Publication Summary

Lake Whatcom is impaired for dissolved oxygen due to phosphorus loading. Lake tributaries also fail to meet fecal coliform bacteria standards. Ecology conducted this technical study to set Total Maximum Daily Loads (cleanup plans) for these pollutants.

Based on 2002 and 2003 data, a CE-QUAL-W2 lake model and an HSPF watershed model were developed. Land uses in the watershed model were adjusted to evaluate Lake Whatcom′s response to phosphorus. Loading capacities for total phosphorus and for developed acres were calculated to protect dissolved oxygen in the lake.

Bacteria levels in 11 tributaries did not meet standards. Bacteria concentration and reduction targets were calculated.

Lake Whatcom is impaired for dissolved oxygen due to phosphorus loading. Tributaries to the lake fail to meet Washington State standards for fecal coliform bacteria. The goal of this study is to determine Total Maximum Daily Loads (TMDLs) of these two pollutants. During 2002-03, several agencies conducted monitoring surveys of the lake and tributaries.

For dissolved oxygen (DO), a CE-QUAL-W2 lake model was calibrated for those two years. An HSPF watershed model was developed to predict streamflow and phosphorus lake model tributary inputs based on land-use conditions.

Watershed model land uses were adjusted to produce scenarios for evaluating Lake Whatcom′s response to phosphorus. Land uses for 2002-03 conditions (Base scenario) were changed to mixed forest to estimate natural loading of phosphorus (Full Rollback scenario). Base land uses were changed to maximum allowable development levels to estimate future loading (Full Buildout scenario). Finally, land uses in the Base and Full Buildout scenarios were each partially modified to meet water quality standards.

DO levels were compared between scenarios using the cumulative distributions of lake volumes with different DO values. The DO lake criterion of 0.2 mg/L was subtracted from the Full Rollback scenario to create site-specific targets for this TMDL.

Loading capacities for total phosphorus and for developed acres that generate phosphorus loading at 2003 levels were calculated for two pollutant-reduction scenarios. This was done to provide information for the future selection of final loading capacity and allocations.

Bacteria levels in 11 tributary streams and drains did not meet standards. The statistical rollback method was used to determine geometric mean targets for bacteria corresponding to the 90th percentile criteria of 100 cfu/100 mg/L. A Beales ratio estimator formula was used to calculate the annual fecal coliform loads, and bacteria reduction targets were calculated. Pollutant allocations are recommended for tributary fecal coliform bacteria.

Link to EIM data for User Study ID WHATCOM