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

Treatment Gravity

Peak flows from I/I

STEG

Peak flows from I/I; May minimize treatment requirements

Disposal/Reuse Construction Private Property O&M Emergency Readiness

Potential salinity in coastal areas Depth and dewatering concerns; conflicts with other utilities Minimal post-construction access needs Facilitates access for routine maintenance Self sufficient during outages if pump stations have generators Potential salinity in coastal areas Depth and dewatering concerns; conflicts with other utilities Septage management required Slightly lower mainline pipe O&M needs than conventional gravity Self sufficient during outages if pump stations have generators

Low Pressure, Vacuum & STEP Sewers

Treatment Disposal/ Reuse Construction Private Property O&M Emergency Readiness Low Pressure

Lowest I/I & high flow potential; pre treatment

Vacuum

Relatively low I/I potential

STEP

Condition of existing septic tanks impacts I/I Minimal salinity impacts Shallow construction minimizes duration Significant access needs Slightly higher salinity impacts Moderate construction impacts; need to site vacuum station Moderate access needs May minimize treatment requirements Shallow construction minimizes duration Significant access needs Odor control needs Significant concerns during power outages Odor control needs Moderate concerns during power outages Odor control needs; septage management 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