WASTEWATER INFRASTRUCTUREDraft – April 2017

1. OVERVIEW

Wastewater, if not properly conveyed or treated, is a significant source of pollution to surface water and groundwater. Domestic sewage contains pathogens, nutrients, and emerging contaminants and may result in impacts to ecological resources and human health. During the textile and industrial era, raw sewage emptying directly into Narragansett Bay contributed to the collapse of the once-thriving oyster industry. In response, from the 1880s to the early 1900s the population served by sewer systems increased from 5 percent to 50 percent of the total population in the watershed.

Currently, there are 37 wastewater treatment facilities in the Narragansett Bay watershed discharging approximately 203 million gallons of treated water per day. These plants serve approximately 62 percent of the population in the watershed. The remaining 38 percent of the population is served by individual systems such as septic systems (both conventional and advanced) or even antiquated cesspools. An analysis by the Narragansett Bay Estuary Program of We analyzed septic system density within the watershed and identified numerous high-density areas that may be contributing to nutrient and pathogen water quality concerns. It is estimated that 8 percent of the total population in the watershed dwells in high-density developed areas that are served by on-site wastewater treatment systems.

2. INTRODUCTION

The population in the Narragansett Bay watershed produces over 200 million gallons of treated wastewater daily. If this wastewater is not properly conveyed or treated, it can have significant negative impacts on ecological resources and human health. Bacterial and viral pathogens found in raw sewage can render waterways and beaches unsafe for recreation and can result in areas being closed to shellfishing. Excess nutrients can cause eutrophication, a phenomenon in which algal blooms choke out light and oxygen from aquatic systems, harming aquatic plants, fish, and wildlife. Finally, emerging contaminants such as pharmaceuticals and personal care products can pose acute and long-term risks to human health and to aquatic organisms, and in many cases these risks are not yet well understood.

Several types of wastewater infrastructure serve the population in the Narragansett Bay watershed, including sewered areas serviced by wastewater treatment facilities (WWTFs) as well as on-site wastewater treatment systems (OWTS), which include conventional septic systems and advanced septic systems, or small package plants. This chapter presents a

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watershed-scale analysis of wastewater infrastructure in the Narragansett Bay watershed to evaluate the coverage and influence of wastewater infrastructure in relation to human population and the downstream effects on environmental condition. Because population growth drives demand for wastewater infrastructure, the Narragansett Bay Estuary Program developed a metric that quantifies the number of buildings served by WWTFs and OWTS. The analysis calculated sewer service areas and buildings outside those areas, which were assumed to be served by various forms of OWTS. Using building density as a proxy, an estimate of OWTS density can help identify areas of higher concern. High densities of septic systems have been linked to fecal pollution in adjacent waters in developed watersheds (Sowah et al. 2017).

Historically, population growth and industrialization led to significant negative impacts on the Bay through wastewater inputs, including the collapse of the once-thriving oyster industry (Schumann 2015). Vadeboncoueur et al. (2010) documented a 400 percent increase in population and urban development in the coastal upper Bay from 1850 to 1900, and a doubling in the upper and lower Bay from 1900 to 1950. Concurrently, they reported that the sewered population in the upper Bay increased from 14 percent in 1880, to 50 percent in 1900, and finally to 83 percent in 1950. In the lower Bay, which includes the islands and coastal areas bordering the Sakonnet River, they found that 4 percent of the population was sewered in 1890 compared to 31 percent by 1950.

Despite improvements in wastewater treatment infrastructure, the twentieth century brought the worst pollution from raw or poorly treated sewage in Narragansett Bay’s history, as population growth continued to exceed the capacity of wastewater treatment plants. Schuman (2015) reported that in the early part of the century anecdotal evidence suggested that 260 pipes located throughout the Bay transported raw sewage directly to receiving waters. Mid-century, Shea (1946) observed that pollution in those areas was due to partially treated sewage and raw industrial waste emptying directly into the waterways. Most notably, the WWTF at Field’s Point was overwhelmed in 1946 and poorly treated sewage flowed directly into the Bay, resulting in extremely high fecal coliform bacteria concentrations (Shea 1946). By 1970, Field’s Point poured 65 million gallons of untreated or inadequately treated sewage into the Bay daily, contributing to the collapse of shellfish beds (Schumann 2015).

