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Case Study: Load Reductions and Allocations
Table of Contents
The allocation modeling framework is used to identify the combination of best management practices and technology options that will meet fecal coliform criteria for secondary recreation contact under three different allocation scenarios:
- Minimize total abatement costs (Minimum Cost),
- Equal percent load reductions (Equal % Red.), and
- Equal loads.
Figure 1: Load reductions are greatest for allocations based on equal percent reductions. Total load reductions are lowest for the minimum cost allocations.
Fecal coliform criteria include 30-day average and 90% upperbound limits of 200 and 400 cfu/100ml respectively, and a maximum criterion of 2000, not to be exceeded at any time. Modeling results indicate that average daily fecal coliform loads must be reduced by 95% to 97% to meet applicable criteria, regardless of the allocation option selected (Figure 1).
The largest load reduction is needed when allocations are based on equal percent load reductions (11,500E7 reduced to 320E7 cfu/day) across stakeholders, and load reductions are smallest for the minimum cost allocations. Minimum cost allocations impose few constraints on abatement strategies, thereby providing opportunities for maximizing abatement efficiency.
Approximately 75% of load reduction achieved under each of the three scenarios is due to the exclusion of beef cattle from streams. Most of the remaining load reductions are attributable to septic system repairs by wastewater treaters. Cattle exclusion and septic system repairs can be characterized as being necessary practices because fecal coliform criteria can not be met without these practices (details about abatement decisions under each scenario).
The load reductions achieved under the cost minimizing scenario are not constrained by equity considerations and are achieved almost exclusively by cattle exclusion and septic system repairs. Allocations based on equal load reductions and equal percent load reductions are more restrictive because they force hog and dairy operations and wastewater treaters to try to match the levels of necessary load reductions achieved by beef cattle operations. As a consequence, the wastewater treatment plant must install advanced technology and hog and dairy operators must establish a composting program in the equal percent load reduction scenario. Load allocations for wastewater treaters and hog and dairy operations are therefore lower for the equal percent reduction scenario (figure 2).
Figure 2: Comparing load allocations to different sources under each of the three allocation scenarios. Allocations to the Beef source remain the same for each scenario, but allocations change for the hog and dairy source as well as the wastewater treaters.
The equal loads restriction requires no additional abatement by wastewater treaters, but hog and dairy operation must alter manure application schedules to try and match the loads from beef cattle operations and waste treaters. As a result, the load allocation to hog and dairy operations under the equal load constraint is less than the minimum cost allocation.
The predicted concentrations associated with minimum cost allocations satisfy all criteria (figure 3). The average concentration in May is reduced from 5,800 under baseline conditions to 70 cfu/100 ml after minimum cost allocations. Predicted concentrations resulting from the other allocation options satisfy all criteria as well.
Figure 3: average, upperbound, and maximum criteria for fecal coliform bacteria are satisfied for each month under the minimum cost allocations.
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