Souhegan Watershed Association

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1998 Souhegan E-coli results
1997 Souhegan E-coli results
Stream Flow Measurements

Water Testing Results
Summer 1998

Executive Summary
Souhegan River Results
Merrimack River Results
Analysis of Each Test

Executive Summary

The Souhegan Watershed Association water quality monitoring project was funded under a non-point source pollution grant from the NH Department of Environmental Services in order to provide additional data to supplement the collective data of previous years by the SWA, Merrimack River Watershed Council (MRWC) and the NHDES. This report includes the findings for the 1998 monitoring season.

With the exception of pH, the methods used for water quality analysis comply with state and federal guidelines. Samples collected by trained volunteer monitors were analyzed for dissolved oxygen, E.coli bacteria, total phosphorus, pH and temperature. In addition several physical parameters were noted including water level, color and odor as well as observed recreational uses which are not included in this report.

The goal of this project was to collect quality data in order to determine if the Souhegan and Merrimack Rivers support their designated uses. The numerical data was compared to the NH water quality standards for class B waters in order to assess the rivers health within the confines of these parameters and to identify problem areas and possible sources of pollution.

The 1998 monitoring season provided some unique wet weather sampling opportunities. Significant rainfall events in June, with a cumulative monthly precipitation exceeding 10 inches, provided excellent conditions for monitoring the river system under "stressed" conditions and assessing the impact of extreme riparian run-off. The data collected from rainfall events on June 2 and June 16 provided further documentation to support the effects of NPS run-off pollution. Sites on the Merrimack River within the confines of the Combined Sewer Overflow (CSO) outfalls showed E.coli counts greatly exceeding the 88 colonies/100 ml. Standard for class B waters with many even exceeding the instantaneous standard of 406 col/100 ml for partial body contact. On the Souhegan River, which lacks CSOs, all sites during this period greatly exceeded 88 col/100 ml., although all fell within safe levels for partial body contact recreation.

Impact sites in the centers of Wilton and Milford continued to show higher than acceptable levels of E.coli throughout most of the monitoring season as did sites downstream of the Milford Waste Water Treatment Facility through the towns of Amherst and Merrimack to the Davidson Rd. site. Following the recovery from the June rainfall events, bacterial levels on the Merrimack River generally stayed within safe levels.

Results for dissolved oxygen and temperature on both the Souhegan and the Merrimack fell within an acceptable range with but a couple of exceptions.

Measurements of pH showed lower than acceptable values on the Souhegan although there is some question as to the reliability of these results due to the method used and the room for sampler error. The results do seem to show a low degree of variability throughout most of the watershed with a slightly lower (more acidic) pH towards the headwaters.

This season marked the first year total phosphorus was monitored by the SWA on the Souhegan River. Data collected from this season indicated several potential problem areas where total phosphorus exceeded the .05 mg/l level of concern. The impact sites for both the Greenville and Milford wastewater treatment plants showed a sharp increase in phosphorus levels as well as excessive algal growth observed by volunteer monitors. Phosphorus levels continued to increase downstream of the Milford WWTF all the way to the Turkey Hill Bridge site in Merrimack, the extent of our study reach, indicating possible additional sources of phosphorus loading entering the river system along this stretch. It may be noted that portions of this area of Amherst/Merrimack also showed higher than acceptable levels of E.coli bacteria throughout the monitoring season. (see Appendix E, SoR E.coli vs. Phosphorus).


Souhegan River


The unusually heavy rainfall accumulation of greater than 10 inches in the month of June clearly documented the increase in fecal contamination in the river system during heavy terrestrial run off. (see Appendix F, Rainfall vs. E.coli comparison). On the Souhegan River, bacterial counts greatly exceeded the 88 standard for total body contact at nearly all sites during the storm events in the first half of June yet never exceeded the 406 standard for partial body contact recreation at any one site. On June 30 and July 14, the river began a gradual recovery beginning near the headwaters. Although this wet weather sampling documented results of heavy run off, it gave us fewer data points to work with to isolate problem areas.

The impact site for the Greenville WWTF showed high variability throughout the monitoring season with elevated counts that were independent of any significant rainfall event. It is unclear whether this variation is due to wastewater discharge or urban impact from the town of Greenville which is directly upstream of the plant. In the future, sites which bracket the town of Greenville upstream of the plant should be monitored to determine the source.

