Penobscot County SWCD News

Agricultural Producers located in Nickerson Lake/Meduxnekeag River Watershed and Sebasticook Lake Watershed will be able to participate

Bangor, ME — May 8, 2012 — Juan Hernandez, State Conservationist for the USDA Natural Resources Conservation Service in Maine, has announced the launch of a new National Water Quality Initiative committed to improving two impaired waterways in Maine. USDA’s Natural Resources Conservation Service (NRCS) will manage the initiative by making funds available to farmers and forest landowners in the selected watersheds.

“I am happy to announce that Nickerson Lake in the Meduxnekeag River Watershed in southern Aroostook County and the Sebasticook Lake Watershed in Penobscot County are the two priority watersheds that have been selected to participate in this initiative,” said Hernandez. “The Water Quality Initiative in these watersheds will further NRCS’ partnership efforts to improve water quality using voluntary actions on private lands. This initiative is a focused approach in areas facing significant natural resource challenges. It bolsters the positive results of landscape conservation initiatives NRCS and its partners already have underway.”

Through this effort, eligible producers in the Nickerson Lake and Sebasticook River Watershed priority areas will invest in voluntary conservation actions to help provide cleaner water for their neighbors and communities. The selected watersheds were identified with help from state agencies, partners, and the NRCS State Technical Committee.

Using funds from the Environmental Quality Incentives Program, NRCS will provide funding and advice to producers to install conservation practices such as cover crops, filter strips and stream crossings in watersheds with impairments where the federal investment can make a difference to improve water quality.“American farmers are good stewards of the environment, especially when they have the tools they need to protect or improve fish and wildlife habitat and water quality,” said NRCS Chief Dave White. “We look forward to collaborating with producers in key watersheds to help them have a positive impact on streams with impaired water quality.”

NRCS accepts applications for financial assistance on a continuous basis throughout the year. Remember to check with your local NRCS office to see if you are located in a selected watershed. NRCS offices are listed online at http://offices.usda.gov or in the telephone book under United States Government, Agriculture Department. To be considered for funding in 2012, applications for the National Water Quality Initiative must be received by June 15, 2012. This summer, NRCS will notify all applicants of the results and begin developing contracts with selected applicants.

Since 1935, NRCS’s nationwide conservation delivery system works with private landowners to put conservation on the ground based on specific, local conservation needs, while accommodating state and national interests. For more information about NRCS’ programs, initiatives and services in Maine, visit www.me.nrcs.usda.gov.

Crane Brothers Farm was featured in the April edition of Spudman Magazine. Congratulations! You can read the article at http://spudman.com/index.php/magazine/issue/april-2012

Figure 1

The first article (part 1) in last years newsletter, concerned insulating underground CLOSED PIPE SYSTEMS such as water lines, sewer lines, or process supply lines. That article contained some data that may be referred to here. See the previous article if you have a copy or refer to the PCSWCD web site where it is posted.

This second article (part 2) concerns the insulating of OPEN PIPE SYSTEMS such as road culverts, or underground outlets that carry water between catch basins, and that serve as an open ended outlet pipe. These systems may experience several cold weather problems.

Problem #1 (freeze ups) is where significant updrafts during freezing weather result in the freeze up of long duration low flows, that cause a plugging of part or all of the pipe cross section of the pipe and a loss of carrying capacity.

In addition to the freeze up problem there is the additional problem #2 (frost heave) of freezing of the soil below the pipe that results in significant ice lens growth that causes significant frost heave of both the pipe and the road surface. The degree of Problem #2 is related to the local climate (freezing degree days), the texture of the soil, and the depth to the water table.

 Problem #1 (freeze ups)

Problem #1 is easier to understand and solve and will be discussed first. Please refer to Figure 1 as needed during this discussion. The freezing behavior of open pipe systems is a more complex process than the closed pipe systems. Several freeze-up pathways can occur. The first pathway occurs when long duration low flows freeze up within the pipe on contact with a cold pipe that has high thermal conductivity like metal or aluminum, and the second pathway is from strong updrafts of cold outside air between the open ends due to a “chimney effect” similar to that in a wood stove.

Problem #1 will not occur if small long duration flows are not present during extended periods of cold weather. Larger winter runoff events of short duration, require too much energy in a short period of time for freezing to occur and are not usually a problem no matter what pipe material is present.

If small flows will occur during freezing weather than several actions can be taken. One action that can be taken is that of placing a submerged reverse elbow at the inlet catch basin (if one is present). See Figure 1. If no catch basin is present then placing a solid flap valve at the outlet end is possible. If a flap valve is used one needs to be sure that valve movement is not obstructed by soil, rocks, brush and other debris.

If a new pipe is being planned or a pipe replacement is scheduled, then the third option for freeze up protection for locations with low flows throughout the winter is to use either Corrugated Polyethylene pipe or reinforced concrete pipe. Both types have a much lower heat transmission potential than metal, PE probably being the better. Steel or Aluminum pipe have an extremely high heat transmission potential that allows rapid freezing of low flows. Think of the “tongue on the cold metal storm door syndrome” that we have all heard about or experienced.

Think of all the cooling or heating coils on machinery you are familiar with. Usually the coils are of some type of metal like steel, aluminum, or copper for the maximum dissipation or absorption of heat.

