DPW Update: North Easton Village Wastewater Treatment Plant Surface - - PowerPoint PPT Presentation

DPW Update: North Easton Village Wastewater Treatment Plant – Surface Water Discharge Report Easton Board of Selectmen’s Meeting on January 7, 2019

Agenda

• Summary of the Discharge
• Detailed Time Lines to date
• Immediate Actions to investigate
• Immediate Remedies
• Long Term Actions and Remedies
• Lessons Learned & Process Improvements
• Discussion & Questions

December Sewer Tank Leak caused liquid to reach Shovel Shop Pond Summary: Dec 4th - Easton confirmed sewage was in the drainage system. Dec 4th to 5th - Town investigated matter, found & stopped source of sewage leaking into ground and migrating to the drainage system. Informs regulatory agencies as required. Dec 6th to 7th - Confirmatory tests, water quality tests, continued cleaning drain pipes & WWTF operations back to normal.

December Sewer Tank Leak caused liquid to reach Shovel Shop Pond Summary (cont’d): Dec 10th to 12th – Empty and cleaned Leaking Tank entered for investigation from inside. Four joint seam locations were identified as possible the leak. Dec 12th to 21th – Tank design & installation records from 2011 to 2013 pulled from archives. Tank Manufacturer & installer informed of Leak and put on

• notice. Assistance in long term remedy requested.

Jan 3rd – Structural Engineers enter Tank to design repairs and to propose “belt & suspenders” corrective actions. Currently awaiting their report.

So Exactly Where Did It Happened?

Shovel Shop Pond

So What Happened?

A buried sewer tank had an underground leak here The liquid migrated out, some leaked into a drain manhole here Drainage system pipes discharged the liquid at Shovel Shop Pond here

So What Exactly Happened?

L E A K

To Shovel Shop Pond

Tank Tank Drain Manhole Long Shop Building 4

December 3rd to 5th Timeline

Dec 3rd at 4:39 PM – Resident email Planning Dept about cloudy liquid and odor coming from a Mechanic Street pipe into Shovel Shop Pond. Dec 3rd at 4:56 PM – Planning staff responded indicating that Town staff will investigate in morning. Dec 4th in morning – Planning staff investigated and confirmed cloudy liquid and septic odor coming from drainage system discharge pipe. Immediately contacted Easton DPW.

December 3rd to 5th Timeline (cont’d)

Dec 4th around 11 am –DPW and Plant Operation staff investigate the discharge, the upstream drainage system, and sample the liquid. Dec 4th at 11:30 am – Field testing of discharge confirmed that ammonia, was present, indicating that is was coming from a sewer system. Dec 4th by 12:45 pm – Through investigation and manually opening tanks and vaults it was determined that one of the influent sewer tanks must be leaking somewhere between 8 and 12 feet underground.

December 3rd to 5th Timeline (cont’d)

Dec 4th by 1:00 pm – Leaking tank was isolated to prevent any new sewage from entering. Other tanks and vaults confirmed as not leaking. Dec 4th by 1:30 pm – Suspect tank level not dropping, confirming flow source of SSO was terminated. Dec 4th in the afternoon – Drainage system treated with chlorine

• tablets. Pumping trucks and wash down equipment ordered.

Dec 5th in early morning – Leaking tank pumped out and washed down.

December 3rd to 5th Timeline (cont’d)

Dec 5th all morning – Confirmatory measurements and investigations performed to reconfirm no other tanks were leaking and no new odors were emerging in drainage system. Dec 5th morning – Tank level records and plant flows reviewed in detail to estimate that 25,000 gallons of sewage had leaked out of the tank into the ground between Saturday, Dec 1st & Tuesday, Dec 4th. Dec 5th midday – MassDEP, EPA, and Easton Board of Health notified and a Sanitary Sewer Overflow (SSO) Notification Form completed.

Shovel Shop Pond Water Quality Sampling

Dec 7, 2018 Samples

• E. Coli

(MPN/100 ml)

Fecal Coliform after a WWTF (MPN per 100) Sampling Results Used for Comparison At Drainage System Outfall off Mechanic St >2419.6 200 Mid-Pond along Shoreline 191.8 200 Spillway to Lagoon 152.9 200 Dec 7, 2018 Samples

• Bio. Oxygen Demand

(Mg/L)

• Bio. Oxygen Demand

after a WWTF (mg/L) Sampling Results Used for Comparison At Drainage System Outfall off Mechanic St 36 30 Mid-Pond along Shoreline 10 30 Spillway to Lagoon 8.5 30

Red result confirmed wastewater had reached Shovel Shop Pond Blue results achieve Class B Bathing & Recreation Standards

Regulatory Notifications & Follow-up

Required Form is called a “Sanitary Sewer Overflow” Form or SSO Form.

• Stipulated and Guided by Town’s WWTF Discharge Permit from MassDEP
• Brief Information on estimated volume and cause / source
• Brief Description of Immediate Remedies and Planned Actions
• Send to MassDEP, EPA, and local Health Department

Summary Report of permanent repairs to be submitted to MassDEP once the Town has made all repairs and closed the matter.

Details on how to make long term repairs

Tank that leaked was a concrete tank made of multiple tunnel sections

How to make permanent repairs

Joints between the tunnel sections are grouted & sealed from the inside

Joints / Seams

Repairs to Joint Seals for tunnel sections

Structural Engineer is considering:

• A. Regrouting with a modified drill path to fill space
• B. Flexible membrane over each joint
• C. Two layers of troweled sealant
• D. All of the Above

Photo from Dec 11th inspection inside tank showing compromised seal between tunnel sections

Permanent Operational Changes

Per industry standards Tanks are currently monitored for liquid level and alarmed at high & low levels. Consider programming changes to monitor & trended for slowing decreasing levels (i.e., a leak)

Snapshot of a level monitoring and trending screen.

Next Steps

Work with Structural Engineer to implement recommendations Consider operational (trending and monitoring) adjustments Submit summary report to MassDEP, EPA and Easton Health Dept

Questions and Discussion

Various liquid types in wastewater processes

AFTER MIGRATION THRU GROUND

THIS GETS TRUCKED AWAY AS SLUDGE THIS IS SIMILAIR TO SEPTIC SYSTEM OUTFLOW

Septic System Description

Different treatment system outcomes

Raw Sewage ranges before system After North Easton WWTF System After Wrentham Village Reuse System Suspended Solids (mg/L) 200 – 300 3.7 3 Total Nitrogen (mg/L) 80-130 6.7 2 Fecal coliform (MPN per 100) 106-107 Less than 1 Less than10

• Bio. Oxygen Demand (mg/L)

200 – 300 6.3 Less than 4

Groundwater Travel time from NEV to Well field

Groundwater travel time = 4-5 years

Leaking Groundwater: small holes add up