Improvements in the capacity and technology of WWTFs have drastically changed the amount of pollution in Narragansett Bay. Contemporary WWTFs reduce pathogens and nutrients in wastewater through primary, secondary, and tertiary treatment, followed by disinfection using chlorine or ultraviolet light. The Narragansett Bay Commission (NBC) ensures that effluent from the Field’s Point and Bucklin Point WWTFs contains

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acceptably low levels of fecal coliform bacteria and nutrients (NBC 2016). Nevertheless, severe rain events can exceed the capacity of the system, which results in combined sewer overflows (CSOs) carrying untreated effluent and stormwater directly to the rivers and the upper Bay. The resulting nutrient, pathogen, and contaminant loadings continue to be serve as stressors for to ecological and public health (see “Nutrient Loading” and “Marine Beaches” chapters). In Providence and Fall River, significant engineering efforts are underway to dramatically abate CSO discharges to the Bay. Moreover, in response to a 2004 RIDEM directive, WWTFs discharging to Narragansett Bay have reduced nitrogen loading by more than 50 percent of l995/1996 loadings.

Outside of sewered areas, homeowners are required to treat sewage either on their property or via locally sited package treatment plants. Unfortunately, pollution from these systems remains an issue. Domestic wastewater from septic systems has been linked to nitrogen loading in coastal bays via transport through groundwater (e.g., Valiela et al. 1992). Outdated and poorly designed septic systems are known to deliver fecal pathogens to groundwater and surface waters, and areas of high density septic systems have been shown to contribute more to pathogen loading in waterways compared to low density areas (Sowah et al. 2017).

While conventional septic systems deliver roughly 24 pounds (11 kilograms) of nitrogen per year to the groundwater, advanced septic systems reduce nitrogen contributions by 50 to 75 percent through nitrification and denitrification processes that remove nitrogen from wastewater before it enters a leach field (Lancellotti 2016). Advanced septic systems are required by Rhode Island in areas of the Narragansett Bay watershed that are impacted by nitrogen loading (RIDEM 2009). Nevertheless, in many areas across the watershed, failing septic systems and cesspools remain an issue. with mMany are located on shorelines of Narragansett Bay in unsewered residential areas (Nowicki and Gold 2008). It is likely that nutrient and pathogen loading from these outdated systems contributes to ecological stressors for a variety of ecosystem services. Understanding the effects of OWTS is significantly more complex than quantifying the impacts from point sources, as the geomorphological characteristics and land use in the watershed can alter the groundwater flow and the ultimate delivery of nitrogen to Bay waters (Nowicki and Gold 2008). Unfortunately, the same needs identified by Nowicki and Gold (2008) to quantify nutrient loadings from groundwater inputs in Narragansett Bay remain today. The lack of direct studies related to the inputs of groundwater to the Bay and freshwater systems is probably the most critical data gap (Nowicki and Gold 2008). One of the most studied areas in the Bay with respect to groundwater inputs is Greenwich Bay, where Urish and Gomez (2004) estimated that 60 to 70 percent of the freshwater inputs from the land into this watershed were derived from groundwater recharge, and most of the

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nutrients, approximately 65 to 75 percent of loadings entering the Bay, were from OWTS.

3. METHODS

The Narragansett Bay Estuary Program analyzed wastewater infrastructure throughout the Narragansett Bay watershed to determine the areas served by sewer systems and population densities of areas served by onsite wastewater treatment systems. In addition, the population served by those systems was estimated for the watershed, as well as in the 42 watershed planning areas (WPAs) in the watershed. In collaboration with representatives from the Massachusetts Department of Environmental Protection (MADEP) and the Rhode Island Department of Environmental Management (RIDEM), the Estuary Program gathered and reconciled data at the state level to analyze the extent of wastewater infrastructure (Table 1). The following two categories of wastewater infrastructure were developed, and for each the Estuary Program calculated the total area within the watershed, including acreage and percent, and the population served by these categories, including total population and percent:

Areas (in acres) served by wastewater treatment facilities (WWTF) in the watershed delineated as sewer system areas.

