Onsite Wastewater Treatment Systems

Transcription

1 Onsite Wastewater Treatment Systems Municipal Officials Conference: Managing Onsite Wastewater Treatment Systems to Protect Long Island s Waters March 25, 2014 George Loomis New England Onsite Wastewater Training URI

2 URI We are a USDA, state and training class fee funded program Outreach through URI Cooperative Extension Coverage area: Regions 1&2 New England, NY, NJ, PR & USVI Provide third party, non-biased technical assistance Clientele includes federal and state regulatory agencies, communities, NGOs, wastewater professionals, homeowners Conduct approx. 50 classes a year reaching over 1,800 wastewater practitioners and decision makers We perform onsite wastewater research Work closely with local and state regulatory programs

3 Long Island and Block Island Sound

4 What we will cover 1) Conventional OWTS basics 2) Cesspools 3) Contaminant treatment potential 4) System management - inspection and tank pumping 5) Intro - Advanced treatment technologies (more in afternoon session talk)

5 1) Conventional septic system has 3 main components Septic tank D-Box Soil absorption area Source: URI Cooperative Extension, New England Onsite Wastewater Training Center

6 Conventional Septic Tank Inlet scum sludge

7 As scum and sludge layers build and come closer together, the retention time becomes less and solids removal efficiency drops, as well as BOD and FOG removal

8 Conventional D-Box Operates on trickle flow to the lowest pipe invert D-Box leveling devices readjust outlet pipe inverts. Manufacturers make these for various pipe sizes.

9 Drainfield options Separation distance Defined as: The distance between the base of a drainfield and the elevation of the seasonal high water table (or a restrictive layer) This varies with jurisdiction. Nassau Co. has a minimum separation to SHWT of 24 Suffolk Co. has a minimum separation to SHWT of 36

10 Drainfield sizing criteria Depends on the soil type Number of bedrooms The design of a soil treatment area also depends on the type of system. Leaching pools are designed differently than pipe on stone (tile drainfields).

11 Min. separation distance to water table = 3 or 4 feet (Rhode Island)

12 Produces a deep installation base (8 ft.) Poor oxygen diffusion Poor aerobic treatment potential In 2008, galleys prohibited in RI for new construction Block Island will phase out existing ones

13 Alternative system (shallowest chamber type for shallow SHWT) Leaching pools /- 8 2

14 Typical 4 bedroom leaching pool design (for SHWT 9 or greater) 6

15 Typical 4 bedroom leaching pool design (for SHWT 11 or greater) 8

16 Typical 4 bedroom leaching pool design (for SHWT 17 or greater) 14

17 A very deep installation Concentrated footprint Small infiltrative surface 25 max

18 2) Cesspools Source: URI Cooperative Extension, New England Onsite Wastewater Training Center NO septic tank Substandard system Antiquated and inadequate Often violates vertical separation distance regulations In coastal areas - may be tidally connected Prioritize replacement with approved system

19 Treatment and safety issues 2) Cesspools defined - Dry-fit, or minimally mortared: Concrete block, brick, fieldstone Into which flows sanitary sewage from a structure Impractical - solids storage and liquid infiltration

20 3) Pollutants common in septic TSS, BOD5 tank effluent Nutrients - nitrogen, phosphorus Volatile organic chemicals (VOCs) Pathogenic organisms - Helminths (septic worms) - Protozoa - Bacteria - Viruses

21 Vadose zone wastewater treatment Controlling factors Environmental Temp., moisture, oxygen levels Wastewater char. Loading rates, strength, types of pollutants Soil properties Physical, chemical, biological Retention time Unsaturated soil Water table Saturated soil Biomat

22 Soil-based wastewater treatment The Goal : Unsaturated conditions Thin film flow of wastewater around soil particles Pore space in between particles and/or soil peds (structural units of soil) Gases and air move in/out

