River Testing: Swimming Not Recommended

Sporadic, localized rain showers, some heavy, right before testing occurred produced uneven E. coli counts in the Souhegan and Merrimack Rivers this week, according to a press statement.

After large rainstorms, bacteria is washed into the rivers from riverbanks and storm drains. Generally the bacteria die after three days of clear weather following moderately high counts. Both rivers showed vastly different results this week.

The Merrimack River between Manchester and Tyngsborough tested clean, but the Souhegan River had very high bacteria counts when tested this Tuesday morning. Counts on theMerrimack averaged only 53 colonies of bacteria per hundred milliliters of water. Counts less than 88 are considered healthy for swimming. The Souhegan, however, averaged much higher. Some sites between Wilton and Milford were even higher than the 2419 maximum that the test can measure. That the bacteria counts improved as the river continued downstream indicates that heavy localized thunderstorms on Monday in the Lyndeborough area were responsible for the pollution. By the time the river reached Watson Park at the mouth of the river, the bacteria level dropped to 110, still higher than the 88 level recommended for swimming at public beaches in NH – but probably OK for healthy adults.

A high count was measured on the Merrimack River at Arms Park in Manchester, but lower counts nearby meant that large flocks of ducks at the park were responsible for that aberration.

The Souhegan Watershed Association tests the two rivers every two weeks during the summer. This season has been unusual because of heavy rainstorms right before the tests were taken. This is what causes the high bacteria counts and it’s completely natural.

The Souhegan is a smaller river that meanders seriously from Milford through Amherst andMerrimack. This means that the river becomes longer, has more riverbank per gallon of water, which allows for more bacterial riverbank surface and storm drains to drain into the river. There is less water to dilute the pollution.

Normally the Merrimack River tests very clean for bacteria and has for the last several years. There may be other contaminants in the river, but E. coli doesn’t seem to be a concern. E. coli bacteria are an indicator species for other bacteria that would cause gatrointestinal problems for humans swimming in the water. Counts higher than 88 colonies of bacteria are the safe limit for swimming areas. Counts between 88 and 126 may be OK for healthy adults; counts higher than 126 should be avoided.

The flow on both rivers is still slightly higher than its expected, historical average for this time of year. It has been most of the summer. Dissolved oxygen levels, which indicate the general health of the river itself, continue to be very acceptable, even high for this time of year.

Monitors noted the abundance of flowering plants and animal tracks along the riverbanks. Cardinal flowers, especially noted, are in full bloom.

Besides the 30 monitors that have adopted their sites and deliver their samples and data, certified lab personnel in the Greenville, Milford, Merrimack, Manchester, and Nashua waste treatment facilities perform the tests for dissolved oxygen and E. coli bacteria.

Tests are collected every two weeks during the summer. The next test will be done on August 11; results will be available the following day. The results for individual sites tested on both rivers is available at souheganriver.org.

Here are this week’s results:

E-COLI MONITORING RESULTS FOR TESTS TAKEN ON JULY 28, 2015

SOUHEGAN RIVER SITES:

1. Billy Ward Pond, Ashburnham #1 1.0, #2 3.1
2. SoR 333 Water Loom Pond, New Ipswich 60.9
3. SoR 320 Highbridge, New Ipswich 547.5
4. SoR 309 Above Greenville Mill Pond, Greenville >2419.6
5. SoR 296 Downtown Greenville upstream of WWTP 325.5
6. SoR 291 Green Bridge off Rte 31 below Greenville WWTP 1203.3
7. SoR 218 Below the Horseshoe, Wilton 1203.3
8. SoR 210 Downtown Wilton 2419.6
9. SoR 201 Pine Valley Mill, West Milford >2419.6
10. SoR 170 Behind Hayward Field, West Milford NA
11. SoR 155 Souhegan Valley Boys and Girls Club, Milford >2419.6
12. SoR 146 Swing Bridge, Milford 1986.3
13. SoR 133 Riverside Cemetery, Milford 1413.6
14. SoR 130 Behind Lorden Plaza, Milford 1413.6
15. SoR 122 Amherst Country Club 1413.6
16. SoR 116 Amherst Conservation land Fairway Road, Amherst NA
17. SoR 095 Boston Post Road Canoeport, Amherst 1046.2
18. Sor 070 Seaverns Bridge, Merrimack 613.1
19. SoR 057 Indian Ledges, Merrimack NA
20. SoR 034 Turkey Hill Bridge, Merrimack 198.9
21. SoR 001 Watson Park, DW Hwy, Merrimack 110.0

MERRIMACK RIVER SITES:

1. Mer 600 Above Amoskeag Dam, Manchester 18.7

2. Mer 590 Arms Park, Manchester 410.6

3. Mer 570 Goffs Falls, Litchfield 70.6

4. Mer 560 Depot Street, Merrimack 49.6

5. Mer 550 Upstream of Souhegan River, Merrimack NA

6. Mer 540 Thorntons Ferry, Merrimack 135.4

7. Mer 530 Greeley Park, Nashua NA

8. Mer 520 Taylors Falls Bridge, Nashua NA

9. Mer 510 Sagamore Bridge, Hudson 20.6

10. Mer 500 Pheasant Lane Mall, Hudson NA

11. Mer 490 Upstream of Tyngsboro Bridge 22.6

Flow on Upper Souhegan was 121 CFS and expected flow for that date is 39

Flow on Lower Souhegan was 106 CFS and historic flow for that date is 48

Flow on Merrimack was 2600 CFS (fluctuating) and historic flow for that date is 1660

RAINFALL - Showers with occasional bursts prior to test date; heavier rain upper river

River temperature: Souhegan 21C; Merrimack 23C