Areas served by onsite wastewater treatment systems (OWTS), including conventional septic systems, advanced septic systems, cesspools, and treatment plants discharging to groundwater. A density analysis was completed to determine areas of OWTS where there was a high density of buildings not served by sewer systems.

Table 1. State data sources for wastewater infrastructure in the Narragansett Bay watershed. Type of wastewater treatment information

Data availability and information provided by state agencies

Massachusetts Rhode Island

Location of sewered areas served by wastewater treatment plant facilities (WWTF)

MADEP estimated municipal sewered areas with assumptions based on estimated service areas - December 2016.

RIDEM sewer service areas - September 2015.

Location of individual onsite wastewater treatment systems (OWTS) as conventional

No statewide coverage. Data on OWTS treating less than 10,000 gallons per day maintained by municipal boards of health and outside the

RIDEM - October 2015. Locational information included plat and lot numbers and limited street addresses. Emergency 911 data used to match 46

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septic systems scope of this report. percent of the sites. Data included OWTS that were approved, installed, and under construction; however, some properties may have been connected to the sewer system.

OWTS as advanced septic systems

Data not readily available.

RIDEM – 64 percent of all advanced septic systems were mapped.

Cesspools Data not readily available.

Data not readily available but estimated.

Groundwater discharge over 10,000 gallons per day

MADEP digitized parcels served by permitted treatment plants.

RIDEM data on total flow used as proxy; however, areas of service were not available.

The results generally reflect existing areas served by sewer systems and OWTS, with an acknowledgement that there is a range of error in this analysis given the numerous assumptions that were made (Table 2).

Table 2. Data sources, processing methods, and assumptions for wastewater infrastructure in the Narragansett Bay watershed.

Type of Information

Data Processing Assumptions

Sewer Service areas

Integrated data from both states

Assumed all buildings within the sewered areas are connected to the sewer lines using a buffer area around existing or planned sewer lines. Assumed that state data represents current information on extent of sewered areas.

Wastewater treatment facilities (WWTF) discharging to surface waters

Merged MADEP and RIDEM sewer service areas. Assumed service for entire municipality for MADEP where greater than 80 percent sewered but with unknown extent.

Groundwater discharge over 10,000 gallons per day

Where information was available, included parcel areas as part of the sewered areas.

Location of buildings served by OWTS (septic systems or cesspools)

RIDEM - Building structure point locations outside of sewered areas used to estimate unsewered buildings. MADEP – eliminated

Assumed each point corresponds to a building that generates domestic sewage. Assumed each point discharges to individual or shared

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polygons of outbuildings (garage or shed) less than 50 square meters (538 square feet).

OWTS and buildings have not been connected to the sewer system.

Density areas of estimated buildings served by OWTS (septic systems or cesspools)

Point data for unsewered buildings were used to calculate density of points (number of buildings within 1 hectare [2.5 acres]) within a defined area (250 meters; 820 feet) or neighborhood using the Kernel Density Analysis tool.

Assumed that 250-meter (820-foot) search radius corresponds to average distance between houses in high-density residential areas. Assumed that high-density OWTS area is where unsewered building densities are 90 percent higher than densities in the rest of the watershed.

Table 2. ContinuedExclusion Removed lakes and ponds

from the above data. Assumed no buildings within ponds or lakes.

Population (2010) served by WWTFs

Population distribution data (dasymetric analysis in “Population” chapter) were intersected with sewered areas to calculate population and percent served by WWTFs.

Assumed distribution of population within the sewered areas intersects with areas where people reside rather than work, recreate, worship, etc.

Estimates of population served by each WWTF were available for 90 percent of all WWTFs discharging to surface waters.

Estimated sewered population is within 10 percent of the available estimates by WWTF.

Population (2010) served by OWTS (septic systems or cesspools)

Same as above, except the distribution of the population was intersected with density areas of OWTS. Total population residing in high-density areas or high-density OWTS were calculated accordingly.

Assumed distribution of population within the high-density OWTS areas intersects with areas where people reside. Assumed that buildings are highly populated within high-density OWTS.

