5.7 Phosphorus Load Reduction

One of the water quality goals for this subwatershed is the achievement of the Schutz Lake in-lake phosphorus concentration goal of 40 μg/L.  Reduction of phosphorus loads from the subwatershed to achieve that goal will require the combined efforts of the regulatory program, operational programs, and capital projects.  Table 12 below sets forth a summary plan for how this could be accomplished.

The table breaks down modeled phosphorus loading in the subwatershed by source: atmospheric deposition, external sources, and internal sources.  Atmospheric deposition is a regional issue and is not dealt with here.  The primary means of addressing external loading are through the regulation of new loads generated by development and the reduction of existing loads.  The HHPLS identified a 14 pound upstream load reduction that could be achieved through the general application of BMPs to residential and agricultural land, such as phosphorus-free fertilizer, rain gardens, infiltration basins, agricultural BMPs, shoreline restorations, and retrofit projects.

Application of the current regulatory program to new development would also reduce the expected load from ultimate development conditions.  As Table 8 above indicates, more stringent regulation of new development could significantly reduce the need for or size of capital projects.  A detention pond at the outlet of subwatershed unit SL-2 could provide a significant phosphorus load reduction.  As shown in this plan, it is sized to provide the removal necessary should no changes be made to the regulatory program.

Table 12.  Phosphorus load reduction plan for Schutz Lake.

Source 

Reduction 

Ultimate Phosphorus Load [lb/yr]

 

Planned Reductions [lb/yr]  

Final Loading [lb/yr]  

  

Atmospheric 

 Atmospheric deposition

NA

25

NA

25

 

External Loads 

 External load determined

 from modeling land use

 

242

 

 

  

 

 LGU load reduction allocation (Table 11)

 

14

 

 

 

 Existing regulations

 

54

 

 

 

 Schutz Lake Wet Detention Pond

 

56

 

S of Hwy 5

(50% of 112 lb)

 Total After Reductions

 

 

 

118

 

Internal / "Unknown" Loads 

 Internal / "unknown"

 loads determined from   

 modeling land use

 

83

 

 

  

 

NA

 

-

 

 

 Total After Reductions

 

 

 

83

 

Total Load 

 TOTAL 

 

350

124

226

  

 LOAD GOAL  

 

 

 

226

 

 DIFFERENCE 

 

 

 

0