By Rebecca McEnroe P.E. and Savas Danos
Abstract
The Sudbury (MA) Water District experienced chronic total coliform (TC) issues at its Well No.
9 for several years, including a specific capacity decrease. After exhausting traditional sanitary
survey techniques, the District determined that the presence of TC was possibly the product of
naturally occurring biofilm associated with high levels of iron and manganese. To potentially help
the matter, the district turned to enhanced redevelopment. Results included the reduction of the
chronic TC problems, as well as observation of increased specific capacity and an initial decrease
in raw water iron concentrations. Despite temporary TC reoccurrences, enhanced redevelopment
for biofilm removal ultimately proved effective at reducing TC in Well No. 9
Introduction
The Sudbury (MA) Water District had struggled
with chronic total coliform (TC) issues at its Well
No. 9 for at least five years, especially in the
warmer summer months. In addition, as is the
case with many wells in New England with high
iron and manganese levels, the district observed
a specific capacity decrease in this well over time.
The troublesome well was one of eight in the
town of 18,300, with an average daily flowrate
of 1.8 MGD. It is also one of three wells treated
at the Raymond Road Water Treatment Plant
(RRWTP) for manganese and iron removal and
corrosion control with the addition of fluoride
and chlorine for disinfection.
Drilled in 1989, gravel-packed Well No. 9 is
75 feet deep by 24 inches in diameter. TC was
found to be present in intermittent samples
beginning in 2010. In 2014 and 2015, 19 of 24
samples found TC to be present. Due to this
ongoing issue, the Massachusetts DEP required
and approved treatment for 4 log inactivation
of viruses (99.99% removal).
When total coliform levels rise in a municipal well,
the culprit can sometimes be an external source of
contamination. The district, using traditional sani
tary survey evaluations, searched for a peripheral
condition that might be compromising the well’s
water quality, such as direct infiltration or storm
water runoff. At that time, the district was unable
to discover the source of the contamination
Source of the Problem
The district then researched the well’s design
and installation to determine if any structural
issues were causing the total coliform presence.
They retained two separate well installers, includ
ing the company that originally drilled the well, to
visually inspect it; neither could identify a struc
tural flaw responsible for the presence of TC.
By this point, the well had experienced a 33%
reduction in specific capacity – decreasing from its original capacity of 125.0 gpm/ft to 83.3 gpm/
ft prior to cleaning. Records were not available
for the previous well cleaning, but anecdotal
evidence indicated that the last cleaning had
occurred before the first presence of TC was
discovered in the well.
Several factors can cause well degradation,
including:
• Lower water table due to drought or aquifer
depletion
• Reduced pump efficiency due to worn, cor
roded and/or plugged pumping parts
• Mineral plugging (e.g., iron, manganese, calcium
carbonate)
• Microbial corrosion (i.e., sulfate-reducing bacteria)
• Mud, sand and/or silt fouling
• Slime formation (bio-fouling) caused by iron
and slime-forming bacteria
Through the process of elimination, the district
suspected that biofilm was responsible for the
presence of TC and possibly some of the loss of
specific capacity in Well No. 9.
A biofilm is comprised of aggregates of micro
organisms, including bacteria, fungi, diatoms, pro
tozoa, algae and any exogenous materials. These
microorganisms are embedded in a hydrated
extracellular matrix and attached to a solid sur
face such as a well screen or pipe. Biofilm can
also be found on a ship’s hull, human teeth (i.e.,
dental plaque) and many other places1.
With all other reasonable options exhausted,
the district scheduled a well rehabilitation for
January 2016. This complete disinfection and
cleaning of the well used muriatic acid to address
mineral build-up and chlorine as a disinfectant
after chemical treatment.
Because of the concern that biofilm may be the
cause of the TC and some of the well degradation and the fact that typical redevelopment methods
are not designed to resolve biofilm issues, the
district took the additional step of enhanced
redevelopment in an effort to ensure a successful outcome.
