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Nutrient Source Inventory

The Great Lakes Water Quality Agreement is a commitment between the U.S. and Canada to restore and protect the waters of the Great Lakes. A major goal of the agreement is to reduce the amount of phosphorus entering Lake Erie by 40 percent by 2025. Most of the current research is focused on agricultural practices that contribute nutrients to the lake, but other sources also have been identified.

A new TMACOG study is looking at home sewage treatment systems (HSTS), which have been identified as a potential source of nutrients to surface waters and ultimately Lake Erie. This is a two-year study that is federally funded through the U.S. EPA in its 604b program. The goal of the study is to identify critical sewage areas and target resources to reduce nutrient inputs throughout the western Lake Erie basin (WLEB). Information gained by the study will help communities support their need for funding to extend sewer lines, secure grants to assist households with costs for HSTS repair or replacement, or invest in other sewage infrastructure needs.

Phase one of the study included nine Ohio counties and phase two will add 10 more Ohio counties and six to seven counties each in Indiana and Michigan. The strategy to identify unsewered areas and estimate their nitrogen and phosphorus loads to Lake Erie is complex. TMACOG staff – Vice President of Water Quality Kurt Erichsen and Water Quality Planner Kris Barnswell– first created sewered area maps using data obtained from municipalities and counties. Based on the sewered maps, all other areas were determined to be not on sewers and so are using HSTS. Next, the types of HSTS were determined using data obtained by a 2012 survey completed by the Ohio Department of Health, and 2010 Census Block Data were used to estimate the number of persons in specific areas. Finally, a formula developed by the Ohio EPA was used to estimate nitrogen and phosphorus loads at county and watershed scales.

Preliminary results of the study are that nutrient loads were higher in counties with greater populations in unsewered areas: the top four counties with the highest loads being Lucas, Wood, Fulton, and Defiance. The next steps are to continue using this approach for the remaining counties in the WLEB. Data will then be analyzed to identify clusters of populations with elevated nutrient loads in unsewered areas and make comparisons between the counties and HUC 8- and 12-digit watersheds.

Priority HUC 12-digit watersheds. Selection of the watersheds is based
on a population greater than 3,000 in unsewered areas.


By virtue of their larger populations in unsewered areas, Lucas and Wood
counties have the highest loads for nitrogen and phosphorus, followed by
Fulton County.

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