Boston Harbor Wastewater Conveyance System Executive Summary Draft Supplemental Environmental Impact Statement United States Environmental Protection Agency Region I J.F.K. Federal Building Boston, Massachusetts 02203 1988 ------- Boston Harbor Wastewater Conveyance System Prepared by: Uciited Stat Environmental Protection Agency Region I J.F.K. Federal Building Boston, M t chusetts 02203 88 Technical Assistance by: Metcalf & Eddy 10 Ia,va,o MU Souare WakaIPJŘ Massacri n ,4 IC L R. DEL ND Date Regional Administrator, U.S. EPA, Region I This Draft Supplemental Environmental Impact Statement (SEIS) - has been prepared by the U.S. Environmental Protection Agency (EPA) with assistance form the U.S. Army Corps of Engineers. This Draft SEIS identifies and evaluates the environmental impacts of the wastewater conveyance system for Greater Boston’s wastewater treatment facility in compliance with Federal and State water pollution control laws. ------- DPAF” STPPLF.. ’r!’A E VI N]’TN”AL IMPACT STATE’ ENT P POS ACTION: SITI AND EVALUATION OF CONSTRUCTION F T H S FOR ?ThIST AA1’ER CONVEYANCE SYST 4 FOR SE NDAPY ¶‘REATh ’rr PLA 7r, BOS’! HARBOR LOCATION: BC TON, MASSA USt iS DATE: APRIL 1988 &Th MARY OF ACTION: Draft SEIS considers the enviror ental accepta- bility of alternative locations for the wastewater conveyance and outfall syste s of the ne waste- water trea ent Yacilities for Boston Harbor. The Draft SFIS rec mends deep rock tunnels for the inter—island and outfall conduits and a diffuser located at least seven miles east of Deer Island. \7OLtJ? : I. SUPPLEf . N ’rAL E?ivIw) !N’rAL IMPACT STAT EN” II. APPEUDICES LEAD AG CY: U. S. VI ?rAL P Yrf ’TION A’ ENCY, P!X IO ’ I JFK Federal Ruilding, Boston, Massachusetts 02203 COOP ATING A(’,EV : Ti • S • A f CORPS OF ENGINEE TF ICAL CONSULTA ”: ! TI’CALF & EDDY, INC. Wakefield, Massachusetts FOR FtY fl R P ’TORMA”IO”: Mr. David ‘lUney Water Management Division U.S. EPA, Region I JFK Federal Building oston, MA 02203 617—565—4420- FINAL nA ’E BY W9ICH c2 N’rS PUST BE R IVED: May 16, 1988 ------- Boston Harbor Wastewater Conveyance System Draft Supplemental En ironnienta1 Impact Statement EXECUTIVE SW4XARY INTRODUCTION Boston Harbor is presently being degraded by wastewater from 43 cities and towns served by the Massachusetts Water Resources Authority (MWRA) sewerage system. During an average day of operation, MWRA’s two existing wastewater treatment plants discharge 450 million gallons of inadequately treated wastewater and 70 dry tons of digested sewage sludge into the harbor. To remedy this problem, a secondary wastewater treatment facility is being- constructed on Deer Island. Two essential components of this wastewater treatment facility are a conduit to connect the southern portion of the MWRA sewerage system to the new treatment plant and an effluent outfall system to convey treated wastewater to an ocean discharge location. This Draft Supplemental Environmental Impact Statement (SEIS) describes the effects of the construction and operation of the conduit and outfall. This Draft SEIS builds upon earlier documents which evaluated the siting of the wastewater treatment plant on Deer Island, particularly the Final Environmental Impact Statement on the Siting of Wastewater Treatment Facilities on Boston Harbor prepared by EPA in 1985. Technical information and data from MWRA’s Secondary Treatment Facilities Plan, which describes and evaluates the design and construction of the inter-island conduit and effluent outfall system along with other facets of the proposed treatment facility, were used in developing this Draft SEIS. The preparation of this Draft SEIS and the MWRA Secondary Treatment Facilities Plan involved a cooperative effort between EPA and MWRA, including the sharing of data. Both documents use data gathered by MWRA as their basis . While avoiding duplication of effort in data gathering, the independent analyses and opportunity for public review provided by the Facilities Plan and this Draft SEIS offer exhaustive review of impacts and an opportunity to tailor each document to fit precisely the applicable regulatory requirements. This Draft SEIS explains the need for the conduit and outfall and the various siting, design and construction alternatives 1 ------- considered. Volume I of this Draft SEIS describes the existing problem caused by wastewater discharges, the existing environment, the alternatives examined, and the process used to select recommended alternative3. Enviromnental consequences of the various alternatives for an effluent outfall location, outfall tunnel and inter-island conduit construction methods, and diffuser design are