Bacterial counts for the 1998 season, on the whole, were significantly higher than the previous year (see Appendix D). Counts from site SoR201 (below Wilton) to site SoR 095 (the Boston Post Rd. Canoeport in Amherst), were almost without exception, higher than acceptable for swimming throughout the entire monitoring season. Data from previous years have revealed problems in the centers of Wilton and Milford . (see Appendix D). The congregating of urban-associated waterfowl and domestic animals such as Canada geese, pigeons, ducks and dogs may be responsible for the elevated counts. More investigation needs to be done at the Pine Valley Mill site (SoR 201), where a stagnant culvert associated with the dam may be a source of fecal contamination. It is only in the last two years that high bacteria counts have been a problem at the Boston Post Rd. site in Amherst. Bacterial results were reported by area newspapers after each monitoring date to warn of possible health risks to swimmers. The town of Amherst was alerted to the high counts and posted a warning to swimmers at the Boston Post Rd. Canoeport as a direct result of the monitoring efforts. Bacterial counts peak along this stretch of the river at the Fairway Rd. site in Amherst, the impact site for the Amherst Country Club. This area of the river has not been monitored by the SWA/MRWC until this season. It is fairly unique in its physical aspects being characterized by sandy bottoms, an extremely sinuous path and 6-40 ft sand/silt banks which are heavily eroded in areas. The riparian land consists of mostly grassy fields with a golf course directly abutting the banks with little or no buffer zone. Apart from the golf course, the area is mostly undeveloped. The high sandy banks provide prime habitat for a number of wild birds and burrowing animals which have been observed and whose holes litter the banks. Also observed are large gatherings of Canada geese and deer on the golf course and surrounding fields. This section of the river abuts conservation land which presumably hosts a variety of wildlife. Samples taken at Beaver Brook, a tributary which passes through a wild bird sanctuary wetland and beaver habitat, showed very high E.coli counts. This empties into the river just upstream of the Fairway Rd. site and is likely contributing to the high E.coli counts at this site. Because of the lack of development in this section of the river and the observed resident animal populations, high E.coli counts are most likely naturally occurring. Drainage pipes from the golf course and the lack of a natural buffer zone may be contributing to irrigation and rainwater runoff causing influxes of bacteria from terrestrial riparian sources.


Phosphorus at the impact sites of both the Milford and Greenville wastewater treatment facilities clearly showed excessive phosphorus levels from effluent discharges. Levels exceeded the .05 level of concern on every date except during the storm event dates where excessive water volume may have caused dilution of the phosphorus concentrations. After the Milford WWTF, nutrient levels remained higher than acceptable through Amherst and Merrimack to the Turkey Hill bridge. (see Appendix B, Phosphorus table). Several factors may be the cause of this nutrient loading. Wastewater discharge is certainly a contributing factor although other sources may be contributing phosphorus. At the Greenville wastewater treatment site, where total phosphorus levels were generally higher than at the Milford wastewater treatment plant site, the river has recovered 5 miles downstream from the site. The impact site for the Milford wastewater treatment plant and downstream sites show levels increasing rather than decreasing 3, even 10 miles downstream of the facility. Recovery is not seen 5 miles downstream as it is at the Greenville site. This seems to indicate that other sources of phosphorus loading may be occurring downstream of the treatment plant. This segment of the river flows past the Amherst Country Club, the Souhegan Woods Country Club and several large developments displaying well manicured lawns, whose storm drains empty directly into the river. Lawn and golf course fertilization may be contributing phosphorus to the river as phosphorus levels increase toward the end of the summer. (see appendix B, phosphorus table).

Phosphorus released from the soil through bank erosion in the Amherst area as well as phosphorus from animal waste, as E.coli was elevated in this area also, may also be a factor.(see Appendix E, E.coli vs. Phosphorus).


Temperatures on the Souhegan were nearly all below 24C supporting cold water fish species such as Trout and Atlantic Salmon.

Dissolved Oxygen

Dissolved oxygen levels generally fell within acceptable levels on the Souhegan with the exception of sites SoR034, Turkey Hill bridge site and SoR201, Pine Valley Mill Site. At these sites D.O. numbers were low but field duplicates taken at these sites revealed variable results indicating possible error in collection technique.

Merrimack River


Bacterial samples taken below the CSO outfalls on the Merrimack during the storm events in the month of June show bacteria counts in most cases surpassing the instantaneous standard of 406 colonies/100ml. for partial body contact recreation. Following these storm events, bacteria levels generally remained below safe levels for swimming. Nashua has finally started the 20 year process of correcting CSOs.

Temperature and Dissolved Oxygen

Temperature and Dissolved oxygen generally fell within acceptable levels on the Merrimack.

Appendix D, yearly E.coli comparisons, shows natural yearly variations in bacteria levels. Long term trends will be important to understand and pinpoint sources of ecological impairments to the river system.

Analysis of Each Test

September 8th results

Bacteria tests performed on the Souhegan and Merrimack Rivers indicate both good and bad results for area towns. Samples taken in downtown Milford had the lowest E. coli bacteria counts of the entire year. Normally bacteria levels from downtown Milford, or any downtown area for that matter, should be higher than acceptable for human recreational contact. But tests taken at the Swing Bridge, Emerson Park, and Riverside Cemetery all were well below the 88 standard for public swimming areas for the first time this year. George May, president of the Souhegan Watershed Association (SWA), speculated that the large number of ducks and geese that normally inhabit this area may have already headed south and could have been responsible for high E. coli counts during the summer.

