​Rainstorm Raise E. Coli Levels In Souhegan, Merrimack River​s

MERRIMACK, NH — A fairly heavy rainstorms just before the latest water monitoring on the Souhegan and Merrimack Rivers was the probable cause of an E. coli level to jump into a less than favorable condition, according to recent testings. Rainstorms wash bacteria into the rivers and raise E. coli bacteria levels.

The upper stretch of the Souhegan had excellent E. coli levels, but the levels jumped when the river reached Milford and all its storm drains. The highest level was measured at the Swing Bridge, near the Oval, a very unhealthy 410. As the river moved downstream from here, the levels lessened all the way to the mouth of the river in Merrimack; however, the quality never reached a safe, less than 88, level. The lowest level here was 96 at Watson Park in Merrimack. This is a questionable level for swimming – probably OK for healthy adults but not for small children or those with compromised immune systems. Watson Park has been posted with a yellow flag to indicate this.

As the Souhegan merged with the Merrimack River, it brought the Merrimack’s excellent E. coli level up slightly, but still the much larger river quickly absorbed that pollution and continued at an excellent level. The Merrimack typically has had excellent E. coli levels for the last several years. An exception occurred during this test. The level measured near the Taylors Falls Bridge jumped to 91, higher than the 88 upper level for excellent. The monitor here noted that there was a muddy discharge from an outfall pipe here – probably a CSO sewage discharge that often occurs here. It was quickly absorbed and diluted by the river.

Monitors reported that both rivers had higher than normal flows. The Merrimack was running at 3820 cubic feet per second. Normally at this time of year it would be around 2700 cfs. Further downstream near Tyngsborough monitors reported that the river was considerably lower than normal, even though the flow was higher, because of the removal of flashboards at the Lowell dam while doing maintenance. The Souhegan has come down to one third the flow of two weeks ago, but it still was flowing at about one third more than its historic average for this time of year. Clearly the drought is over at least for surface water levels.

Water temperatures averaged 20C in the Souhegan and 21C in the Merrimack – close to 70F. pH levels measured on the Souhegan were slightly less than 7 – or slightly acidic – and very normal. The same was true for the Merrimack.

Another test is for dissolved oxygen. This test generally indicates the general health of the river for fish, animals, and habitat. These levels were excellent but normal for this time of year. Dissolved oxygen levels diminish as the summer goes along and the weather heats up and flow levels go down. Past years have shown both rivers to be in good health and still improving.

Beavers were the animal spotted the most this week. Monitors on both rivers noted them. Another monitor got a closeup of a low flying eagle near Watson Park. Others saw herons, turkeys, and tracks of lots of animals coming to the rivers. A sculler was out early from the Independence Rowing Club in Nashua, near the Taylors Falls Bridge. Unfortunately monitors also noted, and picked up, lots of trash – especially lots of beer cans. And poison ivy abounds.

The rivers will be tested again on July 11. Thirty volunteers, many of whom have been with the program for many years, adopt a site and test every other Tuesday morning and carry the samples to local wastewater treatment plants in Greenville, Milford, Merrimack, Manchester and Nashua where the samples are processed by certified professionals. More information is available at souheganriver.org.

Here are the individual results for E. coli for this week:

SOUHEGAN RIVER SITES:

1. Billy Ward Pond, Ashburnham #1 3.1; #2 6.3
2. SoR 333 Water Loom Pond, New Ipswich 35.9
3. SoR 320 Highbridge, New Ipswich 26.9
4. SoR 309 Above Greenville Mill Pond, Greenville 36.3
5. SoR 296 Downtown Greenville upstream of WWTP 35.5
6. SoR 291 Green Bridge off Rte 31 below Greenville WWTP 37.9
7. SoR 218 Below the Horseshoe, Wilton NA
8. SoR 210 Downtown Wilton 68.4
9. SoR 201 Pine Valley Mill, West Milford 59.4
10. SoR 170 Behind Hayward Field, West Milford 86.2
11. SoR 155 Souhegan Valley Boys and Girls Club, Milford 130.9
12. SoR 146 Swing Bridge, Milford 410.6
13. SoR 133 Riverside Cemetery, Milford 344.8
14. SoR 130 Behind Lorden Plaza, Milford 261.3
15. SoR 122 Amherst Country Club 224.7
16. SoR 116 Amherst Conservation land Fairway Road, Amherst NA
17. SoR 095 Boston Post Road Canoeport, Amherst 272.3
18. SoR 057 Indian Ledges, Merrimack 129.1
19. SoR 034 Turkey Hill Bridge, Merrimack 111.2
20. SoR 001 Watson Park, Merrimack 96.0

MERRIMACK RIVER SITES:

1. Mer 600 Above Amoskeag Dam, Manchester NA
2. Mer 590 Arms Park, Manchester NA
3. Mer 580 Upstream of Piscataquog River, Manchester NA
4. Mer 570 Goffs Falls, Litchfield NA
5. Mer 560 Depot Street, Merrimack 26.2
6. Mer 550 Upstream of Souhegan River, Merrimack 40.4
7. Mer 540 Thorntons Ferry, Merrimack 63.7
8. Mer 530 Greeley Park, Nashua 33.1
9. Mer 520 Taylors Falls Bridge, Nashua 90.8
10. Mer 510 Sagamore Bridge, Hudson 38.4
11. Mer 500 Pheasant Lane Mall, Hudson NA
12. Mer 490 Upstream of Tyngsboro Bridge 30.1

Flow on Upper Souhegan was 67CFS. Expected flow for that date is 58

Flow on Lower Souhegan was 108CFS. Historic flow for that date is 101

Flow on Merrimack was 3820CFS. Historic flow for that date is 2700

RAINFALL: Spotty showers prior three days. Rain Monday night 0.13”

Temperature: Souhegan 20C; Merrimack 21C

Caption: SWA volunteer Rob Clemens of Amherst collects water quality samples from the Souhegan River early Tuesday morning. Credit: George May

Submitted by George May.