described. Recommended alternatives for each are selected in Volume I. Volume II provides detailed technical appendices which support the information and analysis in Volume I. This Executive Summary provides a brief description of the major findings conclusions of this Draft SEIS. PURPOSE A.ND NEED FOR ACTION Effluent and sludge discharges from the Deer Island and Nut Island treatment plants represent over half of the suspended solids and oxygen consuming pollutant matter entering Boston Harbor. Raw wastewater bypassing the treatment plants puts additional stress on marine life and results in bathing beach and shellfish bed closings. The 1986 Record of Decision (ROD) issued in connection with the treatment plant siting EIS determined that the best way to provide secondary treatment for the MWRA service area would be to consolidate treatment at a single facility on Deer Island. The ROD also directed additional environmental review regarding the location and construction of an inter-island conduit and an effluent outfall system. This Draft SEIS provides the additional environmental review required. Improvements in wastewater treatment will result in a two- thirds reduction in sewage solids discharged to Boston Harbor and the Massachusetts Bay system when the entire system is operational in the year 2000. Public benefits include improvements in public health, aesthetics, recreation and commerce. PROPOSED ACTION The proposed action considered by this Draft SEIS consists of three elements: - Construction and operation of an effluent diffuser in Massachusetts Bay to provide dispersion of treated effluent into the marine environment outside Boston Harbor; - Construction and operation of a conduit to transport treated effluent from Deer Island to the diffuser site; and - Construction and operation of a conduit delivering wastewater from Nut Island to the new Deer Island secondary Treatment Plant. 2 ------- ALTERNA’rIvEs The first step in prep&ring this draft SEIS was to define the alternative methods of accomplishing the proposed action. In order to produce a reasonable number of alternatives, covering the range of proposed actions, MWRA alternatives were reviewed and supplemented where necessary in Chapter 3 of this Draft SEIS. A screening level analysis was then performed to determine the alternatives for detailed evaluation. The screening results for each element of the proposed action are summarized below. Outfall Location. The Final EIS on siting a secondary treatment facility for Boston Harbor designated an area east of Deer Island for the discharge of MWRA effluent. The area had to be more precisely defined for evaluation in this Draft SEIS. This was done by first establishing a limited area in Massachusetts Bay suitable for discharge of effluent from the secondary treatment plant on Deer Island. A landward or western boundary was established beyond which: 1.) shoreline impacts could be avoided by minimizing transport of effluent to the shoreline; 2.) Water Quality Criteria Goals could be achieved by providing a minimum initial dilution. This boundary eliminates Sites PR, 1 and 3 (considered by MWRA) and maintains Sites 2, 2.5, 3.5, 4, 4.5, 5 (considered by MWRA) and 6 (suggested by a concerned citizens group) (Figure 1) The eastern or seaward edge of the area could not easily be established by application of a single criterion. The impacts from factors of concern such as sediment and water quality and marine ecosystems generally decrease along a gradient in an offshore direction. Costs increase along the same gradient. Therefore a screening level analysis was performed comparing a secondary discharge at the nearshore and offshore regions. This comparison was based on a line extending from MWRA Site 2 to Site 6 (Figure 1). The comparison revealed that there were significant benefits achieved at locations beyond Site 2 and potentially beyond Site 4. However no substantial additional benefits were identified during screening for a discharge beyond Site 5 especially when traded off against increased costs. Consequently, three Sites (2, 4 and 5) were identified for detailed evaluation within the area bounded by and including Sites 2 and 5 (Figure 1). These three Sites span the range of conditions within the screened area and represent a reasonable range of alternatives. Intermediate Sites 2.5, 4.5 and 3.5 were within the range of conditions represented by the other sites and did not offer sufficient distinguishing characteristics to warrant detailed 3 ------- PR SITE 1 SITE 2 SITE 2.5 SITE 3 SITE 3.5 SITE 4 SITE4.5 SrrE SITE 6 DISTANCE IN ST TUTE MILES TO: DEER EAST POINT ISLAND POINT ALLERTON 0.1 5.2 2.3 32 4.0 4.3 4.0 2.4 5.2 4.8 2.5 5.6 5.6 6.5 2.6 7.0 5.9 4.9 6.6 3.5 6.1 8.0 5.4 7.0 9.4 6.0 8.1 11.5 9.0 9.0 M G . I , —- ---I Gts ,— EASTERN / BOUNDARY LANDWARD BOUNDARY 6 0 STATUTE MILES tA3 sos o. OG ’. SCS N N — - N . PI ESIDE dT OA 0 S La I ‘ ________ / — j V J .. Ou wCT FIGURE 1 •\RE.A OF POTE\TIALLY ACCEPTABLE SECO\D R\ EFFLIE\T DISCHARGE LOCAT1O\S 1.5 2.0 0 - NAUTICAL MILES 2.0 $ ( \ 2.5 0 4.5 0 4 . 