Twelvemile Creek IA 05-GRA-6572
from siltation pond (T3N R30W Sec27 Union Co.) to headwaters (T74N R31W Sec35 NE NE Adair Co.)
- Cycle
- 2016
- 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
- 9/22/2016 10:22:21 AM
- Updated
- 12/27/2016 2:04:24 PM
The presumptive Class A1 (primary contact recreation) uses remain “not assessed” (IR 3a) due to lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “fully supporting” (IR 3b). The source of data for this assessment is the results of monitoring at STORET stations 13010001, 13880010, 13880008, 1388006, and 13880004 (Sites 12m-12, 12m-10, 12m-8, 12m-6, and 12m-4, respectively) conducted as part of a Clean Water Act Section 319 water quality project from 2012 to 2014.
The presumptive Class A1 uses remain “not assessed” due to lack of monitoring for indicator bacteria (E. coli) in this assessment segment. The presumptive Class B(WW1) aquatic life uses are assessed (monitored) as “fully supporting”. Monitoring at site 12m-4 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.5 mg/L), or 21 Temperature samples (maximum = 27.2° c) occurred during monitoring from May 2012 to October 2014. Three of the 21 samples (14%) analyzed for Dissolved Oxygen (minimum = 1.4 mg/L) and one of the 21 samples (5%) analyzed for pH (range = 6 to 8.7) violated the Class B(WW1) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen, or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters are not greater than 10 percent, these results do not suggest impairment and suggest "monitored/full support" of the Class B(WW1) aquatic life uses. In contrast sites 12m-6, 12m-8, 12m-10, and 12m-12 do indicate the potential for impairment, however, 2012 was a very stressful year. Subsequent years data at site 12m-4 showed improvement in dissolve oxygen conditions. Monitoring at site 12m-6 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.1 mg/L), or 8 Temperature samples (maximum = 25.9° c) occurred during monitoring from May 2012 to August 2012. Four of the 8 samples (50%) analyzed for Dissolved Oxygen (minimum = 1.5 mg/L) and two of the 8 samples (25%) analyzed for pH (range = 4.6 to 8.2) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. Monitoring at site 12m-8 showed no violations of Class B(WW1) water quality criteria for 7 Ammonia samples (maximum = 0.5 mg/L), or 8 Temperature samples (maximum = 27.4° c) occurred during monitoring from May 2012 to August 2012. Three of the 8 samples (38%) analyzed for Dissolved Oxygen (minimum = 1.5 mg/L) and two of the 8 samples (25%) analyzed for pH (range = 6 to 8.3) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. Monitoring at site 12m-10 showed no violations of Class B(WW1) water quality criteria for 8 pH samples (range = 6.5 to 8.4), or 8 Temperature samples (maximum = 29.5° c) occurred during monitoring from May 2012 to August 2012. One of the 7 samples (14%) analyzed for Ammonia (maximum = 9.4 mg/L) and four of the 8 samples (50%) analyzed for Dissolved Oxygen (minimum = 1.9 mg/L) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. Monitoring at site 12m-12 showed no violations of Class B(WW1) water quality criteria for 7 Temperature samples (maximum = 28.6° c) occurred during monitoring from May 2012 to July 2012. Two of the 7 samples (29%) analyzed for Dissolved Oxygen (minimum = 1.3 mg/L) and two of the 7 samples (29%) analyzed for pH (range = 6.1 to 8.4) violated the Class B(WW1) criteria during the 2012-2012 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as Dissolved Oxygen, or pH suggests impairment of aquatic life uses. Because the frequency of violations for these parameters are greater than 10 percent, these results do suggest impairment of the Class B(WW1) aquatic life uses. However, due to the improved dissolved conditions at site 12m-4 this site will be assessed (monitored) as “fully supporting”. [Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are presumptively designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]