Cambridge water treatment plant
Nov. 17th, 2008 11:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
magidI toured the Walter J. Sullivan Water Purification Facility tonight. It's a new building, completed in 2001, and I'd never managed to see the building before. It's quite nice.
The first thing I noticed inside is the floor of the lobby, which is a map of the water system in Cambridge. There are brass strips in different widths showing the diameter of the pipes (a nice touch: over on one side, there are filled-in cross-sections of pipe, both visual reminders and places to sit), with parks, ponds, fountains, and pools shown in different colors. Near a lot of the schools there are 15 water value plates, each with a different image on it, the same size as the ones on the streets/sidewalks, designed to encourage kids to find them. It's a fascinating map, showing the three huge pipes that the MWRA uses as they cross Cambridge, where there are pipes under the Charles, and things like the curious triplicate nature of the pipes under Magazine St. (I asked about that, among other things, and the guide didn't know.).
Side note: after 9/11, some security experts suggested they black the floor, so terrorists wouldn't be able to get critical information about the water supply. The city decided that this was not necessary. (And as the system changes, pipes replaced, and so on, it will become a less accurate picture over time.)
Also in the lobby: a fountain made of parts of the old building (in use 1922-1998), and riffle plates (used to aerate water), and a bubbler attached to an outside water fountain. The art was commissioned as part of Cambridge's 1% for art program.
Upstairs, there's a huge painting that's almost an aerial map of the area, with Cambridge, the watershed, and other relevant parts of the water system in bold colors, the rest of the region faded back. Next to it are two bubblers, labeled "Free Samples" of Cambridge water :-).
The basic outline of how water works in Cambridge: water comes from the watershed area out in the Waltham-Lincoln area (purchased back in the 1860s after the Civil War), from Stony Brook and Hobbs Brook (I never knew that those reservoirs I could see next to Rte. 128 near the Trapelo Rd. exit were Cambridge water), where is is much higher than the city, through an aqueduct (roughly paralleling the Charles on the north) to Fresh Pond, which is 16 feet above sea level (and mostly about 30 feet deep, though in spots it's 40-50 feet deep, a kettle pond left by a melting glacier). From the pond, the water is taken into the facility, treated (more detail on this later), then piped up to Payson Park Reservoir, 87 feet above sea level (bought by the city in 1890). There are two covered holding tanks there, each holding 16 billion gallons of water, each about a day's supply for the city. The facility is the city's largest user of electricity, with bills running about $100K/month, 60% of which is the cost of pumping the water uphill, using 500 horsepower pumps. If there are problems, there's redundancy in the system, and this gives at least a day to fix things. If it's something larger, the back up is to use MWRA water, which is what was done for the 2.5 years that it took to build the facility (costing the city $15 million for water from the MWRA, plus $56 million for the building).
When there is excess water in the system, it flows out into the Charles. There are a couple of reasons the water isn't used elsewhere, having to do with it being far from the treatment facilities for other towns (read: MWRA, with Quabbin and Wachusett reservoirs in the middle of the state), and Cambridge being lower than other towns around. Other people on the tour seemed concerned that this water was being 'wasted,' somehow.
Oh, and the reason that Cambridge built this new plant rather than joining the MWRA like the other 40 communities around here is that there is a state regulation about not abandoning viable water sources.
The facility treats about 14,000 gallons of water a minute, using carbon particle filters, among other treatments (the MWRA doesn't do this, because their water is purer at the source). First, though, Fresh Pond is aerated, which helps keep the manganese that comes from the surrounding soil from going into solution (mostly done at night, to work with the plant respiration cycles. However, it's not necessary to do this step during the winter.). Once the water is brought in, there are a number of treatments, starting with adding ozone to oxidize any manganese, and alum(inum?) to pick up other particles. There's a dissolved air filtration system, and an intermdiate ozone treatment (caveat: my science knowledge is not extensive, and there was too much information flying by fast, so I'm likely missing a step or two in this description). There's two points in the cycle when the water is disinfected, and it's treated with amonia and fluoride (1 ppm required by law) as well. The pH is raised from 6 to 9.2, to minimize leaching from pipes. The whole process takes about 4 hours.
