There are numerous factors that can play a part on the volume you use. So you may end up using 800, 1000, 1200, 1500, 2000 or 3000m. It can depend on if you are doing it for the sole purpose of active recovery or you are also seeking some continual conditioning improvement. You will need to consider your overall periodisation and that particular weeks goal. Obviously, the session pre-ceeding and time of year may influence the volume and variety in distance and the rest you may use. You will also have to consider the training history of the individual, the stage of preparation, the event they compete or intend on competing in and if they are explosive or strength type athletes and / or male or female. Whatever volume you consider using look at it with respect to your overall periodisation to ensure you have the overall volume of work periodised effectively to enable you to taper with more confidence at the required period. The last thing you want is this huge undulating volume of work week to week because on one day you prescribe 1000m and next week the same day you have them doing 2500m with no rhyme or rhythm to your application.