By Bob Otwell
In the Great Lakes state, we think of water as abundant, if not inexhaustible. Not far from Grand Rapids and Muskegon, Ottawa County is bordered on the west by the bulging waters of an engorged Lake Michigan. However, over the past 30 years, increasing use of groundwater is causing water shortages and increasing pollution within the groundwater supply.
In terms of population, Ottawa County is the fastest growing county in the state. Grand Haven is in the northwest corner and Holland is in the southwest corner of the county, and Grand Rapids sits just to the east in Kent County. Ottawa County has four sources for its water supply; Lake Michigan, inland lakes, a glacial drift aquifer, and a deeper bedrock aquifer. Most of the population receives drinking water from public water systems supplied by Lake Michigan, while the major groundwater users are irrigated farms and rural homeowners.
Michigan State University (MSU) completed two comprehensive Ottawa County groundwater reports between 2011 and 2016. The reports tabulated groundwater use, and defined geology and hydrology for the county and the region. The chart below from the MSU studies shows a sharp increase in water use starting in about 1990, led by increases in irrigation (IRR), followed by domestic wells (DOM), with smaller uses by industry and public groundwater systems. Total water use quadrupled between 1990 and 2015.
The MSU reports found that the primary issue for groundwater supply is that the bedrock aquifer water levels have declined by as much as 45 feet. This means that more groundwater is being taken out of the aquifer than is being recharged by rainfall. This lowering of groundwater levels has caused a change in flow patterns within the bedrock aquifer, resulting in increased salinity and higher chloride levels. Eight percent of samples are now above the Secondary Drinking Water Standards for chloride of 250 milligrams per liter (mg/L), which are designed to protect against taste, odor and color impacts. Many more are at levels harmful to agricultural irrigation, which can be as low as 70 mg/L. Background chloride concentrations in Michigan are typically 10-30 mg/L. The following chart from MSU studies shows increasing chloride levels since around 1995.
The bedrock aquifer, part of the Marshall sandstone formation, is an old seabed, and in some places has salinity levels higher than the ocean. Historic freshwater recharge has diluted these levels to create potable water, but the increased pumping has changed the flow regime. This groundwater conundrum is not confined to Ottawa County. Intensive groundwater pumping in other Michigan counties in the Saginaw Bay area and southeast Michigan has caused similar situations of increasing salinity.
So, what should be done about these situations? How can we live in a state with what seems like so much available water and yet have water shortages? Steps are being taken to reduce future use of the bedrock aquifer in Ottawa County. Allendale Township bans new housing developments from using groundwater. Ottawa County has prepared a groundwater sustainability plan to influence future groundwater use. The plan hopes to balance economic growth and preserve the groundwater resource. Groundwater level and quality monitoring are an important part of the plan, along with closer monitoring of water use.
But how long do we watch as degradation to the aquifer occurs before more decisive action takes place? Methodically switching irrigation supply and rural homes from the bedrock aquifer to a Lake Michigan source could permanently halt this degradation. Lack of action could harm the aquifer for future generations.
FLOW board member Bob Otwell is a hydrologist and founder of Otwell & Mawby