A GAC filtration system will require significantly more equipment and footprint for interim treatment. In this case, the equivalent amount of GAC vessels would require four semi-trailers instead of two.
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PFAS6 is defined as the sum of the concentrations of the following six PFAS compounds:
Currently, the United States Environmental Protection Agency (USEPA) has a health advisory level of 70 parts per trillion (ppt) for PFOA and PFOS.
Effective October 2, 2020, the Massachusetts Department of Environmental Protection (MassDEP) finalized revisions to the drinking water regulations (310 CMR 22), which now include a maximum contaminant level (MCL) for PFAS6. According to 310 CMR 22.07G, 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. Because the Town of Wellesley (Town) serves between 10,000 and 50,000 customers, the new regulations required the Town to begin PFAS6 compliance sampling in April 2021.
The USEPA released a PFAS Strategic Roadmap in October 2021, which anticipates federal regulation of PFAS in drinking water. This includes issuing formal regulatory limits for PFOA and PFOS in about a year and ongoing assessment of other PFAS compounds for potential future regulation. Additionally in the spring of 2021, the USEPA announced the Fifth Uncontaminated Monitoring Rule (UCMR5) compound list which includes 29 PFAS compounds. Monitoring for UCMR5 will begin in 2023. EPA uses the Unregulated Contaminant Monitoring Rule (UCMR5) to collect data for contaminants that are suspected to be present in drinking water and do not have health-based standards set under the Safe Drinking Water Act (SDWA)
There is another testing method (USEPA Method 533) that can detect 25 PFAS compounds in the approved analyte list, but it is not currently approved by MassDEP for public drinking water supply testing. A combination of USEPA Method 533 and 537.1 will be used for UCMR5 analyte list.
Other PFAS compounds are likely present in Wellesley drinking water; however, the accepted laboratory testing method (USEPA Method 537.1) can detect a suite of 18 PFAS compounds.
Common sources of PFAS contamination in the environment include use of aqueous film forming foams (AFFF) used for fighting fires; manufacturing of water-resistant and non-stick consumer products, such as non-stick cookware, stain resistant coatings, water resistant clothing, cleaning products, and personal care products to name a few. The Agency for Toxic Substances and Disease Registry provide additional information regarding the health effects of PFAS and possible sources of exposure: https://www.atsdr.cdc.gov/pfas/health-effects/exposure.html
The foam used by WFD is Nova Cool for years and has no PFAS. Previously WFD used FireAid, no PFAS as well. There is no inventory at either station of any foam products that contain PFAS’s.
MassDEP has been supporting some municipalities with environmental due diligence related to PFAS. The Town is currently exploring conducting a preliminary environmental due diligence assessment of the surrounding area to investigate potential source(s) of PFAS contamination.
There are three different treatment alternatives most commonly considered effective in the removal of PFAS from drinking water: adsorption using activated carbon, ion exchange using resins, and reverse osmosis using permeable membranes.
Granular Activated Carbon (GAC)
GAC contactor vessels are the most common units on the market for PFAS removal for both surface water and groundwater sources. The pressure vessels remove PFAS via adsorption to the GAC media and require backwashing of the vessels once they reach a certain differential pressure. GAC has been found to have greater efficacy removing of long-chain PFAS compounds than short-chain PFAS compounds. According to the USEPA, GAC has a maximum demonstrated removal rate of between 90% and 98% of the PFAS6 compounds regulated by the new MCL.
Ion Exchange (IX)
Similar to GAC vessels, IX resins are typically installed in pressurized, contactor vessels in a lead-lag configuration. The positively charged resin attracts the negatively charged PFAS particles, removing them from the water. In many applications, IX has been found to have greater removal of short-chain PFAS compounds than long-chain PFAS compounds. According to the USEPA, IX has a maximum demonstrated removal rate of between 94% and 99% of the PFAS6 compounds regulated by the new MCL. Unlike GAC, IX resins have a finite capacity, and typically cannot be reactivated and reused, requiring an ultimate off-site disposal location. Additionally, IX resins require pre-filtration using bag filters to capture any solids in the raw water, adding to the capital, operations, and maintenance costs; however, IX resins typically have a longer lifespan before reaching this ultimate capacity when compared to GAC.