1 0 3.5 / I 3 / / c 2 ------- evaluation. For approximately ie years while the secondary treatment facility is under ccw.structicn, primary efflueLit will have to be discharged. The discharge locatthi at irterim primary effluent was also addressed in a screening analysis. The alternatives screened were: 1.) continued discharge at the existing location (President Roads) and 2.) discharge at the sites considered for the secondary discharge (Sites 2,4 and 5). The primary effluent screening analysis revealed that a primary discharge at the existing location in President Roads would produce more severe and more frequent violations of the Massachusetts dissolved oxygen standard than a discharge at sites farther offshore. A President Roads discharge would also further degrade the already stressed marine ecosystem in the northern portion of Boston Harbor as well as directly impact for five more years the high-use shoreline and island areas of the Harbor and surrounding shore. Consequently, the interim primary discharge evaluated in detail were the offshore Sites. Wastewater Conveyance. For both the inter-island conduit (the system to carry sewage from Nut Island to Deer Island) and the outfall conduit (from Deer Island to the discharge site), seafloor pipelines and deep rock tunnels were considered in the screening analyses. For both conveyance systems, the deep rock tunnel was significantly less costly, produced fewer environmental impacts and was equal or superior to the pipeline alternative for reliability and constructability. Therefore the tunnel was the only conveyance alternative evaluated in detail. Two basic alternative diffuser systems were considered during screening. One diffuser alternative was a pipe (or set of pipes) in a covered trench on the sea floor connected to the outfall tunnel by one or several vertical riser shafts. The other alternative was a series of individual vertical risers (about 80) drilled into the outfall tunnel to provide a multiport diffuser. Although the impacts of the pipe diffuser were considered greater than those of the drilled riser, the results of screening were not conclusive, indicating that both systems should be evaluated in detail. AFFECTED ENVIRONXENT The affected environment, as described in Chapter 4 of the Draft SEIS, for the proposed action includes the area potentially affected by effluent dispersion from a discharge at any of the sites, or construction of any of the conveyance systems. The existing conditions in the potentially affected 4 ------- area are summarized below for each major segment of the environment. Physical Oceanography and Water Quality. The major area of potential impact from effluent dispersion and outfall construction is Massachusetts Bay, which is generally defined as the area bounded by Cape Ann and Provincetown. This is a coastal embayment of the Gulf of Maine and is heavily influenced by the adjacent land and tributary water bodies, such as Boston Harbor. A major component of the circulation in Massachusetts Bay is the twice daily flood and ebb of the tide. This circulation, particularly near shore, is largely in an east-west direction and near the mouth of Boston Harbor the tidal currents can produce significant exchanges of ‘water between the Harbor and Massachusetts Bay. There are also non-tidal currents which result in a net drift, either to the north or south. These are produced by large scale storms and weather systems and by fresh water discharges to Massachusetts Bay. Storms or other wind events can also produce more localized net movement of surface water of occasionally large amplitude. Storm events can also generate strong bottom currents which can resuspend and redistribute bottom sediments. Water quality in Massachusetts Bay generally meets established Massachusetts Water Quality Standards and EPA Water Quality Criteria. However two chemicals (PCB and the metal arsenic) currently exceed the most stringent criteria by large amounts. Dissolved oxygen in Massachusetts Bay is generally within the Massachusetts standard, but during worst -case conditions of water column stratification there is some data indicating that present ambient dissolved oxygen levels could be near the 6.0 mg/i standard. Marine Geology. The geology and sediment characteristics of the area are heterogeneous over a small area. There are areas of bedrock outcrops, interspersed with areas of mud, sand and cobble. Some of the mud areas could be depositional or of geologic origin. There does appear to be a pattern of deposition throughout much of the Bay during the summer, followed by resuspension and redistribution during heavy storms. Levels of potential contaminants in sediments are generally low throughout the area. The metal and organic compound concentrations can be classified under the Massachusetts dredged material guidelines as relatively low with no apparent toxic effects on marine organisms living in the sediments. 