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The Water Master Plan (Plan) provides a comprehensive overview of Weston’s water system and infrastructure, taking into account current and projected water usage over the next two decades. It allows the Town to take stock of current population trends and water usage patterns, to make reasonable projections of population and water needs, and to identify where infrastructure investments are needed to ensure that the system can provide service to the community. Twenty years is a standard planning period for this type of study: far enough into the future that currently observable trends can be anticipated, and not so far into the future that the time frame exceeds our confidence. Mechanical equipment has a service life of about 20 years, but water pipes and storage tanks have a long useful life and thus require long planning periods of 50 or more years. The purpose of the Water Master Plan is to provide the Town with a road map to take us from the present to the future, confident that we have anticipated likely issues pertaining to our water service.
The Plan provides a detailed-enough look at our existing infrastructure and our likely future needs that we can confidently begin to address areas of concern regarding the Town’s provision of water. Weston is primarily a residential community. Increases in residential population, including increases due to 40B housing projects, have a nominal effect on water supply needs and therefore these plans typically only need to be updated every ten years, and in some cases every five years. Because our Plan is three years old, an update at this time would not provide appreciably different conclusions. Instead, it is now time to move to implementation of the Plan that we have.
The Plan is a flexible document that gives us the data we need to shift our priorities as needed. The highest priority identified in the Plan is to increase the system’s hydraulic conditions by increasing storage capacity and raising the height of the tanks. The need for increased storage capacity and increased height are critical and fundamental components of this Plan and would be part of any future plan. Further, the Paine’s Hill Tank has continued to deteriorate since 2019, giving the Town even more reason to focus on the Paines Hill Tank project as its first action item. Prior to construction, the Town will confirm final overflow elevations and system hydraulics and operations, identify suitable properties on which to construct tanks, and detail construction sequencing and hydraulic needs while each of the tanks are being integrated into the system.
Thankfully, tank failure is not imminent, giving us a little time to plan. Our current water tank infrastructure presents us with two major issues: 1) the existing tanks are of inadequate height to serve the Town’s current and future water needs; and 2) the tanks are very old and nearing the end of their useful lives. The greatest water supply risk facing the Town is due to the inadequacy of the height of the tanks, which nearly ran dry during the drought of 2016. The Town was extremely lucky to avoid a catastrophic water failure in 2016, but counting on luck is no way to run a water system.
All of our water tanks are old; on average, nearly 80 years old. Since we know that we will need to replace them soon anyway, we want to be prudent and take future needs into account in designing new tanks. We continue to maintain Paines Hill Tank, our most vulnerable tank, but we have reached the point where replacement makes more sense than expensive repairs. Paines Hill, which is a concrete tank, is of an old, outdated design and cannot be repaired to provide any meaningful service life: it is at the end of its serviceable life. Even if this tank were repaired, it would require constant ongoing repairs because of the continuous deterioration that will occur. Repairs on this tank will become increasingly expensive and will provide diminishing returns. Paines Hill Tank is our largest tank; it is the lead tank of the entire water system. The failure of this tank would be catastrophic. The bottom line is that it is time to replace the Paines Hill tank.
Regarding the other two tanks, Cat Rock and Doublet Hill, we could maintain those tanks for a few more years. Generally, painting a tank can give it an additional 10-20 years depending on the quality of the application and environmental conditions. However, as noted above, repairing the tanks without making them higher does not address the Town’s critical need for active storage capacity.
Replacement of the Paines Hill Tank was listed as the highest priority action item and is still the Town’s first priority. (Plan section 8.3.1.) Active storage volume is a function of the height of the water tanks. The tanks all need to be the same height eventually because they function together as a single system, and the system is only as effective as its lowest tank. Increases in tank height also require improvements in pumping to lift water to the new, higher, elevation. As it happens, the main pump station is also due for an upgrade. It is a fortuitous coincidence that the pumping system needs to be replaced at the same time the Town needs to raise its tank elevations.
