wp_query with multiple arguments with AND

You want to use the newer meta_query methodology…

You establish a meta_query and then use arrays for the different conditions you want met, preface them with the relationship relation => 'AND' or relation => 'OR'

$loop3 = new WP_Query( array( 
    'posts_per_page' => 10000, 
    'post_type' => 'volunteers',  
    'meta_query' => array(
        'relation' = 'AND',
        array(
            'key' => 'state',
            'value' => $stateselect,
            'compare' => '=',
        ),
        array(
            'key' => 'volunteer_type',
            'value' => 'painter',
            'compare' => '=',
        ),
    ),
) );

Codex has a write-up here:
https://developer.wordpress.org/reference/classes/wp_query/#custom-field-post-meta-parameters

Note
That’s a lot, like A LOT, of posts_per_page.