ANNUAL SSO REPORT FOR 2014

Transcription

1 WEST VALLEY SANITATION DISTRICT ANNUAL SSO REPORT FOR 2014 Introduction The Annual Sanitary Sewer Overflow (SSO) Report provides a summary of West Valley Sanitation District s (District) SSO performance information for the last calendar year. Prior to calendar year 2012 the Annual SSO Report was required by the San Francisco Bay Regional Water Quality Control Board (RWQCB), but has now been discontinued per RWQCB s letter, dated October 3, The District s Annual SSO Report is now required to meet the District s obligation (Section II.D) cited in its Settlement Agreement with Northern California River Watch (NCRW). This requirement will be in effect until the end of the Agreement on August 29, In addition to the Annual SSO Report for 2014, a Summary of Obligations and the 2014 SSMP Audit are included. The Summary of Obligations shows the District s progress towards the completion of the Settlement Agreement tasks. The 2014 SSMP Audit is performed every other year in accordance with SWRCB Order No DWQ, and was completed prior to its due date on May 2, District Background The District owns and maintains a gravity sewer wastewater collection system serving the populations of the City of Campbell, City of Monte Sereno, Town of Los Gatos, portions of the City of Saratoga and intervening unincorporated portions of the County of Santa Clara. In total there are approximately 45,400 connections serving a population of over 109,000 people. The wastewater collection system is comprised of 415 miles of sewer main and 210 miles of sewer lateral (lower lateral) located within the public right-of-way. In 2014 WVSD s collection system transported an average daily flow of approximately 9.32 million gallons of wastewater, or about 3.4 billion gallons over the course of a year in 2014, to the San Jose/Santa Clara Regional Wastewater Facility for treatment, disposal, and reuse. Description of SSO Events The description of SSO events are divided between those caused by sewer mainline blockages and those caused by sewer lateral (lower lateral) blockages. Sanitary sewer overflows caused by blockages or failures of a private lateral or system are not included. The District s 2014 SSO Summary Report for mainlines and laterals are included with this report to support the analysis of information shown. The separation of information between sewer mains and sewer laterals facilitates the comparison of data with those agencies that own and maintain only sewer mainlines. In describing these SSO events, the number, volume and historical trends of the SSOs are discussed, along with the suspected causes of the blockages. One of the obligations of the NCRW Agreement (II.B.4.) requiring collection and delivery of samples from Category I SSOs for CAM17 toxic Page 1 of 9

2 metals analysis ended after two years on August 29, This effort is described in the Sewer Main SSO and Sewer Lateral SSO discussions. Benchmarking SSO Records Traditionally, the common benchmark, or spill rate indices, utilized by wastewater collection agencies has been the total number of mainline SSOs per 100 miles of sewer main owned and maintained. In CIWQS, they have compiled similar indices, but have broken this down into SSO spill categories for main lines and laterals. Similarly, CIWQS has also provided indices for SSO volumes in much the same manner, except they use net gallons (unrecovered volume) per 1,000 capita. For comparative purposes, they also provide data for both statewide and regional indices (SFRWQCB Region 2). This type of benchmarking is an important measure of the District s current and past performance as well as an indicator of future performance trending. The total number of mainline SSOs the District experienced during 2014 was sixteen (16), resulting in an overall spill rate index of 3.86 SSOs/100 miles. This is very close to the commonly accepted excellent spill rate indices of 3.0 SSOs/100 miles. The CIWQS comparisons for Spill Rates are shown in the tables below, showing a very favorable indicator of the District s performance measured against statewide and regional indices. As an example, the District has a Category 1 spill rate indices for mainlines of 0.72 spills/100 miles, compared to 5.13 and 6.68 for state and regional averages, respectively. For Category 3 mainline spill rate indices, the District has 2.9 spills/100 miles, compared to 8.19 and for state and regional averages, respectively. The District did not have any Category 2 SSOs for mainlines. The total volume of mainline SSOs the District experienced during 2014 was 4,190 gallons (gross) or 1,661 gallons (net). The CIWQS comparisons of Net Volume Spills are shown in the tables below, again showing a very favorable indicator of the District s performance. As an example, the District has a Category 1 Net Volume Spill Indices of a gallons/1000 capita for mainlines, compared to 1,304 and 2,906 for state and regional averages, respectively. For Category 3 Net Volume Spill Indices, the District has 0.56, compared to 84 and 44 for state and regional averages, respectively. Comparative data for sewer laterals are also shown in the CIWQS Tables below. These are presented in the same identical fashion as sewer main information. Again, this shows a very favorable indicator of the District s performance measured against statewide and regional indices. Page 2 of 9