Reverse Osmosis (RO)
RO utilizes high-pressure, small pore size, permeable membranes to separate PFAS compounds from feed water. The concentrated waste water is continually recirculated into the feed water or fed through secondary and tertiary RO systems, resulting in high recovery rates and non-detect PFAS levels. The remaining waste water is flushed out of the system, requiring a separate GAC or IX treatment system before the waste water can be disposed of. Additionally, the RO-treated water requires remineralization prior to entering the distribution system. RO membranes can provide removal over a typical lifespan of 10 years before requiring replacement. RO has been found to remove both short- and long-chain PFAS compounds. According to the USEPA, RO has a maximum demonstrated removal rate of 99% of the PFAS6 compounds regulated by the new MCL.
The lead time for the PFAS vessels drives the critical path of the construction schedule regardless of media type. Manufacturers are quoting 24-40 week lead-times from approval of shop drawings. The procurement schedule for treatment equipment and building materials (e.g. Pre-engineered metal buildings) has grown over the course of 2021. The 24-40 week time frame does not include time for design, bidding, shop drawing review, or construction. An option for improving timeline for commissioning a long-term PFAS system is to pre-purchase the equipment.
In order to meet peak demands last summer without the Morses Pond WTP, the Town operated the existing MWRA interconnection at full capacity. Demands last summer were depressed by a combination of water conservation measures and unusually high precipitation. We expect that the summer of 2022 will be hotter and drier than 2021, which means the Town will be further challenged to meet peak summer demands without the Morses Pond WTP available to supplement supply.
Both GAC and IX have proven effective methods of PFAS treatment. While each water supply is unique, there are advantages and disadvantages to each treatment media. IX systems have smaller footprint than a comparable GAC system as they can handle higher loading rates (gallons per square foot) and have shorter contact times than GAC. IX media is more expensive to purchase and is currently considered one-time use and then it has to be removed/disposed, while GAC can be reactivated and reused. IX systems require additional pre-treatment considerations (e.g. dechlorination and bag filtration) as opposed to GAC systems.
RO is a viable treatment option for PFAS removal. RO requires additional pre-treatment/pumping/post-treatment systems and has higher capital/O&M costs than IX/GAC systems. RO also produces a highly concentrated PFAS waste stream that requires special handling and disposal considerations. This would not be the most sustainable option for the Town.
The accepted laboratory testing method (Method 537.1) can detect a suite of 18 PFAS compounds. Adsorption media such as GAC and IX have proven effective at treating PFAS compounds from this analyte list.
Based upon current regulations PFAS GAC and IX media, expended media is not considered hazardous waste; however, the regulatory environment regarding PFAS is evolving and environmental service providers have indicated that they manage PFAS waste similar hazardous substances in terms of disposal in landfills or incinerators. Reactivation of GAC media is an option. IX resin is currently considered single-use.
GAC is commonly used to remove other contaminants of concern in drinking water such as taste and odor compounds, disinfection by-product precursors, volatile organic compounds, naturally occurring organic matter. Public water systems have been required to test for other unregulated contaminants as part of the UCMR process.
Regarding disposal, the spent carbon media can be reactivated by heating at high temperatures, which breaks up the PFAS molecules and restores the pores in the spent GAC. The reactivated media can be reused for treatment, which saves money and reduces the environmental impact. Typically, the replacement media will include mostly regenerated media and a portion of virgin media (approximately 80% and 20%, respectively). Calgon Carbon is one of the primary GAC suppliers in the area and they have an overview of the process on their website: https://www.calgoncarbon.com/reactivation-services/
Calgon also has an FAQ sheet on their website: https://www.calgoncarbon.com/app/uploads/Reactivation_Services_FAQ.pdf
There’s no direct way to piggy back on Natick’s PFAS treatment since we have no pipe that goes from their location to ours. However, we do have the ability to interconnect with Natick at other locations for emergency purposes. Prior to finding elevated PFAs levels at Morses Pond we explored the opportunity for Natick to take water from Wellesley’s system.. We found that the pressure differences between our two systems were incompatible and it would take a lot of effort and new equipment to make such an interconnection feasible. Another factor to overcome is that the chemical differences between our water supplies would create some potentially unpleasant characteristics (e.g., dis-colored water) that might require additional treatment. For these reasons, we decided to not pursue establishing a more permanent connection.
We are in regular contact with our colleagues in Natick (and other towns) and will be paying close attention to the performance of their system. We also continue to work together to assist each other whenever possible.
