Corrosion control
in the water conveyance systems as a
source reduction solution to meeting NPDES Permit
limits in Northbridge, Massachusetts
Kelly Hyun Jung Park
This thesis was based on the Toxic Diet Project initiated by Save The bay, Inc.
in Northbridge, Massachusetts in order to help the town to meet the effluent discharge
limits for copper, lead and zinc as delineated by the 1992 National Pollutant
Discharge Elimination System (NPDES) Permit. A preliminary mass balance by Save
The Bay, Inc. indicated that more than 50% of copper metal measured in the POTW
influent is due to corrosion of the water conveyance system from the water company
at the source to the tap in the residences, while a significant portion of lead
and zinc comes from commercial/industrial contributions to the wastewater. One
of the principal objectives of the thesis was to review the mass balance protocol
used in the Toxic Diet Project and ascertain the major sources of the metals to
the POTW. Once it was determined that the corrosion of copper metal along the
water conveyance system is indeed the primary source of copper metal in the POTW
influent and the effluent discharge, the next objective was to review the current
corrosion control program used by Whitinsville Water Company to treat the water
used by Northbridge, and to investigate methods of further improvements to the
program. The protocol for the mass balance calculations and the assumptions that
were made at each step of the calculations were analyzed and questioned and then
revised to determine the uncertainties resulting from the assumptions. In cases
where there was insufficient information for an accurate calculation, estimations
were used and suggestions for further sampling and study were made, including
flow data from the different regions of the residential areas, flow due to inflow
and infiltration (I & I), and a more definite method of measuring the metal concentrations
in I & I. Depending upon the value used to represent undetectable concentrations
in the samples, as much as 75% of the copper metal in the POTW influent could
be due to corrosion along the water conveyance system. Previous case studies and
experiments with corrosion control were used to determine some of the more effective
methods of corrosion control and to rule out those methods that were unsuccessful.
In addition, an experiment performed by the Massachusetts Water Resources Authority
was modified to design a bench-scale testing of the corrosion control methods
using some of the most effective mixture(s) of chemical inhibitors to adjust both
the pH and alkalinity of the water. The proposed technological improvements to
the POTW facilities in order to enhance the removal of the metals from the influent
and the relocation of the outfall pipe to the Blackstone River, are not only costly,
but also may prove to be temporary solutions, depending upon the new metal limits
in the 1995 NPDES Permit. Rather than attempting to remove the metals from the
wastewater after they have become a problem, reducing the metals at the source
before they enter the sewage system through control of corrosion and usage of
corrodable parts would be a more effective solution to reducing the amount of
metals in the POTW effluent discharge to the Blackstone river.