Despite Rain and High River Flow, Bacteria Counts Are Low

The heavy, continuous rainfall this summer has kept lots of water in rivers all summer long. Both the Merrimack and Souhegan Rivers have exceeded their 70-year average flows all summer long. One has to go back to May to find expected levels. This week’s water quality testing by the Souhegan Watershed Association and Merrimack River Local Advisory Committee recorded flows two to three times higher than normal. The Merrimack was flowing at 3,240 cubic feet per second at the time of the test on Tuesday morning; historic flow is 1,640 cfs.

The river through Nashua and further south looks lower because the Pawtucket Dam removed the flashboards weeks ago and they are still continuing repairs. This has caused some pollution problems and danger to boats not used to maneuvering around submerged rocks. The work being done on the Jackson Falls Dam in Nashua will prevent this kind of extended lowering and damage to the river. LMRLAC has called for the Pawtucket Dam to install this same kind of structure in the future to prevent damage.

Because of the heavy flows this summer, the dissolved oxygen levels that are critical for the health of the fish and indicators of the general health of the river have remained very high and very acceptable.

E. coli levels, which measure the level of bacteria that may indicate dangers to swimmers, are another story. Generally heavy rains wash bacteria into the rivers from riverbanks, storm drains, and small tributaries and increase the bacteria levels for the three days that the bacteria live. This summer has produced a number of gully-washers and the monitoring program has documented it. “Swimmers generally should avoid the rivers for two days after a heavy rainstorm,” suggested monitoring coordinator Karen Mattor. “Or at least keep your head out of the water if possible,” she said.

E. coli levels higher than 88 can cause swimmer’s eye and ear or gastrointestinal problems especially for the vulnerable. This week’s tests, however, showed very acceptable E. coli levels in both rivers. The Merrimack, especially, is very clean as far as bacteria goes. A very high number, 365, was recorded at Thorntons Ferry in Merrimack; however, the rest of river between Manchester and Tyngsborough came in at less than 50, very clean, and by the time the river got downstream to Greeley Park it had cleared up to 31. Except following heavy rains the Merrimack is a success story.

The Souhegan River is much smaller and reacts differently. The upper stretch between New Ipswich and Wilton is rocky and moves much more quickly than downstream. Usually the bacteria level here is at an acceptable level. The middle stretch through Milford and Amherst slows down and meanders back and forth through sandy soil. Here the warmer, slower water and extensive tributary brooks increase the bacteria levels. And this week’s tests showed exactly those results. The highest number in the upper stretch was 81 above Greenville Mill Pond and 210 behind Riverside Cemetery in the middle stretch. The river usually clears up by the time it gets to the mouth in Merrimack, and it did so again this week, coming back down to 74.

Results for known swimming holes were: 126 for the Amherst Canoeport at Boston Post Road, 56 at Indian Ledges, 106 at Turkey Hill Bridge, and 74 at Watson Park, all in Merrimack, and all generally acceptable. The Horseshoe in Wilton was not tested this week; however, nearby tests would indicate that it was clean.

Monitors collect water samples between five and eight in the morning and so get to see the animals that expected to have the morning to themselves. A deer was lounging near theSagamore Bridge, an osprey was circling the Milford Oval, and lots of geese were roamingWatson Park in Merrimack. Monitors also reported the cardinal flowers out in full bloom.

Monitoring will continue for another month to the middle of September. This all-volunteer program has been ongoing for 17 years under SWA sponsorship. Several of the volunteers have been with the program since the beginning. All of the local wastewater treatment plants volunteer to do the dissolved oxygen and E. coli tests in their certified labs. Citizens can follow the E. coli results all summer on a map on the Nashua Telegraph website. 

Although not reported, the program is also collecting data on three tributary streams in New Ipswich.

Here are all of the E. coli results for both rivers collected on August 13:

E-COLI MONITORING RESULTS FOR TESTS TAKEN ON AUGUST 13, 2013

SOUHEGAN RIVER SITES:

1. Billy Ward Pond, Ashburnham  #1, #2  NA
2. SoR  333  River Road above Water Loom Pond, New Ipswich  17.3
3. SoR  320  Highbridge, New Ipswich  72.7
4. SoR  309  Above Greenville Mill Pond, Greenville  81.3
5. SoR  296  Downtown Greenville upstream of WWTP  48.0
6. SoR  291  Green Bridge off Rte 31 below Greenville WWTP   43.7
7. SoR  218  Below the Horseshoe, Wilton   NA
8. SoR  210  Downtown Wilton  150.0
9. SoR  201  Pine Valley Mill, West Milford   116.2
10. SoR  170  Behind Hayward Field, West Milford  NA 
11. SoR  155  Souhegan Valley Boys and Girls Club, Milford  129.1
12. SoR  146  Swing Bridge, Milford  187.2
13. SoR  133  Riverside Cemetery, Milford   209.8  
14. SoR  130  Behind Lorden Plaza, Milford  166.4
15. SoR  122  Amherst Country Club  139.6
16. SoR  116  Amherst Conservation land Fairway Road, Amherst   137.4
17. SoR  095  Boston Post Road Canoeport, Amherst  125.9 
18. SoR  070   Seaverns Bridge, Merrimack 135.4
19. SoR  057  Indian Ledges, Merrimack  55.6
20. SoR  034  Turkey Hill Bridge, Merrimack  105.8   
21. SoR  001   Watson Park, DW Hwy, Merrimack  73.8

MERRIMACK RIVER SITES:

1.      Mer  600  Above Amoskeag Dam, Manchester  49.6

2.      Mer  590  Arms Park, Manchester  44.3

3.      Mer  570  Goffs Falls, Litchfield  25.6

4.      Mer  560  Depot Street, Merrimack    38.8

5.      Mer  550  Upstream of Souhegan River, Merrimack   NA

6.      Mer  540  Thorntons Ferry, Merrimack  365.4

7.      Mer  530  Greeley Park, Nashua  31.3

8.      Mer  520  Taylors Falls Bridge, Nashua   34.5

9.      Mer  510  Sagamore Bridge, Hudson  42.6

10.  Mer  500  Pheasant Lane Mall, Hudson   NA

11.  Mer  490  Upstream of Tyngsboro Bridge  28.2

Flow on Upper Souhegan was 65 CFS and expected flow for that date is 27

Flow on Lower Souhegan was 133 CFS and historic flow for that date is 45