Pathways for Bacteria to Enter into the Well Wells can be constructed to reduce or eliminate the number of pathways for contaminants to enter the water supply, however, deterioration of old wells and improper siting and installation of new wells could allow pathways for bacteria to enter a well directly (fig. 11). Bacteria could enter a well if 1) the top of the casing is not sealed and vented properly, 2) the annulus around the outside of the casing is not grouted, 3) there is leakage around the pitless adaptor, or 4) the casing is cracked or otherwise deteriorating. As previously noted, some differences in well-construction regulations exist, however, only six wells in Maryland and four wells in Chester County, Pa. were sampled. Therefore, information on the effect of regulations was inadequate to conduct statistical analysis for this study. Casing caps, regulations and standards for well construction, well deterioration and other age factors are discussed here as important considerations to minimize the number of pathways into the well. Most wells sampled had a loose-fitting well cap on the top of the casing instead of a sanitary seal. Many of these wells had spiders, ants, earwigs, or other insects inside the well at the top of the casing. These insects can fall down the inside of the casing and introduce bacteria into the well (Wisconsin Department of Natural Resources, 1993). Some casings were cut off flush with the ground. This situation, combined with a loose well cap, could increase the chance that dirt or surface water could enter the well. Sanitary seals have an expanding rubber gasket that can prevent such things as dirt, spiders, insects, and surface water from entering the well through the top of the casing. Because only three of the 146 wells sampled had sanitary seals, analyzing the significance of this factor statistically was not possible. Nevertheless, the field observations made for this study show that casing caps were generally not sealed and represent a potential pathway for contaminants to enter the well. Ungrouted wells are vulnerable to contamination. Regulations for well construction are written to include detailed requirements and standards for grouting (Chester County Health Department, 1993). Well-completion records for 108 wells indicated that grout was installed in 29 wells, 23 in Pennsylvania and 6 in Maryland. The annulus of loose dirt or fill around the casing of an ungrouted well may be a pathway for bacteria-laden water to move down along the casing. Physical defects such as leakage around the pitless adaptor may have existed in some of the wells sampled. Wells in Maryland and Chester County, Pa. that do not pass the initial potability test must be retested, checked to ensure that there are no physical defects in the construction of the well, and evaluated for treatment options. Leakage around the pitless adaptor is another possible pathway for bacteria to enter a well. The competence of a well casing is commonly related to the age of a well. The median age of the wells sampled was from 7 to 10 years old and only 3 of the 146 wells sampled were more than 20 years old. Because so few old wells were sampled, problems commonly associated with older wells such as well pits with standing water, inadequate casing length, and cracked or corroded casings were minimized. Lack of grouting could increase the deterioration rate of the well casing. Any crack or hole in the casing that is in the saturated zone provides a pathway for bacteria to enter into the well.
Posted on: Fri, 03 Oct 2014 09:00:16 +0000