html5-img
1 / 28

Wake County Field Performance and Operation & Maintenance Survey of Systems Installed 1982-2002

Authors: Everette Lynn, Wake County Env. Services Mike Hoover, Soil Science Dept., NCSU Larry King, Soil Science Consulting

temima
Download Presentation

Wake County Field Performance and Operation & Maintenance Survey of Systems Installed 1982-2002

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Authors: Everette Lynn, Wake County Env. Services Mike Hoover, Soil Science Dept., NCSU Larry King, Soil Science Consulting Additional persons making significant contributions: Suzanne Harris, Wright Lowery, Steve Bristow and Kent Daeke, all of Wake County, Trish Angoli,Currently OSWS, NCDENR and Larry Nelson, consulting statistician Wake County Field Performance and Operation & Maintenance Survey of Systems Installed 1982-2002

  2. Introduction • In Wake County there are approximately 55,000 septic systems (based on data from CDM groundwater study), with the vast majority of the population within public water supply watersheds utilizing septic systems.

  3. Introduction • Wake County Watershed Management Task Force Recommendations (11/02, BOC adopted 2/03) • Recommendations relative to on-site wastewater disposal: • Improve the data tracking system • At the sale of a home provide education materials • Promote certification of system installers & home inspectors • Develop and conduct a pilot study of systems • Based on pilot study results, make recommendations relative to, and evaluate system management options

  4. Purpose • The survey represents the implementation of the recommendation for a pilot study. Note that recommendation of the Task Force and subsequent adoption by the Wake County Board of County Commissioners provided impetus and a commitment to the study.

  5. Purpose and Problem Statement • Determine system failure rates in defined population • Determine the degree and type of maintenance provided to systems over the past twenty years • Provide scientific data relative to the need for enhanced system management • Based on results, evaluate failure rates, degree of operation and maintenance/relationship to failure rates and need for expanded management

  6. Study Design • Development of design involved a collaborative effort between WCDES and Dr. Mike Hoover, NCSU. Trish Angoli, OSWS, NCDENR and Dr. Larry King, Soil Scientist & Professor Emeritus NCSU also participated. • Design utilized a protocol under development by Dr. Hoover employing a scientific approach including problem definition, hypothesis development, statistical testing, defined sample size, specified research protocol, taking measures to minimize bias, characterization of the study population and sample selection.

  7. Study Design • Population chosen was all facilities served by septic tank systems installed between 1982 and 2001 (Systems of this vintage were required to have access risers on tankage and were sited utilizing uniform soil and site criteria) • Initial population within the selected age range of ~ 33,000 sites (out of ~ 55,000 total, based on CDM database) • Selection of sample size to achieve a 95% confidence limit

  8. Study Design • A random sample of 450 sites was selected utilizing Excel random number generation • The number of sites were “over selected” to account for unusable sample sites

  9. Study Execution • Preparation for execution included notification of elected officials, the public and those selected for survey • Assembly of survey packets by staff: Copy of permit & associated information. Orthophoto of site with land record information Survey forms (field data and homeowner interview). Letter of intent. • Division of packets into 9 survey districts utilizing GIS maps (based on desired 3 day time frame of survey and projected number of surveys/team/day)

  10. Study Execution Survey teams made up of Wastewater/Technical Assistance staff member and at least one team member from another program/cooperating agency (NCSU, DENR, LHD, Ag Ext., Wake S&E, Wake Soil & Water, etc.) Team members: Mike Hoover, Everette Lynn, Larry King, Bob Uebler, David McCloy, Trish Angoli, Steve Bristow, Kent Daeke, Suzanne Harris, Ed Duke,Brett Martin, Glen Johnson, Vince Manzi, Ron Dudley,Todd Becker, Everett Coates, Mitch Woodward, Quincy Adams, Tom Hill, Maria Cox, Robert Brown, Chris Niewohner.

  11. Study Execution • Survey conducted April 1 – 4, 2003. • 310 out of 323 were field surveyed, 13 non-viable sites (home vacant, could not access system, owner refusal) • Homeowner interviews conducted on 199 of sites

  12. Data Analysis & Survey Results • Survey Results: • 310 of 323 sites were considered viable-96% • Homeowner surveys were completed for 199 sites-64% • 25 of 310 sites were identified as exhibiting current failure at time of survey (8%), 5 of 30 sites identified as past potential failures were identified as failing when revisited, yielding a total of 30 failures (10%) Note: Hoover, ASAE 2004, observed that other studies in NC and across the US have yielded failure rates for conventional systems of 11-30+%.

