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Water Testing Results
Summer 2007

Souhegan and Merrimack Rivers

George May's Latest Results Summary

The Souhegan Watershed Association monitors the entire length of the Souhegan River and part of the Merrimack River for their aquatic health. Water samples are tested for pH, phosphorus, dissolved oxygen, temperature, and bacteria. Weather and streamflow information was also recorded when water samples are collected. Previous results, beginning in 1997, are available in reports that can be found in local libraries. Summaries and original results are available here.

This monitoring program is conducted by trained volunteers who believe in cleaner rivers. Financial support for the program comes from your memberships and donations. If you would like to help continue this monitoring effort, please contact George May at 883-3409 or "georgemay (at) comcast (dot) net" or send a check to SWA, PO Box 1474, Merrimack, NH 03054.

E-Coli Bacteria Counts

Our E-coli samples are prepared and counted by professionals at the local wastewater treatment plants in Greenville, Merrimack, Milford, and Nashua on a volunteer basis. The results are reported as the number of e-coli bacteria colonies observed under a microscope in 100 ml of water. Bacteria levels below 88 colonies per 100 ml. are considered safe for public swimming areas. Anything above that level may cause ear and eye infections, diarrhea or other gastrointestinal problems in a percentage of swimmers. These bacteria numbers being reported are good for only a few days. They do indicate the general health of the river water at a particular moment in time. The next measurement can be considerably different, depending on water level and temperature, and what has recently washed, flowed, or been poured into the river. The current E-coli results this year are available here.

Dissolved Oxygen Measurements

Dissolved oxygen is "breathed" by fish and insects that live in the water. Dissolved Oxygen requirements for different species vary greatly, even if only fish are considered. One of the more sensitive family groups is trout. The lower limit for them is about 5 mg/L (or 5 ppm). The maximum value attainable is called O2 saturation. The concentration of O2 equal to the saturation limit in water increases with DECREASING temperature and INCREASING pressure. At 1 atmosphere pressure and 20 degrees centigrade the concentration of saturated O2 is 9.1 mg/L, while at 1 atmosphere pressure and 25 degrees centigrade O2 is saturated at 8.2 mg/L. The rate of oxygen usage, the rate of oxygenization (turbulence) and the rate of mixing of the different strata of water all contribute to surface oxygen levels. The simplified conclusion is that adequate oxygen levels indicate a healthy, balanced river habitate.

Cumulative 2007 E-Coli Data

September 18th Report

About 30 volunteer monitors have collected river samples from the Merrimack and Souhegan Rivers to be tested for E. coli bacteria, dissolved oxygen, phosphorus, temperature and turbidity every two weeks all summer long. Some have been doing it as a program of the Souhegan Watershed Association and Merrimack River Local Advisory Committee for the past 11 years. The data collected has been instrumental in cleaning up pollution sources on both of these rivers. "Both rivers are pretty clean right now," according to George May, SWA president, "but there is still pollution that we need to identify and eliminate. Every year things get a little bit better thanks to our dedicated volunteers."

One of the Souhegan monitors put it poetically on the final test day. "As I approached my site, a heron flew downstream and disappeared into the mist rising golden from the water. It felt like a sign of gratitude for our work."

May apologized for the lack of results for this past week. "All of the samples have to be processed within a short period of time and that did not happen with the majority of the bacteria samples and all of the dissolved oxygen samples. They were all collected, but there was a mix-up in the delivery," he said.

The results for the E. coli testing done on the Nashua River showed that the New Hampshire stretch of the river to be fairly clean compared with the Massachusetts section. Numbers below 88 are considered clean. These tests are collected by the Nashua River Watershed Association on a monthly basis. There will be one more test for the Nashua. This was the final test for the Merrimack and Souhegan Rivers for this season.

Volunteers are always needed to collect these water samples. If anyone is interested in helping next season, he can contact for more information. Donations are always welcome too to help keep the program going. Past results are available on the Souhegan website at

All of the testing for bacteria and dissolved oxygen is done by the wastewater treatment labs in Nashua, Merrimack, and Milford. Phosphorus testing is done by the Department of Environmental Services in Concord.

September 4th Report

The water quality testing program of the Souhegan Watershed Association and Lower Merrimack River Local Advisory Committee showed very clean E. coli readings on both the Souhegan and Merrimack Rivers this week, but the river levels were as low as seen for some time. Several monitors noted that the Souhegan was as low as they'd ever seen it. Flow on the Souhegan should be around its historical average of 37 cubic feet per second (cfs) at this time of year but its reading on the USGS gauge was 21 cfs on Tuesday when the tests were taken according to George May, SWA president. May also noted that the river had been pretty close to that same level for more than a week which he thought indicated that it was about as low as it could possibly get. "You can walk across much of the Souhegan headwaters right now," he noted.

