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.


Sewer System Expansion Program
The WSA continues its aggressive sewer expansion program intended to mitigate on-lot sewage disposal systems as a source of pathogens to Greenwich Bay and Narragansett Bay.

Sewer expansion projects that are presently under construction are:

  • Old Buttonwoods
  • Warwick Cove IIB
  • Capron Farm

By the year 2013, the WSA plans to initiate construct the following sewer extensions. Sewering of these areas is contingent upon the availability of local and state funds.

  • Strawberry Road Phase II
  • Bayside Phases I, II, III and IV
  • Governor Francis Farm Phases II and III

The WSA also plans to initiate the design phase of several other projects that include:

  • Northwest Gorton Pond
  • Greenwood East
  • Sherwood Park
  • Sandy Lane/Cedar Swamp

The areas identified above have all been included in the City’s approved Facilities Plan. Information regarding their specific location and the number of residential properties to be served can be obtained from the WSA.

Total Maximum Daily Load Analysis for Greenwich Bay Waters
The RIDEM Office of Water Resources, in December 2005, completed a Total Maximum Daily Load (TMDL) plan for Greenwich Bay. The TMDL plan addresses fecal coliform impairments to Greenwich Bay, Brush Neck Cove, Buttonwoods Cove, Warwick Cove, Hardig Brook, Tuscatucket Brook, two additional Coves, and seven tributaries within the Greenwich Bay watershed, located in the City of Warwick and the Towns of East Greenwich and West Warwick, Rhode Island. These waters are listed on Rhode Island’s 2002 303(d) List of Impaired Waters as Group 1 waters. Two of the Greenwich Bay coves and the seven other tributaries included in this TMDL were found to violate standards during the course of the project and are addressed in the TMDL plan. These waters do not support their designated uses. Designated uses for these waters include primary and secondary contact recreation, fish and wildlife habitat, and for those waters classified as SA, shellfish harvesting.

The TMDL plan aims to restore Greenwich Bay waters by identifying necessary pollutant reductions, locating pollution sources, and outlining an implementation strategy to abate fecal coliform sources such that water quality standards can ultimately be attained during all weather conditions.

With a few exceptions, bacteria impairments in the Greenwich Bay watershed arise directly following wet weather events. In dry weather, all stations in Greenwich Bay and the coves meet the geometric mean criterion, while five of the stations exceed the 90th percentile criterion for the shellfish use. Following rain events, only one station in Greenwich Bay meets both parts of the Class SA water quality standard. The Greenwich Bay coves exhibit the highest bacteria concentrations, with Apponaug Cove and Brush Neck Cove requiring the largest percent reductions for the entire bay.

The Greenwich Bay tributaries reflect the same water quality trends as Greenwich Bay. Water quality is generally good in dry weather and exceeds standards in wet weather. Required percent reductions in the tributaries range from no reductions at some stations along the Maskerchugg River to a 100 percent reduction required from Southern Creek in Brush Neck Cove. The largest bacteria sources to Greenwich Bay are found in Apponaug Cove (Hardig Brook) and Brush Neck Cove.

Recommended implementation activities focus on storm water and wastewater management. Ongoing efforts to ensure adequate treatment of wastewater through the planned sewer extensions, and the proper operation and maintenance of septic systems should continue. Achieving water quality standards will also require that both the amount of storm water and the bacteria concentrations in that storm water reaching Greenwich Bay are reduced. To reduce runoff volumes and treat storm water, use of infiltration basins or similar structures is recommended. A targeted approach to construction of storm water retrofit best management practices (BMPs) at state and locally owned storm water outfalls is recommended. Priority areas for BMP construction within the City of Warwick are Apponaug Cove and Brush Neck Cove, for the Town of East Greenwich, Greenwich Cove, and for the Town of West Warwick, the Hardig Brook headwaters. This TMDL also recommends pollution prevention efforts to discourage residents from feeding birds, encourage residents to pick up after their pets, and ensure that boats comply with the No Discharge requirements of Rhode Island marine waters.

Rate Structure
There are two classes of users that contribute to City sewer system: Residential and Commercial/Industrial. Residential users are billed a Service Charge of $56.78 per unit and a Consumption Fee based on 85 percent of water usage at $23.89 per 1,000 cubic feet. Commercial/Industrial users are billed a Service Charge of $56.78 per unit and a Consumption Fee based on 100 percent of water usage at $31.69 per 1,000 cubic feet.