We saw the pipes and tubes and such, and one of the filtering tanks where stuff is floated to the top, looking rather like oatmeal. One of the people who works there showed how that sludgy stuff is taken off the top (and sent into the sewer system, though they do have 'good' bacteria to eat the waste from another step in the process), with the water underneath white from all the oxygen in it. There were doubled life preservers hanging by the end of each 16-foot-deep tank, necessary because with so much air in the water, were someone to fall in, they'd sink.
The watershed area is bounded on one side by Rte. 128, and the runoff from the highway, especially in the winter, is why Cambridge water is saltier than MWRA water, about 60 mg/L (I think that's the correct second unit) compared to about 20 mg/L. I obviously do not have a very sophisticated palate, since I've never noticed this.
There are some wells in Cambridge: apparently Harvard and MIT use a few of them for irrigation purposes, though not for potable water.
There was talk about bottled water (overpriced and not as carefully regulated), distilled water (not enough stuff in it), and reverse osmosis water (ditto). Someone asked about using a Brita, and the answer was that some people notice the chlorine used in the process, so for them it definitely makes sense. If not, the water's already been filtered at the plant, so it's not necessary. Now that the holding tanks at Payson Park are covered, there's not a lot of chlorine used, 2mg/L compared to 7-8 mg/L when they were open.
We went into the labs, where they test the water. One lab has a number of taps running continuously, labeled with which part of the process it's being diverted from. In addition to this sampling, there are daily samples from the watershed area and from Payson Park. There are also 100 samples monthly from end users around Cambridge, none of them individual due to the trickiness of getting access. Samples are taken from fire houses, schools, municipal buildings, hospitals, the universities, and one of the hotels (these change, but the state has to approve all changes).
All of these samples are tested for chemical issues and microbiological issues. We went into the labs for each kind of testing. On the microbiological side, there are a variety of coliforms that could lead to concern. For a general test, the water is filtered through a filter that has holes 0.45 microns wide. The residue is cultured on a sugary food (tryptic soy agar) for 24 hours in a warm place (35 C being about body temperature). This gets the colonies up to visible size. We saw cultured samples from the watershed and after treatment, and there are a lot of coliforms being gotten out of the water supply! The two particular coliforms that can lead to healh issues are fecal coliforms, which have a similar culturing process, though warmer (45 C) and wetter, and E. coli, which has a completely different process, involving water in little 'bubbles' after adding a reagent to make them visible under black light.
On the organics side, there are tests to check the levels of a lot of different things, including nitrates and nitrites, bromates and bromites (if I've got that correct), plus a lot of other things. The lab is recertified each year as well.
A bonus for Cambridge residents: if there are concerns about lead in the water (such as elevated levels when kids are tested), there are kits available at the facility with directions for how to collect samples to be tested, and they will test the water there. It takes about 2 weeks, but (a) it's free, and (b) they'll call if there are results of concern. (Interestingly, there are two bottles, one for collecting water than has been sitting in pipes for at least 6 hours, to test the house pipes, and one for collecting water after the temperature has gone cold, to test the city's pipes.)
There was a bit of MWRA rivalry, which basically seemed to boil down to the MWRA doesn't filter the water, because the source water is purer, but they have to keep showing test results to keep this status. My impression is that the Cambridge people think the MWRA is going to have to install filters someday, though it's likely good that they didn't have that expense at a time that they couldn't afford it. We were told about the MWRA shooting at birds with BBs in the winter, to keep them from hanging out on the ice, generating waste that goes into the water, and thus requiring treatment.
The first thing I noticed inside is the floor of the lobby, which is a map of the water system in Cambridge. There are brass strips in different widths showing the diameter of the pipes (a nice touch: over on one side, there are filled-in cross-sections of pipe, both visual reminders and places to sit), with parks, ponds, fountains, and pools shown in different colors. Near a lot of the schools there are 15 water value plates, each with a different image on it, the same size as the ones on the streets/sidewalks, designed to encourage kids to find them. It's a fascinating map, showing the three huge pipes that the MWRA uses as they cross Cambridge, where there are pipes under the Charles, and things like the curious triplicate nature of the pipes under Magazine St. (I asked about that, among other things, and the guide didn't know.).
