Bob White Lake IA 05-CHA-1338
Wayne County S4T68NR22W 1 mi W of Allerton.
- Cycle
- 2022
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Hypereutrophic
- Trend
- Improving
- Trend Comment
- Based on the delisting of the algal impairment and Disolved oxygen impairment. Beach Indicator bacteria also shows improvement.
- Created
- 12/30/2021 11:11:58 AM
- Updated
- 2/17/2022 11:08:52 AM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2014 | Class BLW | Organic Enrichment: Low Dissolved Oxygen | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
| 2008 | Class A1 | Algal Growth: Chlorophyll a | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency due to large amounts of suspended sediment and due to violations of the state water quality standard for indicator bacteria. The Class BLW use was assessed (evaluated) as "WINOFI" due to impacts from large amounts of suspended sediment. The Class C use was assessed (monitored) as “fully supported.” All other designated uses were “not assessed.” Note: A TMDL for siltation at Bob White Lake was prepared by DNR and approved by EPA in 2002. Because the Section 303(d) impairments for indicator bacteria were not addressed in the TMDL, this waterbody was placed into IR Category 5a (impaired; TMDL required.)
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2019-2020 21930001 Bob
White Beach
Iowa DNR 6 WQ CY 2016-2019 22930001 Bob
White Lake
Class A1 - Indicator Bacteria: Site ID Data Source ID # Samples per Year (2018/ 2019/2020) 2018 Geometric Mean 2019 Geometric Mean 2020 Geometric Mean Violates Annual Geometric Mean? # 2018 SSM violations / SSM Violations needed for impairment # 2019 SSM violations / SSM Violations needed for impairment # 2020 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 21930001 6 0/15/16 NA 47 45 NO NA 2 / 4 3 / 4 NO Monitored Full According to DNR's methodology, a lake must meet water
quality standards for two consecutive cycles to suggest
de-listing. Therefore, Bob White Lake will remain listed for the
2022 cycle as "not supported" its Class BLW uses due to Ecoli
Bacteria. Class A1 - pH Site ID Data Source ID # Samples / # Years Minimum Value Maximum Value Mean Value # Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22930001 6 12 / 4 7.3 8.8 7.9 0 4 NO Monitored Full Class A1 - Lake TSI's Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation? Assessment Type Support Level 22930001 6 Chlorophyll a TSI 12 / 4 26 63 46 NO Monitored Full 22930001 6 Secchi TSI 12 / 4 59 103 83 YES Monitored Not 22930001 6 Total Phosphorus TSI 12 / 4 69 95 83 NA NA NA 22930001 6 Inorganic suspended solids 12 / 4 2 50 18 NA NA NA DNR's assessment methodology indicates that at least two
assessment/listing cycles with a TSI value less than or equal to 63 are
necessary to suggest de-listing of an impairment. The chlorophyll a
TSI value for the 2018 assessment listing cycle was 69, which based on DNR's
assessment/listing methodology indicated an impairment based on the narrative
criteria protecting against aesthetically objectionable conditions. Because the
TSI value for the 2020 assessment/listing cycle was less than the trigger of 65
(2020 listing for chlorophyll a was 56), and because the TSI value for the
current listing cycle is also 46, based on DNR's methodology, these values
suggest "full support" of the Class A1 uses protecting against aesthetically
objectionable conditions and the impairment (5a) for chlorophyll a is suggested
for delisting for the 2022 assessment/listing cycle. Class BLW - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value # Violations # Acute / Chronic Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22930001 6 Ammonia 12 / 4 0.018 0.683 0.21 NA 0 / 0 4 NO Monitored Full 22930001 6 Dissolved Oxygen 12 / 4 4.8 11.1 7.1 1 NA / NA 4 NO Monitored Full 22930001 6 pH 12 / 4 7.3 8.8 7.9 0 NA / NA 4 NO Monitored Full 22930001 6 Temperature 12 / 4 17 30.6 24.6 0 NA / NA 4 NO Monitored Full Bob White Lake was assessed as "not supported" for
the 2014 assessment/listing cycle based on Dissolved Oxygen. Based on DNR’s
assessment methodology 2 consecutive assessment/listing cycles without
significantly greater than 10% of the samples violating the single-sample
maximum criterion are necessary to propose delisting based on Dissolved Oxygen
violations. There were less than 10% of the samples exceeding the single-sample
maximum criterion for the 2020or current 2022assessment listing
cycle. Therefore, the impairment for Dissolved Oxygen is suggested for
delisting for the 2022 assessment/listing cycle. Class BLW - Lake Planktonic Cyanobacteria: Site ID Data Source ID # Samples Maximum Cyanobacteria Wet Mass Maximum Cyanobacteria % Composition Median Cyanobacteria Wet Mass Median Cyanobacteria % Composition Median Cyanobacteria Concentration = 75th Percentile Assessment Type Support Level 22930001 6 6 50.00 98.5% 0.13 4.1% NO Evaluated NA Class C - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value Median Value # Violations Violates Significantly >10% Rule? Assessment Type Support Level 22930001 6 Inorganic nitrogen (nitrate and nitrite) 12 / 4 0 3.7 0.7 0.2 0 NO Monitored Full 22930001 6 pH 12 / 4 7.3 8.8 7.9 7.8 0 NO Monitored Full
Class HH: No Data