Sewered and unsewered areas, high density

Intersected sewered areas, OWTS density analysis, and population

Assumed population distribution represents total sewered population

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OWTS, and population by watershed planning area (WPA)

distribution with total area (acres) of WPA. Total population and percent were computed for each WPA.

within a WPA, even when WWTF discharge or outfalls are outside the watershed or basin. Assumed that WPA with a large percent of high-density OWTS pose risk to surface and groundwater based on literature.

Estimated daily average flow from WWTFs in millions of gallons per day (MGD)

Total average daily flow, from 2013 to 2015, for each WWTF that discharge directly to the Bay or rivers in the watershed. WWTFs discharging into Rhode Island Sound were not included.

Assumed WWTF average daily flow is representative of both wet and dry years between 2013 and 2015. Available data used from the monitoring periods; not all of WWTFs had data for all years or seasonal flow.

4. STATUS AND TRENDS

In the Narragansett Bay watershed, sewers serve 62 percent of the population, and the total sewered area constitutes 24 percent of the total watershed area (Figure 1; Table 3). The sewered portion of the Narragansett Bay watershed is served by a total of 37 wastewater treatment facilities (WWTFs) (Figure 1). Onsite wastewater treatment systems (OWTS) serve 38 percent of the watershed’s population, and the area served by OWTS encompasses 44 percent of the total watershed area.

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Figure 1. Extent of service areas and population served by the major wastewater treatment facilities (WWTFs) within Narragansett Bay’s watershed planning areas (WPA).

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Table 3. Areas and population served by sewers and onsite wastewater treatment systems in the Narragansett Bay watershed.

Type of Wastewater Infrastructure

Service Areas Population Population

DensityAcres

Percent of

Watershed

Total Percent

Areas served by sewer service and wastewater treatment facilities(WWTF)

262,566 24 1,213,

045 62 4.62

Areas served by Onsite Wastewater Treatment System (OWTS)

483,888 44 731,18

5 38 1.51

Of the 42 watershed planning areas (WPAs) in the Narragansett Bay watershed, 10 have 75 percent or more of the population served by sewer systems (Figure 1; Table 4). In the Providence-Seekonk Rivers WPA and the Moshassuck River WPA, over 95 percent of the population within each WPA is connected to sewer systems (Table 4).

Table 4. Watershed planning areas (WPAs) with the largest percentages of sewered population (greater than or equal to 75 percent of the population within WPA) in the Narragansett Bay watershed.

Watershed Planning AreaPercent of Population Sewered(1)

Total Sewered

Population (2010)(2)

Percent of WPA that

is Sewered(3)

Providence - Seekonk Rivers 99 126,335 98Moshassuck River 96 80,397 81Tatnuck Brook-Blackstone River 96 133,874 71Barrington - Palmer - Warren Rivers 88 17,864 12Greenwich Bay 84 38,254 77Buckeye Brook 84 14,289 79Stafford Pond 83 41,311 27Woonasquatucket River 70 98,613 33Matfield River 76 82,487 47Mount Hope Bay 75 27,314 53

(1)Percent of the total population in the WPA.(2)Calculated using population from dasymetric analysis.(3)Percent of the WPA area not including lakes or ponds.

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The 37 WWTFs discharge an estimated 203 million gallons per day of treated sewage into the Bay and rivers of the watershed (Table 5). More than half of the daily discharge (112 million gallons per day) occurs in the Coastal Narragansett Bay Basin, followed by discharges into the Blackstone River Basin and the Taunton River Basin (Table 5).

Table 5. Average daily flow (in millions of gallons per day) discharged by WWTFs into Narragansett Bay and its watershed, and estimated population served. Sorted by receiving waterbodies from highest to lowest daily flow.Receiving Waterbodies Basins

Average Daily Flow (MGD)(1)

Population Served(2)

Narragansett Bay Coastal Narragansett Bay Basin

103 609,364

Blackstone River Blackstone River Basin 40 294,935 Taunton River Taunton River Basin 30 206,559 Pawtuxet River Pawtuxet River Basin 21 165,000 Ten Mile River Coastal Narragansett

Bay Basin7 54,514

Woonasquatucket River

Coastal Narragansett Bay Basin

2 14,000

Total for Narragansett Bay and its Watershed

203 1,344,372(3)

(1) Based on data from 37 WWTFs between 2013 and 2015. (2) Estimated by 34 WWTF permits (2010); 3 WWTFs did not have population estimates. (3) Margin of error between the population using dasymetric analysis and the population as estimated by the WWTF permits is 10 percent.

