Drainfield options after advanced pretreatment. George Loomis, David Kalen, Mark Stolt, Steven Holden, David Dow, and Arthur Gold

Transcription

1 Drainfield options after advanced pretreatment George Loomis, David Kalen, Mark Stolt, Steven Holden, David Dow, and Arthur Gold

2 Topics to be covered Shallow narrow drainfields Bottomless sand filters Both used in Rhode Island only with advanced treatment technologies achieving 30/30 BOD/TSS and 5 mg/l FOG

3 Funding Sources Rhode Island Aqua Fund USEPA Nat l. Comm. Decent. Demo Project USEPA National Onsite Demonstration Project II II RIDEM Nonpoint Source Program ( Section 319) RIDEM Individual Sewage Disposal Section URI Agricultural Experiment Station URI Cooperative Extension Community, industry, private sector partners Special thanks to: Brian Moore - RIDEM, ISDS RIICA Justin Jobin - JD Septic Services

4 (cross section) What is is a pressurized shallow narrow drainfield?

5 SNDF installation in Rhode Island Near surface placement More biochemically reactive soil Used only with advanced treatment systems No biomat development Easy, cost effective Site friendly Increases vertical separation distance 1 foot reduction in req d. vertical separation

6 SN drainfield applications in RI 3-25 ft. SNDF lines 2 bedroom home 5,000 sq. foot lot PL

7 Excerpts from Table 3 - SN DF hydraulic loading rates. Soil Soil Soil Loading rates Texture Structure Consistence g/sf/d cos,vcos structureless loose gravelly, v. single grain 2.3 gravelly soils fsl, sl, l granular to subangular blocky friable 3.7 ls, sl, l structureless massive; dense till firm to extremely firm 2.0 Maximize treatment and minimize disposal Medium textured, structured surface soils get the highest loading rates, not the gravelly soils.

8 Visually it looks like something is happening

9 Treatment performance in shallow narrow drainfields Holden et al., ASAE 2004 Steven Holden MS Thesis Mark Stolt mstolt@uri.edu

10 Sampling Procedure Filter HOUSE Pump Chamber Grass Sample Lysimeter Soil Samples Obs. Port 3 Meters Septic Tank SND X Water Table Well Recirculating Splitter Ball Water Meter/Valve Drainfield Pump Control

11 Lysimeter and Well Placement Lysimeter -30cm (12 ) Effluent Line Shield Trench Bottom WT Well -60cm

12 Sampling Protocol Soil-porewater (lysimeters) 14 total sampling events 2 events X 7 seasons winter 2002 through summer 2003 summer 2002 dry conditions - limited soil porewater samples obtained

13 Example (SIS) - Biomass of Grass 6.0 Mass Mass (g/ft (g) 2 ) SND CON Fall 01' Winter 01' Spring 02' Summer 02' Fall 02' Winter 03' Spring 03' Summer 03' P-Value / Sample 5 out of 8 seasons biomass SND > biomass Control (0.05 level)

14 Percent TN reduction and [mean TN] in soil pore water at 30 cm below the SND System Winter Spring Summer Fall Mean % Red. % % % % [mg/l] TWE % [33 mg/l] SIS % [36] HAZ % [28] TAR % [10] There were no statistical differences between seasons.

15 Summary: Fertilized lawn sites Soil pore water [TN] in controls much higher than in SNDF area Exceeded drinking water standard 4 out of 7 seasons No seasonal effects on reductions Lawn fertilizer appears to satisfy all grass N needs Additional N from effluent is leached Excess fertilizer & watering potential problem Need to regulate all potential N inputs

16 Percent TP reduction and [mean TN] in soil pore water at 30 cm below the SND System Winter Spring Summer Fall Mean % Red. % % % % [mg/l] TWE % [0.0] SIS % [1.5] HAZ % [0.03] TAR % [2.6] There were no statistical differences between seasons.

17 Using bottomless sand filters to disperse advanced treated wastewater in in Rhode Island Cooperative Extension New England Onsite Wastewater Training Center Natural Resources Science University of Rhode Island

18 What is a BSF? Top view - NTS 101 length width 1 manifold laterals Landscape timbers 99

19 At-grade BSF Separation distance datum point = Top of sand

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21 Where are BSFs used? Tight lots where PSND or conventional trenches require fill material Drainfield inverts would be above existing grade Shallow water table sites Restrictive layers are present

22 First R.I. BSF 1997 Portsmouth Bluebill Cove Poorly flushed coastal pond Shell fishing area Pathogen sensitive critical resource area Recreational water contact

23 How are they used in Rhode Island? Only with pretreated effluent coming from a time dosed pump. Time dosing accomplished by a Cat 1 or after a Cat 2 system Hydraulic loading rates dependent on soil texture, structure, consistence and type of advanced treatment technology

24 Typical BSF treatment trains in RI Gravity Flow Processing Tank Building Sewer Secondary Treatment Unit Pump Time-Dosed CAT 1 Pump Demand Dosed Bottomless Sand Filter Gravity Flow Building Sewer Socially Dosed Secondary Treatment Unit 450 gal. minimum time dosing tank Pump CAT 2 Bottomless Sand Filter (1 ½ ± x CAT 1) Time Dosed

25 Table 1. Hydraulic loading rates for bottomless sand filters

26 Category 1 Systems Time dosed (= defacto time dosing to BSF) < 20 mg/l (ppm) for BOD and TSS < 5 mg/l (ppm) FOG Includes: Time dosed media filters: peat, sand, textile, and trickling.

27 Category 2 Systems NOT time dosed < 30 mg/l (ppm) for BOD and TSS < 5 mg/l (ppm) FOG Non-time dosed technologies: extended aeration, fixed film, or fixed activated sludge systems. Time dosing must be included after advanced treatment step.

28 Bottomless Sand Filters Can be configured in ways to work with site features. PL

29 BSF Media Specifications ASTM C - 33 Sand plus E.S. ) = 0.33 mm (D10 U.C. / (D60 D10) = inches deep Maximum allowable fines passing a # 200 sieve shall be < 1%

30 BSF Enclosures Timbers vs. plywood support walls Lined with 30 mil PVC Permanent top frame min. 6 inches above grade Don t bury timbers for atgrade filters

31 Adding BSF Sand Media Use a clean bucket for sand Mix and scarify base Fill inside and outside evenly Protect liner from damage Not to be done in the rain or when soil is wet!!!

32 BSF Installation Mark elevations on liner Walk sand down on edges Only clean boots go inside filter Fill box evenly Watch that sides do not deflect

33 Provide temporary and permanent bracing

34 BSF Installation 24 of sand in filter Adding 3 of 3/8 inch washed peastone Super Sack holds 1.5 tons of stone Observation port in place

35 BSF laterals 1/8 orifices (6:00 position) use free-draining shields inch spacing 2 up-facing orifices per lateral 0.25 gallons per orifice per dose (maximum) 2 ft. min. distal head pres. clean outs at lateral ends

36 Finished BSF - Ready for Landscaping

37 BSF approvals in RI 2001 Mar. Mar. Mar. Feb. Total and to date

38 For more information - Guidelines for the Design and Use of Bottomless Sand Filters November 2001 RI Department of Environmental Management - ISDS