant source of I/I in the public sewer system. Numerous structural defects were identified but also do not appear to create a significant source of I/I in the public sewer system. It is assumed this is the case because the majority of the public sewer system is located under impermeable surfaces. Infiltration of ground water (as opposed to rainfall dependent I/I) does not appear to be a problem in basin B. The video inspection did reveal 708 tap locations (not capped) as active services. 601 service laterals were confirmed as the � 02 ��►�►►�uIIIII�Iip�u�ilU city of San-LUIS OBISpo MRIMINi COUNCIL AGENDA REPORT I Investigation Components and Results Page 3 actual number of services in drainage basin B. Subsequently, there are 107 service laterals that may have been improperly abandoned and may be a significant source of I/I. The video inspection also revealed that 11% of the tap locations identified showed roots entering the public sewer main from the service lateral. During wet-weather video inspections numerous service laterals were observed infiltrating rain water at the tap location. • Flow Monitoring Flow monitoring records average flow and peak flows. The flow monitoring was performed during dry and wet weather. During wet weather the flow monitor showed a significant increase to the average and peak flows. The increase shows the amount of I/I entering the system for that specific rain episode. • Flow Monitoring Results Flow monitoring performed in drainage basin B evaluated the basin in three sub-areas, upper, middle and lower. Several different locations through-out the basin were flow monitored. The data recorded from one monitoring location at the intersection of Ramona and South Tassajara (upper basin B) will be used as an example. This location monitored a specific reach of sewer mainline (8,842 feet of public sewer that serves 201 residences). Dry weather flows at this location recorded an average of 7 gpm (gallons per minute) in July 1991, at 2:00 am. An average of 446 gpm was recorded during wet weather flows in February 1992, at 2:00 a.m. in the same location. The data recorded shows the difference between dry and wet weather flows during a specific rain episode. The overall results of the flow monitoring in drainage basin B indicate the I/I problem is wide spread through-out the basin. • Physical Inspection Physical inspection of manholes identifies and records defects, infiltration of water from defects, inflow sources, material used and physical location of the manhole (if the manhole is located in street or drainage channel etc.). Physical inspections are also performed on all sewer mainlines and the surface area above sewer mainlines to identify surface material, surface material defects, location, type of pipe etc., to assist in the evaluation process. • Physical Inspection Results There are 173 manholes in drainage basin B. All of the manholes were inspected and the results were recorded. Numerous manhole problems were identified and will be repaired as priorities dictate. Manholes that are found to be in drainage channels which 9-3 �un�►U►►�IIIII�� U city of San 1Uis OBISp0 Njj% COUNCIL AGENDA REPORT 1/1 investigation Components and Results ' Page 4 may contribute significant I/I are scheduled for immediate repair. The manhole problems appear to be a less significant source of I/I as related to the overall collection system. • Dye Testing Dye testing is performed to verify inflow and infiltration sources. The dye test will also verify service lateral locations in mainlines. Extensive dye testing was not performed in basin B, however, the dye test was used to verify the source of water observed entering the main at a tap location as being infiltration. • Dye Testing Results A test was performed on one of the service laterals that appeared to be infiltrating rain water during a video inspection and also revealed smoke during the smoke testing. Ten gallons of water mixed with tracing dye was poured onto the ground above the lateral, the camera was positioned in the City main at the tap location of the service connection, the tracing dye appeared at the tap location in 3 minutes. Three inflow sources were also verified through dye testing, a roof drain, floor drain and storm drain. These inflow sources were identified through smoke testing and verified through dye testing as sources of inflow to the wastewater collection system. These inflow sources have been corrected. OVERALL