The average daily flow discharged directly to Narragansett Bay was far higher than discharges to any other receiving waterbody (Table 5). In total, the 12 WWTFs discharging directly to the Bay had approximately the same average daily flow (103 MGD) as all 25 riverine WWTFs combined (100 MGD) (Table 6). There were twice as many riverine WWTFs than Bay WWTFs, and the riverine WWTFs served 17 percent more residents.

Table 6. Average daily flow (in millions of gallons per day) discharged by Bay and riverine WWTFs.

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Type of WWTF (Number of facilities)Average

Daily Flow (MGD)

Population Served

Narragansett Bay WWTFs (12) 103 609,364

Riverine WWTFs (25) 100 735,008

Total for Narragansett Bay and its Watershed 203 1,344,372

The Field’s Point WWTF, discharging into the Providence River, and the Upper Blackstone WWTF, adjacent to Worcester and discharging into the Blackstone River, had the largest average flow discharge among all 37 WWTFs—approximately 41 and 29 million gallons per day respectively (Figure 1; Table 7). This is not surprising since combined they serve 35 percent of the total sewered population in the watershed (Figure 1; Table 7).

Table 7. Average daily flow and population served by WWTFs discharging over 10 million of gallons per day to Narragansett Bay and its watershed. Wastewater Treatment Facility

Receiving Waterbody

Average Daily Flow (MGD)

Population Served(1)

Field’s Point Narragansett Bay 41 226,000

Upper Blackstone Blackstone River 29 207,535

Fall River Narragansett Bay 21 92,164

Bucklin Point Narragansett Bay 19 120,000

Brockton Taunton River 15 126,256Cranston Pawtuxet River 12 73,200

(1) Based on estimates by individual WWTF.

The historical trend of developing sewer systems started in the late 1800s in urbanizing areas. At the turn of the nineteenth century, the sewered

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population increased by thirteen-fold for the entire Narraganset Bay watershed, including almost seven-fold in the upper Bay (Table 8; Vadeboncoeur et al. 2010). During the twentieth century, the sewered population was maintained between 55 and 65 percent of the watershed’s total population (Figure 2; Vadeboncoeur et al. 2010).

Table 8. Rates of sewered population growth in Narragansett Bay watersheds (Vadeboncoeur et al. 2010).

Watersheds Rate of Sewered Population GrowthBy 1900 1900–1950 1950–2000

Blackstone R. above Millville(1) 2.5 1.6 1.0Blackstone R. Millville to Manville(2) 0 2.3 1.2

Pawtuxet R. above Pettaconsett(3) 0 0 5.0

Taunton R. above Bridgewater(2) 0 1.5 2.0

Taunton R. Bridgewater to Taunton(2) 0 2.2 1.8

Taunton R. below Taunton(3) 0 0 9.2Small watersheds(1) 4.5 1.5 1.6Upper Bay(4) 6.6 1.6 1.1Lower Bay(1) 2.3 6.2 1.3Total Narragansett Bay Watershed 13.3 1.7 1.3

(1) Started in 1890s.(2) Started in 1900s.(3) Started in 1940s. (4) Started in 1880s.

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Figure 2. Total population and percent of population in the Narragansett Bay watershed served by sewers from 1880 to 2010. Sewered population data from 1880 to 2000 from Vadeboncoeur et al. (2010); 2010 data from Narragansett Bay Estuary Program’s dasymetric analysis (see “Population” chapter).

In the Narragansett Bay watershed, an estimated population of 731,185 is served by onsite wastewater treatment systems (OWTS), using a variety of systems including conventional or advanced septic systems, cesspools, and package treatment plants that discharge to groundwater (Table 3; Figure 3). We classified OWTS areas from low to high density. High-density OWTS areas were defined as areas where building densities served by OWTS were 90 percent higher than densities in the rest of the watershed (Table 9; Figure 3). We estimated that 3 percent of the entire watershed is high-density OWTS area and that 146,363 residents, or 8 percent of the watershed’s population, are served in these high-density OWTS areas (Table 9).

