Henniker, NH Conservation Commission Natural Resources Inventory

A Report by the

Henniker Conservation Commission

October 2002

Prepared by:

E. Ann Poole, Ecologist & Environmental Planner

Concord, NH

The Henniker Conservation Commission extends their appreciation to the UNH Cooperative Extension

Community Assistance Program, New England College Department of Environmental Sciences, and the Henniker residents and NEC students who generously volunteered their time and energy to collect water samples.

This project was funded by The Town of Henniker, New Hampshire, through Warrant Articles (2000 and 2001) and the Town Conservation Fund.

For more information about the Commission or copies of this report, please contact:

The Town of Henniker is situated in an area of great natural beauty and encompasses a wide variety of natural resources. These natural resources played a significant role in shaping the development of the town and its economic base, and they continue to play a significant role today. The river, which once powered mills, now supports white-water boating and fishing; the woodlands support the forest products industry; the geologic formations yield sand and gravel; and the rural character and convenient location attracts residents and businesses to the town. Clearly, the town’s economic base is closely linked to the quality of its environment and natural resources.

As the population of Henniker has grown and become more mobile, the natural resources and the economy they support are threatened by development pressures. Other New Hampshire communities have already experienced negative consequences from this pressure including wildlife displacement, loss of recreation corridors and scenic vistas, surface and groundwater contamination, and increased erosion and flooding.

As understanding of the importance and value of natural resources has increased, so too has awareness of how land use can affect them. Various state agencies, such as the Department of Environmental Services, Fish & Game, Department of Resources & Economic Development, and Office of State Planning can provide technical assistance and information; however, primary control and decision-making regarding land use is vested in the municipality.

The Town of Henniker Natural Resources Inventory (NRI) is a comprehensive, geographically-based catalog of land use and natural resources in Henniker. It provides scientifically valid, timely, and relevant information that will enable town officials to monitor and assess the status of natural resources, such as public drinking water supplies, wildlife habitat and water quality. As such, the NRI can be a basis for assessing local land use proposals, updating plans for future growth and economic development, developing town policies and programs, and enhancing residents’ understanding of natural resources and environmental conditions.

The NRI began in March 2000 with funding from the Town of Henniker. Over the next two years, the Henniker Conservation Commission (HCC) and its consultant compiled and analyzed existing digital information and documents about natural resources town wide. This progress report summarizes the information produced and available to date.

To map land uses and natural resources in the Town of Henniker, the HCC used existing digital geographic data from several sources, including the Central NH Regional Planning Commission (CNHRPC), NH Department of Environmental Services (NH DES), US Geological Survey (USGS), and UNH Complex Systems. On the basis of this information, the HCC prepared eleven maps, reduced versions of which are depicted in Maps I – XI at the end of this report. The following sections summarize the natural resources information that was found in the course of the inventory.

Documents used in the course of preparing this report and of potential interest to the reader are listed in Appendix B, “Resources.”

The objective of the NRI has been to gather and present data regarding Henniker’s natural resources. In this two-phase project, the HCC and its consultant undertook to compile existing information and produce a set of large-format natural resource maps for public display.

· Compiling, analyzing and/or digitizing information not presently available (i.e., historical and archaeological sites, soil types, tax maps, land use);

· Ascertaining critical natural resources and potentially significant habitat through review of digital data, surveys, and reports;

· Encouraging community participation in efforts to identify and quantify additional natural resources in the Town of Henniker.

Rivers, streams, 100- and 500 year floodplains are illustrated in Map II, “Water Resources”. Perennial rivers and streams are identified and described in Table 1.

Fly-fishing, paddling, and tubing on the Contoocook River are increasingly important recreational activities generating local economic activity. Best known is a 6.5 mile reach of the river extending from Hillsboro to West Henniker that presents paddlers with challenging and technical Class III-IV whitewater:

“The Contoocook is one of New Hampshire’s largest rivers and offers some of the best heavy water canoeing in all of New England. Because it holds water much better than smaller streams, the Contoocook can be run late in the season and even after heavy rains. In terms of personality, this section is definitely schizophrenic and manic-depressive; it is either disquietingly calm or ravagingly mad, changing almost without warning. Rocks of all shapes and sizes populate this people-eating run, and the level of the water determines how they affect the boating. Low or medium water requires much maneuvering. At higher levels the rocks are responsible for the extreme turbulence. This trip is short: the first part can easily be eliminated and it can be repeated several times in a day. The lower half can be viewed from [Old] Route 202 except for two or three places and, as things would have it, these places are Class 4.”

