Decentralized Wastewater Collection and Treatment Alternatives

Transcription

1 Decentralized Wastewater Collection and Treatment Alternatives Bethel Heights, Arkansas A Case Study 9/9/09 #1

2 Introduction and Background

3 Introduction and Background

4 Introduction and Background 2000 Census 714 people, 280 homes. Town is bounded within a highly urbanized area. Densely populated adjacent municipalities; Springdale, Fayetteville, etc. No existing wastewater collection or treatment infrastructure. Small community, with limited resources Mayor Fred Jack also Police Chief.

5 Problem and Challenges Extreme growth pressure Home to several National and International Companies; Wal-Mart, JB Hunt, Tyson Chicken, etc. In US Top Five Fastest Growing Areas ( ). Several developers petitioning for subdivision approvals within Bethel Heights

6 Problem and Challenges, Cont. State legislation passes Act 779 in 1999 Act 779 Allowed de-annexation Allowed landowners to exit municipality if essential utilities (water, wastewater, etc) could not be provided. Bethel Heights began losing lands to neighboring municipalities Several developers requesting sewer services, ultimately deannexed. Tax base decreasing

7 Problem and Challenges, Cont. Standard septic systems did not apply Underlying karst landscape (cave and aquifer contamination fears) Densely populated developments (0.15 to 0.2 acre lots proposed) No monitoring or performance requirements on traditional individual home septic systems once installed Nutrient surplus zone (Nitrogen and Phosphorus stemming from poultry industry)

8 Problem and Challenges, Cont. Surface discharge permit (NPDES) difficult to acquire Less than 1 mg/l Total Phosphorus and Total Nitrogen Limits Conventional gravity collection system cost prohibitive Hilly Ozark topography several lift stations deep excavations required Pockets of dense but spread out small community Limited up-front funds available Slow build-out expectation

9 Solution 2002 Hired Engineer Design Associates (EDA) as WW consultant. EDA defined project parameters Low initial implementation cost Ability to incrementally expand to large capacity Build initial wastewater system to meet present developer needs prevent de-annexation Expand wastewater capacity as new development dictates Run trunk-lines to new development, sometimes up to four miles Existing homes and businesses connect to system as needed Low operation and maintenance costs part time operator

10 Solution: Technical Description On-Lot: Orenco STEP package Collection: Small diameter PVC; shallow burial (30 ) Treatment: AdvanTex textile treatment system Dispersal: Subsurface drip field

11 Technical Description, Cont. On-Lot Components Watertight tank, 1,500 gallons Biotube pump vault High-head effluent pump, 10 gal/min, 3/4 Hp Control panel Splice box Float assembly Discharge assembly

12 Pre-assembled, pre-wired STEP units Ready to place into the excavation

13 Technical Description, Cont. Collection Components Small diameter lines 2, 3 and 4 diameter up to 4 miles Shallow bury 30 Follows contour of land no deep excavations No lift stations Watertight flows per dwelling unit approximately 150 gal/day.

14 Traditional Decentralized

15 Technology Collection System Effluent sewers No manholes Can eliminate Infiltration and Inflow Eliminate the need for solids-handling lift stations and emergency generators

16 Technical Description, Cont. Secondary Treatment System AdvanTex AX100 Treatment System Modular expanded as necessary. Physical specifications Footprint: ~128 sq. ft. Treatment capacity Design flow: 5,000 gpd

17 System Implementation Phase I Effluent Sewer (STEP System) On-Lot Components Approximately 50% total project costs Deferred until homes were constructed Collection Component 200+ EDU capacity 9,000 LF, 4 PVC sewer main

18 System Implementation Phase I Treatment Component AdvanTex Treatment System 30,000 gal/day design flow 85+ EDU capacity 6 AdvanTex AX100 pods Capacity for 27 additional AX100s

19 System Implementation Phase I Dispersal Component Subsurface Drip Dispersal System 9,000 gal dose tank 50,788 SF drip field Average hydraulic loading rate of 0.24 gal/day/ft 2

20 System Implementation Phase II Effluent Sewer Expansion Additional On-Lot Connections Additional collection system infrastructure Treatment - 12 more AX100 pods Additional 60k gpd flow Total 170 EDU capacity Dispersal - Expanded drip field

21 System Implementation Current Status Two Treatment Sites Site One ,000 gal/day 36 AX100s (Phase I, II, IIIa and IIIb) 400+ homes currently connected Site Two -- 45,000 gal/day 9 AX100s (Phase IVa) Space available for 27 additional AX100s Started up in March of 2007

22 System Implementation Current Status, Cont. Phase I, II, IIIa, and IIIb

23 System Implementation Current Status, Cont. Phase IV

24 Total Project Costs Phase I Orenco STEP $5,000 per EDU Low Pressure Sewer $900 per EDU AdvanTex Treatment $2,400 per EDU Subsurface Drip $1700 per EDU Total Costs $10,000 per EDU

25 System Performance Data Influent Characteristics BOD5 TSS TKN NH3-N ph mg/l mg/l mg/l mg/l s.u Mean Median Effluent Characteristics BOD5 TSS NH3-N TP ph mg/l mg/l mg/l mg/l s.u. Mean Median

26 System Performance Data Nutrient Removal Over a two-month period in 2006 Total nutrient load applied as effluent TP, lbs NO3-N, lbs NH3-N, lbs Total Nutrient removed as Fescue hay TP, lbs NO3-N, lbs 49.8 (51%) 9.6 (3.5%) During this two-month period, over 24,000 lbs of hay were removed from the site

27 Results and Conclusion New development influx >500 connections to the wastewater system. Many existing businesses connected into wastewater system. Tax base increasing Nearby communities developing Orenco STEP-AdvanTex and subsurface drip wastewater systems. Lowell Elm Springs Fred Jack now Mayor, Police Chief and Wastewater System Operator.

28 Benefits of Decentralized Option Just-in-Time, Just-The-Right-Size service without excessive capital costs. Built to the exact needs of the community at the time needed. Minimized secondary impacts of sprawl. Continue to allow for modern development concepts. Promotes smart growth and low impact development concepts that incorporate integrated water resource management. Infiltration and Inflow issues can be readily addressed and completely eliminated. Lower risk due to smaller size and greater dispersion.

29 Decentralized Wastewater Collection and Treatment Alternatives Bethel Heights, Arkansas A Case Study Questions?