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4 SEWER MAIN SSO Number, Size, and Historical Trend There were a total of sixteen (16) sewer main SSOs experienced during Three were Category 1 events, zero Category 2 events, and thirteen were Category 3 events. There were no SSO samples collected for these three Category 1 events as two of them discharged into dry creek beds and fully recovered, while the third event occurred during a heavy rain storm. The third Category 1 event occurred on December 2, 2014 at Calle Estoria in Los Gatos. The overflowing manhole was immediately adjacent to a storm catch basin which discharged directly into Smith Creek. A significant volume of storm runoff was evident and the creek was flowing very swiftly. Since hazardous conditions existed, no attempt was made to take creek samples for biological indicators or CAM17 testing. The Sewer Main SSOs experienced are distributed into one of three volume ranges and are summarized in Table 1 and illustrated in Figure 1. Table 1. Number of Sewer Main SSOs in 2014 Gross SSO Volume (gallons) Number Percent of Total Greater than or equal to 1, % From 100 to % From 1 to % Total % Figure 1. Sewer Main SSO Volume Distribution 2013 SSO Volume Distribution 62.4% 6.3% 31.3% SSO Volume (Gallons) 1 to to or More Page 4 of 9

5 The total gross volume of sewer main SSOs is estimated to be 4,190 gallons, of which 2,529 gallons were recovered. The volume of these spills contained and returned to the system, as well as the volume not recoverable, is shown in Table 2. Table 2. Volume of Sewer Main SSOs in 2014 Volume (gallons) Percent of Total Total volume contained and returned 2, % to sewer system for treatment Total volume reaching a drainage 1, % channel, surface water, or storm drain but not recovered Total volume not recovered and not % reaching a drainage channel, surface water, or storm drain (everything else) Total SSO Volume 4, % The following graph presents two data sets representing the District s sewer main SSO history from calendar year 2005 to The two data sets shown in Figure 2 include the number of SSO occurrences and gross SSO volume. A 5-year running SSO volume average trend line is also shown which effectively illustrates that the District s increased O&M efforts have resulted in a continuous downward mainline SSO volume trend since OCCURRENCES Figure 2. Sewer Main SSO Occurrence and Volume History Sewer Main SSO History Total SSO Occurrences Total SSO Volume Running 5-Yr Volume Avg YEAR VOLUME (1,000 Gal) Page 5 of 9

6 Cause of Sewer Main SSOs The predominant cause of SSOs experienced during 2014 was primarily root intrusion, accounting for nearly 70% of the total sewer main SSOs, as illustrated in Table 3. Table 3. Causes of Sewer Main SSOs in 2014 Cause of SSO Number Percent of Total Blockage: Grease/Soap % Roots % Debris (paper/rags) 4 0 % Other (grit, etc.) % Subtotal Blockages % Other Causes: Hydraulic Deficiency 0 0 % Other (Landslide) 0 0 % Subtotal Other Causes 0 0 % TOTAL % Page 6 of 9

7 SEWER LATERAL SSO Number, Size, and Trend There were a total of six (6) sewer lateral SSOs experienced during 2014, four of which were designated as private lateral sewage discharge (PLSD) and two were Category 3 events. Lateral SSO s determined to be PLSDs are not included in the tables or graphs below. The lateral SSOs experienced during 2014 are distributed into one of four volume ranges. These are summarized in Table 4 and illustrated in Figure 3. Table 4. Number and Size of Lateral SSOs in 2014 Gross SSO Volume (gallons) Number Percent of Total Greater than or equal to 1, % From 100 to % From 10 to % From 1 to % Total % Figure 3. Sewer Lateral SSO Event Distribution By Volume 2014 SSO Volume Distribution 0 % SSO Volume (Gallons) % 1 to 9 10 to to or More Page 7 of 9

8 The total gross volume of sewer lateral SSOs is estimated to be 66 gallons, of which 10 gallons was recovered. The volume of these spills contained and returned to the system, as well as the volume not recoverable, is shown in Table 5. Table 5. Volume of Sewer Lateral SSOs in 2014 Volume (gallons) Percent of Total Total volume contained and returned % to sewer system for treatment Total volume reaching a drainage % channel, surface water, or storm drain but not recovered Total volume not recovered but not % reaching a drainage channel, surface water, or storm drain (everything else) Total % The following graph presents two data sets representing the District s sewer lateral SSO history from calendar year 2005 to The two data sets shown in Figure 4 include the number of SSO occurrences and gross SSO volume. A 5-year running SSO volume average trend line is also shown which effectively illustrates that the District s increased sewer lateral O&M efforts, have resulted in a continuous downward mainline SSO volume trend since Figure 4. Sewer Lateral SSO Occurrence and Volume History OCCURRENCES Lateral Sewer SSO History 89 Total SSO Occurrences 74 Total SSO Volume Running 5-Yr Volume Avg YEAR VOLUME (Gal) Page 8 of 9

9 Cause of Lateral SSOs In 2014 there was no specific cause for the occurrence of lateral SSOs, although in the past roots were the typical culprit. The structural deficiency noted in one of the lateral SSOs was a severe offset joint. The distribution of Lateral SSOs by cause is shown in Table 6. Table 6. Causes of Sewer Lateral SSOs in 2014 Cause of SSO Number Percent of Total Blockage: Roots % Grease/Soap % Grit % Debris (paper & rags) % Subtotal for Blockages % Other Causes: Hydraulic Deficiency 0 0 % Structural Deficiency % Maintenance Operation 0 0 % Subtotal for Other Causes % TOTAL % Page 9 of 9