Table 9. Areas and population served by high-density onsite wastewater treatment systems (OWTS) in the Narragansett Bay watershed.

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Type of Wastewater Infrastructure

Service Areas Population Population

DensityAcres

Percent of

Watershed

Total Percent

Areas served by high-density OWTS

31,762 3 146,36

3 8 4.61

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Figure 3. Extent of low to high density areas of buildings served by OWTS in Narragansett Bay’s Watershed Planning Areas.

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In four of the watershed planning areas (WPAs)—Buckeye Brook, Aquidneck Island, Sakonnet East and Prudence Island—over 50 percent of the population is served by high-density OWTS (Table 10). Three of these WPAs have a population density between 4.3 and 6.4 people per acre, and the other (Prudence Island) has 1 person per acre, the lowest population density among all WPAs.

Table 10. Watershed planning areas (WPAs) in the Narragansett Bay watershed with the highest percentages of their population served by high-density OWTS. Includes only WPAs with greater than 20 percent of population served by high-density OWTS.

Watershed Planning Areas (WPAs)

Population served by OWTS(1)

Total within

the WPA(2)

Within High-Density OWTS Areas(3)

TotalPercent

of All OWTS(4)

Population Density(5)

(People per acre)

Buckeye Brook 2,780 2,063 74 6.4 Aquidneck Island 22,216 12,601 57 4.3 Sakonnet – East 11,952 6,356 53 5.1 Prudence Island 216 112 52 1.0 West Bay 12,979 5,544 43 4.2 Pawtuxet River 65,441 26,495 40 5.1 Jamestown 3,464 1,357 39 3.3 Bristol - Kickemuit River 20,034 7,082 35 5.2 Hunt River 16,280 5,125 31 4.8 Stafford Pond 8,126 2,351 29 3.5 Matfield River 26,380 6,845 26 4.6 Greenwich Bay 7,236 1,799 25 4.6 Annaquatucket River 4,460 1,083 24 3.6 Barrington - Palmer - Warren Rivers 21,032 4,538 22 4.5

(1) Calculated population distribution using dasymetric analysis within OWTS areas.(2) Population within OWTS areas.(3) Population within high-density OWTS areas.(4) Formula: (Population within high-density OWTS areas)/(Total population within OWTS areas).(5) Formula: (Population within high-density OWTS areas)/(Acres of high-density OWTS areas).

There are 10 WPAs with 5 percent or more of high-density OWTS areas relative to the total WPA area (Table 11). On Aquidneck Island, for example, there are 2,949 acres of the WPA with high-density OWTS, representing 12 percent of the total planning area. Population density ranges from 3.3 to 6.4 people per acre of high-density OWTS area. Many high-density OWTS areas

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are located along the coastal areas of Narragansett Bay, including the Sakonnet River, Mount Hope Bay, and the East Passage (Figure 3).

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Table 11. Watershed planning areas (WPAs) with the largest percent area of high-density OWTS (>5 percent of the WPA area) in the Narragansett Bay watershed, and population served.

Watershed Planning Areas

High-Density OWTS Areas

Population within High-Density OWTS Areas

Acres(1) Percent(2)

Percent Population

of Total WPA (3)

Population Density(4)

Aquidneck Island 2,949 12 22 4.3 West Bay 1,324 9 30 4.2 Buckeye Brook 324 7 12 6.4 Sakonnet – East 1,252 7 16 5.1 Jamestown 415 7 25 3.3 Hunt River 1,071 7 31 4.8 Annaquatucket River 304 6 24 3.6 Pawtuxet River 5,207 6 14 5.1 Matfield River 1,498 6 6 4.6 Bristol-Kickemuit River 1,360 5 16 5.2

(1) Total acreage of high-density OWTS areas within WPA.(2) Percent of WPA acreage that is high-density OWTS areas.(3) Formula: (Total population within high-density OWTS areas)/(Total population of WPA).(4) Formula: (Total population within high-density OWTS areas)/(Acres of high-density areas per WPA).

