Unnamed Tributary to Big Creek Lake IA 04-UDM-6546
from mouth (T81N R25W Sec9 Polk Co.) to headwaters (T82N R25W Sec35 Boone Co.)
- Cycle
- 2018
- Release Status
- Final
- Overall IR
- 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
- Trend
- Unknown
- Created
- 7/19/2019 10:26:50 AM
- Updated
- 7/19/2019 10:29:06 AM
The presumptive Class A1 (primary contact recreation) uses remain assessed as “fully supported” based on results of bacteria monitoring in 2011. The presumptive Class B(WW1) aquatic life uses remain "not assessed" due to the lack of sufficient water quality information upon which to base an assessment. The source of data for this assessment remains the results of monitoring at STORET station 13770003 (BCW-8) conducted as part of a Clean Water Act Section 319 water quality project from March to September 2011. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment categories are considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
The presumptive Class A1 uses remain assessed (evaluated) as “fully supported" due to levels of indicator bacteria (E. coli) that meet the Class A1 geometric mean criterion. The geometric mean of indicator bacteria (E. coli) in the seven samples collected at Site BCW-8 during the recreation season of 2011 was 102 orgs/100 ml. Two of the seven samples (29%) exceeded the Class A1 single sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if a recreation season geometric mean is below the the respective criterion (126 orgs/100 ml for Class A1), the primary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Also according to the Iowa DNR assessment/listing methodology, too few samples (< 10) were collected during the 2010-12 assessment period in order to determine whether the percentage of samples exceeding Iowa's Class A1 single-sample maximum criterion of 235 orgs/100 ml is significantly greater than 10%.