Where sewers are available, residences are charged an assessment of $82.00 per foot of frontage. For large lots (1 or more acres) the assessment is based on a complicated formula to account for development potential. The assessment is payable over 20 years and the assessment charge is applied whether or not the property is connected. As discussed above, 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.

The WWTF also accepts septage from licensed haulers. The fee for disposing of septage has been set at $47.00 per 1000 gallons. Septage is accepted only from Warwick residents, and each load is monitored for compliance with WSA standards to prevent any toxicity to the biological processes employed at the treatment facility. The WSA limits the volume of septage received on a given day to 25,000 gallons. Over 2.7 million gallons of septage was accepted and treated in 2005. With the implementation of mandatory sewer connection program, we would expect to see a gradual decline in the volume of septage being treated on a daily basis in Warwick.

Industrial Wastewater Pretreatment Program
The Warwick Sewer Authority (WSA) established an Industrial Pretreatment Program (IPP) back in the early 1980’s as required by the Federal Government through the provisions of the General Pretreatment Regulations (40 CFR Part 403). The mission of the IPP is to protect our sewer collection system, treatment facility, Pawtuxet River and Narragansett Bay by preventing the discharge of toxic pollutants and excessive conventional pollutants from the industrial/commercial user base. The permitting of industrial and commercial businesses is the most effective way of making companies aware of the surveillance conducted by the WSA. Maintaining a compliant user base is accomplished through the issuance of wastewater discharge permits for all Warwick based industrial and commercial facilities discharging wastewater, either directly or indirectly (via septage hauler), to the Warwick Sewer System. Ultimately, it is the IPP’s goal is to strive to eliminate the release of toxic and conventional pollutants into the collection system/environment through a cost effective and environmentally sound program. There currently are 676 permitted businesses in Warwick regulated by the IPP. These include 376 industrial/commercial users, 281 restaurants/food preparers and 19 septage haulers. Of the 376-industrial/commercial users, 14 are classified as Significant Industrial Users (SIU) based on the following criteria:


Any User subject to Categorical Pretreatment Standards under 40 CFR 403.6 and 40 CFR Chapter I, Subchapter N (2);

Any User discharging an average of 25,000 gallons per day or more of process wastewater to the Warwick Sewer Authority or contributing a process wastestream which makes up to five percent (5%) or more of the average dry weather hydraulic or organic capacity of the Treatment Facility;

Any user that has a reasonable potential, in the opinion of the Authority, to adversely affect the operation of the Treatment Facility and/or to violate any Pretreatment standard(s) or requirement(s).

A staff of two full-time persons and one half-time person manages the program. WSA personnel monitor the incoming wastestream (raw influent) to the WWTF on a 24-hour per day basis to ensure that elevated levels of pollutants, in excess of permitted levels, are not present. Should monitoring demonstrate elevated levels of pollutants, IPP personnel deploy 24-hour sampling devices in select manholes throughout the City in order to determine the origin of the elevated pollutants. Non-compliant discharges are traced back to the business in violation of their permit discharge limits and enforcement action ensues.

The total metals concentration has been reduced from approximately 1.85 mg/L (1986) to approximately 0.24 mg/L (2005), a testament to the effectiveness of the program and the application of local limits (LLMP). Wastewater discharge limits, as derived from ongoing local limits research, maintain headworks loadings that facilitate optimum treatment conditions within the plant. Optimum treatment conditions have indeed provided for an effluent compliant with RIPDES effluent limitations.

Where non-compliance has been detected within the industrial base, the ERP has provided for an essential fining mechanism, which has certainly acted as a deterrent to repeat violations. Over the past reporting period, the WSA has, in good faith, allowed for two of our SIU’s to defer payment of fines and instead use the fine monies to upgrade their systems. This has provided our SIUs with an incentive to maintain compliance.

Over the past 4-5 years, the Warwick Sewer Authority has worked closely with the RIDEM Pretreatment division in revisiting and updating our Sewer Use Ordinances (SUO), Rules and Regulations (specifically Regs. 9, 10, 40, 48, 54 and 55) to be consistent with EPA requirements. Back in October 2000, our IPP had its SUO/ERP modified to indicate a maximum fine penalty increase from $5,000/violation/day to $25,000/violation/day. Additionally, within that same 3-4 year time frame, improvements (approved by RIDEM) were made to the Spill Control Plan and Permit Templates. These improvements have allowed the IPP to assist its Commercial and Industrial user base in discharging compliant wastewaters, as well as, enforce rules where non-compliance has been encountered.