Big Lake Water Quality Monitoring, 2009

Nonpoint Source Water Pollution Control
Waters in the Spotlight

State of Alaska > DEC > Division of Water > Non-Point Source Water Pollution Control

Big Lake Water Quality

Introduction
In 2006, DEC listed portions of the east basin of Big Lake as a Category 5 impaired water under the Clean Water Act section 303(d). Water quality studies conducted by DEC in the summer’s of 2004 and 2005 documented petroleum hydrocarbon pollution in excess of the state water quality standard for the protection of aquatic life found in 18 Alaska Administrative Code [AAC] 70.

In 2009, the DEC tasked OASIS Environmental, Inc. (OASIS) to conduct petroleum hydrocarbon water quality monitoring at Big Lake during the summer of 2009. Project objectives included determining the loading (amount) of petroleum hydrocarbons in the lake, the volume of the lake impaired with too much petroleum, and how motorized watercraft may affect the loading process. The monitoring included collection of water samples from 12 separate sample sites on 13 different sample dates throughout the summer. In addition, some of the sample dates included intensive sampling efforts for which multiple samples were collected from three of the sample sites throughout the day to track the pattern of hydrocarbon concentrations. OASIS also observed and measured watercraft activity on these intensive sample dates to attempt to correlate watercraft types and activities with results for hydrocarbons samples. The project Sample Plan is available on the right of the screen.

Summary of 2009 results Click to view the complete report
Over 300 individual water quality samples were collected and analyzed for total aromatic hydrocarbons (TAH) which are specific types of petroleum hydrocarbons that are constituents of gasoline. Analytical results demonstrate that the water quality standard for TAH is frequently exceeded on holiday weekends. In fact, slightly more than 50% of all samples collected on sample dates associated with Memorial Day, Independence Day, and Labor Day weekends had a TAH concentration greater than the water quality standard. In contrast, only about 7% of samples collected on other days during 2009 had TAH concentrations greater than the water quality standard. The sample sites that had the highest percentage of exceedances for the TAH water quality standard were the locations near watercraft launch sites: BL-4 at the South Shore State Recreation Site, BL-6 at the Southport Marina, BL-8 at the Burkeshore Marina, and BL-10 at the North Shore State Recreation Site.

What does it mean?
The results of the water quality monitoring indicate that areas of the east basin in Big Lake are impaired for petroleum hydrocarbons, which means that concentrations of petroleum hydrocarbons exceed the state water quality standard; however, the exceedances mostly occur during expected high-use days and are focused near watercraft launches where watercraft conditions and density are likely to magnify hydrocarbon concentrations. Therefore, corrective actions should focus on methods to improve water quality for these high-use days, particularly near the identified locations where persistently elevated TAH concentrations occur.

For more information please contact:
Laura Eldred
1700 E Bogard Rd, Bldg B, Ste 103
Wasilla, AK 99654
Phone: (907) 376-1855
Fax: (907) 376-2382
Email: laura.eldred@alaska.gov