5. DISCUSSION

The total population in the Narragansett Bay watershed has increased 85 percent since 1850 and 25 percent since 1950, driving urbanization and generating household and industrial sewage. The majority of the people residing in the watershed rely have been relying upon wastewater treatment systems with more than 50 percent of the population served by sewer systems since 1910. Today, 62 percent of the nearly 1,950,000 people residing in the watershed are served by sewer systems. The remaining population is served by various types of onsite wastewater treatment systems (OWTS), including septic systems. Sewered areas encompass approximately 24 percent of the watershed area, and 44 percent is served by OWTS. The remaining 30 percent is land area without development. Wastewater treatment facilities serve almost double the population that is served by OWTS.

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Wastewater treatment facilities were once the major sources of pollution in the Bay (Shea 1946). Over the last several decades, they have been upgraded to reduce pollutant loadings (see “Nutrient Loading” chapter). In terms of ecological and public health benefits, shellfish acreage in the Upper Bay and Mount Hope Bay showed an increase of conditionally open areas between 2010 and 2015 due in part to combined sewer overflow abatement projects (see “Shellfishing Areas” chapter). However, sea level rise due to climate change is a threat to operations at WWTFs. A recent RIDEM study examined 7 WWTFs in Rhode Island, 6 of them coastal, that will be predominantly inundated using 1 to 5 feet of sea level rise scenarios (Woodard and Curran 2017; see “Sea Level” chapter).

It is difficult to quantify the impacts of OWTS as they range from advanced nitrogen removing septic systems to cesspools that provide limited treatment. The challenge lies in the limited information on the location and type of OWTS in Massachusetts and Rhode Island. Nevertheless, the preliminary results in this report are helpful at the watershed scale, and additional planning efforts in watershed planning areas could provide a more comprehensive understanding of the total flow discharged through OWTS. This report includes the identification of high-density development served by OWTS—areas that can be useful to target for enhanced management and research. Using unsewered buildings as a proxy for septic system density, and population density as proxy for sewage generation, the watershed planning areas with the greatest population density and high-density OWTS acres were identified. Areas of high-density of septic systems are correlated with increased pathogen loadings in waterbodies, more so than low-density areas (Sowah et al. 2017).

Advanced septic systems, those that efficiently remove nitrogen, have been required in Rhode Island for sensitive areas of the state. In the Narragansett Bay watershed, nearly 1,500 advanced systems have been constructed, over 250 systems have been approved but not yet constructed, and over 250 systems were under construction (as of November 2015). The advanced systems that have been installed are clustered primarily in coastal areas in the towns of Portsmouth, Jamestown, Tiverton and North Kingstown, mainly within high-density OWTS areas. Researchers at the University of Rhode Island recently examined the performance of advanced nitrogen-removing OWTS in Rhode Island and found that these systems are capable of lowering total nitrogen in the effluent to meet regulatory standards (Amador et al. 2017).

6. DATA GAPS AND RESEARCH NEEDS

Currently, there is a lack of research that describes groundwater flow regimes in the Narragansett Bay watershed, and models are needed to estimate or predict groundwater direction or input into the Bay or

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freshwater bodies (see “Emerging Contaminants” chapter). Understanding groundwater flow paths and magnitude will be useful in identifying high-density septic system areas that may result in significant nutrient and pathogen loadings to the Bay and watershed. A study similar to Sowah et al. (2017) should be replicated in the Narragansett Bay watershed to develop more robust mapping and information related to high-density OWTS and the effects on water quality. An analysis of OWTS total flow (gallons per day), type of system (conventional or advanced septic system, or cesspool), condition of the system (failing, properly operating), soil type where the systems are sited, groundwater inputs (depth to groundwater, flow direction) and proximity to resource concern areas (to streams, tidal creeks, coastal areas, water wells) would be important information. Soil types are important contributors to effective septic systems, and the Estuary Program is exploring research with soil scientists at USDA’s Natural Resources Conservation Service. Lastly, and critically important, there is a need to identify OWTS that will be impacted due to sea level rise, similar to the WWFT evaluation completed by RIDEM.