(AMC New England White Water River Guide, 1981)

Anglers and paddlers seeking calmer waters of the Contoocook can gain access via a small boat launch on River Road in the Hopkinton Dam Reservoir area (“accessible by conventional vehicles,” NH F&G, 2002). Access to smaller streams and brooks is gained via public lands, stream crossings and rights-of-way. Access across private property is at the discretion of the property owner.

Surface water quality is characterized on the basis of class designations. Class A waters are of the highest quality and are considered potentially acceptable for water supply use after disinfection. Class B waters are of the second highest quality and are considered to be “acceptable for fishing, swimming and other recreational purposes, and after adequate treatment, for use as water supplies” (NH DES, 2000). All surface waters in the town of Henniker are designated ‘Class B’ by the State of New Hampshire.

Numerical standards and narrative criteria set forth in state and federal water quality regulations serve as benchmarks for assessing whether a waterbody is supporting its designated uses. Water quality information from a variety of sources is assembled and reviewed. Sources include the: NH DES Ambient Monitoring Program, Nonpoint Source Program, and Coastal Shellfish Program; New Hampshire Estuaries Project; NH Department of Health and Human Services; US Fish and Wildlife Service; USDA Natural Resources Conservation Service; US Geological Survey; and various volunteer monitoring groups. The data gathered is used cumulatively to determine whether there is an exceedance or a violation of State water quality standards.

Rivers, streams and estuaries that are not fully supporting all designated uses (i.e., ‘impaired’) are listed by the NH DES. This list, called the ‘305(b) List’, includes: the location of impairment, the cause of impairment, the probable source of impairment, the estimated miles (or square miles) that are considered impaired, and recommended abatement action.

In Henniker, a 1-mile reach of the Contoocook River in the vicinity of the Dean Edna Proctor Bridge (Route 114) is considered “Partially Supporting” one or more uses. Ambient surface water samples taken in 1995, 1996, and 1999 revealed zinc concentrations that exceed the US EPA recommended levels for protection of aquatic life (NH DES, 2000). The probable source is “unknown” and further investigations will be required to determine the source(s).

Ponds and wetlands are illustrated in Map II, “Water Resources.” Ponds are identified and described in Table 2.

The New Hampshire Department of Fish and Game maintains two small boat ramps in Henniker that provide access to anglers and paddlers. The French Pond ramp is located off French Pond Road and the Keyser Pond ramp, off Old Concord Road (“accessible by conventional vehicles,” NH F&G, 2002). Access to Pleasant Pond is via a town-owned right-of-way on Quaker Street. Access across private property to the remaining ponds is at the discretion of the property owner. There are no designated public swimming areas in the Town of Henniker.

A survey of water quality of Henniker ponds was conducted in the fall of 2000 and 2001 as part of the Natural Resources Inventory. Members of the Conservation Commission, volunteers from the community, and New England College students and staff collected water samples and measured dissolved oxygen, temperature, and clarity in 12 of the town’s lakes and ponds. Samples were tested for phosphorus, chlorophyll A, specific conductivity, pH, and turbidity. The information establishes baseline data for all the major ponds in town. Ponds that were sampled include: Colleague, Craney, French, Keyser, Long, Middle, Morrill, Mud, Pleasant, Upper, and two other unnamed ponds--designated “Craney Rookery” and “Mud Pond 2”. (See Map II.)

Based on the results of this survey the water quality of Henniker ponds is good. No specific water quality problems (e.g., algal blooms) were reported during the period of the fall 2000 and fall 2001 surveys though, according to the 2000 NH DES 305(b) Report, Keyser Pond is considered “Partially Supporting” one or more designated uses. It fails to fully support swimming use due to periodic excessive algal growth. The probable source is “unknown” and further investigations are underway to determine the source(s).

Craney Pond and Pleasant Pond have very low total phosphorus concentrations. There are three ponds with very high total phosphorus concentrations: French Pond, Morrill Pond, and Mud Pond 1. Although Mud Pond 1 had high total phosphorus levels measured in fall 2000, the fall 2001 survey results were lower. Considerable efforts continue to be put forth to address the high total phosphorus concentrations in French Pond.

