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50 FORT AVENUE-SESD NOTICE OF PSS 5-30-23 i 156 RECEIVED SIMMONS ,SUN 0 6 2023 Environmental Services, Inc. May 30,2023 CITY OF SALEM Project#190702 BOARD OF HEALTH Mayor's Office Salem City Hall 93 Washington Street Salem,MA 01970 RE: Notice of Permanent Solution Statement South Essex Sewerage District Sodium Hypochlorite Release Release Tracking Number(RTN)#3-35700 To Whom it May Concern: We are pleased to submit this notice that a Phase H Comprehensive Site Assessment, Phase III Remedial Action Plan, and Permanent Solution with Conditions Statement 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). The South Essex Sewerage District (SESD) owns and operates a regional municipal wastewater treatment plant located at 50 Fort Avenue in Salem Massachusetts. The treatment process requires the use of sodium hypochlorite for disinfection of wastewater and for odor control. The District stores the sodium hypochlorite in several storage tanks in the Chemical Storage Building and Odor Control Buildings A and B and prior to June 2019, distributed the sodium hypochlorite through an underground double wall chemical containment pipe to several locations onsite. On average the District uses approximately 1,700 gallons per day of 12% sodium hypochlorite solution. On June 29, 2019, a sudden and accidental release of sodium hypochlorite from an underground double wall pipe was detected near Odor Control Building B at the treatment plant at 50 Fort Avenue. After further investigation, the release was estimated to have occurred between June 16th and 27th, 2019, with a total volume of approximately 5,400 gallons of 12% sodium hypochlorite solution (5,400 pounds of sodium hypochlorite). Following the release, the underground double walled chemical piping from which the release occurred was decommissioned and is no longer in use. Much of the hypochlorite mass was discharged to surface water through groundwater seepage (Seep A)at the rocky shoreline. The hypochlorite solution quickly dissipated with tidal action and mixed with ocean water without any observed acute effect on the local ecology. For several months following the release hypochlorite was tracked at the Seep A discharge location initially by measuring Total Residual Chlorine(TRC). After several months, TRC levels were non-detect. 213 Elm Street Salisbury,MA 01952 978-463-6669 info@simmons2le.com r K SIMMONS Em imnnxnhl Services.Inc. May 30,2023 The sodium hypochlorite solution after being released into the ground, interacted with the soil to degrade over the course of several months into chloride and chlorate salts and several volatile chloromethane compounds including chloroform. After the TRC had dissipated, chlorate was monitored at Seep A until there was confirmation of no significant ecological risk. Chloroform in the release area remains present in groundwater at levels below the GW-2 groundwater standard, which is intended to be protective for vapor intrusion. Chloroform also remains trapped in soil gas beneath the Odor Control Building B building on the site. Chloroform concentrations beneath Odor Control Building B do not pose a Significant Risk to current commercial/industrial occupants but could pose a Significant Risk to future occupants if the vapor integrity of the building floor slab was compromised or if the building use was changed to residential occupancy. The remediation for the site release included groundwater pumping and treatment near the release source area, as well as sub-slab vapor extraction from directly beneath the Odor Control Building B. Following this treatment and remediation, Chloroform concentrations in sub-slab soil gas beneath the Odor Control Building B were reduced to a level that poses No Significant Risk to human health with commercial/industrial worker exposure. In addition, an Activity and Use Limitation (AUL) has been recorded to prohibit changes in the building occupancy use on site and maintain a condition of No Significant Risk to human health. The Activity and Use Limitation maintains a condition of No Significant Risk and allows for the Permanent Solution to the previous sodium hypochlorite release. This Permanent Solution with Conditions Statement summarizes previous response actions at the Disposal Site and identifies that a condition of No Significant Risk has been achieved. A full copy of the report can be viewed by entering the RTN#3-0035700 on the MassDEP Waste site at https://eeaonline.eea.state.ma.us/portal#!/search/wastesite. Please contact our office if you have any questions regarding the contents of this report at 978-463-6669. Respectfully, William A. Simmons,LSP Simmons Environmental Services,Inc. CC: David Greenbaum,Health Agent David Knowlton,P.E., Salem DPS Director MassDEP BWSC Northeast Regional Office David Michelsen,P.E., South Essex Sewerage District J. Andrew Irwin,P.E.,LSP,IRWIN Engineers,Inc. Z:190702/SESD/SESD PSS Notice Letter-May 25,2023