The Merrimack River was flowing at about half its historical average also, May noted, but the river level is largely determined by the Pawtucket Dam in Lowell which ponds it up so the lack of flow is not as noticeable in the Nashua area.

The Merrimack River continued to show very acceptable E. coli counts again this week, just as it has all summer and most of last year, May noted. Every one of the sites tested between Manchester and Tyngsboro were well below the 88 level required for public swimming. Several of the sites showed no detectable bacteria at all. The tests for dissolved oxygen, which is required for healthy fish and plant life, were also excellent. May noted, however, that they test for only certain chemicals and that the Merrimack may harbor other harmful chemicals that we don't test for.

The Souhegan River also had very clean bacteria counts this week. Only two of the sites tested exceeded the 88 level. The site at the bridge on Rte 122 next to the Amherst Country Club tested at 220, the highest noted on the river. The site at Highbridge in New Ipswich showed no bacteria at all this week; two weeks ago the reading here was an exceptionally high 686 and a month ago was 579. "We're looking at this site now and hope that it stays cleaned up in the future," said May.

May also noted that quite a few of the sites were not tested this week due to volunteers going back to school, work, or on vacation. He also suggested that citizens interested in helping out with testing on one site on one of the two rivers can contact him now to help out next year. The next test on September 18 will be the last one of this year.

The labs at the Milford, Merrimack, and Nashua Wastewater Treatment Facilities perform all the bacteria and dissolved oxygen tests from samples collected and delivered by SWA volunteers.

August 21st Report

The Merrimack, Souhegan and Nashua Rivers all produced relatively clean results when tested for E. coli bacteria recently. There were a few hot spots on the Souhegan and Nashua Rivers, but on the whole they were quite acceptable according to Karen Mattor, coordinator of the Souhegan Watershed Association's water quality monitoring program. The Merrimack tested very clean, as it usually does, according to Mattor. The highest reading on the Merrimack was 25 near the Sagamore Bridge. Any number less than 88 is considered clean. Several of the Merrimack River test sites between Manchester and Tyngsboro showed no bacteria at all.

The Souhegan River also tested at an acceptable level throughout most of its length, from Ashburnham, MA, to Merrimack, NH. All five of the popular swimming holes on the river came in at a clean level. However, the lack of rain, which probably accounts for the clean readings, meant that all of the volunteer testers noted that the water level was extremely low. The average flow on the Souhegan at this time of year is a very low 43 cubic feet per second; when the tests were taken on Tuesday, the flow was an even lower 27 cfs. Some of the testers noted that you could almost walk across the river at certain sites without getting your feet wet.

The flow level on the Merrimack River was also quite low -1180 cfs, but the level of the river is controlled by the Pawtucket Dam in Lowell so it appears at the same height most of the time. What was significant was that the Amoskeag Dam in Manchester was releasing and holding back water so that the flow fluctuated wildly between 1000 and 2000 cfs every day last week.

The only test site of concern on the Souhegan River was at Highbridge in New Ipswich, near Warwick Mills. The reading there was 686, way over the 88 level considered acceptable for swimming or bathing. There has been a pattern of very high readings at this site this summer. "There is something there that is not acceptable and that will have to be looked at," said George May, SWA president. He also noted that the high readings seen below downtown Greenville at the testing two weeks before seemed to have cleared up. The readings in this area were well below 88 this time.

The Nashua River is tested throughout its length by the Nashua River Watershed Association once a month. The last test was done on Saturday the 18th, just three days prior to the Merrimack and Souhegan, so the weather was comparable. The highest reading of any of the sites tested in the NH section of the river was near BAE on Canal Street in Nashua. The reading there was 145. The Nissitisit River, one of the Nashua's main tributaries, had the next highest readings near the West Hollis Road bridge. The reading there was 135. There has been a pattern here also of higher than acceptable readings.

August 76th Report

Normal summer weather and normal summer flows produced normal E. coli levels on the Souhegan and Merrimack Rivers when tested last Tuesday according to Karen Mattor, coordinator of the Souhegan Watershed Association water quality monitoring program. With the exception of two areas on the Souhegan River, both rivers had very acceptable E. coli levels, indicating safe swimming and bathing. SWA, which sponsors the testing program, looks for 88 as the maximum E. coli bacteria level acceptable for swimming. None of the sites tested on the Merrimack River exceeded that level. Many of the sites showed no trace of bacteria at all. This is very unusual but indicates how clean this river has become.