Enhanced Redevelopment
Enhanced redevelopment is advisable when
other typical methods fail and one or more of
the following occurs:
• Videotaping of bore hole finds no structural
failure
• Pump components are in good working order
• Chronic total coliform bacteria and/or back
ground bacteria are found to be present
after membrane filtration testing or Biological
Activity Reaction Testing (BART)
• Excessive heterotrophic bacteria counts are
discovered
Biofilm analysis can be conducted through
advanced laboratory methods such as electron
microscopy and immunofluorescence micros
copy (i.e., most probable number testing). It may
also be done through field analyses, including
biological activity reaction analysis (BART Assay)
or adenosine triphosphate analysis (ATP Assay).
BART is a simple yet effective method for
monitoring the population size and activity of
specific groups of bacteria. Results are obtained
by observation after two to eight days of room
temperature incubation. With BART, water profes
sionals can monitor for iron-related bacteria (IRB),
sulfate reducing bacteria (SRB) and heterotrophic
aerobic bacteria (HAB) – the three most impor
tant agents involved in biofouling. Sudbury tested
for all three types of bacteria using the BART test
before and after the well cleaning. All the “before”
tests showed signs of all three types of bacteria.
ATP Assay is a molecule found in and around
living cells. As such, it gives a direct measure of
biological concentration and health. ATP is quan
tified by measuring the light produced through
its reaction with the naturally occurring firefly
enzyme luciferase using a luminometer. The
amount of light produced is directly proportional
to the amount of ATP present in the sample.
Several enhanced treatment techniques exist
for biofilm elimination, including wire charge
methods (e.g. sonar-jet, shock blast, prima cord),
fluid percussive methods (e.g., airburst, air shock,
nitro burst, jetting) and CO2
injection. There are also several proprietary blends (e.g.
Pantonite, Johnson nu 310/400, Cotey dry acid, Laval
Boresaver) that are far more complex than a simple
mineral acid such as muriatic, phosphoric or sulfamic.
The district chose an enhanced redevelopment
chemical method to attack the biofilm problem
and selected PantoniteTM PM77, a blend of organic
and inorganic acids, as an add-on approach fol
lowing the typical redevelopment process.
The aim of this enhanced redevelopment was
to combine physical and biological methodolo
gies to break down the encrustation (physical)
and eliminate it (biological). The proposed min
eral acid and chlorine treatment alone would be
insufficient to accomplish this
Results
Well No. 9 went back on line in February 2016.
BART tests were done after the well cleaning,
and the results were negative for all three types
of bacteria. From then until October 2016, TC
was absent from all samples. TC was found in
three of 14 samples taken from November 2016
until January 2017. However, this may have been
caused by very dry soil from drought conditions
followed by heavy rains in October. By February
and March, all samples were again clean of TC.
Conclusion
The primary lesson of Well No. 9 in Sudbury
is that water professionals need to sometimes
look beyond the traditional causes of increas
ing chronic microorganism concentrations
and decreasing well yield and specific capac
ity. When no structural compromise or exter
nal contamination is found, a prudent step
is to test for biofilm as the possible origin of
the problem.
With the assistance of these testing techniques
and the knowledge that naturally occurring fac
tors can cause TC to be present in a well such
as Sudbury’s Well No. 9, enhanced redevelop
ment can help resolve chronic TC bacteria issues,
reverse specific capacity loss and return a well
to good working condition.
References
1. J.W. Costerton and P.S. Stewart: Battling Biofilm”. 2001.
Scientific America, Volume 285, No.1, pp. 74-81.
2. P. Dirckx: “Biofilm Basics, Section 1”. 2003. Biofilms: The
Hypertextbook. Center for Biofilm Engineering, Montana
State University.
Acknowledgements
• Sudbury Water District, Sudbury MA.
• Maher Services Company, North Reading, MA.
July 6, 2026
by
PantoniteLLC