Duck Creek IA 01-NEM-1895
from Sec 17-18 line T78N R3E Scott Co. to unnamed trib (SE Sec14 T78N R2E Scott Co.). (Note: Lower segment boundary changed in 2010 to match 2009 WQ Standards.)
The presumptive Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" (IR 4a) due to high levels of indicator bacteria that routinely violate state water quality standards. The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of information upon which to base an assessment. The source of data for this assessment is the results for IDNR/UHL TMDL-related monitoring conducted at one location in this assessment segment during 2008: DC-Site 16 (at the west edge of Davenport, west of I-280). Additional monitoring for indicator bacteria was conducted at Site DC-16 from May to November 2013.
Note: A TMDL for the bacterial impairment in the Duck Creek basin was prepared by Iowa DNR in March 2010. This TMDL was approved by U.S. EPA in 2011. Due to completion of the TMDL, the Integrated Report category for the presumptive Class A1 recreational uses is changed from 5a (impaired; TMDL needed) to 4a (impaired; TMDL approved). Additional monitoring for indicator bacteria was conducted at station DC-16 from May to November, 2013. The geometric mean of the six samples was 1,229 orgs/100 ml; thus far exceeding the Class A1 criterion of 126 orgs/100 ml. All six samples (100%) exceeded the single-sample maximum criterion of 235 orgs/100 ml. Although the number of samples collected during the 2012-2014 monitoring period for the 2016 IR cycle does not meet Iowa DNR data completeness criteria (i.e., at least seven independent samples collected during a recreation season), the geometric mean of 1,229 orgs/100 ml suggests an ongoing impairment of the Class A1 uses in this assessment segment.
EXPLANATION: Results of monitoring for indicator bacteria conducted weekly from April through October 2008 suggest that the presumptive Class A1 uses of this segment of Duck Creek should be assessed (monitored) as "not supported." A total of 29 samples were collected at station DC-16 during this period; these data allowed calculation of twenty-five, 30-day/five-sample geometric means. All of the 30-day geometric means exceeded Iowa’s Class A1 criterion of 126 organisms / 100 ml. The minimum and maximum geometric means were 235 and 6,794 orgs/100 ml, with 24 of 29 samples (83%) exceeding Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines and IDNR’s assessment/listing methodology, these results suggest non-support of the presumptive Class A1 (primary contact recreation) uses due to geometric means that exceed Iowa’s water quality criterion of 126 E. coli organisms/100.
The Class B(WW2) aquatic life uses remain “not assessed” due to the lack of information upon which to base an assessment. Levels of dissolved oxygen, however, were measured during the TMDL-related sampling in 2008 with no violations of the Class B(WW2) criterion occurring in the 29 samplings conducted at station DC-16. The minimum level of dissolved oxygen was 5.1 mg/l. Although these results suggest “full support” of the presumptive aquatic life uses, the lack of additional data for ammonia, toxic metals, and/or pesticides, and the lack of biological data for this segment, prevents development of a complete assessment of the aquatic life uses. Thus, these uses are considered “not assessed”.