The Town of Easton retained the services of Environmental Partners (EP) to complete a Conceptual Design for the proposed per- and polyfluoroalkyl substances (PFAS) treatment systems at Wells 1, 2, and 4R. This website presents the results and conclusions of the conceptual design phase for the proposed Well 1, 2, and 4R facilities associated with new PFAS treatment. The report builds upon the prior studies and work completed by EP, and incorporates feedback from various representatives, including officials from the Town and regulatory agencies. It is the intent of this website to describe the framework for the three new treatment systems.
INTRODUCTION AND BACKGROUND
The Town’s water supply system consists of six independent groundwater sources and one wellfield. Existing treatment at each well station includes ultraviolet light (UV) for disinfection, calcium hydroxide (lime) for pH adjustment and corrosion control, and sodium hypochlorite (NaOCl) for residual disinfection. Additionally, the Town is in the process of designing a new treatment plant to remove iron and manganese from the source water at Wells 3, 5, and 7.
In October 2020, the Massachusetts Department of Environmental Protection (MassDEP) finalized revisions to the drinking water regulations (310 CMR 22) to include a maximum contaminant level (MCL) for PFAS6. According to the new regulations, a water supplier is in violation of the MCL if PFAS6 exceeds 20 parts per trillion (ppt) at an entry point to the distribution system on a regular basis. When sampling detects PFAS6 levels above 10 ppt but below 20 ppt, the regulations require monthly PFAS6 sampling at each affected source. A summary of PFAS6 levels at each of the affected wells is provided in Table 1, and includes voluntary samples collected by the Town ahead of the PFAS6 MCL implementation. In accordance with MassDEP standards, any PFAS6 compound that was measured at less than the minimum reporting limit (MRL) was reported as zero ppt.
The sample results indicate that PFAS6 levels are typically at or above the MCL of 20 ppt at Wells 1 and 4R. At Well 2, PFAS6 levels are typically at or below 10 ppt, but have occasionally increased to levels greater than the MCL. In response to the recently implemented MCL, the Town sought to address the elevated levels of PFAS6 in the source water at Wells 1, 2, and 4R. The existing treatment practices at these wells are not effective in removing PFAS, and each site will require significant upgrades in order to continue operating while meeting the new drinking water regulations for PFAS6.
In December 2020, EP completed an alternatives analysis for all three sites, reviewing potential sources of PFAS contamination along with potential treatment alternatives and opportunities for combining water sources. Based on the results of the alternatives analysis, the Town elected to move forward with granular activated carbon (GAC) filters for PFAS6 removal at each individual well site, and EP completed the conceptual design work for GAC filters at Well Stations 1, 2, and 4R.
In April 2021, Evoqua Water Technologies (Evoqua) collected water samples from Wells 1, 2, and 4R and conducted three rapid small-scale columns tests (RSSCTs) to evaluate the effectiveness and potential bed life of GAC. The results of the RSSCTs were approved by MassDEP on July 16, 2021 and were used to finalize the conceptual design of the GAC treatment systems.
SUMMARY OF CONCEPTUAL ENGINEERING AND PLANNING
The proposed PFAS treatment systems at Wells 1, 2, and 4R will be rated for a maximum flow of 750 gallons per minute (gpm), 1,000 gpm, and 850 gpm, respectively. Well Stations 1, 2, and 4R will pump raw water to each respective PFAS treatment building, which include two vertical pressure filters containing GAC media in a lead-lag setup. Filtered water will return to each well station for chemical addition. The Town will continue to use the existing chemical feed systems, UV equipment, well pumps, and finished water mains at each well station. The proposed treatment buildings will be located at their respective well sites, near the existing well stations.
Each PFAS treatment system will include a pair of 12-foot diameter GAC pressure filters operating in series (lead-lag) and a backwash drying bed with a hydrodynamic separator. Each filter will undergo backwashing periodically based on differential pressure across the vessel. Backwash waste will discharge to a hydrodynamic separator for solids removal prior to entering one of two on-site, unlined drying beds for disposal.
The existing paved areas around the well stations will remain in use, and gravel strips will be added along the existing access drive to widen the road for large delivery trucks. Gravel access drives installed at each PFAS treatment building allow access for GAC media replacement, emptying of drying beds, and maintenance of hydrodynamic separators.
The PFAS treatment systems will be housed in a pre-engineered metal building with a concrete
foundation. An architectural three-dimensional sketch is provided below:
The existing buildings at Wells 1, 2, and 4R will remain in place, with modifications required to connect to the existing piping and electrical systems. Modifications to Well 1 include:
- Demolition of existing raw water pipe spools and fittings;
- Installation of filter influent piping, filter effluent piping, and filter bypass piping; and,
- Replacement of existing Main Distribution Panel circuit breakers.