After replacing the tanks and making some smaller, localized water system investments, the Plan’s next priority is to add a second, redundant, connection to the Massachusetts Water Resources Authority (MWRA), the source of the Town’s water. We should note that the MWRA pipeline has not had any reported breaks and appears to be in good condition. In the unlikely event that the MWRA connection fails, the MWRA, working with the Town, has the capacity to remedy any breakdown within a very short time, likely within hours or at most a day. The MWRA has initiated a process to coordinate with Weston and the Town of Wellesley regarding the secondary line, and the Town is taking preliminary steps to address the issue of the redundant pipe. The recommendation for a second MWRA line is for contingency purposes only and is thus has a lower priority than increasing the active storage in our tanks. Our ability to provide water and fire protection, and to protect houses and businesses, is more important than the addition of a redundant pipe to back up an existing pipe that shows no signs of imminent failure. We have plenty of water; what we lack is the storage capacity to use it.
We have been asked whether adding a second feed main from the MWRA that would operate in parallel with the existing pipe, and adding a fourth pump to the pumping station, would increase the water system’s reliability and capacity. The answer is that it would not, because the Town’s existing pump station has adequate pump capacity now, and pumping alone cannot remedy the lack of storage capacity; only additional water tank height can do that.
Water conservation is a goal we should all strive for, but our aspirations to be better water stewards is not reliable enough for an engineering design. Weston can and should increase its promotion of conservation to reduce water use, and we have taken steps to encourage water conservation. The Town requires green building certification standards for new municipal buildings. For houses that come under Planning Board review, the Town mandates the use of water efficient fixtures and “smart” irrigation systems for newly constructed or renovated homes. The Select Board has established a three-tiered water rate system so that consumption of water above certain thresholds is charged at much higher rates.
Conservation of water might help Weston lose the distinction of having the highest per capita water consumption in the state. Water use in Weston is largely driven by lawn irrigation. Average daily demand for water during the summer months increases between 35-50% over average annual water use. Education of residents regarding the detrimental impact of large lawns on our water consumption rates may help to bring down water consumption. However, unless water conservation is mandated and enforced, which will be very unpopular and difficult, any reduction in water use would be purely speculative and could not form the basis for design of a water system. Further, the reduction in water usage by conservation will not change our need for additional water storage capacity.
The water that is “stored” in the tank is like the savings in a bank account. It is there for the times that current demand exceeds current pumping capacity and when needed for firefighting purposes. When there is no storage capacity (e.g., savings), pumps have to work nonstop to provide water into the tanks as fast as demand draws it out. Further, the volume of water needed to fight a fire, on top of daily water usage, is significant and can only come from storage. When a fire occurs on a day of peak demand, when water users are drawing water out as fast as it is pumped into the tanks, water to fight the fire must come from water stored in the tank. The requirement that water for firefighting come from water stored in the tank is a standard condition of water engineering, in addition to being required by the State and the Insurance Services Office that sets the Town’s insurance rates.
If water in the tanks is flowing out faster than it is pumped in, the level of water in the tanks will drop. During the drought of 2016, there were only 30 inches of water left in the bottom of the Paines Hill tank. This would not have been enough to fight a fire if one had occurred in that moment. We were lucky to avoid a disaster. It was our wake-up call to address the system’s deficiency.
The storage capacity of the tank is directly related to the height of the water tank and the height of the buildings that it serves. If buildings are located as high as, or higher than the tank, the water level in the tank must remain as high as possible to maintain the proper pressure.
In technical terms, the lack of active storage in the system is directly related to the maximum serviceable grade line (or elevation) at which the system can provide customers with a reliable minimum pressure. As discussed in detail in Section 5 of the Plan, Weston has a significant deficit of active storage, or usable water volume, beyond daily needs. The active storage is based on the operational range of the tank and the service elevations of the system’s customers; it is not the same as the total volume of water in the tank. Under current conditions, in order to maintain service to higher elevations, the pumps run continuously during times of high demand to keep the tanks as full as possible.