Concrete has a relatively low thermal conductivity compared to metals and is resistant to freeze ups. Smooth interior Corrugated PE pipe also has a lower thermal conductivity than metals in addition to the dead air space in each corrugation. PE pipe is also much smoother on the inside than concrete and difficult for ice to grab on to. Where the depth of cover over the pipe is less than 12 to 18 inches than concrete is preferred. Either type should be considered at locations where long duration low flows are present during cold weather. If Catch basins are in the system then reverse elbows (downward facing) should be considered at each catch basin. Besides helping reduce the freezing problem they also add to the water quality of flows from the system.

Problem #2 (frost heave)

The second problem is that of frost heave of culverts at road crossing which is both a structural and public traffic safety problem, not to mention the effect on snow plows and road maintenance crew safety.

The major influencing factors for frost heave are: 1- freezing weather, (Central Penobscot County has a design freezing index – DFI – of about 2000), 2- the availability of water from a high water table, and 3- frost susceptible soils (fine grained silts and sands). The DFI for an area is not subject to change and the value must be considered a constant in all solution options.

In poorly drained swampy areas, and hydric soils, the water can be assumed to be at the invert of the pipe. At some locations standing water may be at or above the invert of the pipe. Usually the depth of water table can not be changed at a project location by the use of drainage practices unless no impact on local wetlands will occur.

The presence of frost susceptible soils is one aspect of a project site that can be modified. The most valuable of frost heave resistant soils are clean sands and gravels (soils that do not leave much of a stain on the hands when handled wet). The other frost heave resistant soil class is true clays. This is because clay is so impermeable that water can not pass through the clay soil fast enough to feed the freeze zone where the ice lenses are forming.

There is some confusion on this matter, as often the soil is classified as clay when in fact the soils are silts (clay look-a-likes). It is safer to assume the soil is frost susceptible unless soil test are done, or someone who is qualified does a proper field identification. If this option is used (without the aid of insulation) the soil under the pipe should be replaced with frost resistant soil to a depth equal to the frost penetration at the road surface. The inside of the pipe, just like the plowed road surface, is not protected from freezing temperatures by the presence of snow. Frost penetration on a plowed road can be from 6 to 8 feet or deeper depending on shading from trees, buildings, or hills. For maximum safety this depth of frost penetration (or close to it) under and around the pipe should also be assumed in the design process for preventing frost heave.

Note: water in the soil expands only about 7 % to form ice and then stops expanding if no additional water is coming in from below. If the soil is not saturated, the expansion of freezing water simple fills up the voids if available. This amount usually will not cause problems and often goes unnoticed.

The frost heave prevention design aspect of a project that is subject to control is the actual penetration of the frost into the soil. If there is no frost penetration into the soil, then there is no frost heave of the road! As shown in article 1 on insulating underground pipes, the thickness of extruded polystyrene that is needed for maximum protection in large projects in central Penobscot County is from 2.5 to 3.0 inches. A single layer of 2.0 inches or two lapped layers of 1.0 inches extruded polystyrene can be used on smaller projects such as driveways and low speed gravel roads. However remember that the insulating board is usually a small cost and should not be skimped on if used. It also needs to be carefully protected from damage during installation. The reader should refer to article 1 for the discussion on insulation materials.

Figure 2

Figure 2 shows a condition where the frost depth extends below the invert of the pipe. It also shows frost penetration radially from the walls of the pipe. This redial frost penetration can be equal to that of frost from the road surface. This is true with metal pipes, but somewhat less using concrete or corrugated PE pipe. The width of the insulation board placed under the pipe is equal to twice the frost depth plus the pipe diameter, and runs the entire length of the pipe.

Remember that during construction several inches of silty sand should be placed below and above the insulation board for damage protection.

A high water table will decrease the frost penetration significantly but it is safer to ignore this effect on small projects. If a large project is involved, than hiring an engineer familiar with thermal soil mechanics is advised.

Figure 3

Figure 3 shows a condition where the frost depth is at or above the invert of the pipe. A box of insulation surrounding the pipe is advised in this condition. The condition of a high water table should not change the recommendations for small projects in this situation either.

This is a short article concerning a complex issue, so if any questions come up an engineer should be consulted. However the recommendations should suffice for many of the projects that occur on farms and town roads.

SUMMARY

The following “decision tree” should be referred to in the planning stage before design activities are started on a open pipe system to protect from pipe freeze ups or frost heave on roads. Refer to the preceding discussion and figures as questions arise.

Decision Tree

 Question 1 – Concerning pipe freeze ups. Are long duration low flows present during the winter months of the year?

If NO. Then use any pipe material and no reverse elbows or flap valves are needed.

If YES. Then consider using only Reinforced Concrete Pipe or Corrugated Polyethylene Pipe. Consider an inlet elbow or exit flap valve if applicable. Remember that a PE pipe needs a minimum of 12 to 18 inches of cover, otherwise use RCP.

 Question 2 – Concerning pipe frost heave. Is there is a water table at or above the pipe invert?

If YES. Then little benefit is obtained in most cases in insulating the pipe. However since insulation board is inexpensive some use may be prudent to be on the safe side.

If NO. Then is fine grained (frost susceptible) soil below the pipe invert down to the water table?

If NO. Then insulation board beneath and/or around the pipe is not needed.

If YES. Then insulate the pipe according to the preceding recommendations in this article and shown on Figures 2 and 3.

NOTE: Neither the author nor the Penobscot County SWCD assume any responsibility for the use of information in this article on any projects. If questions arise on a large project, consult with a civil engineer that is competent in thermal soil mechanics.

John J. Simon, P.E. 1/23/2012