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Alaska Section, American Water Resources Association Michael R. Lilly, Alaska Section AWRA Northern-Region Director I would like to invite you to the January 1999 Brown-Bag presentation by Charlie Collins, CRREL. Please note this meeting is the second Wednesday in January. Charlie's talk will be a presentation on the environmental hydrology solutions being applied at firing ranges on the Eagle River Flats Firing Range on Ft. Richardson, Alaska. We look forward to seeing you. Please feel free to bring a colleague to the meeting. February 10, 1999 "Remediation of a White Phosphorous Contaminated Salt Marsh, Eagle River Flats, Alaska" ABSTRACT Deposition of white phosphorus (P4) from smoke munitions in the saturated wetland sediments and shallow ponds of the Eagle River Flats Firing Range on Ft. Richardson, Alaska, has resulted in the deaths of large numbers of dabbling waterfowl. Eagle River Flats is an 865 ha tidal salt marsh complex located at the mouth of Eagle River along the shore of Cook Inlet. It has been used as an artillery impact range for the last fifty years. Shallow pond areas within this salt marsh where waterfowl feed are ideal locations for preserving white phosphorus and are the sites of greatest waterfowl mortality. Our previous work has shown that if pond sediments contaminated with P4 were allowed to dry below saturation, the P4 particles within the sediment would begin to sublime when soil temperatures are above about 15°C. The unsaturated conditions of the sediment allow the P4 vapors to disseminate through the soil pores away from the P4 particle and oxidize into P4O10. This in-situ natural attenuation of P4 contamination occurs normally in the intermittent flooded shallow ponds during periodic long intervals between flooding tides when the ponds dry up due to evaporation. Our data indicate that these ponds will be mostly decontaminated after about five to seven years. Thus many contaminated sites in Eagle River Flats can be left alone to naturally decontaminate. Deeper ponds that remain flooded or where the sediments remain saturated throughout the year will remain a problem, however. We have looked at several strategies for remediating sediment contaminated with P4 in these sites. The first involved using a remote-controlled dredge to remove contaminated sediments to an upland containment basin. Here the dredge spoils were allowed to settle, the supernatant decanted off, and the dredge spoils allowed to dry, resulting in the complete loss of P4 within a year. Although successful in removing contaminated sediment from permanent ponds within Eagle River Flats, the process was slow and quite expensive. Draining of ponds to expose the contaminated sediments and allowing in situ decontamination was undertaken in a treatability study using an automatic remote pumping system to dewater a contaminated pond. Remote controls allow automatic cycling of the large (2000 gpm) dewatering pump to keep water out of the pond basin throughout the summer allowing contaminated pond bottom sediments to dry. During the first season of this treatability study one pump system was deployed. During the second season, five additional pump systems were deployed in both the original treated pond and in other ponds with different hydrologic characteristics. For each of the ponds treated, the sediments were sampled at the beginning and end of the season and analyzed for white phosphorous to assess effectiveness of the remediation strategies. For the first pumped pond basin P4 contamination levels were reduced by over 88% in one season. Based on the success of the treatability study, pond pumping has been chosen as the preferred alternative for cleanup of this site. |