Section 9
Total Maximum Daily Load for
the Washington County Lake and Beaucoup Creek Watersheds
v 9-5
FINAL REPORT
9.1.2.4 Waste Load Allocation
The WWTP in the Washington County Lake Watershed contributes minimal loadings
to Washington County Lake as discussed in Section 5.1.7.1; therefore, no WLA is
recommended at this time.
9.1.2.5 Load Allocation and TMDL Summary
Table 9-3 shows a summary of the TMDL for Washington County Lake. On average, a
total reduction of 89 percent of total phosphorus loads to Washington County Lake
would result in compliance with the water quality standard of 6.0 mg/L DO (16 hours
of any 24-hour period) based on modeling efforts.
Table 9-3 TMDL Summary for Total Phosphorus in Washington County Lake
LC
(lb/yr)
WLA
(lb/yr)
LA
(lb/yr)
MOS
(lb/yr)
Reduction Needed
(lb/yr)
Reduction Needed
(percent)
3,031 0 2,880 152 22,370 89%
Table 9-4 shows the respective reductions needed from internal cycling, atmospheric
loads, and nonpoint sources in the watershed to meet the TMDL. The reduction of
atmospheric loads is zero because atmospheric contributions cannot be controlled by
watershed management measures. The percent reduction from internal cycling is
estimated as 90 percent based on attainable reductions from management measures that
will be discussed in Section 10. An approximate 85 percent reduction of nonpoint
sources from the watershed, in addition to the reduction of internal cycling, would be
necessary to meet the load allocation presented in Table 9-3. Methods to meet these
targets will be outlined in Section 10.
Table 9-4 Sources for Total Phosphorus Reductions
Source
Current Load
(lb/yr)
Load Reduction
(lb/yr) Percent Reduction
Internal Cycling 19,378 17,440 90%
Atmospheric 65 0 0%
Nonpoint Sources 5,807 4,930 85%
9.2 TMDL Endpoints for Beaucoup Creek
The TMDL endpoints for manganese, sulfates, TDS, and DO in a stream segment are
summarized in Table 9-5. For manganese, sulfates, and TDS, the concentrations must
be below the TMDL endpoint. For DO, concentrations must be greater than 6.0 mg/L
for 16 hours of any 24-hour period. These endpoints are based on protection of aquatic
life in Beaucoup Creek and its tributaries. Some of the average concentrations, which
are based on a limited data set, meet the desired endpoints. However, the data set has
maximum or minimum values, presented in Section 5.1.5.2.1, that do not meet the
desired endpoints, and this was the basis for TMDL analysis. Further monitoring as
outlined in the monitoring plan presented in Section 10, will help further define when
