Final Approved TMDL
Final Report Page 34 August 2007
phosphorus residence time in the three lakes is on the order of a few months. Loads
entering the lake in the fall through early spring period do not directly affect summer
phosphorus concentrations, and therefore were excluded from the TMDL analysis.
6.1.5 Margin of Safety
The TMDL contains an explicit margin of safety of 10%. The 10% margin of safety is
considered an appropriate value based upon the generally good agreement between
the BATHTUB water quality model predicted values and the observed values. Since
the model reasonable reflects the conditions in the watershed, a 10% margin of safety
is considered to be adequate to address the uncertainty in the TMDL, based upon the
data available. This margin of safety can be reviewed in the future as new data are
developed. The resulting explicit loads allocated to the margin of safety are 0.087
kg/day for Mt. Olive New Lake, 0.018 kg/day for Mt. Olive Old Lake, and 0.081
kg/day for Staunton Lake.
6.2 ATRAZINE TMDL (MT. OLIVE NEW AND MT. OLIVE OLD LAKES)
A load capacity calculation was applied to support development of an atrazine TMDL
for Mt. Olive New Lake and Mt. Olive Old Lake.
6.2.1 Loading Capacity
The loading capacity is defined as the maximum pollutant load that a waterbody can
receive and still maintain compliance with water quality standards.
6.2.1.a Mt. Olive New Lake
The loading capacity for Mt. Olive New Lake was defined over a range of specified
flows, based on expected flows to the lake. The allowable loading capacity was
computed by multiplying flow by the TMDL target (3 ug/l). The atrazine loading
capacity for Mt. Olive New Lake is presented in Table 3.
Table 3. Mt. Olive New Lake Load Capacity
Mt. Olive New
Lake Flow (cfs)
Allowable
Atrazine Load
(lbs/day)
0.07 0.0011
0.70 0.0113
3.50 0.0566
7.00 0.1133
14.00 0.2265
35.00 0.5663
70.00 1.1327
140.00 2.2653
350.00 5.6633
