Posted on July 25, 2023 by Ronald R. Janke
The Ohio EPA has adopted and submitted to US EPA for approval the Maumee Watershed Nutrient Total Maximum Daily Load (TMDL) to address impairments to drinking water, aquatic life and recreational uses in shoreline and open waters of the Western Basin of Lake Erie caused by harmful algae blooms (HABs). This document, issued pursuant to section 303(d) of the Federal Water Pollution Control Act, is a major step in addressing a problem that has garnered national attention.
In the Western Basin of Lake Erie HAPs contain cyanobacteria algae which are capable of producing toxins harmful to humans and other life forms. These blooms, after having been reduced by controls on phosphorus discharges, began reappearing in the 1990s. These algae blooms are seasonal and occur primarily from July to October. The onset and severity of the blooms have varied over the last two decades. These year-to-year differences in HAPs are caused primarily by variations in the amount and intensity of rainfall from March to July. Greater and more severe runoff produces greater phosphorus transport via stormwater. Through the TMDL the Ohio EPA seeks to achieve a 40 percent reduction in total phosphorus loading, based on a 2008 baseline, with a three percent margin of safety. This reduction is calculated to achieve a target severity index that has been exceeded most years by varying amounts since 2008.
The primary reduction target of the TMDL is agriculture, which composes 70 percent of the land use in the Maumee watershed and which is the principal source of phosphorus entering the Western Basin of Lake Erie due to the use of fertilizer, commercial as well as manure. The TDML identifies a number of programs for reducing total phosphorus from the agricultural sector. Complicating the reduction of phosphorus from agricultural areas is the presence of legacy sources in the form of soil containing phosphorus at higher than background levels due to past nutrient applications. Legacy phosphorus operates as a persistent source of total and dissolved phosphorus transmission to streams via drain tile and surface flow in the Maumee watershed.
Wastewater treatment facilities, principally municipal sanitary plants, controlled by National Pollution Discharge Elimination System permits are estimated to contribute only six percent of the spring total phosphorus load to the Maumee watershed. As a whole, these facilities are discharging less than half their permitted phosphorus loads. For larger facilities, the Ohio EPA plans to issue general permits with a grouped waste load allocation for the covered point sources which would avoid the need to incur additional costs as long as the grouped waste load allocation is maintained. The Ohio EPA notes that under this general permit, the opportunity for wastewater trading will exist.
The TMDL considers other sources of phosphorus discharges, such as stormwater, home sewage treatment systems, atmospheric deposition and natural sources. Also, portions of the Maumee watershed are in Michigan and Indiana, and 25 percent of the 2008 baseline total phosphorus load enters the Maumee watershed from these two states. Accordingly, the TMDL establishes an allocation reflecting a proportionate reduction to the baseline total phosphorus load for these waters where they enter Ohio. Ohio EPA notes that it is discussing with Michigan and Indiana how these allocations will be achieved.