Lime Creek IA 02-CED-525
from confluence with unnamed tributary (S1 T87N R10W Buchanan Co.) to confluence with unnamed tributary in SW 1/4 S11 T88N R10W Buchanan Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Unknown
- Created
- 8/16/2016 8:42:40 AM
- Updated
- 12/1/2016 8:19:04 AM
The presumptive Class A1 uses remain assessed (monitored) as “not supported” (IR 5p) due to levels of indicator bacteria that violate Class A1 criteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of IDNR-sponsored monitoring in 2010 and 2011. The sources of data for this assessment remain the results of monitoring at two stations on Lime Creek sampled from May 2010 to July 2011: STORET station 15100007 at 240th Street and STORET station 15100008 at 250th Street.
The presumptive Class A1 uses remain assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E. coli) at the two stations. The geometric mean of indicator bacteria (E. coli) in the 12 samples collected at Station 15100007 at 240th Street during the recreational season of 2010 (637 orgs/100 ml), and the geometric mean of the 12 samples collected during 2011 (946 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Twenty of the 24 samples (83%) collected at this station exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. Similarly, the geometric mean of indicator bacteria (E. coli) in the 12 samples collected at Station 15100008 at 250th Street during the recreational season of 2010 (677 orgs/100 ml), and the geometric mean of the 11 samples collected during 2011 (957 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml. Twenty-one of the 23 of the samples (91%) from this station exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as “impaired” (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW-2) aquatic life uses remain assessed (monitored) as "fully supported" based on results of chemical/physical water quality monitoring from 2010 to 2011 at stations 1510007 and 15100008. No violations of Class B(WW2) water quality criteria for temperature occurred in the combined 48 samples analyzed from May 2010 to July 2011. One of the 24 samples (4%) collected at station 15100007 violated the Class B(WW2) criterion for dissolved oxygen. The sample collected on August 3, 2010, contained 4.0 mg/l of dissolved oxygen, thus violating the criterion of 5.0 mg/l. Similarly, one of the 24 samples (4%) collected at this station violated the Class B(WW2) criterion for pH. The sample collected on June 8, 2011, contained a pH of 6.3 units, thus violating the Class B(WW2) criterion of 6.5 units. 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 or pH, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, however, the results from station 15100007, however, do not indicate that significantly greater than 10% of the samples exceed the Class B(WW2) criterion. Thus, the results of chemical/physical water quality monitoring in 2010 and 2011 in this segment suggested that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported.”