Collection Systems for Community Wastewater Systems CAWPCA Spring Meeting April 26, 2013 Dave Prickett, PE

OVERVIEW Wastewater Management Community Systems Plans Collection Systems Alternatives System Selection Considerations Examples

Wastewater Management Alternatives

Community Systems (> 25 homes)  Wastewater Needs  Existing on-site systems insufficient  Permitting Requirements  Sub-surface disposal/reuse  Infrastructure Needs  Treatment system  Collection system  Implementation Plan Work Backwards from Here

Collection System Alternatives  General  It’s not sewer vs. non-sewer  From home to treatment system  Gravity  Conventional  STEG  Pressure  Low pressure  Vacuum  STEP

Why Is Sewer Selection Important?  Downstream Impacts  Treatment  Disposal/reuse  Residential Impacts  Construction  Private Property Access  Sustainability Needs  Operation & Maintenance  Emergency Readiness  Storm Preparedness

Gravity & STEG Sewers GravitySTEG Treatment Peak flows from I/I Peak flows from I/I; May minimize treatment requirements Disposal/Reuse Potential salinity in coastal areas Construction Depth and dewatering concerns; conflicts with other utilities Private Property Minimal post-construction access needs Septage management required O&M Facilitates access for routine maintenance Slightly lower mainline pipe O&M needs than conventional gravity Emergency Readiness Self sufficient during outages if pump stations have generators

Low Pressure, Vacuum & STEP Sewers Low PressureVacuumSTEP Treatment Lowest I/I & high flow potential; pre- treatment Relatively low I/I potential Condition of existing septic tanks impacts I/I Disposal/ Reuse Minimal salinity impacts Slightly higher salinity impacts May minimize treatment requirements Construction Shallow construction minimizes duration Moderate construction impacts; need to site vacuum station Shallow construction minimizes duration Private Property Significant access needs Moderate access needs Significant access needs O&M Odor control needs Odor control needs; septage management Emergency Readiness Significant concerns during power outages Moderate concerns during power outages Significant concerns during power outages

Example  Community System  Coastal neighborhood  200 homes on ¼-acre lots  Mix of seasonal and year-round use  Area subject to high groundwater and storm impacts  Will use off-site sub-surface disposal with reuse for irrigation purposes  Collection System Options  Option #1 – Gravity sewer  Option #2 – Low pressure sewer

Example (continued)  Option #1 – Gravity sewer  No post-construction private property access needs  Concerns with siting pump station(s)  I/I could easily exceed sanitary flow  Salinity concerns for reuse irrigation  Option #2 – Low pressure sewer  Minimizes secondary growth  Minimizes I/I potential and preserves disposal capacity  Odor control provisions needed  Power concerns during storm events  Long-term private property access needs

QUESTIONS & ANSWERS