Municipal System Overview and Description

Approximately 70 percent of the developed parcels in the City of Warwick are currently sewered. Approximately 9,000 residential properties have elected not to connect to the sewer system at this time. In response to growing concerns about the environmental impact of on-site septic systems leaching pollutants into Greenwich Bay, the Warwick Sewer Authority has implemented a mandatory connection program that will require developed parcels with access to the collection system to tie-in within one year of notification.

There are approximately 250 miles of sanitary sewer in the City. Sewers range in size from 2-inch diameter low pressure force mains to 48-inch diameter gravity interceptors. Due to the diverse topography throughout the City, particularly the low lying coastal regions, the sanitary sewer system utilizes 45 sewage pump stations owned, operated and maintained by the Warwick Sewer Authority (WSA) to convey wastewater. In addition to these publicly owned stations, there are approximately 100 privately owned pump stations that discharge into the sanitary sewer system. Individual grinder pumps and low pressure force mains are also used in several sections of the City that could not be serviced with conventional gravity sewers.

The City’s Wastewater Treatment Facility (WWTF) is located at 125 Arthur W. Devine Boulevard, just west of Route I-95 between exits 13 and 14 in an industrial park. The WWTF is one of three municipal facilities (West Warwick and Cranston) that discharge treated effluent directly to the Pawtuxet River. Over the past several years each of these facilities has been upgraded to comply with stringent effluent limitations for nitrogen and phosphorus. As a result of these improvements, the water quality in the Pawtuxet River has improved substantially.

The City entered into a Consent Decree with the Rhode Island Department of Environmental Management (RIDEM) and the Environmental Protection Agency (EPA) to provide advanced wastewater treatment capable of removing nitrogen and phosphorus as well as conventional pollutants from the City’s waste stream. A $32 million dollar upgrade to the WWTF was completed in September, 2004 and the plant is now equipped with a biological nutrient removal process that can reduce concentrations of total nitrogen and total phosphorus to below 10 mg/l and 1 mg/l, respectively. The final disinfection process was also modified to eliminate chemical toxicity associated with chlorine residual in the plant effluent. Other upgrades that were constructed included:

  • A new Administration Building
  • Renovations to the Operations Building and Laboratory
  • A new PC-based operating and supervisory control system, along with a radio frequency telemetry system for the 45 remote pumping stations throughout the City.
  • Inlet and Preliminary Treatment Facilities
  • Primary Sedimentation and Sludge/Scum Pumping
  • Process Aeration and Automatic Control
  • Final Clarification and Sludge/Scum Pumping
  • Odor Control
  • Chemical Feed Systems
  • Sludge Thickening

The upgraded facility has a capacity to treat an average daily flow of 7.7 million gallons per day (MGD) and a peak hourly flow of 17.7 MGD. The average daily flow for 2005 was 5.0 MGD. Of this total, 30% is from commercial/industrial sources, 70% is from residential sources.

The growth of the sewer system has followed the recommendations of the Wastewater Facilities Plan completed by C.E. Maguire Inc. in 1979 and updated by BETA Group, Inc. in 1996. Since 1996, significant growth in the number of condominiums and hotels, as well as increased development relating to a new train station has resulted in the need to update the WSA’s Facilities Plan. BETA Group, Inc. has been retained by the WSA to perform a capacity analysis of the major pumping stations and collection system interceptors to determine if there are any issues with respect to their ability to safely convey present and projected wastewater flows.

The update to the Facilities Plan will also include an evaluation of the feasibility of providing sewer service to all sections of the City, including Warwick Neck, Cowesett, and Potowamut/Sandy Point. Sewers were not recommended for Cowesett and Warwick Neck in the 1996 Facilities Plan because predominant lot sizes and soil types were deemed favorable for on-lot sewage disposal systems. However, the continued presence of high pathogen levels in Greenwich Bay necessitates the reassessment of sewering these sections of the City. Potowamut is in a remote area of the City and is several miles from the nearest point in the existing wastewater collection system. Consideration is being given to researching alternative wastewater treatment systems for Potowamut and establishing a wastewater management district to regulate the use of on-lot disposal systems.

Many of the western sections of Warwick are connected to the Town of West Warwick’s regional wastewater treatment facility in accordance with agreements between the Town and the City, dating to 1980 and 1983.