Stafford Creek IA 01-NEM-6370
from mouth (SE1/4 S21 T78N R4E Scott Co.) to headwaters in SW1/4 S9 T78N R4E Scott Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 3/14/2016 2:25:27 PM
- Updated
- 11/18/2016 2:09:59 PM
The presumptive Class A1 (primary contact recreation) uses remain assessed (evaluated) as "not supported" (IR 5p) due to high levels of indicator bacteria that routinely violate state water quality standards. The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supported” (IR 3b) due to violations of the Class B(WW1) criterion for dissolved oxygen. The source of data for this assessment is the results for IDNR/UHL TMDL-related monitoring conducted station SFC1A (STORET station 11820002) from April through October 2008.
Note: A TMDL for the bacterial impairment for streams in the Duck Creek basin was prepared by Iowa DNR in March. This TMDL was approved by U.S. EPA in 2011. According to U.S. EPA, however, the TMDL for the Duck Creek watershed does not assign the required elements to Stafford Creek; thus, this stream remains Section 303(d) impaired and in Category 5p of Iowa's Integrated Report.
EXPLANATION: Results of monitoring for indicator bacteria conducted weekly from April through October 2008 at Station SFC1A suggest that the presumptive Class A1 uses of Stafford Creek should be assessed (monitored) as "not supported." A total of 29 samples were collected at station SFC1A 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 849 and 9,144 orgs/100 ml, with 28 of 29 samples (97%) 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 for E. coli that exceed Iowa’s water quality criterion of 126 E. coli organisms/100.
The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supported” due to violations of criteria for dissolved oxygen. Four of the 29 samples (14%) collected in 2008 at station SFC1A violated the Class B(WW1) criterion of 5 mg/l. The minimum level of dissolved oxygen was 3.6 mg/l. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station SFC1A do not indicate that significantly greater than 10% of the samples exceed the Class B(WW1) criterion for dissolved oxygen. Thus, these results suggest that the presumptive Class B(WW1) uses should be assessed (monitored) as “fully supported.” Despite this indication of full support, the occurrence of four violations of the dissolved oxygen criterion in a single year is unusual and suggests a potential adverse water quality impact. Thus, this assessment segment will be added to Iowa’s list of waters in need of further investigation. Additional monitoring is needed to better determine any potential water quality impacts on the aquatic life of this stream.