E. Coli Levels Rise on Merrimack, Souhegan Rivers

Rain again raised E. coli levels on both the Merrimack and Souhegan Rivers when tested last Tuesday, according to a press release.

This was the third biweekly test this summer and each test was preceded by a heavy rainstorm which rinsed pollution into the rivers. E. coli levels higher than 88 are not acceptable for public swimming areas in NH; all of the tests on both rivers were higher than that.

The Merrimack River between Manchester and Tyngsborough, which normally tests very clean for E. coli, had an average reading of 188, well over the recommended level for swimming. Greeley Park this week had a reading of 144.

The Souhegan River tested higher in the 300-400 level, well above a safe swimming level. The Horseshoe in Wiltonwas 276; the Boston Post Road Canoeport in Amherst was 517; Indian Ledges was not tested, Turkey Hill Bridge was 649, and Watson Park was 488. The last three are in Merrimack.

Dry weather for three days in a row should bring the pollution levels back down to acceptable swimming levels since that is the life span of the bacteria in the water. But Wednesday’s rain doesn’t bode well for swimming in rivers on the 4th. Ponds generally have less exposure to E. coli pollution after rainstorms and would be a better bet. All public swimming areas require testing for E. coli and would be closed if above the safe level.

Swimmers are subject to gastrointestinal problems and ear and eye infections when E. coli levels are higher than 88. The SWA program suggests that levels less than 88 are acceptable for swimming for everyone; less than 126 are probably OK for healthy adults; and levels over 406 are dangerous and should be avoided.

Both rivers had very high flows on Tuesday after the rainstorm on the weekend. At least one of the normal sites was not tested because it was too high to monitor safely. The Merrimack has been running at higher than normal flow for the last week.

Dissolved oxygen levels in both rivers continued to show healthy conditions. This is the primary test for the actual health of the river itself; and both rivers almost always show healthy levels. The E. coli levels determine how healthy the river is for human use; DO levels determine how healthy it is for the fish, insects, and plant life in the rivers.

The program no longer tests for pH since the tests are difficult to interpret, but past testing shows that both rivers are in the normal range for pH - although both show the effects of acid rain after rainstorms.

The testing program is done at the same time every other Tuesday morning by approximately 30 volunteers who collect samples and record data at a specific site. The chemical tests are performed by certified personnel in the labs of the wastewater treatment plants in Manchester, Nashua, Milford, and Merrimack. The E. coli tests require 24 hours to grow the bacteria colonies to determine the correct levels.

There are still a couple of sites that could use a volunteer monitor. Anyone interested can contactswawatertesting@gmail.com for more information.

The Souhegan Watershed Association has been sponsoring this testing program for almost 20 years. Much of that data is on the website at www.souheganriver.org. All of this week’s data is on the site.

The next test will be done on July 14; results will be available the following day.

Here are this week’s results:

E-COLI MONITORING RESULTS FOR TESTS TAKEN ON JUNE 30, 2015

SOUHEGAN RIVER SITES:

1. Billy Ward Pond, Ashburnham #1 10.9; #2 14.5
2. SoR 333 Water Loom Pond, New Ipswich 146.7
3. SoR 320 Highbridge, New Ipswich 307.6
4. SoR 309 Above Greenville Mill Pond, Greenville 275.5
5. SoR 296 Downtown Greenville upstream of WWTP 214.3
6. SoR 291 Green Bridge off Rte 31 below Greenville WWTP 248.1
7. SoR 218 Below the Horseshoe, Wilton 275.5
8. SoR 210 Downtown Wilton 435.2
9. SoR 201 Pine Valley Mill, West Milford 410.6
10. SoR 170 Behind Hayward Field, West Milford NA
11. SoR 155 Souhegan Valley Boys and Girls Club, Milford NA
12. SoR 146 Swing Bridge, Milford 547.5
13. SoR 133 Riverside Cemetery, Milford 248.9
14. SoR 130 Behind Lorden Plaza, Milford NA
15. SoR 122 Amherst Country Club 378.4
16. SoR 116 Amherst Conservation land Fairway Road, Amherst NA
17. SoR 095 Boston Post Road Canoeport, Amherst 517.2
18. Sor 070 Seaverns Bridge, Merrimack 613.1
19. SoR 057 Indian Ledges, Merrimack NA
20. SoR 034 Turkey Hill Bridge, Merrimack 648.8
21. SoR 001 Watson Park, DW Hwy, Merrimack 488.4

MERRIMACK RIVER SITES:

1. Mer 600 Above Amoskeag Dam, Manchester 103.9

2. Mer 590 Arms Park, Manchester 139.6

3. Mer 570 Goffs Falls, Litchfield 108.6

4. Mer 560 Depot Street, Merrimack NA

5. Mer 550 Upstream of Souhegan River, Merrimack 307.6

6. Mer 540 Thorntons Ferry, Merrimack 275.5

7. Mer 530 Greeley Park, Nashua 143.9

8. Mer 520 Taylors Falls Bridge, Nashua 248.9

9. Mer 510 Sagamore Bridge, Hudson 172.2

10. Mer 500 Pheasant Lane Mall, Hudson NA

11. Mer 490 Upstream of Tyngsboro Bridge 187.2

Flow on Upper Souhegan was 264 CFS and expected flow for that date is 49

Flow on Lower Souhegan was 489 CFS and historic flow for that date is 93

Flow on Merrimack was 8380 CFS and historic flow for that date is 2570 (high all week)

RAINFALL - Heavy rain on Sunday. Otherwise clear.

Temperatures: Souhegan 17C; Merrimack 19C