Tipton Creek IA 02-IOW-754
mouth (S21 T87N R20W Hardin Co.) to confluence with unnamed tributary in SE 1/4 S17 T87N R21W Hardin Co.
The presumptive Class A1 (primary contact recreation) uses are assessed as "partially supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed as “fully supported” based on results of water quality monitoring in 2010. The source of data for this assessment is the results of water quality monitoring near the mouth of Tipton Creek from March to August 2010 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, at station TC325 approximately 3.5 miles NNW of New Providence, Hardin County.
The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partiallysupported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean of E. coli in the sevensamples collected at station TC325 during the recreation season of 2010 (308 orgs/100 ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Four of the seven samples (57%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to DNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 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(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on results of monitoring at station TC325 during 2010 by the NLAE. This monitoring included continuous monitoring for dissolved oxygen, pH, and water temperature. Data for daily maximum, mean, and minimum values were provided to Iowa DNR. None of the 104 daily maximum values for pH exceeded the Class B(WW2) pH criteria of 9.0; the maximum pH reported for this period was 8.5 units. Similarly, none of the daily minimum values violated the pH criterion of 6.5 pH units (minimum daily value = 6.8 units). None of the 162 daily maximum values for water temperature exceeded Iowa’s added “heat criterion” of 32C. Of the 144 daily minimum values for dissolved oxygen, none were below the either the 5.0 mg/l Class B(WW2) criterion or the 4.0 mg/l criterion which applies during any 24-hour period (minimum value = 5.39 mg/l). According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen, pH, and temperature suggest "full support" of aquatic life uses.