Wilton, however, is another story. Tests taken at Stony Brook and near the Pine Valley Mill are considerably higher than normal for this season. These two tests bracket downtown Wilton and show pollution is coming into the river from the downtown area.

Once again the test taken at the Horseshoe, a very popular swimming hole on the Souhegan River in Wilton, shows that this spot is safe for swimming. This has been true throughout the summer.

The stretch of the Souhegan River that meanders through Amherst still continues to show higher than acceptable levels of bacteria for public swimming. Generally the stretch of river from the Rte 101 bridge to the Merrimack town line has tested marginally high throughout the summer. The popular swimming hole at the Boston Post Road Bridge has had higher than acceptable levels of bacteria all summer. The Town of Amherst has posted warnings to swimmers at this spot.

The Merrimack River continued to show low bacteria counts throughout its tested length. However, counts both upstream and downstream of the confluence with the Souhegan River showed sharply increased bacteria levels this week. The test taken at Thorntons Ferry was three to four times the expected level. The Merrimack River has shown excellent cleanliness throughout the summer. It has been only during rainstorms when Combined Sewer Overflows (CSOs) in Manchester and Nashua have dumped raw sewage into the river that the Merrimack has not been completely safe for swimming. When these CSOs are corrected -- and both cities are already digging up streets to separate sewer and stormwater pipes to eliminate CSOs -- the Merrimack should be an exceptionally clean river.

This is the last test for this summer. Volunteers from the SWA and the Lower Merrimack River Local Advisory Committee have conducted eight biweekly tests since June to measure the health of these two local rivers. Joanne King, coordinator of the project, said, "Thanks to the many unpaid volunteers who ventured out early before work every other Tuesday morning to collect samples, thanks to the unpaid volunteers at the local wastewater treatment plants in Nashua, Merrimack, Milford, and Greenville who performed bacteria tests, and thanks to the unpaid volunteers at the Nashua Fish Hatchery who performed the tests for dissolved oxygen, we have a substantial amount of data to compare with past years. We hope that this year's data will help us to discover ways to improve the health of our rivers."

August 25th results

The Merrimack River had extremely low bacteria levels when tested on Tuesday, August 25 according to the Merrimack River Local Advisory Committee (LAC). Most of the readings were in single numbers, well below the 88 standard for public swimming areas. The Merrimack between Manchester and Tyngsboro has tested at acceptable levels through much of the summer. This test is the seventh biweekly test done by the group this summer. There will be one more test on September 11.

The Souhegan River showed approximately the same results as the tests done two weeks ago according to Joanne King, monitoring coordinator for the LAC and the Souhegan Watershed Association (SWA). Swimming spots at the Horseshoe in Wilton, Indian Ledges in Merrimack, and Turkey Hill Bridge in Merrimack all tested OK for swimming. The swimming hole at Boston Post Road Bridge in Amherst, however, again showed bacteria levels higher than acceptable. This spot has not had acceptable results at any time this summer.

Generally the Souhegan River from Wilton to Amherst had bacteria readings higher than acceptable for swimming. The river through Amherst has been the focus of the attention for SWA monitors for the last several tests. Additional testing was done on Beaver Brook in Amherst in an effort to find polluting tributaries. Readings here showed a high level of bacteria, though down from the last test two weeks ago. Two weeks ago the level was 360; this week's test was 210.

August 11th results

Testing for E. coli bacteria on August 11 indicated that the entire length of the Merrimack River from Bedford to Tyngsboro met state health standards for public swimming areas. The Merrimack River is one of the success stories of the Clean Water Act. Since the passage of that legislation in the 1970s, the Merrimack has slowly cleaned itself up to the point that it is now virtually swimmable and fishable throughout its length when the weather is clear. The testing this year has shown that rainstorms clearly impact the river when CSOs in Manchester and Nashua dump raw sewage into the river. CSOs are Combined Sewer Overflows that bypass the sewage treatments plants because the rain water flows into the same single sewer pipe and the impact overwhelms the capacity of the treatment plant. Both Manchester and Nashua are in the process of installing stormwater pipes as a result of requirements by EPA. When this process is finished, the Merrimack should be swimmable under all weather conditions.
What was good for the Merrimack however was not good for the Souhegan. The lack of rain and the larger size of the Merrimack River provided excellent conditions for the quality of that river during this testing period. The smaller size of the Souhegan does not allow it to absorb the higher water temperatures and low flow that contribute to higher bacteria counts.
The Souhegan River, although marginal, still does not meet the state standards for public swimming through most of its length. Of the best known swimming areas on the Souhegan, only Weston Park at the Turkey Hill Bridge in Merrimack met the acceptable standards. The Horseshoe in Wilton, Boston Post Road Bridge in Amherst, and Indian Ledges in Merrimack were all slightly higher than acceptable. Boston Post Road Bridge, the most popular swimming hole on the river, has not met acceptable standards at any time all summer. The Town of Amherst has recently posted warnings against swimming there as a result of this testing program.