5 ------- Marine Ecosystems. The biological community in the area is generally typical of unstressed nearshore temperate areas. Alt-houqh some pollution tolerant species are present, they do not dominate the community. Phytoplankton production in the 3ffected area is generally high and appears to be greater closer to shore and in Boston Harbor. Winter flounder and lobster are the major important commercial fisheries species in the area. These species are taken throughout the area, although they do not seem to be concentrated in a particular area. Harbor Resources. Harbor resources include the natural, recreational, and commercial resources of Boston Harbor potentially affected by construction of the project. Construction entails transport of materials and workers to Deer Island from various locations in and out of the Harbor, thus increasing marine traffic. These resources are potentially affected by the dispersion of the effluent during operation of the outfall and by movement of workers and material during construction. Navigation channels and anchorages support commercial and recreational navigation in Boston Harbor, and will also be used by marine traffic related to construction of the treatment plant, inter-island conduit, and effluent outfall and diffuser. Two navigation channels passing through President Roads and Nantasket Roads and an anchorage area west of Deer Island are the major navigational resources serving the harbor. Conunercial shipping contributes significantly to local and regional economies. The Inner Boston Harbor waterfront supports roughly two dozen public and private port facilities, and nearly 7000 commercial vessels per year call at the port of Boston. Commercial fishing takes place in Boston Harbor and Massachusetts Bay, with support facilities for fishing vessels located in the harbor. Shellfish and lobster are harvested in the harbor and lobster and finfish are harvested from Massachusetts Bay. Recreation areas and facilities are located along the shoreline throughout the area potentially affected by the project. These include bathing beaches, parks, recreational boating facilities, and the Boston Harbor Islands State Park. CONSEQUENCES OF ALTERNATIVES AND RECOMMENDED ALTERNATIVE Criteria for evaluation of consequences of the various discharge location alternatives are described in detail in Chapter Five of the Draft SEIS. After evaluation, certain criteria showed no major differences among the alternative Sites. Under these criteria, discharge at site 2, 4, and 5 6 ------- are predicted to have similar and acceptable impacts. These criteria are: —Air emjssj ons -Noise -Safeguarding protected Epecics -Sensitive or important habitat -Cultural and historic resources -Commercial fishing activities -Water traffic -Reliability -Constructabil ity -Permitting —Demand on unique or scarce resources Other criteria demonstrated differences among sites. These are: -Water quality standards -Aquatic life water quality criteria -Public health water quality criteria -Shoreline and recreational impacts -Sediment enrichment -Water column enrichment -Sediment toxicity -Commercial. and recreational species -Cost -Duration of construction -Materials disposal Table 1 shows a comparison of the data for worst case conditions regarding each of these criteria for each alternative discharge location. The comparison was first performed for secondary discharge and the results of the comparison reviewed for interim primary discharge. The siting decision is based on secondary discharge. However if a primary discharge would produce unacceptable or irreversible impacts, the alternative was reevaluated. For secondary discharge, violations of Massachusetts water quality standards for dissolved oxygen (DO) would occur at Site 2 under extreme conditions; no violations of the DO standard would occur at Sites 4 and 5 under the same extreme conditions. Under normal conditions, dissolved oxygen levels would be well above the water