Technical Report: Results of Laboratory Experiments in Support of PAM-Related Research

Linear, anionic polyacrylamide (LA-PAM) has been examined in laboratory, field and numerical environments to evaluate its efficacy in reducing seepage in unlined water delivery canals and potential environmental impacts from its use. This report describes the laboratory-based research conducted on LA-PAM. The report is divided into chapters that present specific research experiments and findings. The final chapter is a synopsis that attempts to tie together the project findings into three categories: LA-PAM hydration and reactivity, acrylamide (AMD) fate and transport, and LA-PAM transport. The results show the following:
• LA-PAM will begin to hydrate within about 5 minutes of introduction into water and continue hydrating for about 20 minutes, depending on field conditions. Reduction in seepage in laboratory columns was shown to progress along these time periods; of course, field conditions with variable temperature, suspended sediment concentration and flow rates will affect the hydration period and subsequent sealing of the canal bottom.
• AMD fate was found to be influenced by sorption onto (primarily) fine-grained sediments, biodegradation and UV degradation. Taken together, it appears that AMD longevity would be on the order of 3 to 5 days in the environment, so that AMD accumulation is unlikely to occur.
• Numerical developments have proceeded such that model predictions of LA-PAM concentrations in downstream canal water can be made with good accuracy. Parameters that affect the transport rates in the model can be obtained through site-specific characterization of the geometry of the canal prism (e.g., wetted perimeter), and/or knowledge of water properties (e.g., water chemistry and velocity).
On-going field and laboratory experiments will further clarify questions regarding LA-PAM efficacy and potential environmental risks.

Download full document: 41237_PAM_Lab_Experiments_July_2007.pdf
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Application Guidelines: Use of Granular, Linear Anionic Polyacrylamide (LA-PAM) in Water Delivery Canals for Seepage Control

Polyacrylamides are a broad family of polymers that possess a wide range of physical and chemical properties. One formulation, granular, linear anionic polyacrylamide (LA-PAM), has recently been used for water conservation purposes. When applied to an unlined water delivery canal, LA-PAM flocculates suspended sediment and settles to the bottom of the canal forming a layer that can reduce seepage. This document provides guidelines for applying LA-PAM to unlined water delivery canals in a manner that reduces the risks associated with treatment, while still providing seepage reduction benefits.

These guidelines manage environmental health risks by requiring the use of LA-PAM certified to have a low concentration of the residual acrylamide monomer (AMD), a known animal and suspected human carcinogen. In addition, the quantity of LA-PAM applied is limited to only those canal reaches known to have significant seepage rates and by limiting the rate of LA-PAM applied to no more than 10 lbs/canal acre per treatment and no more than 20 lbs/canal acre per year. The application rate of LA-PAM should be further reduced when optimum suspended sediment concentrations are not available. Although the human health risk from LA-PAM is small, common-sense safety procedures are required to minimize both direct contact and the accidental creation of secondary health hazards, such as slip hazards. As the canal water can transport LA-PAM beyond the treatment reach, downstream stakeholders and the potential for unintended consequences must also be considered before application commences.

These guidelines describe application techniques that can maximize seepage reduction effects. Techniques include applying LA-PAM only when there is sufficient suspended sediment to react with all the LA-PAM added, and applying LA-PAM upstream of the desired treatment reach to account for the time that LA-PAM needs to hydrate before it becomes reactive.

Download full document: 41239_PAM_Application_Guidelines.pdf
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