trying to pass a variable into an add_filter

I have a list of posts that I want to allow the user to filter based on information in custom fields. Both $iTimeframe and $iRegion are user inputs from dropdowns. If they have a value then the query needs to be updated. This is being done with the add_filter to the post_where. The first one for $iTimeframe works as expected, however the one for $iRegion–where it is necessary to actually pass the string for the region in order to get a match–doesn’t work.

$args = array(
    'offset' => $setOffset,
    'category_name' => $pdOutput[0],
    'orderby' => 'meta_value',
    'meta_key' => 'EventDate',
    'order' => 'ASC',
    'paged' => $paged,
    'posts_per_page' => LIMIT_PD
    );

    if ($iTimeframe == "upcoming") {
      add_filter( 'posts_where', 'filter_where_pd_upcoming' );
    } else {
      add_filter( 'posts_where', 'filter_where_pd_past' );
    } 

    if ($iRegion !="") {
      add_filter( 'posts_where','filter_where_pd_region', '', 1 );
    } 

    $pdlist_query = new WP_Query( $args );
    [and Loop...]

function filter_where_pd_upcoming () {
    $where .= " AND meta_key = 'EventDate' AND FROM_DAYS(TO_DAYS(meta_value))+0 >= CURDATE()";
    return $where;
}
function filter_where_pd_past () {
    $where .= " AND meta_key = 'EventDate' AND FROM_DAYS(TO_DAYS(meta_value))+0 < CURDATE()";
    return $where;
}
function filter_where_pd_region ($iRegion) {
    $where .= " AND meta_key = 'RegionBC' AND meta_value='".$iRegion."'";
    return $where;
}

Based on the tests I’ve done, I don’t think $iRegion is making it inside the function. When I tried echoing $iRegion inside the function I got the following:

AND ( wp_term_relationships.term_taxonomy_id IN (24) ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') AND wp_postmeta.meta_key = 'EventDate'

…which I’m guessing is actually the where statement being picked up.

Help would be greatly appreciated.