it is possible, just check if value is there
but for that you need to re-arrange / re-write your code.
here a part of it. just add the other rows the same way.
<?php if( have_rows('model_specifications') ):
while( have_rows('model_specifications') ): the_row();
$ms_model = get_sub_field('model');
$ms_gpm = get_sub_field('gpm');
endwhile;
echo '<div id="model-specifications">';
echo '<dl>';
if ($ms_model) {echo '<dt class="model">Model</dt>';}
if ($ms_gpm) {echo '<dt class="gpm">GPM</dt>';}
if ($ms_model) {echo '<dd class="model">'.$ms_model.'</dd>';}
if ($ms_gpm) {echo '<dd class="gpm">'.$ms_gpm.'</dd>';}
echo '</dl>';
?>