The Souhegan had two areas that showed higher bacteria levels than are healthy. The first was in the stretch downstream of Greenville where the levels were around 400; the second was in the stretch downstream of Milford center where the levels were around 170. The area upstream of the Milford Oval near the Boys and Girls Club tested at a reasonable 92, well below higher test numbers seen there earlier in the summer. The Souhegan cleaned up completely by the time it flowed to the Merrimack. All three of the sites tested in Merrimack showed no trace of bacteria at all.

Tests are performed every two weeks all summer long by a group of volunteers and bacteria tests are done in the labs of the wastewater treatment plants of Milford, Merrimack, and Nashua. There is always a need for additional people who could devote half an hour in the morning every other week through September. Anyone interested can contact for more information. Volunteers this week noted lots of wildlife, flowers, fishermen, boaters, and even swimmers early in the morning. Unfortunately, a volunteer also reported a large number of dead fish floating in the Merrimack just upstream of the mouth of the Souhegan and several noted trash left at various access points along the Souhegan. Another volunteer reported a continuing oil slick oozing out of the banks of the Beazer property on the Merrimack just upstream of Greeley Park. This has been observed all summer long.

July 24th Report

The Merrimack and Souhegan Rivers are back to their normally expected E. coli levels after having horrible E. coli levels at the last test two weeks ago according to Karen Mattor, coordinator for the water quality testing program sponsored by the Souhegan Watershed Association and Lower Merrimack LAC. Testing on both rivers showed they are both in good health for swimmers and bathers. Levels higher than 88 are not considered safe for public swimming beaches. None of the sites tested on the Merrimack between Manchester and Tyngsboro were above this level. And only a few sites on the normally higher-reading Souhegan River were above 88. A test at Highbridge in New Ipswich came in at 579, but by the time the river got downstream of Greenville, it had recovered to a very acceptable 21. The Horseshoe in Wilton, a popular swimming hole, tested at 20. Even Wilton, where the river comes through the densely packed downtown area tested at only 40. Readings increased above the acceptable level through the densely packed downtown Milford area. Readings taken above and below the Oval respectively were 140 and 120. "These are still relatively benign readings for where the river slows down and the riverside population increases," said Mattor. "There was some rain the day before the tests and that usually brings the E. coli levels up," she said. "These are generally acceptable numbers."

The Nashua River Watershed Association conducts volunteer monitoring on the entire Nashua River and all of its major tributaries on a monthly basis. The tests were done last weekend after a rainstorm that brought its E. coli counts up. The sites listed are only for the river and tributaries that influence the NH side of the border. Additional information can be found at

The volunteer monitors test every other Tuesday morning between 6 and 8 am. Besides E. coli, samples of water are tested for dissolved oxygen, phosphorus, temperature, turbidity and general observations. Testing is done in the Milford, Merrimack, and Nashua wastewater treatment plants and at the Department of Environmental Services in Concord. Monitors noted fishermen, boaters and even bathers out early Tuesday morning. One monitor noted a family of mink along the Souhegan near Wildcat Falls. Also it was noted that Cardinal flowers are in bloom.

There is still room for additional volunteers or donations to help pay for the tests. Interested citizens can contact Mattor at for more information.

July 10th Report

Swimming on the Souhegan or Merrimack Rivers after the heavy rainfalls at the beginning of the week was not a good idea. The regular E. coli bacteria tests done by the Souhegan Watershed Association and the Lower Merrimack Local Advisory Committee showed very high levels of bacteria on both rivers. The acceptable level of bacteria for NH public beaches is 88 colonies per 100 milliliters of water. A reading higher than that requires the beach to be closed until the levels go down. Readings on the Souhegan reached over 3000 at several sites tested.

High numbers were expected according to George May, SWA president. "E. coli counts almost always rise after heavy rainfalls when the bacteria and its sources get washed into the river." There were several heavy rainfalls within the three days prior to Tuesday morning's testing. The bacteria being tested for generally have a lifespan of three days. There was extremely heavy rain the day and night before the test. Parts of Wilton at high elevation had roads washed out and trees knocked over as this severe storm came through Monday evening. All of the volunteers that monitor the 20 different sites the length of the Souhegan noted how high the river had come up in just a day. Indeed, the Souhegan had been tracking its normal historic flow of about 60 cubic feet per second but rose to 300 by the time of the testing and continued to rise to 400 until 2pm on Tuesday.

