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Title: Water Quality Sampling Report : Additional Sediment/Soil Sampling Conducted at the Little Sioux Bend Shallow Water Habitat Project Site During October 2013
Authors: United States. Army. Corps of Engineers. Omaha District
Keywords: Water quality
Aquatic habitats
Pallid sturgeon
Sedimentation and deposition
Environmental management
Environmental protection
Publisher: United States. Army. Corps of Engineers. Omaha District.
Abstract: The U.S. Army Corps of Engineers (USACE) is proposing a project to construct shallow-water habitat (SWH) along the Little Sioux Bend of the Missouri River between RM666 and RM669. The construction of SWH will enhance the aquatic habitat of the Missouri River and benefit the endangered pallid sturgeon (Scaphirhynchus albus) population. Although on the Nebraska side of the Missouri River, the project area is located in Harrison County, Iowa and Burt County, Nebraska and will basically run down the old river channel that is the legal boundary between the States of Iowa and Nebraska. The USACE is proposing to use hydraulic dredging to excavate sediment/soil from the old river channel and discharge the dredge spoil to the Missouri River adjacent to the proposed project area. Section 404 of the Federal Clean Water Act (CWA) requires that a §404 permit be appropriately obtained prior to the discharge of any dredge or fill material into waters of the United States. Under §401 of the Federal CWA an applicant for a federal license or permit (i.e. §404 permit) must obtain a certification that the discharge and activity is consistent with appropriate State or Tribal water quality regulations. Regarding the Little Sioux project, a §401 water quality certification has been requested from the Iowa Department of Natural Resources (IDNR) and Nebraska Department of Environmental Quality (NDEQ) regarding compliance with State water quality standards and implementation plans. The Water Quality Sampling Report and Factual Determinations, “Results of Sediment Sampling and Elutriate Testing at the Proposed Little Sioux Bend Shallow Water Habitat Project Site” (USACE, April 2013) was previously prepared to support Section 404 permitting and State §401certification considerations at the proposed Little Sioux project. Subsequent to that report and conducted sediment sampling, the State of Iowa expressed concerns that the proposed hydraulic dredging to construct SWH at the Little Sioux project may lead to unacceptable nutrient loading to the Missouri River. An expressed concern was that the conducted sediment/soil sampling was not extensive enough (both spatially and depth of sampling) to allow nutrient loading questions to be adequately assessed. Additional sediment/soil sampling was conducted by the USACE at the proposed Little Sioux project site to further address the concerns expressed by the IDNR. The collected sediment/soil samples were analyzed for particle size, total phosphorus, total Kjeldahl nitrogen, and nitrate-nitrite nitrogen. Thirty-seven sediment/soil samples were collected among eight sampling locations at the proposed Little Sioux project site on 16 and 21-October-2013. Sediment/soil core samples were collected and composited every 2 feet to a depth of 10 feet where possible. Sampling depth was limited to 8 and 6 feet, at two of the sites due to the collapse of the bore hole in saturated soils below the water table – resulting in the collection of the 37 additional sediment/soil samples. The composition of the 37 collected sediment/soil samples ranged from 42.4 to 91.1 percent sand (8.9 to 57.6 percent fines) and averaged 73.6 percent sand (26.4 percent fines). Nutrient levels measured in the 37 collected sediment/soil samples ranged from 271 to 624 mg/kg (430 mg/kg average) total phosphorus, 52 to 1,070 mg/kg (282 mg/kg average) total Kjeldahl nitrogen, and non-detectable to 2.6 mg/kg (non-detectable 75th percentile) nitrate-nitrite nitrogen. The measured nutrient levels were statistically-tested for significant differences (α = 0.05) between sampling location and depth. Regarding the measured total phosphorus levels, there was a significant difference among sampling sites, but no significant difference with sample depth. Regarding measured total Kjeldahl nitrogen levels, there was a significant difference among sampling sites, but no significant difference with sample depth. Regarding nitrate-nitrite nitrogen, there was no significant difference among sampling sites and with sampled depth. It is noted nitrate-nitrite nitrogen was nearly significantly different with depth. The total tonnage of nutrients likely present in the sediment/soil proposed for excavation at the Little Sioux project area was estimated from the measured sediment/soil nutrient levels and the design excavation volumes. It is estimated that the total 430,000 CY of sediment/soil to be excavated at the proposed Little Sioux project area contains 236 tons of total phosphorus, 145 tons of total Kjeldahl nitrogen, and less than 1 ton of nitrate-nitrite nitrogen. The estimated total nutrient tonnage was appropriately allocated, based on design excavation volumes, to the three depth layers (i.e. 0-3 feet, 3-6 feet, and > 6 feet) that have been proposed by the IDNR for alternative disposal. The total phosphorus tonnage estimated to be in the three layers is 71.3 tons (0-3 feet), 57.4 tons (3-6 feet), and 107.7 tons (>6 feet). The National Research Council of the National Academies published the report, “Missouri River Planning – Recognizing and Incorporating Sediment Management” which assessed nutrient loadings to the Missouri River and Gulf of Mexico (NRC, 2011). The report concluded that potential nitrogen loading from hydraulic dredging to construct SWH along the Missouri River was likely not a concern, but total phosphorus loadings could be a concern regarding Gulf of Mexico hypoxia. Currently, the total phosphorus load to the Gulf of Mexico is estimated to be 154,300 metric tons per year, with the contribution of the Missouri River to this total load estimated to be between 16.8% and 20% (NRC, 2011). Assuming the proposed SWH construction at the Little Sioux project area would be completed within one year, the total phosphorus tonnage in the proposed 430,000 CY to be excavated represents 0.76% of the current yearly total phosphorus loading in the Missouri River, and 0.14% of the annual total phosphorus load delivered to the Gulf of Mexico. These percentages are upper bound estimates, as sediment deposition processes in the Missouri and Mississippi River channels would reduce total phosphorus loads delivered to the Gulf, and actual downstream deliveries would be significantly less than these values. Total phosphorus in Iowa soils tends to be higher in the surface horizon, decreases to a minimum and then increases with depth within members of the biosequence (Fenton, 1999). The general trend of the distribution is similar whether the parent material is loess or glacial till (Fenton 1999). The total phosphorus levels measured in the collected sediment/soil samples at the proposed Little Sioux project area are within the range of expected values based on soils and land use present at the project site, and exhibit a similar relationship with depth as indicated for Iowa soils by Fenton, 1999.
Description: Technical Report
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Technical Reports