Here are recommended places to check for local jobs and internships for summer:
City/Village Offices & Department employment pages; City Park District; County Forest Preserve District; Local design firms; County Green groups/projects; Local corporations with sustainability in the news; Non-profit organizations. Keep in mind YOU might bring some knowledge in sustainability to a role or you might bring more of the design element to a role. Think about the skills you can gain in different types of roles!
Searching for these will take researching on the specific websites, not relying on google or handshake.