The Merrimack also rose, but the monitors on the Tyngsboro end still noted that the river was low. This was caused by the lowering of the pond above the Pawtucket Dam in Lowell that backs the pond all the way back to Merrimack a couple weeks ago. The river will continue to fill the pond till it recovers its normal level within a few more days. The river actually rose from 1500 cfs, less than its historic average, to 3850 by the time of Tuesday's test and continued to rise to over 5000cfs until 10am on Tuesday.

E. coli readings on the Merrimack River are usually quite good according to May. "Usually all of the 13 Merrimack sites tested are acceptable - except when it rains a lot," he said. "Heavy rains can force the wastewater treatment facilities to release combined stormwater and untreated sewage directly to the river. This is when we see the bacteria levels go out of sight." There are 8 combined sewer outfalls in Nashua and 28 in Manchester. There was one short half hour release four days before the tests right after a rainburst, but all of the pollution should have been diluted before the testing according to May. Manchester also can dump combined sewage and stormwater into the river during heavy rains, but the people at the Manchester treatment plant didn't return a phonecall to see if there were any releases during the Monday storm. Both cities are under EPA orders to eliminate dumping into the river.

Monitors all noted how muddy the water was. In many cases they could not see the bottom even in shallow areas. The heavy rains washed lots of silt into the rivers and roiled the bottom so that it was quite muddy.

The monitoring program was joined by two new volunteers this week. But there is always room for more who could help. Testing takes about a half hour every other Tuesday morning. Anyone wanting to help can contact coordinator Karen Mattor at

In spite of the very foggy morning and high flow, monitors noted several fishermen and boaters who were out early. Several Great Blue Heron were also out fishing. And even a beaver was spotted near the Taylors Falls Bridge. Unfortunately, an oily slick was noted between Greeley Park and Taylors Falls. There is still creosote leaching into the river from the Beazer property upstream of Greeley Park and this may have caused the slick according to May. Trash and evidence of kids' partying was noted near Water Loom Pond on the Souhegan in New Ipswich.

Besides the E. coli, the program tests for turbidity, temperatures, dissolved oxygen, and phosphorus. E. coli counts are done by the labs at the wastewater facilities in Nashua, Merrimack, and Milford.

June 26th Report

Recent tests done for E. coli bacteria on the Nashua, Merrimack, and Souhegan Rivers show that all three rivers are fairly clean at this point in the summer. Several sites along the Souhegan through Milford showed higher that acceptable E. coli levels, but all other sites tested showed low levels of this dangerous bacteria. The highest level was seen at the site behind Lorden Plaza. The reading here was 400, well above the acceptable 88 level. The levels dropped to 110 at the next downstream site and continued to drop as the river continued downstream.

Flow on both rivers was lower than historical averages. The Souhegan was running at 73 cubic feet per second and the historical average for this date is 85 cfs. The Merrimack was running at 1820 cfs, below its average of 2600. Monitors on the lower part of the Merrimack noted how low the water was this week, but the Pawtucket Dam in Lowell is the reason for this. Boott Mills Hydro is replacing the flashboards on the dam and so began lowering the pond above the dam on Sunday, June 24. This pond extends all the way back to Merrimack. It is expected that the work on the dam will be completed by the end of this week and the pond will fill back to usual levels in the next couple of weeks.

Temperatures on both rivers are up to comfortable swimming temperatures. The Souhegan was 20C/68F; the Merrimack was 22C/72F. This means that the E. coli readings are more significant. E. coli readings above 88 are not acceptable for public swimming beaches. The state would require that any beach with counts higher than this be closed. There are no public swimming beaches on the Souhegan, Merrimack, or Nashua, but SWA uses the same standard to warn bathers on any of these rivers that they could experience diarrhea, eye and ear infections, or other medical problems. As the E. coli count increases, so does the percentage of swimmers who would experience illnesses. There are a number of 'swimming holes' on the Souhegan and Merrimack. The only one that had an E. coli count higher than the acceptable 88 count was the Amherst Canoeport on Boston Post Road. The reading here was 90, barely over the acceptable level. The Horseshoe in Wilton, a popular swimming spot, was not tested this week, but readings here have normally been good in all past years' tests. All of the other known swimming holes were acceptable. The level at Turkey Hill Bridge in Merrimack, for example, was too low to count, almost completely clean.

