Black Hawk Lake IA 04-RAC-1134

Assessment Comments

Assessment is based on (1) surveys by the DNR Fisheries Bureau and (2) results of the IDNR beach monitoring program in 1999.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "fully supporting."  The Class B(LW) aquatic life uses remained assessed as fully supporting / threatened"; fish consumption uses were considered "not assessed."  EXPLANATION:  Levels of indicator bacteria at Black Hawk Lake beach were monitored approximately twice per week during summer 1999 by DNR Parks, Recreation and Preserves Division as part of a beach monitoring program at 11 state-owned lakes.   Results of the 34 samples collected at this beach showed that levels of indicator bacteria (fecal coliforms) were generally low, with the overall geometric mean (17 orgs/100 ml) well below the state WQ criterion of 200 orgs/100 ml.   The maximum level of fecal coliforms in the 34 samples was 350 orgs/100 ml on June 14, 1999; thus, no samples exceeded the EPA-recommended single sample maximum density for fecal coliform bacteria of 400 orgs/100ml.   None of the sixteen 30-day periods during summer 1999 had geometric means (N from 6 to 10) greater than the state WQ standard of 200 orgs/100ml.; the maximum 30-day geometric mean was 28 orgs/100ml.   The Class B(LW) aquatic life uses remain assessed as "fully supporting / threatened" based on review and approval of the previous (1998) assessments by the DNR Fisheries Bureau in 2000.   Fish consumption uses were previously assessed as fully supported (=FS) based on results of EPA/DNR fish tissue (RAFT) monitoring in 1992 that showed levels of all contaminants < ½ of respective FDA action levels.   Results of this monitoring are now considered too old (greater than five years) to assess the current levels of contaminants in fish.   Thus, the assessment of fish consumption uses was changed from "fully supporting" to "not assessed."