7. ACKNOWLEDGEMENTS

This chapter was written by Eivy Monroy (Watershed and GIS Specialist with the Narragansett Bay Estuary Program), Jessica Cressman (University of Rhode Island), and Juliet Swigor (Massachusetts Department of Environmental Protection). Assistance with data analysis and the substance of the chapter was provided by Anne Kuhn (U.S. Environmental Protection Agency, Office of Research and Development, Atlantic Ecology Division), and Michael Charpentier (GIS Analyst with SRA International, Inc., A CSRA Company), and Julia Twichell (Narragansett Bay Estuary Program). In addition, Peter August (University of Rhode Island) and staff from the Rhode Island Department of Environmental Management—Brian Moore, Jonathan Zwarg and Jennifer Rayan—provided data and valuable insight.

8. REFERENCES

Amador, J.A., G. Loomis, B.V. Lancellotti, K. Hoyt, E. Avizinis, and S. Wigginton. 2017. Reducing Nitrogen Inputs to Narragansett Bay: Optimizing the Performance of Existing Onsite Wastewater Treatment Technologies. Department of Natural Resources Science and New England Onsite Wastewater Training Program, Coastal Institute, University of Rhode Island. 82 pp. Available at: http://nbep.org/publications/NBEP-17-178.pdf

Lancellotti, B.V. 2016. Performance Evaluation of Advanced Nitrogen Removal Onsite Wastewater Treatment Systems. Open Access Master's Thesis. Paper 941. http://digitalcommons.uri.edu/theses/941

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Narragansett Bay Commission (NBC). 2016. Narragansett Bay Commission 2015 Data Report. Prepared by the Staff of the Environmental Monitoring and Data Analysis Section. Available at: https://www.narrabay.com/en/ProgramsAndProjects/Environmental%20Monitoring%20and%20Data%20Analysis%20Program/NBC%202015%20Data%20Report.aspx

Nowicki, B.L., and A.J. Gold. 2008. Groundwater nitrogen transport and input along the Narragansett Bay coastal margin. In: Science for Ecosystem-based Management: Narragansett Bay in the 21st Century (A. Desbonnet and B.A. Costa-Pierce, Eds.). Springer: New York.

Rhode Island Department of Environmental Management (RIDEM). 2009. Rules Establishing Minimum Standards Relating to Location, Design, Construction and Maintenance of Onsite Wastewater Treatment Systems. Available at: http://www.dem.ri.gov/pubs/regs/regs/water/owts09.pdf

Sowah, R.A., M.Y. Habteselassie, D.E. Radcliffe, E. Bauske, and M. Risse. 2017. Isolating the impact of septic systems on fecal pollution in streams of suburban watersheds in Georgia, United States. Water Research 108:330–338.

Schumann, S. 2015. Rhode Island’s Shellfish Heritage: An Ecological History. Rhode Island Sea Grant. Available at: http://shellfishheritage.seagrant.gso.uri.edu/

Shea, W.J. 1946. Report to his excellency, John O. Pastore, governor of Rhode Island: on pollution of the waters of the state. Rhode Island Department of Health, Division of Sanitary Engineering.

Urish, D.W., and A.L. Gomez. 2004. Groundwater discharge to Greenwich Bay. Paper No. 3. Restoring Water Quality in Greenwich Bay: A Whitepaper Series. Narragansett RI: Rhode Island Sea Grant. 9 pp.

Vadeboncoeur, M.A., S.P. Hamburg, and D. Pryor. 2010. Modeled nitrogen loading to Narragansett Bay: 1850 to 2015. Estuaries and Coasts 33(5):1113–1127.

Valiela, I., K. Foreman, M. LaMontagne, D. Hersh, J. Costa, P. Peckol, B. DeMeo-Andreson, C. D’Avanzo, M. Babione, C.H. Sham, and J. Brawley. 1992. Couplings of watersheds and coastal waters: sources and consequences of nutrient enrichment in Waquoit Bay, Massachusetts. Estuaries 15(4):443–457.

Woodard and Curran. 2017. Implications of Climate Change for RI Wastewater Collection & Treatment Infrastructure. Rhode Island

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Department of Environmental Management. 246 pp. Available at: http://www.dem.ri.gov/programs/benviron/water/pdfs/wwtfclimstudy.pdf

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