Side note: after 9/11, some security experts suggested they black the floor, so terrorists wouldn't be able to get critical information about the water supply. The city decided that this was not necessary. (And as the system changes, pipes replaced, and so on, it will become a less accurate picture over time.)
Also in the lobby: a fountain made of parts of the old building (in use 1922-1998), and riffle plates (used to aerate water), and a bubbler attached to an outside water fountain. The art was commissioned as part of Cambridge's 1% for art program.
Upstairs, there's a huge painting that's almost an aerial map of the area, with Cambridge, the watershed, and other relevant parts of the water system in bold colors, the rest of the region faded back. Next to it are two bubblers, labeled "Free Samples" of Cambridge water :-).
The basic outline of how water works in Cambridge: water comes from the watershed area out in the Waltham-Lincoln area (purchased back in the 1860s after the Civil War), from Stony Brook and Hobbs Brook (I never knew that those reservoirs I could see next to Rte. 128 near the Trapelo Rd. exit were Cambridge water), where is is much higher than the city, through an aqueduct (roughly paralleling the Charles on the north) to Fresh Pond, which is 16 feet above sea level (and mostly about 30 feet deep, though in spots it's 40-50 feet deep, a kettle pond left by a melting glacier). From the pond, the water is taken into the facility, treated (more detail on this later), then piped up to Payson Park Reservoir, 87 feet above sea level (bought by the city in 1890). There are two covered holding tanks there, each holding 16 billion gallons of water, each about a day's supply for the city. The facility is the city's largest user of electricity, with bills running about $100K/month, 60% of which is the cost of pumping the water uphill, using 500 horsepower pumps. If there are problems, there's redundancy in the system, and this gives at least a day to fix things. If it's something larger, the back up is to use MWRA water, which is what was done for the 2.5 years that it took to build the facility (costing the city $15 million for water from the MWRA, plus $56 million for the building).
When there is excess water in the system, it flows out into the Charles. There are a couple of reasons the water isn't used elsewhere, having to do with it being far from the treatment facilities for other towns (read: MWRA, with Quabbin and Wachusett reservoirs in the middle of the state), and Cambridge being lower than other towns around. Other people on the tour seemed concerned that this water was being 'wasted,' somehow.
Oh, and the reason that Cambridge built this new plant rather than joining the MWRA like the other 40 communities around here is that there is a state regulation about not abandoning viable water sources.
The facility treats about 14,000 gallons of water a minute, using carbon particle filters, among other treatments (the MWRA doesn't do this, because their water is purer at the source). First, though, Fresh Pond is aerated, which helps keep the manganese that comes from the surrounding soil from going into solution (mostly done at night, to work with the plant respiration cycles. However, it's not necessary to do this step during the winter.). Once the water is brought in, there are a number of treatments, starting with adding ozone to oxidize any manganese, and alum(inum?) to pick up other particles. There's a dissolved air filtration system, and an intermdiate ozone treatment (caveat: my science knowledge is not extensive, and there was too much information flying by fast, so I'm likely missing a step or two in this description). There's two points in the cycle when the water is disinfected, and it's treated with amonia and fluoride (1 ppm required by law) as well. The pH is raised from 6 to 9.2, to minimize leaching from pipes. The whole process takes about 4 hours.
We saw the pipes and tubes and such, and one of the filtering tanks where stuff is floated to the top, looking rather like oatmeal. One of the people who works there showed how that sludgy stuff is taken off the top (and sent into the sewer system, though they do have 'good' bacteria to eat the waste from another step in the process), with the water underneath white from all the oxygen in it. There were doubled life preservers hanging by the end of each 16-foot-deep tank, necessary because with so much air in the water, were someone to fall in, they'd sink.
The watershed area is bounded on one side by Rte. 128, and the runoff from the highway, especially in the winter, is why Cambridge water is saltier than MWRA water, about 60 mg/L (I think that's the correct second unit) compared to about 20 mg/L. I obviously do not have a very sophisticated palate, since I've never noticed this.
There are some wells in Cambridge: apparently Harvard and MIT use a few of them for irrigation purposes, though not for potable water.
