Monday, August 13, 2007

Water Quality Conditions and Vulnerability Analysis of Little River

By Don Clement, Chair, Exeter Conservation Commission

The Exeter Conservation Commission participates in the New Hampshire Volunteer River Assessment Program (VRAP). This entails conducting water quality sampling of the local river and streams throughout the summer months. Exeter has been collecting data since 2000 at five sites on the Exeter River and one site on the Little River. Concerned with poor quality results we expanded our monitoring to 2 other sites on the Little River starting in 2006.

Measurements are taken for the following: Dissolved Oxygen, Turbidity, pH, Specific Conductance, water and air temperature. Historically the worst results have occurred in the Little River.

From 2000 to 2005 each of the sites were sampled on the same day. In summary the Little River measured the worst results 70% of the time for turbidity, 60% of the time for Dissolved Oxygen and 80% of the time for specific conductance.

For the most part with few exceptions the tests met the State of NH Class B Surface Water Quality Standards. Parameter failures were noted during this period at the Little River Gilman Park location.

All of the following data is from the Little River Gilman Park site.

Chemical Parameters

Dissolved Oxygen

Concentration (milligrams per liter) and saturation (percent); mg/l and %.

Class B NH Surface Water Quality Standard is 5mg/l and 75% minimum average.

The presence of dissolved oxygen is vital to organisms, fish and amphibians.

Failure to meet the 5 mg/l has been noted in 21% of the tests and failure to meet 75% minimum noted in 57% of the tests. The historic low for mg/l was

4.73 and the low for % was 56.3.


Measurement of the amount of suspended material in the water. The Class B NH Surface Water Quality Standard shall not exceed more than 10 NTU. Higher turbidity increases water temperature, which also in turn reduces the concentration of dissolved oxygen. Failure to meet this standard has been noted in 14% of the tests. The historic high for turbidity was 14.2 NTU.

Specific Conductance

The numerical expression of the ability of water to carry an electrical current and a measurement of charged particles in the water. High conductance readings may indicate pollution from road salting, septic systems and/or urban runoff. There is no Class B NH Surface Water Quality Standard. However any reading higher than 201 indicates a moderate impact to the waters. Readings of greater than 200 were recorded 28% of the time. The historic high for conductivity was 256.7.


The measurement of acidity in the water. The Class B NH Surface Water Quality Standard is between 6.5 and 8.0. All tests were within the standard.


In a recent draft report by NH Department of Environmental Services, the Little River ranks as one of the most vulnerable systems in the Exeter River Watershed. Most of the river's issues are due to the high density development with little shoreland protection starting downstream of Colcord's Pond. Another report indicates that this section of the river has aggraded due to increased sediments washing into the river and constricting channel widths.


Minimize the amount of impervious surface in the watershed

Increase riparian stream buffers

Maintain dense overhead canopy

Lessen impact to adjacent wetlands

Utilize Best Management Practices for drainage