quality standard at Sites 2, 4, and 5. Minimal differences in exceedances of the EPA Aquatic Life Water Quality Criteria among sites are expected and no significant impacts are predicted from the exceedances. Public health impacts were evaluated by comparing predicted pollutant concentrations at the edge of the effluent mixing zone to the EPA Water Quality Criteria for both a 1 in 100,000 and 1 in 1,000,000 risk. For the 1 in 100,000 risk level, two compounds (PCB and arsenic) exceeded criteria in the ambient water at all sites. No additional compounds were 7 ------- Table 1. OUTFALL SITE COMPMUSON Criteria Measure SECONDARY SITES 2 4 5 PR.IIIARY SITES 2 4 s Water Quality Standards Mm DO mg/i 5.9 6.3 6.4 2.2 5.0 5.7 Aquatic Life Criteria Nu.mber Exceeding 2 1 0 5 5 4 Public Health Criteria - Number Exceeding 4 2 2 5 5 4 Shoreline and Recreation Impacts Hours to Shore 6.6 9.4 15.5 6.6 9.4 15.5 % Effluent at Shore 1.3 0.6 0.6 1.3 0.6 0.6 Sediment Ertrichment 2 Degraded i 0 0 2 1 1 2 Changed 5 3 3 33 19 12 Water Column Enrichment 2 Degraded i 0 0 1 0 0 2 Changed 160 5 4 160 5 4 Sediment Toxicity 2 of Effect o 0 0 3 2 2 PCB Area >.1 ppm 6 5 4 18 13 10 Commercial and Recreation Species Minor Minor Minor Moderate Minor M or Cost $ Millions 276 389 468 276 389 468 Construct ion Duration Months 47 51 56 47 51 56 Materials Disposal Million cu yds 0.8 1.3 1.9 0.8 1.3 1.9 ------- predicted to exceed criteria from discharge at Sites 4 or 5, while two additional compounds (aidrin and DDT) exceeded critsria at Site 2. Discharge from any of the sites is not expected to p:oduce significant shoreline or recreational impacts, even under extreme conditions. Sediment enrichment, water column enrichment, and sediment toxicity impacts are relatively equal for all sites under secondary treatment discharge. The cost of constructing a tunnelled outfall system increases with the length of the outfall tunnel. Site 2 is the least expensive discharge point while Site 5 is the most expensive. The range of time required for the completion of the outfall tunnel to Sites 2, 4, and 5 would be 47, 51, and 56 months respectively. Construction to any of the sites is expected to coincide with or precede completion of the primary treatment facility. Length of the outfall tunnel determines the amount of tunnelled material, with Site 2 resulting in the least material and Site 5 resulting in the most. Based on the analysis of the various criteria factors, the discharge of secondary effluent at Site 2 is not preferred due to major differences in the level of impacts expected from discharges at Site 2 as opposed to Sites 4 or 5. In particular, shoreward travel of pollutants and nutrients entering Boston Harbor are of concern. No great differences are found between Sites 4 and 5, other than additional cost for construction of an effluent tunnel to Site 5. Evaluation of interim primary discharge demonstrates that Site 2 is unacceptable even for a five year interim discharge of primary effluent due to severe DO violations and large area of sediment contamination. The potential impacts on commercial fish species are also greater at Site 2 for the discharge of primary effluent. The impacts at Sites 4 and 5 are comparatively small and similar to each other and more importantly, they are reversible and therefore acceptable over the five year period. Consequently it is recommended that the diffuser lie entirely within the area bound by Site 4 on the landward side. The seaward side of the recommended location is the vicinity of Site 5. The recommended area is a corridor wide enough to allow for flexibility in diffuser orientation and geotechnical conditions (Figure 2). Deep rock tunnel construction is recommended for both the inter—island conduit and the effluent outfall tunnel, and individual drilled risers are the recommended diffuser design. Mitigation measures and additional studies are recommended. These include monitoring of treatment plant influent to fully 8 ------- NAUTICAL. MILES t*gT P WT 2 0 ç cCO — — lIII #lII_ 5 4’ 0 I — — — — 2 FIGURE 2 RECOMME\DED LOCATION OF THE DEER ISLAND WWTP DISCHARGE ------- identify nonconventional pollutant loadings. Also a pilot wastewater plant is recommended to determine if anticipated removal efficiencies are being achieved. Additional geotechnical investigations to determine the precise site for the diffuser siting and physical modeling of the diffuser are also essential to the implementation of the recommended plan. Coordination with other projects in the area is needed for waste construction material disposal and management of scarce resources to insure timely implementation of the project. ------- |