SESD IRA Completion 6-18-20 Phone(508)653-8007 ` 33 West Central Street
Fax(508)653-8194 Natick,MA 01760-4503
CHEMICAL & ENVIRONMENTAL
RECEIVED
J U N 2 3 2020
June 18, 2020 CITY OF SALEM
BOARD OF HEALTH
Kimberly Driscoll
Mayor, Town of Salem
Salem City Hall
93 Washington Street
Salem, MA 01970
RE: Notice of Phase I Initial Site Investigation, Tier Classification, IRA Completion
South Essex Sewerage District Sodium Hypochlorite Release
Release Tracking Number(RTN)#3-35700
Dear Ms. Driscoll;
We are pleased to submit this notice of IRA Completion Statement, Phased I Initial Site
Investigation, and Tier Classification has been filed for a release of sodium hypochlorite
from a broken underground chemical distribution pipeline at the South Essex Sewerage
District treatment plant property at 50 Fort Avenue in Salem, Massachusetts (the Site).A
copy of the report can be
IRA Activities
The initial release discovery was in June 2019 with detection of"bleach odor"from
seepage at the base of a headwall on the shore of Cat Cove during an outgoing tide. The
Massachusetts Department of Environmental Protection(MassDEP)was informed of the
release of a reportable quantity and the Condition of Substantial Release Migration into a
surface water. The initial response actions identified the ruptured pipe as the source of
the release and its proximity to the alignment of a deep force main sewer that crosses Cat
Cove and enters the Site at the headwall location. The force main trench was serving as a
preferential pathway for flow of the bleach and contaminant movement was influenced
by daily tidal flushing of ground water. Sampling of Seep A at the base of the headwall
was conducted daily for free chlorine residual and by the end of July it was estimated that
the majority of the contaminant mass had already escaped into surface water and
dissipated with no evidence of Readily Apparent Harm to the environment.
By the fall of 2019 we concluded that the residual sodium hypochlorite had reacted
within soil and ground water and been transformed into degradation products consisting
primarily of chlorate with some chloroform and lesser concentrations of other tri-
halomethanes and bromate that were also appearing within the discharge to Cat Cove in
Seep A even though there was no residual free chlorine. Assessment of extent was
complicated by the congested network of electrical, sewer lines, chemical piping, and
776-01 E C6 L01 SESD Tier Classification Notice Letter
June 18, 2020
Page 2
drainage utilities within the densely developed Site. Later in the fall, a number of wells
were carefully installed with the finding that a remaining mass of chlorate appeared to be
concentrated in an area near the Odor B Building, situated over 200 feet from the sea
headwall.
IRA Plan Implementation
Beginning in January 2020 and continuing through March 2020 we implemented
pumping of groundwater in the area near the Odor B Building from IEI-102 to remove
residual chlorate and halomethane mass to the extent feasible. After three months of
pumping chlorate and VOC concentrations in IEI-102 had decreased by a full order of
magnitude and had approached an asymptotic decline. However, VOC concentrations at
IEI-102 remain above the applicable GW-2 Standard which is protective for vapor
intrusion.
Odor B Building is an unoccupied structure where sodium hypochlorite is used in air
scrubbers to control odors from the sewage treatment process. Sampling of sub-slab soil
gas beneath the Odor B building detected concentrations of chloroform above MassDEP
screening criteria. Sampling of indoor air at Odor B Building would be confounded by
the presence of hypochlorite reaction byproducts from the process operations. Thus an
Imminent Hazard Evaluation was conducted using the MassDEP default vapor intrusion
attenuation factor with the finding that there is no Imminent Hazard for current use of the
building or to utility repair workers for active utilities in the vicinity.
Ecological risk characterization was conducted to develop the No Significant Risk target
concentration for chlorate in the Seep A as an average of 6 mg/L of chlorate. Since the
ground water pumping, dry weather discharge concentrations are below that target and
analytical detection limits. However, chlorate concentrations in Seep A after rain events
are above that concentration; and the average concentration in the past months is about 10
mg/L of chlorate. These conditions do not pose a Substantial Hazard to the environment
in Cat Cove.
IRA Completion Summary
Immediate Response Action(IRA)activities were initiated at the Site to assess and
control the sodium hypochlorite release. At this point we conclude that there is no
Imminent Hazard or Substantial Hazard posed to human health,public safety, or the
environment, and IRA activities are complete.As Permanent Solution has not yet been
achieved,the Site will enter Phase II Comprehensive Response Actions as a Tier Il
Disposal Site.
1111 Mgi� ,MIT 1 E 776-01E C6 LO1 SESD Tier Classification
CHEPAI(At S EHVIRONMEHTAt Notice Letter
June 18,2020
Page 3
Phase II Scope of Work
The scope and schedule of proposed Phase II activities is described further within the
report and will focus on characterization of post-storm event sampling of Seep A,
characterization of the vapor intrusion pathway at the Odor B Building, and whether it
may be feasible to address the chloroform vapors in the ground by removal through a soil
vapor extraction pilot test.
Please contact our office should you have any question regarding the information
presented in this IRA Completion Statement, Phased I Initial Site Investigation, and Tier
Classification.
Very tr ly y urs,
i
IRW :n tiers, nc.
J. ii rew Irwin, P.E., LSP
P esident
CC: Salem Board of Health
MassDEP BWSC Northeast Regional Office
Alan Taubert, South Essex Sewerage District
William A. Simmons, Simmons Environmental Services, Inc.
776-01E C6 LO1 SESD Tier Classification
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