Get images alt tag and display

I am trying to get the alt tag from images uploaded as attachments and display it. Currently my code finds the images and places them in a container ( a slideshow ) but I can’t get the alt tags to show up..

<div class="project-slide-holder clearfix">
				<?php if ( have_posts() ) : while ( have_posts() ) : the_post();    

		 			$args = array(
		 			  'post_type' => 'attachment',
		 			  'numberposts' => -1,
		 			  'post_status' => null,
		 			  'post_parent' => $post->ID
		 			 );

		 			 $attachments = get_posts( $args );
		 			    if ( $attachments ) {
		 			       foreach ( $attachments as $attachment ) {
		 			          echo '';
		 			          echo wp_get_attachment_image( $attachment->ID, 'project-page-image' );
		 			          echo '';
		 			         }
		 			    }
		 			?>

		</div>
				<div class="project-caption">
					<p><strong class="blue"><?php the_title(); ?>
					<span class="image-descript">
					<?php $alt = get_post_meta($attachment_id, '_wp_attachment_image_alt', true);
						if(count($alt)) echo $alt;?>

					</span></p>
				</div>
				<?php endwhile; endif; ?>

Any ideas? Im not sure why it isn’t showing up at all?