I/I EVALUATION • Public Sewers A less significant number of sources were identified infiltrating rain water in the public sewer system. A majority of the public sewer system is located under impermeable surface material such as, asphalt and concrete. No significant ground water infiltration problem was found in drainage basin B and identified inflow sources have been corrected. • Service Laterals The video inspections performed in drainage basin B during the wet weather in January through March of 1992, revealed numerous service laterals that appeared to be infiltrating rain water. The laterals were observed at the tap location in the City main. The tap locations that appeared to be infiltrating water, displayed a continuous flow at a high velocity that appeared to be abnormally clear. The water did not display the usual signs of wastewater, such as, debris, human waste or steam that is generated from a shower or dishwasher. To substantiate the source of the water the I/I crew contacted. several of the residences in question. 'They found that some of the residences were not occupied, and others were not using any facilities at the time of the inspection. ��mm► ►I�IIIIlII�II►iu�u�l��l city of San LUIS OBISpo =Mign COUNCIL AGENDA REPORT I/I Investigation Components and Results Page 5 The investigation indicates that a significant portion of the I/I in basin B is coming from the service laterals. A video inspection of all service laterals should be performed to identify the condition of the service lateral system and insure the most cost effective repair. SIGNIFICANT NEXT STEP If the recommended action is approved by Council, staff will present the results of the I/I investigation of basin B and seek input from public interest/neighborhood groups to help define and incorporate public concerns in the development of a comprehensive lateral rehabilitation program. Staff will return to Council with a program that will be designed to correct I/I and manage the private and public sewer system. SUNIMARY The recent comprehensive investigation of drainage basin B was completed for publicly owned sewer mains and manholes but could only partially address the private service laterals through smoke testing. The privately owned service laterals need to be investigated, rehabilitated and maintained in conjunction with the City maintained collection system. This will enable the City to achieve the highest impact on reducing W. A service lateral inspection and rehabilitation program will enable the City to manage this portion of the system and insure its safe/sanitary operation. FISCAL MWACT There is no fiscal impact associated with the recommended action. However, a service lateral rehabilitation program could have a significant fiscal impact. If the recommended action is approved by Council, staff will provide a detailed cost analysis with the lateral rehabilitation program once developed. ALTERNATIVES Take no action. This alternative is not recommended. The wastewater collection system and service laterals are aging and in need of rehabilitation to correct I/I. The on-going rehabilitation of the entire wastewater collection system through long and short range programs will correct the problems, enhance customer service and provide improved management. '1 MY Of Sa' , ,UIS OBISPO MEMORANbUM " 955 Morro Street•San Luis Obispo,CA TO John Dunn/CAO JUL, 15 1994 / •� / ADM.I N IS'TPoW:O N FROM John Moss/Utilities SAN LUIS OBISPO,CA SUBJECT Council Age a 7/19/94,)Item 9 (Business) DATE 7/14/94 Dave Romero requested that a drainage map of Basin B be attached to the Infiltration and Inflow Investigation report on the July 19, 1994 agenda. These are attached for your review. c: Kim nann ET fAUNCIL El CDD DIR �O ❑ FIN DIR �EAO ❑ FIRE CHIEF MRNEY ❑ PW DIR CLBOVO ld ❑ POLICE CHF ❑ MGMTTEAM ❑ REC DIR ❑ C EAD FILE W"UTIL DIR ❑ PERS DIR , MEETING AGENDA DATE ITEM # g 69.66 ATTACHKENT 1 DRAINAGE BASIN B IN SHADED AREA ------- Ap N a crcy of san Ims owspo om � � y JNOf111d31i U o < / IJOSIdHOf a y >>�y101 \ a�tP fs �CtvdaO o ,`/ Ob to H d AtlN,H1tlH r ivfeH1tlH C801 * G \� 61%1S eS � pS Ln CC Q� c CALIF�NIP a - 4 S i.' FERR�NI o _ . h�ry� hd 8RE'S, O 8� ATTACHMENT 2 y per^ W ti �O�3n S1H913H DRAINAGE BASIN B OM+iRi3S IN SHADED AREA Ln o tl1S3f10. IV I G vddfVSShc HIWK' :wfy 1 H1nOS �P \�GF10 o tlObNvO bl I l3d�bt1 a v10f11 vUdvS , ¢ Z G3 LJJ3P C tl101Hltld L, o w 350r Id S CD tn lIH-lb tl11S0a Ln LOS EROSO b z � . � •