# Presentation: 510665

## BACKGROUND AND TECHNOLOGY

## DEFINITIONS

- CENTRALIZED SOLUTIONS
- Conventional gravity sewers to treatment and surface water discharge
- DECENTRALIZED SOLUTIONS
- Onsite Systems
- Cluster Systems
- Mixed Systems

## Slide 3

## PROS AND CONS

- PROS
- Universally understood technologies
- Well-suited for dense urban populations
- CONS
- 	Costly (capital and labor intensive)
-    Generally serves entire town to spread cost
-    Adds additional permit monitoring costs
-    May stimulate unwanted growth and impacts

## Slide 5

## CHARACTERISTICS OF DECENTRALIZED SOLUTIONS

- Area divided into sections by problems, drainage basins, and other common features
- Each area is evaluated and prioritized by relative risk to health and environment, and  solutions to those problems
- Mixed solutions can include onsites, clusters, and centralized zones under a single management authority

## DECENTRALIZED SOLUTION EXAMPLE

## PROS AND CONS

- PROS
- Generally less expensive than centralized
- Less disruption during construction, continues aquifer recharge, simpler O/M and monitoring
- Can phase solutions by addressing priority areas first
- CONS
- Not taught in engineering schools
- Regulatory and financing rules generally discourage applications
- More complex rate structures may be necessary

## TRADITIONAL WASTEWATER SOLUTIONS

- ONSITE SEPTIC SYSTEMS
- No management after prescriptive code design and cursory installation inspections (if site meets code requirements, it is assumed to perform until complaints from citizens)
- CENTRALIZED SEWER SYSTEMS
- Continuing high-level management required to maintain performance and comply with NPDES permit (administration, O/M, monitoring)

## RESULTS OF THIS PARADIGM

- Many small communities could not afford the centralized solution, and with problem septics  homes had no or depressed value
- If a conventional system was built, the town often couldn’t afford to manage it, so unanticipated, unwanted growth was encouraged to pay for it,  cancelling or delaying other needed investments

## TRADITIONAL  SEPTIC SYSTEMS

## MODERN CHANGES TO THAT PARADIGM

- Grants have become scarce
- Septic system contamination of ground water (source of 90% of US rural drinking water) now widely documented
- Smaller communities, shut out of grants because of size dependence for priority, cannot afford centralized solutions
- Properly managed new onsite and cluster technologies have reduced costs and increased capability of decentralized solutions
- Inclusion of decentralized solutions in the array of engineering solutions may reduce costs and permit more communities to be addressed by limited assistance funds

## WHAT ARE SOME OF THESE DECENTRALIZED TECHNOLOGIES 

- BETTER ONSITE TREATMENT SYSTEMS
- Media filters
- Enhanced activated sludge designs
- Constructed wetlands
- BETTER SOIL APPLICATION SYSTEMS
- Pressure distribution
- Drip distribution
- LOW-COST COLLECTION SYSTEMS
- Effluent sewers
- Vacuum and grinder pump sewers

## BETTER PRETREATMENT CAPABILITY

- Better treatment often permits smaller soil systems in many states
- Systems are available to produce lower concentrations of organics (BOD, COD), nutrients (nitrogen, phosphorus), and pathogens (bacteria, virus, and parasites)
- All require higher levels of management than traditional septic systems

## SINGLE-PASS MEDIA FILTERS

## Slide 16

## Slide 17

## Slide 18

## BETTER DISTRIBUTION

- Better distribution allows the entire soil infiltration area to be used, provides better oxygen diffusion for aerobic treatment by microbes, and increases the contact time between the wastewater and soils
- This type dose/rest application is required for larger (cluster) soil dispersal systems and most elevated onsite systems

## BETTER DISTRIBUTION

## Slide 21

## CLUSTER SYSTEMS

- Powerful tool to service problem areas or areas where lots are too small to accommodate conventional septic systems
- Permit significant reuse in the area close to the wastewater contributors
- Accommodates targeted solutions that address the main problem sources at an affordable cost

## LOW-COST COLLECTION SYSTEMS

- These collection systems all consist of shallowly-buried plastic pipes, low-cost cleanouts instead of frequent/costly manholes, and a minimum number (if any) of lift stations
- They have 40 years of successful experience in the US and worldwide (less I/I, exfiltration, construction duration and disruption)
- Their management requirements are equal or lower than conventional gravity sewers (depends on number of lift stations)

## EFFLUENT SEWERS

- Septic Tank Effluent Gravity (STEG) Sewers
- “Small Diameter Gravity Sewers”
- “Small-Bore Sewers”
- Septic Tank Effluent Pressure (STEP) Sewers

## Slide 25

## Slide 26

## GRINDER PUMP PRESSURE SYSTEM

## WHAT DO THESE DECENTRALIZED TECHNOLOGIES HAVE IN COMMON?

- They all require management to assure proper operation....no more free ride
- The more complex onsite systems require at least 4 visits per year, less complex 1 to 2.
- The cluster systems of any significant size require oversight and management.
- Management can be public, private or a combination of both

## CONCLUSIONS

- The traditional paradigm for smaller communities must be revised to include full consideration of decentralized approaches to solving wastewater problems
- However, it cannot be overstated that such solutions must have appropriate management arrangements, just as the conventional engineering solutions have