Middle market private equity firm Calera Capital has acquired United Site Services (USS), in partnership with the company's management team. USS provides portable restrooms, VIP restroom and shower trailers. The company, headquartered in Westborough, Massachusetts, also offers temporary fences and other services to the construction, event, industrial and government sectors. Terms of the deal were not disclosed. Calera and the company's management team plan to grow the company organically and through acquisitions. The San Francisco and Boston-based firm has about $2.8 billion in capital under management. Formerly known as Fremont Partners, Calera seeks to invest in business services, consumer and retail, financial services, health care, building products and industrial manufacturing companies. Calera's other investments include mattress retailer Sleepy's, screening company Sterling Backcheck and freight company Rock-It Cargo.