Claim: USACE is “mud dumping” in Mobile Bay.
Truth: “Mud dumping” is locally used phrase to describe the practice of thin layer thin layer placement of dredged material. The phrase is misleading as it diminishes the intentional placement practices required for thin layer placement. This placement strategy is used nationally throughout the United States. Thin layer placement strategy is the product of a study performed under the guidance of the interagency working group from 2011-2014. The finding of the study informed a placement strategy to mimic the natural condition within the bay. Native sediment from the rivers and bay enter the federal navigation channel. The material is dredged and placed at least 2,500 feet from the channel, placed in thicknesses less than 1 foot, and placement sites are rotated every 4-6 years to the greatest extent possible. Thin layer placement activities are monitored with before and after dredge surveys and intermediate checks as needed. Background and mixing zone turbidity is monitored at the dredge and placement sites for the duration of the dredge event to ensure water quality standards are met.
Claim: USACE started thin layer placement in Mobile Bay 1.5-2 years ago.
Truth: Dredging in Mobile Bay and Mobile River began in 1826 with enactment of the River and Harbor Act of 1826. Thin layer placement of dredged material was an alternative utilized from 1826 to 1986. In the early 1980s, there was opposition to a placement alternative identified in the Final Supplemental Environmental Impact Statement for the Mobile Harbor Project. The Water Resources Development Act of 1986 required that “…for reasons of environmental quality, dredged material from such project shall be disposed of in open water in the Gulf of Mexico in accordance with all provisions of Federal law. Notwithstanding any other provision of law, no dredged or fill material shall be disposed of in the Brookley disposal area, referred to in such report of the Chief of Engineers.” From 1986 to 2014, maintenance dredged material was placed offshore in the ODMDS, except for emergencies and a placement action in September 2012 where approximately 9 million cubic yards of maintenance dredged sediment was placed within the historically established open water sites. Mobile District subsequently implemented a monitoring and modeling program to demonstrate and predict the behavior and fate of the placed sediment. The results of these studies were used to determine thin layer thin layer placement strategies. Thin layer thin layer placement strategies have been utilized since 2014 when the District Commander approved long term thin-layer placement in the STATEMENT OF FINDINGS for a MODIFICATION TO MOBILE HARBOR OPERATIONS AND MAINTENANCE ADDITION OF A LONG TERM OPEN BAY THIN-LAYER DISPOSAL OPTION MOBILE COUNTY, ALABAMA (PUBLIC NOTICE NO. FP14-MH01-10).
Claim: USACE is dumping 90 MCY in the bay over the next 20 years
Truth: Estimated future maintenance dredging volumes are documented in the Engineering Appendix, Table 4-9 of the Mobile Harbor Integrated General Re-evaluation Report (GRR) with Supplemental Environmental Impact Statement (EIS). Based on the Recommended Plan, future operation and maintenance activities are estimated to be 4,519,000 in the bay channel segment between station 244+66 and 1760+09.28. The material placement has not been determined for the next 20 years. The material placement is evaluated prior to each dredge event. Placement alternatives are determined based on a variety of factors including: volume of material, placement site proximity, the 4 to 6 year rotational cycle, and equipment availability.
Claim: The dredged material smothers and destroys vital seagrass beds and oyster reefs.
Truth: Thin layer placement is performed in water depths ranging from 5-12 feet deep and in open areas devoid of protected habitats (i.e. oyster reefs and submerged aquatic vegetation (SAVs)), where the bay's natural wind and currents constantly mix the water and sediment from top to bottom, ensuring healthy oxygen levels are maintained throughout the placement area.
Claim: Thin-layer placement causes increased turbidity and sediment in the water harming a wide range of marine life and submerged aquatic vegetation (SAVs), fish, crabs, and shrimp, by disrupting their feeding and breeding grounds.
Truth: Dredging activities can cause temporary and localized increases in turbidity; however, best management practices are used to minimize turbidity generation. The Alabama Department of Environmental Management (ADEM) requires that turbidity not exceed 50 Nephelometric Turbidity Units (NTUs) above background. Turbidity is monitored above (upstream) the dredge location, at the dredge location, and downstream at the mixing zone. If the turbidity at the mixing zone exceeds the background sample, dredging operations must cease until turbidity is restored to acceptable levels with notification submitted to the ADEM. The turbidity attributable to dredging activities remains within the established range of natural variability for Mobile Bay, which is characterized by inherently elevated turbidity levels due to its position at the terminus of a large deltaic system, significant riverine sediment inputs from multiple river sources, and additional sediment (and pollutant) loading associated with urban stormwater runoff from adjacent developed watersheds.
Claim: Thin layer placement leads to increased water turbidity, making the bay perpetually muddy.
Truth: Mobile Bay Watershed is the sixth-largest in the United States, covering 43,662 square miles and extending into parts of Mississippi, Georgia, and Tennessee. The Mobile Bay Watershed contributes an average freshwater flow of 62,000 cubic feet per second into Mobile Bay, making it the fourth-largest freshwater inflow in the United States. The bay is a naturally depositional system. Dredging activities cause temporary and localized increases in turbidity; however, the turbidity is within the natural variability of the system.
