| OCR Text |
Show section 3.2.4 ( see Figure 3.6, equations 3.3 to 3.6) . The flow rate Fm across a linear section m, of a boundary of length dm, centered around a pair of nodes ( ij) and ( IJ) may be evaluated using a finite difference approximation through equation ( 4.6). Tw.. d ( H..- H„) Fm = NlJ m' * Hi ( 4.6) » j where T^ jj is the aquifer transmissivity normal to the boundary for section m, and djj is the distance between nodes ( ij) and ( I J). Aggregating over all M sections of the boundary b between two water agencies, the net exchange across the boundary is stated as A ^ T d ( H..- H„) Fb- XFm- X ^ V J ( 4' 7) • • 1 ( i, j)£ m y The net exchange F5 across a boundary may then be constrained to be within some tolerance of the predetermined level of exchange Fb°. The predetermined exchange of water across a boundary may also be determined by equation ( 6) with the heads Hjj and Hi j estimated through a simulation model for the appropriate historical pumping configuration considered. One such constraint is developed for each boundary between any two contiguous water agencies. For the ten water supply agencies in Salt Lake County this resulted in 47 boundary constraints. A typical water rights maintenance constraint for a boundary b may be written as X Tvr. d ( H.. - H„) NlJ m XJ Hi . p£ £ TOL ( 4.8) ( ij) em « where TOL represents a tolerance that may be determined as a percentage of Fb°. ( 5) Water Quality Maintenance There are often areas in the aquifer where the groundwater is contaminated. The nature and degree of contamination usually varies from site to site. This makes it difficult to explicitly embody considerations of groundwater quality in a model for yield determination. The primary concern is that water supply development in the aquifer not lead to a degradation of the water quality in the aquifer, by accentuating the transport of pollutants through the aquifer system. A similar strategy to the one used in Chapter 3 is adopted here. Two water quality concerns are addressed. The first concern is the migration of poor quality water from the upper shallow aquifer to the deep, confined aquifer used for water supply. This was addressed earlier by specifying constraints on the permissible drawdown in the deep aquifer. The second concern is the transport of pollutants from a contaminated site in the deep aquifer to other parts of the aquifer. Where artificial recharge is considered, or attempts are made to pump out and dispose of the contaminated groundwater, treatment of the contaminated area, and removal of the pollutants from the groundwater system is possible. Often, such alternatives are not considered, because of the extent of contamination in a certain area. For the Salt Lake County applications, in situ treatment or containment measures were not deemed admissible. The objective was to develop a pumping plan that would not accentuate the migration of contaminants from the 96 |
