mounted between the brackets by nut bolt combinations 45 extending therethrough the length of the upper fastening arms 44 is such that they extend to upper arm fastening brackets 42 where they are pivotally mounted by nut bolt combinations 46 with this fastening structure as threaded rod 32 is rotated lower pivot plate 34 will be moved toward or away from upper pivot plate 35 to cause resultant motion of the outer end portions of lower fastening arms 40 away from or toward each other to allow fastening and release of the fastening structure within neck 20 having described the structure of my invention its use may be understood a skimmer cover 12 and associated fastening structure 13 are constructed according to the foregoing specification with parameters determined by known engineering methods for use with a particular catch basin 10 and dry well structure 11 of the type described the threaded rod 32 of the fastening structure is rotated to move the outer ends of the lower fastening arms 40 radially inwardly toward each other until the distance between them is less than the internal diameter of the neck 23 of a dry well to be serviced the skimmer cover then is manipulated to position it over the neck 23 of that dry well with the fastening structure extending downwardly through the orifice 25 defined by the neck and the cover structure resting with its cross supports 28 on the top of the.