23 When organic inputs exceed removals and all soil pore spaces are clogged, then hydraulic failure occurs.

24 Source: URI Cooperative Extension, New England Onsite Wastewater Training Center Failure defined (usually in regs): Surfacing wastewater = off site movement of contaminants, loss of treatment, water quality impairment, and environmental and public health risks

25 Biochemical reactivity in soils 99% of soil bioreactivity is within inches of soil surface Sources: Introduction to Soil Microbiology, Second Edition Martin Alexander - John Wiley & Sons,1977. "Soil Microbiology" Selman Waksman - John Wiley & Sons, MOST OWTS regs promote deep drainfield placement, well below this reactive zone

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27 Summary - Nitrogen removal in conventional septic systems Less than 15 percent removal in septic tank Septic tank effluent composed of organic-n and ammonium-n Limited ammonium adsorption by soil below drainfield Ammonium conversion to nitrate-n Nitrate-N very mobile and conservative 10 ppm EPA nitrate-n drinking water standard

28 Summary - Phosphorus (P) removal in conventional septic systems Phosphorus adsorbed to iron, aluminum, manganese, calcium, and magnesium in soils P removal depends on soil surface area Sands have far less surface area than finer soil particles P saturation can and does occur Wet soils conditions result in iron removal, so less P removal potential

29 Summary - Wastewater microorganism movement Organism Helminths Protozoa Bacteria Viruses Approx. Size sand c. silt f. silt - c. clay v.f. clay Mobility Potential low high Enhanced removals with aerobic soils and long retention times

30 Summary Emerging contaminants of concern Pharmaceuticals Antimicrobials Endocrine disrupters Personal care products (PCPs) Removals based upon complex biochemistry and they are compound and site specific Aerobic soil conditions and long retention times are key treatment factors

31 4) Management Life cycle of an unmanaged conventional septic system Years T 0 T ff T (first flush) hf siting design permitting installation home first occupied // T = time USE system hydraulically fails

32 The onsite system O&M image crisis Anything beyond nothing seems like too much!

33 Onsite wastewater industry challenge Managed centralized treatment plants Unmanaged conventional systems Managed advanced treatment onsite systems

34 Conventional system inspections and tank pumping Identifies problems Creates an inventory Protects Owner investment Public health Water quality Resources Property values Costs - $250 (pumping) and $50 to150 (inspection) Frequency every 3 to 5 years Managed systems last longer than neglected ones

35 Onsite Wastewater Treatment System Inspector Training Class Dates & Times: April 22 23, 2014 (2-day class) 8:00 am 5:30 pm (registration at 7:30 am) or April 24 25, 2014 (2-day class) 8:00 am 5:30 pm (registration at 7:30 am) Location: Oyster Bay Community Center, Church Street, Oyster Bay, NY Cost: FREE (normal cost $450) Class size is limited to 25 people, so please register early to assure a seat.

36 5) Alternative technology treatment train 1. Primary treatment zone 2. Alternative technology Secondary treatment 3. Drainfield - Dispersal and advanced secondary / tertiary treatment 4. Controls - timers

37 Rhode Island southern coast Totally unsewered watersheds % of systems are cesspoo Very permeable unconfined aqu Groundwater contamination risk 8 houses / acre on shallow wells Surface water eutrophication risk Shellfish closures Typical application for I&A technologies Water quality standards for coastal pond systems mg/l TN and 14 counts / 100 ml F. coliform

38 Advanced treatment technologies approved in RI ca.1983 ca.1996 ca.2014 RUCK ATUs Single pass sand filters Recirc. sand filters Early textile filters Foam biofilters Shallow narrow pres. drainfields Bottomless sand filters - early Modular peat filters Textile filters Fixed activated sludge systems Bottomless sand filters current Denite upflow filters Trickling filters UV disinfection Soil treatment area renovation technologies N removal systems

39 Bottomless sand filter

40 Thanks for your attention! George Loomis