Combined Sewer & Sanitary Sewer Overflows

During heavy rains, stormwater can enter the municipal sewer system which can cause the system to surcharge and overflow; this is known as a Combined Sewer Overflow (CSO). The wastewater collection system wasn't designed to handle large amounts of water accumulated during heavy rain. A CSO diversion system was put in place to direct these high stormwater flows to Clemson's Holding Pond. The pond discharges through a permitted outfall and tide gates to the Squamscott River.

A Sanitary Sewer Overflow (SSO) is a discharge of untreated sewage from a sanitary sewer which can occur from broken pipes, malfunctioning pump stations, or blockage of sewer lines. These are not always related to rain events.

Each overflow event must be reported to the appropriate regulatory agencies. In some cases, shellfish beds in the Great Bay are closed for harvesting.

The town has been working to eliminate CSOs from the wastewater collection system for the last 20 years through extensive separation projects. The Town was issued an administrative order on September 30, 2010 requiring a Long Term Control Plan to abate CSO's. In addition, the Town is under order to create a Collection System Capacity, Management, Operation and Maintenance plan including a proposed implementation schedule to prevent CSO's and SSO's in the future. However, CSO events still occur during heavy rains.

The primary ways that stormwater enters the sanitary sewer system are infiltration and inflow (I & I):

Infiltration results from surface water or groundwater seepage into the sewer system through defective pipe joints, cracked, broken, or collapsed sections of pipe and manhole walls.
Inflow is extraneous water which enters the wastewater system from other sources including private catch basins, sump pumps, roof drains, and any other connection of stormwater to the wastewater system.

The Town must reduce and eventually eliminate overflows to Clemson Pond. Sump pumps, roof drains, and other stormwater connections to the sewer system significantly contribute to overflows. Efforts to reduce overflows include:

Letters have been sent to residents and businesses that were identified in earlier studies as potential sources of stormwater connections to the sanitary sewer. Public Works has been and will be working closely with property owners to determine if there is a stormwater connection, and identify possible solutions. See the link below regarding illegal sump pump hook-ups.
Certain areas in town were identified as potential sources of inflow from sump pumps. Public Works will inspect these areas and notify property owners of possible stormwater connections as well as identify solutions.
The Sewer Department uses televising equipment to examine pipes and manholes in the cross country lines and in the older sections of town, areas that are prone to infiltration.

Non-disinfected Discharge

Dec 12, 2023 - Due to an unexpected power outage at approximately 10:16 pm, there was a non-disinfected discharge of 9,646 gallons from outfall 001.

May 30, 2023 - Due to an unexpected power outage, there was a non-disinfected discharge of 4,720 gallons from outfall 001.

March 18, 2023 - A non-disinfected discharge of approximately 2,000 total gallons from outfall 001 due to the restart of the UV disinfection system.

January 23, 2023 - Due to an unexpected power outage due to severe weather in our area, a non-disinfected discharge of 2,000 total gallons from outfall 001. The lapse in disinfection occurred during the restart of the UV disinfection system.

December 23, 2022 - Due to an unexpected power outage due to severe weather in our area, a non-disinfected discharge of 18,611 total gallons from outfall 001. The lapse in disinfection occurred during the restart of the UV disinfection system.

July 21, 2022 - Due to an unexpected power outage due to strong storms in the area, a non-disinfected discharge of 5,000(EST) gallons from outfall 001. The lapse in disinfection occurred during the restart of the UV disinfection system.

May 28, 2021 - Due to an unexpected power outage, there was a non-disinfected discharge of 10,000 gallons from outfall 001.

April 20-21, 2020 - Due to an unexpected power outage there was a non-disinfected discharge of 800,000 gallons from outfall 001.

September 19, 2019 - Due to a programming issue with the chlorine pump used to disinfect there was a non-disinfected discharge of 18,750 gallons from outfall 001.

April 25, 2019 - Due to a power interruption the disinfection system failed resulting in 40,270 gallons of non-disinfected sewerage into the Squamscott River.

Notice of Combined Sewer Overflow (CSO) at Outfall #003 Located at Clemson Pond

Date	Total Gallons	Description
2023-12-12	14,072	CSO discharges from the Spring St and Water St CSO structures: Spring Street CSO of 968 gallons, Water Street CSO of 13,104 gallons occurred at approximately 10:50 pm and ended at 11:05 pm due to a power outage caused by a car crashing into a telephone pole. Equipment failed during the power surge and was reset by on call staff as soon as possible.
2019-05-22	164,850	The final connection of a temporary force main caused an anticipated CSO event.
2019-03-10	420,170	A sewer force main break caused two CSO discharges
2019-02-21	20,120	A sewer force main break caused two CSO discharges
2019-01-24	31,442	A wet weather CSO discharge from the Spring St CSO structure. The total measured precipitation was 1.29”.
2018-11-28	25,660	A CSO discharge from the Spring St structure
2018-11-27	1,635,450	Wet weather CSO discharges from the Spring St and Water St CSO structures: Spring Street CSO of 1,325,510 gallons, Water Street CSO of 309,940 gallons
2018-11-03	10,920	Wet weather CSO discharges from the Spring St and Water St CSO structures: Spring Street CSO of 9,250 gallons and Water St CSO of 1,670 gallons
2018-09-18	518,790	Two wet weather CSO discharges from the Spring St and Water St CSO structures: Spring Street CSO of 291,390 gallons, Water Street CSO of 227,400 gallons
2018-08-03	12,760	Two wet weather discharges from the Spring St CSO structure
2018-04-16	260,790	Wet weather CSO discharge from the Spring St CSO structure
2018-04-16	132,990	Two wet weather CSO discharges from the Water St CSO structure
2017-04-6 & 7	398,160	Wet weather CSO discharges
2016-10-21	18,191	Wet weather CSO discharge due to 3.07" of precipitation

Notice of Sanitary Sewer Overflow (SSO) Events

Date	Total Gallons	Description
2023-4-20	100	110 Front Street - Blockage in a sewer manhole
2022-7-17	100-150	Exeter Hospital, 5 Alumni Dr
2020-12-17	65	115 Court St
2020-02-28		Hilton Ave SSO
2019-11-26		45 Hilton Ave SSO
2019-11-23		Between 45-47 Hilton Ave SSO
2019-07-09	180	11 Newfields Rd, air release valve on the force main was hit during the installation causing a SSO
2019-03-9 & 10	700,000	A sewer force main break caused SSO
2019-02-21	26,750	A sewer force main break caused two SSO's
2018-11-27	2,200	SSO
2018-06-20	5	30 Charter St
2017-04-09	320,100	SSO reported into Exeter River
2016-03-09	102	SSO
2016-01-10	6,200	Wet weather SSO due to 1.87" of precipitation