There was talk about bottled water (overpriced and not as carefully regulated), distilled water (not enough stuff in it), and reverse osmosis water (ditto). Someone asked about using a Brita, and the answer was that some people notice the chlorine used in the process, so for them it definitely makes sense. If not, the water's already been filtered at the plant, so it's not necessary. Now that the holding tanks at Payson Park are covered, there's not a lot of chlorine used, 2mg/L compared to 7-8 mg/L when they were open.
We went into the labs, where they test the water. One lab has a number of taps running continuously, labeled with which part of the process it's being diverted from. In addition to this sampling, there are daily samples from the watershed area and from Payson Park. There are also 100 samples monthly from end users around Cambridge, none of them individual due to the trickiness of getting access. Samples are taken from fire houses, schools, municipal buildings, hospitals, the universities, and one of the hotels (these change, but the state has to approve all changes).
All of these samples are tested for chemical issues and microbiological issues. We went into the labs for each kind of testing. On the microbiological side, there are a variety of coliforms that could lead to concern. For a general test, the water is filtered through a filter that has holes 0.45 microns wide. The residue is cultured on a sugary food (tryptic soy agar) for 24 hours in a warm place (35 C being about body temperature). This gets the colonies up to visible size. We saw cultured samples from the watershed and after treatment, and there are a lot of coliforms being gotten out of the water supply! The two particular coliforms that can lead to healh issues are fecal coliforms, which have a similar culturing process, though warmer (45 C) and wetter, and E. coli, which has a completely different process, involving water in little 'bubbles' after adding a reagent to make them visible under black light.
On the organics side, there are tests to check the levels of a lot of different things, including nitrates and nitrites, bromates and bromites (if I've got that correct), plus a lot of other things. The lab is recertified each year as well.
A bonus for Cambridge residents: if there are concerns about lead in the water (such as elevated levels when kids are tested), there are kits available at the facility with directions for how to collect samples to be tested, and they will test the water there. It takes about 2 weeks, but (a) it's free, and (b) they'll call if there are results of concern. (Interestingly, there are two bottles, one for collecting water than has been sitting in pipes for at least 6 hours, to test the house pipes, and one for collecting water after the temperature has gone cold, to test the city's pipes.)
There was a bit of MWRA rivalry, which basically seemed to boil down to the MWRA doesn't filter the water, because the source water is purer, but they have to keep showing test results to keep this status. My impression is that the Cambridge people think the MWRA is going to have to install filters someday, though it's likely good that they didn't have that expense at a time that they couldn't afford it. We were told about the MWRA shooting at birds with BBs in the winter, to keep them from hanging out on the ice, generating waste that goes into the water, and thus requiring treatment.
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no subject
Date: 2008-11-18 12:37 pm (UTC)no subject
Date: 2008-11-18 02:44 pm (UTC)The Friends of Fresh Pond have other events during the year (some not on Shabbat, even), including talks on geology, birding walks, a mushroom walk (wish I'd known about that beforehand!), etc.
no subject
Date: 2008-11-18 01:35 pm (UTC)no subject
Date: 2008-11-18 02:47 pm (UTC)no subject
Date: 2008-11-18 03:00 pm (UTC)no subject
Date: 2008-11-19 12:48 am (UTC)1) They use Ozone rather than Chlorine for 'primary disinfection'; it oxidizes lots of stuff, including stuff that may be alive that you'd rather have dead. The benefit is that you don't get nasty Carbon-Chlorine compounds in the drinking water. The do end up adding Chlorine for 'secondary disinfection' (keeping stuff from growing in the water) but much less than is needed for primary disinfection.
2) The water fountain outside of the facility has some of the best tasting water around. All the goodness of that low Cl treatment, without having gone through lots and lots of pipes.
3) I think that Cambridge should sell bottled water, and catch some $$ from the marketing craze. Most bottled water is just municipal water, and they have good stuff at that treatment plant.
-ETR
no subject
Date: 2008-11-19 03:44 am (UTC)2. I didn't try the fountain outside, though I saw the bubble tank inside the lobby that goes with it. (And, I admit, kept wondering what it would be like to host a party in the lobby.)
3. They had a hard enough time fitting the new plant onto the 7 acre footprint of the old plant; I don't know where the bottling would happen!
A friend visiting from NYC this weekend said that, while it didn't taste as good as her home water, it was much better than Miami water...