Fecal Indicator Bacteria in Groundwater Adjacent to Three On-site Wastewater Treatment Systems in the North Carolina Coastal Plain

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1 Fecal Indicator Bacteria in Groundwater Adjacent to Three On-site Wastewater Treatment Systems in the North Carolina Coastal Plain 1 Charlie Humphrey, PhD, Assistant Professor of Environmental Health Sciences at East Carolina University 2 Michael O Driscoll, PhD, Associate Professor of Geological Sciences at East Carolina University 3 Jonathan Harris, MA, Environmental Health Sciences Research Technician at East Carolina University What is Next? Overview of on-site wastewater treatment systems and fecal indicator bacteria Research questions Methods Results and discussion Summary Questions 1

2 Water Quality and On-site Wastewater Treatment Systems 2 million OWS in NC, 60% of coastal NC use OWS OWS treat effluent with elevated fecal indicator bacteria (FIB) concentrations E. coli (10 4 to 10 6 MPN/100 ml) Enterococci (10 3 to 10 5 MPN/100 ml) Total coliform (10 6 to MPN/100 ml) (US EPA, 1986) Bacteria Concentration Reductions Filtration, die off, predation, adsorption, dilution and dispersion Onsite Wastewater Treatment Systems Septic Tank Distribution Box Trench and Soil 2

3 On-site System Technologies Conventional OWS with Distribution Box Low Pressure Pipe (LPP) OWS Pump to Conventional OWS with Distribution Box LPP systems can be installed on sandy sites with less soil depth in relation to conventional OWS. Also, LPP systems typically require 25-30% less area than conventional trench OWS. Biomat Influence on Wastewater Distribution (Hoover et al., 1996) (Loudon et al., 2005) 3

4 Research Questions Is there a more even distribution of FIB in groundwater beneath a LPP system in comparison to a pump to distribution box system? What are the treatment efficiencies (FIB concentration reductions) at 2 large OWS and one residential OWS? Methods 4

5 Monitoring Networks FIB comparisons and environmental readings including ph, DO, specific conductivity, depth to water, and temperature Pitt County Residential Site Site Install Date Septic Tank Capacity (L) Max Design Flow (L/d) Distribution Device Dispersal Area (m 2 ) Vertical Separation (m) Soil Series Residential 1998/ D-box 151 < 0.2 m Goldsboro/Lynchburg 5

6 James Smith Elementary Septic Tank Max Design Grease Pump Tank Distribution Dispersal Area Vertical Site Install Date Capacity (L) Flow (L/d) Trap (L) (L) Device (m 2 ) Separation (m) Soil Series JWS ,800 37, ,144 D-box (2) 892 > 3 m Autryville West Craven High Septic Tank Max Design Grease Pump Distribution Dispersal Vertical Site Install Date Capacity (L) Flow (L/d) Trap (L) Tank (L) Device Area (m 2 ) Separation (m) Soil Series WCHS ,827 73,827 11,340 11,340 LPP (2) 1115 > 1 m Tarboro 6

7 Groundwater FIB Spatial Distribution (JWS) Groundwater FIB Concentrations Fronts and ends of trenches; Field 1 and Field 2 Groundwater FIB Spatial Distribution (WCH) Groundwater FIB Concentrations Fronts and ends of trenches Field 1 and Field 2 7

8 FIB Treatment (Residential Site) FIB Comparisons Septic Effluent, Background, Drainfield Groundwater, Down-gradient, Stream FIB Treatment (JWS) FIB Comparisons Septic Effluent, Background, Drainfield Groundwater, Down-gradient, Spring, Stream 8

9 FIB Treatment (WCH) FIB Comparisons Septic Effluent Background Groundwater Drainfield Groundwater Down-gradient Groundwater Surface Water Standards Results and Discussion 9

10 Groundwater FIB Spatial Distribution Geometric Mean Enterococci F1-F = 336 MPN/100 ml F1-E = 1329 MPN/100 ml Fronts = 110 MPN/100 ml Ends = 445 MPN/100 ml F1 = 667 MPN/100 ml F2 = 73 MPN/100 ml p = 0.05 p = p = F1 = 820 MPN/100 ml F2 = 106 MPN/100 ml p = *More even distribution of Enterococci in GW at WCH Groundwater FIB Spatial Distribution Mean E. coli F1-F = 1 MPN/100 ml F1-E = 7 MPN/100 ml Fronts = 1 MPN/100 ml Ends = 5 MPN/100 ml p < 0.10 p < 0.10 *More even distribution of E. coli in GW at WCH 10