Water tank height is what provides water pressure. More height is needed to serve customers close to the tanks, who currently have inadequate pressure.
The Plan suggests that the Town’s current yearly pipeline replacement program has been underfunded. The recommendation is that Town should target replacement of 1-2% of the total system length per year, so that the total system is fully replaced every 50-100 years. The Plan recommends that the yearly pipeline replacement budget be increased to a minimum of $1.8M per year. This suggestion was reviewed in light of the Town’s experience with pipe conditions and maintenance. The useful life of distribution system piping is impacted by several factors: pipe material, water quality and hydraulic conditions such as water pressure and velocity. The Town believes that the distribution system is in relatively good shape and that our investments in the pipeline program are appropriate.
The Town has in fact been increasing its investment in the water distribution system: we budgeted $678K for this purpose in FY 23, and are proposing $475k in FY 24. The Town has been working diligently to replace the few remaining Asbestos Cement pipes in the distribution system. Only about 3% of the Town’s pipes remain Asbestos Cement.
We cannot solve our water issue by relying on pumps. It is true that in very small water systems consisting exclusively of residential customers, pumps can be sized to provide peak-hour demand and firefighting volume. In fact, that is exactly how our small Black Oak pump station is designed to work. But this station only serves a very small population. In large systems, meeting peak-hour demand and firefighting volume would require prohibitively large and expensive pumps.
Under standard water engineering practice, pumps are designed to meet the maximum-day demand, and tank water storage is designed to supply the peak-hour demand above the capacity of the pumps. To instead design a system that relies on pumps to meet the peak-hour demand would be complex, requiring more pumps to supply a greater range of flows. Not only would we need more pumps, but the pumps would need to be more powerful. Furthermore, system piping would need to be significantly upsized to convey the significantly higher flows while minimizing friction losses which further increases the size of pumping systems needed , all of the electrical systems in the pump station would need to be increased, the capacity of the emergency generator would need to be increased, and the control systems for the additional pumps would need to be upgraded. Using pumps rather than tank storage to meet peak-hour demand would be complicated and less reliable than using water tanks with adequate storage capacity. Furthermore, the Insurance Services Office, which sets the Town’s insurance rates, does not consider reliance on pumps alone to be a suitable or reliable provider of water for large fire flows. The State also requires that water needed for firefighting come from water storage.
Engineering practice and state guidance both dictate that pumps be designed to meet only the maximum-day demand. Water demands that are higher than that, such as peak-hour demand, should come from water storage. Our pumps were designed so that one pump meets average-day demand, and two pumps meet maximum-day demands. The third pump is a backup pump.
Besides being the economical way to provide water pressure, storage from a water tank of adequate size and elevation harnesses the power of gravity, which is much more reliable than electric pumps. Gravity works even when the power goes out. That is why tanks of adequate size and height are the standard, tried and true approach to the provision of municipal water. As climate change increases our need for resilient systems in the face of ever-fiercer storms, a water system based on the power of gravity rather than the electrical grid is by far the wiser approach.
Weston should consider requiring a review of all new homes proposed at higher elevations to determine the impact they will have on the capacity of the system to provide water service. Unlike other towns, Weston does not require the water department to review new development and approve or deny the development based on the system’s hydraulic capacity.
The Town should consider curtailing any future development until storage can be added to the system to ensure that adequate firefighting capacity is available.
The Water Department prefers to maintain a three-tank system. A three-tank system allows the Town to provide better water service by spreading the storage throughout the system. If one tank requires repairs or maintenance, the other two tanks can meet the Town’s needs temporarily. On the other hand, if we had only two tanks, taking one tank out of service would reduce Weston’s storage by half and would mean that we would need to build even larger tanks to compensate for the smaller size of the system.