Alaska Section, American Water Resources Association

Tom Douglas, Alaska Section AWRA Northern-Region Director

This is a tentative list of winter speakers for AWRA, Northern-Region Section. Dates and locations vary and are subject to change for the 2003 talks, and we will make every attempt to keep you informed of any changes as they occur. We plan to send an email out the Monday prior to each talk, so if you have not been receiving E-mails and wish to, please contact Tom Douglas at (907) 353-9555 or Thomas.A.Douglas@erdc.usace.army.mil. Brownbag talks are from 12:00 pm to 1:00 pm on the second Wednesday of each month. We meet in the conference room at the Department of Natural Resources, 3700 Airport Way (across from the Airport Way Fred Meyer Store)

February 12th

Julie Ahern
(ftjaa@uaf.edu)
University of Alaska Fairbanks Graduate Student

Title: Capture Zone Delineation in Alaska: Current Methods and Future Possibilities

Abstract:
Over 95% of the world's usable fresh water lies in the subsurface. If a groundwater source becomes contaminated, public health is obviously threatened, and clean-up and treatment can render high costs. Moreover, another water source may not be readily available, which could pose serious problems if water treatment is not feasible. Thus, protecting our groundwater resources from contamination is necessary to avoid a potential crisis.
On a national level, the US EPA recognized and responded to this need by creating the Wellhead Protection Program (WHPP), established in the 1986 amendments to the Safe Drinking Water Act (1974). Further amendments were issued in 1996 that included the Source Water Assessment Program (SWAP), which called for states to study and report on basic information regarding all public water supply systems within their boundaries. Following this legislation, the Alaska Department of Environmental Conservation (ADEC) developed the Drinking Water Protection Program (DWPP), under which both the WHP and SWA programs fall. The EPA approved DWPP in April 2000.

The Alaskan source water assessments are currently underway and scheduled for completion by June 2003; ADEC must assess nearly 1800 public water systems (PWS), roughly 90% of which are wells. The first step of a SWA is delineation of the drinking water protection area, also known as the capture zone or zone of contribution. ADEC staff calculate these areas via analytical models using the Thiem equation. Because the areas are time-dependent, multiple zones are delineated based on chosen times-of-travel (TOT), with longer TOT corresponding to larger zones. In terms of protection efforts, priority is given to shorter TOT zones, as their susceptibility to contamination is more immediate. The zones are then enlarged to account for uncertainty that may result from lack of knowledge of factors such as aquifer parameters and pumping rates. SWA and WHPP do not apply to private or tribal water systems. For these parties, EPA simply provides guidebooks suggesting practical wellhead protection options and general rules of thumb such as maintaining a set distance between the well and potential sources of contamination.
In examining national trends concerning implementation of WHPP and SWAP, state programs vary greatly. This is due to the non-regulatory nature of both programs (i.e., no enforceable groundwater standards exist at the federal level). Some are regulatory while others rely on educational outreach to encourage voluntary action. PWS delineations may be as simple as fixed-radius circles. Such rudimentary methods are often used due to budget and time constraints. Unfortunately the shape and volume of the zone may exhibit considerable error because the underlying assumptions are invalid in many situations.

However, upon completion of a SWA for a given water system, a community can opt to build on the delineation process by employing more accurate techniques. Assistance may be provided from local universities or environmental consulting firms. Besides conventional analytical solutions, numerical modeling via finite-difference or finite-element methods are also possibilities. If detailed information on hydrogeologic conditions is unavailable and too costly to obtain, several statistical methods may be used to determine affects of uncertainty on the delineation.