Claim: Dredged sediment contains pollutants that are then resuspended and dispersed throughout the bay.
Truth: The sediment dredged from the federal navigation channel is natural material from the watershed. The material dredged from the federal navigation channel has been rigorously tested in accordance with Section 103 of the Marine Protection, Research, and Sanctuaries Act (MPRSA) that is required for sediment to be placed in offshore ocean dredge material disposal sites (ODMDS). The testing follows the EPA/USACE “Green Book” which evaluates chemical, physical, toxicity, and bioaccumulation testing to determine if the sediment is safe for ocean placement. No pollutants have been identified above threshold levels.
Claim: Thin layer placement only occurs in Mobile Bay
Truth: Thin-layer placement of dredged material which is a widely accepted practice throughout the United States. See image below from the USACE Regional Sediment Management Sediment Placement Data Viewer. (https://experience.arcgis.com/experience/448e41753a1f408e9dd2c98896e818c0/page/2022-Present)
Claim: USACE started referring to thin-layer placement as beneficial use after WRDA 2024 passed requiring at least 70% of dredged materials be used for beneficial use.
Truth: Thin layer placement is an intentional placement practice that is a beneficial use of dredged material that is in alignment with “Expanding Beneficial Use of Dredged Material in USACE” memo dated 28-Aug-23. Prior to this memo, thin layer placement was required to be classified as transitional. Thin layer placement is beneficial use of dredged material because the native material remains within the system based on physical, chemical and biological data (USACE Gulfport Harbor Studies 1999, Fly Creek 1990, and Mobile Harbor 1990s). Thin layer placement mimics the natural sediment transport within the Bay. Thin-layer placement is also the least costly alternative consistent with sound engineering practices and meeting the environmental standards established by the 404(b)(1) evaluation process.
Claim: The dumping of 90 million cubic yards of sediment is projected over the next two decades, which Baykeeper claims is enough to cover the entire bay in 2.5 inches of mud.
Truth: Based on estimates from the Mobile Harbor GRR, approximately 4.5 MCY of sediment will be dredged from the federal navigation channel annually. This equates to approximately 90 million cubic yards of sediment over the next 20 years. The calculations in this statement are correct, but misleading. The Mobile District does not place material in the entire bay. The thin layer placement areas are identified and shown on the GIS dashboard. Typically, the annual placement area covers approximately 2,800 - 5,600 acres, which is approximately 1-2% of the Mobile Bay footprint.
Claim: USACE should stop thin layer placement and use the dredged material for beneficial use such as coastal restoration projects.
Truth: USACE Mobile District has a long history of supporting beneficial use projects. The Mobile District regularly participates in conferences and meetings to further beneficial use coordination. The District also meets with potential Beneficial Use partners when requested. Additionally, the Mobile Bay National Estuary Program (NEP) facilitates an Interagency Working Group to identify Beneficial Use placement project within Mobile Bay. The Interagency Working Group consists of multiple governmental and non-governmental organizations. USACE is an active participant in this group and has successfully implemented Beneficial Use projects because of this participation.
There are currently no Beneficial Use placement options that meet the annual quantity of O&M dredged material removed from the channel. The maintenance material from the federal navigation channel is typically fine-grained sediment which is not historically the most desirable material to use when constructing coastal restoration projects. USACE is also held to the federal standard which is defined in 33 CFR 335.7 as “…means the dredged material placement alternative or alternatives identified by the Corps which represent the least costly alternatives consistent with sound engineering practices and meeting the environmental standards established by the Clean Water Act Section 404(b)(1) evaluation process or ocean dumping criteria.” Beneficial Use placement projects are site specific and the cost to construct, place material, and maintain the sites vary widely. A non-federal sponsor is required to cover the additional cost beyond the federal standard.
The cost to construct a Beneficial Use site varies depending on the containment required (if any) and physical conditions for the site. Recently, Mobile District and the Alabama Port Authority partnered with Mobile County and the Mobile Bay NEP as part of the deepening project to construct the Dauphin Island Causeway and Deer River projects. The delta cost beyond the federal standard was funded by a National Fish and Wildlife Foundation (NFWF) grant through the Gulf Environmental Benefit Fund.
Containment for recently constructed Beneficial Use projects in the Mobile Bay area has cost $1,500 - $2,000 per linear ft. The cost to place material varies $10 - $90/cubic yard of material based on placement methodology. To date, opportunities to participate in direct marsh creation type projects represent a small fraction of the annual placement capacity needed to maintain the Mobile Harbor project. The cost to construct containment to support the O&M dredged volume for 20 years of capacity would cost hundreds of million dollars.
Claim: Questionable Use of Taxpayer Money: Opponents of the practice argue that it is inefficient use of taxpayer funds, as the dumped material often needs to be re-dredged when it moves back into the shipping channel.
Truth: Thin layer placement is the most efficient use of taxpayer money because it is the least costly placement option for Bay channel material. Based on modeling results, approximately 35% of sediment that erodes from designated placement areas is transported and deposited into the navigation channel. Although the material mobilized back into the federal navigation channel, this placement method is still the federal standard.