As the air and water temperatures have been rising, so has the activity monitors noted at their sites early on Tuesday morning. Fishermen, swimmers, dog walking, boating were all observed. Evidence of lots of wildlife was also reported, and is usually reported. Monitors in the upper reaches of the Souhegan were also treated to seeing the Mountain Laurel and water lilies in full bloom. Several Souhegan monitors also noted how clear the water looked this time.

Besides the E. coli, the program tests for turbidity, temperatures, dissolved oxygen, and phosphorus. All tests are performed by volunteers with the Souhegan Watershed Association or the Nashua River Watershed Association. E. coli counts are done by the labs at the wastewater facilities in Nashua, Merrimack, and Milford. There may still be volunteers needed for some sites. Anyone willing to help can contact coordinator Karen Mattor at karenmattor at gmail dot com.

June 12th Report

The Souhegan Watershed Association and Lower Merrimack River Local Advisory Committee will continue testing both rivers for the eleventh year in a row thanks to volunteers who responded to a request published in a Telegraph article early in the spring. After several years coordinating the water testing program, Dr Ken Butenhof had to give up the all-volunteer program. Luckily three talented people stepped forward and will share the efforts required to continue the program. Karen Mattor, an Environmental Science teacher at NH Community Technical College and longtime site monitor, will be the overall coordinator for all the volunteers; Gene Kuczewski, a retired biology teacher, will be responsible for all the equipment and biological testing; and John Slater, Assistant Professor in Engineering, Math, & Science, at Daniel Webster College, will collect and do all the data analysis.

After assuming her role, Ms. Mattor was awed by the tremendous amount of work that her predecessor Ken Butenhof managed to do. "I've been in touch with Ken almost daily trying to understand how everything fits together. He's just been great in helping us get up and started again this season. We are using all the data sheets and organization that he created. We couldn't have done this without him. And Ken is still monitoring two sites in Manchester for the program."

The testing program will monitor 20 sites along the Souhegan River and 13 sites on the Merrimack River between Manchester and Tyngsborough every other Tuesday morning from now until fall. Tests will be done for E. coli bacteria, phosphorus, temperature, turbidity, and dissolved oxygen. Special DNA testing is also being continued for the third season on selected locations on the Souhegan through a continuing grant from ENSR International and UMass Boston. All of the E. coli testing is done by the labs at the Milford, Merrimack, and Nashua Wastewater Treatment Plants. All of the dissolved oxygen testing is done by the Merrimack Wastewater Treatment Plant.

A number of the sites marked NA still need volunteers. If anyone would like to find out more or offer to help, contact Ms. Mattor at 578-5543 or "This year," she said, "we have two Boy Scouts from Merrimack who are volunteers, Kevin Grosso and Ethan Randall. It's not difficult; it doesn't take a lot of time; and it will make you feel good."

All of the sites tested along the Merrimack came in quite clean this week. At a couple of the sites, the Sagamore Bridge in Hudson and at Goffs Falls in Litchfield, the bacteria were barely detectable. A new site added this year to test the effects of the numerous wildfowl at Cromwells Falls didn't show a problem and came in with an acceptable reading of 44.

E. coli bacteria readings taken on the Souhegan River showed higher than the accepted 88 colonies at all of the sites in Milford and Amherst. Rain showers within the three days prior to the Tuesday morning testing would have washed bacteria into the river and showed up mainly in that section of the river with a slow moving, meandering riverbed. The site at the Souhegan Valley Boys and Girls Club had the highest reading at 300. Both the upstream and downstream sections of the Souhegan came in quite clean.

It was also noted that lots of macro-invertebrates that live only in very clean water were found at the Milford site where the Souhegan Watershed Association has been helping local school children release their classroom-raised salmon for the last two months. Finding macro-invertebrate animals that require clean water is the 'gold-standard' for water testing. The animals that live in the river test for any pollution that may be in the river; the chemical testing only monitors the certain selected parameters. In the past, additional testing for heavy metals showed higher than acceptable amounts of mercury in both rivers and high levels of lead in the Souhegan.

A number of monitors on the Souhegan noted changes in the riverbed caused by this April's extremely high flooding. Large rocks and trees were moved and new beaches and channels created or washed out. The site at Pine Valley Mill in West Milford was completely washed clean of vegetation and debris collected there in the past. Volunteers also noted wildlife spotted along both the Souhegan and Merrimack, fishermen on both rivers, boats on the Merrimack; but the predominant note was that the mosquitoes were out.

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