- Demolition of existing raw water pipe spools and fittings;
- Installation of filter influent piping, filter effluent piping, and filter bypass piping;
- Installation of new pump discharge check valve;
- Installation of new 150KW standby power generator; and
- Replacement of existing Main Control Center with a new Main Distribution Panel.
- Connection to the existing raw water main outside of the well station; and
- Replacement of the existing Main Control Center with a new Main Distribution Panel.
- Massachusetts Department of Environmental Protection;
- Town Conservation Commission;
- Massachusetts Historic Commission; and
- Town Site Plan Review.
CIVIL DESIGN AND SITE LAYOUT
The proposed PFAS treatment systems for Wells 1, 2, and 4R will be located at their respective well sites, shown in webmap below:
The Town of Easton owns these parcels, which are zoned for municipal use. A wetlands scientist delineated the wetland resource areas surrounding each well site in March 2021 and a professional land surveyor performed an existing conditions survey in April 2021.
Well 1 is located on a 17.1 acre site in a wooded area at 218R Center Street, Easton, MA (Map 32U, Parcel 21). The site is accessible from Gary Lane, which is a dead-end side street off Center Street. The access road is paved up to the existing well station building. A locked steel swing gate restricts vehicular access to the well station to Town-approved vehicles only. A locked chain link fence surrounds the existing building.
Well 2 is located on a 12.1-acre site in a wooded area at 95R Washington Street, Easton, Massachusetts (Map 27U, Parcel 36A). Well 4R is located on a 9.8-acre site in a wooded area at 100R Washington Street, Easton, Massachusetts (Map 27U, Parcel 39A). The sites are accessible via an access road off Washington Street between Holy Cross Drive and Eisenhower Drive; Wells 2 and 4R share an access road. The paved access road travels west towards the two well stations before splitting north to Well 2. The access road continues west for a distance before turning south to Well 4R. A locked steel swing gate located at the Washington Street intersection restricts vehicular access to the well stations to Town-approved vehicles only.
Environmental Partners conducted a vehicle turning analysis to review access for vessel deliveries during construction and GAC deliveries during future operation of the facilities. Currently, the WB-40 Intermediate Semi-Trailer truck is the largest truck that enters the existing well sites. The types of trucks anticipated to access the site include dump trucks for removing material from the hydrodynamic separators, WB-40 Intermediate Semi-Trailer trucks for construction deliveries, and GAC delivery trucks for filter installation and future GAC deliveries.
WB-40 Intermediate Semi-Trailer
Well Station 4R was designed to allow the WB-40 Intermediate Semi-Trailer to fully maneuver around the site. A vehicle turning analysis conducted with this truck confirms the maneuverability of this truck in and out of the Well 4R site. The analysis also suggests that this truck can access the Well 1 and Well 2/4R sites from the main road and maneuver around each individual well site within the existing limits of pavement and adjacent cleared areas.
At the PFAS treatment buildings for each of the three wells, a gravel access driveway was provided to allow the truck to back into the driveway and pull forward out of the site. The trucks can access each well site within the existing limits of pavement and adjacent cleared areas.
Clearing will be limited to the maximum extent practicable to prevent disturbing existing forested areas. A minimum 50-feet wide forested buffer will remain in place along all property lines to minimize disturbance for the abutting parcels in accordance with setback requirements for the Municipal Open Space zoning district. Some clearing is required within the 50-foot “no disturb” wetland buffer zone and the 100-foot wetland buffer zone. All proposed work is outside the limits of the FEMA Zone AE flood plain.
Well 1: Site work for Well 1 PFAS treatment includes clearing for the utilities and backwash drying bed; the proposed treatment building and stormwater BMPs will be located in an existing open area. Some clearing will occur within the 100-foot wetland resource area buffer zone; no clearing will occur within the wetland resource area.
Wells 2 and 4R: Site work for the Well 2 and 4R PFAS treatment includes clearing for the treatment buildings, utilities, site access, backwash drying bed, and stormwater BMPs. Clearing will occur within the 50-foot “No Disturb” buffer zone and the 100-foot buffer zone for utility installation behind the Well Station 2 building; no clearing will occur within the wetland resource area. Some clearing will also occur within the 100-foot buffer zone along the existing access road and adjacent to the Well Station 4R building.
Complete report from Environmental Partners can be viewed here.