Something like this should do what you want:
<?php
$query = $modx->newQuery('modResource');
$query->join('modTemplateVarResource', 'lat', array('tmplvarid' => $tvLat, "lat.contentid = modResource.id"));
$query->join('modTemplateVarResource', 'lng', array('tmplvarid' => $tvLng, "lng.contentid = modResource.id"));
$query->select($modx->getSelectColumns('modResource', 'modResource', 'modResource_'));
$query->select(array(
'distance' => "SQRT(POW((69.1 * (lat.value - 27.950898)) , 2 ) + POW((53 * (lng.value - -82.461517)), 2))"
))
$query->sortby('distance', 'ASC');
$query->limit(5);
$resources = $modx->getCollection('modResource', $query);