The clarity of Henniker ponds was less than the mean of NH VLAP (NH Volunteer Lake Assessment Program) lakes and ponds sampled in 2000. Clarity is influenced by a number of factors including algae, suspended sediment, and the color of the water. The lower levels of clarity are consistent with levels of turbidity that are greater than the VLAP mean value. However, there is no indication that there is a single cause for decreased clarity or that these results indicate a problem with water quality. The clarity measurements of Keyser Pond and French Pond have historically been low and attributed to excessive algae growth. However, in the fall 2000 and fall 2001 surveys the transparency levels for both of these ponds were comparable to other Henniker ponds.

Acid Neutralizing Capacity (ANC) is a measure of the ability of a solution to neutralize acids entering the lakes from an acidic input such as acid deposition -- the higher the ANC the greater the acid neutralizing ability. The lowest levels of ANC were measured in Craney Pond and the Craney Rookery. Mud Pond 1 was the only Henniker pond categorized as not sensitive to acidification. However, based on the available water chemistry data there is no indication that any of Henniker’s ponds are impacted or influenced by acidic inputs.

The report summarizing the results of the 2000 and 2001 surveys and comparing the results with lakes and ponds that were sampled statewide in the NH VLAP in 2000 can be found in Appendix D.

Wetlands greater than 20 acres in size are illustrated in Map VIII, “Riparian & Wetland Habitat” and are identified and described in Table 3.

Wetlands in Henniker are identified on the basis of the US Fish & Wildlife Service National Wetlands Inventory and Survey (NWIS) data. Large isolated wetlands are found just north of Upper Pond, south of the Contoocook River by Mud Ponds 1 and 2, and in lands lying between the Contoocook River and US Route 202. Based on the NWIS mapping, seven hundred seventy acres of wetlands, excluding surface water and streams, exist in Henniker. Wetlands depicted in the NWIS mapping were identified by interpretation of 1985 and 1986 aerial photographs at the 1:58,000 scale. Forested wetlands, which are more difficult to identify from aerial photographs, may be under-represented. Small wetlands may have also been omitted. Changes to wetlands which may have occurred since the data were assembled will not be represented. Thus, the NWIS data is not all-inclusive and unmapped wetlands, such as vernal pools, certainly exist throughout town. Field investigations are necessary in order to confirm the locations of both mapped and unmapped wetlands.

Soil drainage classes are a commonly used tool for identifying potential wetlands. When complete in 2003, the revised USDA NRCS Merrimack County Soil Survey Map will show the location of poorly- and very poorly-drained soils thereby providing an indication of the location of some of these smaller riparian and isolated palustrine wetlands, as well as intermittent drainages.

Between 1990 and 1994, the HCC conducted evaluations of thirty-four wetlands greater than 1 acre in size (twenty-two wetlands 1-10 acres in size; eight wetlands 11-25 acres; and four wetlands over 25 acres). The evaluations were performed by HCC members and other volunteers using the manual, Method for the Comparative Evaluation of Nontidal Wetlands in New Hampshire (“The New Hampshire Method”) by the USDA NRCS and the Audubon Society of New Hampshire. The results were compiled into a database and graphed by the CNHRPC.

The NH Method is a wetland evaluation process designed for use as a tool to compare the relative Functional Values that wetlands within a defined study area perform. The results produced by the method are a set of relative Functional Values for up to 14 different functions: Ecological Integrity, Wildlife Habitat, Finfish Habitat, Educational Potential, Visual/Aesthetic Quality, Water-based Recreation, Flood Control Potential, Ground Water Use Potential, Sediment Trapping, Nutrient Attenuation, Shoreline Anchoring and Dissipation of Erosive Forces, Urban Quality of Life, Historical Site Potential, and Noteworthiness. Each of these functions is assigned a numerical value based upon the answers to a series of questions. The questions are answered using existing data (e.g. soils, topographic, and NWIS) and by conducting field surveys. The results for a particular wetland can then be compared with the results for other wetlands in the study. An overall score for each wetland is not determined thus allowing the study to focus on those functions deemed most important.

The graphs depicting the results of the NH Method wetlands evaluation will be available for the next update of this document.

