Lake Whatcom is impaired for dissolved oxygen due to phosphorus loading. Lake tributaries
also fail to meet fecal coliform bacteria standards. The goal of this study is to determine total
maximum daily loads of these pollutants.
Monitoring surveys were conducted in 2002 and 2003. For dissolved oxygen, a CE-QUAL-W2
lake model was calibrated for those two years. An HSPF watershed model was developed to
develop flow and phosphorus lake model inputs based on land use conditions.
Watershed model land uses were adjusted to produce scenarios for evaluating Lake Whatcom’s
response to phosphorus. Base (2002-03) land uses were changed to mixed forest to estimate
natural loading (Full Rollback). Base land uses were changed to maximum allowable
development levels to estimate future loading (Full Buildout). Finally, land uses in the Base and
Full Buildout scenarios were each partially rolled back to meet water quality standards.
For evaluating standards, the lake model was looped multiple times by rerunning 2003
conditions as if they were consecutive years. Dissolved oxygen levels were compared between
scenarios using cumulative lake volumes. The dissolved oxygen 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 developed acres that generate phosphorus loading at
2003 levels are calculated for two pollutant reduction scenarios, to provide information for the
future selection of final loading capacity and allocations.
Bacteria levels in eleven tributary streams and drains did not meet standards. The statistical roll
back 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.
Source: Lake Whatcom TMDL Technical Report InfExt DRAFT Main.pdf