Yes the results are consistent with other research in sandy shallow aquifers and also our practical experience here in the Philippines: after a distance of around 10m or more E.coli is rarely detected in boreholes otherwise well protected against bacterial contamination (from surface water intrusion etc.).
But I would caution a bit against only looking at easy to measure bacterial (E.coli) contamination. Viruses are likely to be transported into the aquifer quite a bit further and other likely chemical pollutants will also be present in the water of the wells.

A 2011 paper, titled Implications of Fecal Bacteria Input from Latrine-Polluted Ponds for Wells in Sandy Aquifers, available at pubs.acs.org/doi/abs/10.1021/es202773w, gives a good review of fecal contamination of shallow wells, an aspect that quite often comes under discussion, even on this forum.

In Bangladesh, a major population use shallow wells for water needs. The paper says that in rural Bangladesh, the population density is high, sanitation is poor, and diarrheal disease morbidity is very high, causing an estimated 11% of all deaths. The majority of villagers obtain their drinking water from shallow tube wells in sand aquifers. The high level of diarrheal disease might be attributable to exposure to fecal-contaminated well water.

Perhaps, unique to Bangladesh, the authors say that ponds are typically excavated for foundation material and are ubiquitous in rural Bangladesh. This is not the case in Pakistan, though, in rural areas, depression are used for discharging toilet’s contents. The ponds in Bangladesh, therefore, contaminate shallow wells, if ponds receive latrine effluents.

While the paper describe the research methodology adopted, the paper says that E.coli was rarely detected along the transects during the dry season and was only detected near the ponds extending to medium sand up to 7 m away during the monsoon. A point worth noting here is that the contamination of wells occurs during wet season, and not during dry season.

An interesting “take home” point, highlighted in the paper is: “Only the transect radiating from the freshly excavated pond showed a rapid response to an artificial increase in pond level, suggesting that older ponds, which typically have accumulated a lining of finer grained sediments, provide a greater measure of protection against rapid microbial contamination of shallow groundwater.”

Copyrights issues may be involved in the paper - I'm not quite sure. Hence, I’m unable to share the whole paper. Only few interesting points have been briefly highlighted here.

F H Mughal