  13. Data Analysis & Survey Results • Failure rates were significantly related to: • Age of system (primarily for less suited soils) although regression equations indicated that system age only accounted for a small amount of the variability • Site maintenance factors such as landscaping (drainfield shaped to shed rainwater), vegetation type, vegetation maintenance, and placement of fill material over the drainfield (indications of past potential failure) • Number of adults in the household, however, there was no significant relationship for total number of occupants, number of teenagers or number of children in cloth diapers

  14. Data Analysis & Survey Results Failure rates were significantly related to: • Pumping of the septic tank (although the relationship was an inverse one) • Interactions between site maintenance, soil properties or landscape factors • linear depressions over trenches on poor landscape positions (30% vs. 9%) • no diversion of on-lot surface waters when the drainfield was not shaped to shed rain water (19% vs. 9%) • drainfield not shaped to shed rain water and soil score < 20 (67% vs. 9%)

  15. Data Analysis & Survey Results • Other observed relationships: • Failure rates were significantly higher when structures were located on the drainfield (22% vs. 8%) • Homeowner possessing educational materials as related to spreading laundry events over the week (93% vs. 61%) and not pouring harsh chemicals down the drain (36% vs. 13%)

  16. RECOMMENDATIONS • Failure rates when looked at in the context of comparable studies indicate that the program is working reasonably well (other studies have reported failure rates for conventional septic systems to at times exceed 20%). • However, a failure rate of 8-10% is deemed to be higher than desired (likely a cumulative number of malfunctions of between 2,600 and 5,500+ systems in a wet season).

  17. RECOMMENDATIONS • Homeowner-impacted site maintenance, system use and periodic system maintenance were related to failures, including: Type and maintenance of vegetative cover, no. of adults, failed attempts to repair system ( tank pumping/fill over system), and spreading of laundry washing during week/not pouring harsh chemicals down drain (related to possession of educational materials). Evaluation of overall O&M indicated maintenance was not being carried out in the preferred manner.

  18. RECOMMENDATIONS • Possible responses from an educational perspective include: • Expansion of current educational opportunities and partnerships – NCCE, NCSU, etc. [Current efforts focus on dissemination of educational materials at time of system permitting & at time of home sale (in cooperation with Raleigh Regional Assoc. of Realtors), realtor training (in cooperation with NCCE), & educational materials on web-site] • Direct mailings to system owners, public service spots, educational programs, web-based materials & coordination with EE/EI • Staff training to make the most of educational opportunities in client contacts

  19. RECOMMENDATIONS • Failures were related to a number of site maintenance/ landscaping parameters that affect additions of rain water to the drainfield area including: • Lack of drainfield “crowning” or shaping to shed rain water, more pronounced on sites with low soil scores. • Linear depressions over trenches for systems located on poor landscapes. • On-lot water not diverted and lack of drainfield shaping to shed rain water.

  20. RECOMMENDATIONS • It is recommended that: • WDES address through the current permitting process - more attention to utilization of water control structures (necessitates layout & inspection of additional drainage structures by staff). • Encourage planning/design of lots to accommodate drainage structures and minimize concentrations of water from impervious surfaces (also requires education of Development community/consultants and acceptance).

  21. RECOMMENDATIONS • It is recommended that: • Follow-up inspections of landscaping be conducted 6-12 months after system installation (necessitates an additional inspection by staff). This approach also provides an additional opportunity for interaction and education of facility owners/operators.

  22. RECOMMENDATIONS • Failures were clearly related to certain unauthorized uses of system areas (e.g. location of outbuildings, sheds, garages, etc.). It is recommended that: • WDES expand review and permitting process for all proposed additions to properties served by on-site systems (currently carried out under Wake’s inspection jurisdiction, expand to all building permitting authorities)

  23. RECOMMENDATIONS • Failure rates were significantly higher for low-pressure pipe systems that lacked professional operation (certified subsurface system operator). It is recommended that: • Consideration be given to requiring professional operation for all systems utilizing such technology (including those predating this regulatory mandate). Such requirement would necessitate overcoming opposition by system owners and rule/regulation revision.

  24. RECOMMENDATIONS • WDES currently conducts regular O&M inspections on a limited number of systems (approximately 500) that employ complex technology or dispose of large volumes of wastewater. It is recommended that: • Consideration be given to provision of resources to- • Inspect all LPP systems (including those installed pre-1992) and • Meet the review criteria set forth in State Rules (inspection of systems employing effluent pumps every 5 years). • A much more far-reaching approach would entail inspection of all wastewater systems at an interval of possibly 5-7 years.

  25. RECOMMENDATIONS • WDES currently issues about 400 repair permits per year resulting from citizen complaints, citizen requests for service, observations by staff and limited community surveys (compared to study based cumulative number of wet season failures of 2,600 –5,500). • It is recommended that consideration be given to conduct of time of sale inspections on systems by “certified inspectors”. (Proposed SB 568 addresses certification of installers and inspectors but does not mandate inspection) • Pending outcome of legislation, County could pursue establishing requirements.

  26. RECOMMENDATIONS • Accurately locate (by GPS) new on-site systems and maintain a GIS layer of all system locations. • Evaluate fees and pursue funding sources to provide for expanded management of on-site systems. • Pursue development of funding proposals and study development (in conjunction with appropriate partners, NCSU, NCCE, etc.) for assessment of impacts of failing systems. • Pursue loan/grant programs to remediate failing systems where appropriate.

More Related