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Causes. Seasonally recurring low dissolved oxygen is attributed to nutrient 

 enrichment and treatment plant effluent (Pickett 1992). Water withdrawal 

 exacerbates the problem (Figure 22), by cumulatively reducing instream flow, 

 raising temperatures, and lowering the ability of the water to retain oxygen. 



A total phosphate-phosphorus standard of 100 micrograms per liter applies to 

 the Chehalis Basin (Aroner 1991). Excessive nitrogen or phosphorus loading 

 supports a boom-and-crash cycle of algal growth; this occurred often at 

 Centralia and sometimes at Porter and Hontesano (Aroner 1991). 



At Centralia, ammonia, total phosphorus, and ortho-phospohorus all showed a 

 negative correlation to discharge, which may be the result of point source 

 discharges providing most of the loading (Pickett 1992), while nonpoint 

 sources dominate in the other reaches. 



Effects on Fish 



The combination of high temperatures and low oxygen probably form a block to 

 fish migration, particularly for spring Chinook. These fish reach the 

 Oakville area in May and June and hold there until spawning in the Newaukum 

 and upper Chehalis from late August until early October. If the range of 

 summer eteelhead is to be extended to the upper Chehalis, the same concern may 

 limit their migration. Wolfe (FWS, pers. comm. ) believes deteriorating 

 temperatures and oxygen levels over the last several decades have also hurt 

 American shad. 



High summer temperatures and low oxygen may prevent juvenile salmon and trout 

 from using otherwise suitable rearing areas in the main stem Chehalis. In 

 August 1989 spot-check snorkeling surveys, no juvenile coho or steelhead were 

 found in habitat where expected (Bisson, Weyerhaeuser Co., pers. comm.). 



Total Maxiaua Daily Load Process 



TMDL is a WDOE program intended to achieve full and permanent compliance with 

 water quality standards in river systems where existing point-source pollution 

 controls have not achieved the standards (WDOE 1990). TMDL is required by the 

 Clean Water Act when conventional technology-based controls fail to protect 

 water quality. In the Chehalis system, the process includes all waters from 

 Porter upstream. WDOE h»e identified biological oxygen demand and colifonn 

 bacteria as the key pollutants and will now determine the total amount of 

 pollutants that can be assimilated without harming designated uses. This 

 level of pollution is called the Total Maximum Daily Load (TMDL) which is 

 being determined by intensive monitoring of Basin water quality and modeling 

 to predict water quality conditions at the most susceptible times and 

 locations. This phase will be completed by September 1993. 



After WDOE identifies point sources and nonpoint sources, the agency 

 establishes a forum in which representatives of each pollution source allocate 

 shares of the TMDL among themselves in a binding agreement with WDOE. This 

 Waste Load Allocation (WLA) agreement also allows a share for anticipated 



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