11 Groundwater FIB Spatial Distribution Geometric Mean Total Coliform F1 = 2007 MPN/100 ml F2 = 1178 MPN/100 ml p < 0.10 *More even distribution of total coliform in GW at WCH FIB Treatment at Schools Treatment Efficiency (%) Tank-DF Tank-Spring Enter E. coli >99.99 >99.99 Total C Enter and Total C. (r =0.446, p = 0.011) Treatment Efficiency (%) Tank-DF Tank-Down Gradient Enter E. Coli >99.99 >99.99 Total C Enter and Total C. (r = 0.328, p = 0.07) 11

12 FIB Treatment at Residence Residential Enterococci Treatment Tank-Down Gradient = 37.13% Residential E. coli Treatment Tank-Down Gradient = 99.88% Correlation between E. coli and Enterococci r = 0.52, and p = Physical and Chemical Parameters JWS Specific Conductivity Depth to Water ph Temp (C ) (µs/cm) (m) Field (246) 6.37 (0.57) 18.3 (1.1) 4.56 (0.91) Field (237) 6.89 (0.75) 18.9 (1.1) 6.21 (1.02) Front 547 (204) 6.45 (0.80) 18.4 (0.9) 4.92 (1.25) Ends 754 (268) 6.78 (0.58) 18.8 (1.2) 5.85 (1.15) Background 98 (51) 5.12 (0.65) 18.1 (0.5) 4.32 (0.31) Tank 1057 (387) 7.31 (0.26) 17.8 (2.9) Down Gradient 620 (69) 7.23 (0.27) 17.5 (0.8) 0.34 (0.02) Spring 445 (29) 6.91 (0.37) 18.2 (0.6) Upstream 144 (12) 7.22 (0.25) 13.7 (1.1) JWS SC Trends F1 > F2 Ends > Fronts SC and Enterococci (r = 0.428, p = 0.007) WCH Specific Conductivity Depth to Water ph Temp (C ) (µs/cm) (m) Field (401) 5.97 (0.65) 16.4 (2.1) 1.76 (0.16) Field (302) 6.53 (0.34) 16.7 (1.8) 1.62 (0.11) Front 521 (327) 6.32 (0.55) 16.6 (2.0) 1.69 (0.16) Ends 340 (397) 6.17 (0.63) 16.4 (1.9) 1.69 (0.16) Background 49 (12) 6.56 (0.99) 15.5 (2.2) 1.53 (0.31) Tank 1196 (432) 6.91 (0.28) 17.9 (3.5) Down Gradient 710 (212) 6.53 (0.22) 17.2 (1.5) 1.44 (0.13) Residence Specific Conductivity Depth to Water ph Temp (C ) (µs/cm) (m) Up Gradient 181 (44) 5.0 (0.6) 18 (5.5) Tank 855 (183) 6.5 (0.2) 18.4 (4.6) Down Gradient 326 (132) 6.2 (0.2) 17.8 (5.9) < 0.20 Stream 150 (19) 6.4 (0.1) 14.6 (8.0) WCH SC Trends F2 > F1 Fronts > Ends SC and Enterococci (r = 0.387, p = 0.014) SC and Total Coliform. (r = 0.534, p = 0.001) SC Trends All Sites Tank > DF > DG/Spring > Stream 12

13 Summary A more even distribution of FIB in groundwater beneath the LPP in comparison to pump to conventional system All 3 systems were less efficient at reducing enterococci concentrations relative to the other FIB The OWS at JWS and WCH were more efficient at reducing FIB in comparison to the residential OWS possibly because of the limited vertical separation at the residential OWS Specific conductivity was correlated to some of the FIB, and generally showed similar trends with regards to FIB Matt Smith Sarah Hardison John Woods Jim Watson Eliot Anderson-Evans Acknowledgements NC WRRI NC Dept. of Environment and Natural Resources (319 Program) East Carolina University Coastal Water Resources Center Craven County School System Craven County and Pitt County Environmental Health Volunteers ECU Geological Sciences Department ECU Environmental Health Sciences Program Guy Iverson Caitlin Van Dodewaard Ashley Williams Hannah Postma Amberlynne VanDusen 13