Marathon County staff outline winter-spreading proposal, estimate phosphorus reductions and costs for new manure storage

County planning and zoning staff presented updated analysis Feb. 4 on potential amendments to Marathon County’s animal waste ordinance, focusing on proposed winter-spreading restrictions and options for affected farms.

Kirsty (CPZ staff) told the Environmental Resources Committee that the department has moved away from animal-unit categories toward watershed-based or geographically targeted restrictions and that staff had performed a deeper review of farm demographics since the committee’s January discussion. Matt Repking (CPZ) presented farm-level data: of roughly 348 dairy farms in Marathon County, about 198 have some manure storage and approximately 150 do not. Using a subsample of 22 farms that had nutrient management plans, staff estimated that about 41% of that subsample spread liquid manure in winter months; extrapolated countywide, staff estimated roughly 62 farms without storage could be affected by a 60-day winter-spreading ban.

Using an average herd size of 77 cows for the affected group, staff estimated the 62 farms represent more than 9 million gallons of manure that would not be land-applied during a 60-day ban, which the team calculated could prevent roughly 16,000 pounds of phosphorus from reaching waterways. Staff presented a conservative conversion that compared the avoided phosphorus to wastewater treatment removal cost estimates, noting one facility’s removal cost at about $200 per pound of phosphorus and that treating the avoided load could cost several million dollars at municipal treatment plants.

On costs and options for storage, staff provided current (early 2025) estimates: concrete vertical-wall storage for a 25-cow operation was estimated at $40,000–$50,000; for a 77-cow operation $60,000–$80,000; for a 180-cow operation $140,000–$160,000. Earthen lagoon (lined clay) estimates were lower: roughly $25,000–$35,000 for a ~500,000-gallon earthen storage sized around the high end of the sample; staff emphasized many western Marathon County soils have clay that can lower costs. Staff noted transfer systems (pumps and piping) were excluded from the lowest-cost estimates and would add several thousand to tens of thousands of dollars depending on configuration.

Staff also discussed underused/idle manure storages in the county. They reported an inventory of roughly 100 idle storages compiled about 18–24 months ago and said reuse or rental of existing facilities could be a major part of any solution. Staff suggested the county could consider incentives, grant-seeking or a small cost-share to encourage renting existing storage (for example, a supplemental payment per gallon moved) and said they would continue outreach to stakeholders, including a planned meeting with the County Farm Bureau.

Committee members raised implementation concerns for smaller farms and emergency situations; staff said the draft approach would include provisions for emergency spreading permits and encouraged one-on-one outreach. Tom Miller (agricultural interest representative) described nutrient management plans as a positive farm practice that can improve profitability and targeting of nutrients.

The committee did not adopt a local ordinance at the meeting. Members directed staff to continue stakeholder outreach, develop additional data (including capacity and proximity of idle storages), and return with more information at subsequent meetings. Staff said they plan two open houses and direct mailings to affected farms, and will report back to the committee.