estimates of current watershed-based phosphorus loads, and the following LAs based on those
estimates, were derived from the L-THIA model, which may overestimate nutrient loading. The
nutrient loading aspects of the model use curve numbers that have been calibrated for small
watersheds in the Midwest, but the specific area within the Midwest (Indiana) naturally has more
enriched soil and therefore higher phosphorus loads than occur in Marquette County, Michigan.
Also, loadings for larger watersheds (larger than a few square miles) may be overestimated in
L-THIA because the curve numbers were developed using data from small (less than a few
square miles) watersheds. However, because we do not know the scale of the overestimation
of watershed-based phosphorus loading, we have also set aside 10 percent of the LC,
equivalent to 80 pounds, within the MOS to ensure that the allocations in this TMDL are
protective of Goose Lake.
SEASONALITY AND CRITICAL CONDITIONS
Concurrent with the selection of numeric targets, development of the LC requires identification
of the critical conditions. The “critical condition” is the set of environmental conditions (e.g.,
flow) used in developing the TMDL that result in attaining WQS and has acceptable low
frequency of occurrence. The critical conditions for Goose Lake are the elevated summer
temperatures and nutrient loadings, which promote nuisance aquatic plant growth. The target
goal of 0.03 mg/L phosphorus in this TMDL will apply during the months of July, August, and
September. The concentration target, if achieved, is expected to restore designated uses by
reducing the frequency and magnitude of nuisance algal blooms and fish kills and eliminate
odor problems.
MONITORING
Occasional future monitoring of the Goose Lake Outlet will be conducted to assess whether
conditions within the lake are improving. Summer monitoring of nutrient concentrations at the
outlet of Goose Lake may be more feasible than open lake monitoring and show very similar
phosphorus concentration compared to lake data. Because of the difficulty at reducing the
current internal load to Goose Lake, frequent monitoring of the lake is likely not needed since
improvements will be long-term. If any lake management activities are conducted on the lake
(e.g., alum treatments or dredging), monitoring should be conducted on Goose Lake to
document both the short-term and long-term in-lake response.
REASONABLE ASSURANCE ACTIVITIES
Because this TMDL does not require large reductions to the WLA or external load component of
the LA, there are very few reasonable assurance activities that can be conducted in the Goose
Lake watershed that will produce measurable improvements in lake water quality. Reducing the
internal load of phosphorus to Goose Lake is not very practical. Dredging the lake might be
successful in removing a mass of phosphorus from the lake sediment and therefore reducing
internal loading, but it is costly and logistically difficult. Alum treatments are another option, but
beyond cost, which is estimated at $400,000 per treatment, may not be successful in Goose
Lake because it is so shallow and mixes frequently. The lack of riparian homes and land
owners or a watershed association also makes any lake management practices unlikely in
Goose Lake.
All of the NPDES permits contain TMDL-related language. The language in the Empire Iron
Mining permit and the storm water general permit states that “the Stormwater Pollution
Prevention Plan shall identify the level of control for those materials necessary to comply with
the TMDL, and an estimate of the current annual load of those materials.” The MDOT MS4
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