1.14 BMP C127 - Polyacrylamide for Soil Erosion Protection
Polyacrylamide (PAM) is used on construction sites to prevent soil erosion.
Applying PAM to bare soil in advance of a rain event significantly reduces erosion and controls sediment in two ways. PAM helps maintain soil structure, which increases the ability to infiltrate.
Do not apply PAM directly to water or allow it to enter a waterbody. In areas that drain to a sediment pond, PAM can be applied to bare soil under the following conditions:
During rough grading operations.
Balanced cut and fill earthwork.
Haul roads prior to placement of crushed rock surfacing.
After final grade and before paving or final seeding and planting.
Sites having a winter shut down. In the case of winter shut down, or where soil will remain unworked for several months, PAM should be used together with mulch.
1.14.3 Design and Installation Specifications
PAM may be applied in dissolved form with water, or it may be applied in dry, granular or powdered form. The preferred application method is the dissolved form.
PAM is to be applied at a maximum rate of 2/3 pound PAM per 1,000 gallons water (80 mg/L) per 1 acre of bare soil. Higher concentrations of PAM do not provide any additional effectiveness.
Pre-measure the area where PAM is to be applied and calculate the amount of product and water necessary to provide coverage at the specified application rate (2/3 pound PAM per 1,000 gallons per acre).
PAM is water soluble, but dissolves very slowly. Dissolve pre-measured dry granular PAM with a known quantity of clean water in a bucket several hours or overnight. Mechanical mixing will help dissolve the PAM. Always add PAM to water - not water to PAM.
Pre-fill the water truck about 1/8 full with water. The water does not have to be potable, but it must have relatively low turbidity – in the range of 20 NTU or less.
Add PAM and water mixture to the truck.
Completely fill the water truck to specified volume.
Spray PAM and water mixture onto dry soil until the soil surface is uniformly and completely wetted.
PAM may also be applied as a powder at the rate of 5 pounds per acre. This must be applied on a day that is dry. For areas less than 5 to 10 acres, a hand-held “organ grinder” fertilizer spreader set to the smallest setting will work. Tractor-mounted spreaders will work for larger areas.
The following benefits and limitations should be considered:
PAM shall be used in conjunction with other BMPs and not in place of other BMPs.
Do not use PAM on a slope that flows directly into a stream or wetland or any other waterbody.
PAM has little to no effect on sandy soils with little clay content.
Do not add PAM to water discharging from site.
When the total contributing area is greater than or equal to 5 acres, PAM treated areas shall drain to a sediment pond.
Areas less than 5 acres shall drain to sediment control BMPs.
On all sites, use silt fences to limit the discharges of sediment from the site.
Cover and protect all areas not being actively worked from rainfall. PAM shall not be the only cover BMP used.
PAM can be applied to wet soil, but dry soil is preferred due to less sediment loss.
PAM will work when applied to saturated soil but is not as effective as applications to dry or damp soil.
Keep the granular PAM supply out of the sun. Granular PAM loses its effectiveness in three months after exposure to sunlight and air.
Proper application and re-application plans are necessary to ensure total effectiveness of PAM usage.
PAM, combined with water, is very slippery and can be a safety hazard. Care must be taken to prevent spills of PAM powder onto paved surfaces. During an application of PAM, prevent over-spray from reaching pavement, as pavement will become slippery. If PAM powder gets on skin or clothing, wipe it off with a rough towel rather than washing with water, which makes cleanup messier and take longer.
Some PAMs are more toxic and carcinogenic than others. Only the most environmentally safe PAM products should be used.
The specific PAM copolymer formulation must be anionic. Cationic PAM shall not be used in any application because of known aquatic toxicity problems. Only the highest drinking water grade PAM, certified for compliance with ANSI/NSF Standard 60 for drinking water treatment, will be used for soil applications. PAM use shall be reviewed and approved by the City. The Washington State Department of Transportation (WDSDOT) has listed approved PAM products on its web page: https://wsdot.wa.gov/Business/MaterialsLab/QPL.htm
PAM designated for these uses should be "water soluble", "linear", or "non-crosslinked". Cross-linked or water absorbent PAM, polymerized in highly acidic (pH<2) conditions, are used to maintain soil moisture content.
The PAM anionic charge density may vary from 2 to 30 percent; a value of 18 percent is typical. Studies conducted by the United States Department of Agriculture (USDA)/ARS demonstrated that soil stabilization was optimized by using very high molecular weight (12-15 mg/mole), highly anionic (>20% hydrolysis) PAM.
PAM tackifiers are available and being used in place of guar and alpha plantago. Typically, PAM tackifiers should be used at a rate of no more than 0.5 to 1 pounds per 1,000 gallons of water in a hydromulch machine. Some tackifier product instructions say to use at a rate of 3 to 5 pounds per acre, which can be too much. In addition, pump problems can occur at higher rates due to increased viscosity.
PAM may be reapplied on actively worked areas after a 48-hour period.
Reapplication is not required unless PAM treated soil is disturbed or turbidity levels show the need for an additional application. If PAM treated soil is left undisturbed, a reapplication may be necessary after two months. When PAM is applied first to bare soil and then covered with straw, a reapplication may not be necessary for several months.
Loss of sediment and PAM may be a basis for penalties per RCW 90.48.080.