128 REPORT OF INVESTIGATIONS NO. 50
DRAINAGE WELLS
HISTORY
The first drainage well in Orange County was drilled about 1904. Since that time about 400 drainage wells have been drilled in the county. The data on 392 drainage wells will be listed in an Information Circular in preparation (1967) that will be titled "Water Resources Records of Orange County, Florida." Quite a few drainage wells probably are not included because prior to 1939 it was not necessary to obtain a permit to install such wells; and even after 1939, a number of wells probably were installed without permits. No public record has been kept of many drainage wells. The most active year for drilling of drainage wells was 1960 when about 35 wells were constructed.
POLLUTION
The possibilities of pollution of ground-water supplies by drainage wells was described in detail by Unklesbay (1944) and by Telfair (1948). Unklesbay states (Ibid p. 25), "water which drains from roadside ditches or street gutters, and especially that discharged from septic tanks, is almost certain to be polluted, and the freedom of circulation allowed by cavernous limestone may permit such waters to enter supply wells without being subject to filtration." Telfair (p. 8-9) shows that in a test at Live Oak, where the limestone aquifer is similar to that in Orange County, salt put in a well was detected in an observation well 600 feet away 15 minutes later. Thus, water can move through the aquifer at speeds of at least 40 feet per minute if hydrologic conditions are favorable.
Under natural conditions, ground water moves very slowlyusually less than a few feet a day. However, when the natural conditions are altered, as occurs when drainage from a well builds up a local mound and pumping from a nearby supply well creates a cone of depression, the gradient between the two wells is greatly steepened so that in cavernous limestone, water moves rapidly from a drainage well to a supply well.
The quality of the water flowing down drainage wells in Orange County varies from practically pure rain water to highly polluted water. An example of polluted water entering the aquifer is a drainage well (826-125-1) that receives water used to flush cow barns at a dairy as well as surface drainage. The water entering