Aquifers are geologic formations that have the potential to yield significant amounts of groundwater. The Hopkinton Lake sub-watershed unit underlying most of Henniker, southern Warner and West Hopkinton contains one large contiguous aquifer along the main Contoocook River valley (‘Henniker-Contoocook aquifer’) and three separate small aquifers. The 6.23 mi² Henniker-Contoocook aquifer begins in western Henniker and continues to the Hopkinton Dam (USGS, 1995). There, it joins a long, continuous aquifer extending eastward to the Merrimack River in Concord. It and the small aquifer located in West Henniker along the Contoocook River are depicted in Map II, “Water Resources”.

The sediments composing the aquifers in Henniker were deposited at the waning end of the last ice age some 15,000 years ago. They were deposited as 1) ice-contact deposits in western Henniker along the Contoocook River, 2) deltaic deposits near the confluence of Amey Brook and the Contoocook River, 3) eskers and kames in the valleys of Colby Brook and Hopkinton Reservoir, 4) glaciolacustrine deposits along the Contoocook River valley in eastern Henniker, and 5) a large ice-contact delta on the northern side of Craney Hill (USGS, 1995).

The sorted and layered sediments of the aquifers include 1) coarse-grained sand and gravels intermixed with till in the small, isolated aquifer along the Contoocook River in western Henniker, 2) interlayered coarse- and fine-grained sediments in the large, contiguous main valley of the Contoocook River in central Henniker (coarse-grained deltaic deposits border this aquifer on the north and south sides), 3) a thin upper layer of sand underlain by fine-grained silts and clays in eastern Henniker, and 4) layers of coarse-grained sand and gravel in the Colby Brook valley (USGS, 1995).

Henniker depends on the high yield Henniker-Contoocook aquifer for its drinking water supply. Two gravel packed wells, located on the south side of Route 114, supply water to Henniker Village. Other wells are found on Depot Hill Road and off of the Foster Hill Road Extension. The Town does not use any surface water bodies for its public drinking water supply.

Ground water withdrawals include the three municipal wells for the town of Henniker and domestic supplies. The three municipal wells withdraw 0.24 Mgal/d. Domestic use, estimated at 0.19 Mgal/d, is primarily from bedrock water supplies. Commercial withdrawals also are from bedrock (USGS, 1995).

Groundwater recharge to the aquifers is from precipitation. The effective recharge rate is 7.5 in/yr – the lowest rate for any subbasin within the Contoocook River basin. Except where streams enter the main valley aquifer, horizontal rates of flow are probably slow in the principal aquifer along the Contoocook River and groundwater residence time is probably longer than other subbasins (USGS, 1995).

According to the USGS, the potential for increased aquifer yield is probably greatest near Mud Pond in southeast Henniker. Using a ground water flow model, the agency estimated aquifer yield in this vicinity to range from 1.13 to 1.14 Mgal/d (1995). The three municipal-supply wells consume less than 5 percent of the average annual precipitation recharge to the aquifer, and withdrawals from these wells would not interfere with aquifer yield in the model area (USGS, 1995).

Ground water quality from the aquifers is generally suitable for drinking and for other domestic and commercial uses. Concentrations of sodium in excess of the USEPA Health Advisory limit and concentrations of iron and manganese in excess of the USEPA Secondary Maximum Contaminant levels occur throughout the sub-watershed and are relatively common. Sodium is introduced through natural atmospheric deposition and anthropogenic sources (i.e., road salt). Iron and manganese are common elements in minerals of bedrock and stratified drift in NH and are common dissolved and suspended solids in ground water of these deposits (USGS, 1995).

The US EPA requires that the NH DES assess all sources of public drinking water for susceptibility to contamination by materials regulated in the federal Safe Drinking Water Act, 1996. The NH DES maintains a geographically-referenced database of potential contamination sources to aquifers and public drinking water supplies. The map, “Drinking Water Resources and Potential Contamination Sources: Henniker, NH”, is available for review at Town Hall and from the NH DES.

Per state regulation, Env-Wr 701 ‘Water Use’, any person using an average of 20,000 gallons of water or more per day averaged over a 7 day period, or 600,000 gallons in any 30 day period, must register and report the use with the following exemptions:

· one time or occasional uses of water in excess of 600,000 per 30 day period (such as filling swimming pools or fire fighting);

· water used for irrigation that does not exceed 140,000 gallons per week, or the area irrigated does not exceed 5 acres.