Interim PFAS treatment will include the following components:
The interim system has been sized to treat the maximum amount of water (1 million gallons per day [MGD]) that the Morses Pond wells can pump given the additional hydraulic constraints imposed by the additional treatment equipment. The interim treatment media (GAC/IX) are estimated to last more than 16 months based on current PFAS levels and proposed system flow rate (1 MGD). The current cost to purchase water from the MWRA is $4,000 per 1 million gallons. There is both a cost savings component and a demand component of the interim solution that will benefit the Town. There are times during peak demand that the MWRA system will be at maximum pumping capacity and we will still need the additional million gallon supply to meet the system demand.
The interim system could be procured under an extended rental agreement or the Town could opt to purchase the interim system so that it could be deployed at the Town’s other well fields if needed. Purchasing the equipment is not a guaranteed option.
The GAC vessels would be sized for a minimum of 1 year. The pre-selection process would include a provision for the GAC vendor to conduct testing to confirm GAC estimated lifespan so we can use that information in final design. Ideally we will have a GAC system design that provides for 14-18 months so GAC reactivation is on a regular schedule once every 2 years, but the rapid small scale column test results will help inform that design. PFAs levels will be monitored before and after the filters to determine when the filters are approaching breakthrough
Our current MWRA connection provides a maximum of 4.2MGD. Current max day demand is over 6MGD, so our existing connection cannot meet demand in the peak use months. We count on our Morses Pond Treatment Plant as our largest local source to help meet that demand. Also, MWRA water is much more expensive than our locally produced water and rate increases will be needed for additional amounts of MWRA water used. This is especially true in the non-peak months because of the cost. In the summer, our peak rates are designed to cover the added costs of MWRA water.
Basically, the Morses Pond Treatment Plan produces 1 to 1.4 MGD and the premium for MWRA water is about $2,500/MG. So, 1MGD x $2,500 x 30 days = $75,000 per month at a minimum. A reasonable estimate is that the added cost is about $1,000,000 per year.
We propose renting this system. We’ve looked at a purchase option but decided that renting was more prudent since it produces a waste stream that might be more difficult (and more expensive) to deal with if we owned versus rent.
If we purchase an interim system it could be re-deployed. However, without knowing how long it would be out of service between uses it is unknown what kind of performance we would get. Also, since it has not yet been determined what will happen at the other plants it seemed that renting would be preferable. Also, we propose doing the interim solution as a demonstration test. We expect it to be successful, but until that data is in we felt more comfortable with a rental option.
If purchased, a system could be sold or loaned to others especially in the current market. We don’t have any good data on the potential residual value or the complexity of resale of this type of equipment but they are certainly in high demand these days.
The 3 to 5 year estimate is a conservative estimate due to the regulatory, design, and construction requirements that are likely to be involved.
This evaluation would require further study to analyze the regulatory, design, construction, operation and maintenance costs. The costs associated with MWRA option include expansion in water use (MWRA charges approximately $4.4M for each million gallons per day in capacity for new water system members), infrastructure improvement costs (interconnecting community and within Wellesley), and increased water rates
The MWRA water system currently has access to a safe yield of approximately 300 million gallons per day and its current water customers utilize approximately 200 million gallons per day.
Maximum pumping is about 3,000 gallons per minute or 4.3 MG per day. This is due to the physical limitations of the piping, pumps and other equipment in the station.
If something were to go wrong with the supply line or the station itself (power outage, pipe break, other failure) we would have no water if our existing three treatment plants were not available. We spend a lot of time planning redundancy and resiliency in our system. Our MWRA Pump Station has 2 pumps and a backup generator to handle more routine interruptions. Still, a serious or catastrophic failure to our station or the MWRA supply line would leave us with no water if this were our only source. We do have inter-connections to our neighbors for use in an emergency but there is no guarantee that they will be able to provide us water. For example, we contacted Weston this past summer to see if they could supply us with water but they were not able to do so due to their own constraints.
We think so. This is something that we have been working on with the MWRA since 2019. We have made many improvements to our connection over the years including redundant pumps. However, we believe that a separate entry point should be developed so that if anything ever happened to the station we could still draw MWRA water. The MWRA has been working with us on developing concepts that could be pursued. We’re still years away from any type of solution, which is currently being viewed by us and the MWRA as a potential regional solution for Wellesley and neighboring towns.