Septic System Impacts on Stormwater and Impaired Waterbodies. December 8, 2016 Tim Denison, Johnson Engineering Marcy Frick, Tetra Tech

Transcription

1 Septic System Impacts on Stormwater and Impaired Waterbodies December 8, 2016 Tim Denison, Johnson Engineering Marcy Frick, Tetra Tech

2 Presentation Overview Charlotte County: Many areas adjacent to impaired waterways Wastewater septic systems Stormwater overland drainage flows County-wide plan to provide central sewer and improve stormwater quality North Shore neighborhood: Pilot project for septic system removal East and West Spring Lakes area: First large-scale septic system removal project 2

3 North Shore Neighborhood Pilot Project 3

4 North Shore Small scale pilot project of 42 lots along Charlotte Harbor Typical ¼ acre residential area with roadside swales Septic systems from 1960s are inadequate and failing Pose health hazard during large rain events 2008 DOH standing water samples >47,000 cfu/100ml fecal Drains to Peace River & Charlotte Harbor Both impaired for nutrients 4

5 BMPs Remove septic tanks and connect to central sewer Restore and rehabilitate swale system Re-establish original swales Replace culvert pipes Replace sediment with proper fill Replace vegetation Public education Neighborhood meetings/workshops Florida Friendly Landscaping book Fertilizer ordinance information Pre-construction 5

6 Monitoring Stormwater (pre/post construction rain events) 3 grab sample sites - DOH site comparison - Distributed runoff inflow - Northshore Drive swale outflow 1 combined stormwater outfall site - Automated composite sampler - Rain gauge and flowmeter Ground water (quarterly throughout) 3 ground water monitoring wells Pre-construction 6

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8 Stormwater Sampling 3 sets of pre-construction samples in summer 2013 Pre-construction Pre-construction 8

9 Construction Septic tanks removal, sewer connection, and swale restoration fall 2014 spring

10 Stormwater Sampling 5 sets of post-construction samples in summer 2015 Pre-construction Post-construction 10

11 Stormwater Sampling - TN 11

12 Stormwater Sampling - Ammonia 12

13 Stormwater Sampling - NOx 13

14 Stormwater Sampling - TP 14

15 Stormwater Sampling - TSS 15

16 Ground Water Sampling 16

17 Ground Water Sampling, cont. 17

18 Ground Water Sampling, cont. 18

19 Conclusions Stormwater monitoring Significant reduction in stormwater runoff water levels observed No reduction in nutrient concentration measured within first 6 months Ground water monitoring Significant reduction in nitrogen concentrations at GW1 and GW3 No measurable reduction in nitrogen concentrations at GW2 due to tidal influence 3 neighboring properties outside of project area that are still on septic systems Pollutant volume removal Annual septic tank effluent converted to treated wastewater is approximately 2,100,000 gallons 19

20 Challenges Flow volume data Problem: Stormwater discharge flow velocity too low to measure Solution: County provided metered water use data for all properties Sewer connections Problem: A few homes along west project boundary still on septic Solution: Collect additional samples Ground water level data Problem: Not able to determine drain field level vs. ground water level Solution: Recommend continuous water level instruments in future Problem: Area is saturated at all times with the tides Solution: Sample only on the outgoing tide 20

21 East and West Spring Lakes Full-Scale Project 21

22 East and West Spring Lakes Septic systems were constructed between the 1950s and early 1980s Many are in failure and do not meet current regulations Area ultimately discharges to Charlotte Harbor and Peace River Project goals: Construct central wastewater service to 2,455 properties Restore the stormwater conveyance system Educate property owners on BMPs for fertilizer, pesticide, and herbicide application 22

23 Monitoring 49 ground water monitoring wells and 22 canal monitoring sites Ongoing since 2012 Slight modifications to canal locations in stormwater outfall monitoring sites Monitoring to meet grant requirements Pre-construction samples from September 2015 May

24 Phase I sample sites: Sunrise Canal Elkham Waterway 24

25 Phase II sample sites: West Spring Lake Tarpon Waterway East Spring Lake 25

26 Sampling Parameters Parameter Analysis Type Sample Type Total suspended solids Laboratory Composite Total phosphorus Laboratory Composite Nitrate + nitrite Laboratory Composite Total Kjeldahl nitrogen Laboratory Composite Ammonia Laboratory Composite Total nitrogen Laboratory Composite Biochemical oxygen demand Laboratory Composite Fecal coliform Laboratory Grab Temperature Field Meter ph Field Meter Specific conductance Field Meter Dissolved oxygen Field Meter Turbidity Field Meter Water level (at ground water monitoring wells) Field Meter Rainfall Field Meter 26

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28 Regulatory Standards Canals and stormwater outfalls: West Central Nutrient Region: TN = 1.65 mg/l and TP = 0.49 mg/l Fecal coliforms = 400 cfu/100 ml Ground water monitoring wells: Drinking water standards: NOx = 11 mg/l Fecal coliforms = presence detected 28

29 Canal Results - NOx Year Number Minimum Maximum Median Mean (mg/l) (mg/l) (mg/l) (mg/l)

30 Canal Results - TN Year Number Minimum Maximum Median Mean Number of (mg/l) (mg/l) (mg/l) (mg/l) Exceedances % Exceedances % % 30

31 Canal Results - TP Year Number Minimum Maximum Median Mean Number of (mg/l) (mg/l) (mg/l) (mg/l) Exceedances % Exceedances % % % % % 31

32 Canal Results Fecal Coliforms Minimum Maximum Median Mean Number of Year Number (#/100 ml) (#/100 ml) (#/100 ml) (#/100 ml) Exceedances % Exceedances % , % , % % , % 32

33 Ground Water Results - NOx Year Number Minimum Maximum Median Mean Number of (mg/l) (mg/l) (mg/l) (mg/l) Exceedances % Exceedances % % % % % 33

34 Ground Water Results - TN Year Number Minimum Maximum Median Mean (mg/l) (mg/l) (mg/l) (mg/l)

35 Ground Water Results - TP Year Number Minimum Maximum Median Mean (mg/l) (mg/l) (mg/l) (mg/l)

36 Ground Water Results Fecal Coliforms Year Number Minimum Maximum Median Mean (#/100 ml) (#/100 ml) (#/100 ml) (#/100 ml) , ,

37 Stormwater Pre-Construction Results - TN Area Number of % Samples Exceedances Phase I % Phase II % 37

38 Stormwater Pre-Construction Results - TP Area Number of % Samples Exceedances Phase I % Phase II % 38

39 Stormwater Pre-Construction Results Fecal Coliforms Area Number of % Samples Exceedances Phase I % Phase II % 39

40 Data Loggers Installed data loggers on existing ground water monitoring wells: 1 in Phase I 2 in Phase II Purpose is to demonstrate the change in water levels prior to and after removal of septic systems Change in water level is an important factor in determining pre- and post- project trends 40

41 Next Steps County has been removing septic systems and connecting properties to central sewer in Phase II Post-construction sampling planned for the 2017 wet season County is now constructing the wastewater collection system in Phase I Septic system abandonment will begin in 2017 Post-construction sampling planned for the 2018 wet season Continue to collect ground water well and canal data Data will be used to evaluate the nutrient and fecal coliform reductions from project implementation 41

42 Questions? Tim Denison, Johnson Engineering Senior Environmental Scientist (239) Marcy Frick, REM, Tetra Tech Water Resources Engineer (850)