Comapare get_user_meta value

You can use meta_key or meta_query to fetch users where get_user_meta() ‘val’ == 1

Option 1:

$users = get_users(array(
    'meta_key'     => 'val',  // your_meta_key
    'meta_value'   => '1',   // value you want to compare
    'meta_compare' => '=',
));

Option 2:

$args = array(
    'meta_query'   =>array(
        array(
            'key' => 'val',  //your_meta_key
            'value' => 1,    // value of key to compare
            'compare' => "="
        ),
    )
);
$users = get_users( $args );

You can run through the loop to get email address of user and send email.