Results from an experiment to find sources of fecal coliform bacteria in stormwater runoff

David Tomasko, Ph.D.

Emily Keenan, M.S. Joanne Vernon, P.E.1

December 10, 2015

1 Charlotte County Public Works - Engineering

In Florida hundreds of WBIDs declared impaired for fecal coliform bacteria, or with TMDLs for such

Important considerations • Fecal coliform bacteria are indicators of

contamination by pathogenic organisms – Bacteria such as Salmonella sp. (typhoid), E. coli

(gastroenteritis), Vibrio sp. (cholera) – Viruses such as enteroviruses, Hepatitis A – Parasites such as Giardia sp., Cryptosporidium sp.

• Used for decades as more precise indicator of threat of contamination than total coliform bacteria

However… • “Fecal” coliform bacteria can survive and multiply

in sediments to numbers far higher than in original dosage from sewage

• (LaLiberte and Grimes 1982, Ksoll et al. 2007)

• Both E. coli and enterococci can survive and multiply on the surface of rotting vegetation

• (Byappanahalli et al. 2003, Whitman et al. 2003)

• Klebsiella pneumoniae

• (Caplenas and Kanarek. 1984) – Normal constituent of human intestines – Problematic if aspirated into lungs – But also a natural constituent of soils

Situation in Sunshine Lake • Hypereutrophic lake in Charlotte County • Massive algal bloom of benthic-associated

cyanobacteria • Public demand to “do something” led to dredging

of lake • Concurrent and ongoing work to determine the

source(s) of nutrients that enabled the algal bloom to form – Ambient water – Groundwater sampling – Bottom seepage – Surface water runoff

• Nutrient species (nitrogen and phosphorous) • Bacteria as potential indicator of sewage

Summary of findings • Minimal levels of nutrients in the water column

– Uptake by benthic cyanobacteria bloom, not phytoplankton

• Stormwater runoff and groundwater – – Extremely high levels of phosphorous – Average to below average levels of nitrogen – Very high levels of fecal coliform bacteria

• (> 1 million cfu / 100 ml)

• If fertilizer alone – Elevated nitrogen and phosphorous, moderate bacteria

• If sewage alone – Elevated nitrogen and phosphorous, high bacteria

• If combination – both nutrients elevated, at least • How to explain findings?

Interpretation of findings • Elevated phosphorous from influence of

phosphorous-rich soils (adjacent to Bone Valley Formation)

• Low nitrogen indicates lack of sewage and/or fertilizer influences

• But what about elevated bacteria? – Source Molecular Laboratories (Miami)

• Used in FC TMDL for Wagner Creek (FDEP 2006) • 3 locations sampled twice • ESP gene of Bacteroidetes bacteria for humans • Maximum frequencies for humans and dogs

(combined) of less than 1%

• So where did those bacteria come from, if not from humans or dogs??

Follow up steps

• Consistent with guidance from FDEP (2011) – Work with Utilities to

determine possibility of wastewater problems

– Walk the WBID • Some evidence of

dog feces • Locations with

bare soils • LOTS of grass

clippings

Experimental design • Four treatments with three replicates each

– 50 grams of dog feces – 50 grams of bare soil – 100 grams of grass clippings – Controls

• 12 five-gallon buckets held in an abandoned trailer with no AC or fans

• Ambient lake water with added materials • Project done from June to July 2015 • Fecal coliform bacteria sampled (APHA standard

methods by NELAC-certified laboratory) on days 0, 2, 4, 8, 16 and 30

Overall set up

Dog feces Soil

Grass clippings Controls

So, what did we find??

Summary of findings • Day 0

– Soils, controls and dog feces at ca. 100 cfu / 100 – Grass clippings at 100,000 cfu / 100 ml

• Pre-loaded with bacteria

• After 2 days – Dog feces up to 100,000 – Grass clippings in excess of 1,000,000

• After 8 days – Controls and soil down to 10 – Dog feces in excess of 5,000 – Grass clippings in excess of 1,000,000

• After 30 days – Controls, soils and dog feces at 10 – Grass clippings in excess of 50,000

Interpretation • Elevated “fecal coliform” bacteria sources

– Not from sewage – Not from soils – Not from dogs

• Microbial source testing and Walk the WBID • Although can be a source, obviously

– Mostly from grass clippings • Not fecally-contaminated grass clippings

Implications for Charlotte County • Sewage not the source of bacteria

– No need to “fix” the sewage collection system

• Dogs could be a source – Public education

• Soils not likely a source • Grass clippings likely a source

– Public education – Consistent with existing literature

Broader Implications • > 150 TMDLs for fecal coliform bacteria in Florida • > 300 WBIDs “impaired” for fecal coliform bacteria • But…

– Fecal coliform bacteria not specific to humans – Not specific to mammals – Not specific to animals, even

• Recent moves by FDEP to move to E. coli and enterococci – However, both these indicators can also survive and

grow associated with rotting vegetation • (Byappanahalli et al. 2003, Whitman et al. 2003)

– And…impairment levels for enterococci of under 40 – Changing one problematic criteria for a less-

problematic one?

Questions?