132 REPORT OF INVESTIGATIONS No. 50
well, was sampled 20 minutes and 150 minutes after the salt was put in the drainage well, no rise in chloride content was noted. However, the chloride content of the water in the Northcrest supply well rose sharply (from 12 ppm to 47 ppm) when the well was sampled 18 hours after the salt was put into the well. The salty water reached the supply well sometime between the 21/ hour and the 18 hour sample collections. Water was not injected into the drainage well during the test and this may have somewhat delayed the dispersal of the injected salt. The other supply wells which were closer to the drainage well but shallower than the Northcrest well and which were pumped at a lower rate showed rises in their chloride content at times ranging from /. hour to 26 hours after the salt was put into the drainage well.
Some of the major factors which control the rate of movement of water from a drainage well to a supply well are:
1. The distance between wells.
2. Rate of flow down the drainage well.
3. Pumpage rate of supply wells.
4. Relative depth intervals of the open-hole part of the two
wells.
5. Permeability of the material between the two wells.
6. Relative orientation of the two wells.
The limestone underlying Orange County is like a huge sponge with large and small cavities and channels interconnected both horizontally and vertically. Little is known of the maximum horizontal extent of the channels in the rock, but it is possible that some may extend thousands of feet-perhaps even for miles. Therefore, one supply well a considerable distance from a drainage well may be polluted while another well, much closer but with a poorer hydraulic connection to the drainage well, may be uncontaminated.
Drainage wells expose a large part of the artesian aquifer to radioactive contamination in the event of a nuclear attack. In its natural state, the artesian aquifer is protected from radioactive fallout by the overlying clayey sand which would filter out any fallout. However, rain water would wash the fallout from roofs and streets and carry it down drainage wells. Radioactive material so distributed throughout a large part of the aquifer would cause contamination that might last for many years.
Water running down drainage wells often carries large quantities of air into the aquifer. This air sometimes blows back through the drainage well causing the well to spout and sometimes