Bacteria readings throughout Amherst have been high on every test so far this summer. This has prompted discussion of the problem at the recent SWA monthly meeting. Additional testing was done at the mouth of Beaver Brook, one of the Amherst tributaries coming into the Souhegan, and the results show high levels of bacteria there (360 colonies/ml of water). Joanne King, the SWA coordinator, believes that beaver, geese, and other wild animals may be the cause of the problem, but further testing needs to be done.

July 28th results

Levels have generally risen slightly since the last biweekly tests but are mostly in the healthy-for-human-use category. Virtually all of the Merrimack River from Bedford to Tyngsboro met public health standards for the first time this season.

The Merrimack drains most of the state's rivers and streams and so until recently has had high water levels that were caused by the heavy rains in June. But as the water level has come down, the pollution level has dropped. The boat ramp at Greeley Park tested acceptable for the first time this season.

Most of the Souhegan River also met acceptable standards. However, the section through Amherst from Rte 101 to Merrimack continues to have unhealthy bacteria levels. This stretch has not met acceptable standards at any of the five tests conducted so far this year. Included in this stretch of the Souhegan is a very popular swimming hole at the Boston Post Road bridge. Swimmers there stand a good chance of getting eye and ear infections, diarrhea, and other gastrointestinal problems.

The Horseshoe in Wilton is another story. This popular swimming hole has tested well below the the 88 E. coli level acceptable for public swimming throughout the season. Tuesday's test showed 25 at the Horseshoe.

The swimming hole at Weston Park at Turkey Hill Bridge in Merrimack squeaked by with a reading of 86.

July 14th results

Tests done by the Souhegan Watershed Association and the Merrimack River Local Advisory Committee on Tuesday, July 14, show that the levels of E. Coli bacteria have dropped substantially in the last two weeks.

Bacteria levels had been extremely high as a result of the heavy rains experience in June. But now that the rains have decreased, so have the bacteria levels.

None of the known swimming holes on either the Souhegan or Merrimack tested above 88 with the exception of the Souhegan River at the Boston Post Road bridge in Amherst. The level there was 140. The Souhegan through the center of Milford also showed higher than acceptable levels of bacteria.

June 30th results

In spite of continuing heavy rains within the Souhegan watershed, E. coli bacteria counts have diminished considerably according to the Souhegan Watershed Association. "Bacteria counts that were alarming in the upper stretches of the Souhegan in Greenville two weeks ago are now well below the limits for human recreational use," according to George May, president of the SWA.

Two known swimming holes were tested. Upstream of the bridge at Turkey Hill in Merrimack is slightly elevated but generally OK. Indian Ledges in Merrimack was OK. The Boston Post Road bridge area and the area at the Horseshoe were not tested this week.

Readings on the Merrimack River showed generally acceptable levels of bacteria for human recreational use until the river reaches Nashua. Below the confluence with the Nashua River bacteria levels are still not acceptable for human use -- probably because of raw sewage being discharged directly to the rivers from nine CSOs when it rains in Nashua.

June 16th results

Again because of the recent heavy rains, most of the bacteria counts exceed safe levels. Heavy rains usually increase the pollution carried into a river from non-point sources (ie runoff from animals, parking lots, roads, septics, lawns, etc).

June 2nd results

The bacteria counts at most of the test sites along both rivers exceeded safe levels. This is a result of the heavy rainstorm that crossed this area Sunday night. Heavy rains always increase the pollution carried into a river. Some of this is naturally occurring (from the feces of birds and other wildlife) and some is from human non-point source pollution (ie from parking lots, roads, yards, septic systems, etc).

In the Nashua area Combined Sewer Overflows (CSOs) dramatically affected the Nashua and Merrimack Rivers. Merrimack River sites 6-9 are all impacted by CSOs. The bacteria counts at these sites all exceed 400 colonies of bacteria per 100 ml. of water, which is too high to be accurately counted. Combined Sewer Overflows occur where stormwater and sewage are transported in a single pipe instead of two. When it rains, the sewage treatment plant cannot handle the increased load and the raw sewage and stormwater is discharged directly into the rivers. There are 9 CSO discharges into the Merrimack in Nashua. There are no CSO discharges into the Souhegan. Nashua is presently working on a plan to separate their sewage and stormwater pipes over the next twenty years.